Interlayer Expansion : Synthesis, Structure and Characterisation of Metal Intercalated Layered Silicates

Interlayer Expansion: Synthesis, Structure and Characterisation of Metal Intercalated Layered Silicates

Dissertation

submitted in partial fulﬁlment of the requirement for the degree Doctor rer. nat. (Ph. D.) at the Faculty of Geosciences at the Ruhr-University Bochum

presented by Isabel Großkreuz

Bochum, January 2020

1. Superviser: Prof. Dr. HERMANN GIES

2. Superviser: Prof. Dr.-Ing. GUNTHER EGGELER

❆❜❛❝

The layered silicate RUB-36 serves as an ideal precursor for the process of interlayer expansion to create new crystalline, microporous framework materials. Here, the incorporation of speciﬁc metal cations as linker sites is investigated and extended to cobalt (Co), titanium (Ti), vanadium (V) and zinc (Zn). In a hydrothermal reaction, Co-, Ti-, V- or Zn-acetylacetonate (acac) are added to the hydrous silicate precursor RUB-36 in a hydrous acidic suspension to obtain an interlayer expanded zeolite (IEZ). The introduced cations act as linker between the silicate layers of the starting material and yield new, three- dimensional metallosilicate framework structures with following trivial name and chemical denomination

Co-IEZ-RUB-36 Si51.95Co0.05O88,

Ti-IEZ-RUB-36 Si51.75Ti0.25O88,

V-IEZ-RUB-36 Si51.88 V0.12O88 and

Zn-IEZ-RUB-36 Si51.82Zn0.18O88.

All four materials are stable upon calcination, which has been conﬁrmed by thermal analyses (differential thermal analysis (DTA) and thermal gravimetry (TG)) and powder X-ray diffraction (PXRD). The new materials crystallise in the monoclinic space group (SG) Pm with lattice parameters

a0 = 23.875(12) Å, b0 = 14.053(7) Å, c0 = 7.417(4) Å and β = 90.00(5)° for Co-,

a0 = 24.207(59) Å, b0 = 14.002(33) Å, c0 = 7.398(14) Å and β = 89.91(28)° for Ti-,

a0 = 23.782(25) Å, b0 = 14.024(7) Å, c0 = 7.404(4) Å and β = 90.08(9)° for V- and

a0 = 23.782(16) Å, b0 = 14.056(9) Å, c0 = 7.421(4) Å and β = 89.98(4)° for Zn-material.

All β-angles are 90° (orthorhombic unit cell (UC)/metric but monoclinic symmetry). Atomic structure and framework topology have been conﬁrmed by PXRD RIETVELD analysis and automated electron diffraction tomography (ADT), as well as nuclear magnetic resonance (NMR) and infrared (IR) spectroscopy. Chemical composition and incorporation of cations were determined by energy-dispersive X-ray spectroscopy (EDX) and atomic

V Abstract absorption spectroscopy (AAS) analysis. Preservation of microporous structure was tested by nitrogen gas (N2) adsorption.

Selected materials have been studied for catalytic activity by ammonia (NH3)-temperature programmed desorption (TPD) and 1-octene cracking/isomerisation reaction.

VI ❩✉❛♠♠❡♥❢❛✉♥❣

Das Schicht-Silikat RUB-36 ist ein ideales Ausgangsmaterial für den Prozess der Zwis- chenschicht Expansion um neue kristalline, mikroporöse Gerüstmaterialien herzustellen. Hier wird die Eingliederung von speziﬁschen Metall-Kationen als Verbindungsposition untersucht und auf Cobalt, Titan, Vanadium und Zink ausgedehnt. In einer hydrother- malen Reaktion wird Co-, Ti-, V- oder Zn-acac zum hydrierten Silikat Material RUB-36 in wässrig-saurer Suspension gegeben um einen Zwischenschicht expandierten Zeolith zu erhalten. Die aufgeführten Kationen dienen als Verbindungspositionen zwischen den Silikatschichten des Ausgansmaterials und ergeben neue, dreidimensionale Metallgerüst- silikate mit folgenden Trivialnamen und chemischer Bezeichnung

Co-IEZ-RUB-36 Si51.95Co0.05O88,

Ti-IEZ-RUB-36 Si51.75Ti0.25O88,

V-IEZ-RUB-36 Si51.88 V0.12O88 und

Zn-IEZ-RUB-36 Si51.82Zn0.18O88.

Alle vier Materialien sind nach Kalzinierung stabil. Dies wurde mithilfe der thermischen Analyse (Differential Thermo Analyse (DTA) und Thermogravimetrie (TG)) und Pulverrönt- gendiffraktometrie (PXRD) geprüft. Die Syntheseprodukte kristallisieren in der monokli- nen Raumgruppe Pm mit Gitterparametern

a0 = 23.875(12) Å, b0 = 14.053(7) Å, c0 = 7.417(4) Å und β = 90.00(5)° für Co-,

a0 = 24.207(59) Å, b0 = 14.002(33) Å, c0 = 7.398(14) Å und β = 89.91(28)° für Ti-,

a0 = 23.782(25) Å, b0 = 14.024(7) Å, c0 = 7.404(4) Å und β = 90.08(9)° für V- und

a0 = 23.782(16) Å, b0 = 14.056(9) Å, c0 = 7.421(4) Å und β = 89.98(4)° für Zn-Material.

Alle β-Winkel betragen 90° (orthorhombische Einheitszelle/Metrik mit monokliner Sym- metrie). Atomarer Aufbau und Gerüst-Topologie ließen sich durch PXRD RIETVELD Ver- feinerung und ADT Analyse, sowie NMR und IR Spektroskopie veriﬁzieren. Der Einsatz von EDX und AAS Verfahren lieferte Informationen zu chemischer Zusammensetzung und

Eingliederung der Kationen. Durch N2 Adsorption konnte ein Erhalt der mikroporösen Struktur getested werden.

VII Abstract

Eine Analyse hinsichtlich katalytischer Aktivität erfolgte für ausgewählte Materialien in

NH3-TPD und 1-Octen Spaltung bzw. Isomerisierungsreaktion.

VIII ❚❛❜❧❡ ♦❢ ❈♦♥❡♥

❆❜❛❝ ❱■

❩✉❛♠♠❡♥❢❛✉♥❣ ❱■■■

❚❛❜❧❡ ♦❢ ❈♦♥❡♥ ❳■

▲✐ ♦❢ ❛❜❜❡✈✐❛✐♦♥ ❳■■■

✶✳ ■♥♦❞✉❝✐♦♥ ❛♥❞ ▼♦✐✈❛✐♦♥ ✶

✷✳ ❈✉❡♥ ❛❡ ♦❢ ❡❡❛❝❤ ✾ 2.1. Zeolites ...... 9 2.1.1. Composition ...... 13 2.1.2. Stability ...... 14 2.1.3. Functionality ...... 14 2.2. Catalysis ...... 15 2.3. Interlayer Expansion and Topotactic Condensation ...... 22 2.4. Problem and objective of this work ...... 26

✸✳ ❍②❞♦❤❡♠❛❧ ②♥❤❡✐ ✷✾ 3.1. Hydrothermal zeolite genesis and synthesis ...... 32 3.2. Hydrothermal synthesis of RUB-36 hydrous layer silicate ...... 34 3.3. Post-synthesis treatment ...... 36 3.3.1. Interlayer Expansion ...... 36 3.3.2. Metal Interlayer Expansion ...... 37

✹✳ ❘❯❇✲✸✻ ❧❛②❡ ✐❧✐❝❛❡ ✹✶ 4.1. Structure and Properties ...... 41 4.2. Framework type FER ...... 41 4.2.1. fer-type layers ...... 47 4.3. Framework type CDO ...... 49 4.4. Crystallographic structure of RUB-36 ...... 51

IX Table of Contents

4.5. Disorder of layer stacking ...... 53

✺✳ ❈❤❛❛❝❡✐❛✐♦♥ ♦❢ ②♥❤❡✐❡❞ ♣♦❞✉❝ ❛♥❞ ♠❡❤♦❞ ✺✾ 5.1. Powder X-ray diffraction (PXRD) ...... 59 5.1.1. Basic principles of PXRD ...... 61 5.1.2. Rietveld reﬁnement ...... 65 5.1.3. Program Suite FullProf ...... 68 5.1.4. Analysis of polycrystalline material RUB-36 ...... 68 5.1.5. Analysis of Me-IEZ-RUB-36 ...... 71 5.2. SEM and EDX ...... 81 5.2.1. Basic principles of SEM and EDX ...... 81 5.2.2. SEM and EDX experiments ...... 83 5.3. ADT ...... 86 5.3.1. Basic principles of ADT ...... 86 5.3.2. ADT experiments ...... 87 5.4. Inductively coupled plasma (ICP)-atomic absorption spectroscopy (AAS) . . . 90 5.4.1. Basic principles of ICP-AAS ...... 91 5.4.2. ICP-AAS experiments ...... 91 5.5. X-ray ﬂuorescence (XRF) analysis ...... 93 5.5.1. Basic principles of XRF ...... 93 5.5.2. XRF experiments ...... 94

5.6. Ammonia (NH3)-temperature programmed desorption (TPD) ...... 95

5.6.1. Basic principles of NH3-TPD ...... 96

5.6.2. NH3-TPD experiments ...... 97

5.7. Nitrogen gas (N2) adsorption ...... 99

5.7.1. Basic principles of N2 adsorption ...... 99

5.7.2. N2 adsorption experiments ...... 101 5.8. Thermal analyses (TA) ...... 105 5.8.1. Basic principles of TA ...... 105 5.8.2. TA experiments ...... 106 5.9. Nuclear magnetic resonance (NMR) spectroscopy ...... 108 5.9.1. Basic principles of NMR spectroscopy ...... 109 5.9.2. Experimental NMR spectroscopy ...... 114 5.9.3. 29Si ZG and 29Si HP DEC ...... 114 5.9.4. 13C CP MAS ...... 118 5.9.5. 1H MAS ...... 119

X 5.10.Infrared (IR) spectroscopy ...... 121 5.10.1. Basic principles of IR spectroscopy ...... 122 5.10.2. IR spectroscopy experiments ...... 124 5.11.Ultraviolet (UV) - visible (vis) spectroscopy ...... 127 5.11.1. Basic principles of UV-vis spectroscopy ...... 128 5.11.2. UV-vis spectroscopy experiments ...... 130

✻✳ ❈❛❛❧②✐❝ ❡①♣❡✐♠❡♥ ✶✸✺ 6.1. Epoxidation of 1-hexene ...... 135 6.1.1. Theory ...... 136 6.1.2. Experiment ...... 138 6.2. Catalytic cracking and isomerisation of 1-octene ...... 140 6.2.1. Theory ...... 140 6.2.2. Experiment ...... 141 6.2.3. Material Analyses ...... 146

✼✳ ❙✉♠♠❛② ❛♥❞ ❖✉❧♦♦❦ ✶✹✾

❆♣♣❡♥❞✐① ✶✺✾ A. List of Figures ...... 159 B. List of Tables ...... 162 C. List of crystallographic symbols ...... 163 D. Detailed Synthesis protocol ...... 164 E. List of atomic positions ...... 170 F. Curriculum Vitae ...... 183 G. Declaration in lieu of oath ...... 184 H. Digital Appendage ...... 185

❘❡❢❡❡♥❝❡ ✶✽✼

❆❝❦♥♦✇❧❡❞❣❡♠❡♥ ✷✵✼

▲✐ ♦❢ ❛❜❜❡✈✐❛✐♦♥

③❡♦❧✐❡ ✉❝✉❡ ❛♥❞ ❝❤❛❛❝❡✐✐❝

❝❛ caesium aluminosilicate type layer ▼❖❋ metal-organic framework ❈❇❯ composite building unit ▼❖❘ mordenite ❈❉❖ cylindrically double saw-edged ✐♥❣ formerly: membered ring structure - one ♠✇✇ MWW type layer ❈❉❙ cylindrically double saw-edged ▼❲❲ Mobil-twenty-two structure ❇❯ primary building unit ❈❍❆ chabazite ❈❘ Institute of Physical Chemistry ❈❖❑ Centrum voor Oppervlakechemie (Acad. of Science, Czech Republic) en Katalyse - Four ❝✐ CRISTOBALITE type layer ❡❇❯ periodic building unit ❉❤ host dimensionality ▲❙ pentagonal cylinder layered silicate ❊❋ extra framework position ❘❊❋❊❘ FER precursor ❊❘❙ eniricerche molecular sieve ❘❘❖ Ruhr University-(forty-one) ❋❆❯ FAUJASITE ❘❯❇ Ruhr University Bochum ❋❉❙✐ framework density ❘❲❘ RUB twenty-four ❢❡ FER type layer ✇ RUB twenty-four type layer ❋❊❘ FERRIERITE ❙❇❯ secondary building unit ❤❡✉ HEULANDITE type layer ❙❖❉ SODALITE ❤✉ HUS type layer ❚❉ topological density ❍❯❙ Hiroshima University silicate ❚❙✲✶ titanium SILICALITE-1 ■❊❩ interlayer expanded zeolite ❚❯❉ Technische Universiteit Delft ■❚◗ Instituto de Tecnologia Quimica ❯❖ Universal Oil Products ▲❚❆ LINDE Type A ❯❩▼ UOP zeolitic materials ▼❈▼ Mobil composition of matter ❨◆❯ Yokohama National University ▼❋■ Mobil ﬁve ❩❙▼ zeolite Socony Mobil

❝②❛❧❧♦❣❛♣❤✐❝ ❝❤❛❛❝❡✐✐❝

❖❤ octahedral ❙❖❋ site occupation factor ● point group ❚❞ tetrahedral ❙● space group ❯❈ unit cell

XIII List of abbreviations

♠❡❤♦❞ ❛♥❞ ♦♣❡❛✐♥❣ ✜❣✉❡

❆❆❙ atomic absorption spectroscopy ▼❆❙ magic angle spinning ❆❉❚ automated electron diffraction ▼❚● methanol-to-gasoline conversion tomography ▼❚❖ methanol-to-olefin conversion ❆❚❘ attenuated total reflectance ◆■❘ near infrared ❇❊❚ BRUNAUER–EMMETT–TELLER ◆▼❘ nuclear magnetic resonance ❇❏❍ BARRET-JOYNER-HALENDA ✶ transmitter pulse ❈ cross polarisation ❳❘❉ powder X-ray diffraction ❈❙❆ chemical shift anisotropy ❘✲✈❛❧✉❡ residual value (GOF) ❉✶ relaxation delay time ❘❉▲❙ DLS reliability index ❉❊ free scan delay time ❙❈❘ selective catalytic reduction ❉▲❙ distance least squares ❙❈❳❘❉ single crystal X-ray diffraction ❉❘❙ diffuse reflectance spectroscopy ❙❊▼ scanning electron microscopy ❉❙❈ differential scanning calorimetry ❙❚❊▼ scanning transmission electron ❉❚❆ differential thermal analysis microscopy ❊❈❉▼ experimental charge density ❙❲❍ spectral width mismatch ❚❆ thermal analyses ❊❉❳ energy-dispersive X-ray ❚❈❉ thermal conductivity detector spectroscopy ❚❊▼ transmission electron microscopy ❋❈❈ fluid catalytic cracking ❚● thermal gravimetry ❋❊❙❊▼ field emission scanning electron ❚●❆ thermal gravimetry analysis microscope ❚❖◆ turnover number ❋❚■❘ FOURIER-transform infrared ❚❉ temperature programmed ❋❲❍▼ full width at half maximum desorption ●❈ gas chromatography ❯❱ ultraviolet ●❖❋ goodness of fit ✈✐ visible ❍ ❉❊❈ high power proton decoupling ❳❘❉ X-ray diffraction ■❈ inductively coupled plasma ❳❘❋ X-ray fluorescence ■❘ infrared ❩● zero gain ▲▼❈❚ ligand to metal charge transfer

♣♦❣❛♠

❉■❋❋❛❳ diffracted intensities from faulted ❘■❊❚❆◆ RIETVELD analysis xtals ❱❊❙❚❆ Three-Dimensional Visualization ❉■❙❈❯❙ Diffuse Scattering and Defect System for Electronic and Structure Simulation Structural Analysis ❉▼❋✐ DOMINIQUE MASSIOT Fit

XIV ❝❤❡♠✐❝❛❧ ❛❣❡♥

✶✸ ❈ NMR active carbon isotope ▼❡❈◆ acetonitrile ✶✹ ◆ NMR active nitrogen isotope ▼❡❖❍ methanol ✶ ❍ NMR active hydrogen isotope ▼♦ molybdenum ✷✾ ❙✐ NMR active silicon isotope ◆✷ nitrogen gas ❛❝❛❝ acetylacetonate ◆❛ sodium ❆❣ silver ◆❍✸ ammonia ❆❧ aluminium ◆✐ nickel ❇ boron ◆❖① nitric oxide and nitrogen dioxide ✷ ✕ ❈❖ carbon monoxide ❖ oxygen anion ✕ ❈♦ cobalt ❖❍ hydroxide ❈ chromium phosphorus ❈❚❆❖❍ cetyltrimethylammonium ❙❆❖ silicoaluminophosphate hydroxide ❙❉❆ structure directing agent ❈✉ copper ❙♥ tin ❉ deuterium ❚❊❖❙ tetraethoxysilane, tetraethyl ❉❈❉▼❙ dichlordimethylsilane orthosilicate ❉❊❉▼❆ diethyldimethylammonium ❚✐ titanium ❊✉ europium ❚▼❆ tetramethylammonia ❋❡ iron ❚▼■ transition metal ions ●❛ gallium ❚▼❖❙ tetramethoxysilane, tetramethyl ●❡ germanium orthosilicate ✰ ❍ proton ❚▼❙ tetramethylsilane ✰ ❍✷❖ water molecule ❚❆ tetrapropylammonia+ ❍❈❧ hydrochloric acid ❱ vanadium ❍❋ hydroﬂuoric acid ❲ tungsten ▲● liquid petroleum gas ❩♥ zinc ▼❡ metal

✐♥✐✉✐♦♥

■❯❆❈ International Union of Pure and ■❩❆❙❈ International Zeolite Association Applied Chemistry Structure Commission ■❩❆ International Zeolite Association ❘❯❇ Ruhr University Bochum

♦❤❡ ❛❜❜❡✈✐❛✐♦♥

❯❙❉ United States dollar

✶✳ ■♥♦❞✉❝✐♦♥ ❛♥❞ ▼♦✐✈❛✐♦♥

HCl 433K,2d + → (a) RUB-36 (b) Me-acac (c) Me-IEZ-RUB-36

Calcination←

← ← (d) products (e) Me-IEZ-RUB-36 (f) 1-octene

Figure 1.1.: Concept and aim of this work as (schematic) wire or skeletal frame representation: Starting material HLS RUB-36 (a) is hydrothermally treated with Me-acac (b) and HCl to create Me-IEZ-RUB-36 (c), which, in turn, are calcined (e) for the application in catalysis; here, in the cracking and isomerisation of 1-octene (f) into oleﬁns (d).

Nowadays, microporous materials such as zeolites, metal-organic frameworks (MOFs) and HLSs are indispensable in everyday life - both industrially and in the private sector - due to their unique structure and structure related properties. Since the discovery of natural zeolitic minerals and their first mention by name in 1756 [1], a myriad of different structures has been discovered at geologic sites but also synthesised in the laboratory. Key fields of application include the utilisation as sorbent material, the consumer detergent, and the oil-refining process technologies [2]. The sorbent functionality of certain zeolites can be applied in the desalination in sea water and absorbency of oil spills, encapsulation of methane or radioactive isotopes, whereas

1 1. Introduction and Motivation ion exchange is mainly applied in the water softening during laundering and water puriﬁ- cation. One of the main applications, however, is that of catalysis. The use of microporous materials in catalytic processes has revolutionised the industry and shifted the focus to a more sustainable employment. Solid acid catalysts are an environmentally-friendly replacement for liquid acids catalysts such as sulphuric acid which is toxic and expensive in its recycle course and hydroﬂuoric acid (HF) which presents a serious health hazard [3]. Even though the synthesis of a zeolite for the application in industrial processes is much more expensive than the use of a liquid acid, the negative environmental aspects of liquid acids and the recoverability of solid acid catalysts weigh more heavily toward the latter. Depending on the utilised reaction, waste emergence might not differ between solid and liquid acid catalysts, however, solid acid catalysts are easier to separate and reusable. The same applies to other heterogeneous catalysts such as amorphous silicates, Me-supported silicates and Me supported MOFs. Still, these materials lack the presence of acid sites and the size and shape selectivity that zeolites provide [4].

Literature regarding the general topic of microporous materials has grown exponentially over the past decades and even more so if one considers MOFs as part of the material class. A special type of material is the hydrous layer silicate (HLS). It is a layered silicate consisting of a tetrahedral layer of interconnected [SiO4]-units that contain equal numbers of terminal silanol/siloxy groups on either side of the layer and also exhibit an interlayer region where (organic) cations of low charge density and water molecules are contained [5]. The layer type of the material (e.g., fer) is distinguished from the three-letter code of the framework type (e.g., FER) which, in turn, is differentiated from a real microporous material (e.g., FERRIERITE). Officially, letter codes for novel microporous frameworks are assigned by the Interna- tional Zeolite Association Structure Commission (IZASC). These framework types should be considered along the lines of purely theoretical mathematical constructs in contrast to real zeolite minerals and synthesised materials with distinctive chemical composition. During investigation and analysis of new materials, internal lab codes are commonly used for zeolites, HLSs and MOFs that are somewhat indicative of the corresponding synthesising lab or institution in addition to a consecutive number (e.g., Ruhr University Bochum (RUB)-36 or ZSM-5) in a similar three-code manner as for the official framework structures [6]. In contrast to classical zeolites and MOFs, HLSs are not fully condensed and, therefore, not considered as zeolites. However, the building blocks or specific layers are generally

2 identical. To describe the structure of an HLS, the speciﬁcation of the type of layer is provided instead of a framework topology as for zeolites. In many cases though, the encountered individual layers are found to be essential building blocks in different framework topologies. For RUB-36, this layer type is the layer also found in the framework type FER. To emphasise the difference between framework type and layer type, the layer type is denoted by an underlined lower-case three-letter-code, fer in case of RUB-36. Based on the principle of the Database of Zeolite Structures [6], the Database of Hydrous Layer Silicates has been launched by MARLER et al., to provide a collection of well characterised HLS materials [7]. The special structure of HLSs of individual layers separated by an organic cation makes them exceptionally interesting in the use as precursors for the condensation reaction to three-dimensionally linked microporous materials.

In 1993, INAGAKI,FUKUSHIMA and KURODA proposed an alternative preparation route of porous materials from layered silicates in addition to the then established post-synthesis modiﬁcation of pillaring. Pillaring is applied to microporous materials by an insertion of robust inorganic species as pillars between layers, effectively swelling the material and eventually delaminating (separating) individual layers for later reassembly. The alternative route aimed for an interlayer cross-linking of a layered silicate in the ion exchange reaction with organic cations. As an exemplary layered polysilicate material, KANEMITE

NaHSi2O5 ·3H2O was ion exchanged (typically with alkyltrimethylammonium ions) and condensed to form highly ordered mesoporous three-dimensional silicate networks. The resulting micro- and meso-porous materials exhibited uniform pore-size distributions with speciﬁc surface areas of the calcined products of 900 m2 g−1. Pore sizes were alterable by the variation of the alkyl chain length of the alkyltrimethylammonium ions used. Nonetheless, resulting PXRD diagrams showed very low crystallinity [8]. Following these ﬁrst experiments, the topotactic condensation or conversion process has been applied to other materials as well.

GIES et al. give an overview of the different organic ammonium cations to be used as structure directing agent (SDA) to create the different HLSs ERS-12, MCM-47, MCM-65, PLS-1 , -3, -4, PREFER, RUB-20, -36, -38, -40, -48 and UZM-13, all of which are exhibiting fer-type layers. These HLSs serve as ideal starting materials for the topotactic condensation reaction to produce new three-dimensional zeolite frameworks. An advantage of the condensation procedure is the adjustability of the starting material and the production of a calcined microporous framework in a single iteration. In the following, aluminium (Al)-, boron (B)-, iron (Fe)-, gallium (Ga)-, zinc (Zn)-, titanium (Ti)-, and germanium (Ge)-

3 1. Introduction and Motivation substituted precursors have been the subject of investigation for the conversion into catalytically active silicate zeolites. Still, of the investigated materials, only the RUB-36 precursor material with diethyldimethylammonium (DEDMA) SDA showed potential for a condensation product with promising surface area and pore volume in comparison to the other materials. This testimony is only strengthened by the successful substitution of Al for Si leading to the formation of an active acid microporous catalyst [9].

The condensation process has been applied to a MWW-type lamellar precursor by FAN, WU,NAMBA, and TATSUMI in 2004 to create a novel titanosilcate catalyst (denoted as Ti- YNU-1) exhibiting substantially improved oxidation ability, epoxide selectivity, and stability in the liquid-phase epoxidation of cycloalkenes [10]. Ti-containing zeolites are of particular interest in the chemical industry due to their ability to be applied in environmentally beneﬁcial chemical processes for the liquid-phase catalytic oxidation of a variety of organic compounds by using H2O2 as a clean oxidant. In titanium SILICALITE-1 (TS-1), the purely siliceous titanosilicate analogue of ZSM-5 exhibiting MFI-type framework, only one Ti is located in each UC and, therefore, every fourth channel intersection, provided the material displays a perfect crystallinity. This favourable structure makes for a high hydrophobicity due to lacking defects in the form of silanol/siloxy groups which presents an essential factor in the epoxidation of alkenes. Water is created during the reaction as a side product which can only leave the pore structure of the catalyst in absence of silanol nests (representing the main cause of material hydrophobicity). The presence of defects creates a hydrophilic character causing the water side product to remain inside the catalyst, effectively blocking the channels and decreasing the catalyst turnover frequency [11] Nonetheless, in contrast to TS-1, Ti-YNU-1 does not show the disadvantageous medium- sized pores with 10-rings restricting the application to molecules of relatively small size. A problem similarly inherent (albeit to a smaller degree) in other Ti catalyst materials such as Ti-Beta, Ti-MOR, Ti-ITQ-7 and Ti-MCM-41 in addition to lower activity and stability [12].

Later, INAGAKI,YOKOI,KUBOTA and TATSUMI introduced the organic-inorganic hybrid zeolite IEZ-1 with dimethylsilylene moieties as an interlayer silylation product of pure silica PLS-1 by using silylating agents, such as dichlorodimethylsilane. Whereas IEZ-1 exhibits absorption properties regarding benzene molecules, its calcined product, IEZ-2 hardly adsorbed benzene [13].

These works were followed by IKEDA and SANO et al. who prepared RWR type materials by topotactic conversion of various precursors obtained from Na-RUB-18 [14]. New layered materials were steadily added to the portfolio of HLSs to be used in topotactic condensation reactions [15, 16], whereas the addition of a Me species during this proce-

4 dure became the focus of attention. In this work, the emphasis is placed upon the HLS RUB-36 in particular.

RUB-36 is indicative of the crystal chemistry lab in which it has been ﬁrst synthesised, located at the Ruhr University Bochum (RUB). It is the 36 th unique structure introduced by scientists of the aforementioned laboratory. This material is of particular interest in the conversion to novel three-dimensionally linked materials due to its periodical stacking of fer type layers. RUB-36 is one among a number of different HLSs exhibiting fer type layers that can be hydrothermally prepared by the use of an organic SDA in a mixture with H2O and SiO2 [17]. By calcination, i.e., heating over a certain period of time at temperatures of 773 K and above, the organic cation is removed from the starting material RUB-36 and the fer-type layers are topotactically condensed to form the three-dimensionally fully-linked microporous framework silicate RUB-37 exhibiting a framework typology of CDO and BET surface 2 3 area of 334 m g (from N2 isotherm) and a single point pore volume of 0.22 cm g [5, 9].

Adding to the considerations given by MARLER and GIES in their review [5] of precursors for zeolites obtained through topotactic condensation, the interlayer expansion of HLSs as a preliminary step to topotactic condensation has been investigated by GIES et. al. as well as ZHAO et al. by using silylating agents such as dichlordimethylsilane (DCDMS) and hydrochloric acid (HCl) to connect neighbouring layers of RUB-36 and RUB-39 [9, 18, 19]. To indicate the post-synthesis treatment of interlayer expansion, the code IEZ may be added to the code of RUB-36 to form IEZ-RUB-36. In this case, the internal lab code COE has been used for a fully condensed material. The IEZ designation has been introduced by TATSUMI and co-workers in applying interlayer expansion to PLS-1 material in 2007 [13].

WU,RUAN,FAN,TATSUMI et al. have demonstrated a methodology for the synthesis of crystalline metallosilicates with expanded pore windows through alkoxysilylation of zeolitic lamellar precursors using diethoxydimethylsilane. Zeolitic lamellar precursors exhibiting layers of type mww and fer such as MWW, FER, CDO and MCM-47 have been subjected to an interlayer expansion procedure with the aid of Me cations such as Al, Ga, Fe or Ti in acidic media. Results indicated that interlayer expanded zeolites prepared from the metallosilicate precursors of MWW topology exhibited higher catalytic activities in the redox and solid acid-catalysed reactions of bulky molecules than that of their counterparts with conventional MWW topology [20]. In a similar procedure, the formerly layered RUB-36 material can be topotactically

5 1. Introduction and Motivation condensed into a three-dimensionally linked, uninterrupted microporous material. This process is conducted at temperatures of 773 K with simultaneous expulsion of interlayer molecules. If a metal cation is introduced during this process or in a separate procedure, it is also added to the denotation of the resulting material. An example is the inclusion of Fe to form Fe-IEZ-RUB-36 or Fe-COE-3. Since the materials prepared in the course of this work are not exhaustively solved, and no uniformly applicable codes have been suggested, the designated denotations will be assigned as "Me-IEZ-RUB-36" with the corresponding metal (Me) cation [5].

TSUNOJI and SANO et al. were successful in their synthesis of layered silicates incorporating Ti(IV)-acac between the layers of HUS-2 for the improvement of catalytic activity and the application in chemoselectivity in photooxidation of cyclohexane [21].

Similarly, DE BAERDEMAEKER et. al. [22] have performed the insertion of Fe as a linker between the IEZ layers of RUB-36, subsequently connecting them. GIES et. al. [23] have successfully extended this process to other metal heteroatoms such as tin (Sn), whereas BIAN et al. [24, 25] used Sn as a linker between layered zeolite precursor COK-5.

YANG,WU et al. [26] have, furthermore, shown a facile method of combined isomorphous substitution of Ti for Si and interlayer expansion in a single step. The resulting IEZ-Ti-PLS-3 material exhibited unique catalytic properties in the epoxidation of alkenes with hydrogen peroxide, and was active not only for linear alkenes but also for bulky cyclic alkenes.

All these results lead to the assumption that speciﬁcally designed IEZ materials can be used in a wide variety of chemical applications. While exhibiting extraordinary stability, they can be applied in catalysis in the chemical industry in reactions such as the acylation of anisole with acetic anhydride or the alkylation of toluene with benzyl chloride [22]. Pin- point incorporation of catalytically active centres/heteroatoms such as Fe, Ti or Zn may lead to a new class of industrially applicable materials with desired functionality. Novel materials combine the functionalities necessary for an effective catalysis procedure. These properties are essentially realised in the materials as shape and size selectivity due to the microporous nature, as well as a sufﬁcient number of acid sites.

A promising zeolite material reported on to have successfully undergone interlayer expansion treatment including a metal cation and determination of catalytic capability is the iron material Fe-IEZ-RUB-36 [22]. The structure solution of the corresponding material

6 Sn-IEZ-RUB-36 has been provided in a following paper [23]. The authors propose the extension of the synthesis procedure to other metal cations such as Al, Zn, Eu and Ti. A variety of heteroatoms is currently investigated for the interlayer expansion process of RUB-36. Following these considerations, RUB-36 serves as an ideal precursor material in the interlayer expansion to a subsequent or simultaneous topotactic condensation using Me linker positions. As demonstrated by TSUNOJI,SANO et al. [21], the introduction of Me heteroatoms by its corresponding Me-acac is feasible and shall be applied in the post- synthesis treatment of RUB-36 during the course of this work. The aim of this research is to prove the general applicability of the alteration concept by demonstrating the successful incorporation of different cations as linker between the layers of HLS RUB-36 and to ﬁnd a facile production route for this new type of material. Hereby, a generalisation of this concept is to be proven to be used as a sort of templated process.

An abstraction of such a complex procedure presents new and unique challenges that have to be overcome. These include, but are not limited to, problems during the preparation of the precursor material, in this case RUB-36, difficulties during the post-synthesis treatment and challenges in sample analysis and characterisation. For the creation of a sufficiently crystalline post-treated product, a high crystallinity of the starting material is imperative. An unsuccessful post-synthesis treatment due to limited crystallinity of the starting material should - in theory - be easily avoidable by quality assurance with the use of PXRD analysis. However, an unsuccessful post-synthesis treatment may be caused by a myriad of adjustable parameters, among them temperature, time, pH-value and chemical composition of the reaction mixture. Therefore, these parameters should be varied in a sensible range for the determination of ideal reaction variables. As the starting material consists of fer type layers, a starting model for the structure solution of the reaction products is oriented towards a similar framework topology. Previous research has shown that only RUB-36 with its DEDMA cation may be successfully converted to three-dimensionally linked microporous framework materials, whereas other related structures exhibiting fer type layers cannot be thus transformed. The influence and presence of the DEDMA cation should be taken into account and not be neglected in the post-synthesis treatment. How- ever, many interlayer expansion and topotactic condensation procedures lead to three- dimensionally linked framework materials of limited crystallinity which is hindering a reliable structure solution. The uncertainty of a modification of layered materials resulting in a highly crystalline, but layer disordered, material is always a possibility. The Database of Zeolite Structures gives an overview of partially disordered structures and marks each

7 1. Introduction and Motivation framework affected by this phenomenon with an asterisk. An example is presented by the ZEOLITE BETA polymorphs A and B, whose disorder is characterised by each layer being rotated by ± 90° with respect to the previous one. In a typical synthesis, the stacking is random [6]. This type of layer disorder is generally observable by signal peak broadening in the PXRD pattern. As this challenge impedes the assignment of a reliable model, a number of programs have been launched that are dedicated to the simulation of layer disorder, among them DISCUS [27] and DIFFaX [28]. To ensure a most complete picture of the investigated material, many analysis methods are readily available to be applied, among them diffraction, spectroscopy and chemical tools. A combination of these techniques is imperative, as chemical analyses reveal chemical composition, spectroscopic methods give insight to the local environment and diffraction techniques clarify the long-rage order of the microporous material. Diffraction techniques, on the other hand, may be divided into PXRD and electron diffraction techniques. Whereas information collected by PXRD analysis is gleaned from the bulk of the sample, electron diffraction analysis delivers information on single particles. The overall intention of the material synthesis and analysis lies in the application of the functionalised novel materials in industrially interesting catalyst reactions.

8 ✷✳ ❈✉❡♥ ❛❡ ♦❢ ❡❡❛❝❤

✷✳✶✳ ❩❡♦❧✐❡

Zeolites represent a group of hydrated, micro- and mesoporous, crystalline aluminosilicates containing different cations of Group 1A and 2A elements (i.e., Na+,K+, Mg2+ and Ca2+). The property of reversibly adsorbing and desorbing water is the zeolites eponym, which was coined in 1756 by Swedish mineralogist AXEL FREDRIK CRONSTEDT [1] (Fig- ure 2.1). By heating a natural zeolite, water molecules desorb from the inner channels and cavities, giving an appearance of a ‘boiling stone’, which lead to the name zeolite from the Greek words for boiling - zein and stone - lithos [2, 29].

Today, they cover a fundamental role in modern industry and science as adsorbents, ion- exchangers, and catalysts [2].

Zeolites are described as ordered microporous or mesoporous materials, whose nature can be illustrated as a host or pore structure, which may then accommodate guest species. An unambiguous terminology is necessary to describe the particular properties of host framework and pore space. Of notable relevance are the characteristics controlling dif-

Figure 2.1.: First mention of zeolites by AXEL FREDRIK CRONSTEDT in Kongl. Svenska Vetenskaps Akademiens Handlingar: Rön och beskrifning om en obekant bärg art, som kallas Zeolites - "Row and description of an unknown rock species, called Zeolites" [1].

9 2. Current state of research fusion of guest molecules and the space restrictions for reaction intermediates as these materials are generally used as ion exchangers, catalysts and molecular sieves as well as drying agents.

Microporous materials can be identiﬁed and characterised by their unique properties, which are mainly caused by the materials inherent micro- and or mesoporosity. If a zeolite material is dehydrated, it exhibits exceptionally low density and a high void volume as described by framework density (FDSi) compared to other known minerals. Even though zeolites possess a large internal surface, the crystal structure remains generally stable in its dehydrated state. Also inherent in the dehydrated crystals are the molecular channels with molecular dimensions of 0.2 nm to 1.0 nm, which directly correlate with the materials cation exchange properties and its sorption properties (gases, vapours, etc.) as well as catalytic qualities. A high hydration energy is another very important feature in addition to the property of high stability of the silicate framework which is, generally, non-collapsible [2, 30].

Structurally, natural zeolites are complex inorganic polymers of inﬁnitely connected

[SiO4] and [AlO4] tetrahedra three-dimensionally linked by shared oxygen atoms. Although silicon (Si) and aluminium (Al) are the most common tetrahedral atoms, the chemical variety is nearly unlimited provided charge balance and ion size are taken into account. Since the range of possible [TO4] tetrahedra connections is so high, another descriptive value has been introduced, the secondary building unit (SBU). SBUs will be described in more detail in the following chapter (Chapter 3).

A characteristic feature to distinguish individual microporous materials with an inorganic, three-dimensional framework composed of fully linked, corner shared tetrahedra is the framework topology. It describes the connectivity of its host atoms without reference to chemical composition or observed symmetry (including crystallographic translations). The symmetry of a host structure is determined by the symmetry of its topology. How- ever, it is not uncommon that the presence of guest species in the channel structure or an altered chemical composition causes a framework distortion and a subsequent symmetry reduction [31].

It is important to distinguish the framework topology or type from actual zeolite materials. Whereas the former is characterised as a pure framework structure of covalently bonded atoms, the latter describes concrete materials of deﬁned composition as found

10 2.1. Zeolites

(a) FER framework (b) FER channels (c) FER framework wrap

Figure 2.2.: Graphical representation of FER framework type in a projection along ~c with (a) O atoms displayed in red and T-atoms located on vertices in yellow, (b) wire frame presentation with internal channel surface indicated in blue and (c) complete framework wrap surface in green [31, 33]. Representation generated with JSmol on the Database of Zeolite Structures [34]. in natural deposits or synthesised in the laboratory. As mentioned before, a three letter code is designated to the zeolite framework type. Nonetheless, many synthesised zeolite materials often receive three letter codes in the style of framework types and a consecutive number. Popular examples include the FAU framework type for the type material FAUJASITE [31] or MFI framework topology with its type material ZSM-5. Other well-known materials exhibiting MFI type topology are SILICALITE-1 (purely siliceous), TS-1 (purely siliceous with Ti species) and BORALIT (purely siliceous with B species) [32]. The Atlas of Zeolite Framework Types (formerly the Atlas of Zeolite Structure Types) maintained by the IZASC presents an overview of the 234 currently known structure types with an additional 11 partially disordered structures. It also lists corresponding type materials as well as related materials for each framework type [31, 33]. Nevertheless, many zeolite materials exist, whose structure has not yet been solved, who do not pertain to a known structure type or who are only hypothetical in nature [32]. These materials are listed in a supplementary list. A hyphen preceding the three letter code indicates structures that are not fully four-connected or interrupted. The three letter code will be referred to as International Zeolite Association (IZA) code [31].

A feature of utmost importance for the application in industrial processes is the host dimensionality (Dh), describing the dimensionality of the pore system as zero (ﬁnite), one (chain), two (layer), or three (framework). Whereas the majority of exploited microporous materials exhibits a three-dimensional host structure, lower dimensionality in ordered ma-

11 2. Current state of research terials is not uncommon [31].

In Figure 2.2, the exemplary FER framework topology is visualised as a projection along ~c [31, 33] using the program JSmol [34], in which Figure 2.2(a) displays the the pure framework topology consisting of only O (red balls) and T-atoms (located at the vertices of the yellow wires). In Figure 2.2(b), the O atoms are omitted in favour of clarifying the framework topology in a wire frame or skeletal representation. Here, the free space inside the channels of the framework is highlighted in blue. Along the projection, the channel is proceeding in a straight manner. The last image (Figure 2.2(c)) consists of a full framework wrap or surface simulation of the FER type framework in green. The channels along the projection are pronounced in this representation as well.

12 2.1. Zeolites

✷✳✶✳✶✳ ❈♦♠♣♦✐✐♦♥

The general equation

+ + n1 n2 x− x1 M1 ..., x2 M2 , [(y1T1 , y2T2 ...)O2(y1+y2+...) ] z1A1 , z2A2 ... (2.1)

describes the zeolite composition with the framework components in brackets, and the other terms describing extra framework species in the pores and channels.

•M1,M2 represent cations with charge n1, n2 which compensate the negative charge

of the framework (x1 n1 + x1 n2 + ... – x),

•T1,T2, . . . are tetrahedral atoms, e.g. Si, Al, Ti, etc.,

•A1,A2, . . . describe water, electro-neutral molecules or ion pairs.

Silicon (Si) and oxygen (O) represent the key elements of a zeolite framework. If another element is substituted for Si, it needs to be compatible in a tetravalent environment with O. Possible T-atoms must follow certain rules regarding condensation behaviour and oxidation state in relation to the overall framework charge, in addition to the coordination state. The most frequent substitution to be observed is that of aluminium (Al) with Si/Al ratios ranging from 0.5 (e.g., BICCHULITE) to inﬁnity (e.g., SILICALITE-1). Regarding the Si/Al ratio, zeolites may be divided into one of these three groups [32]:

• zeolites with low Si/Al ratios ( < 5),

• zeolites with medium Si/Al ratios (5 to 10),

• zeolites with high Si/Al ratios ( > 10).

In general, the Si/Al ratio cannot fall short of one due to LOEWENSTEIN’S rule or the principle of Al avoidance in dependence on the PAULING electrostatic valence rule. Few known exceptions include BICCHULITE or Al-SODALITE. It states that whenever two tetrahedra are connected by an oxygen-bridge, the centre of only one of them can be occupied by Al, whereas the other centre must be occupied by Si or any other small ion of electro valence four or more, e.g., phosphorus (P). To ensure stability, at least one of two neighbouring Al ions bridged by the same O anion must have a coordination number larger than four (ﬁve or six) towards O. This rule results in the maximum substitution of 50 % of the Si in three- dimensional frameworks and plane networks of tetrahedra by Al. In practice, a rigorous alternation between Si and Al tetrahedra is imperative for a 50 % substitution, i.e., Si/Al = 1

13 2. Current state of research

[35].

Due to the exchange of the tetravalent Si4+ with trivalent (e.g., Al3+) or even divalent elements (e.g., Mg2+) and monovalent cations (e.g., K+), the framework is charged negatively, a process which leads to stabilisation of the structure through interaction with compensating cations, facilitating a synthesis in laboratory conditions. The cations in the pores and + channels of the materials are usually alkali, alkaline-earth metal cations or R4N (R = H, alkyl, aryl) ammonium cations, the latter of which decompose yielding charge compensation through protons during calcination, whereas the former may be exchanged with other cations [32].

Typically, the cations are hydrated (in particular when strongly polarised). In agreement with the composition of the reaction mixture and with the structure type, ionic pairs (e.g.,

NaCl, BaCl2, Pr4NF etc.) or molecules (e.g., amines, alcohols, etc.) are located inside the framework void spaces. By removing these species through calcination or exchange, the microporous volume becomes accessible for application and post-synthesis treatment [32]. The general procedure of hydrothermal synthesis will be discussed in the following chapter in more detail.

✷✳✶✳✷✳ ❙❛❜✐❧✐②

Even though zeolites are considered to be metastable materials, they exhibit remarkable chemical and thermal stability. Their microporous framework allows for a repeated hydration-dehydration reaction without structural collapse. This property makes it interesting as ion exchange material, molecular sieve or catalyst, as the material remains intact during and after reaction and may be recycled for renewed application.

✷✳✶✳✸✳ ❋✉♥❝✐♦♥❛❧✐②

The functionality of microporous materials is the integral property in many areas of modern science and industry. Cation exchange, sorption (gases, vapours), encapsulation and catalysis are the main areas of application for modern microporous materials. An important property for the functionality of a zeolite material is its interaction with water. Porous silicates contain silanol groups (≡Si-OH) and ≡Si-O-Si≡ bonds which interact with water in a homopolar and even hydrophobic manner. On the other hand, aluminosilicate zeolites, both natural and synthetic, display a strong interaction with water to the point of excellent drying capabilities. A direct relationship can be postulated for the sorption

14 2.2. Catalysis behaviour of water in crystalline aluminosilicate zeolites to the amount of tetrahedrally coordinated Al and its associated charge-compensating cations [36]. Due to the absence of framework charges and, consequently, the absence of compensating cations in the purely siliceous ZSM-5 end-member SILICALITE-1, strong hydrophobicity and organophilicity of the internal surface is observed. This property is exploited in the application as molecular sieve and as a catalyst, as water is not blocking valuable pore space during sieving and catalysis [32].

✷✳✷✳ ❈❛❛❧②✐

Naturally occurring aluminosilicate zeolites such as CLINOPTILITE, MORDENITE, OFFRETITE, FERRIERITE, ERIONITE and CHABAZITE are of great interest for the hydro- and petrochemical, as well as fine chemical industry, and more specifically, in heterogeneous catalysis. Since natural zeolites are of low chemical purity and only few deposits are actually large enough to mine, they are less interesting for industrial application. Therefore, synthetic porous materials come to use, on the forefront, the synthetic FAUJASITE (ZEOLITE X and Y) as catalyst in fluid catalytic cracking (FCC) with an added value of 10 billion USD per year worldwide. Catalysis is the solitary most significant application of zeolites in terms of financial market size (not in terms of tons produced) and amounts to 1 billion USD per year worldwide [32]. In contrast to conventional homogeneous catalysts, these zeolites can be considered as "green" catalysts, as they exhibit potential for reuse, produce low to no waste, save energy and are benign [37]. Still, a few of the natural zeolites are found in sufficient quantity and purity to be useful in industry. These are, in the order of importance: silica-rich HEULANDITE (also denoted as CLINOPTILOLITE), MORDENITE, CHABAZITE, ERIONITE, PHILLIPSITE, ANALCIME, and FER- RIERITE. They can be found in altered volcanic tuff deposits obtainable by open-pit mining in large quantities [29]. Approximately up to nine out of ten chemical processes are making use of heterogeneous catalysts, of which zeolites represent a major part. The global catalyst market is estimated to comprise of 15 to 20 billion USD per year. Whereas one half of this market is oriented towards the chemical industry and the other half geared towards environmental and refinery applications, the estimation of all these industrial catalytic processes ranges up to a multi- trillion USD level.

In conclusion, the value created by applying catalysts in industrial reactions is about three orders of magnitude higher than the amount invested in them [38].

15 2. Current state of research

The major use of zeolites in the area of reﬁnery and petrochemicals are cracking (e.g., oleﬁnes), epoxidation (e.g., propylene oxide), hydroxylation (e.g., phenol), hydrocracking (e.g., liquid petroleum gas (LPG)), alkylation (e.g., ethylbenzene, cumene), shape-selective reforming (e.g., hydrocarbons), de-waxing (e.g., heavy petroleum distillates and lubricat- ing oils), isomerisations (e.g., xylene to para-xylene, octane number enhancement of light gasoline), oximation (e.g., cyclohexanone oxime), synthesis of ethylbenzene from benzene and ethene, disproportionation of toluene to benzene and xylenes and methanol-to- gasoline conversion (MTG) [32, 38].

In the field of fine chemicals and clean technology, zeolites are utilised in organic oxidation catalysis, shape-selective fine catalysis and in the form of de-NOx and selective catalytic reduction (SCR) catalysts [2].

Catalysis represents one of the most important examples for a correlation of structure and property in microporous crystalline materials. Three fundamental zeolite characteristics lead to a suitable application in catalysis. These are hydrophobic or hydrophilic character, shape and size selectivity, as well as the acid strength, which is directly correlated to the number and adjustability of both BRØNST- EDT and LEWIS acid sites [2].

Shape and size selectivity are commonly achieved by the use of catalysts of nanoporous nature. Internal surface area and pore volume range around approximately 800 m2 g−1 and 0.35 cm3 g−1 respectively. The reaction selectivity of a catalyst may depend on reactant, product or intermediate [2, 32, 38]. Figure 2.3 shows the three possible discrimination processes of microporous materials during catalysis. An example of educt/reactant shape selectivity is illustrated in Figure 2.3(a), in which

(a) educt/reactant (b) product (c) transition state

Figure 2.3.: Schematic representation of different types of shape-selectivity important for catalysis in zeolites [2].

16 2.2. Catalysis only a specific type of reactant (e.g., solely linear, not branched or cyclic) can access the channel system of the zeolite. ZEOLITE A is an example for educt/reactant shape selectivity in the dehydration reaction of 1-butanol to butene. 1-butanol, as a linear chemical, may penetrate the narrow pores of ZEOLITE A, whereas its isomer iso-butanol can, due to its bulky shape, not. Product shape selectivity is defined as shown in Figure 2.3(b), in which many different products and isomers may form inside the pore structure of a zeolite. However, as the available space in the pore often exceeds the space inside the channel, only those products can leave the bulk material that stay below the channel dimension restrictions. ZSM-5 is a zeolite that exhibits product shape selectivity in the toluene transalkylation. Toluene enters the pore space of ZSM-5, in which all three isomers of xylene (ortho-, meta- and para- xylene) are formed. However, only the linear p-xylene isomer may leave the pore system due to the size restriction of the channels [32]. Figure 2.3(c) displays transition-state or intermediate shape selectivity, in which a reactant enters the pore space, and, due to the characteristic form and amount of space, only one type of transition-state is able to form. Thus, only one specific product is admitted. MORDENITE shows transition-state shape selectivity in the transalkylation of meta-xylene. Meta-xylene enters the pore space. Here, the transition product trimethyl- diphenylmethane forms (methyl-substituted diphenylmethanes). However, the 1,2,4- trimethylbenzene isomer is favoured over the 1,3,5-trimethylbenzene as its corresponding 1,3,5-transitional form is too large to be accommodated in the pore space of the catalyst and, consequently, not formed during reaction [39].

In order to provide a reliable selective behaviour regarding size and shape, the catalyst needs to have uniform pores with molecular dimensions. To ensure such a uniform pore system, the material has to exhibit a highly ordered crystalline structure as realised by zeolites and HLSs, whose frameworks inherently provide pores and channels. This intrinsic feature of the material class allows for the preferential adsorption of small molecules and the discrimination against larger ones. Because the variety of different three-dimensional crystalline framework topologies is almost inﬁnite (and theoretically is), the potential for corresponding unique functional and chemical application is, as well. The property of size and shape selectivity is the basis for molecular sieving [38].

The cation exchange potential has been applied for many years now in mundane tasks like water softening in the laundry detergent industry, but also in critical assignments such as radioactive waste encapsulation of 137Cs after the CHERNOBYL nuclear disaster in 1986

17 2. Current state of research

[2]. Zeolites were also employed after the FUKUSHIMA nuclear disaster in 2011 for the removal of primary caesium and the removal of radiocaesium from water [40]. This capability is also crucial for the application in catalysis. Due to their internal geometry of channels and pores and the resulting high surface area, nanoporous catalysts can be synthesised to contain a high density of active sites, which are imperative in reactions on a molecular scale [38].

Depending on the synthesis route or post-synthesis treatment, structure type and chemical composition, the zeolite framework may possess defects in the shape of non-bridging oxygen, vacancies or mesopores [31]. A typical zeolite material designed to possess mesopores is MCM-41 (now known as a hierarchical zeolite, since it maintains a hierarchy of micropores and mesopores within the material). Also, the coordination of T-atoms may be modiﬁed by extra framework species such as organic molecules in the pores and channels of the material [32, 38, 41].

The important basis for zeolite catalysis is the presence of BRØNSTEDT and LEWIS acid sites. The acidity in conjunction with the porous nature of the material is the key feature for catalysis.

ALEWIS acid site is deﬁned as a molecular species (and the corresponding chemical species) that, due to an empty orbital, is an electron-pair acceptor and, therefore, able to interact with a LEWIS base to form a LEWIS adduct, by sharing the electron pair supplied by the LEWIS base in a coordinative bond. Any species containing an orbital not involved in bonding can represent a LEWIS base. An example for a LEWIS base is NH3, since it is able to donate a lone pair of electrons, whereas Me3B (trimethylborane) would be a LEWIS acid, as it is able to accept a lone electron pair.

In a catalyst, the LEWIS acid site is a positive ion (cation) such as Al3+ rather than an ionizable proton (H+)[42, 43].

The BRØNSTEDT acid on the other hand, is described as a molecular species (hydron donor) suited to donate a hydron/H+ to a base or the corresponding chemical species. + 4 – Examples include H2O, H3O , CH3CO2H, H2SO4, HSO , HCl, CH3OH, NH3. In a catalyst, the BRØNSTEDT acid site is an ionizable H+ [42, 44, 45].

The basis for this theory is that as soon as an acid and a base react with each other, the acid forms its conjugate base, and the base forms its conjugate acid by trading a proton (H+). In general, this theory is closely related to the ARRHENIUS theory [44, 45].

18 2.2. Catalysis

Catalytic activity in the form of BRØNSTEDT and LEWIS acid sites in microporous framework materials is caused by an imbalance between metal oxygen stoichiometries and the formal charge on the cations. The formal charge is 4+ for the silicon (Si) ion and 2− for the oxygen (O) ion. In a three-dimensional zeolite, every O atom belongs to two tetrahedra respectively, causing internal framework neutrality and resulting in no acidic properties whatsoever. By partial substitution of Si by Al (but also other trivalent metal cations, such as B), the formal charge on the metal cation reduces from 4+ to 3+, causing a negative charge of the tetrahedron containing the Al cation. Figure 2.4 highlights the balancing of the negative charge by a H+ or a metal cation, effectively constituting a BRØNSTEDT and a LEWIS acid site, respectively. It has been established that the bare negatively charged tetrahedron is denominated as the corresponding base. The charge of the metal cation or H+ and the O will govern acidic or basic properties in the zeolite material and, thus, be identiﬁed as solid acid or base. Chemical composition and framework structure are of great importance for the acid or base strength [2].

It is prudent to state that the Al concentration in the framework is directly correlated to the number of acid sites and the lattice polarity. Indirectly, this correlation can be extended to the strength of the acid sites. A very well known example is the direct relationship between the activity of H-ZSM-5 and the Al content for hexane cracking. However, it is difﬁcult to conduct exact measurements and quantiﬁcations of the acid/base strength. A comparison to a liquid catalyst is not unambiguously possible since the stabilisation of carbocations and carboanions in a microporous material differs from that in strongly polar acid and base solutions. To establish an ideal Al content for a maximum amount of BRØN-

Figure 2.4.: Acid sites important in zeolites. The BRØNSTEDT acid sites can be seen as a resonance of structures I and II [2].

19 2. Current state of research

STEDT acid sites, the zeolite should be prepared with the lowest possible Si/Al ratio (as part of the feasibility regarding LOEWENSTEIN’S rule). However, due to the resulting average low electronegativity of the framework, only weakly demanding reactions are to be catalysed by present acid sites. For strongly demanding reactions, a higher Si/Al ratio is necessary due to the decreased proton bond-dissociation energy that correlates with an increasing Si/Al ratio. The BRØNSTEDT acid site strength is highest when the Al tetrahedron is completely isolated in the regarded framework. Therefore, a small amount of Al is advantageous in conjunction with a small particle size.

By isomorphic substitution, the BRØNSTEDT acid site strength may also be altered, provided the substitution is conducted using TIV or TIII transition metal ions.

Controlling the location and strength of acid sites can have a major effect on catalytic activity. Not only Al, but also other trivalent atoms such as B can isomorphously substitute Si. By introduction of a heteroatom other than Al, the location of Al may be directed due to the preferential incorporation of B on speciﬁc sites. By then removing B in a post-synthesis deboronation step, the BRØNSTEDT acid site framework Al is positioned and concentrated at desired sites to enhance catalytic activity [46]. An example is the H-MCM-22 zeolite, in which the preferential location of B in T positions facing surface pockets and super- cages of the MWW structure are suffering from carbonaceous depositions. This location concentrates the BRØNSTEDT acid sites associated with Al into the 10-ring sinusoidal channels, where the alkene-based cycle is sterically favoured. Hence, the catalyst shows a high selectivity toward propene and butenes and an improved long-term stability [47]. New chemical compositions of known structures are prepared in this manner. An example represents AlPO4 based on [AlO4] and [PO4] derived from silicoaluminophosphate (SAPO) structures by exchanging Al3+ by Ga3+ or B3+ atoms, or Si4+ by Ge4+ atoms [2].

A special role is taken by Ti4+, since, according to PAULINGS criterion, the ionic radius of Ti4+ is too large to fit the silicate framework and prefers hexa-coordinated complexes. The assumption that both cation and anion radii vary with coordination number still applies [48]. However, some materials exhibit extraordinary framework flexibility to contain Ti4+ cations. TS-1 and Ti-MCM-41 represent two of those microporous materials resulting in lattice distortion around the Ti4+-cation and many defect groups (Si–OH, Ti–OH), which, in turn, influence catalytic activity of the zeolite [49].

Ti-zeolites are generally recognised for their efﬁcient and selective epoxidation of oleﬁns.

20 2.2. Catalysis

TS-1 additionally catalyses a broad range of oxidation reactions with hydrogen peroxide as oxidant. In Ti-zeolites, Ti is isolated and specifically tetrahedrally coordinated in an isomorphous substitution with two positions easily accessible for electron-donating ligands such as water, alcohols, peroxides and amines. The result is a higher resistance of the Ti site against hydrolysis compared to isolated Ti species on amorphous silica. Also, the resulting relatively strong hydrophobicity makes for an ideal adsorption of alkanes and enabling fast desorption of a catalyst product. The low concentration of permanently present hydrogen peroxide during reaction favours an efficient catalyst application. Oxidation is performable up to high conversion with high selectivities and high efficiencies [32]. It is of importance to note the low amount of Ti in TS-1 of only 1 %, resulting in only one Ti atom out of 96 T-atoms. This small quantity of Ti is enough for a favourable functionality in catalysis, provided a small size of crystallites and a perfect framework. The flawlessness of the TS-1 framework is imperative for successful application in catalysis. Introducing non-framework transition metal cations into microporous and mesoporous matrices can unlock the potential for novel catalytic applications by investigating their electronic, adsorptive and catalytic properties, which differ fundamentally from the properties of the same cations on bulk oxides, supported on amorphous carriers or adsorbed to microporous solids. It is known that non-framework cations are drastically impacted by the environment of the zeolite since it provides a strong localised electrostatic field that, in turn, changes the chemistry of the cation. However, the exchange or introduction of metal cations into the framework structure of a zeolite is not always as trivial as simple impregna- tion or precipitation as is common for the preparation of supported oxidic catalysts [50, 51].

Common techniques for the inclusion of metal cations beside the direct introduction during synthesis include precipitating a salt into or onto the zeolite, exchanging cations by aqueous techniques and vapour transport of a metal salt/complex in addition to the mixing of solid oxides with zeolites or precipitating the metal in the presence of the zeolite [51]. Transition metal cations such as Fe3+, Ti4+ and V4+ in the zeolitic framework can appear on any position, such as framework positions, surface defect sites (Si-O-Me), cation exchange sites, oxide clusters inside or outside of the pores of the microporous material or as bulk oxides on the external surface. The relative distribution of these metal cations may be limited to one of these positions or span them all in differing concentrations and depends predominantly on the synthesis procedure and post-synthesis treatments such as drying and calcination. For example, in a basic medium (pH 9-13), Fe3+ and Ti4+ form insoluble oxides or hydroxides, whereas V4+ and V5+ produce soluble oxides. Ti4+ forms stable alkali metal titanates as well [52].

21 2. Current state of research

Exemplary successful incorporation of Fe3+ cations on framework Si4+ positions of ZSM-5 is highly dependent on the Fe3+ and Al3+ concentration of the synthetic mixtures, pH value + + of the initial solution, stepwise exchange of Na by NH4 ions, and the calcination of the 3+ 4+ 3+ NH4 to the H form. During this experiment, a Fe saturation limit at ratios of Si /Fe < 30 was observed. Also, a preferable position of Al3+ - if present - is observed while Fe3+ are preferentially found in the pores of the microporous material [53]. The position of Al, but also of other heteroatoms has some influence on the catalytic properties of the material. Therefore, the pinpoint incorporation to specific positions in the framework is of particular interest and the centre of further studies. The utilisation of microporous materials in the field of catalysis is a science in and of its own. It is tied to a large variety of conditions needing to be considered. At the same time though, these conditions enable a myriad of opportunities to tweak and optimise known catalytic properties and, furthermore, to open up completely new fields of application.

✷✳✸✳ ■♥❡❧❛②❡ ❊①♣❛♥✐♦♥ ❛♥❞ ❚♦♣♦❛❝✐❝ ❈♦♥❞❡♥❛✐♦♥

The process of interlayer expansion is mentioned as early as the 1950s in the application to natural layered silicates such as MICA, VERMICULITE, BIOTITE and MONTMORILLONITE [54, 55], whereas in recent years, there has been a gradual rise in research, both in natural and increasingly in synthetic layered materials. Per deﬁnition, an interlayer expansion is described as a breaking of interlayer bonds and subsequent widening of individual layers of minerals, such as phyllosilicates, clays or synthetic zeolites and layered metal oxides and is also known as swelling [56, 57]. The layers need not to be connected at all, but charge matching cations may occupy the void space between single layers that are only weakly bonded to the framework host. ROTH et al. [57] give a very extensive overview of layered materials (two-dimensional zeolites), many of which belong to the class of HLSs, and their various synthesis routes and post-synthesis modiﬁcations, while MARLER and GIES [5] and GIES et al. [9, 18] concentrate on an elaborate review with particular emphasis on HLSs to be used as precursors for the creation of three-dimensional zeolites via topotactic condensation and interlayer expansion. MARLER et al. discuss on the topotactic condensation of fer-type layers to three-dimensional porous tectosilicates [58].

Already in 1950, BARSHAD demonstrated in his papers that an interlayer expansion is

22 2.3. Interlayer Expansion and Topotactic Condensation

possible in MICA type layered minerals by immersing them in liquids of varying dipole moments and dielectric constants. Hence, the process of interlayer expansion was determined by size, charge, and total amount of the interlayer cations and by the magnitude of the dipole moment and the dielectric constant of the immersion liquid [55, 57].

Whereas zeolites possess a three-dimensional open-framework and crystallise under hydrothermal conditions, another method of synthesising microporous materials exists with particular emphasis on layered zeolitic materials [59]. The term of topotactic condensation has been coined in recent years in the application to synthetic zeolites and layered silicates, especially in the works of MARLER et al. [5, 17, 58, 60, 61] and YOKOI et al. [56], as well as [62] and has not been illustrated as ubiquitously as the classical hydrothermal synthesis route yet [5].

Different post-synthesis procedures are illustrated in Figure 2.5. By structural conversion of hydrous layer silicates (HLSs), three-dimensional framework materials of microporous nature can be produced. The process is that of a topotactic (poly-)condensation of silanols on the HLSs. During this process, or in a separate step, the interlayer spacings can also be expanded to create interlayer expanded zeolite (IEZ) materials. IEZ materials are crystalline and demonstrate comparable physical and chemical properties to ordinary zeolites. By generating larger interlayer space, bulkier reactants may penetrate the structure, effectively decreasing diffusion constraints during catalytic reactions. To date, the MWW-, MFI-, RRO-, SOD-, PCR-, FER-type zeolites [56, 57, 63], but also natural minerals like KANEMITE [64] and materials with CRISTOBALITE type layer (cri), caesium aluminosilicate type layer (cas), FER type layer (fer), HEULANDITE type layer (heu), HUS type layer (hus), MWW type layer (mww), RUB twenty-four type layer (rwr)[7] are under investigation to beneﬁt from interlayer expansion for the application in industrial catalysis. Theoretically, any layered precursor my serve to establish new and commercially interesting microporous materials.

For a successful topotactic condensation reaction of layered materials, the precursor should already consist of a well ordered structure without defects and contain strong interlayer hydrogen bonds while simultaneously not containing strong intra-layer hydrogen bonds. Also, a suitable cation should be part of the precursor since it takes a major role in the formation of a three-dimensionally connected microporous material with regards to size, geometry, ﬂexibility and thermal stability, as well as stacking sequence and order [58].

ROTH et al. [67] have initially reported on a complete swelling of MCM-22P as the ﬁrst swollen precursor in an intermediate step toward the pillared zeolite MCM-36.

23 2. Current state of research

Swelling Deswelling → → (a) RUB-36 (b) RUB-36SW (c) PREFER-1 Delamination Calcination Calcination ↓ ↓ ↓

(d) RUB-37 (CDO) (e) fer layers (f) ZSM-35 (FER)

Figure 2.5.: Post-synthesis modiﬁcations of layered zeolite precursor RUB-36 as (schematic) wire or skeletal frame representation. T-atoms are located at the vertices and the lines connecting them represent T-O-T bonds. Displayed are the layered precursor (a) and the products of swelling (b), deswelling (c), calcination (d) and (f), delamination (e) [19, 65, 66].

Swelling of MCM-22 has later been reported to be the kick-off toward synthesis of the delaminated ITQ-2 [68]. Delamination of a layered precursor yields crystalline monolay- ers with around 700 m2 g−1 of deﬁned external surface with preserved microporous pore systems. The resulting material possesses strong acidity and stability similar to that of conventional zeolites but simultaneously presents high accessibility to large molecules the likes of amorphous aluminosilicates. Pillaring, on the other hand, is a further step after initial swelling. The swelling molecules are removed, whereas new species are added to connect individual layers to a new microporous three-dimensional framework [69].

ROTH et al. later investigated the various modiﬁcations on the FER- and CDO-type zeolites [66] whereas ZHAO and co-workers demonstrated similar conversion procedures for the HLS RUB-36, a CDO precursor, into FER by a swelling-deswelling procedure [19]. Figure 2.5 illustrates the numerous post-synthesis alterations on starting material RUB-36.

24 2.3. Interlayer Expansion and Topotactic Condensation

RUB-36 (Fig. 2.5(a)) starting material is an HLS and possesses fer-type layers in a CDO-type stacking. These layers, however, are not connected, but the SDA DEDMA (represented by the blue spheres) occupies the space between neighbouring layers. By simple calcination, these layers can be condensed topotactically to form the CDO-type three-dimensionally connected zeolite RUB-37 (Fig. 2.5(d)). A swelling, on the other hand, may be achieved by + using the long chained quaternary ammonium molecule C16TMA (cetyltrimethylammonium hydroxide (CTAOH), C19H42OHN) to create RUB-36SW (Fig. 2.5(b)). The molecule (represented by the green elongated ellipsoids) replaces the SDA and widens the distance between neighbouring layers. During deswelling, the largest part of the CTAOH molecules is removed. Nonetheless, a few molecules persist in the interlayer region (represented by the green ellipsoids) to produce the FERRIERITE precursor PREFER-1 (Fig. 2.5(c)). By cal- cining PREFER-1, a typical FER-type zeolite is created (Fig. 2.5(f)). Instead of deswelling, delamination may be performed to produce single fer-type layers (Fig. 2.5(e))[19].

The swelling or interlayer expansion process has been thoroughly investigated by application to the PLS-1 material [13]. To indicate an interlayer expanded material, TATSUMI and co-workers have introduced the (unofﬁcial) designation IEZ to be added to the structure type, as has been the case for RUB-36. Figure 2.6 shows the interlayer expansion process as applied to RUB-36 (2.6(b)) to form IEZ-RUB-36 or COE-3 (2.6(c)) in contrast to mere calcination to obtain RUB-37 (2.6(a))[9, 70]. In a further step, a combined isomorphous substitution of Ti for Si and interlayer expansion for the use in catalysis has been suggested by YANG et al. [26]. Several different three- dimensionally linked IEZ structures with tetrahedrally coordinated Ti in the framework to produce IEZ-Ti-PLS-3. This new structure shows catalytic properties in epoxidation reac-

∆ ←+ T DCDMS→ (a) RUB-37 (CDO) (b) RUB-36 (c) COE-3 (IEZ- CDO)

Figure 2.6.: Materials derived from layered zeolite precursor RUB-36 as (schematic) wire frame representation. T-atoms are located at the vertices and the lines connecting them represent T-O-T bonds. Displayed are the layered precursor (b) and the products of topotactic condensation (a) and interlayer expansion with DCDMS (c) [9, 70].

25 2. Current state of research tions of alkenes with hydrogen peroxide.

Sn as a linker has been utilised by BIAN et al. [24, 25] in layered zeolite precursor COK-5 using interlayer expanding agent DCDMS and, optionally, a Sn-salt creating COE-5 and Sn- COE-5 materials. Compared with the starting material COK-5, calcined COE-5 exhibits a higher catalytic performance in the acetalisation of glycerol with acetone to produce solke- tal. Similarly, and, due to the presence of Lewis acidic sites in the Sn-COE-5, the material also shows much higher activity in the conversion of glucose to levulinic acid than COK-5. Both post-synthesis modiﬁed materials exhibit higher activity in certain catalytic reactions compared to their starting material analogues.

On a another note, DE BAERDEMAEKER et. al. [22] have successfully inserted Fe as a linker between the IEZ layers of RUB-36, subsequently connecting them, whereas GIES et. al. (2016) [23] were able to extend this process to other metal heteroatoms such as Sn in a single step of interlayer expansion and topotactic condensation. The Fe-IEZ-RUB-36 shows remarkable stability and catalytic properties. Due to the success of this conversion process, other metal cations such as aluminium (Al), zinc (Zn), europium (Eu) and titanium (Ti) come into consideration for a metal interlayer expansion on RUB-36 starting material.

✷✳✹✳ ♦❜❧❡♠ ❛♥❞ ♦❜❥❡❝✐✈❡ ♦❢ ❤✐ ✇♦❦

This work aims to investigate the process of interlayer expansion using metal (Me) cations as reactive centres on linker sites of HLSs to produce zeolites of different framework topology.

Today, several HLSs with different layer topologies have been converted into fully condensed zeolites of different framework types by topotactic condensation at temperatures of around 773 K and simultaneous expulsion of interlayer species such as water or organic cations [5].

Whereas preceding papers have presented the successful topotactic condensation and interlayer expansion using Sn and Fe as linkers into the framework of RUB-36, this work is extending the synthesis route to other cations such as Co, Ti, V and Zn. The synthesis parameters are based on previously reported syntheses, wherein cations are incorporated via cation acetylacetonate (acac) instead of the corresponding cation salt [23].

26 2.4. Problem and objective of this work

The goal is not only a feasibility study, but also an investigation as to whether the same synthesis route is applicable to any type of cation for the production of industrially applicable Me-IEZ-RUB-36 as catalyst materials with identical, or at least similar framework structure. The suggested synthesis route is very straightforward and only requires one simple step in the post-synthesis modiﬁcation as opposed to the two-step approach of interlayer expansion and introduction of metal cations to the interlayer region of the investigated material.

✸✳ ❍②❞♦❤❡♠❛❧ ②♥❤❡✐

There are numerous approaches to the synthetic production of microporous and mesoporous materials, among them hydrogel processes, clay conversion and hydrothermal synthesis. The hydrothermal synthesis is a powerful tool to generate microporous materials for industrial application. During natural zeolite genesis, large crystals grow in cavities of basic volcanic or metamorphic rocks in the presence of mineralising solutions over geological time scales. In a metamorphic transformation, volcanic glass and sedimentary marine rocks are recrystallised as zeolite micro-crystallites [71]. The hydrothermal synthesis is a branch of solvothermal synthesis, which requires a solvent for the reaction. In the case of hydrothermal synthesis, this solvent is water. Non-aqueous solvothermal methods use viscous solvents such as ionic liquids or, speciﬁcally, pyridine and mineralising agents. In addition, small amounts of water might be employed. Since the reactant gel favours diffusion processes rather than convection, synthesis yields larger crystals [72, 73].

Even though the exact formation process of natural zeolites is not yet fully understood, and is not adequately described by the traditional deﬁnition of reactant composition, temperature and pressure, the laboratory synthesis approach mimics natural conditions, i.e., low temperature, low pressure, and basic aqueous solutions. The crystallisation regimen for natural zeolites is called the zeolite facies and serves as an indicator for the temperature and pressure domain. Derived processes like polymerisation-depolymerisation, solution- precipitation, nucleation-crystallisation, and other complex phenomena encountered in aqueous colloidal dispersions play a no less important role in hydrothermal synthesis [74]. Unless the synthesis process is stopped prematurely, a more stable, denser phase such as QUARTZ is likely to form. This kinetically controlled limitation is also a reason for the frequent emergence of planar faults [28]. OSTWALD’S rule of stages states that if a system is far away from equilibrium, intermediate metastable phases closest in energy to the original state (lower surface energy) generally crystallise before the thermodynamically stable phase with the least amount of free energy. This applies as well for zeolites, as the metastable zeolitic polymorphs display a more complex structure, drastically lower density and lower surface energy than the stable,

29 3. Hydrothermal synthesis more denser phases [32]. A more commonly known example for this rule is realised in two polymorphs of titanium dioxide. The ﬁrst phase to crystallise from amorphous precursors or solutions will be the metastable ANATASE exhibiting lower surface energy, whereas RUTIL represents the equilibrium phase on the entire temperature and pressure spectrum [75].

OSTWALD himself suggested that the solid ﬁrst formed on crystallisation of a solution or a melt would be the least stable polymorph on account of irreversible thermodynamics, structural relationships, or a combined consideration of statistical thermodynamics and structural variation with temperature. OSTWALD’S rule of stages should not be regarded as a universal law but only as a possible tendency in nature [76]. Therefore, the conditions imperative for a successful synthesis include reactive starting materials, a relatively high pH value and hydrothermal temperatures of 353 K to 523 K at pressures ranging from 100 kPa to 2000 kPa at saturated autogeneous water pressure. To ensure formation of a large number of crystals, the degree of supersaturation of the starting mixture should be high. In a typical synthesis, Si and Al compounds are added to a structure directing agent (SDA) with alkali metal cations in a hydrothermal teﬂon-lined steel reaction cylinder or a silica glass capillary, the latter of which represent a more volatile synthesis vessel.

A generalised reaction scheme can be written as

y p,T n y xSiO2 + yAl2O3 + zH2O + cat → cat [Six Aly O]zH2O (3.1) n n where cat represent cations paramount for the charge-balance. By raising the temperature, an autogeneous pressure is developed inside the vessel. This is the pressure at which the liquid and its gaseous form co-exist for the chosen temperature (for example at 453 K, water and steam co-exist at about 1 MPa pressure) [77, 78]. Next to the traditional hydrogel process, it is also possible to synthesise zeolites by con- verting natural clay materials, such as KAOLIN to lower purity zeolite powders. Still, this process is not favoured, as many starting parameters such as chemism and consistent quality are not as readily guaranteed as pure and synthetic materials.

BARRER and co-workers have successfully synthesised the ﬁrst zeolite materials in the early 1940s by combining SiO2 and Al2O3 units in a hydrothermal environment [79, 80]. Zeolite TYPE A, on the other hand, has been the ﬁrst synthetic zeolite material produced, which was later established to be produced in a commercially large-scale synthesis. Sili- con sources include co-precipitated gels, colloidal/amorphous silica, waterglass, pyrogenic silica or silicon alkoxides such as tetraethoxysilane, tetraethyl orthosilicate (TEOS) and

30 tetramethoxysilane, tetramethyl orthosilicate (TMOS), each inheriting a different degree of polymerisation. The addition of Al occurs through compounds such as GIBBSITE, PSEUDO- BOEHMITE, aluminate salts, aluminium alkoxides or as metal powder. Water contents differ greatly with each silicon source, which is why they have to be taken into account in the synthesis composition [2, 71, 81].

Zeolites are one of the most versatile material classes with over 250 individual framework types, each of which can be realised by exhibiting varying chemical composition. For example, the natural type material for the chabazite (CHA) framework type is CHABAZITE with a CaAlSiO composition. In addition, all-silica, aluminosilicate, AlPO4, MeAlPO, as well as SAPO materials exist that exhibit CHA type topology. The same applies for the majority of the other framework types. Each material has its own speciﬁc synthesis and stability ﬁeld, in which it crystallises with differing stoichiometric composition. Natural zeolite materials generally exhibit a large chemical variety. Purely siliceous materials are rarely found. As the Si-Al zeolite framework needs a charge compensation provided by cations such as Na or K, they are usually added to the reaction mixture. The experimental charge density mismatch (ECDM) approach follows the rules of framework charge balance. The aluminosilicate reaction mixture is described by the mismatch of charge density on the SDA and the formation of the potential aluminosilicate network [82]. Certain alkali cations were associated with the presence of cage-like structures, leading to the templating aspect of these cations. By addition of a template or SDA, the synthesis is guided through polymerisation or organisation of the anionic building blocks that form the framework toward a desired output. The size and shape of the SDA is of great importance as it represents nucleating centres of similar size and shape around which the microporous framework will form. Since there is a number of microporous materials that may be synthesised without an SDA, but with the addition of appropriate seeds, today, a templating agent is not strictly necessary. However, the majority of syntheses still makes use of templating molecules such as alkali metal hydroxides and quaternary tetraalkylammonium hydroxides. A mixture of larger organic and smaller alkali cations provides an improved synthesis composition. Hereby, the general form of the SDA as a template determines the type of cage and, thus, the framework type generated during synthesis.

As bulky molecules lead to more cage-like structures, larger and more complex ones generate the formation of channels (e.g., 1,8-diaminooctane in ZSM-48) and even channel- intersections (e.g., TPA+ in ZSM-5) [74]. Increasingly large and elaborate organic SDAs are being investigated to produce new and unique framework types for size and shape selective

31 3. Hydrothermal synthesis applications. Likewise, cost reduction and improved efﬁciency play an important role in ﬁnding novel SDAs for zeolite synthesis [83, 84].

For the direct synthesis of high-silica zeolites with Si/Al ratios of 10 and above, organic templates are used and later removed from the framework by calcination. The higher the Si/Al ratio, the lower the crystal growth rates (hours to days rather than minutes to hours) and the higher the necessary synthesis temperature (373 K to 473 K rather than 353 K to 393 K) [85].

An alternative or further synthesis step is on the rise for the formation of new three- dimensional framework materials from layered precursor structures of pure Si or high Si/Al ratio with one- or two-dimensional channel structures in the form of solid state topotactic transformations (see Chapter 2 Section 2.3)[83].

✸✳✶✳ ❍②❞♦❤❡♠❛❧ ③❡♦❧✐❡ ❣❡♥❡✐ ❛♥❞ ②♥❤❡✐

Figure 3.1 exhibits the secondary building units (SBUs), which represent a theoretical topological building unit assigned to corresponding zeolites in an attempt to express their structure of ﬁnite or inﬁnite (i.e., chain- or layer-like) component units [6, 33]. Primary building units (PBUs) are single [TO4]-tetrahedra. In a SBUs, each T-atom is located at a corner or termination (in Figure 3.1 as small circles), whereas O-atoms are not explicitly depicted but positioned near the mid-points of connecting lines. Many zeolite frameworks can be described by using simple, single SBUs [2].

Figure 3.1.: Common SBUs identiﬁable in zeolite frameworks [2, 33]. T-atom are located at vertices and O near the mid-points of connecting lines. Numbers represent the quantity of T-atom.

32 3.1. Hydrothermal zeolite genesis and synthesis

PBU

SBU 4-Ring 6-Ring

CBU d4r sod d6r

Framework Type LTA SOD FAU

Figure 3.2.: Building Zeolite TYPE A (left), SODALITE (centre) and FAUJASITE (right) using PBUs to SBUs to CBUs [2].

Some of the units are very prominent and appear in several different framework structures. Examples are the double 6-ring, CANCRINITE cage, SODALITE cage and the alpha cavity. They can be used to identify relationships between different framework types [6]. An extensive list of composite building units (CBUs) is given by VAN KONINGSVELD in the Compendium of Zeolite Framework Types [86]. The distinction between SBUs and CBUs is that the latter is not necessarily achiral or used to build the entire framework. The denotation of CBUs is kept in lower case italic three-character code. With the exception of d4r, d6r and d8r, a code corresponding to one of the Framework Types containing the CBU has been used for this purpose. Figure 3.2 depicts the formation of a complete zeolite structure from smallest to largest building unit as it is rationalised today. Single [TO4] tetrahedra as PBUs represent the initial assembling blocks. Colloidal silicon dioxide, silicic acid, TMOS and silica gels are common starting materials for the synthetic zeolite genesis. With the aid of SDAs in the form of organic cations such as TPA+, more complex SBUs, and by extension, CBUs are generated. A very common and well investigated CBU is the sod- or β-cage as depicted in the middle of Figure 3.2. In the wire frame depiction, single atoms are neglected in favour of the connecting Si-O-bond in which Si is located at the vertices and O near the mid-point of the line between two neighbouring vertices. Regarded along these lines, the sod-cage takes the form of a cubo-octahedron and builds the basis for many zeolite framework types by the use of 4- and 6-ring SBUs. An example is the theoretical connection of individual sod-cages by double 4-ring-units (CBU d4r, tetragonal prisms, SBU 4-4 in Figure 3.1) to construct the TYPE A zeolite (Figure 3.2 left hand side), with the three-letter code LINDE Type A (LTA). The direct connection of the β-cage square sites results in the SOD-type structure of the

33 3. Hydrothermal synthesis same name (Figure 3.2 centre). By connecting them via their hexagonal faces or double 6-ring-units (CBU d6r, hexagonal prism, SBU 6-6 in Figure 3.1), the FAUJASITE type zeolite framework (structures ZEOLITE X and ZEOLITE Y are of the same framework type) can be constructed (Figure 3.2 right hand side) [2, 87].

These theoretical building units should not be equated with physical species actually present in the reaction gel. The assembly of framework types by linking SBUs or CBUs solely serves the understanding of the framework, as only (poly-)condensation of [TO4] tetrahedra is needed during synthesis for the zeolite assembly.

Theoretically, using the common SBUs or CBUs and linking them by different symmetric operations under the conditions of adequate energy minimisation and framework density, an infinite number of framework types may be generated. In fact, the IZASC has provided a supplementary list of these hypothetical structures of which more than 5 million are listed in a specialised database [88]. Each zeolite material can be depicted in a phase diagram, where there are no narrow limits regarding temperature, pressure, pH-value and starting materials. Different SDAs produce the same zeolite under the same conditions and vice versa. The Atlas of Zeolite Framework Types lists each acknowledged framework type in addition to the type material, but also the crystallographic information file (cif) from which the structure can be plotted graphically, as well as experimentally measured powder diffraction patterns [31, 33]. Standard synthesis procedures for known structure types are described in the listed references and also in a separate compendium in the Verified Syntheses of Zeolitic Materials for a quick and straightforward synthesis [89]. For example, it is feasible to synthesise the FER-type material using propylamine, buty- lamine or pentylamine as SDA, respectively. Crystallisation times vary, as do crystal shape and size and Si/Al ratio [90].

✸✳✷✳ ❍②❞♦❤❡♠❛❧ ②♥❤❡✐ ♦❢ ❘❯❇✲✸✻ ❤②❞♦✉ ❧❛②❡ ✐❧✐❝❛❡

In a similar fashion as HLSs, lamellar polysilicates are found in nature (albeit very seldom) in minerals such as CARLETONITE, KANEMITE, KENYAIITE and MAGADIITE [91]. They can be synthesised in the presence of ethyl alcohol as organic co-solvent starting from hydrogels and alkaline solution and even transformed to three-dimensionally linked materials [92].

34 3.2. Hydrothermal synthesis of RUB-36 hydrous layer silicate

The synthesis of purely siliceous HLS RUB-36 is much more straightforward, requires little preparation and ensures a high reproducibility and crystallinity of the product. Figure 3.3 exhibits the reaction and conditions for the hydrothermal synthesis of purely siliceous HLS RUB-36 (Figure 3.3(c)) with DEDMA (Figure 3.3(a)) and silicic acid (Fig- ure 3.3(b)) as proposed by GIES et al. [9] in addition to the stoichiometric conversion speciﬁed in Equation (3.2).

As-made RUB-36, [(CH3)2(C2H5)2N]4(OH)4Si36O72 is synthesised using silicic acid (gel, water content 9.4 %) as a silicon source and DEDMA hydroxide in water (20.62 wt%) as organic structure directing agent at autogeneous pressure and a temperature of 413 K in a teflon-lined stainless steel autoclave for 20 d without stirring. Starting materials are placed in the teflon cup, stirred for two hours and then placed in the autoclave, which is put in the oven. In Figure 3.4(b), a custom made stainless steel autoclave is shown with the teflon cup 3.4(a). The molar composition of the synthesis mixture is 0.5 SDA : 1.0 SiO2 : 10-12 H2O.

413K,20d + → (a) DEDMA (b) silicic acid (c) RUB-36

Figure 3.3.: Materials and synthesis procedure for RUB-36 [9, 17, 58, 63]. (a) SDA DEDMA (b) Si source silicic acid (c) hydrothermal product RUB-36.

+ 4(CH3)2(C2H5)2N + 36SiO2 + 4H2O → [(CH3)2(C2H5)2N]4(OH)4Si36O72 (3.2)

After synthesis, the material is cooled at room temperature, recovered, washed with deionised water, decanted and dried at room temperature for two nights. Calcination is conducted at 873 K with a heating rate of 1 Kmin−1 in air atmosphere and yields yellow- brown material, the condensed product RUB-37 [9, 17, 58, 63].

material SiO2 DEDMA temp. time g g K d RUB-36 1.3363 5.78 413 20

Table 3.1.: Synthesis conditions and starting chemicals of RUB-36 [9].

35 3. Hydrothermal synthesis

(a) teﬂon container (b) stainless steel autoclave

Figure 3.4.: Teﬂon container (a) and stainless steel autoclave (b) for the hydrothermal synthesis.

An Al-containing RUB-36 may be produced analogously by adding an Al source with an Si/Al ratio of approximately 100 via direct synthesis to produce a highly shape-selective catalyst for hydrocarbon conversion. The channel system of the calcined product Al-COE-4 possesses 10-rings as opposed to the 8-rings of the not interlayer expanded, calcined RUB- 36, RUB-37 [63].

Figure 3.4 depicts the equipment needed for hydrothermal synthesis of the microporous material. There are different procedures for preparing the starting materials of the reaction mixture. The easiest and fastest methods is to mix the initial reactants directly in the teﬂon container while continuously stirring using a stirring bar to ensure a uniformly distributed blend. To avoid hydrolisation and precipitation, it may be necessary to add a liquid silicon source such as TMOS in a drop wise fashion to the other starting materials. In other cases, the starting materials are mixed in a water quench.

✸✳✸✳ ♦✲②♥❤❡✐ ❡❛♠❡♥

✸✳✸✳✶✳ ■♥❡❧❛②❡ ❊①♣❛♥✐♦♥

Figure 3.5 depicts the interlayer expansion process in combination with the topotactic condensation of RUB-36 (3.5(b)) using the DCDMS (3.5(a)) molecule to form COE-3 (other possible denotations are [SiO4]-IEZ-RUB-36, IEZ-CDO) depicted in Figure (3.5(c)).

Interlayer expansion of the starting material RUB-36 is achieved by adding DCDMS and, optionally, HCl. After four hours of stirring, the reaction mixture is poured into a teﬂon-

36 3.3. Post-synthesis treatment

453K,24h + → (a) DCDMS (b) RUB-36 (c) COE-3

Figure 3.5.: Materials and synthesis process for the interlayer expansion of RUB-36. (a) DCDMS is added to (b) RUB-36 to create interlayer expanded product (c) COE- 3 [17]. lined autoclave and treated thermally at 453 K for 24 hours. The recovered product is ﬁl- tered and dried to obtain purely siliceous crystalline COE-3. By calcination, the interlayer expanded COE-3 materials (hydrophobic Si – (CH3)2) are converted to form COE-4 type −1 material (hydrophilic Si – (OH)2) at 773 K for six hours (heating rate 1 Kmin )[9].

✸✳✸✳✷✳ ▼❡❛❧ ■♥❡❧❛②❡ ❊①♣❛♥✐♦♥

Figure 3.6 shows the interlayer expansion process in combination with the topotactic condensation of RUB-36 (3.6(b)) using a Me-acac (3.6(a)) to form Me-IEZ-RUB-36, Me-IEZ- CDO or COE-3/Me (3.6(c)). The procedure is based on that of DE BAERDEMAEKER et al., who use the corresponding Me salt as a linker [22].

HCl 433K,2d + → (a) Me-acac (b) RUB-36 (c) Me-IEZ-RUB-36

Figure 3.6.: Materials and synthesis process for the Me interlayer expansion of RUB-36. Me-acac and HCl (a) are added to the HLS starting material RUB-36 (b) to produce Me-IEZ-RUB-36 (c) in a hydrothermal reaction.

HCl (depending on the synthesis route, concentrated or in a 1:1 solution with H2O), H2O and Me-acacs were added to purely siliceous RUB-36 in a teflon-container and stirred at room temperature until homogeneous. The teflon-container was put into an autoclave and hydrothermally treated at 423 K to 443 K without a heating rate and autogeneous pressure for one to three days. A variety of these conditions was applied to each individual cation material to find a successful synthesis route. After synthesis, the materials, which still exhibited a low ph-value, were recovered and washed with deionised water and decanted

37 3. Hydrothermal synthesis until the pH was neutral and dried for two nights. The individual synthesis routes are displayed in Table 3.2. A full list of applied synthesis routes can be found in the Appendix 7 in Table 7.1.

RUB-36 acac type acac HCl H O time temp. success material 2 g g ml ml d K Co-IEZ-RUB-36 0.200 Co(III) 0.115 0.4 0.40 1 433 X Cu-IEZ-RUB-36 0.200 Cu(II) 0.198 0.8 0.05 3 433 × Fe-IEZ-RUB-36 0.200 Fe(III) 0.100 0.8 0.05 2 433 × Ga-IEZ-RUB-36 0.200 Ga(III) 0.070 0.8 0.05 2 433 × Sn-IEZ-RUB-36 0.200 Sn(IV) 0.160 1.4 0.05 2 433 × Ti-IEZ-RUB-36 0.200 Ti(IV) 0.133 0.9 0.05 1 433 X V-IEZ-RUB-36 0.200 V(IV) 0.151 0.8 0.05 2 433 X Zn-IEZ-RUB-36 0.200 Zn hydr. 0.114 0.4 0.40 2 433 X

Table 3.2.: Synthesis conditions and starting chemicals of Me-IEZ-RUB-36.

Co-, Ti-, V- and Zn-IEZ-RUB-36 have been synthesised successfully, whereas Cu-, Ga- and, surprisingly, also Fe- and Sn-IEZ-RUB-36 synthesis routes failed. Whereas Co materials exhibited a very light grey or blue-grey colour, V and Fe samples displayed very light green or green-grey colour. Ti-, Zn-, Sn- and Ga- samples, on the other hand were characterised by a white sample colour. The Fe- and Ga-material actually showed almost no signs of post-treatment at all whereas the Sn-material exhibited a ﬁrst signal shift to higher d-values, albeit with a very low crystallinity. The latter two materials have successfully been reported on by DE BAERDEMAEKER et al. [22]. However, the synthesis conditions included

FeCl3 [22] for the creation of Fe-IEZ-RUB-36. Apart from the colour of certain samples, single crytallites did not differ largely from the starting material RUB-36 as each sample consisted of a very ﬁne powder. Individual sample yield was very small for each synthesis, considering the starting amounts of 200 mg of RUB-36 only yielded below 50 mg of sample products. Also, upscaling experiments produced very few usable samples.

The varying success of the synthesis becomes most evident when comparing different syntheses runs with identical conditions, as is the case for samples Zn-082 to Zn-087 (see Table 7.1), displayed in Figure 3.7 in comparison to RUB-36 starting material. Success- ful synthesis is readily identiﬁable by the position of the ﬁrst signal as an indicator for the interlayer distance, also marked by grey vertical lines at position 8.44 °2θ for RUB-36 and 7.93 °2θ for Zn-IEZ-RUB-36. Zn-082 and Zn-083 are completely amorphous, whereas Zn-085 represents a successful synthesis. Zn-086 appears to have a reasonable crystallinity,

38 3.3. Post-synthesis treatment but a closer inspection of the first signal reveals a position between that of RUB-36 and Zn-IEZ-RUB-36 which, additionally, shows significant broadening, presumably due to a mixture of both positions in the form of layer stacking disorder. The same applies to Zn- 087 which, in addition, exhibits a previously unknown excess signal at 10.4 °2θ. Zn-084 displays, once more, another picture of an unchanged first signal position, but with a very broad shoulder. Even though only Zn-085 is a successful product, Zn-084 to Zn-087 exhibit the beginnings to a conversion observable in the signals at 12.87 °2θ and 13.82 °2θ, which are only present in post-treated samples. In direct comparison with the starting material RUB-36, even the successful material Zn-085 shows a decreased crystallinity. The intensity at 38.02 °2θ stems from the metal sample holder (see Figure 5.4(a)) due to the low amount of sample and an irradiation effect and should be neglected in the analysis of materials.

2200 7.93° 8.44° 2000 Zn-087 1800 Zn-086 1600

1400 Zn-085

1200 Zn-084 1000 Zn-083 800 Intensity / arb. units / arb. Intensity 600 Zn-082 400 RUB-36 200 0 10 20 30 40 50 2 ѳ / ° Figure 3.7.: PXRD diagrams of samples RUB-36 and Zn-082 to Zn-087. RUB-36 displays high crystallinity with ﬁrst peak position at 8.44 °2θ.

✹✳ ❘❯❇✲✸✻ ❧❛②❡ ✐❧✐❝❛❡

The HLS RUB-36 layer silicate has been ﬁrst introduced in 2007 by MARLER,WANG,SONG and GIES at the 15 th International Zeolite Conference in Beijing, China.

The material was proposed as a new silicate with fer-type layers, obtained by hydrothermal synthesis [17].

✹✳✶✳ ❙✉❝✉❡ ❛♥❞ ♦♣❡✐❡

The basic building block of the RUB-36 layer silicate is the fer-type layer which is stacked in a CDO-type fashion (see Figure 4.4). Both framework types are discussed in the following sections before going into a detailed description of RUB-36.

✹✳✷✳ ❋❛♠❡✇♦❦ ②♣❡ ❋❊❘

The framework type FERRIERITE (FER) is represented by the naturally occurring mineral FERRIERITE, a zeolite material first discovered at the north shore of Kamloops Lake in British Columbia, Canada. It was found in 1917 during a survey for the Munition Re- sources Commission of Canada, named and described in 1918 by GRAHAM in honour of WALTER FREDERICK FERRIER (1865-1950), well known mineralogist and mining engineer of the Canadian Geological Survey. The material appears in spherical aggregates of radiating blades enclosed in CHALCEDONY. This CHALCEDONY is filling veins in basalt flows of the Kamloops Volcanic Group of lower Miocene age [93]. FERRIERITE is a good example of a zeolite with a wide range of exchangeable cations and exhibits a general chemical composition of (Na2,K2, Mg, Ca)3[Al6Si30O72]18H20. Usually, it is Mg-dominant, but Na- and K-rich FERRIERITES are also observed having low Mg-content. The mineral has been found in colourless, white, pink, orange and red varieties with a white streak and vitreous to silky lustre. It exhibits a MOH’S hardness of 3 to 3.5 with a density of 2.06 g/cm3 to 2.23 g/cm3

41 4. RUB-36 layer silicate

and an uneven fracture. The cleavage is perfect in {100} and imperfect in {001}. FERRIERITE crystals are small, in a range of 3 mm to 10 mm, but large blades of 8 cm have been observed occasionally. It is a high-silica zeolite generally found in a silica-rich environment. The crystallisation temperature is not known, since FERRIERITE has not been found in active geothermal areas. Its presence in sedimentary (diagenetic) deposits hints to a possible crystallisation at low temperatures. Blades of orthorhombic FERRIERITE are elongated with the c-axis, commonly {100} dominant, with small {010} and {110}, and terminated by {101} [29].

In 1955, STAPLES conducted PXRD experiments on a FERRIERITE sample with a general chemical composition of (Na, K)4Mg2(Si30Al6)O72(OH)2 18H2O (calculated from cell content). Indexing yielded an orthorhombic, body-centred lattice in SG Immm (but also compatible with I222, Imm2, I2I2I2) with lattice constants a0 = 19.12(6) Å, b0 = 14.14(3) Å and c0 = 7.48(2) Å varying from the conventional orthorhombic orientation of c0 < a0 < b0. Due to its high magnesium (Mg) content, FERRIERITE was a rather unusual specimen among zeolites at the time. Rehydration and other tests, however, pointed to a tectosilicate framework rather than a sheet structure, conﬁrming its status as true zeolite [94].

VAUGHAN solved the crystal structure from measurements on zero-layer WEISSENBERG photographs in 1966. The results were in good agreement with the data reported by GRA-

HAM and STAPLES (lattice constants a0 = 19.156(5) Å, b0 = 14.127(3) Å and c0 = 7.489(3) Å). Systematic absences hint to the same selections of SG Immm, Imm2, or I222 with a density at room temperature of 2.136 gcm−3. A notable feature is the existence 2+ of large cavities which contain Mg(H20)6 ions and the structural resemblance to MORDENITE and DACHIARDITE.FERRIERITE possesses an ideal chemical composition 2+ + of |Mg2 Na2 (H2O)18| [Al6Si30O72]-FER [95] and occurs abundantly in nature with an

SiO2/Al2O3 ratio varying around an average value of 12 with an amount of 36 T-atoms. The FER structure code is directly derived from the mineral name FERRIERITE and its namesake FERRIER [96].

In 1976, WISE and TSCHERNICH analysed FERRIERITE samples from localities at Altoona, Washington, Silver Mountain, Alpine County, California, Pinaus Lake, Monte Lake, and Francois Lake, British Columbia using microprobe methods. They concluded that the chemical range for FERRIERITE would lie between (Al7.5Si27.5O72) and (Al5Si31O72). The varying Si content causes a linear distortion of a0 and the material can accommodate between 3 and 5 exchangeable univalent or divalent cations per UC of 72 O-atoms.

42 4.2. Framework type FER

Due to its broad compositional range, FERRIERITE zeolites can crystallise from solutions with a wide variety of alkali and alkaline earth cations. The presence of these cations is not essential to the structure and Mg cations are fractioned, if present. The zeolite crystallises in response to high silica activities and must also obey temperature and pressure variables as well as water content to prevent the crystallisation of other high silica zeolites [97].

Compared to other zeolites, FERRIERITE, as well as DACHIARDITE (78 % to 86 %), BOGGSITE (80 %) and MORDENITE (81 % to 84 %) exhibits a fairly high percentage of 76 % to 87 % Si (Si/(Si + Al) x 100 %) in the framework causing the mineral to show a higher resistance to acid treatment and mechanical force [29].

In 1984, GRAMLICH-MEIER,MEIER and SMITH re-examined the crystal structure of a FERRIERITE supplied by TSCHERNICH from Silver Mountain, California using X-ray precession and WEISSENBERG photographs. The material possesses a chemical composition of

(Na0.2K0.8Ca0.5Mg2)Al7Si29O72 18H20 (from WISE and TSCHERNICH, 1976 [97]) and the ex- tinction condition h + k + l = 2n conﬁrming the results of VAUGHAN. Additional information has been gathered using transmission electron microscopy (TEM) analyses of FERRIERITES from three localities, concluding that the majority of crystals exhibits no deviation from

Immm SG with lattice constants a0 = 19.220(11) Å, b0 = 14.124(9) Å and c0 = 7.493(5) Å [98].

A monoclinic variety of the zeolite FERRIERITE from Altoona in Washington, US, has been analysed via X-ray structure analysis by GRAMLICH-MEIER,GRAMLICH and MEIER [99, 100] with lattice constants a0 = 18.886(9) Å, b0 = 14.182(6) Å, c0 = 7.470(5) Å and β = 90.0(1)° in SG

P2 1/n and an approximate UC content of Na3KMg0.5Al5Si31O72 18H2O. This variety of FER- RIERITE is relatively uncommon with predominantly rhombical crystallites of (100), (201) and dominant (010) faces. The conformation of the framework of monoclinic FERRIERITE differs from that of the more common orthorhombic FERRIERITE due to the Mg content [99]. The monoclinic framework is created by a slight distortion of the orthorhombic framework, whilst the β-angle remains at 90°. The deviation makes the monoclinic structure energetically favourable over the orthorhombic structure due to low Mg content [29].

Another FERRIERITE from Monastir, Sardinia has been reﬁned by ALBERTI and SABELLI with systematic absences hinting toward Immm SG but orientation of the Mg(H2O)6 octahedron indicating a true symmetry of subgroup Pnnm. The chemical composition is

(Na0.56K1.19Mg2.02Ca0.52Sr0.14)(Al6.89Si29.04)O27 17.86H2O[100].

43 4. RUB-36 layer silicate

(a) (b)

Figure 4.1.: (a) SEM picture of naturally occurring samples of FERRIERITE [29] by ©MILTON L.SPECKELS from the type locality Kamloops lake and (b) photograph of FER- RIERITE from Pinaus lake, British Columbia [101] by ©ELMAR LACKNER (picture width 5 mm).

Today, many localities are known to include zeolite minerals and, therefore, they are not considered rare any more. Next to the type locality of Kamloops Lake, FERRIERITE in particular has been discovered in more than 30 localities throughout the world, among them Antarctica, Australia, many countries of Europe, including Germany and Italy, Japan, Madagascar, New Zealand and the US in basic volcanics, sedimentary deposits, and metamorphic rocks [29, 101].

Figure 4.1(a) shows an SEM picture of transparent, colourless blades of FERRIERITE, up to 1 mm wide, ﬂattened on {100}, from the type locality Kamloops lake. Figure 4.1(b) shows a photograph of FERRIERITE-MG from the Pinaus lake [29].

Differing from the natural FERRIERITE, whose main cations are Mg, Na and K, synthetic FERRIERITES have an important impact in industry as they exhibit a large cation variability. The same can be observed for the T-atom diversity, e.g., in all-silica-FER, B-FER and Ga- FER.

A 2 hour synthesis of Na and Na-tetramethylammonia (TMA) FERRIERITES has been conducted using the hydrothermal method at temperatures of 573 K to 598 K by application of seeds for the later conversion of the alkali forms into FERRIERITE-H by direct exchange with mineral acids, as well as by the usual ammonium ion exchange and calcination. FERRIERITE-H is stable up to 1223 K in air, but loses cracking activity if steamed at 1023 K

44 4.2. Framework type FER

[102]. FERRIERITE-H, or protonated FERRIERITE, is an active and very selective catalyst for n-parafﬁn cracking and can be used as a pore-mouth catalyst in the chemical industry for alkyl isomerisation of oleic acid and elaidic acid as well as butene to isobutene alkyl isomerisation [103].

The hydrophobic all-silica FERRIERITE (Si-FER) has very high selectivity in the separation of alcohol–water mixtures, due to the very restrictive shape and space constraints of the FER framework type. At high pressure, Si-FER can achieve the separation of an ethanol–water liquid mixture into supramolecular blocks of its components, namely, ethanol dimer wires and water tetramer squares [104].

Successful synthesis of FERRIERITE zeolites has been achieved as early as the 1960s using different templates (n-alkylamines) and synthesis methods (hydrothermal, solvothermal) [105]. Even large single crystals of all-silica and aluminium bearing FERRIERITE have been produced in the 1990s using non-aqueous solvothermal synthesis methods under ﬂuoride medium [72, 73].

An example for solvothermal synthesis of large crystal all-Si FERRIERITES, but also FER- RIERITES in which Si is isomorphously substituted by heteroatoms such as Al and Fe, is presented by MARTHALA and co-workers [90]. They make several references to the successful incorporation of Al [72, 106–108], Ga [109], Fe [110], Ti [111] and V [112] cations into the framework of pure FERRIERITE crystals [90].

The Database of Zeolite Structures, maintained by BAERLOCHER and MCCUSKER, gives a very extensive overview of the most important properties of the framework type FER, derived from the information extracted from the aforementioned scientiﬁc articles [6]. Some of the more important FER properties are listed in Table 4.1.

Table 4.2 highlights the classiﬁcation scheme of zeolites in seven distinct groups according to BRECK et al. [114, 115]. FERRIERITE is classiﬁed as a group 6 zeolite, which, in contrast to lower group zeolites, consist of T8O16 units sharing a common structural element [115].

This common structural element is the fundamental feature of the mineral FERRIERITE, the 5-ring [5 1] SBU consisting of six tetrahedra as depicted in Figure 4.2(a). The special conﬁguration of four of these SBUs build a [5 4] polyhedral unit or periodic building unit (PerBU) as shown in Figure 4.2(b) and Table 4.1 as mor (t-tes). Some of these polyhedral units, called composite building units (CBUs), reappear in various zeolite frameworks. A

45 4. RUB-36 layer silicate

Cell Parameters: orthorhombic I m m m (No. 71) a0 = 19.0180 Å b0 = 14.3030 Å c0 = 7.5410 Å α = 90.000° β = 90.000° γ = 90.000° Volume = 2051.3 Å RDLS [113] = 0.0036 T FDSi: 17.6 1000Å3 topological density (TD): TD10 = 1021 TD = 0.887635 Ring sizes (No. T-atoms): 10 8 6 5 Channel system: two-dimensional Maximum diameter of a sphere that can be included: 6.31 Å ~ that can diffuse along: ~a : 1.56 Å b : 3.4 Å ~c : 4.69 Å Accessible volume: 10.01 % SBU: 5-1 CBU: mor (t-tes) fer pcr (t-fer)

Natural Tiling: t-dac-1 t-dac-2 t-fer t-tes

Table 4.1.: Most important properties of framework type FER [6]. popular example for a CBU is the SOD or β-cage (see Figure 3.2 in Chapter 3 Section 3.1) [33]. The mor-unit shown in Table 4.1 is one of those CBUs. By linking mor-units, complex chains can be formed, which are linked to each other in a variety of ways, consequently building a three-dimensional framework and creating the complete fer layer by sharing common edges [58, 95]. Neglecting the VANDER WAALS radii of layer terminating oxygen ~ atoms, one layer has a thickness of 9.5 Å which amounts to nine atomic layers. In the ab- plane, the structure consists of chains of 5-rings, which are interconnected successively through 10-ring and 6-ring elements. The FERRIERITE channel system is two-dimensional, wherein two intersecting channel-systems lie perpendicular to each other creating a two- dimensional network of 10-ring and 8-ring pores. The ring size of these channels is marked by the number of tetrahedral atoms. The main channel system runs along the c-axis [001] in a 10-ring, whereas other channels run parallel to the b-axis [010] in 8-rings. Free channel dimensions account for 0.43 nm × 0.55 nm and 0.34 nm × 0.48 nm for the 10-ring and 8-ring pores, respectively [96, 115].

Regarding the plane of the layer, it is possible to assign a two-dimensional UC with lattice parameters b0 ≈ 14.0 Å and c0 ≈ 7.5 Å. For the FER-type framework, the a-axis [100] is

46 4.2. Framework type FER

Group SBU/CBU example zeolite

1 (S4R - single 4-ring) ANALCIME, PHILLIPSITE, GISMONDINE 2 (s6r - single 6-ring) ERIONITE, OFFRETITE, SODALITE 3 (d4r - double 4-ring) ZEOLITE A 4 (d6r - double 6-ring) FAUJASITE, CHABAZITE 5 (complex 4-1 - T5O10 units) NATROLITE, SCOLECITE 6 (complex 5-1 - T8O16 units) MORDENITE, DACHIARDITE, FERRIERITE 7 (complex 4-4-1 - T10O20 units ) HEULANDITE, CLINOPTILOLITE, STILBITE

Table 4.2.: Classiﬁcation of SBUs with exemplary materials according to BRECK et al. [114, 115]. orientated perpendicular to the plane of the layer, which represents the stacking direction.

Intra-layer dimensions account for 14.0 Å and 7.5 Å respectively. Four out of the 18 [SiO4]- tetrahedra per UC are only three-connected and represent terminal oxygen atoms. The distance between these terminal silanol (≡ Si–OH) or siloxy (≡Si–O-) groups accounts for 5.7 Å. Due to this relatively large distance, an intra-layer condensation of these groups during calcination is not very probable. This property of the fer-type layer is rather desirable for the topotactic condensation process to form three-dimensionally microporous materials [58]. Accessible volume amounts to 205.34 Å3 (10.01 %) with an occupiable area of 343.76 Å2 (957.07 m2 g−1) and a speciﬁc occupiable area of 1675.85 m2 cm−3, whereas maximum diameter of spheres able to be included are 6.31 Å and 1.56 Å to 4.69 Å for diffusion. These values have been calculated by TREACY from the ARIZONA STATE UNIVERSITY, using his codes "TOTOPOL" and "DelaneysDonkey" [116].

FERRIERITE crystals exhibit a plate-like morphology, which can be explained by the fact ~ that the bc-plane-layers are interconnected by T-O-T bonds exhibiting a high bond density and the corresponding interlayer bond density being much lower [117]. Orthorhombic FERRIERITE blades are elongated along the c-axis, commonly {100} dominant, with small {010} and {110}, and terminated by {101} [29].

✹✳✷✳✶✳ ❢❡✲②♣❡ ❧❛②❡

The fer-type layers represent a predominant formation product in hydrothermal synthesis from aqueous solutions of silicic acid and an SDA. A number of different SDAs are reported to lead to the formation of layer silicates exhibiting fer-type or -fer-type (interrupted) layers. By heating these materials in air at temperatures of 673 K to 873 K, they can be

47 4. RUB-36 layer silicate

(a) 5 1 (b) 5 4

Figure 4.2.: (a) [5 1] SBU and (b) [5 4] PerBU constructed from four [5 1] SBUs (bold/blue) [6]. transformed to tectosilicates in a topotactic condensation reaction. Table 4.3 displays the investigated structures and corresponding SDAs. However, with the exception of precursor material DEDMA-RUB-36, porosity is blocked in most of these HLS precursors [7, 17, 58].

layer type type material (intercalated cation) -fer RUB-20 (tetramethylammonium), interrupted layer -fer RUB-40 (tetramethylphosphonium), interrupted layer fer ERS-12 (tetramethylammonium) fer RUB-36 (diethyldimethylammonium) fer RUB-48 (trimethylisopropylammonium) fer RUB-38 (methyltriethylammonium) fer MCM-47 (tetramethylene-bis[N-methylpyrrolidinium]) fer PLS-3 (tetraethylammonium) fer PREFER (amino-tetramethylpiperidinium)

Table 4.3.: SDAs used in the synthesis to create microporous materials exhibiting layer type fer or -fer [7].

Figure 4.3 displays the fer-type layer viewed from different angles visualised in VESTA [118].

Figure 4.4 shows the two types of three-dimensional frameworks that can be generated stacking fer-type layers via topotactic condensation. The framework on the left is the FER framework already discussed above. To obtain such a structure, individual layers are assembled in a pattern of ABAB by shifting in b0 and c0-direction in a shift vector of

0a0 + 1/2b0 + 1/2c0 [58].

The sole difference between the CDO and the FER-framework illustrated on the right is

48 4.3. Framework type CDO

~ (a) along ~c (b) along b

~ Figure 4.3.: fer-type layer viewed (a) along~c axis, (b) along b axis and (c) along ~a axis [6, 17]; atoms are labelled as blue: silicon (Si), red: layer oxygen (O), yellow: terminal O of the layer/silanol groups. The black rectangle indicates the position of the UC. Visualisation generated using VESTA [118]. the shift vector of stacking. The stacking sequence is ABAB as well, but a shift between individual layers only occurs in the c0-direction with a shift vector of 0a0 + 0b0 + 1/2c0 if the UC exhibits a setup of a0 > b0 > c0 as is common for FER-type materials.

The fer-type layers, which are shown in Figure 4.3 are the building blocks of the RUB-36 material, in which the layers are stacked in a CDO-type fashion. It is a non-porous layer consisting only of 5-rings of [SiO4]-tetrahedra [6, 58].

✹✳✸✳ ❋❛♠❡✇♦❦ ②♣❡ ❈❉❖

In contrast to the FER-type framework, no naturally occurring CDO-type framework has been observed yet. Instead, the type material for the corresponding framework is a synthetic one, with other layered silicates also exhibiting the CDO framework.

The type material for the CDO framework type is CDS-1 with a chemical composition of

49 4. RUB-36 layer silicate

FER

CDO

Figure 4.4.: Scheme of the possible stacking procedures of the fer-type layer, obtaining FER (top) and CDO (bottom) [58].

[Si36O72]-CDO [119]. The CDS-1 material is obtained by heating the layered parent material PLS-1, which exhibits shared faces of pentagon cylinders made up of silicon 5-rings, or pentasil rings [119]. PLS-1 is applied as a solid base catalyst for C-C bond forming reactions and produces CDS- 1 above 673 K under vacuum in a topotactic (poly-)condensation reaction between the pentasil layers. PLS-1 possesses high-density silicate sheets made up of 5-rings with Me4NOH molecules and K+ ions in the pore-like interlayer space. Still, in contrast to DEDMA-RUB- 36, CDS-1 obtained from PLS-1 has almost no internal surface or pore volume. The CDS-1 is a pure silica and thermally stable [120] and can, along with its layered precursor PLS-1, also be synthesised as a germanosilicate [121] or titanosilicate material [122].

In 2017, MARTÍNEZ-FRANCO and co-workers introduced an Al-containing CDO precursor, which they interlayer expanded by mild acid treatment to create IEZ-CDO with high crystallinity and porosity. Al-containing CDO and IEZ-CDO exhibit good activity and selectivity in the SCR of NOx, and methanol-to-oleﬁn conversion (MTO) processes, respectively [123]. Other than PLS-1, further CDO-related silicate layered materials have been reported, including as-synthesised MCM-47 [124], as-synthesised MCM-65 [125], the former of which does not, the latter of which does retain its crystallinity after calcination. UZM-25 [126] and

50 4.4. Crystallographic structure of RUB-36

RUB-36 [17] are further examples for CDO-type materials.

CDO properties are listed in Table 4.4.

Cell Parameters: orthorhombic C m c m (No. 63) a0 = 7.5566 Å b0 = 18.7151 Å c0 = 14.0986 Å α = 90.000° β = 90.000° γ = 90.000° Volume = 1993.9 Å RDLS [113] = 0.0094 T FDSi: 18.1 1000Å3 TD: TD10 = 1053 TD = 0.930227 Ring sizes (No. T-atoms): 8 5 Channel system: two-dimensional Maximum diameter of a sphere that can be included: 5.78 Å ~ that can diffuse along: ~a : 3.44 Å b : 1.52 Å ~c : 3.35 Å Accessible volume: 7.82 % SBU: 5-1 CBU: mor (t-tes) fer

Natural Tiling: t-cdo t-tes t-unj

Table 4.4.: Most important properties of framework type CDO [6].

As mentioned above, the generation of a CDO-type framework occurs in a similar manner as that of FER albeit with a slightly different shift vector. The corresponding structure is orthorhombic as well, albeit with a different SG symmetry of Bbmm, No. 63 if the UC setting is chosen in the same fashion as for FER with a0 > b0 > c0.

✹✳✹✳ ❈②❛❧❧♦❣❛♣❤✐❝ ✉❝✉❡ ♦❢ ❘❯❇✲✸✻

RUB-36, [(CH3)2(C2H5)2N]4(OH)4Si36O72, is synthesised using silicic acid and diethyldimethylammonium (DEDMA) in water at autogeneous pressure and a temperature of 423 K in a teﬂon-lined stainless steel autoclave for 15 days. RUB-36 possesses very strong hydrogen bonds (d[O···O] ≈ 2.4 Å), and calcination at 873 K in air atmosphere leads to a highly ordered CDO-type silica zeolite, RUB-37 [17, 58].

51 4. RUB-36 layer silicate

A direct conversion of as-made RUB-36 with CDO-type stacking to pure silica zeolite ZSM-35 with FER-type topology has been performed in the presence of surfactant CTAOH, which is shown in Figure 2.5 in Chapter 2 Section 2.3 in a swelling and deswelling procedure. During this process at room temperature, the originally intercalated SDA DEDMA is exchanged for the surfactant CTAOH, effectively breaking the strong hydrogen-bonding interactions and widening the interlayer distance between neighbouring layers. The polar heads of the surfactant is observed to approximate fer-layers in the swollen material. In the deswelling step, a residue amount of CTAOH with long tails occupy the void space between layers in the pre-10ring of layered PREFER-1, presumably acting as an SDA for the formation of an FER-type zeolite (ZSM-35). This process may be considered as a (poly- )condensation of the silanol groups on the neighbouring layers or topotactic condensation by a layer re-stacking approach [19].

Figure 4.5 depicts the crystal structure of as-made RUB-36 with incorporated DEDMA ~ along b (Figure 4.5(a)) and along ~c (Figure 4.5(b)). To build RUB-36, individual fer-type layers are stacked in a CDO-type fashion, connected by strong hydrogen-bonding interactions. Layers are completed by terminal silanol groups.

RUB-36 is orthorhombic with a stacking sequence of ABAB and a shift vector of

0.5a0 + 0b0 ±0.36c0 and SG Pnma with a0 = 22.232(2) Å b0 = 14.019(1) Å and c0 = 7.388(1) Å.

~ (a) along b (b) along ~c

~ Figure 4.5.: As-made RUB-36 viewed (a) along b-axis and (b) along ~c-axis; atoms are labelled as blue: Si, red: layer O, yellow: terminal O of the layer/silanol groups, grey: nitrogen (N), brown: carbon (C). The black rectangle indicates the position of the UC. DEDMA occupies void space between neighbouring fer layers [58].

52 4.5. Disorder of layer stacking

~ In Figure 4.3, the fer-type layer is exhibited. It spans the bc plane and is stacked along ~a.

In accordance with the type material CDS-1 for the CDO zeolite framework type, RUB-36 possesses a chemical composition of |SDA4| [Si36O72(OH)4] with four additional O-atoms necessary due to the broken bonds between neighbouring layers, whereas the SDA is rep- + resented by DEDMA with a chemical composition of [(CH3)2(C2H5)2N] .

✹✳✺✳ ❉✐♦❞❡ ♦❢ ❧❛②❡ ❛❝❦✐♥❣

The preparation of three-dimensional microporous materials from layered precursors is often cause for a decreased crystallinity in the product. This holds for the post-synthesis treatment even though the applied precursors generally exhibit moderate to good crystallinity. The condensation of individual layers does not always occur in a completely periodic way causing framework defects and stacking disorder. These are observable by signal broadening in both 29Si MAS NMR and PXRD experiments in addition to low adsorption capacity due to a blocked pore system. Defects associated with HLSs can be assigned to incomplete condensation of silanol groups, formation of Si-O-Si bridges in a non-periodic manner and stacking disorder of individual layers. Many silicate layers such as fer in RUB-36 may be connected to form three-dimensional frameworks in more than one way. In the case of fer, layers are linkable with two differing shift vectors to create frameworks of topology FER or CDO. This feature is often cause for stacking disorder and should be taken into account when dealing with the modiﬁcations of HLSs. It is observable in PXRD diagrams in a combination of sharp and broad reﬂexions. Still, relaxed bond distances and bond angles are found in the regarded structures [5].

An array of programs have been developed to simulate structures with layer disorder, among them, DISCUS and DIFFaX. DIFFaX is a Fortran 77 computer program that computes diffraction intensities from layered crystals containing coherent stacking faults by using a general recursion algorithm. It has been created by MICHAEL M.J.TREACY,JOHN M.NEWSAM and MICHAEL W. DEEM and is maintained by MICHAEL M.J.TREACY [28]. It enables the user to simulate powder X- ray (and neutron) diffraction patterns and single crystal electron (kinematical) diffraction patterns based on the recursion algorithm, which uses the self-similar stacking sequences occurring in crystals whose layers stack non-deterministically.

53 4. RUB-36 layer silicate

In their paper [28], TREACY and co-workers highlight the recursion method as a set of simple relations between average interference terms from a statistical crystal, which can be solved as a set of simultaneous equations. This interference term then gives diffracted intensities for a hypothetical polycrystalline sample by the incoherent sum of scattered intensities over an ensemble of crystallites.

½(x + z) ½(x + y + z) ← → (a) CDO (b) fer-layer (c) FER

Figure 4.6.: Sheets of fer (b) stacked with a shift of ½(x + z) and ½(x + y + z) to create CDO (a) and FER-type (c) framework respectively. In this example, only one type of layer with only two stacking options is considered.

The recursion algorithm is valid for all types of planar faults and easier to apply than previous procedures. Only a ﬁnite number of layers can be implemented into the simulation, while simultaneously containing long-range stacking correlations.

Since there is no such thing as a perfect crystal, planar faults, in addition to lower dimensional defects are a very common phenomenon in natural, but also synthetic crystals. While it is difﬁcult to detect lower dimensional defects using conventional scattering techniques, planar faults are often times revealed by streaking in single crystal diffraction patterns and by index-dependent peak widths and diffuse scattering in powder diffraction patterns. Only by simulating these types of stacking defects, an experimental pattern can be interpreted accordingly.

Due to their low temperature and low pressure facies, zeolite materials are considered to remain in a metastable phase which, if hydrothermal synthesis is not interrupted prematurely, proceeds to form a more stable and denser phase such as QUARTZ. This results in frequent planar faulting. Some framework types, such as FER and CDO only differ by the manner in which individual layers are assembled along a certain direction, allowing for a high degree of intergrowth between related materials. By analysis via diffraction experiments, these faults and intergrowth phases can be observed. Variations in signal peak shapes and intensities are hints to possible deviations from a perfect stacking order [28]. Here it is important to consider the whole system, not just the pure zeolite and pure

54 4.5. Disorder of layer stacking

(a) (b)

Figure 4.7.: Schematic crystal structures viewed along~c illustrating the σ fault models, new bonds generated by σ-operations are marked as grey dotted lines [98].

QUARTZ. So, according to QIU and WHITE et al., both NaX and NaY are found to be thermodynamically stable with respect to their elements because of enthalpic stabilisation [127]. This might be true for most natural zeolites. In the laboratory, kinetic effects might sup- press the formation of the most stable products. However, there are only a few experimental quantitative studies in the open literature. Analogous to the visualisation for the stacking of layers for FAU illustrated by TREACY et al. in 1991 [28], Figure 4.6 shows stacking of sheets (Figure 4.6(b)) to form predominantly FER (Figure 4.6(c)) or CDO-type (Figure 4.6(a)) regions. The two domains are build by connection of neighbouring PerBUs as depicted in Figure 4.2(b) along x in two different ways ~ [6]. The directions of x, y and z are not synonymous with the crystallographic axes ~a, b and ~c but exclusively relate to a ﬁctional coordinate system to facilitate the theoretical building of the structure and to compare the two types of resulting domains, since, by deﬁnition, the set-up of the crystallographic axes of FER and CDO does not coincide.

• Connection mode (1) CDO: PerBUs, related by a shift of ½(x + z), are connected through 8-rings,

• Connection mode (2) FER: PerBUs, related by a shift of ½(x + y + z), are connected through 6-, 8- and 10-rings.

While most natural FERRIERITE crystals show no deviation from their Immm structure, several diffraction patterns have been found to exhibit streaking parallel to [010]* and [110]*. These streaking phenomena can be explained by σ fault models. The σ-operation is a common tool to create theoretical novel materials or to transition from one framework to another. Many relations between zeolite structures can be found by applying the σ-operation, introduced by SHOEMAKER, which mimics a ﬁctional symmetry

55 4. RUB-36 layer silicate operation such as a mirror plane to extend or convert a known structure [128, 129]. Fig- ure 3.2 in Chapter 3 Section 3.1 exhibits an example for three zeolites related by SBUs or CBUs and inter-convertible via σ-operation. The SOD-cage ([4 66 8]) as a space-ﬁlling unit is directly connected by face-sharing of the 4-ring to six other cages to form the SOD-type zeolite framework. By extending the 4-ring to form a cube by the use of Si-O-Si-bridges, the LTA-type zeolite is created.

By application of a σ-operation, not only other zeolite frameworks may be generated, but also natural stacking faults can be explained. In case of FERRIERITE, both σ-contraction, in which an existing bond is shortened, and σ-expansion, in which a bond is extended (as in SOD → LTA), can be observed [98].

Figure 4.7 shows the faults by way of σ-operations along A···A for σ(010) (Figure 4.7(a)) and B···B for σ(110) (Figure 4.7(b)).

Stacking faults and defect structures resulting from a σ-type operation modiﬁcation can be modelled using DIFFaX. To provide an introduction to the computation of the PXRD diagrams of the synthesised products, a series of different combinations of fer-type layers in a FER- and CDO-type stacking are calculated.

For the generation of fault defects using DIFFaX, a faulted sequence is applied to one speciﬁc direction (formally direction ~c, [001]), in this case, the stacking direction is as shown in Figure 4.6, for the FER-type material along ~a, [100], and CDO-type material along ~c, [001]. Both FER- and CDO-type zeolites as well as the HLS RUB-36 contain the same fer-type layer, albeit in a slightly different stacking. Since the type of layer remains the same and only the stacking is variable, differences between the two end members are small but still pronounced. Figure 4.8 shows a graphical representation of the results from the DIFFaX calculation of the PXRD pattern of end members FER (Connection mode 2, top) and CDO (Connection mode 1, bottom) and a statistical distribution of a mixture between these two conﬁgura- tions in 10 % steps. It is evident that the PXRD diagrams of both materials are very similar, however, differences are distinct. By increasing the amount of CDO-type stacking, new signals appear at 11.7 °2θ, 19 °2θ, 21 °2θ and 23 °2θ that the pure FER-type stacking does not possess. Some

56 4.5. Disorder of layer stacking

320

280

240 11. FER-100% 200 10. CDO-10% 9. CDO-20% 160 8. CDO-30% 7. CDO-40% 120 6. CDO-50% 5. CDO-60% 80 4. CDO-70% 3. CDO-80% Intensity / arb. units / arb. Intensity 40 2. CDO-90% 1. CDO-100% 0 5 10 15 20 25 30 35 40 45 50 55 2 ѳ / ° Figure 4.8.: Presentation of PXRD diagrams of DIFFaX calculated series between the two end members CDO and FER in stacking sequence of 10 % steps, whereas the bottom diagram represents 100 % FER and the top diagram represents 100 % CDO. As the stacking probability is varied, certain peaks disappear and other peaks experience peak broadening. Instrumental peak broadening was simulated using a PSEUDO-VOIGT function with u = 0.5 , v = −0.2 , w = 0.05 and γ = 0.6 A step size of ∆θ = 0.02° was adopted [28, 130]. signals appear only between 90 % and 100 % CDO stacking, such as the signal at 21.5 °2θ. Other signals, such as the one at 11.7 °2θ appear gradually and uniformly over the span of every 10 % step, whereas formerly sharp signals broaden and become sharp again during this transition. The systematic broadening of sharp signals can, therefore, in many cases be attributed to stacking disorder in microporous materials. An exemplary wire diagram of a ﬁctional framework with a statistically alternating CDO and FER type stacking is depicted in Figure 4.9. The transition from one type of layer to another is ﬂuent. The results of the DIFFaX calculations for the Me-IEZ materials are discussed in the next chapter (Chapter 5).

57 4. RUB-36 layer silicate

Figure 4.9.: Exemplary faulted sequence of CDO and FER type stacking consisting of ﬁve individual layers.

58 ✺✳ ❈❤❛❛❝❡✐❛✐♦♥ ♦❢ ②♥❤❡✐❡❞ ♣♦❞✉❝ ❛♥❞ ♠❡❤♦❞

The comprehension of the crystal structure of newly synthesised materials is essential in understanding and presuming industrially relevant properties. In this context, not only the atomic arrangement, but also the presence of defects, dislocations and stacking disorder determine technologically exploitable characteristics. For the structure determination and characterisation, a large variety of investigation tools are available, both physical and chemical. The atomic geometry is determined by the three-dimensional arrangement and the chemical bonds of atoms in a crystalline structure most commonly depicted by chemical formulae and molecular models. There is no almighty routine that can be implemented to solve the atomic structure of a previously unknown substance. Instead, an array of analysis methods is applied to gain a deeper understanding on the newly synthesised and post-treated materials, among them diffraction routines, as well as spectroscopic methods and chemical analyses. Each of these techniques supplies a ﬁnite puzzle piece to the overall picture of real structure and properties of the analysed material. In most cases, a combination of these often complementary methods leads to a satisfactory solution closest to the true structure of the material. In the following, the employed methods are listed, explained and applied to selected synthesised samples.

✺✳✶✳ ♦✇❞❡ ❳✲❛② ❞✐✛❛❝✐♦♥ ✭❳❘❉✮

The ﬁrst and most frequently used method in identifying the products of synthesis and post-synthesis treatment as well as evaluating the grade of crystallinity and, thus, success of the experiment is the analysis via single crystal X-ray diffraction (SCXRD). However, if synthesis micro-crystalline materials only, PXRD analysis is the method of choice, as is the case in the course of this work [131, 132]. Most likely, the synthesised substances will

59 5. Characterisation of synthesised products and methods crystallise as ﬁne powders with grain diameters of only ≤ 1µm .

PXRD continues to be one of the most powerful characterisation methods of crystalline samples from its initial application by DEBYE,SCHERRER, and HULL and their ﬁrst PXRD experiments in 1916/17 [133].

Data collected by PXRD has been referred to as a fingerprint method in the identification of crystalline matter. However, identification of unknown substances is only one useful aspect obtainable from PXRD experiments [134]. The various information extractable from a powder diffraction pattern are depicted in a schematic overview in Figure 5.1 and extends to both background and diffracted signals. Background is both generated by the sample and sample holders as well as interaction of the radiation with the atmosphere. It admits conclusions on the local structure of the investigated material, amorphous fractions - if present - and lattice dynamics. As gathering information about the bulk material, disorder and micro-structure is not available by the use of SCXRD, PXRD enables insight into macroscopic stress and texture of powdered materials [132]. Not in a classical experiment, however, using reciprocal space mapping or, in a simpler experiment, scanning along a reciprocal lattice direction, disorder and defect structure can also be detected and analysed. Diffracted signals, on the other hand, may be investigated with regards to their °2θ angle, full width at half maximum (FWHM), shape and intensity. Lattice parameters, as well as SG are deduced from signal position in addition to macro-strain - if present - and allow for a qualitative phase analysis in the case of the presence of more than one phase. The intensity of a signal admits conclusions on the specific atomic arrangement of individual positions as well as their temperature factors and site occupation factors (SOFs) in addition to the potential for a quantitative phase analysis. Lastly, the profile function is determined by the instrumental part (e.g., zero point correction), and the line shape and broadening of the signals, which reveal real structure phenomena such as micro-strain and domain size.

Whereas spectroscopic techniques provide only information on the local environment of a probe element, diffraction methods serve to represent the long-range order of the analysed material. Due to the sole focus on long-range order, the analysis by PXRD is usually not sufﬁcient to completely and unambiguously describe a crystalline material. Additionally, chemical analyses should be taken into account to verify the completion of available data. A combination of diffraction and spectroscopic methods, as well as chemical analyses as

60 5.1. Powder X-ray diffraction (PXRD)

Information content of a powder pattern

Background Reflections

Profile Sample Scattering from Position Intensity (FWHM, peak shape) sample holder, air etc. Compton scattering Instrument Line function broadening

Diffuse scattering: Lattice parameters, Crystal structure: Real structure: Space group: Local structure Macro-strain Atomic positions Micro-strain Amorphous fraction Qualitative phase Temperature factor Domain size Lattice dynamics analysis Occupancy Texture Quantitative phase analysis

Figure 5.1.: General information content of a PXRD pattern. The two sources of information are individual reﬂections and the background of a measurement which, in turn, yield information on crystallographic structure and atomic arrangement of the sample [132]. complementary data, therefore, ensures a more wholesome picture with regards to atomic structure and crystal chemism.

✺✳✶✳✶✳ ❇❛✐❝ ♣✐♥❝✐♣❧❡ ♦❢ ❳❘❉

After WILHELM CONRAD RÖNTGEN’S discovery of a novel type of radiation (NOBEL Prize 1901), whose origin and nature he could not precisely determine, in 1895 [135, 136], MAX VON LAUE,WALTER FRIEDRICH and PAUL KNIPPING experimented with these, now called, X-rays. The invisible radiation was able to pass through solid matter and, therefore, studied by the use of crystals. During one of these experiments, the group was able to evidence that X-rays were electromagnetic waves with very short wavelengths. The diffraction experiment that started as an attempt to explain this new type of radiation soon became a tool to investigate the regular order and symmetry of crystals, which further opened the possibility of atomic structure determination [137, 138]. Subsequently, WILLIAM LAWRENCE BRAGG and his father, WILLIAM HENRY BRAGG con- ﬁrmed the discovery with an alternate method and proposed the use of X-rays for the understanding of crystals on an atomic level, culminating in the, then, new sciences of X-ray crystallography and spectroscopy [139–141].

61 5. Characterisation of synthesised products and methods

The analysis of crystalline materials by PXRD is based on this fundamental observation by MAXVON LAUE,WALTER FRIEDRICH and PAUL KNIPPING in 1912, who applied X-rays to a crystal of SPHALERITE (ZnS) and for which MAXVON LAUE received the NOBEL Prize in 1914.

Also, in 1912, WILLIAM HENRY BRAGG and WILLIAM LAWRENCE BRAGG conducted experiments regarding the interaction of short electromagnetic waves with crystalline matter for which they received the NOBEL Prize in 1915 respectively [139, 141]. Their observations have been visualised in Figure 5.2 and condensed in the following BRAGG equation ((5.1))

n · λ = 2d · sinθ, (5.1a)

λ = 2dhkl · sinθ, (5.1b)

with the order of the wavelength n (integer number), the wavelength of the irradiated radiation λ (X-ray, Neutron or Synchrotron), distance between two layers in the crystalline material d, and diffraction angle θ [139, 140]. If Equation (5.1a) is fulfilled, an amplification of reflected radiation is achieved for every integer n. At constant wavelength λ, the diffraction angle θ dictates the diffraction geometry and depends on the lattice spacing d. Reflected waves may oscillate in phase if the path difference between all the lattice layers is an integer multiple of the wavelength λ. When working with X-rays, it is advantageous not to utilise higher order n but instead incorporate n into the indices (h k l) and treat higher order wavelengths like 1 st order wavelengths, which leads to Equation (5.1b).

Figure 5.2 shows the visualisation of the BRAGG equation in a stylised crystal. Blue spheres represent atoms in the crystalline framework arranged in layers separated from each other by the interlayer distance d. Incoming radiation is indicated by green arrows in a diffraction angle θ, which interacts with the lattice planes of the crystal framework to create constructive or destructive interference.

By application of the BRAGG equation in a diffraction experiment, it is possible to extract three different kinds of information regarding the crystal lattice. Additionally, background radiation occurs that originates from the interaction with air and from coherent or incoherent radiation of the investigated material. The diffraction angle θ depends on the wavelength λ of the applied X-ray radiation and is determined by the size and geometry of the crystal unit cell (UC). By application of Equa- tion (5.1b) and inputting θ, it is possible to calculate the d-spacing of the regarded crystal

62 5.1. Powder X-ray diffraction (PXRD)

UC. By using an indexing program, geometry and symmetry of the UC can be determined from dhkl . The higher the symmetry of the crystal, the more straightforward this indexing becomes. The Intensity I of the diffracted radiation is determined by the number of electrons and the arrangement and the type of atoms in the crystal lattice and admits estimations about the three-dimensional arrangement of atoms in the material. Particle size and crystallisation form is investigated by observing the line shape of the diffracted intensities.[142, 143]. By applying a monochromatic X-ray beam to a powdered sample, X-ray radiation is diffracted on all lattice planes that fulﬁl the BRAGG equation (Equation (5.1)). The diffracted rays create cones with half the aperture (apex) angle °2θ.

After creating the characteristic X-ray radiation by applying a voltage to a metal anode, usually silver (Ag), copper (Cu), molybdenum (Mo) or chromium (Cr), the rays are being lead through a filter and slit system for the purpose of parallelisation. The parallel rays then impact on the powdered sample. Diffraction cones are created in the emission range, as well as the reflective range. The emitted diffraction cones are counted by a sensitive film or counter tubes [142, 144]. Approximate monochromatisation of the X-ray radiation is achieved by the application of a monchromator, usually in the form of a cut single crystal such as (111)-Ge, graphite or by a filter.

The necessary monochromatic radiation is commonly provided by the K α1α2 doublet.

dsin

Figure 5.2.: Visualisation of the BRAGG equation with lattice planes and atoms in blue, incoming and diffracted radiation in green, lattice constant d and diffraction angle θ [139, 140].

63 5. Characterisation of synthesised products and methods

(a) BRAGG-BRENTANO (b) transmission

Figure 5.3.: Different types of PXRD set-ups; (a) (i) BRAGG-BRENTANO with (ii) primary and (iii) secondary monochromator, (b) transmission geometry [142].

Meanwhile, a ﬁlter needs to ensure a K absorption wavelength between the K α1 and K α2 wavelengths. Using a CuK α1α2 doublet (λ = 1.542 Å) with a nickel (Ni) ﬁlter (λK = 1.488 Å) is very common [131]. The choice of wavelength ranges in an area of typical crystal bond distances, such as the Si-O-bond distance in zeolites which accounts for a value of 1.60 Å. Other frequently used wavelengths are that of Fe, Mo and W.

A few different equipment geometries exist for the PXRD experiment. Peak profiles of the investigated material differ on various instruments and measuring conditions. Taking into consideration the effect of the experiment geometry, the observed peak profile is generally recognised to be expressed as the convolution of the intrinsic peak profile with the instrumental function. A diffractometer can either be operated in transmission or in reflection set-up, where the reflection set-up is more commonly used since sample preparation and orientation is more straightforward. The two experimental set-ups that have been used in the course of this work shall be illustrated shortly [131, 132].

Figure 5.3(a) depicts the BRAGG-BRENTANO type geometry of diffraction. A powdered sample is stored on a flat sample holder usually consisting of a cubic metal (see Fig- ure 5.4(a) in Section 5.1.4) and flattened to the edge. The sample holder is routinely oriented so that the diffraction peaks of the cubic material it consists of does not contribute to the resulting powder pattern, provided a sufficient amount of sample is used. This disc is placed on one axis of the diffractometer and tilted by the diffraction angle θ in conjunction with the detector rotating around the sample at the corresponding angle 2θ. Disadvantages of this method include the requirement of a sufficient amount of sample to fill the sample holder completely and the probability of preferred orientation and texture effects due to the flattening of the sample surface on the sample holder.

64 5.1. Powder X-ray diffraction (PXRD)

The second type of diffractometer used during the course of this work is a transmission type diffractometer operated in quasi DEBYE-SCHERRER-mode which is advantageous for high resolution experiments and for an exact correction of absorptions. Figure 5.3(b) illustrates the experimental set-up of the transmission type diffractometer. An advantage of the method is the requirement of only small amounts of sample and an increased avoidance of preferred orientation and texture effects. By rotation of the sample, it is possible to enhance the counting statistic of detected intensities [131, 142].

Originally, the DEBYE-SCHERRER method, also called HULL-DEBYE-SCHERRER method ensures a detection of a part of the diffraction cone on a cylindrically bended film. Today, diffractometers are equipped with digital sensors that move in a circle around the sample to follow the varying diffraction angles 2θ. The sample is either pressed into a small cylinder, already produced in the shape of a thin wire or, in the case of powdered materials, filled into a fine glass capillary. The capillary consists of nearly X-ray transparent (silica) glass and displays an inner diameter of 0.3 mm or 0.5 mm and a thickness of 0.01 mm. Due to high chemical and thermal stability, it is also possible to use capillaries made of kapton, a polyimide film as shown in Figure 5.4(b) on the top [145, 146].

✺✳✶✳✷✳ ❘✐❡✈❡❧❞ ❡✜♥❡♠❡♥

A typical PXRD pattern is shown in Figure 5.1 and depicts the intensity I in arbitrary units dependent on each individual angle 2θ. For the analysis and interpretation of PXRD data, the RIETVELD method has been introduced by HUGO RIETVELD.

The RIETVELD refinement was first implemented in 1967, and reported in 1969 for the diffraction of monochromatic neutrons where the reflection position is described in terms of the BRAGG angle 2 θ. It operates as a structure refinement procedure, adjusting calculated and observed intensities measured at equal angular intervals in a least-squares fit. This method shows an increased reliability of structure parameters in comparison with previously applied procedures of using the integrated intensities of overlapping peaks [147, 148]. Using this novel technique, it is possible to refine nuclear and magnetic structures as well. The application of the least-squares refinement enables the user to introduce linear or quadratic constraints between the parameters.

The RIETVELD method basically works directly on the whole diffraction pattern by consideration of each observed intensity yi(obs) at the angle θi of the scanned data with the value of the calculated intensity yi(calc). The summation over all angles of the pattern S will

65 5. Characterisation of synthesised products and methods then be minimised with

2 2 2 S = wi (yi(obs) − yi(calc)) = wi Di = ai , (5.2) i i i X X X where wi represents a weighing factor, usually related to the variance of the observation yi(obs) with the difference Di and the normalised or weighted ai . An adequate description of the principle of the profile refinement method can be accomplished in the form of the function M which has to be minimised with respect to the parameters. While for the normal refinement procedure on separated integrated intensities this function is described by

2 2 1 2 M = wi S (obs) − S (calc) . (5.3) i c i i ½ ¾ X The integrated intensities of groups of overlapping reﬂections are given by

2 2 1 2 M = wi Sk (obs) − Sk (calc) , (5.4) i ( k c k ) X X X while this function becomes

2 2 1 2 M = wi y (obs) − y (calc) , (5.5) i c i i ½ ¾ X in the case of profile refinement, where i is the sum over the independent observations, and sumk represents the sum over the overlappingP reflections in each k group. This process is conducted using a computer program, which carries out the least-squares refinement. Approximate starting values and, therefore, a model for the material itself is required to start the process in the first cycle. With each iterative step, the parameters are refined until a predefined convergence criterion is reached [148].

To estimate the GOF, R-values are examined. In full-pattern reﬁnements, two R-values are generally considered, the proﬁle R value,

Rp which can be contemplated as a true quantity based on the discrepancies between observed and calculated intensity values, and the BRAGG R value, RBragg which is regarded as an artiﬁcial quantity generated in order to get values similar to the single-crystal R- values. Weights wi may be taken into account from the experimental error margins, usually ′ ′ OISSON = counting P statistics, i.e., wi 1/yi(obs) with yi(obs) observed counts including background points. The R-values can be deﬁned as

66 5.1. Powder X-ray diffraction (PXRD)

S 2 = Rwp 2 (5.6) wi yi(obs) whose limit, for purely statistical ﬂuctuations,P is for N observations and P parameters

N − P 2 = Rexp 2 . (5.7) wi yi(obs) P 2 2 The quality of the ﬁt is then assessed by comparing Rwp with its theoretical limit Rexp which, however, is only reached if proﬁle differences Di do not contain any systematic contributions [149, 150].

The BRAGG R value RBragg can be considered more important than the proﬁle R value as it is an agreement index and based on integrated BRAGG intensities [151].

As the minimum of the sum S is reached, the estimate of the standard deviation sk associated with the kth parameter is also minimal and its value is in simple relation to

−1 (M )kk S s2 = , (5.8) k (N − P) with the matrix of the least-squares algorithm M, the indicator of the overall variance of S S the fit (N−P) and the actual GOF (N−P) [149, 150]. For the improvement of the structureq refinement, a distinct peak shape needs to be assumed for the experimental PXRD pattern. Here, the simplified formula given by CAGLIOTI, PAOLETTI and RICCI is used to express the angular dependence of the FWHM of the diffraction peaks. It can be abstracted to [148, 152]

2 2 Hk = u · tan θk + v · tanθk + w, (5.9)

where u, v, and w represent the FWHM parameters. Peak broadening resulting from the particle-size effect describing the experimentally observed variation of FWHM with scattering angle is considered as well. Initial and approximate values for these parameters are found by graphically measuring the FWHM Hk of selected single peaks in the diagram. Since plate-like crystallites have a tendency to align their normals along the axis of the cylindrical sample holder, it can be sensible to perform a preferred orientation correction. The intensity correction is deﬁned as

2 Icorr = Iobs · exp −Gα , (5.10) © ª with the acute angle between the scattering vector and the normal to the crystallites α and the preferred orientation parameter G. The parameter G is a measure for the FWHM of

67 5. Characterisation of synthesised products and methods

the assumed GAUSSIAN distribution of the normals about the preferred orientation direction [150].

In a typical RIETVELD reﬁnement, standard deviations are obtained as a useful tool to determine the accuracy of the calculated parameters. These standard deviations tend to decrease towards zero with the recording step while simultaneously serial correlations emerge. BÉRAR’S formula, introduced in 1991 by JEAN-FRANÇOIS BÉRAR, takes into account local correlations for a reliable estimation of the values they would assume if these correlations vanish [149]. The program used during the course of this work (see Section 5.1.3) automatically calcu- lates and provides the factor with which the standard deviations have to be multiplied in the corresponding output ﬁle.

✺✳✶✳✸✳ ♦❣❛♠ ❙✉✐❡ ❋✉❧❧♦❢

For the evaluation of the PXRD data, the program Suite FULLPROF by JUAN RODRÍGUEZ- CARVAJAL is used [153, 154]. It provides support for the display, analysis and interpretation of powdered samples analysed by X-Ray, Neutron or Synchrotron radiation from lattice constant determination to RIETVELD reﬁnement. The RIETVELD Method serves to reﬁne a crystal structure by minimising the weighted squared difference between the observed and the calculated pattern against the parameter vector α = (α1,α2,α3,...αp )

n 2 2 χ = wi yi(obs) − yi(calc) (α) , (5.11) i=1 X © ª = 2 2 has to be minimised with the variance wi 1/σi and σi of the observation yi(obs) [154]. The lattice constant determination is conducted using DICVOL06 [155], which is a well- known program for indexing powder diffraction patterns. It is supplied in the FULLPROF Program Suite and used to derive UC parameters from the peak positions of marked experimental signals. For the indexing, the ﬁngerprint area of 3 °2θ to 30 °2θ is chosen, where individual peaks are well resolved. All DICVOL06 runs for the tested materials provided indexing solutions in monoclinic or orthorhombic UCs.

✺✳✶✳✹✳ ❆♥❛❧②✐ ♦❢ ♣♦❧②❝②❛❧❧✐♥❡ ♠❛❡✐❛❧ ❘❯❇✲✸✻

PXRD analysis was carried out on as-made RUB-36, as well as cation intercalated Me-IEZ-

68 5.1. Powder X-ray diffraction (PXRD)

(a) ﬂat sample holder (b) capillaries

Figure 5.4.: Sample holder for PXRD experiments; (a) ﬂat specimen holder for measurements on PHILIPS diffractometer; (b) top: kapton capillary for measurements on HUBER diffractometer; bottom: silica glass capillary for measurements on SIEMENS diffractometer.

RUB-36 samples.

For the phase identification, PXRD analysis was performed on a PHILIPS diffractometer Type 1830/40 (MALVERN PANALYTICAL GMBH, Kassel, Germany) and on a RIGAKU RINT UltimaIII (RIGAKU CORPORATION, Tokyo, Japan) in BRAGG-BRENTANO geometry on a flat sample holder using monochromatic Cu K α radiation (λ = 1.5418 Å) at room temperature. Figure 5.4(a) exhibits such a flat sample holder.

The HUBER transmission geometry diffractometer (HUBER DIFFRAKTIONSTECHNIK GmbH & Co. KG, Rimsting, Germany) has been used to identify phases as well. Samples were stored in a kapton capillary (sealed by modelling clay), depicted in Figure 5.4(b) top.

High resolution PXRD data were collected at room temperature using a SIEMENS D5000 diffractometer (SIEMENS, Berlin, Germany) in quasi DEBYE-SCHERRER mode equipped with a (111)-Ge monochromator and a BRAUN position sensitive detector using monochromatic Cu K α1 radiation λ = 1.54059 Å). Transmission geometry was implemented by using silica glass capillary sample holders to minimise preferred orientation of the platelet samples. An exemplary capillary is shown in Figure 5.4(b) bottom. The diagrams have been recorded using a step size of 0.007887 °2θ with a step time of 7 s in a range of 3 °2θ to 65 °2θ. For every recorded diagram, the °2θ-range has been covered a total of three times.

The ﬁrst results of the analyses are presented in Figure 5.5, which depicts the PXRD diagrams of the starting material as-made RUB-36 (violet), Co-IEZ-RUB-36 (yellow), Ti-IEZ- RUB-36 (red), V-IEZ-RUB-36 (green) and Zn-IEZ-RUB-36 (blue). The intensity is displayed in arbitrary units and in dependency of the diffraction angle °2θ. The ﬁrst signal is very

69 5. Characterisation of synthesised products and methods

120000

Zn-IEZ-RUB-36 100000

80000 V-IEZ-RUB-36

60000 Ti-IEZ-RUB-36

40000 Co-IEZ-RUB-36

20000 as-made RUB-36

0 10 20 30 40 50 60

Figure 5.5.: PXRD diagrams of as-made RUB-36 (violet), Co-IEZ-RUB-36 (yellow), Ti-IEZ- RUB-36 (red), V-IEZ-RUB-36 (green), Zn-IEZ-RUB-36 (blue). distinctly pronounced in each material and, at the same time, representing the highest signal. A lot of information lies hidden in this peak, since it allows estimations about the interlayer distance and the degree of stacking disorder - if present. The indexing has revealed an (h k l) value of (200) for this signal at a position of around 7.95 °2θ for RUB-36 and around 7.38 °2θ for the Me-IEZ-RUB-36 materials. The shift between these two values also confirms a successful interlayer expansion process. A sharp first signal indicates a high order and conformity of neighbouring layers in the material, as is the case for as-made RUB-36 with a FWHM of approximately 0.14. In contrast to that, the four Me-IEZ-RUB-36 materials depict significant peak broadening with FWHMs of about 0.39 for Co-, ca. 0.50 for Ti-, approximately 0.39 for V- and ca. 0.42 for Zn-IEZ-RUB-36 indicating a degree of layer disorder and/or a lower degree of crystallinity.

The structure of as-made RUB-36 has been solved by MARLER et al. [17, 58] and the corresponding structure model has been provided in a cif-file in the supplementary information of the paper in question [58] (see Figure 4.5 in Section 4.4). Figure 5.6(a) displays the PXRD patterns of as-made RUB-36 (red), RUB-36 as calculated from cif-data by VESTA (green) [58, 118] and simulated by DIFFaX (blue) [28]. The background of the experimental pattern has been subtracted by linear interpolation and all three diagrams have been normalised to an intensity of 100 to facilitate comparison. The two calculated patterns are in very good agreement with the experimental data. However, whereas the simulation in DIFFaX allows for the modification of the peak profile parameters to adjust the peak form, the calculation

70 5.1. Powder X-ray diffraction (PXRD) in VESTA from cif-data yields strictly sharp reflections. VESTA utilises the RIETAN routine [156] to simulate PXRD patterns from lattice and structure parameters. A small discrepancy between model and experimental pattern has been found in an area around 24.00 °2θ. The three signals in question (Figure 5.6(b), indicated by black arrows) are located at 23.990 °2θ representing (006), 24.062 °2θ representing (020) and 24.181 °2θ representing (115) and (115), respectively. In the experimental pattern, the first signal is the highest, whereas in the cif-calculated pattern the last signal is the highest. This variance can be accounted for by the addition of a water (oxygen) position in the model between neighbouring layers and the DEDMA molecule. The resulting DIFFaX pattern has improved the fit, however, it is still not perfect, only equalising both signals and not reversing intensity entirely. Therefore, the cif-model does not yet depict the real crystal structure of the as-made RUB-36 sample in an ideal manner. At the same time, this small deviance from the actual crystal structure serves to illustrate the sensitivity of the DIFFaX program, and the powder diffraction technique in general. The good agreement between the experimental pattern and the two calculated models confirms the accuracy of the cif-file and the correct application of the DIFFaX program in the simulation of the stacking disorder described in the following chapters.

✺✳✶✳✺✳ ❆♥❛❧②✐ ♦❢ ▼❡✲■❊❩✲❘❯❇✲✸✻

The reﬁnement procedure has been carried out uniformly for all as-made materials. The ﬁngerprint area of the PXRD diagram is chosen since individual signals are well resolved and peak overlap is minimal. A maximum of 20 signals is selected for indexing, whereas

130 50

110 40

90 30 70 20 DIFFaX 50

10 30 experimental Intensity / arb. units / arb. Intensity DIFFaX units / arb. Intensity 10 0 experimental calculated from cif calculated from cif

0 10 20 30 40 50 60 17 19 21 23 25 27 29 31 2 ѳ / ° 2 ѳ / ° (a) (b)

Figure 5.6.: PXRD diagrams of as-made RUB-36 (red), RUB-36 as calculated from cif-data by VESTA (green) [58, 118] and simulated by DIFFaX (blue) [28].

71 5. Characterisation of synthesised products and methods

40000

30000

20000

10000 Intensity / arb. units / arb. Intensity 0

0 10 20 30 40 50 60 70 2 ѳ / °

Figure 5.7.: Visualisation of RIETVELD refinement for as-made RUB-36, with experimental pattern y1(obs) (green), simulated pattern yi(calc) (black), BRAGG reflections (red) and difference plot yi(obs)-yi(calc) (blue). triclinic solutions are rejected beforehand. Solutions are listed by lattice parameters, crystal system and point group (PG), which are then used for the lattice constant refinement. Every material yields at least one orthorhombic and one monoclinic solution, but since the starting material RUB-36 already exhibits an orthorhombic PG and since it is a higher symmetric solution, these results are favoured for a later RIETVELD refinement. Symmetry relations can be taken into account to determine a corresponding SG from the list of generated (h k l)-values due to systematic absences.

In the following LE BAIL Fit, integrated intensities are extracted for the profile matching process [157]. Here, the peak profile is fitted to a modified PSEUDO-VOIGT function that has been introduced by THOMPSON,COX and HASTINGS [158]. The PSEUDO-VOIGT profile is an approximation function of the VOIGT profile V (x), which is a convolution of a GAUSSIAN curve G(x) with a LORENTZ curve L(x). During this process, the scale factor is not allowed to vary and integrated intensities are refined individually using the RIETVELD formula for obtaining the integrated observed intensity. The background radiation stemming from the glass capillary is usually subtracted by a model of linear interpolation. Structural information in the form of atomic positions is not yet used in this step [159]. The peak shape is described by profile parameters u, v, w for the GAUSSIAN fraction and x and y for the LORENTZIAN part. Also, two asymmetry parameters are taken into account. Asymmet-

72 5.1. Powder X-ray diffraction (PXRD) ric distortions are more pronounced at lower angles, thus, a limit for the applicability of asymmetry is given at around 18 °2θ. Another important point is the usage of monochro- mators or collimators, which can be accountable for polarisation effects. Here, a (111)-Ge- monochromator is used. The resulting polarisation is corrected via BRAGG equation ((5.1)) by insertion of the Ge d-value 3.266 Å and the applied wavelength λ = 1.54059 Å of order n = 1 giving an angle θM of 13.642°. The resulting polarisation factor may be calculated by 2 PM = cos [2θM ] yielding PM = 0.7899. Since the RIETVELD formula is applied, the GOF can already be taken into account as a means to interpret the success of the ﬁt. The χ2 residue factor should ideally take a value below 3 and above 1 to continue with the actual structure reﬁnement.

To solve the structures of novel Me-IEZ-materials after the determination of the lattice constants and the LE BAIL Fit, a starting model is necessary. This model is a convolution of information derived from symmetry considerations and DIFFaX-simulations, the already solved structures of RUB-36, COE-3 and -4, as well as known framework types FER and CDO. A super symmetry group of the latter two structures is orthorhombic Cmmm. Related framework models are explored using POWDERCELL 2.3 [160] by generating klassengleiche and/or translationengleiche subgroups [161] and by simulating different stacking orders and interlayer distances using DIFFaX [28]. The space group (SG) is a characteristic derived from group theory, in which symmetry operations like mirror planes and rotational axes represent its group elements. To create a subgroup, some of the symmetry operations of a certain group are removed. If no intermediate group exists between a SG and one of its subgroups, then this subgroup is a maximal subgroup. The integer index of the symmetry reduction is the factor, by which the number of symmetry operations has been reduced. HERMANN’S theorem states that a maximal subgroup is either a translationengleiche or a klassengleiche subgroup. In a translationengleiche subgroup, the complete translation lattice is preserved; its primitive UC has an unchanged volume. A klassengleiche subgroup belongs to the same crystal class; it has lost translational symmetry. In consequence, the conventional UC is either enlarged or it has lost centring translations [162, 163].

RUB-36 can be refined to an orthorhombic solution in SG P2 1cn (see Figure 5.7). Or- thorhombic solutions were attempted for Me-IEZ-RUB-36 samples. However, these refinements were not successful beyond a certain point. Therefore, all four materials were refined in a space group (SG) in the monoclinic crystal system. Starting with the FER structure in SG Immm, Pmmm can be derived in the klassen-

73 5. Characterisation of synthesised products and methods gleiche subgroup IIa, which in turn leads to translationengleiche subgroup I Pmm2 and lastly, translationengleiche subgroup I Pm. In the same manner, the CDO structure in SG Cmcm can be reduced to Pmcm (klassengleich IIa) and needs to be transformed to setting 1 Pmma. From here, the next step is the reduction to translationengleiche subgroup I P2/m and then translationengleiche subgroup I Pm. Even though the symmetry has been reduced from orthorhombic to monoclinic, the β-angle remains at 90° yielding a pseudo- orthorhombic UC. Even though the elementary building block of fer-type layers is known and used as a template for the later Me-IEZ-materials, a good starting model, unfortunately, was not found by means of simulating stacking order. As possible configurations of layers and interlayer distance as well as shift vectors in each direction and combinations thereof are virtually infinite and, likely, infinitely complicated, only a small number of parameters has been adapted. Figure 4.8 shows an example of a straightforward simulation with only one type of layer (fer) and only two different stacking configurations of FER- and CDO-type. Already, the simulation is very sensitive to minor changes such as an increase of 10 % toward CDO-type stacking, discernible by sharp signals successively broadening. During the structure exploration process, FER- and CDO-type stacking orders were applied. Also, the exact starting configuration of RUB-36 was investigated, interlayer expanded to differing values and cations added in between neighbouring layers. In the orthorhombic solution of RUB-36, no bridging atoms exist since individual layers are not connected and interlayer space is occupied by the DEDMA molecule. Only one T-atom position is applied to bridge individual layers. Assuming a special position of x = 0.5, y = 0.5, z = 0.5, with a multiplicity of M = 4, four bridging atoms result in the UC. In the monoclinic solution Pm with a multiplicity of M = 2, two positions are necessary to generate four bridging atoms. Assuming a lower/no symmetry or a type of disorder, four individual positions can be found within the UC. The presence of Me cations on bridging positions other than Si has been confirmed by different experimental techniques in addition to the generation of FOURIER difference maps. However, chemical analyses suggest that less than one out of every four bridging atoms is occupied by a Me cation (see Sections 5.2, 5.4 and 5.5). The resulting different occupation configurations have been taken into account during simulation. During RIETVELD refinement in FULLPROF, however, all bridging atoms are denoted as Me-cations as to avoid symmetry violations and obey increased SOFs.

PXRD diagrams of the post-treated materials appear very similar, so it is prudent to assume matching framework conﬁgurations. Basic (h k l)-values agree to a very high degree. However, individual signals are broadened and intensities vary. For example, the ﬁrst signal

74 5.1. Powder X-ray diffraction (PXRD)

400

11. exp. Zn-IEZ-R36 300

10. Mix-Zn-IEZ-CDO 9. Mix-Zn-IEZ-FER 200 8. IEZ-CDO 7. IEZ-FER 6. Zn-IEZ-R36 5. Zn-IEZ-R36 w. DEDMA 100 4. Zn-R36 1% Zn 3. Zn-R36 50% Zn 2. Zn-R36 w. DEDMA 1. R36 0 0 10 20 30 40 50 60 2 ѳ / ° Figure 5.8.: Different simulation approaches for the novel materials generated with DIFFaX (1.-10.) compared to experimental pattern of Zn-IEZ-RUB-36 (11.) [28, 130]. appears very uniformly broadened for Ti- and Zn-materials, but seems sharper for Co- and V-, whereas the former exhibits a small shoulder. The same idiosyncrasy can be observed for the small signal at position 16.36 °2θ, a signal that displays broadening likely related to stacking disorder, as the neighbouring signal at 17.79 °2θ exhibits a sharper peak shape in all four samples. Figure 5.8 displays different attempted simulations for the Zn-IEZ-RUB-36 materials. Starting with simulations of 1. pure RUB-36, 2. unmodified RUB-36 with Zn in between neighbouring layers in addition to the DEDMA molecule, 3. RUB-36 without DEDMA and with 50 % Zn of bridging atoms, 4. the former with 1 % Zn, 5. IEZ-RUB-36 with DEDMA and Zn, 6. IEZ-RUB-36 with Zn but without DEDMA, 7. IEZ-FER, 8. IEZ-CDO, 9. a mixture of IEZ-FER with alternating Zn and Si bridging atoms, 10. a mixture of IEZ-CDO with alternating Zn and Si bridging atoms, and 11. the experimental Zn-IEZ-RUB-36 PXRD pattern for direct comparison. These patterns are an excerpt of the attempted simulations. The lacking accordance between the pursued solutions and the experimental pattern shows that the real material exhibits a more complex state. The models for IEZ RUB-36 with Zn with (5.) and without the DEDMA molecule (6.) represent the most promising of the simulations. Still, a few signals exhibit the wrong intensity distribution, some signals are not present at all and some are excessive. Especially the signal at 13.5 °2θ was not reproducible with the high intensity of the experimental pattern. The most successful Rietveld refinements have been conducted in SG Pm. The monoclinic SG refinement may show a better fit due to a statistical distribution of the Me-cations,

75 5. Characterisation of synthesised products and methods which randomly occupy every other bridging position between neighbouring layers, or due to small deviations of certain atoms from formerly orthorhombic special positions. Table 5.1 summarises experimental conditions and crystallographic data for the refined Me-IEZ-RUB-36 samples as obtained from the PXRD experiments and subsequent RI- ETVELD refinement, whereas Figures 5.9, 5.10, 5.11 and 5.12 display the structure plots in VESTA as retrieved from the RIETVELD refinement. The visualisation of the RIETVELD refinement for the as-made materials occurs uniformly. The experimental pattern yi(obs) is indicated by green circles, whereas the simulated pattern yi(calc) is represented by a black line. Red vertical bars display BRAGG reflections

(h k l), whereas the blue line on the bottom is the difference plot yi(obs)-yi(calc), giving information on the GOF of the refinement. Regarding Table 5.1, the number of refined parameters is mostly similar for all materials. The only global, or rather instrumental parameter is that of the zero correction, dependent on the diffractometer used. Profile parameters describe the peak shape as explained in Section 5.1.2 and Equa- tion (5.9) as well as lattice constants, scale factor and preferred orientation. The atomic positions, temperature and SOFs can be specified among the structural parameters, which are listed in detail in the Appendix in Tables 7.2-7.5. Geometric restraints are calculated automatically and need to be adjusted for an idealised microporous silicate material, i.e., d(Si − O) = 1.60(2)Å, d(Si − Si) = 3.10(5)Å, d(O −O) = 2.60(3)Å with allowed standard deviations in brackets.

The Zn sample exhibits the best fit out of the four presented with a χ2 value of 5.93, which is reasonable for a material exhibiting stacking disorder. Co and V materials have been refined to χ2 values of 9.19 and 9.64 respectively, showing definite room for improvement. The Ti sample with an χ2 value 26.1 shows the highest degree of mismatch. However, the PXRD diagram of the Co material exhibits the highest intensity, whereas both the Ti and Zn samples range in a similar intensity range. V material on the other hand shows the lowest degree of crystallinity out of the analysed materials with a very broad first signal and the lowest overall intensity. Both, the materials inhomogeneity in terms of stacking faults and the incomplete or imperfect fit of the structure model contribute to the mismatch between experiment and refinement model. Without the implementation of a stacking disorder model, the refinement using the FULLPROF program is limited and the fitting of a model to the experiment will not yield desired R-values as would be feasible for non-disordered materials. In light of the observations about the crystallinity of each sample, the success of the refinement does

76 5.1. Powder X-ray diffraction (PXRD)

13000

11000

9000

7000

5000

3000

Intensity / arb. units / arb. Intensity 1000

0 10 20 30 40 50 60 70 2 ѳ / °

Figure 5.9.: Visualisation of RIETVELD reﬁnement for as-made Co-IEZ-RUB-36 using Win- plotr [130], with experimental pattern yi(obs) (green), simulated pattern yi(calc) (black), BRAGG reﬂections (red) and difference plot yi(obs)-yi(calc) (blue).

11000

9000

7000

5000

3000

1000 Intensity / arb. units / arb. Intensity

0 10 20 30 40 50 60 70 2 ѳ / °

Figure 5.10.: Visualisation of RIETVELD reﬁnement for as-made Ti-IEZ-RUB-36 using Win- plotr [130], with experimental pattern yi(obs) (green), simulated pattern yi(calc) (black), BRAGG reﬂections (red) and difference plot yi(obs)-yi(calc) (blue).

77 5. Characterisation of synthesised products and methods

8000 7000 6000 5000 4000 3000 2000 1000 0 Intensity / arb. units / arb. Intensity

0 10 20 30 40 50 60 70 2 ѳ / °

Figure 5.11.: Visualisation of RIETVELD reﬁnement for as-made V-IEZ-RUB-36 using Win- plotr [130], with experimental pattern yi(obs) (green), simulated pattern yi(calc) (black), BRAGG reﬂections (red) and difference plot yi(obs)-yi(calc) (blue).

11000

9000

7000

5000

3000

1000 Intensity / arb. units / arb. Intensity

0 10 20 30 40 50 60 70 2 ѳ / °

Figure 5.12.: Visualisation of RIETVELD reﬁnement for as-made Zn-IEZ-RUB-36 using Win- plotr [130], with experimental pattern yi(obs) (green), simulated pattern yi(calc) (black), BRAGG reﬂections (red) and difference plot yi(obs)-yi(calc) (blue).

78 5.1. Powder X-ray diffraction (PXRD) sample Co-IEZ-RUB-36 Ti-IEZ-RUB-36 V-IEZ-RUB-36 Zn-IEZ-RUB-36 °2θ range / ° 2.047 - 64.694 2.047 - 59.718 2.047 - 64.694 2.047 - 64.694 no. of points 7970 7337 7970 7970 no. of 943 936 545 1102 reflections position of °2θ 12.47 17.45 11.92 12.58 sharpest reflex FWHM at 0.1240 0.279 0.1046 0.1394 sharpest reflex no. of param. 222 (1; 19; 202) 222 (1; 18; 203) 215 (1; 18; 196) 222 (1; 18; 203) (glo.; prof.; str.) no. of dist. restr. 255 254 255 254 approx. chem. Si Co O Si Ti O Si V O Si Zn O comp. per UC 51.95 0.05 88 51.75 0.25 88 51.88 0.12 88 51.82 0.18 88 molweight per 1240.801 1245.629 1242.288 1254.512 UC / gmol−1 SG Pm (No.6) Pm (No.6) Pm (No.6) Pm (No.6) lattice param. a0 / Å 23.875(12) 24.207(59) 23.782(25) 23.782(16) b0 / Å 14.053(7) 14.002(33) 14.024(7) 14.056(9) c0 / Å 7.417(4) 7.398(14) 7.404(4) 7.421(4) β / ° 90.00(5) 89.91(28) 90.08(9) 89.98(4) no. of atoms 83 84 76 84 UC vol. / Å3 2489(2) 2507(10) 2481(4) 2483(3)

R-factors (resid. of reﬁn.)

Rp / % 5.49 8.97 5.24 4.69

Rwp / % 7.29 12.8 7.63 6.38

Rexp / % 2.42 2.51 2.62 2.62 χ2 9.09 25.9 8.46 5.95

RBragg / % 29.1 39.0 26.8 18.5

SCOR (BÉRAR) 6.2279 8.4888 7.7340 4.8978

Table 5.1.: PXRD experimental conditions and crystallographic data for Me-IEZ-RUB-36.

79 5. Characterisation of synthesised products and methods not mirror the perceived crystallinity as observed by intensity and FWHM signal. Even though Ti and Zn samples exhibit comparable crystallinity, the Ti refinement yields the least successful results in contrast to the most successful one of Zn. Considering the theoretically achievable value of Rexp of around 2.5 with regards to the quality of the collected data, a high accordance between the different materials can be observed. Therefore, it is suggested that the fit of the structure model predominates the success of the refinement, and, that unambiguously suitable models for the Co, Ti and V samples have not been found yet. Provided an appropriate and optimised model, an accordance of experiment and refinement should yield R-values similar to those of Zn for the remaining refinements.

(a) Co-IEZ-RUB-36 (b) Ti-IEZ-RUB-36

Figure 5.13.: Structure plot of sample materials (a) Co-, (b) Ti- (c) V- and (d) Zn-RUB-36 generated using VESTA [118]; atoms are labelled as blue: Si, red: O, brown: C, yellow: Co, violet: Ti, green: V, light blue: Zn. The black rectangle indicates the position of the UC.

Figure 5.13 displays the atomic structure plots as derived from RIETVELD reﬁnement using VESTA. The framework structure for all materials has been assumed in a similar manner. Extra framework positions (EFPs) are added to the framework by running the GFOURIER program 04.06, also implemented in the FULLPROF Program Suite. A FOURIER difference map is generated by subtracting the calculated FOURIER map by the observed

80 5.2. SEM and EDX

map (Fobs-Fcalc). Individual structures exhibit the characteristic fer-layer as well as two different open cages by bridging framework layers, one big cage and the other more or less strained and occupied by EFPs. To account for the additional bridging cations, the interlayer space between neighbouring fer-layers has increased, detectable in the expansion of the lattice constant a0 by 6.9 % for Co-, 8.2 % for Ti-, 6.5 % for V-, and 6.1 % for Zn-IEZ-RUB-36 in contrast to as-made RUB-36. With regards to interlayer distance, two different conﬁgura- tions have to be taken into account, one longer distance for the bigger cage and a shorter distance for the smaller cage. The increase accounts for 9.8 % for Co-, 10.0 % for Ti-, 8.9 % for V- and 10.1 % for Zn-IEZ-RUB-36 by averaging the two different Si-Si distances.

✺✳✷✳ ❙❝❛♥♥✐♥❣ ❡❧❡❝♦♥ ♠✐❝♦❝♦♣② ✭❙❊▼✮ ❛♥❞ ❊♥❡❣②✲❞✐♣❡✐✈❡ ❳✲❛② ♣❡❝♦❝♦♣② ✭❊❉❳✮

SEM pictures are taken to examine morphology and grain sizes of the crystals as well as homogeneity and phase compositions of the samples. In general, HLSs form plate-like crystals. EDX analyses give insight to the qualitative sample composition and serve to illustrate the incorporation of the Me cations. Unsuccessful inclusion of Me-cations is observed when the respective cation content is too high and the acac is solely deposited on crystal surfaces. In this case, small clusters are found on individual planes. In some instances, particular crystallites are partly decomposed, in which case the post-synthesis treatment was not successful either.

✺✳✷✳✶✳ ❇❛✐❝ ♣✐♥❝✐♣❧❡ ♦❢ ❙❊▼ ❛♥❞ ❊❉❳

Whereas in transmission electron microscopy (TEM), a wide beam of electrons passes through a thinly sliced specimen to form an image, SEM makes use of a focused beam of electrons scanning over the surface of thick or thin specimens to produce images one spot at a time in a grid-like raster pattern. Another category is presented in the form of scanning transmission electron microscopy (STEM) which applies a focused beam of electrons scanning through a thinly sliced specimen to form an image. All three types of microscope make use of electric and magnetic ﬁelds to manipulate an electron beam. As electrons hit matter, a number of interactions can be observed between the incident electrons and solid matter. Depending on the necessary information, different interactions can be detected. Electrons may be transmitted, i.e., pass through matter unchanged, and backscattered, continuum and characteristic X-ray radiation can be produced, the latter

81 5. Characterisation of synthesised products and methods

of which in turn can cause the scattering of secondary electrons or AUGER electrons in addition to the generation of cathodoluminescence. Transmitted electrons may either pass matter unscattered, inelastically or elastically scattered, all of which provide valuable informations on the sample. Incident electrons which are transmitted through the thin specimen without interaction inside the sample are called unscattered electrons and may be used to generate a black- and-white image of the specimen. The transmission of unscattered electrons is inversely proportional to the specimen thickness. Therefore, thicker areas have fewer transmitted electrons causing a darker appearance, whereas thinner areas will cause a lighter picture. In contrast, incident electrons (i.e., deflected from their original path) may be elastically scattered (i.e., without loss of energy) by atoms of the specimen which are then transmitted through the remaining portions of the sample. The scattering of these electrons consistently follows BRAGG’S law (see Equation (5.1)). Hence, incident electrons of the same energy E (i.e., wavelength λ) entering the specimen normal to its surface will be scattered by the same atomic spacing d in the same angle θ. The electrons of a specific angle may be collated using magnetic lenses to form a pattern of BRAGG spots similar to those of single crystal scattering techniques. Each spot represents a specific atomic spacing or crystal plane {h k l}, allowing for the extraction of information about orientation, atomic arrangement and phases present in the area being examined. Examples for such a pattern can be found in the next section (Section 5.3.1). Inelastically scattered electrons loose energy during interaction with the specimen atoms and are, as well, transmitted through the remaining sample thickness. They can be used twofold. The inelastic loss of energy by the incident electrons is characteristic of the elements the interaction has occurred with and may be used in the electron energy loss spectroscopy (EELS). The lost energy is unique to each bonding state of each element and can, therefore, be used to extract both compositional and bonding (i.e., oxidation state) information on the specimen region being examined. This technique is superior to EDX when it comes to lighter elements.

KIKUCHI Bands represent bands of alternating light and dark lines formed by inelastic scattering interactions related to atomic spacings in the sample. As their width is inversely proportional to atomic spacing, they can either be measured or trailed to gain insight to the scattered electron pattern. For the imaging of the specimen, both the secondary electrons and the backscattered electrons are utilised. Secondary electrons are those that are ejected of the surface by the electron beam, they are of low energy and yield topological information. Hence, they are typically used for imaging. Backscattered electrons are created by the interaction of the

82 5.2. SEM and EDX atomic nucleus with the primary beam. They generate sufﬁcient energy to leave the sample and deliver material contrast. In the case of microporous materials of low density, mainly consisting of Si, Al and O, not a lot of scattering occurs. The platelet samples in this work are of very low thickness. To increase the scattering, the energy of the electrons or the scattering angle must be decreased. Lastly, the generated characteristic X-ray radiation is used in the form of energy- dispersive X-ray spectroscopy (EDX) for the chemical analysis of the sample. It is created by removing an electron of the corresponding atom from the K-shell, which is replaced by electrons from the L-shell. The energy in keV released in that process is characteristic for the element and is measured in intensity in dependence of the energy of the photon [164]. The resolution of SEM ranges in between that of the optical microscopy and scanning tunneling microscopy (STM) as well as atomic force microscopy (AFM) and the size of the zeolites that can be studied with SEM is, thus, between 20 nm and 20 µm. Electrons in a range of 1 kV to 20 kV are focused on a sample surface and then detected. Due to the ability to directly observe the pore structure of a zeolite and not just the surface, scanning electron microscopy (SEM) is a particularly powerful tool. Powdered samples are dispersed on a metal holder (see Figure 5.14(a)) of polished surface, to ensure a smooth background and no interference with the contours of the crystals. These samples are then coated via a sputter technique with a thin conduction layer of either gold or carbon. When bombarded with an electron beam, the emitted electron energies are picked up by a collector to present a three-dimensional image in contrast to the two-dimensional picture obtained by TEM which, on the other hand, has higher magnifying power [165]. Microporous materials and zeolites in particular are very susceptible to damage and charging by electron beams, so that sophisticated techniques are required to observe them. Long exposure to the electron beam may even destroy the sample [166].

✺✳✷✳✷✳ ❙❊▼ ❛♥❞ ❊❉❳ ❡①♣❡✐♠❡♥

SEM based EDX-analysis of the materials was performed on a high resolution thermally aided LEO (ZEISS) 1530 Gemini ﬁeld emission scanning electron microscope (FESEM) (CARL ZEISS MICROSCOPY GMBH, Jena, Germany) with an attached OXFORD Aztec En- ergy X-ray microanalysis system (OXFORD INSTRUMENTS, Abingdon, UK). Phase purity and qualitative metal detection were probed at 20 kV. Figure 5.14 displays the SEM pictures of sample materials of Figure 5.14(a) SEM sample holder, Figure 5.14(b) Co- and Figure 5.14(c) Ti-IEZ-RUB-36 Figure 5.14(d) RUB-36, Fig- ure 5.14(e) V- and Figure 5.14(f) Zn-IEZ-RUB-36.

83 5. Characterisation of synthesised products and methods

RUB-36 exhibits uniformly clean orthorhombic crystallite plates in the form of elongated and sharp-edged hexagons with dimensions of up to 6 µm × 8 µm. By comparison, the SEM pictures of all Me-IEZ-RUB-36 materials show a much broader variety of sizes and shapes. The clean and sharp edges are partly smoothed out, especially on one side, to form more of an octagonal shape with a maximum particle size of 20 µm × 30 µm. The uniform particle size and form for all four Me-IEZ materials confirms successful post-synthesis treatment. In contrast, Figure 5.15 shows non-successful synthesis products. Pictures 5.15(a) and 5.15(b) exhibit distinct erosion of crystal surfaces, especially at the edges and particularly in a straight fashion along one crystal axis. Additionally, pictures 5.15(a) and 5.15(c) show definite isometric deposits on crystal surfaces. These deposits appear almost star-shaped with individual layer intergrowth. EDX analysis revealed a very high metal content with 21(1) wt% Co for the sample in Figure 5.15(a), 6.2(3) wt% Zn for sample Figure 5.15(b) and 8.6(3) wt% Zn for the sample in Figure 5.15(c). Figure 5.15(d) depicts very small areas of erosion and surface deposits as well. These deposits, however, are not as clearly defined as in the other three pictures. Instead, they are more lumpy and extensively distributed. Even though the metal content on these surfaces is very reasonable for a successful Me-IEZ post- synthesis treatment with 0.2(7) wt% to 0.5(5) wt% Zn, the standard deviation does not allow for a reliable measurement. The common denominator in all four syntheses is the similar original shape of RUB-36 crystal particles of more or less well pronounced hexagons.

10µm 10µm

(a) SEM sample holder (b) Co-IEZ-RUB-36 (c) Ti-IEZ-RUB-36

2µm 10µm 10µm

(d) RUB-36 (e) V-IEZ-RUB-36 (f) Zn-IEZ-RUB-36

Figure 5.14.: (a) SEM sample holder and SEM pictures of sample materials (b) Co-, (c) Ti- RUB-36 (d) RUB-36 (e) V-, and (f) Zn-IEZ-RUB-36.

84 5.2. SEM and EDX

Table 5.2 lists the measured atomic weights for each successfully synthesised material as determined by EDX analyses. The Cu and C content stem from sample holder and sputter- ing respectively, whereas the chlorine may be a residue from post-synthesis treatment of HCl. All samples exhibit a Me content below 0.5 wt%, which ﬁts very well with expected Me contents as previously investigated by DE BAERDEMAEKER et al. for analogues Fe materials [22]. It should be noted that EDX analyses are not as reliable as (ICP-)AAS measurements. Therefore, additional chemical analyses should be conducted in any case.

IEZ- Atom content wt% material Co Ti V Zn Si O Cl Cu C Co-030 0.1(1) - - - 34.7(2) 57.2(7) 0.7(0) 0.7(1) 6.6(2) Ti-001 - 0.4(0) - - 29.0(1) 60.2(2) 0.0(0) 0.4(1) 10.0(2) V-030 - - 0.2(1) - 31.3(2) 58.4(2) 1.1(0) 0.5(1) 8.5(2) Zn-085 - - - 0.4(1) 28.4(1) 60.6(2) 10.5(2) - -

Table 5.2.: Atom content as determined by EDX analyses.

Due to the SGs multiplicity of four, four T-atoms may be introduced by linking individual layers of the starting material RUB-36 with chemical denomination of SDA4Si38O72 by bridging atoms. The same idiosyncrasy can be observed for the purely siliceous IEZ and topotactically condensed COE-4 material, exhibiting a chemical denomination of

2µm 2µm 2µm

(a) Co-007 (b) Zn-001 (c) Zn-003

2µm

(d) Zn-043

Figure 5.15.: SEM pictures of unsuccessfully post-treated sample materials (a) Co-007, (b) Zn-001 (c) Zn-003 and (d) Zn-043.

85 5. Characterisation of synthesised products and methods

Si20O38(OH)4. In both structures, the ratio of T-atoms from the layer structure to T-atoms on linking sites is 9:1. If these linking sites were completely occupied by cationic Me other than Si (which is not necessary for structural stability), then the ratio of Si/Me would account for 9. In Fe-material the Me content of 0.5 wt% leads to the calculation of 6 % Fe on linking sites [22]. This type of determination yields an occupation of 1.1 % for Co material, 4.4 % for Ti material, 2.2 % for V material and 1.1 % for Zn-IEZ-RUB-36. The resulting trivial names and chemical denominations for each material can then be deduced as

Co-IEZ-RUB-36 Si51.95Co0.05O88,

Ti-IEZ-RUB-36 Si51.75Ti0.25O88,

V-IEZ-RUB-36 Si51.88 V0.12O88 and

Zn-IEZ-RUB-36 Si51.82Zn0.18O88. ✺✳✸✳ ❆✉♦♠❛❡❞ ❡❧❡❝♦♥ ❞✐✛❛❝✐♦♥ ♦♠♦❣❛♣❤② ✭❆❉❚✮

Electron diffraction measurements have been conducted as a means to gain complementary information on the atomic structure parameters such as unit cell (UC) and space group (SG) and to validate the results of the PXRD experiments. Structure characterisation may be accomplished "ab initio" for the beam sensitive microporous materials with a very short time of exposure of 3 min to 10 min.

✺✳✸✳✶✳ ❇❛✐❝ ♣✐♥❝✐♣❧❡ ♦❢ ❆❉❚

To obtain three-dimensional electron diffraction data, a set of diffraction patterns at various crystallographic zones is collected by manually tilting a crystal around a selected crystallographic axis. These sets are then assembled to a three-dimensional data-set for the structure analysis. Today, it is possible to collect these sets automatically and "ab initio" by automated electron diffraction tomography (ADT). For the TECNAI microscope, an experimental software package (ADT3D) has been developed for an automated data acquisition by tilting around the goniometer axis. This module combines STEM imaging and crystal tracking with diffraction pattern collection using a quasi-parallel beam with a diameter down to 50 nm in nano-electron diffraction (NED) mode. This allows for an automated recording of diffraction tilt series from nano-particle crystals with a size down to 5 nm. UC parameters, SG and reﬂection intensities can be automatically obtained from these 3D

86 5.3. ADT

Me Co Eu Sn Ti V Zn lattice BIBBBI

Table 5.3.: BRAVAIS lattice of different Me-IEZ-RUB-36 materials. diffraction data sets by extracting peak positions from a recorded data set and a cluster analysis of difference vectors using a dedicated software package (ADT3D). Additionally, a 3D reconstruction of the reciprocal space is viable to visualise special structural features of materials such as partial disorder. Due to full automation of the acquisition procedure, an optimisation of the electron dose distribution is achieved which, in turn, enables analysis of highly beam sensitive samples. Generally, acquired intensity data sets display a high coverage and signiﬁcantly reduced dynamical effects due to "off-zone" acquisition [167–169].

Compared to PXRD, the advantage of ADT is the feasibility of measuring single particles of very small size, much smaller than would be possible for SCXRD, regardless of eventual impurity phases surrounding the investigated material. Nonetheless, this is, at the same time, the drawback of the method, as not the whole bulk of the material is investigated. If the material exhibits a high disorder or low conformity of individual particles, then the method does not accurately depict the real state. Even though "ab initio" structure determination of zeolitic structures is possible, it is difficult to identify the correct solution, as it is not marked by the lowest structural residual and the missing sensitivity to the positions of oxygen and other light elements. On the other hand, diffraction patterns taken with a transmission electron microscope are similar to planar cuts through reciprocal space and, in general, show very few reflection overlap, allowing for a straightforward determination of crystal symmetry and reflection intensities. Due to these unique features, the ADT method serves as an ideal complementary technique to PXRD experiments. Furthermore, as a result of the option of investigating very small crystals, it is possible to analyse crystal particles that would appear "amorphous" in PXRD. In case no module is available, structure solution from the single crystal-like data set using direct methods is possible. [170–172].

✺✳✸✳✷✳ ❆❉❚ ❡①♣❡✐♠❡♥

Automated electron diffraction tomography (ADT) measurements and structure determi- nations have been conducted by HAISHUANG ZHAO at the Johannes Gutenberg University Mainz in a joint project with the working group of Dr. UTE KOLB at the Institute of Inorganic Chemistry and Analytical Chemistry [173].

87 5. Characterisation of synthesised products and methods

Powdered samples were ﬁnely ground in a mortar, added to an ethanol solution, and then highly dispersed by ultrasonic irradiation. Liquid droplets were sprayed onto a Cu micro-grid, dried, and subjected to SEM and STEM observations. ADT analysis was conducted on a JEOL (JEOL, Ltd., Tokyo, Japan) SEM microscope. A challenge is the plate-like morphology of the materials, as the beam continually tilts and unavoidably, the crystal particle moves out of the beam. Also, the location of an appropriate particle is a demanding task. Preliminary analysis and "ab initio" structure determination revealed orthorhombic lat- tices with B- and I-centring as listed in Table 5.3 for different Me-IEZ-RUB-36 materials. RUB-36 exhibits fer-type layers that are stacked, but not connected in a CDO-type fashion. The CDO framework is marked by a Cmcm SG which, for COE-3 material, in which linker positions are occupied by Si, is Bbmm, a stacking of AAAA. In contrast, the FER framework displays an Immm SG by stacking layers in ABAB fashion. Ti and Zn materials are examined exemplary for the two different SG conﬁgurations. Figure 5.16 displays a visualisation of individual slices of the reciprocal space to generate a diffraction pattern of the analysed Ti material. Along a∗ (5.16(a)), the diffraction pattern exhibits diffuse streaking. Similar to the DIFFaX simulation of PXRD diagrams, electron diffraction patterns may be generated.

Figure 5.17 exhibits a similar visualisation of the analysed Zn material in a projection along [001] 5.17(a) and along [010] 5.17(b), as well as assignment of reciprocal UC dimensions in projection along 5.17(c) a∗, 5.17(d) b∗ and 5.17(e) c∗.

Figure 5.18 shows the simulations of both pure stacking of CDO (B-lattice) and FER (I- lattice) as well as a combination of both. As none of these simulations picture the true

c* a* c* b* a* b*

(a) (b) (c)

Figure 5.16.: ADT graphical representation of reciprocal space of Ti-IEZ-RUB-36 with assignment of reciprocal UC dimensions in projection along (a) a∗, (b) b∗ and c∗ (c).

88 5.3. ADT

a* a*

b* c*

[001] [010]

(a) (b)

c* a* c* b* a* b*

Figure 5.17.: ADT graphical projection of reciprocal space of Zn-IEZ-RUB-36 in direction (a) [001] and (b)[010] and with assignment of reciprocal UC dimensions in projection along (c) a∗, (d) b∗ and (e) c∗.

stacking AAAA stacking ABAB [h00] [h00]

[00l] [00l] stacking mix random stacking [h00]

[00l]

Figure 5.18.: Three different stacking variations as compared to the recorded electron diffraction diagram.

situation, the percentages of each stacking type have to be adjusted.

Figure 5.19 displays the ﬁnal simulations to depict the framework situation closest to the real state for the two regarded materials. The stacking probability for the Ti material exhibits AAAA > ABAB & C < 10% (5.19(a)) and Zn material AAAA < ABAB & C < 10% (5.19(b)) with C representing every ﬁfth layer being connected via Me cations instead of Si.

89 5. Characterisation of synthesised products and methods

simulation record simulation record [h00] [h00]

[0k0] [0k0] [h00] [h00]

[00l] [00l] (a) Ti (b) Zn

Figure 5.19.: ADT simulation and record for (a) Ti and (b) Zn material.

✺✳✹✳ ■♥❞✉❝✐✈❡❧② ❝♦✉♣❧❡❞ ♣❧❛♠❛ ✭■❈✮✲❛♦♠✐❝ ❛❜♦♣✐♦♥ ♣❡❝♦❝♦♣② ✭❆❆❙✮

ICP and AAS are useful investigation methods to determine the chemical composition of an unknown zeolite sample. They are applied to verify the synthesis formulations, the bulk silica/alumina ratio (if applicable), the cation concentration, and the detection of contam- inant elements (impurities, poisons). Atoms can be grouped into two categories of metals and non-metals. To determine specific Me contents, ICP, AAS and XRF (see following Section 5.5) are the methods of choice. These techniques are marked by reduced interferences and matrix effects, improved accuracy, precision and speed. ICP is a common method for the determination of the elemental composition of zeolites as it exhibits good sensitivity and precision of most compositional matrix metals of interest, such as silicon, aluminium, phosphorous, titanium, and many others with relative standard deviations of around 1 %. Generally, the precision of ICP elemental analysis is better than conventional flame AAS for many refractory-like metals and phosphorus. On the other hand, AAS exhibits better sensitivity for Group IA elements, including sodium and potassium, and relatively similar sensitivity for many metals of interest, such as calcium, magnesium and iron. As both ICP and AAS measurements require sample input in liquid form, two methods are commonly applied for material preparation. The first method is a dissolution by a fusion with lithium tetraborate (or a similar flux) followed by digestion of the flux in dilute HCl, and the second method is a dissolution with acid in a beaker. The latter method poses a few disadvantages in contrast to the former. The danger of incomplete solubility may be

90 5.4. Inductively coupled plasma (ICP)-atomic absorption spectroscopy (AAS) overcome by higher temperature. However, HF produces volatile ﬂuorides, which in turn can lead to loss of silicon. Also, ﬂuoride may attack conventional ICP sample transport systems containing QUARTZ/glass components making a complexation necessary [174].

✺✳✹✳✶✳ ❇❛✐❝ ♣✐♥❝✐♣❧❡ ♦❢ ■❈✲❆❆❙

AAS analyses utilise the atomic absorption spectrum of a sample to analyse individual atomic concentrations. The use of standards is an essential cornerstone of both techniques to get insight to the relation between the measured absorbency and the analyte concentration by relying on the BEER-LAMBERT Law. A row of standard solutions containing rising concentrations of desired atoms are prepared in an expected range for the sample. Previously liquidised samples have to be atomised for the analysis. Atomisers come in the shape of flames or electrothermal atomisers (graphite tube). After atomisation, an element-specific line radiation source or a continuum radiation source optically irradiates the atoms. Generated radiation passes through a monochromator in order to separate the element-specific radiation from any other radiation emitted by the radiation source, where it is, then, measured by a detector [175]. ICP-AAS makes use of an emission via plasma incitement. ICP is, in contrast to the direct current plasma (DCP) methods, an alternating current plasma. Another method is the microwave induced plasma (MIP).

✺✳✹✳✷✳ ■❈✲❆❆❙ ❡①♣❡✐♠❡♥

ICP-AAS analyses were performed on a SHIMADZU ICPE-9000 spectrometer (SHIMADZU CORPORATION, Kyoto, Japan) and on a VARIAN AA 300 spectrometer (AGILENT TECHNOLO- GIES, Santa Clara, California, USA).

For the first solution, a mixture of H2O, HF and HNO3 is used. 1 ml of H2Odest is filled into a PET-bottle and exactly 10.0 mg of sample are added (Co = 10.3 mg; V = 10.0 mg; Zn = 10.0 mg). Five drops of HF are added to the mixture and put on a hot plate at 353 K. Since the mixture was not fully dissolved after one hour, the mixture was kept on the hot plate overnight and then cooled down in an ice bath. To each solution, 1 ml of HNO3 (60 wt%) is added and and put on a hot plate again. Still, the mixture was not dissolved after one hour and kept on a hot plate overnight once more. The solutions are filled to 100 ml and the ICP-AAS is conducted. Since the Co and V amount were out of range from the calibration curve in the Co- solution, the Si amount was too small compared to Zn in the V-solution, which hints to

91 5. Characterisation of synthesised products and methods an incompletely dissolved sample, and the Si amount was out of range from the calibration curve in the Zn-solution, new solution preparations have been necessary. For the second solution, again 10 mg of sample were placed in a 100 ml PET-bottle

(Co = 10.3 mg; V = 10.1 mg; Zn = 10.1 mg) together with water regia (1 ml of HNO3 and 3 ml of HCl). After 1 h, the solution was not dissolved and, therefore, left to dissolve for two whole days until dissolution was seemingly complete, at which point 5 drops of HF were added. As the Co-solution was still not fully dissolved, another 5 drops of HF were added.

Table 5.4 displays the results of the ICP-AAS on the SHIMADZU ICPE-9000 spectrometer.

Me content wt% material Si Co V Zn Co-029 39.90 0.069 - - V-025 42.18 - 0.0431 - Zn-080 44.26 - - 0.0940

Table 5.4.: Me content as determined by ICP-AAS analyses on SHIMADZU ICPE-9000 spectrometer.

The resulting trivial names and chemical denominations for each material can then be written as follows:

Co-IEZ-RUB-36 Si51.96Co0.04O88,

V-IEZ-RUB-36 Si51.97 V0.03O88 and

Zn-IEZ-RUB-36 Si51.96Zn0.04O88.

For the AAS analysis on the VARIAN AA 300 spectrometer, the sample is dissolved using sodium peroxide (Na2O2). 25 mg of sample and 400 mg Na2O2 are weighed into a zirconium crucible and melted over a sharp burner flame. The melt is taken up in water and, after cooling, mixed with 3 ml of nitric acid. Then the solution is transferred to a 50 ml flask and filled with distilled water. This solution is used for the AAS analysis.

Table 5.5 lists the results of the AAS analyses on three different samples. Both Co- and Zn-samples display a reasonable Me content for a successful post-synthesis treatment. The content of V material, however, is much too high to assume a noteworthy synthesis. A Ti sample was, again, not available at the time of experiment. The resulting trivial names and chemical denominations for each material can then be listed as follows:

92 5.5. X-ray ﬂuorescence (XRF) analysis

Me content wt% material Co V Zn Co-019 0.14 - - V-007 - 4.26 - Zn-043 - - 0.06

Table 5.5.: Me content as determined by AAS analyses on VARIAN AA 300 spectrometer.

Co-IEZ-RUB-36 Si51.93Co0.07O88,

V-IEZ-RUB-36 Si49.52 V2.48O88 and

Zn-IEZ-RUB-36 Si51.97Zn0.03O88.

✺✳✺✳ ❳✲❛② ✢✉♦❡❝❡♥❝❡ ✭❳❘❋✮ ❛♥❛❧②✐

As established in the previous paragraph, analysis by XRF is used alongside AAS and ICP- AAS for the determination of the elemental composition of zeolitic materials. In direct comparison to the other two techniques, the advantages of XRF are the option to determine certain non-metals, an easier sample preparation and improved precision with relative standard deviations of −0.1 % to 0.2 %. On the other hand, disadvantages include poor sensitivity for light elements and sensitivity to changes in the matrix composition. Conse- quently, a complete chemical characterisation is not feasible using XRF analysis (especially for elements such as lithium and sodium). To measure accurate data, the use of a calibration standard and the application of mathematical models may become necessary [174].

✺✳✺✳✶✳ ❇❛✐❝ ♣✐♥❝✐♣❧❡ ♦❢ ❳❘❋

The theory of XRF spectroscopy has been illustrated to some degree in Section 5.2.1. It makes use of the emission of characteristic X-rays from a sample that has been exposed to high-energy X-rays or gamma rays. Continuum and characteristic X-ray radiation is produced when incident radiation hits solid matter. Short-wavelength X-rays or gamma rays may ionise individual atoms within a sample material as long as the radiation possesses an energy greater than the necessary ionisation energy. The removal of inner shell electrons causes instability and higher shell electrons move down to occupy the vacated space left by the ejected electron. During this process, energy is released in the form of a photon. The energy of this photon is equal to the energy difference of the two orbitals and the sample material emits radiation in the form of characteristic X-rays. This type of absorption and emission is denoted as ﬂuorescence.

93 5. Characterisation of synthesised products and methods

The X-ray radiation emitted is characteristic for each atom orbital. As the electron is removed from the inner shell, only a limited number of possible electron transitions processes can occur. The transition from L to K shell is denoted as K α. This is also the radiation generally used by PXRD by the use of a metal anode. Transitions from M to K are marked as K β etc. PLANCK’S law (λ = hc/E) describes the characteristic energy equal to the difference in energy of both orbitals involved. Two methods are used to detect radiation: energy-dispersive analysis separates the energies of the photons, whereas wavelength-dispersive analysis distinguishes the wavelengths of the radiation. Both procedures lead to identiﬁcation of atomic contents in a sample material [164]. Sample preparation is achieved somewhat analogous to the instructions described in the previous section for AAS and ICP analysis. Again, two methods may be employed, one of which is concluded by a hot melt dissolution and subsequent pouring into a platinum mould to form a glass disc. Again, lithium tetraborate is the ﬂux of choice for this process. Whereas a number of calibration techniques exist, direct addition of elements of interest to the crucible prior to the fusion is a valid modus operandi. The second technique includes the pressing of pulverised samples into pellets. A disadvantage of this method is less precision and more sensitivity to changes in the matrix composition. On the other hand, volatile non-metals such as halogens and sulfur, prone to evaporate during fusion, remain in the pellet to contribute to the measured data. In some cases, even non-pressed powders may be analysed [174].

✺✳✺✳✷✳ ❳❘❋ ❡①♣❡✐♠❡♥

XRF analyses were performed on a hand-held BRUKER S1 TITAN (BRUKER CORPORATION, Billerica, Massachusetts, USA), factory calibrated based on ordered configurations. This device is generally used as a portable field analyser depending on energy dispersive X- ray fluorescence (EDXRF) technology and adopts an X-ray tube as its excitation source to measure elemental concentrations of a sample.

Samples have been pressed to small pellets with a few drops of H2Odest to facilitate the measurement with the hand-held instrument. Nonetheless, this method did not work for Ti and V samples. Also, the procedure may have a negative impact on the quality of the measurement due to its sensitivity to matrix composition changes. Still, the additional information serves its purpose as complementary method to AAS and ICP-AAS measurements. The resulting trivial names and chemical denominations for each material can then be denoted as follows:

94 5.6. Ammonia (NH3)-temperature programmed desorption (TPD)

Me content wt% material Co V Co-030 0.1 - V-030 - 0.06

Table 5.6.: Me content as determined by XRF analyses.

Co-IEZ-RUB-36 Si51.95Co0.05O88 and

V-IEZ-RUB-36 Si51.96 V0.04O88.

As the instrument used is somewhat unorthodox for this type of analysis, and is more or less a "quick-and-dirty" kind of approach, the data should not be taken into account without complementary data from other elemental analysis techniques or a conventional XRF spectrometer. However, the measured contents for the Co and V samples are in very good agreement with the data uncovered by EDX, AAS and ICP-AAS experiments and present, therefore, a useful addition to complete the picture of the overall chemical composition of the analysed materials.

✺✳✻✳ ❆♠♠♦♥✐❛ ✭◆❍✸✮✲❡♠♣❡❛✉❡ ♣♦❣❛♠♠❡❞ ❞❡♦♣✐♦♥ ✭❚❉✮

Ammonia (NH3)-temperature programmed desorption (TPD) measurements serve the purpose of identifying total acidity and strength of acid sites in microporous catalysts. It is among the most widely used and ﬂexible techniques for characterising the acid sites on oxide surfaces due to the simplicity of the technique. Characterisation of the quantity and strength of the acid sites is a crucial process to understanding and predicting the performance of a catalyst. A good example material for comparison of the acidic properties is ZSM-5, in which reaction rates increase linearly with Al content (acid sites). This applies to many commercial signiﬁcant processes like n-hexane cracking and MTO reactions. Al- though catalytic activity depends on many factors, BRØNSTED-acid site density is one of the most important parameters. A variety of molecular probes can be used to characterise acid sites using the TPD method. The three categories commonly employed include NH3, non-reactive vapours and reactive vapours. A disadvantage of NH3 as a molecular probe is an overestimation of the quantity of acid sites due to its small molecular size. It allows the penetration into all pores of the solid. For catalysts used in cracking and hydrocracking reactions, this presents

95 5. Characterisation of synthesised products and methods a problem, as these larger molecules only have access to large micropores and mesopores.

Additionally, NH3 is a very basic molecule, capable of titrating weak acid sites which may not contribute to the activity of catalysts. Its strongly polar character is also able to adsorb additional NH3 from the gas phase [176].

✺✳✻✳✶✳ ❇❛✐❝ ♣✐♥❝✐♣❧❡ ♦❢ ◆❍✸✲❚❉

To determine the strength of a surface bond, thermal and other temperature-programmed methods may be applied. The surface bond strength directly correlates with the temperature, at which species are desorbed from the surface of a heated solid - the higher the temperature, the stronger the bond. Therefore, temperature-programmed methods are very widely applied in deﬁning the surface of catalysts and adsorbents. To establish an estimate of the heat of adsorption of a certain species, the temperature coefﬁcient of the rate of desorption from the surface is determined (Equation (5.12)). Re- garding equation

Ed = −∆H + Ea, (5.12)

the activation energy of adsorption Ea is zero and the activation energy of desorption

Ed equals the heat of adsorption −∆H. During an active adsorption process, Ed sets an upper limit to the heat of adsorption. Here, it is of no importance if the experiment deals with the release of small molecules such as CO, H2 and O2 from metal surfaces, or larger compounds like alkenes, alkanes and other products from oxide catalysts, the participating concepts are the same [177].

Sample preparation includes a degassing in helium ﬂux at high temperatures (773 K) to remove strongly bound species and to activate the sample. After this preparation, the sample is saturated at 373 K to 393 K to minimise physisorption of the NH3 or organic amines.

For the NH3-TPD, NH3 may be introduced continuously or in a pulsed loop. The pulsing of NH3 allows for a comparison of the quantity of NH3 adsorbed (via pulse adsorption) to the quantity desorbed for the subsequent TPD. If organic amines are used instead of NH3, a vapour generator becomes necessary. The actual TPD procedure is conducted by ramping the sample temperature at 10 Kmin−1 to temperatures of 773 K to 873 K. A thermal conductivity detector (TCD) monitors the concentration of the desorbed ammonia or the non-reactive probes. In the case of reactive probes (propyl amines), a mass spectrometer is required to quantify the density of acid sites. For these types of probes,

96 5.6. Ammonia (NH3)-temperature programmed desorption (TPD)

several species such as amines, propylene and NH3 may be desorbing simultaneously. The resulting profiles are generated by raising the sample temperature according to a specific heating rate which has some influence on the shape of the profiles. In general, two types of acid sites can be identified [176].

✺✳✻✳✷✳ ◆❍✸✲❚❉ ❡①♣❡✐♠❡♥

Ammonia (NH3)-temperature programmed desorption (TPD) measurements have been conducted in a joint project at the Tokyo Institute of Technology, Yokohama 226-8503, Japan with the working group of TOSHIYUKI YOKOI and the help of SUNGSIK PARK at the Catalytic Chemistry Division, Chemical Resources Laboratory.

step gas ﬂow rate time target temperature fan scm3 min−1 min K 1 He 50 50 773 no 2 He 50 60 773 no 3 He 50 1 373 yes 4 He 50 10 373 no 5 NH3/He 50 30 373 no 6 He 50 15 373 no

Table 5.7.: Sample preparation for NH3-TPD experiments.

Sample preparation includes six individual steps as listed in Table 5.7. Degassing is conducted at elevated temperature in flowing helium to remove water vapour and to avoid pore damage from steaming which may alter the structure of microporous catalysts. For the NH3-TPD experiments, approximately 20 mg of calcined sample are necessary. There- fore, part of the samples were calcined in an ADVANTEC FUW220PA Electric Muffle Furnace (ADVANTEC TOYO KAISHA, Ltd., Tokyo, Japan) for five hours at 723 K using a heating ramp of 1 Kmin−1.

NH3-TPD was conducted using BELCAT-B(MICROTRACBELCORPORATION, Osaka, Japan) with a TCD to estimate sample acidity. During NH3-TPD, prepared samples were treated with a heating ramp of 10 Kmin−1 to a temperature of 873 K. The number of acid sites was determined from the area of h-peak in their proﬁles [178]. The results were compared to a standard sample of 1 mmol ZSM-5.

Figure 5.20(a) shows the results of the NH3-TPD for Co-, V- and Zn-RUB-36-calc samples.

97 5. Characterisation of synthesised products and methods

The ZSM-5 standard material exhibits two distinct signals at around 473 K (1) and 673 K (2) and is displayed in Figure 5.20(b). The higher temperature signal (2) is the interesting signal for the calculation of the amount of acidic sites. By calculating the peak area, the amount of acidic sites is ∼ 1 mmolg−1 for ZSM-5. In contrast, all three measured materials display very low amounts of acidic sites. V-RUB-36 exhibits 0.002 mmolg−1, whereas Zn- RUB-36 displays 0.009 mmolg−1. A special case was found for the Co-material, where three signals are identiﬁed, two of which can be considered as higher temperature signals. These signals are labelled as (2), high temperature weak signal with 0.028 mmolg−1 and (3), high temperature strong signal with 0.013 mmolg−1. For the application as a catalyst, this result is quite unfortunate, as it implies no, or very limited aptitude for catalytic application. For a more complete analysis, a carbon monoxide (CO)-TPD should be conducted as the NH3 molecule might simply be too bulky to penetrate the micropores of the regarded samples.

The inadequate amount of acid sites measured by NH3-TPD might, hence, not signify a deﬁcient catalytic activity, but merely the incapacity of accommodating larger molecules in the pore space of the material. Ti material has not been tested as no appropriate sample was available at the time of experiment.

160 5000 1 Co-RUB-36 1 140 ZSM-5 2 120 4000

molecules 2 100 -molecules 3 3 3000 80 2000 60 1 Zn-RUB-36 40 1 1000 3 20 2 2

Amount of NH Amount 0

Amount of NH Amount 0 V-RUB-36 323 423 523 623 723 323 423 523 623 723 Temperature / K Temperature / K (a) Me-RUB-36-calc (b) ZSM-5

Figure 5.20.: NH3-TPD of (a) sample materials Co-029-calc, V-025-calc and Zn-080-calc and (b) commercial ZSM-5.

98 5.7. Nitrogen gas (N2) adsorption

✺✳✼✳ ◆✐♦❣❡♥ ❣❛ ✭◆✷✮ ❛❞♦♣✐♦♥

Interior and exterior surfaces of catalyst particles may be analysed by physisorption of inert non-polar gases such as nitrogen, krypton or argon. These gases adhere to surfaces of microporous materials by physical forces. Due to the weakness of the interactions between adsorbate and substrate for such gases, removal is easy.

N2 adsorption and desorption by the BET and t-plot method serve the purpose of identifying microporous surface area, pore volume, pore size distribution and active sites in microporous materials.

✺✳✼✳✶✳ ❇❛✐❝ ♣✐♥❝✐♣❧❡ ♦❢ ◆✷ ❛❞♦♣✐♦♥

The adsorption properties are an characteristic feature for porous materials. The distinction between the terms of adsorption and absorption should be followed. Whereas adsorption is considered as the condensation of gas on a free surface, absorption describes gas entry into the bulk of the material. The uptake of a gas by porous materials is often referred to as adsorption or simply sorption, regardless of the physical mechanism involved. Quan- titatively, the gas adsorption by a porous material is described by the adsorption isotherm, which is marked by the amount of gas adsorbed by the material at a fixed temperature as a function of pressure. For a microporous material, characterisation occurs in terms of pore sizes derived from gas sorption data. The International Union of Pure and Applied Chemistry (IUPAC) has issued some conventions regarding the classification of pore sizes and gas sorption isotherms that reflect the relationship between porosity and sorption [179, 180]. For the determination of adsorption isotherms of nitrogen at the temperature of liquid nitrogen (77 K), gas adsorption manometry is utilised. Originally, gas volumes were measured before and after adsorption, hence the denotation of "volumetric determination" or "BET volumetric method". Today, the change of gas pressure is detected, rather than a change in gas volume. The determination of the adsorption isotherm is achieved either in a continuous or, more commonly, a discontinuous point-by-point procedure. The latter technique makes use of a successive introduction of adsorptive gases until equilibrium is reached causing single points in the adsorption isotherm. In the case of continuous introduction, the adsorptive must be infused slow enough to provide a continuous "equilibrium" isotherm, thus, leading to an infinite number of data points [181].

In the BET measurement, the N2 molecules condense, filling the micropore volume. This filled volume is the BET area of a microporous material and, at the same time, the equivalent area that would be coated by the quantity of sorbate required to fill the intra-crystalline

99 5. Characterisation of synthesised products and methods pores if the molecules were arranged as a close packed monolayer. As it corresponds only to a monolayer, the internal area of the framework is a different characteristic. Structural defects may be cause for the generation of mesopores (20 Å to 50 Å) in addition to desired micropores ( < 15 Å). This is observable by a positive slope of the isotherm instead of the almost horizontal saturation plateau characteristic of an ideal microporous structure. Capacity measurements are used to determine speciﬁc micropore volume and to establish the prevailing pore dimensions [182].

The BET equation ((5.13)) is solved regarding the monolayer capacity Wm

1 1 C − 1 P = + ( ), (5.13a) W ((P0/P) − 1) WmC WmC P0 NAWmσ S = , (5.13b) M

where Wm is the mass of gas adsorbed as monolayer at a relative pressure, P/P0, while

P0 is the saturated vapour pressure, C is the BET constant, NA is the AVOGADRO number, M is the molecular weight of adsorbate, σ is the cross sectional area of the adsorbate and S is the total surface area. The linear relationship of the adsorption isotherm is interpreted in the range of

0.05 < P/P0 < 0.35 and from the slope and intercept, whereas Wm and C as well as the surface area (S) are calculated.

To measure the total volume of the pores (at P/P0 = 0.99), the pore volume ﬁlling method is used, while pore size distribution is measured by BARRET-JOYNER-HALENDA (BJH) desorption isotherm [183].

The IUPAC has classified six types of isotherms as characteristic for adsorbents: microporous (type I), nonporous or macroporous (types II, III, and VI), or mesoporous (types IV and V). Figure 5.21(a) exhibits the IUPAC classification of adsorption isotherms. Type IV and V are marked by an adsorption hysteresis, whose form is correlated to the texture (e.g., pore size distribution, pore geometry, and connectivity). They are depicted in more detail in Figure 5.21(b) with type H1 ascribed to porous materials consisting of well-defined cylindrical-like pore channels or agglomerates of approximately uniform spheres, type H2 associated to materials that are often disordered where the distribution of pore size and shape is not well defined and also indicative of bottleneck constrictions, type H3 hysteresis exhibiting slit-shaped pores (the isotherms revealing type H3 do not show any limiting ad-

100 5.7. Nitrogen gas (N2) adsorption

H1 H2

H3 H4 V VI Amount adsorbed relative pressure (a) adsorption isotherms (b) hysteresis loops

Figure 5.21.: IUPAC classiﬁcation of adsorption isotherms (a) and empirical classiﬁcation of hysteresis loops (b) [179, 180].

300 300 adsorption adsorption desorption desorption 200 200

100 100 Va / cm3(STP) g-1 Va / cm3(STP) g-1

0 0 0 0.5 1 0 0.5 1 p / p0 p / p0 (a) Zn-080 (b) Zn-080-calc

Figure 5.22.: N2 sorption experiments on sample materials (a) Zn-080 and (b) Zn-080-calc conducted on the MICROTRACBEL-CORP BELSORP-mini II.

sorption at high P/P0, which is observed with non-rigid aggregates of plate-like particles) and type H4 hysteresis also often being linked to materials with narrow slit pores [179, 180].

✺✳✼✳✷✳ ◆✷ ❛❞♦♣✐♦♥ ❡①♣❡✐♠❡♥

Nitrogen gas (N2) sorption experiments have been conducted in a joint project at the Tokyo Institute of Technology, Yokohama 226-8503, Japan with the working group of TOSHIYUKI YOKOI and the help of SUNGSIK PARK at the Catalytic Chemistry Division in the Chemi- cal Resources Laboratory on a MICROTRACBEL-CORP BELSORP-mini II (MICROTRACBEL

101 5. Characterisation of synthesised products and methods

40 35 adsorption 30 desorption 25 20 15 10 Va / cm3(STP) g-1 5 0 0 0.5 1 p / p0

Figure 5.23.: N2 sorption experiments on sample material Zn-080-calc conducted on the MICROMERITICS ASAP 2420.

CORPORATION, Osaka, Japan).

Further N2 sorption experiments were carried out on a MICROMERITICS ASAP 2420 (MICROMERITICS INSTRUMENT CORPORATION, Norcross, Georgia, USA) accelerated surface area and porosimetry system at the Ruhr-University Bochum at the Chair of technical Chemistry. Prior to the start of the measurements, the sample was kept in vacuo (i.e., degas) at 473 K for 4 h. Nitrogen adsorption/desorption experiments were performed at 77 K. Values for pore volume and surface area were calculated from the N2 isotherms as well, using the t- plot and BET methods, respectively.

Figure 5.22 shows the N2 experiments on Zn material for the as-made (5.22(a)) and calcined (5.22(b)) sample Zn-080. The isotherms of the material exhibit a shape of type II as described by IUPAC in Figure 5.21(a). Therefore, the material displays no presence of mesopores and, presumably, no micropores either. The sample does not, or only to some very small degree, possess available pore space with a BET surface area of approximately 41 m2 g−1 and a pore volume of 0.278 cm3 g−1 for the as-made and, approximately 55 m2 g−1 and a pore volume of 0.304 cm3 g−1 for the calcined sample. For comparison, the as-made IEZ COE-3 is already microporous with a BET surface area of approximately 238 m2 g−1 at a micropore free volume of 0.063 cm3 g−1. These values improve after calcination and substitution of the methyl groups by hydroxyl groups at the bridging silicate unit to form COE- 4, to 350 m2 g−1, indicating accessible free volume between the expanded fer-type silicate layers (micropore free volume: 0.131 cm3 g−1)[9].

As this result was quite unexpected, the measurement of the calcined sample has been

102 5.7. Nitrogen gas (N2) adsorption

140 160

120 140 120 100 100 80 80 60 60 40 40 Va / cm3(STP) g-1 adsorption Va / cm3(STP) g-1 adsorption 20 20 desorption desorption 0 0 0 0.5 1 0 0.5 1 p / p0 p / p0 (a) Co-029-calc (b) Ti-001

120 140 100 120 80 100

60 80

40 60 adsorption Va /Va cm3(STP) g-1 20 40

desorption Va / cm3(STP) g-1 adsorption 0 20 0 0.5 1 desorption 0 p / p0 0 0.5 1 p / p0 (c) V-025-calc (d) Zn-085

Figure 5.24.: N2 sorption experiments on sample materials (a) Co-029-calc, (b) Ti-001, (c) V-025-calc and (d) Zn-085 conducted on the MICROMERITICS ASAP 2420. repeated on the porosimetry system that was also utilised for the remaining samples. Fig- ure 5.23 displays the results of these renewed measurements. However, the outcome remains similarly unfavourable with a BET surface area of approximately 20 m2 g−1 and a pore volume of 0.052 cm3 g−1. On the other hand, the remaining measured samples, as depicted in Figure 5.24, exhibit a different behaviour. They show isotherms of type IV and, therefore, of mesoporosity. How- ever, all four materials display hysteresis behaviour of type H2, an association to disordered materials with pore size and shape not well deﬁned. Table 5.8 lists the corresponding surface areas as calculated from BET method and pore

103 5. Characterisation of synthesised products and methods sizes. The microporous surface area for the four materials in contrast to the first Zn material is quite reasonable for a catalyst material. With the exception of Zn-080, all four materials exceed the volume of starting material RUB-36 by a factor of approximately 10. Ti material exhibits the biggest volume, followed by Zn and Co material. V material, on the other hand, does stay behind the pure calcination product RUB-37. Even though the pore volume for the first measurement of Zn-080 seems quite large, the renewed measurement shows a very low pore volume. Indeed, expected is a value closer to that of the literature value of RUB- 36 [22] judging by surface area. It is sensible to assume that some kind of error falsified the previous data. In all likelihood, the same applies to the value for the average pore diameter. For the other materials, the average pore diameter distribution follows the same order as the surface area. Compared to the literature values of the Ti materials [184], the pore diameters seem, with a multiplication factor of 4, quite large. In direct comparison with commercial catalyst TS-1, all considered materials exhibit sensible values for surface area, pore volume and average pore diameter. Regarding this information, each sample shows promising pore properties for catalytic activity and indicates accessible free volume between the expanded fer-type silicate layers.

microporous pore average sample surface area volume pore diameter m2 g−1 cm3 g−1 nm Zn-080 55 0.278 27.48 Zn-080-calc 41 0.304 21.95 Zn-080-calc-new 20 0.052 10.59 Zn-085 307 0.182 2.37 Co-029-calc 279 0.186 2.67 V-025-calc 208 0.172 3.31 Ti-001 391 0.224 2.28 RUB-36a 34 < 0.01 RUB-37a 231 0.090 Al-COE-4a 364 0.135 COE-4/Fea 423 0.156 Al-COE-4/Fea 389 0.136 TS-1b 285 0.130 0.53 Ti-COE-3b 189 0.090 0.54 Ti-COE-4b 294 0.140 0.55

Table 5.8.: Results from N2 sorption experiments, calculated surface area and pore volumes and comparison to similar materials as published by DE BAERDEMAEKER et al. [22]a and XIAO et al. [184]b.

104 5.8. Thermal analyses (TA)

✺✳✽✳ ❚❤❡♠❛❧ ❛♥❛❧②❡ ✭❚❆✮

Calorimetric methods are employed to determine the behaviour and stability of crystalline material regarding thermal activation. They serve as a straightforward means to identify phase transitions, expansion, determination of the content of hydroxyl groups and loss of water, organic molecules as well as other volatile components within the structure. A wide range of different calorimetric methods exists. Here, polycrystalline powdered samples are provided, hence, the methods of choice are the thermal gravimetry (TG), or thermal gravimetry analysis (TGA), and differential thermal analysis (DTA). These procedures protocol deviations in the sample during a change in temperature [185–187].

✺✳✽✳✶✳ ❇❛✐❝ ♣✐♥❝✐♣❧❡ ♦❢ ❚❆

Thermal gravimetry (TG) is a method that employs a constant heating rate to a powdered polycrystalline material with or without a constant stream of different gases such as oxygen or air. The weight of the sample is measured before and then monitored constantly during the experiment. In contrast to that, the DTA records the temperature difference (in the form of a voltage difference µV) between the sample and a chemically inert reference material, usually Al2O3 or platinum. While the differential scanning calorimetry (DSC) conducts quantitative energy measurements, the DTA analysers do not convert the temperature signal to the heat ﬂux equivalent. However, for the execution of DSC, single crystal material is usually preferred [186]. The interpretation of DTA and TG curves is quite elementary. In a typical TG curve for as-made microporous materials, successive steps in mass deviations can be observed by individual terraces during constant heating. There is a number of processes which induce changes in sample mass. Reactions such as decomposition, dehydration or oxidation may occur. Using different atmospheric conditions, the reaction may be regulated to a certain extent. The sample may not only loose components but also react with the atmosphere, thus, gaining weight. During the DTA experiment, temperature induced exothermic or endothermic events in form of positive or negative amplitudes occur. These reactions elapse in a very short time frame with a high heat difference of at least 0.01 cal. Endothermic reactions are implicated by a temperature decrease of the sample compared to the reference material, whereas exothermic reactions are displayed through a temperature increase of the sample. Example reactions include crystallisation, evaporation, decomposition, melting, oxidation and phase transitions.

105 5. Characterisation of synthesised products and methods

✺✳✽✳✷✳ ❚❆ ❡①♣❡✐♠❡♥

20 0 10 0 TG DTA TG DTA 15 -0.2 -0.1 5 10 -0.4 -0.2 5 0 -0.6 -0.3 ow / µV ow 0 / µV ow ﬂ ﬂ -5 -0.8 -5 -0.4 weight / mg weight weight / mg weight heat heat -10 -10 -1 -0.5

-15 -1.2 -15 -0.6 273 373 473 573 673 773 873 973 1073 273 373 473 573 673 773 873 973 1073 temperature / °C temperature / °C (a) Co-029 (b) V-025

0 0 25 0.2 TG DTA 20 0 -2 -0.5 15 -0.2 -4 -1 10 -0.4

-6 5 -0.6 -1.5 ow / µV ow -8 / µV ow 0 -0.8 ﬂ ﬂ -2 -5 -1 -10 weight / mg weight weight / mg weight heat heat -10 -1.2 -12 -2.5 -15 -1.4

-14 -3 -20 -1.6 273 323 373 423 473 523 573 753 673 752 773 273 373 473 573 673 773 873 973 1073 temperature / °C temperature / °C (c) Zn-080 (d) RUB-36

Figure 5.25.: DTA and TG analyses of sample materials (a) Co-029, (b) V-025, (c) Zn-080 and (d) RUB-36.

To test for thermal properties (water content, thermal stability, occurrence of phase transitions) of the samples, DTA and TG measurements have been conducted on a RIGAKU (RIGAKU CORPORATION, Tokyo, Japan) Thermo plus TG8120 in a temperature range of 298 K to 1073 K. Samples were placed in platinum sample holders using a platinum reference. TG and DTA experiments have been performed on 7.0 mg of the Zn-080 sample with a heating ramp of 1 Kmin−1 to 723 K, which was held for ﬁve hours. The small heating rates have been applied to ensure high resolution of the reactions. 6.7 mg of Co-029, and 6.6 mg of V-025 samples were calcined applying the same heating rate, but at a temperature of 1073 K, also held for ﬁve hours. 7.2 mg of RUB-36 starting material have been analysed with a heating ramp of 10 Kmin−1 to 1073 K. Figure 5.25 displays the results of TA on 5.25(a) Co, 5.25(b) V, 5.25(c) Zn and 5.25(d) RUB- 36 samples. On the abscissa, the temperature of the sample is delineated in K. The left

106 5.8. Thermal analyses (TA) ordinate (green) shows the voltage difference between sample and reference in µV and the DTA curve. The right abscissa (blue) indicates the weight loss of the sample during thermal analysis in mg and the TG curve. Since no reaction occurs on the cooling path, it is not displayed. For the RUB-36 experiment, a weight loss and endothermic signal is expected for the thermal degradation of the DEDMA cation and the expulsion of the degradation products, and an exothermic signal for the condensation reaction to three-dimensionally connected RUB-37 (CDO type framework). The measured data mirrors these expectations very well. In the beginning of the TG curve, minor weight loss of around 1 % at a temperature of up to approximately 383 K can be observed in conjunction with a small endothermic signal in the DTA curve. This early loss in mass can be attributed to the evaporation of water physically adsorbed on the sample. The most drastic reaction has its peak both for TG and DTA at ∼673 K, at which the DEDMA molecule decomposes, partial desorption of organic material occurs and silanol condensation reactions begin. The peak temperature and the exothermic character of the signal are distinctive for the decomposition of organic material. The complete mass loss accounts for 18.1 %. The beginning of the reaction is marked at a temperature of around 553 K, whereas the maximum is identiﬁed at ca. 677 K. The reaction is exothermic due to the fact that a heat excess occurs. Since the reaction is not repeated during the cooling phase, reversible phase transitions may be excluded. However, the organic template as well as silanol groups terminating individual layers evaporate or decompose at the given temperature. Following the quick descent of the TG curve, expulsion of organic remains occurs slower due to the smaller pore openings now created by the condensed framework silicate, impeding the process [58]. The original sample weight accounted for 7.2 mg. With a mass loss of 1.3 mg resulting in 5.9 mg, the weight loss adds up to 18.1 % of the initial mass. Between 573 K to 1073 K, the weight loss constitutes 16.0 %. With regards to the framework structure of

[(CH3)2(C2H5)2N]4(OH)4Si36O72, the expulsion of the DEDMA cation should amount to a mass loss of 15.5 %. Additional weight loss can be accounted for in the form of water generated by the condensation of silanol groups terminating individual layers (4 water molecules per UC). Also, some water has been found in the RIETVELD reﬁnement after PXRD. Table 5.9 displays the initial weight in mg and weight loss both in mg and %. Whereas the weight loss of RUB-36 is in the expected range, the weight loss of the Me-IEZ-RUB-36 materials drift apart in an extreme way. As RUB-36 is post-treated in the as-made state without preliminary calcination or removal of the DEDMA cation, it is sensible to assume that residual organic species still reside inside the channels of the Me-IEZ-materials. How- ever, the amount of weight loss for each material should not exceed the weight loss that was

107 5. Characterisation of synthesised products and methods

material initial weight weight loss mg mg % Co-029 6.7 1.06 15.77 V-025 6.6 0.57 8.63 Zn-080 7.0 3.05 43.63 RUB-36 7.2 1.33 18.54

Table 5.9.: Initial weight and weight loss for Me-IEZ-RUB-36 and RUB-36 during TG/DTA experiments. recorded for RUB-36 this drastically. For Co and V material, this claim is viable, whereas, for Zn material, the weight loss accounts for almost half the product even though calcination temperature was a little above half of that of the other materials. This hints to larger problem during the condensation of the Zn framework and the probable evocation of strong layer disorder. Also, none of the samples exhibit a DTA signal indicative of DEDMA removal and layer condensation as expressive as RUB-36, where weight loss does not occur due to decomposition, but only due to desorption.

✺✳✾✳ ◆✉❝❧❡❛ ♠❛❣♥❡✐❝ ❡♦♥❛♥❝❡ ✭◆▼❘✮ ♣❡❝♦❝♦♣②

In contrast to diffraction experiments which probe the long-range order and periodicity, solid-state NMR spectroscopy examines short range order of crystalline matter. Thus, it presents a very useful and complementary technique to PXRD experiments. In particular, the recording of 29Si NMR spectra is utilised as a cornerstone in the structure determination, as it allows for an investigation of the connectivity of [SiO4]-tetrahedra and a calculation of the Q3:Q4 ratio of Si-atoms. Additional information can be gathered by 1H NMR, as it supports an analysis on the presence of water molecules, organic cations and silanol groups. Particularly HLSs exhibit signals shifted to lower ﬁeld (in the range of 10 ppm to 18 ppm) in 1H MAS NMR spectra indicative of strong hydrogen bonds between neighbouring silanol-siloxy groups. Further studies are conducted via 13C NMR spectroscopy which gives insight to the organic species occluded in the interlayer space of the HLSs. It serves as a measure for the incorporation or expulsion of the organic SDA and/or other organic species during synthesis and post-synthesis treatment [5].

108 5.9. Nuclear magnetic resonance (NMR) spectroscopy

✺✳✾✳✶✳ ❇❛✐❝ ♣✐♥❝✐♣❧❡ ♦❢ ◆▼❘ ♣❡❝♦❝♦♣②

Nuclear magnetic resonance (NMR) spectroscopy is a useful tool to investigate short range inter-atomic relations within the crystal structure of a solid or liquid. The short-range coverage of NMR experiments generally reaches to the second coordination sphere of an excited atom in a molecule in a liquid or an atom in a crystal structure. The method exploits the property of certain atomic nuclei to exhibit a nuclear magnetic moment. A nucleus displays a magnetic moment in the case of an odd number of protons and/or an odd number of neutrons and, hence, may function as a local probe. Correspondingly, an even number of protons and an even number of neutrons causes the atomic nucleus not to show NMR active properties. For the analysis with NMR spectroscopy, it is also important to keep in mind the paramagnetic character of specific nuclei. The analysis of paramagnetic atoms is a challenge, since the magnetic moments of the electrons disturb the magnetic field during measurement [188, 189]. Every atomic nucleus exhibiting a nuclear spin of I 6= 0 also has a magnetic moment µ which may be described as µ = γħI, where γ is the gyromagnetic ratio, and ħ the reduced PLANCK’S constant h/2π in relation to the angular frequency. The gyromagnetic ratio γ is dependent on the nuclear spin I. The higher the ratio, the higher the magnetic moment µ. A high magnetic moment connotes high distances between energy levels and, therefore, high energy transitions which are easier to detect than small transitions. An additional factor for a good quality spectrum is the natural abundance of the isotope. 1H exhibits an abundance of nearly 100 %, whereas the natural abundance of the 13C nucleus is only about 1 % and, consequently, very scarcely occurs within molecules and crystals. The same applies to the 29Si nucleus with about 4 % natural abundance. On top of that, both of these nuclei exhibit a rather small gyromagnetic ratio. In the case of 1H NMR, the low abundance of deuterium (D) is exploited for the analysis of special positions by synthesising complex molecules with deuterated water. However, alternative measuring methods are available to ensure the feasibility of the measurement of nuclei with low abundance or gyromagnetic ratio [190, 191]. The underlying physical process employed by NMR spectroscopy is the application of an external magnetic field B0 to the sample which causes an interaction with the magnetic moment of the considered nucleus in the sample. The measurement of 29Si NMR spectra is one of the most insightful techniques for the analysis of microporous silicate materials. It is a direct indicator for the crystallinity of the siliceous framework of the zeolite, its defects and the connectivity of the Si atoms. Local conditions for the tetrahedrally coordinated Si atoms are displayed in detail during NMR

109 5. Characterisation of synthesised products and methods

Si Si 4 O- O- O- O O Q - O SiO- - O SiO SiSiO SiO SiSi SiO O SiSi SiO O Si O- O- O- O- O Si

Q0 Q1 Q2 Q3 Q4

Q0 Q1 Q1 (

Figure 5.26.: (a) Q-notation of purely siliceous materials and chemical shift of the different Si connectivities [190]; (b) exemplary DMFit modelling of Zn-085, solid blue: measured spectra, dotted red: simulated spectrum [192]. spectroscopy in the chemical shift δ. The chemical shift is determined by the number of Si–O–T bridges formed by the considered central Si which also represents the degree of polymerisation of the [SiO4] groups. The analysis enables the identification of the occupation of the tetrahedral (Td) position of the second coordination sphere (in particular with regard to Al). Using the Q-notation, the different silicon environments within a siliceous framework can easily be identified and described [190, 191]. Figure 5.26(a) displays the Q-notation and the identification of different Q-species in an NMR spectrum. The central Si atom is surrounded by either none, one, two, three or, ideally, four other Si atoms via oxygen bridges. The resulting Q-notation is equivalent to the connectivity of the Si atom, each identifiable by its characteristic chemical shift. With increasing coordination, or n in Qn, the chemical shift moves to more negative values (high field). Since individual types of coordination spheres are distinguished by steps of approximately 10 ppm, it is routinely simple to identify different Si connectivities. For purely siliceous HLSs, such as RUB-36, two types of Q-coordinated Si connectivities 4 are expected, Q for intra-layer Si positions of the type Si( – O – Si)4 (chemical shift of ca. 3 −105 ppm to −116 ppm) and Q for terminating positions of the type Si( – O – Si)3( – OH) or – Si( – O – Si)3(–O ) (the corresponding signal has a chemical shift in the range of approximately −96 ppm to −105 ppm). Condensation products with framework codes FER (ZSM- 35) and CDO (RUB-37) should exhibit a fully four-connected framework and, thus, only Q4 Si, assuming a purely siliceous chemical composition and no presence of defects. In IEZ and condensed materials, such as COE-3 and COE-4, Q2 connectivities are observed on layer bridging positions. Very well resolved spectra may even display symmetrically inde-

110 5.9. Nuclear magnetic resonance (NMR) spectroscopy pendent Si-sites leading to information on the SG symmetry of the structure, the presence of defects and, based on the FWHM of the signals, the degree of structural order [5, 190, 191]. The introduction of Al into the framework has an impact of approximately 5 ppm to less negative chemical shift values. This is cause for some significant peak overlap and results in a more difficult interpretation in Si/Al materials. The introduction of Me cations during interlayer expansion and condensation replaces some Si on bridging positions. This has, in a similar manner as Al, influence on the chemical shift of the 29Si NMR signals and causes peak overlap. The location of the signal intensity for the fully four-connected Si on the Me linker site, therefore, is shifted towards the Q3 chemical shift. Another problem is the fact that 29Si and 1H nuclei interact during the NMR measurements which can cause a signal broadening. This can be prevented by eliminating the heteronuclear dipole interaction between both nuclei in the form of high power proton decoupling (HP DEC) in conjunction with magic angle spinning (MAS). Magic angle spinning (MAS) is conducted by spinning the sample holder around the magic angle of ϑ = 54°44′ at a frequency of several kHz to temporally average the dipole interaction, and the first order anisotropic parts of the spectrum - the chemical shift anisotropy (CSA). This process effectively eases the interpretation of the spectrum and decreases the line width. Physically, the magic angle represents the angle between static external magnetic field B0 and orientation of the sample rotor. Since crystal grains within the sample adopt every possible orientation, they are temporally centred such that their local z-axes align with the external magnetic field B0. Due to the tem- poral centring, the anisotropic parts of the x-y plane are removed from the spectrum and become visible during rotation in the form of equidistant spinning sidebands representing the rotational frequency. These sidebands are caused by the CSA and disappear outside of the measuring range if the sample is rotated fast enough. For a full elimination, the rotation frequency has to exceed the CSA. The isotropic chemical shift, on the other hand, will always remain at the same position since it is independent of time and angle. The NMR diagram features an abscissa on which the ppm scale is displayed relative to a standard sample frequency. The ppm scale is used since it eases comparability on devices operating at different frequencies [190, 191]. As the natural abundance of 29Si is very low, homonuclear dipole interactions do not influence the spectrum in a major way. The slow relaxation of the 29Si nucleus within the crystal lattice, on the other hand, causes a long relaxation delay time (D1). The relaxation delay time (D1) presents a very important experimental value, as it describes the time the framework needs to relax from the incident impulse before a new impulse may be applied.[190].

111 5. Characterisation of synthesised products and methods

Alternatively, the cross polarisation (CP) may be applied to measure the 29Si nucleus. Nuclei with a low gyromagnetic ratio γ or a very low natural abundance such as 13C and 29Si display very low intensities during NMR measurements. As intensities depend on the energy differences between discrete energy levels and the BOLTZMANN distribution on these levels, the relaxation times of the lattice are very long for 13C and 29Si. To make up for these discrepancies, the properties of another nucleus with a high gyromagnetic ratio and a high natural abundance may be used for the measurement of the inferior nucleus. As hydrogen is very often part of the zeolite framework due to the introduction of SDAs during synthesis, 1H is the nucleus of choice for this procedure. By application of two different magnetic fields with different pulse intensities, one for the donor nucleus 1H, and one for the acceptor nucleus 29Si or 13C, an energy transfer occurs. The HARTMANN-HAHN condition describes the condition of this type of measurement with γH B1H = γSi B29Si . The success of this measurement depends on the quantity of donor nuclei and of the distances between donor and acceptor. The advantages of the method are an increase in signal intensity and an amplification of intensities initially too low to be detected [190, 191]. The measurement of 13C nucleus occurs analogous to the procedure of 29Si CP MAS NMR. These experiments are conducted routinely to gather information on the organic species occluded in the interlayer space of microporous materials and HLSs. As these organic species occupy channels and pores, they are of particular interest for the analysis of zeolite structure and formation. As the isotropic chemical shift δ is very sensitive to the chemical environment, the measurement serves as an excellent means to clarify the presence of organic molecules. It is possible to distinguish between different carbon groups within the spectra with a high resolution. 13C measurements give insight to the incorporation of SDA used during synthesis, if it remains intact or if other organic molecules have formed or otherwise occupy void space in the framework. Notably, the interlayer space may be occupied by solvent molecules or modified forms of the SDA in the shape of frag- ments or polymerisation products. Contingent upon the use of an amine as SDA, 13C NMR provides hints as to whether the amine is included in the structure in its protonated or non-protonated form [5]. 1H MAS NMR represents a means to investigate protons in their different environments such as the presence of organic molecules and absorbed water or silanol groups inside the channel structure of microporous silicates or on the terminating positions of layers within HLSs. As the 1H nucleus possesses a high natural abundance of 99.98 % and the highest gyromagnetic ratio among all nuclei, measurements do not need special requisitions beside the application of the MAS technique at a very high frequency. Hydrogen is found within the framework structure in the form of terminal or silanol hydroxyl groups. These silanol

112 5.9. Nuclear magnetic resonance (NMR) spectroscopy groups terminate individual layers, the surface of microporous materials as well as defect sites [190]. As the isotropic chemical shift values gives information on the strength of hydrogen bonds, 1H NMR is a useful tool for the analysis of HLSs. Distinct and well resolved chemical shift values are correlated with particular proton environments. Protons stemming from the organic cation exhibit typical chemical shift values of 0 ppm to 4 ppm. Water molecules interacting with each other or with silanol/siloxy groups, on the other hand, display typical chemical shift values of 3 ppm to 5 ppm. Isolated defect sites (≡Si–OH) are expected at ca. 6 ppm. Signals in the range between 7 ppm to 17 ppm indicate (strong) hydrogen bonds, for example between neighbouring siloxy/silanol groups of silicate layers (≡Si–O – ···HO–Si≡). 1H MAS NMR serves as a good method for the determination of the strength of hydrogen bonds as many HLSs exhibit very low ﬁeld chemical shifts hinting to strong hydrogen-bond interactions between neighbouring siloxy/silanol groups of the silicate layer. Some information also lies in the sharpness of the signal, as it indicates an isolation of these hydrogen bonds from other hydrogen bonds whereas broad and overlapping signals indicate proton exchange processes [5]. A correlation between the proton chemical shift and the average distance of oxygen- bound hydrogen O–H···O, which represents a measure for the hydrogen-bond strength, can be postulated according to

δiso [ppm]= ˆ 79.05 − 0.255 d(O-H···O) [pm], (5.14a)

(79.05 − δiso) d(O-H···O) [pm]= ˆ [ppm] (5.14b) 0.255

by ECKERT et al. [193]. The program DMFit is used to simulate NMR models to measured spectra. It enables fitting of solid, as well as liquid NMR spectra, including one-dimensional and two- dimensional datasets, and has been developed by DOMINIQUE MASSIOT et al. It provides an assortment of different models that account for GAUSSIAN/LORENTZIAN lines and spinning sidebands, CSA (static and MAS), as well as first and second order quadrupolar interaction (static and MAS) [192]. Figure 5.26(b) shows an exemplary modelling of the three Q-signals of Si on sample material Zn-085 using DMFit. The solid blue curve represents the measured spectrum whereas the dotted red line is the final convolution of individual models fitted to the three Q positions. The models fitted to the peaks are of the type CSA in MAS mode and rely on a basic GAUSSIAN/LORENTZIAN profile. As each sample exhibits different properties and cations,

113 5. Characterisation of synthesised products and methods resulting in varying complexity of signals, the number of fitted peaks alternates also with each signal. In the example in Figure 5.26(b), three peak profiles are fitted to the Q4 signal, another three are fitted to signal Q3, and the Q2 signal is described by a single profile.

✺✳✾✳✷✳ ❊①♣❡✐♠❡♥❛❧ ◆▼❘ ♣❡❝♦❝♦♣②

NMR spectroscopy was performed to gain insight to the short-range order distances between framework and extra-framework atoms such as silicon-silicon as well as hydrogen- hydrogen. 29Si, 13C and 1H solid state spectra of the as-made samples were collected at room temperature (293 K) using a BRUKER Avance ASX-400 NMR spectrometer (BRUKER CORPORA- TION, Billerica, Massachusetts, USA). The corresponding frequencies are 79.493 MHz for 29Si, 100.624 MHz for 13C and 400.147 MHz for 1H. Table 5.10 sums up the experimental conditions applied during NMR measurements for each nucleus.

resonance spinning sweep relaxation pulse contact experiment rotor frequency speed width delay length time MHz mm kHz kHz s µs ms 29Si HP DEC 79.493 4 4 20 60 4 - 29Si ZG 79.493 4 4 20 60 4 - {1H}13C CP 100.624 4 4 50 5 7.2 1.5 1H 400.147 4 12.5 125 10 6 -

Table 5.10.: Experimental NMR conditions.

✺✳✾✳✸✳ ✷✾❙✐ ❩● ❛♥❞ ✷✾❙✐ ❍ ❉❊❈

29Si experiments were carried out in a BRUKER probe using 4 kHz spinning speed and a 4 mm rotor. For the 29Si HP DEC spectra, the free scan delay time (DE) was 5 s and the D1 60 s. A transmitter pulse P1 of 4 µs was applied. Spectral width (SWH) was 20 kHz. For the 29Si ZG MAS measurement, a SWH of 20 kHz was applied. The DE was 8 µs and the D1 120 s. A 90° high power transmitter pulse of 4 µs was applied. The 1H high power proton decoupling (HP DEC) effectively removes the 13C– 1H heteronuclear dipolar interaction (line shapes are determined from the CSA) and 13C– 14N

114 5.9. Nuclear magnetic resonance (NMR) spectroscopy

dipolar coupling interactions [194]. The strength of the applied external field B0 accounts for 9.4 T. A magnetic field B1 of 79.493 MHz - which is equivalent to the LARMOR or excitation frequency depending on the strength of the external field - is applied to activate the Si nucleus. The used standard material is liquid tetramethylsilane (TMS) for all 29Si NMR experiments. Figure 5.27 displays the results of the 29Si experiments. Q3-signals and Q4-signals are well resolved at positions of −102.8 ppm and −112.5 ppm, respectively. The Q2-signal, though, is very rudimentary at a position of −90 ppm. By compressing the spectrum along the ppm axis, the Q2-signal becomes more pronounced. The distribution of individual signals appears quite uniform for all displayed materials. By calculating the ratio of the peak area of the Q2-, Q3-, and Q4-signals, it is possible to get insight into the overall ratio of two-, three- and four-connected Si in the microporous lattice. The relative ratio of the Q-notated signals may be estimated by fitting individual models to each signal with the help of the DMFit program [192]. These estimations should be considered as a semi-quantitative tool, as sample weights have not been measured before conducting the NMR experiments. Even though signal distribution and overall peak area greatly conforms, each signal shows some distinctive features. While Zn-085 shows the best resolution with high symmetry signals, the Zn-080 sample exhibits drastically worse resolution with high amounts of peak overlap. The Q2 signal (if present) effectively disappears within the background noise, giving rise to difficulties during assignment of Q positions and calculation of integrated intensities. A high amount of structural defects may explain the irregularity of this spectrum. V-030 greatly corresponds with Zn-085, whereas V-025, also, exhibits worse resolution and some asymmetric shoulder in the Q4 signal. Both the Zn and V spectra exhibit peak overlap of all three Q signals. Ti-001 material, on the other hand, displays almost no peak overlap whatsoever. Also, four individual Q4-signals may be distinguished. Co-030 has a reasonable signal-to-noise ratio as Q3 and Q4 signals are well resolved. However, the Q2 signal almost disappears in this spectrum and only becomes distinguishable by compressing the diagram. Co-029, again, exhibits a low resolution with the Q2 signal falling victim to the background noise. Nonetheless, its Q3-signal is well resolved with a quite sharp profile. In fact, both Co materials exhibit a sharper Q3-signal than the other materials. Table 5.11 displays the calculated integrated intensities and the corresponding ratios of the peak areas for the four IEZ materials exhibiting the most promising crystallinity. As expected for Me-IEZ materials, three types of Si connections can be identified. For the four regarded samples, the Q4 signal shows the highest intensity, indicating an intact fer-layer.

115 5. Characterisation of synthesised products and methods

Q2 Q3 Q4

Zn-085

Zn-080

V-030

V-025

Ti-001

Co-030

Co-029

as-made RUB-36

-80 -90 -100 -110 -120 -130 -140 -150 δ / ppm Figure 5.27.: 29Si MAS spectra of Me-IEZ-materials.

116 5.9. Nuclear magnetic resonance (NMR) spectroscopy

n n integrated intensity Q :Q ratio material signal Q2 signal Q3 signal Q4 Q2 :Q3 Q3 :Q4 (Q2 + Q3):Q4

Co-030 2.4 16.5 81.1 1 : 6.9 1 : 4.9 1 : 4.5 Ti-001 2.5 12.2 85.3 1 : 4.9 1 : 7.0 1 : 5.8 V-030 6.1 11.6 82.4 1 : 1.9 1 : 7.1 1 : 4.7 Zn-085 2.8 21.9 75.3 1 : 7.8 1 : 3.4 1 : 3.1

Table 5.11.: Integrated relative signal intensities of 29Si CP MAS experiment for IEZ materials as calculated with the DMFit program [192].

An idealised fer-layer exhibits an Q3 :Q4 intensity ratio of 1 : 3.5, as it contains four terminal silanol groups and fourteen four-connected SiO2 units per two-dimensional UC of the layer. An interrupted layer may exhibit a ratio of 1 : 1.25, considering that all ≡Si5–O12–Si5≡ groups of the idealised non-interrupted fer-layer are replaced by two ≡Si–OH groups. RUB- 36 exhibits a ratio of 1 : 3.9 as determined by NMR experiments, and 1 : 3.5 from structure analysis. Smaller ratios, as in comparable monoclinic materials such as RUB-20 (1 : 2) are connected to additional defects in the silicate layers which, in turn, lead to an increased number of silanol groups [58]. In a fully condensed Me-IEZ sample, only Q2 and Q4 29Si NMR signals should be observable in addition to a minor signal on the Q3 position caused by fully four-connected Si on the linker position in contact to a corresponding Me. The formerly 8 Q3 Si positions from starting material RUB-36 should be nearly completely condensed to Q4 positions (28 + 8 = 36). Instead, half the amount of former Q3 (8) positions should arise in the form 2 of Q (4) signals. However, the occurrence of Si( – O – Si)3( – O – Me) is expected to a small amount. An NMR signal would overlap with the signal from Q3 species. Therefore, discrim- – ination between Si( – O – Si)3( – O – Me) units and Si( – O – Si)3( – OH) or Si( – O – Si)3(–O ) defect units is not unambiguously possible. Q2 Si positions, on the other hand, should exclusively be represented by linking Si. From the EDX analysis and the calculation of Me-occupied linking positions, a tentative estimation of Qn positions can be made. The ratio of Q2:Q4 should account for 1:9 in the case of 100 % Si occupation. As the bridging positions are occupied only to a very small degree, the major occupation of linking positions is provided by Si. Interlayer expansion of RUB-36 without a silylating agent, an Fe salt or acac may also lead to a shift of the ﬁrst PXRD reﬂection. In this case, the layers are separated by Si atoms from Si debris which is cause for a clear detection of Q2 Si species in 29Si MAS NMR. Still, several structural differences arise between acid treated only and the DCDMS or Fe-IEZ materials.

117 5. Characterisation of synthesised products and methods

Acid treated materials are significantly less crystalline and exhibit different features in the higher angle region of the diffraction pattern compared to the DCDMS expanded COE-4 or Fe-expanded material. Additionally, 29Si MAS NMR spectra display distinctly deviating behaviour for Fe-expanded materials in comparison with materials obtained by acid treatment only. Due to a large amount of defects, for example in the form of unoccupied linking sites, the material from acid treatment only shows a small signal at −91 ppm, correspond- 2 3 ing to Q Si species linking the layers in addition to a strong Q Si( – O – Si)3( – OH) signal at −102 ppm [22]. This is observable accordingly in the Me-IEZ materials. Other sources cite a Q3 :Q4 ratio of RUB-36 amounting to 1 : 2.8 [19]. For the Me-IEZ samples, the different Q ratios are not quite as close to the purely siliceous IEZ and condensed material of 1 : 9 as desired. Due to the occurrence of a small number of Me species on bridging positions and a not insignificant amount of defect sites from incomplete condensation as well as stacking disorder, this ratio changes to a smaller amount of Q4 signals. Naturally, an increase in Me-bridging positions should decrease both the Q2 and the Q4 signal, as well as increase the Q3 signal. The latter of which has a threefold impact, as two former Q4-Si become Q3-Si, and the Q2-Si vanishes, not in favour of a Q3-Si position, but still causing an increase on the position of Q3-Si. By juxtaposition of a combination of Q2 and Q3 with Q4, nevertheless, the amount of Q4 is definitely too low for a full condensation, even when taking into account the metal content of each sample. Out of the four materials, Ti-001 still exhibits the highest ratio of 1 : 5.8. Co-030 and V-030 follow up with ratios of 1 : 4.5 and 1 : 4.7, respectively. Zn-085 shows the lowest ratio of 1 : 3.1, and, therefore the most incomplete condensation. While both regarded Co and both V materials exhibit nearly identical signal positions and Q-peak ratios, an assignment of Q-peak ratios was not sensibly possible for Zn-080 due to the poor resolution. Nevertheless, peak distribution and positions appear similar at least to the remaining signals. A possible Q3 peak area seems larger than the Q3 peak area implying a high degree of incomplete condensation.

✺✳✾✳✹✳ ✶✸❈ ❈ ▼❆❙

During the {1H}13C CP MAS spectra measurement, samples were spun in a 4 mm rotor at 4 kHz. A SWH of 50 kHz was adopted. The D1 was 5 s. A 7.2 µs 90° 1H-pulse with a contact time of 1.5 ms was applied. Figure 5.28 exhibits the 13C MAS spectra. Signals are expected from as-made RUB-36 at chemical shift values of 58.5 ppm, 51.8 ppm, 8.5 ppm which stem from organic groups + of the SDA DEDMA [N(CH3)2(CH2CH3)2] . The positions are associated to the methylene groups attached to the central nitrogen at 60 ppm, the methyl groups attached to nitrogen

118 5.9. Nuclear magnetic resonance (NMR) spectroscopy

at 50 ppm and the methyl groups attached to – CH2 – at 10 ppm [58]. All three signals are still detectable for the four as-made Me-IEZ materials with corresponding positions. How- ever, all three spectra exhibit a very small intensity just barely outside of the background noise. This implies the presence of organic species of the SDA DEDMA, albeit to a very small degree.

✺✳✾✳✺✳ ✶❍ ▼❆❙

Spinning speed was 12.5 kHz for the 1H MAS experiments allowing for a SWH of 125 kHz using a 4 mm rotor. The D1 was 10 s. The 90° high power transmitter pulse lasted for 6 µs. Figure 5.29 displays the recorded 1H MAS spectra. Information on the DEDMA cation, as well as hydrate water and the different framework defects is disclosed by 1H NMR. All spectra are complex, display a broad signal of poorly resolved proton sources and, thus, reveal the nature of the as-made framework structure. A maximum of seven individual signal positions can be identiﬁed for the regarded materials in a chemical shift range of about 0.0 ppm to 10.0 ppm. Each spectrum exhibits the low ﬁeld 7.6 ppm signal as a broad shoulder, except for Zn-080 which displays a distinctly sharp peak at this position. This position indicates (strong) hydrogen bonds, for example between neighbouring siloxy/silanol groups of silicate layers or defect sites, respectively. A low intensity of the 7.6 ppm signal, therefore, corresponds with a very low concentration of defects or isolated layers in the

- 3 3 2 CH 2 N-CH N-CH-CH 60 50 10 Zn-085

V-030

Ti-001

Co-030

120100 8060 4020 0 -20 δ / ppm Figure 5.28.: 13C CP MAS spectra of Me-IEZ-materials.

119 5. Characterisation of synthesised products and methods

7.6 5.5 4.6 3.4 3.1 2.2 1.5

Zn-085

Zn-080

V-030

V-025

Ti-001

Co-030

Co-029

20 1510 5 0 -5 δ / ppm Figure 5.29.: 1H MAS spectra of Me-IEZ-materials.

120 5.10. Infrared (IR) spectroscopy materials. Zn-080 is the only exception. Here, the sharpness and intensity of the signal leads to the assumption of a high amount of silanol groups on defect sites or silicate layers that are not connected. According to Formula (5.14) by ECKERT et al. [193], the O–H···O bond distance is calculated to yield a value of 2.79 Å. This is in good agreement with the known VANDER WAALS bond distance of neighbouring silanol groups [193]. Another signal can unambiguously be identiﬁed at 5.5 ppm (O–H···O ∼ 2.88 Å) in the spectrum of Zn-080. It ranges between chemical shift values of water molecules interacting with each other or with silanol/siloxy groups and isolated defect sites (≡Si–OH). This further cements the peculiarity of the Zn-080 sample of manifesting a high amount of defects and an incomplete condensation. At δ at approximately 4.6 ppm (bond distance 2.92 Å), in the chemical shift area presented by protons from water molecules, both Ti-001 and Zn-085 reveal a high intensity signal. For Ti material, this is the highest signal of the spectrum. V-030 also features a signal shoulder, whereas neither V-025, nor Zn-080 nor the two Co materials disclose a signal at this position. With the exception of Zn-080, which possesses a signal at 5.5 ppm, the absence of this signal in the spectra of the other aforementioned materials hints to the lack of water within the framework channels.

Signals representing protons stemming from the SDA DEDMA can be found at positions between 0 ppm to 4 ppm [58]. Methyl groups attached to carbon are positioned around 1.5 ppm (bond distance 3.04 Å). All materials exhibit this signal with a reasonably strong intensity. V-025 exhibits not one, but rather a convolution of three individual signals at the corresponding position. For Co-029, this signal possesses the highest intensity out of the whole spectrum. Methyl and methylene groups attached to the central nitrogen are observable on chemical shifts around 3.5 ppm (bond distances of 2.96 Å). Three individual locations are found in the spectra at positions of 3.4 ppm, 3.4 ppm and 2.2 ppm (bond distances of 2.97 Å, 2.98 Å and 3.01 Å), respectively. The 2.2 ppm signal is observed, to a very small degree in all spectra but the Zn-085, in which this absence hints to a distinct lack of – N – CH2 and N – CH3 functional groups. In Zn-080, on the other hand, the highest signal is detected and, thus, the highest amount of this type of organic species [58].

✺✳✶✵✳ ■♥❢❛❡❞ ✭■❘✮ ♣❡❝♦❝♦♣②

Infrared (IR) spectroscopy is marked as a type of energy dispersive vibrational spectroscopy. It utilises IR radiation to induce vibration and rotation of different compounds within the chemical structure via absorption. These absorptions are recorded and then trans-

121 5. Characterisation of synthesised products and methods

formed using the FOURIER transformation, hence, FOURIER-transform infrared (FTIR) spectroscopy [195]. The solid state FTIR spectroscopy gives insight to short-range order within the microporous framework. Information about the presence of silanol groups, water molecules and organic matter in the material can be deduced from the spectra. Also, identification of the type of silicate layer is possible. Due to the post-synthesis modifications on the starting material, highly faulted structures can be generated by disordered stacking of layers. The unambiguous characterisation of this disorder by PXRD is difficult, thus, FTIR is applied to confirm whether the silicate layer provided by the precursor is still intact or not.

✺✳✶✵✳✶✳ ❇❛✐❝ ♣✐♥❝✐♣❧❡ ♦❢ ■❘ ♣❡❝♦❝♦♣②

Infrared (IR) is defined as electromagnetic radiation with a wavelength of 0.8 µm to 1000 µm. A differentiation is conducted into the three different wavelength regions of near, mid and far IR. In the high-energy near infrared (NIR), harmonic or overtone vibrations are induced by wavelengths of 0.8 µm to 2.5 µm (14000 cm−1 to 4000 cm−1). The mid-IR, on the other hand, ranges from 2.5 µm to 25 µm (4000 cm−1 to 400 cm−1) and excites rotational, bending or normal vibrations. The excitation of rotations or lattice vibrations is generated by low energy far-IR of 25 µm to 1000 µm (400 cm−1 to 10 cm−1). However, the most common area of interest represents the mid-IR within the field of IR spectroscopy [195]. IR active vibrations are characterised by a change in dipole moment within matter due to BOHR’S frequency condition. However, a permanent dipole moment is not necessary. In this case, some of the IR radiation is absorbed and becomes observable in the spectrum which is displayed in a diagram of wavenumbers in cm−1 on the abscissa and absorption or transmission in percent on the ordinate. When dealing with IR spectroscopy, the reflection or absorbency is displayed more commonly in dependency of reciprocal centimetres or wavenumbers ν˜ in cm−1 = 1/λ rather than in wavelength λ. By the application of IR spectroscopy, both crystalline and amorphous materials may be analysed for content and concentration. Single functional groups in crystalline frameworks or isolated molecules such as carbonyl, hydroxyl, amino, nitrile as well as aromatic groups are directly identifiable with high accuracy from the spectrum using prevalent literature. Although these functional groups are not freely movable within the crystal structure, their behaviour can, as a first approximation, be assumed as that of free molecules with corresponding types of vibrations, characteristic absorptions and wavenumbers. These vibrations include overtone, combination vibrations, symmetric and asymmetric vibrations.

122 5.10. Infrared (IR) spectroscopy

Normal vibrations are observed at higher intensities than the other types of vibrations and may be distinguished into stretching (or valence) and deformational vibration. While vibrations along the axis of the bond of two atoms or parts of the molecule caused by an elon- gation or compression of the bond define stretching vibrations, deformational vibrations are marked by a deformation of the bond angle. Absorption bands for different molecules and groups depend on the strength of the chemical bond and the mass of the associated atoms. A permanent dipole in a measured group is cause for higher intensities. In general, high wavenumbers indicate strong bonds as well as small atomic mass. In contrast to that, low wavenumbers are an indicator for high atomic mass. The signal form in the spectrum gives insight to the symmetry of the sample. The higher the symmetry, the sharper the resulting peaks. The same applies to the strength of the bond, which is proportional to the sharpness of the intensity peak. The non-destructive IR spectroscopy probes similar information on functional groups as NMR spectroscopy since short range relations are subject to the examination within both methods. However, a big advantage of the IR is the unspecific general information extractable from the whole framework in contrast to the limitation to only one nucleus in NMR spectroscopy. Additionally, IR spectroscopy is a very quickly utilised method, independent of the measured material. The main objective of the application of IR spectroscopy is the identification of certain molecule groups, as well as the nature and strength of their bonds [195]. Framework vibrations in zeolites are cause for typical bands in the mid and far IR. Exter- nal and internal vibrations of the [TO4/2] tetrahedra (with T = Si or Al) can be distinguished [196]. Vibrations of the internal tetrahedra are found at ν˜ = 1250 cm−1 to 920 cm−1 for the asymmetrical stretching bands, and at 720 cm−1 to 650 cm−1 for symmetrical stretching bands, while wavenumbers of 500 cm−1 to 420 cm−1 are caused by T-O bending vibrations −1 −1 (δ or ν2). External linkages, on the other hand, are found at ν˜ = 650 cm to 500 cm in structures with double ring vibrations. 420 cm−1 to 300 cm−1 bands are indicative of pore opening vibrations. Asymmetrical stretching bands (νasymm or ν3) are characterised −1 −1 at positions of 1150 cm to 1050 cm and symmetrical stretching bands (νsymm or ν1) are found at 820 cm−1 to 750 cm−1. These external linkage bands are quite sensitive to different framework structures. Still, unambiguous assignment of bands to certain structural features should be verified by complementary techniques, as zeolite framework vibrations appear to be strongly coupled. A lattice vibration observable around 950 cm−1 indicates isomorphous substitution of framework Si or Al by other T atoms. A prominent example is Ti substituted for Si into SILICALITE (TS-1, TS-2) [196]. Here, however, a problem arises due to the closeness of the stretching vibration of terminal Si–OH groups at 960 cm−1.

123 5. Characterisation of synthesised products and methods

In many cases, hydroxyl groups in microporous materials are an essential element of the framework structure. They are observable by IR spectroscopy in their vibration modes (OH fundamental, overtone and combination vibrations). Mainly, stretching vibrations are detected in an area of 3200 cm−1 to 3700 cm−1 [197]. The different types of environments for OH groups can be listed as (i) lattice termination silanol groups, (ii) hydroxyl groups occurring at defect sites (hydroxyl nests), (iii) OH groups attached to extra-framework T-atom- containing species (iv), OH groups attached to multivalent cations which compensate the negative charge of the framework and, most importantly, (v) bridging OH groups (such as ≡Al–(OH)···Si≡ groups with BRØNSTED acidic character). Hydroxyls of type (i), (ii), (iii), (iv) and (v) evoke bands in the fundamental stretch region at about 3740 cm−1, 3720 cm−1, 3680 cm−1, 3580 cm−1 to 3520 cm−1 and 3600 cm−1 to 3650 cm−1 (free bridging OH groups), respectively. Lower wavenumber absorption bands indicate bridging OH groups exhibiting additional electrostatic interactions, for example at 3550 cm−1 and 3520 cm−1 in hy- drogenated FAUJASITE type and H-ZSM-5, respectively. The presence of free bridging OH groups is an important catalytic prerequisite in hydrogen forms of microporous materials in dependence on the nature of the T-atoms in the ≡T–(OH)–Si≡ configuration. The absorption of water and other molecules is routinely probed by IR spectroscopy. These molecules are introduced into and removed from the framework lattice via hydration/dehydration and adsorption/desorption reactions. The pure adsorption of H2O is quickly identified by a typical deformation band around 1640 cm−1. The investigation of occluded template molecules (or their decomposition products) in the form of CH and/or NH vibration bands is feasible as well [196]. Still, the local environment occurs in many framework types with IR frequencies which differ from each other. This makes assignment difficult and often ambiguous.

✺✳✶✵✳✷✳ ■❘ ♣❡❝♦❝♦♣② ❡①♣❡✐♠❡♥

FTIR spectra have been recorded on a Thermo Scientific NICOLET 6700 FTIR spectrometer (THERMO FISHER SCIENTIFIC, Waltham, Massachusetts, USA) equipped with a SMART ORBIT (Diamond-)ATR unit and an AVATAR diffuse reflectance unit. The advantage of the attenuated total reflectance (ATR) method is the small necessary sample amount and the quick and easy measurement preparation. The powdered sample is placed on the ATR unit and the single-bounce-diamond crystal is lowered to the sample. The resolution does not reach that of the diffuse reflectance measurement, however, the sample does not have to be mixed with standard material, preventing the use of the material for other purposes. Therefore, the measurement is 100 % non-destructive.

124 5.10. Infrared (IR) spectroscopy

The crystal framework of all samples is built entirely of [SiO4]-tetrahedra, Si–OH groups on defect sites or interrupted layers and Si–O–Me–O–Si groups in the case of IEZ materials. Additionally, the organic template DEDMA rests between neighbouring layers of the starting material RUB-36 and should arise within the spectrum in the form of N – CH2–,

N – CH3 and – CH3 molecule groups due to its structure. For the post-treated materials, organic species are expected as well, as the organic cation DEDMA was not removed prior to post-synthesis treatment. FTIR spectra were taken between 400 cm−1 to 4000 cm−1 with a resolution of 4 cm−1 from a pure sample using a SMART ORBIT (Diamond-)ATR unit. A standard air measurement is subtracted from the actual sample spectrum to avoid misinterpretation of molecules such as H2O, CO2 etc. Both measurements last no longer than one minute and exhibit a high reproducibility. Figure 5.30 displays the ATR-FTIR spectra of the investigated samples as reflection in % in dependence of wavenumbers cm−1. All recorded spectra exhibit high accordance, especially as-made and calcined materials, respectively. Starting at low wavenumbers, bands between 400 cm−1 to 1200 cm−1 represent predominantly lattice vibrations of the silicate layer and are difficult to interpret due to band overlap [64]. The intensity at approximately 450 cm−1, representing bending vibrations of the silicate framework is very well pronounced in all materials. Between 800 cm−1 to 700 cm−1, bands are assigned to symmetric stretching vibrations of the silicate layer and are found in each material as well. The Database of Hydrous Layer Silicates gives a quick overview not only on powder pattern, list of reflections, fractional atomic coordinates and structure plots but also the IR-spectra of individual HLSs, enabling comparison with spectra of other HLS-type layers and a judgement of the validity of the assignment [7]. An explicit band corresponding to the stretching vibration of terminal Si-OH groups is visible in starting material RUB-36 at about 960 cm−1. However, this specific wavenumber may show overlap to the neighbouring 1050 cm−1 band, that all materials exhibit as their most intense signal. Me-IEZ materials, on the other hand, exhibit a much sharper intensity at 1050 cm−1 as asymmetric stretching vibration of Si-O-Si units. Also, the higher resolution at this position makes the 960 cm−1 band visible quite clearly as a signal or signal shoulder. This specific position displays a problem, as the 950 cm−1 to 960 cm−1 stretching vibration band appears in immediate neighbourhood of the lattice vibrations of Si or Al substituted by other T-atoms such as Ti to form Si-O-Ti units, indicating the incorporation of tetrahedral framework Ti species [198, 199]. As the calcined samples presumably still possess a large amount of defects, or non-condensed terminal Si-OH positions, an unambiguous

125 5. Characterisation of synthesised products and methods

3650-370026002970 215620221630147012001050950 -807717 450

Zn-085-calc

Zn-085

V-030-calc

V-030

Ti-001-calc

Ti-001 ection / % ﬂ

Co-030-calc re

Co-030

as-made RUB-36

intensity scale x 4 4000 3600 3200 2800 2400 2000 1600 1200 800 400 wave number / cm-1

Figure 5.30.: FTIR spectra of RUB-36 and Me-IEZ materials.

126 5.11. Ultraviolet (UV) - visible (vis) spectroscopy assignment is not possible. Nevertheless, as the Me content should not reduce by calcination, a decrease of this signal hints to a further condensation or healing of terminal silanol groups. Especially Zn-085, V-030 and Ti-001 depict this type of behaviour, as the signal decreases to a mere signal shoulder upon calcination. As the resolution for Co-030-calc is not comparable to the other materials, a direct juxtaposition is difﬁcult. Still, a tentative decrease of the signal may be postulated. The weak band at 1210 cm−1 also belongs to the stretching vibration of Si-O-Si units and is, similarly, observable in each spectrum as a −1 small signal or signal shoulder. The signals at 1470 cm are attributed to CH2 bending bands stemming from SDA DEDMA. In starting material RUB-36, these signals are distinctly pronounced, whereas Me-IEZ materials show a drastic reduction of signal intensity, whereas calcined samples depict no intensity at this position whatsoever. This hints to a decomposition of the DEDMA during post-synthesis and a complete, or nearly complete removal after calcination. An absorption band appears around 1630 cm−1 in each spectra. It is strongest in the starting material and may be assigned to bending vibrations of OH groups. The presence of a very broad and intense absorption band can be observed between 2600 cm−1 to 3700 cm−1 with a maximum at around 3200 cm−1. This broad band is quite apparent in as-made and post-treated materials alike but vastly decreased in the calcined samples. An assignment can be conducted to a complex hydrogen bonding system consisting of water molecules and terminal silanol groups of the silicate layer. Other characteristic absorption bands for organic compounds - beside the bending −1 −1 bands at 1470 cm for CH2 - are usually found at 2970 cm for CH asymmetric stretching vibrations, and at 2890 cm−1 for CH symmetric stretching vibrations [64]. The former of which is solely found in RUB-36, the latter of which is not encountered in any spectrum. Still, these two additional organic bands may be hidden within the broad hydrogen bonding system at around 3200 cm−1. −1 The position of 3650 cm illustrates the symmetric stretching band of H2O. The corre- −1 sponding asymmetrical stretching band of H2O at position of 3742 cm is not visible for either material, but rather disappears in the broad band, if at all present [200].

✺✳✶✶✳ ❯❧❛✈✐♦❧❡ ✭❯❱✮ ✲ ✈✐✐❜❧❡ ✭✈✐✮ ♣❡❝♦❝♦♣②

UV-vis spectroscopy is commonly applied in research on heterogeneous catalysts. Many of the catalysts contain transition metal ions (TMI) centres, especially 3d ions, rare earth metal ions, in particular lanthanides and adsorbed molecules, molecular ions and radicals. Metal support is provided in the form of amorphous metal oxides with a high surface area

127 5. Characterisation of synthesised products and methods or porous crystalline materials such as zeolites and mesoporous materials. As a type of absorption spectroscopy, UV-vis spectroscopy exploits the property of electronic transitions within the metal ion centres in parts of the ultraviolet (UV) and the full, adjacent visible (vis) spectral regions. A number of peculiarities of heterogeneous catalysts, and high surface area solids in general, have to be taken into account when dealing with this type of electronic spectroscopy [201]. UV-vis spectra are recorded to probe the coordination environment of the incorporated Me species and to establish the incorporation at isolated sites and not as small Me clusters that would not be detected in the X-ray diffraction (XRD) experiment because of their size.

✺✳✶✶✳✶✳ ❇❛✐❝ ♣✐♥❝✐♣❧❡ ♦❢ ❯❱✲✈✐ ♣❡❝♦❝♦♣②

UV-vis, and NIR spectroscopy as well, are often denoted as electronic spectroscopy techniques since electrons are transferred from low-energy to high-energy atomic or molecular orbitals when the material is irradiated with light of the corresponding electromagnetic spectrum. These electron transfer processes take place in TMI (d − d transitions and ligand-to-metal or metal-to-ligand charge transfer transitions), and inorganic and organic molecules (mostly n − π∗ and π − π∗ transitions). They are also responsible as one source of for the colour of solid matter materials [202]. The whole electromagnetic spectrum of UV-vis-NIR covers the wavelength range 200 nm to 2500 nm (in wavenumbers 50000 cm −1 to 4000 cm −1) which can be grouped into three regions of 200 nm to 400 nm (50000 cm −1 to 25000 cm −1) in the UV range, 400 nm to 800 nm (25000 cm −1 to 12500 cm −1) for vis and 800 nm to 2500 nm (12500 cm −1 to 4000 cm −1) for the NIR area. In the UV-vis region, electronic transitions are probed, while in the range of NIR, over- tones and combination bands of fundamental vibrational transitions are invoked. TMI complexes on surfaces and TMI coordinated to surface oxygen atoms need to be regarded from different angles, as TMI in complexes are not in direct contact with surface oxygen atoms of the catalytic material. Spectroscopic signatures of adsorbed complexes are virtually identical to these complexes in solution with slight variances of band shifts. Therefore, the surface has a similar effect on the TMI complexes as a solvent does. A replacement of one or more ligands by surface oxygen atoms causes the TMI complexes to adopt a different symmetry with different ligands, evoking a signiﬁcant change in their spectroscopic 2+ properties. An illustrative example are aqueous complexes, such as Cu(H2O)6 , being ion exchanged in the super-cages of ZEOLITES X and Y and partially dehydrated around 373 K. 2+ The result is an intermediate [(O1)3Cu(H2O)] , in which O1 represents lattice or surface

128 5.11. Ultraviolet (UV) - visible (vis) spectroscopy oxygen. The metal complex exhibits pseudo-tetrahedral symmetry with a typical UV-vis- NIR spectrum. The spectroscopic signatures of TMI depend on the following three features of the surfaces on which they are positioned, if only surface oxygen atoms coordinate in the first coordination sphere of TMI. Firstly, the sites of TMI (and rare earth ions) are surface sites and have, thus, low symmetry. Since most sites have no symmetry at all, octahedral (Oh) and Td coordination are rare. Secondly, the high amount of different coordination number and coordination geometry sites at the surface leads to a small energetic difference of TMI, leading, in turn, to simultaneous occupation of different sites. The third feature is the sensitivity of a heterogeneous catalyst surface to the presence of a TMI (or a rare earth metal ion). To ensure the best coordination possible, surface oxygen atoms in the immediate neighbourhood of the TMI routinely change positions. This is cause for site distortion and lowering of symmetry. The consequences of these three characteristics are observable in the spectra in the form of absorption bands broadening and overlapping. As the interpretation of spectra exhibiting these hardships is strenuous, the use of spectra databases in conjunction with complementary data from other spectroscopy methods is advised [201]. Common spectroscopic analysis is conducted using transmission mode for sample solutions, gas phases and individual crystals. As it is quite challenging to produce transparent thin films for powdered samples and solids (e.g., heterogeneous catalysts), transmission experiments are seldom applied. Preferably, diffuse reflected light is utilised in the form of diffuse reflectance spectroscopy (DRS). An advantage of this method is the direct information extraction in the form of chemical states as outer shell electrons of the TMI are probed. Oxidation state and coordination environment of TMI, in addition to the nature of adsorbed species and different hydrocarbon species in catalytic solids can be extracted from these measurements. Another benefit is the possibility of applying in-situ conditions and the quantitative nature of spectra. Among the disadvantages is the complexity of spectra due to band broadening and overlapping [202]. Raw diffuse reflectance spectra often exhibit a different quality than the same spectra taken in transmission (stronger than expected absorption from weak bands). To compensate for these differences, a KUBELKA-MUNK conversion is implemented. It is expressed as follows:

(1 − R)2 k f (R) = = (5.15) 2R s with the absolute reflectance of the sampled layer R, the molar absorption coefficient k and the scattering coefficient s. The advantage of the KUBELKA-MUNK equation is the

129 5. Characterisation of synthesised products and methods creation of a linear relationship for spectral intensity relative to sample concentration by assuming an infinite sample dilution in a non-absorbing matrix, a constant scattering coefficient and an infinitely thick sample layer. Since the scattering coefficient is a function of sample size and packing, ideal conditions can be achieved for highly diluted, small particle samples with a sample layer of at least 1.5 mm. High quality and sensitivity results are, therefore, obtainable by a suitable sample preparation [203–205].

✺✳✶✶✳✷✳ ❯❱✲✈✐ ♣❡❝♦❝♦♣② ❡①♣❡✐♠❡♥

DRS UV-vis measurements have been performed on a JASCO V-650 spectrometer (JASCO Research Ltd., Halifax, Nova Scotia, Canada) and on a SHIMADZU UV-2450 spectrometer

(SHIMADZU CORPORATION, Kyoto, Japan) with a BaSO4 standard.

The recorded powder reﬂectance spectra have been transformed according to the KUBELKA-MUNK function (see Equation (5.15)). Figure 5.31 displays the UV-vis spectra of as-made and calcined Me-IEZ-RUB-36 materials Co-029, Ti-001, V-025, and Zn-080. The post-treated Co sample is a powder of a very light grey or blue-grey colour, absorptions in the vis range might be expected in an area of the visible yellow light of 550 nm (complementary colour), if at all. The calcined sample, however, exhibits pure white colour. Co spectra are interpreted with the information available for different Co incorporated materials. Co-ZSM-5 spectra display two absorption bands with maxima at 246 nm and 520 nm, in which the peak at 520 nm may represent Co2+ species coordinated octahedrally as 2+ [Co(H2O)6] [206]. In Co-TUD-1, divalent cobalt ions (Co2+) in Td environment are observed on positions of 525 nm and 654 nm. Oh Co2+ coordination is identiﬁed in signals at around 480 nm and 506 nm. Trivalent framework Co3+ can be attributed to a 410 nm peak. Strong and broad bands in the lower wavelength region may indicate charge-transfer bands associated with non-framework Co3+ species at 356 nm position bands, which is an indicator for the presence of a Co3O4 phase [207].

The spectrum of Co-SiO2 shows three absorption peaks at 525 nm, 584 nm and 650 nm which can be unambiguously assigned to the transition of Co2+ ions in Td environments. At a position around 224 nm, a broad band is attributed to a low energy charge transfer between oxygen ligands and the central Co2+ ion in Td symmetry. A second broad absorption is observed at 356 nm and assigned to Co3+ species [208].

130 5.11. Ultraviolet (UV) - visible (vis) spectroscopy

The Co-029 spectrum produces a maximum at λ = 200 nm and a smaller signal around 217 nm. The corresponding calcined Co-029-calc exhibits a maximum signal positioned at λ = 256 nm, with a smaller signal at 207 nm and a broad absorption around 300 nm. The lower wavelength signals around 200 nm and 217 nm can be assigned to Td Co2+. The 256 nm band is not unambiguously attributed to a speciﬁc environment. However, it is still closer to the signals for Td Co2+ than to Co3+ (Oh) species signal. UV-vis spectra of Ti-RUB-36, in which Ti is part of the framework, have been reported by XIAO et al. These spectra exhibit a peak at λ = 230 nm which marks the presence of

201207217 230 240 256 295 310 325 375

V-025-calc V-025

Ti-001-calc Ti-001 Kubelka-Munk / arb. units Co-029-calc Co-029

Zn-080-calc Zn-080

RUB-36 200 250 300 350 400 450 500 wavelength / nm

Figure 5.31.: UV-vis spectra of Me-IEZ materials.

131 5. Characterisation of synthesised products and methods

4-coordinate Ti species exclusively. By DCDMS treatment and calcination, both Ti-COE-3 and Ti-COE-4 produce an additional broad band centred at λ = 360 nm, which is - similar to (4-coordinated) Zn in ZnO - associated with TiO2 species (6-coordinated). Still, bands indicative of 4-coordinative Ti species appearing at λ = 230 nm are prevalent [184]. The regarded as-made Ti-IEZ-RUB-36 sample exhibits an off-white colour, whereas the calcined sample of Ti-001 is characterised by a brilliant white colour. The very broad λ = 230 nm band marks the exclusive presence of 4-coordinate Ti species since no bands around λ = 360 nm are observable at all, very similar to the spectrum of Ti-RUB-36. Due to its very light green or green-grey colour, absorptions in the vis range might be expected in an area of the visible red light of around 600 nm (complementary colour) for the post-treated V sample. The calcined sample, however, exhibits a pure white colour. The assignment of a certain V environment to a speciﬁc absorption band represents a special challenge since V may appear in many different coordination states. Various V environments can be linked to the corresponding coordination in pure V compounds and zeolites. The occurrence of an absorption band at 240 nm marks a Td [VOx] species, while for the arrangements of square pyramid and octahedron, absorption is expected in 340 nm and 410 nm, respectively. Bands around 256 nm have been linked to distorted tetragonal symmetry [209]. A 300 nm band is indicative of V5+ species in V-ZSM-5. 286 nm and 402 nm have been assigned to Td and Oh V5+, respectively [210]. At positions above 250 nm, charge transfer from oxygen to V occurs, marking Td coordination. Generally, zeolites display bands of wavelengths around 333 nm to 384 nm linked to Td coordination. Oh coordination is found in a pure V compound, exhibiting wavelengths between 333 nm to 500 nm and indicating V5+ [211]. Speciﬁcally, broad bands at 395 nm and 490 nm are attributed to aggregated V species in Oh coordination and bulk vanadium oxides. Meanwhile, UV-vis bands below 300 nm are associated with isolated [VO4] tetrahedra, whereas a band at 315 nm is assigned to oligomeric Td vanadium entities [212]. The maximum absorbency of V-025 is found at λ = 201 nm, with a very broad band at 325 nm. V-025-calc material, on the other hand, displays a maximum at λ = 207 nm, and two other bands at 216 nm and 263 nm. Regarding the observed UV-vis bands, the coordination of V in V-025 and V-025-calc is assumed to be Td as well. However, the broad peak around 375 nm in the calcined sample may also hint to an aggregation of Oh V. The 256 nm band, linked to distorted tetragonal symmetry is clearly observed in both states of V-025. Also, the small 295 nm band in the calcined sample may be assigned to isolated

[VO4] tetrahedra.

132 5.11. Ultraviolet (UV) - visible (vis) spectroscopy

The Zn-080 sample exhibits a maximum signal at λ = 193 nm, and another signal at a position of 218 nm. As the calcined sample is a purely white powder, no absorptions in the vis range are expected. However, the as-made sample is of an off-white colour. For the interpretation of the Zn spectra, the sample is compared to literature specifications of Zn-ZSM-5 and ZnO. Pure ZnO is a hexagonal crystalline powder, in which Zn is coordinated tetrahedrally. It has been applied commercially as a white pigment and additive due to the brilliant white colour (as has TiO2). The material exhibits a large broad absorption band around 350 nm to 360 nm assigned to the O2 – →Zn2+ ligand to metal charge transfer (LMCT) transition [213, 214]. Zn-ZSM-5, on the other hand, shows different absorption bands from that of ZnO, with peaks or shoulders at about 280 nm, 230 nm and 195 nm, respectively. Therefore, a major difference of coordination environment between the Zn species in Zn-ZSM-5 and that in pure ZnO can be postulated. The occurrence of absorption bands below 230 nm is interpreted as the distinguishing proof of incorporation of metal atoms into the framework of the zeolite by isomorphous substitution. In all likelihood, the majority of Zn species have entered the ZSM zeolite framework so that the absorption band of 195 nm and 230 nm may be assigned to the charge transfer transitions of framework Zn species with lattice O2 – . Nevertheless, the detailed Zn coordination states are not confirmed [215]. Neither the Zn-080, nor the corresponding calcined sample exhibit a characteristic ZnO 350 nm to 360 nm absorbency. Hence, just as observed in the Zn-ZSM-5, a different Zn environment is expected in the samples. In agreement with the signals found in Zn-ZSM- 5 and ZnO, the two signals at 193 nm and 218 nm in Zn-080 are interpreted as proof of incorporation of Zn into the framework of zeolite by isomorphous substitution. Detailed Td or Oh Zn coordination states, however, are not attributed either. The literature findings for post-synthesis interlayer expansion with Fe are not unambiguously either. Al-COE-4/Fe and COE-4/Fe materials exhibit a colour alteration from white to green. This fact, in conjunction with the changes observable in the UV-vis spectra, hints to a change of the state of the incorporated Fe after reaction. In comparison with Fe2O3- ZSM-5, COE-4/Fe and Al-COE-4/Fe show a drastically different UV-vis spectrum. These two materials display an oxygen-to-metal charge-transfer (CT) band at 259 nm and 268 nm, respectively. Other Fe incorporated materials show similar behaviour. Bands below 300 nm are assigned to isolated Fe3+ species. However, as both tetrahedrally or octahedrally coordinated Fe3+ have transitions in the same energy range, a specific assignment is not feasible [22].

133

✻✳ ❈❛❛❧②✐❝ ❡①♣❡✐♠❡♥

Catalytic experiments have been conducted in a joint project at the Tokyo Institute of Tech- nology, Yokohama 226-8503, Japan, with the working group of TOSHIYUKI YOKOI and, in particular, the help of SUNGSIK PARK at the Catalytic Chemistry Division in the Chemical Resources Laboratory.

✻✳✶✳ ❊♣♦①✐❞❛✐♦♥ ♦❢ ✶✲❤❡①❡♥❡

Epoxides are highly useful intermediates for the manufacture of a range of important commercial products. The olefin epoxidation is among the main production processes in laboratory and industrial interest. Oxygen, peroxides and peracids are used for direct oxidation of alkenes as the main method for industrial applications. One of the challenges of olefine oxidation is to stop the reaction on the epoxide level and not oxidise to the final product

CO2. This is also the reason why TS-1 is a good catalyst since it is hydrophobic and offers limited space for an ongoing reaction. The epoxidation of ethylene vapour phase oxidation with oxygen or air is accomplished by the use of a silver catalyst, a method not efﬁcient for alkenes with unsaturated hydrocarbon radical CH bonds due to oxidation at this position. Propylene oxide, on the other hand, is created by the metal catalysed liquid phase oxidation of propylene by employment of organic hydroperoxides produced by hydrocarbon autox- idation. This method, however, causes the formation of alcohol co-product tert-butanol [11].

On an industrial scale, the oxidation of alkenes (except for light alkenes) is mostly making use of homogeneous catalysts such as peracids and m-chlorobenzoic acid, the former of which does not represent a clean method as equivalent amounts of acid waste are generated. Additionally, the handling of peracids is a matter of safety concern [216].

Hence, new epoxidation methods that apply safer oxidants and produce less waste are of great interest to the chemical ﬁne industry. This can be achieved by the use of hydrogen

135 6. Catalytic experiments peroxide as it is both economically reasonably available and environmental friendly as its only by-product is water. Already, many catalytic systems based on different metals such as tungsten, manganese, rhenium and titanium have been reported for the epoxidation of a wide range of alkenes using hydrogen peroxide [11].

Here, 1-hexene epoxidation using hydrogen peroxide as an oxidant is applied to test the catalytic properties of the Zn-IEZ-RUB-36 sample Zn-080. As this reaction is exemplary for TS-1, the Ti analogue of ZSM-5, an analysis of the Ti sample would have been preferable. However, no suitable sample was available at the time of analysis and reaction.

✻✳✶✳✶✳ ❚❤❡♦②

A cyclic ether containing a three-atom ring (epoxide functional group) is called an epoxy, epoxide, oxirane or ethoxyline, whereas simple epoxides are often referred to as oxides. Figure 6.1 shows a generic epoxide with its triangle-shaped ring. Due to the triangle shape, the ring is strained and, therefore, highly reactive [217].

Oxidation reactions occur due to a loss of electrons or an increase in oxidation state by an atom, molecule or ion. Some oxidation reactions of alkenes yield cyclic ethers by bonding both carbons of a double bond to the same oxygen atom, the products of which are called epoxides [218].

Epoxides are most interesting intermediate materials in the chemical industry, where oleﬁn epoxidation represents one of the main procedures, both on laboratory and industrial scale. Oleﬁn is the umbrella term for alkenes, cycloalkenes and polyenes [11].

The reaction with peroxy acids (peracids) RCO3H, however, is an important procedure for preparing epoxides. Figure 6.2(a) exhibits a peroxy acid on the left and a carboxylic acid 6.2(b) on the right for comparison.

Figure 6.1.: Chemical structure of a generic epoxide.

136 6.1. Epoxidation of 1-hexene

(a) (b)

Figure 6.2.: Chemical structure of (a) peroxy acid; (b) carboxylic acid.

The suitability for this type of reaction is due to the weakness of the oxygen-oxygen bond of these peroxide derivates, as well as their polarisation, resulting in a negative acyloxy (in acyloxy groups the acyl group is bonded to oxygen: R–C(=O)–O–R’ where R–C(=O) is the acyl group), and a positive hydroxyl group (R–O–H). Assumed electrophilic character for the OH moiety, Figure 6.3(a) exhibits the general reaction equation for the epoxidation with the corresponding transition state 6.3(b).

The dipolar intermediate is only shown for the sake of completeness, since its formation is presumably not effectively happening. More likely, the epoxidation reaction transpires in a single step exhibiting a transition state of all the bonding events. Epoxidations by peracids always show syn-stereoselectivity. The only product of this reaction is the one where two identical species add to the same face of the reactant, as opposed to anti-stereoselectivity, in which two identical species add to opposing faces of the reactant. The reaction is, thus, selective for one stereoisomer over the other. Supposedly, a charge separation induced by the electron shifts marked by blue arrows is immediately neutralised by the green arrow electron shifts [218].

An active and highly selective catalyst in the epoxidation of lower oleﬁns is TS-1 using dilute H2O2. It is proposed that the selective oxidation is carried out through the 5-ring intermediate [219].

(a) (b)

Figure 6.3.: (a) Generalised epoxidation equation with (b) transition state [218].

137 6. Catalytic experiments

→ → (a) 1-hexene (b) 1,2-epoxyhexane (c) 1,2-exanediol

Figure 6.4.: Epoxidation of 1-hexene reaction.

One of the initial categories of molecular sieves including a transition metal cation (Ti4+) in framework positions, TS-1 shows outstanding activity and selectivity for partial oxidation of organic reactants by aqueous H2O2.

Molecular sieve zeolites incorporating a redox metal cation such as Ti4+, Fe3+, or V3+ have an immense capacity in shape-selective oxidation reactions. The potential is comparable to the prominent performance of the aluminosilicate analogues in acid-catalysed reactions. While these aluminosilicate materials are very well documented in terms of catalytic capability, silicate products containing other redox metal cations are still being investigated [49]. Hence, the 1-hexene epoxidation reaction is used to classify the catalytic activity of novel Me-IEZ materials. 1-hexene, in particular, was chosen since cyclohexene may be too bulky for the pore channels of the tested material.

Figure 6.4 shows the chemical equation of the 1-hexene epoxidation reaction with the starting material 1-hexene (6.4(a)) reacting to 1,2-epoxyhexane (6.4(b)), which, in turn, reacts to 1,2-exanediol (6.4(c)).

Other known Zn silicates with catalytic activity in the 1-hexene epoxidation include "mesoporous" Zn-MFI and Zn-ZSM-5 [220, 221].

✻✳✶✳✷✳ ❊①♣❡✐♠❡♥

The epoxidation of 1-hexene was carried out in a 100 ml round-bottom ﬂask immersed in an oil bath with H2O2 at 333 K and methanol (MeOH) as a solvent using Zn-IEZ-RUB (sample Zn-080) as catalyst material.

The reaction was conducted in a 333 K oil bath for 2 hours. Cyclooctanone (C8H14O) was used as an internal standard material in the 333 K oil bath (solid-to-liquid reaction).

138 6.1. Epoxidation of 1-hexene

catalyst solvent Si/Me 1-HX epoxy yield % H2O2 conv. % TON TS-1 (YNU) MeOH 37 19.1 22 86.0 Ti-MWW(D) MeCN 78 12.2 17 112.0 Ti-MWW(P) MeCN 59 37.9 42 270.0 Zn-080 MeOH 10 0.4 3 0.6

Table 6.1.: Results of the epoxidation reaction of 1-hexene with Zn-080 compared to some laboratory Ti standard materials.

Product analysis was carried out via gas chromatography (GC) (SHIMADZU GC-2014

(SHIMADZU CORPORATION, Kyoto, Japan)) and Pontiometric Automatic Titration H2O2 analysis (KEM AT-500N CeSO4). Reaction residual H2O2 was tested by Pontiometric Au- tomatic Titration.

The reaction conditions were implemented as follows: 10 mmol (∼0.841 g) 1-hexene,

10 ml MeOH as a solvent, 10 mmol (∼0.9714 g) H2O2 and 50 mg catalyst. Table 6.1 exhibits the Zn-080 material as compared to typical Ti-catalysts used in 1-hexene epoxidation.

The epoxide reaction depends on the hydrophobicity of the catalyst, which may be determined by the adsorption of H2O. Thus, if the adsorption of H2O is high, the catalyst is less hydrophobic. This may be investigated by TA experiments. A high weight loss indicates a high amount of hydroxide (OH – ) groups. However, since the weight loss is low with 1 wt% of H2O, the amount of H2O in the catalyst should be low.

Compared to the laboratory standard materials, the Zn-080 sample exhibits exceedingly low 1-hexene epoxy yield, H2O2 conversion and subsequent TON.

It is suggested to repeat the epoxidation reaction with half the amount of sample material and 20 % of reactants. If the activity increases with decreased reactants, then 1-hexene can penetrate the pores of the material and the reaction is successful. However, in the case of Zn-080, the information gleaned from NH3-TPD and N2-desorption, as well as the additional reaction of 1-octene cracking (see Section 6.2) leads to the conclusion that the pore space of the material is not available for molecule transport.

139 6. Catalytic experiments

✻✳✷✳ ❈❛❛❧②✐❝ ❝❛❝❦✐♥❣ ❛♥❞ ✐♦♠❡✐❛✐♦♥ ♦❢ ✶✲♦❝❡♥❡

The process of fluid catalytic cracking (FCC), used to convert heavy crude oil into more valuable gasoline and olefinic gases, is gaining relevance faster and faster due to increased worldwide demand. As a result of its consistence of a large amount of olefins and sulphur compounds, the octane number of FCC gasoline is low. Thus, certain processes are necessary to meet the domestic regulation of sulphur emission. One of these processes is hydrogenation, which converts the linear and mono-branched olefin in gasoline into paraffin. This, in turn, leads to a low octane number. By introducing new catalysts or modifying existing catalysts, the octane number or yield of gasoline is aimed to be improved [222, 223].

ZSM-5 zeolite (MFI framework type code) is widely used in FCC units, either to increase gasoline octane numbers or to enhance the production of light oleﬁns. Generally, the performance of zeolite catalysts depends on amount, type and strength of acid sites as well as pore structure [224].

Here, the catalytic cracking and isomerisation of 1-octene serves as a model process to test the catalytic properties of the synthesised and calcined samples Co-029, V-025 and Zn-080.

✻✳✷✳✶✳ ❚❤❡♦②

The establishment of the acidic directed catalytic cracking was conducted in 1947 by HANSFORD [225] in a detailed study of various hydrocarbons on silica-alumina catalysts. It explains the existence of acidic sites on the catalyst along a mechanism involving carbenium ions and thermal decomposition. In 1948, TURKEVICH and SMITH [226] investigated the isomerisation of 1-butene using sulphuric and phosphoric acid. THOMAS has illustrated his investigations of the acidic nature of a silica-alumina catalyst [227], which highlight the importance of the presence of alumina in the catalyst and predict the silica- alumina activity as a function of the acidic level in 1949. The cracking mechanism, on the other hand, was discussed in detail by GREENSFELDER,VOGE, and GOOD [228]. This work demands a dependence of the silica-alumina activity on a tetrahedral (Td) oxygen structure surrounding each silica and aluminium atom while claiming a carbenium ion mechanism and the prediction of the product distribution for cetane cracking over silica- alumina. At this point, the distinction in product distribution from thermal cracking and catalytic cracking was established. The formerly exclusive thermal cracking was replaced

140 6.2. Catalytic cracking and isomerisation of 1-octene by catalytic cracking due to its higher octane rating ability and the production of by-product gases exhibiting more carbon-carbon double bonds (i.e., oleﬁns). This knowledge was fur- thered by HANSFORD,WALDO,DRAKE and HONIG in experiments with deuterium exchange into hydrocarbons [229]. By combining these observations, the catalytic cracking process may be illustrated by an acid catalysed carbonium/carbenium ion mechanism [230, 231].

During the FCC process, large hydrocarbons of petroleum crude oil with high boiling point and high molecular weight are broken and converted to carbocations, such as gasoline, olefinic and other gases. Included in these processes are the cracking of paraffins, napthenes, and aromatics side chains, as well as the isomerisation, condensation or cy- clisation of olefins. Other processes are the transfer of hydrogen, dehydrogenation of napthenes and olefins, as well as alkylation and dealkylation.

Figure 6.5 shows a generalised diagram of the conversion process. High boiling, straight- chain alkane (paraffin) hydrocarbons are cracked into smaller straight-chain alkanes, as well as branched-chain alkanes, branched alkenes (olefins) and cycloalkanes (naph- thenes). This process is more accurately defined as scission of the carbon-to-carbon bonds. A few of the smaller alkanes are, in turn, broken down into even smaller (branched) alkenes such as ethylene, propylene, butylenes, and isobutylenes, all also usable as petrochemical feedstock [232].

The original cracking of the large hydrocarbons produces cycloalkanes, which in turn are transformed to aromatics (benzene, toluene, and xylenes) with higher octane ratings than alkanes.

A by-product of the FCC process is carbon, which is deposited on the catalyst and labelled catalyst coke. As this coke deposit slowly deactivates the catalyst, a measure of the ability to avoid the formation of coke is an important task in the analysis of new catalyst materials [234, 235].

✻✳✷✳✷✳ ❊①♣❡✐♠❡♥

Calcined Co-029, V-025 and Zn-080 samples were tested in the cracking and isomerisation −1 reaction of 1-octene (CH3(CH2)5CH:CH2 = 112.21 g mol ,WAKO pure chemical industries, Ltd., assay (cGC) min. 95.0 %, density (293 K) 0.713 g mol−1 to 0.720 g mol−1). To prepare the

141 6. Catalytic experiments

long chain alkanes

smaller alkanes branched alkenes and and cycloalkanes branched alkanes

aromatics smaller alkenes and branched alkenes

(a) (b)

Figure 6.5.: Schematic overview of catalytic cracking of petroleum hydrocarbons into light cycle oils (LCO), heavy cycle oils (HCO), gasoline and gas [233]. materials for testing, the catalyst was pelletised. 40 mg of previously calcined catalyst was compacted in a manual hydraulic press to a pressure of 40 kN and then sieved to pellets in size between 400 µm to 500 µm.

Figure 6.6 shows the compacting cell (6.6(a)), the compacting equipment and sieves (6.6(b)), and the hydraulic press with compacting cell (6.6(c)).

The 5 mm diameter QUARTZ tubular reactor is filled with a piece of cotton wool, 20 mg of pelletised catalyst without binder and another piece of cotton wool, to keep the material inside the reactor. The length of the catalyst filling in the reactor should roughly equal the diameter of the reactor to facilitate reactant flow.

Figure 6.7 shows the reactor (6.7(a)) before and (6.7(b)) after the reaction.

The 1-octene reaction is conducted for 9 h at 673 K with an air flow rate of 740 to out/real 26 mlmin−1 to 27 mlmin−1 and an argon (carrier gas) flow rate of 37 to out/real 3 mlmin−1. The real flow rate is measured via flow meter. This inspection also provides security that the reactor is closed properly. Also, the reactor is shielded with heat protection tape to minimise unwanted heat release and to maintain the desired temperature during injection into the GC.

142 6.2. Catalytic cracking and isomerisation of 1-octene

(a) (b) (c)

Figure 6.6.: The compacting cell (a), compacting equipment and sieves (b), and the hydraulic press with compacting cell (c).

The liquid 1-octene is ﬁlled into a syringe and pumped into the reactor at a ﬂow rate of − 4.7 µlmin 1 by using a HARVARD 11 plus syringe pump, which uses a six-way valve to inject the product at a steady rate.

Cracking and isomerisation hydrocarbon products are analysed every hour during reaction by GC with a SHIMADZU gas chromatograph GC 14B with a flame ionisation detector (FID) detector. The GC uses helium as a carrier from a gas tank, air from a compressor and hydrogen for the burning of the product from a GL Sciences HG 260 Hydrogen Generator, which needs to be stocked with water at all times. The experimental set-up of the reaction is displayed in the photos in Figure 6.8(a). The flow regulation is shown in Figure 6.8(b) and the final set-up of the reactor in heat protection tape in Figure 6.8(c).

The details of 1-octene conversions and product selectivities obtained with time-on- stream (TOS) of 1 h, respectively, are shown in Figure 6.9. Conversion is depicted in 6.9(a), whereas product selectivities are separated by light oleﬁns (C2=, C3=, and C4=) in 6.9(b) and 1-octene isomers in 6.9(c) as recorded with GC. As expected from observations by NH3-

TPD and the N2-adsorption experiments, the materials exhibit very low catalytic ability. At the operating conditions investigated, the initial conversion ranges are 80 %–85 % for Co-, 80 %–90 % for V-, and 10 %–30 % for Zn-IEZ-RUB-36. Both Co (sample Co-029) and

143 6. Catalytic experiments

(a) (b)

Figure 6.7.: Reactor with Zn-080-calc before (a) and after (b) 1-octene reaction.

V (sample V-025) material show a drastically higher conversion rate than the Zn material (sample Zn-080).

Whereas Zn-080 exhibits no selectivity towards light olefins whatsoever (6.9(b)), V-025 shows a selectivity of 1 % within the first hour on stream. Co-029, on the other hand, displays a selectivity of 9 % within the first hour on stream, which falls to approximately 1 % and then steadily decreases to 0 %. Due to the lacking selectivity towards light olefins, the major part of the reaction is favoured towards isomerisation (6.9(c)). For the Zn material, the selectivity towards 1-octene isomers accounts for 100 % from the start of the reaction, whereas the V material tends towards 96 % of isomerisation within the first hour and then equilibrates at 100 % as well. The reaction in the Co material starts around 83 % of 1-octene isomerisation, rises toward 98 % within the first hour and then steadily converges toward the 100 % mark.

The reference material RUB-37 exhibits a behaviour that is very similar to that of the Zn sample, but even then stays well below the Zn material performance. This demeanour is anticipated, as very low activity is observed in purely siliceous material without the presence of Al or other heteroatoms and a restricted interlayer space.

144 6.2. Catalytic cracking and isomerisation of 1-octene

(a) (b) (c)

Figure 6.8.: (a) Experimental set-up of 1-octene reaction, (b) ﬂow regulation (c) reactor in heat protection tape.

The behaviour of all three materials reﬂects the observations during NH3-TPD and the amount of acid sites calculated. As Co-029 exhibits the highest amount of acidic sites, the catalytic performance is also highest for this catalyst. Even though Zn-080 material displays a slightly higher amount of acid sites, its performance in catalytic cracking is virtually non-existent. This may be explained by the non-accessible pores observed during

N2-adsorption experiments.

120

100 nes / % nes / % ﬁ ﬁ 80

60 V-RUB-36 45 Co-RUB-36 Zn-RUB-36 20 RUB-37 Conversion of ole Conversion Selectivity C8 isomers / % C8 isomers Selectivity no cat Selectivity light ole light Selectivity

TOS / h TOS / h TOS / h (a) (b) (c)

Figure 6.9.: Conversion of 1-octene (a), selectivity regarding light oleﬁns (b) and 1-octene isomers (c).

145 6. Catalytic experiments

✻✳✷✳✸✳ ▼❛❡✐❛❧ ❆♥❛❧②❡

To get insight to the processes that happen during the catalytic reaction, TA- and PXRD- analyses are conducted. The coke formation is calculated by TA analyses, whereas PXRD diagrams show structural changes and a potential decrease in crystallinity.

The ﬁnal amount of coke deposited is determined off-line by a RIGAKU (RIGAKU CORPO- − RATION, Tokyo, Japan) Thermo plus TG8120 thermal analyser using a ramp of 10 Kmin 1 from 296 K to 973 K. The weight loss is determined by two distinct steps in the TG, whereas the weight loss observed from 573 K to 973 K is ascribed to coke. Equation (6.1) illustrates the calculation of the resulting coke deposit.

mcat+coke ∗ ∆m573K−973K mcoke = , (6.1) mcat+coke − (mcat+coke ∗ ∆m296K−973K) −1 with mcoke representing the resulting coke in mgg catalyst, mcat+coke the total amount of catalyst and coke in mg, ∆m573−973 the mass loss in the temperature range of 573 K–973 K and ∆m296−973 the mass loss in the temperature range of 296 K–973 K. Table 6.2 exhibits the mass loss and corresponding temperature range, the total amount of catalyst and coke (sample), as well as the resulting coke catalyst.

Notably, during the reaction, almost no coke formation occurs in any material, which would lead to catalyst deactivation. Nonetheless, the reaction is weighed heavily towards isomerisation, instead of cracking or conversion. From the NH3-TPD and the N2- adsorption experiments, it is evident that the deactivation of the catalyst during the reaction may be ascribed to a structural collapse or change during calcination. This is evident from PXRD diagrams before and after the reaction as can be observed in Figure 6.10. In this case, especially the intensity of the ﬁrst signal sinks drastically. Therefore, it is prudent to assume that the reactant cannot penetrate the material and reactions almost exclusively occur on the catalyst surface.

The information gained from the 1-hexene epoxidation, 1-octene reaction, PXRD and TG experiments show the different weaknesses each material exhibits with regards to catalytic properties. While Co-IEZ-RUB-36 (sample Co-029) displays potential as a catalyst, the overall amount of acidic sites and, thus, catalytic activity of all three materials is vanishingly small in the tested reactions. Whilst Zn material (sample Zn-080) lacks pore space or access in general, Co and V (sample V-025) samples are limited by the low amount of acid sites and

146 6.2. Catalytic cracking and isomerisation of 1-octene

160000 200000

140000 Co-IEZ-RUB-36-calc 180000 V-IEZ-RUB-36-calc Co-IEZ-RUB-36-reac V-IEZ-RUB-36-reac 160000 120000 140000 100000 120000 80000 100000

60000 80000 60000 40000 40000 20000 20000 Intensity / arb. units / arb. Intensity Intensity / arb. units / arb. Intensity 0 0 0 10 20 30 40 0 10 20 30 40 2 ѳ / ° 2 ѳ / ° (a) Co-029 (b) V-025

35000 500000 Zn-IEZ-RUB-36-calc 32000 RUB-37-calc Zn-IEZ-RUB-36-reac RUB-37-reac 29000 400000 26000 23000 300000 20000 17000 200000 14000 11000 100000 Intensity / arb. units / arb. Intensity

Intensity / arb. units / arb. Intensity 8000 5000 0 0 10 20 30 40 0 10 20 30 40 2 ѳ / ° 2 ѳ / ° (c) Zn-080 (d) RUB-37

Figure 6.10.: PXRD diagrams before (blue) and after (green) the 1-octene reaction recorded in BRAGG-BRENTANO geometry on RIGAKU diffractometer [130]. the presumed structural collapse during the reaction as observed by PXRD. Coke formation plays a negligible role in the performance of the catalysts during the reaction.

Even though the results from the NH3-TPD are rather disappointing in consideration of catalytic activity, the N2-adsorption experiments give rise to a potential for a desired microporous functionality. An analysis using CO-TPD might yield conclusions to a functionality regarding smaller molecules. This might, as well, explain the lacking performance during the 1-octene reaction, as the molecule may be too large to properly penetrate the microporous framework, resulting in catalytic reactions solely occurring on the material surface. A natural consequence is the low amount of coke produced during the reaction.

The reaction of 1-hexene over the Zn-080-calc sample did not show promising results. This, however, is quite probably a direct result of the faulty framework structure and missing micropores, rather than of lacking acid sites. A sample exhibiting higher crystallinity (Zn-085) was not available at the time but is postulated to display an improved catalytic performance. Neither 1-octene nor 1-hexene are bulky molecules but, between the two of

147 6. Catalytic experiments

material temp. weight loss sample amount coke amount K % mg mgg−1 Co-029 296–973 6.93 6.5 3.08 573–973 2.87 V-025 296–973 6.68 6.2 3.19 573–973 2.98 Zn-080 296–973 0.91 6.3 0.63 573–973 0.62 RUB-37 296–973 1.17 8.4 0.32 573–973 0.32

Table 6.2.: Amount of coke as calculated from TG measured weight loss. them, 1-hexene is the smaller and, therefore, favourable in a test reaction. It is suggested to repeat the reaction with a higher crystalline sample and with high crystalline Co and V samples as well.

Again, a test reaction using a Ti sample would have been preferable, as many known titanosilicates are successfully applied in similar reactions. However, a suitable sample was not available at the time.

148 ✼✳ ❙✉♠♠❛② ❛♥❞ ❖✉❧♦♦❦

During the course of this thesis, the purely siliceous hydrous layer silicate (HLS) RUB-36 has been interlayer expanded with different d-transition metal (Me) cations in their respective acetylacetonate (acac) form with the help of hydrochloric acid (HCl) applying short heating exposure of one to three days at a temperature of 423 K to 443 K in a hydrothermal reaction. Successful synthesis and promising catalytic activity of corresponding Fe and Sn materials have already been reported on in current literature [22, 23]. However, using the suggested synthesis procedure on Fe and Sn aided interlayer expansions was not reliably reproducible. Out of the investigated cations Co, Cu, Fe, Ga, Sn, Ti, V and Zn, successful synthesis was observed for the four Me cations Co, Ti, V and Zn for the ﬁrst time. The resulting synthesis products were investigated with regards to crystallographic structure, chemical composition and microporous properties with the aim of catalytic application. The success rates with around 0 % to 25 % of individual syntheses runs presented a challenge. This fact also limited the feasibility of up-scaling for the application in catalysis experiments. Three synthesis runs produced sufﬁcient material for the desired purposes.

Each applied characterisation method yielded an individual puzzle piece to the overall picture of crystallographic structure, chemical content and microporous properties of the investigated Me-IEZ-RUB-36 materials.

To test the success of the post-synthesis interlayer expansion, powder X-ray diffraction (PXRD) is the method of choice, as the shift of the first signal to higher d-values allows for a quick identification in conjunction with the information on the grade of crystallinity. Additionally, layer disorder becomes evident from significant peak broadening not only of the first, but also higher angle signals. Compared to the starting material RUB-36, post- treated materials generally exhibit lower grades of crystallinity, which was to be expected from similarly treated HLS materials. Although synthesis parameters remained fixed for some synthesis runs, the results varied. In addition to a completely amorphous material, intermediate phases were observed that exhibited features of both starting material and desired Me-IEZ product. Most of these intermediate phases displayed a drastically reduced

149 7. Summary and Outlook crystallinity as well as a ﬁrst signal position spanning both the range of the starting material at 7.93° and the product at 8.44°. Some intermediate materials even showed an additional signal at higher angles of around 10.3° merging with the lower angle signal, indicating a high degree of disorder resulting from varying interlayer distances. Nonetheless, the diagrams of the IEZ materials with a high degree of crystallinity still exhibit signiﬁcant peak broadening, especially at a position of 16.33 °2θ, hinting to a comparable stacking disorder for all regarded samples.

The program DIFFaX has been used to simulate different stacking sequences using a convolution of the atomic models of the starting material RUB-36, the structures of COE-3 and COE-4 as well as FER and CDO in conjunction with supergroup-subgroup symmetry considerations for a symmetry reduction from orthorhombic to monoclinic SG. To test the accuracy of the simulation, RUB-36 served as a model. DIFFaX reacts very sensitively to small deviations in the atomic model, thus, ﬁnding an exact model to mimic the measured diagram is an arduous task. A perfect model for the Me-IEZ materials has not been found. However, an attempt for IEZ RUB-36 with Zn with and without the DEDMA molecule represents the most promising model. Still, the deviations are too substantial to account for an accurate starting model.

Atomic models for the Me-IEZ materials have been RIETVELD reﬁned in monoclinic space group (SG) Pm with β-angles of 90° (orthorhombic UC but monoclinic symmetry) with lattice parameters

a0 = 23.875(12) Å, b0 = 14.053(7) Å, c0 = 7.417(4) Å and β = 90.00(5)° for Co-,

a0 = 24.207(59) Å, b0 = 14.002(33) Å, c0 = 7.398(14) Å and β = 89.91(28)° for Ti-,

a0 = 23.782(25) Å, b0 = 14.024(7) Å, c0 = 7.404(4) Å and β = 90.08(9)° for V- and

a0 = 23.782(16) Å, b0 = 14.056(9) Å, c0 = 7.421(4) Å and β = 89.98(4)° for Zn-material.

The four refinement procedures yielded residue values of χ2 = 9.09 for Co, χ2 = 25.9 for Ti, χ2 = 8.46 for V, and χ2 = 5.95 for Zn samples. The Zn model exhibits the best of the four refinements considering a certain degree of layer disorder. Co and V samples display reasonable residue values, however, the model displays potential for improvement. Nonetheless, the refinement for Ti shows the highest disparity of experiment and model and, therefore, the model should definitely be revised as the statistics allow for a better agreement in theory. Using the program FULLPROF, stacking layer disorder is generally not considered. Hence, a very good fit between model and experiment with desired χ2 values

150 of below 3 is mathematically not achievable, if physically sensible.

Scanning electron microscopy (SEM) analyses enabled the collection of information regarding morphology, retained crystallography and success of post-synthesis alteration. While a favourable alteration is marked by a change in morphology from pseudo-hexagonal plates to a more octagonal crystallite shape with smoothed edges, eroded plates and star- shaped deposits on the surface of individual crystallites hint to a failed modiﬁcation. Be- tween different Me-IEZ materials, a high degree of conformity was observed in successfully altered materials.

Automated electron diffraction tomography (ADT) experiments have been performed on Zn and Ti samples for further structure elucidation. The plate-like crystal shape represents a problem, as the beam tilts out of focus easily. Along a∗, the diffraction patterns exhibit diffuse streaking. The resulting data has been simulated and hints to a strong layer disorder with alternating stacking in FER (I-lattice, ABAB) and CDO (B-lattice, AAAA) type framework topology. Ti material exhibits stacking probabilities AAAA > ABAB & C < 10% and Zn material AAAA < ABAB & C < 10% with C representing approximately every ﬁfth layer being connected via Me cations instead of Si.

The chemical composition and Me content as a means to prove incorporation of cations has been probed by energy-dispersive X-ray spectroscopy (EDX), AAS and inductively coupled plasma (ICP)-atomic absorption spectroscopy (AAS), as well as X-ray ﬂuores- cence (XRF) experiments. Successfully treated materials exhibit Me contents of 0.1 wt% to 0.5 wt%, which are quite sensible in comparison to corresponding literature Fe- and Sn- IEZ-RUB-36 samples.

The determination via energy-dispersive X-ray spectroscopy (EDX) yields an occupation of linking positions of 1.1 % for Co material, 4.4 % for Ti material, 2.2 % for V material and 1.1 % for Zn-IEZ-RUB-36. Chemical compositions have been determined as

Co-IEZ-RUB-36 Si51.95Co0.05O88,

Ti-IEZ-RUB-36 Si51.75Ti0.25O88,

V-IEZ-RUB-36 Si51.88 V0.12O88 and

Zn-IEZ-RUB-36 Si51.82Zn0.18O88.

Ammonia (NH3)-temperature programmed desorption (TPD) experiments have been conducted in order to examine the number of acid sites in the microporous framework

151 7. Summary and Outlook concerning the suitability for catalytic application. The three investigated samples display very low activity in comparison with a commercial ZSM-5 catalyst material. The lowest activity is found in the V-025 sample, closely followed by Zn-080. Co-029 displays the highest number of acid sites. Still, a commercial sample demonstrates a higher activity by a factor of 30 in comparison with the examined samples. As a means to estimate catalytic activity of the considered materials, this result is problematic. The synthesised materials are purely siliceous with only the Me cations as possible acid sites since no Al is part of the framework structure. Even though the quantity of Me is low, the limited amount present would be sufﬁcient for satisfactory catalytic activity provided a free access of micropores and a small particle size. This is, for example, the case in commercial catalyst TS-1, in which only one Ti position is located in each UC and at every fourth channel intersection, but still ensures an excellent performance in the epoxidation reaction.

The conservation of the microporous character of the samples is tested by nitrogen gas

(N2) adsorption. While the Zn-080 sample exhibits no micro- or mesopores whatsoever, Co-029-calc, Ti-001, V-025-calc and Zn-085 display adsorption behaviour indicative of mesopores. However, the four latter materials show a degree of disorder with pore size and shape not well deﬁned. These results conﬁrm the information gathered by NH3-TPD. As the framework of these samples is lacking in terms of ordered stacking, a penetration of molecules for catalytic processes might be hindered. Still, compared to commercial catalyst TS-1, the investigated samples exhibit sensible values for surface area, pore volume and average pore diameter. Consequently, the samples display promising pore properties for catalytic activity and mark accessible free volume between the IEZ and Me-linked layers.

Stability upon calcination has been conﬁrmed by thermal analyses (TA) (differential thermal analysis (DTA) and thermal gravimetry (TG)) experiments. The calcination of starting material RUB-36 occurs according to literature ﬁndings for reference. The Zn-080 sample looses more than half of its initial weight, hinting to a strong generation of layer and framework disorder, whereas the Co-029 and V-025 samples, on the other hand, display a reasonable thermal behaviour and stability considering the condensation of terminal silanol groups of neighbouring layers and the expulsion of organic species from the DEDMA cation.

Nuclear magnetic resonance (NMR) spectroscopy served the purpose of verifying connectivity of Si positions as well as the detection of terminal and defect silanol/siloxy groups and the preservation of organic species stemming from the starting material RUB-36.

152 These informations disclose facts about the short-range framework configuration as well as the presence of extra framework positions (EFPs). Successfully post-treated materials exhibit comparable NMR diagrams of 1H, 13C and 29Si. 13C measurements display all three organic components of the structure directing agent (SDA) DEDMA, albeit with a very low intensity which marks a conservation of the SDA or organic degradation products to a small degree in all as-made materials. In each measured 29Si spectra, the three Q-notated signal intensities of Q2,Q3 and Q4 are observable. The signal intensities for RUB-36 starting material span only Q3 and Q4 signals, as individual layers are interrupted by terminal silanol/siloxy groups (three-connected Si). As anticipated, the Q4 signal exhibits the highest intensity in each material, as the main part of the framework is build by four-connected Si. All linking Si positions are exclusively represented by Q2 and Q3 type signals. The occurrence of a Q2 signal signifies the connection of neighbouring layers via Si which has already been expected by the low amount of Me (ca. 1 % to 4 %) established by EDX, AAS, ICP- AAS and XRF, however, to a very small degree. Q3 type signals, on the other hand, do not just contain information on three-connected Si, but also facts about four-connected Si that are bound to three other Si and one Me. Analysis via 1H NMR yields insight to the degree of condensation and the presence of residue organic species which all materials reliably displayed. The Zn-080 sample exhibits a high amount of organic species as well as silanol type defects and terminal silanol groups characteristic of interrupted layers. The presence of water is observed by strong signals, especially for the Ti-001 and Zn-085 sample, whereas Co and V samples exhibit no signal on the corresponding position. The presence of defect sites in the form of silanol type defects (indicative of strong hydrogen bonds) is confirmed in all materials to a very small degree.

Application of FOURIER-transform infrared (FTIR) is conducted as a means to determine the presence of organic residue from the SDA DEDMA and to establish information on the short-range order of the framework in the form of organic or inorganic components as well as preservance of fer-type layers. The spectra of all samples conﬁrm the presence of the organic species stemming from the organic cation, as already postulated by NMR exper- −1 iments. Characteristic [SiO4] framework bands are observable similarly. The 950 cm to 960 cm−1 stretching vibration indicates either a substitution of Me heteroatoms other than Si or the stretching vibration of terminal Si–OH groups. An assignment of the broad absorption band with a maximum at around 3200 cm−1 is conducted for a complex hydrogen bonding system consisting of water molecules and terminal silanol groups of the silicate layer. These observations lead to the conclusion that the initial fer-layer is well preserved in the post-treated materials.

153 7. Summary and Outlook

During ultraviolet (UV)-visible (vis) spectroscopy, insight is gained into the Me cation coordination in the siliceous framework. The assignment of a fourfold connection (tetrahedral (Td)) for the Ti cation in the Ti samples is straightforward, whereas the situation becomes more complex for the other samples. Co samples displayed a similar Td environment for Co species with some ambiguous signals. The UV-vis spectra of V is the most complicated case, as V may take many different coordination states. Isolated [VO4] tetrahedra are postulated in conjunction with clear signs for a distorted tetragonal environment. Still, a Td situation is encountered for V species as well. As neither Zn sample exhibits a spectrum similar to that of ZnO, the Zn positions in their respective materials were proposed to occupy a different environment. An unambiguous assignment to tetrahedral (Td) or octahedral (Oh) was not feasible besides the assurance of incorporation of Zn into the bulk of the framework.

The three by NH3-TPD examined samples have been tested for catalytic activity by 1-octene cracking/isomerisation reaction. All three materials performed below the expectations in the applied test reactions.

Only three synthesis runs produced sufﬁcient material for the desired purposes and one of those samples (Zn-080) exhibited both limited crystallinity and no microporosity. The other two samples (Co-029 and V-025) lacked the properties for catalytic activity in the tested reactions. This fact is most likely owed due to the absence of acid sites and the hindered accessibility of micropores, respectively. The inadequacy can not be reliably proven in a complete fashion, as the chosen sample reactions may not be suited for the regarded material, and the deployed molecules might merely be too large or bulky to penetrate the catalyst framework structure. Out of the examined samples, Co-029 displayed the highest amount of acid sites and, consequently, the highest catalytic activity.

Only the faulty Zn-080 sample has been tested in 1-hexene epoxidation. The performance remained, similarly, well below the performance of commercial catalysts. Future test reactions should include higher crystalline Zn-samples (085) as well as a Ti sample, as Ti-containing zeolites are of particular use in epoxidation reactions.

The individual value of a single experimental result is very low, as only one aspect of the investigated materials is illuminated by each analysis method. While studies via PXRD deﬁne the overall degree of crystallinity, long-range order of the framework and layer stack-

154 ing disorder, spectroscopy techniques such as FTIR and NMR enable the gathering of information on the short-range order and conditions on a small scale as small molecule clusters and individual bond distances are highlighted. Similarly, EDX and XRF analyses provide speciﬁcations on the bulk chemical composition, whereas AAS and ICP-AAS yield exact data of individual chemical components. ADT analyses also deliver facts on the crystallographic structure to a high detail. Nonetheless, this technique focuses on only one particle at a time, neglecting the bulk of the material which is highly problematic in an in- homogeneous sample. DIFFaX simulations in conjunction with simulations from the ADT measurements yield data for a better understanding of the layer stacking and its stacking disorder. TA serve the purpose of conﬁrming stability upon calcination, while N2 sorption experiments and NH3-TPD dispense a measure of porosity and number of catalytically active sites.

The complementarity of the experimental investigations is a key factor for a good estimation of a crystallographic model and description. Unfortunately, there is no "quick- and-dirty" approach of a single technique to gain a reliable crystal model, at least not for a structure within this level of complexity. Hence, a broad spectrum investigation is paramount. Previous considerations on the material, its properties and the desired application are of great importance as they will prevent the employment of time-consuming useless investigations. And still, some experiments may turn out to appear unproductive (1-octene cracking of sample materials), but even here, information is gathered as to which property a certain material does not possess.

Microporous crystalline materials with a complex structure exhibiting characteristics of multi-dimensional disorder such as the ones investigated in this work must be contemplated from many different angles and with a myriad of applicable analysis procedures. Only a combination of these complementary techniques ensures the optimum description of an unknown material with a high degree of accuracy. Still, the complexity and the presence of disorder lead, in many cases, only to an approximation of the true structure rather than an exact model. Even the limitation of the experimental parameters to the knowledge of the basic building blocks (fer-type layer, RUB-36 starting material, etc.) and the overall chemical content (purely siliceous, Me cations Co, Ti, V, Zn, etc.) can only lead so far. This holds as well, and maybe especially, for the hydrothermal synthesis and post-synthesis alteration which are regarded more as a "black box" than an exact science. Applying the same synthesis route without a (conscious) change of synthesis parameters resulted in the generation of different materials with a small percentage of sufﬁciently crystalline samples.

155 7. Summary and Outlook

Still, the high importance of the diffraction analysis should be noted at this point. Ulti- mately, no other investigation method serves to illustrate the three-dimensional structure of the contemplated materials. Spectroscopic techniques and sorption analysis can only be regarded from another angle, as they deliver no information on the three-dimensional long-range order of the framework and are somewhat inferior to the diffraction analysis in the context of the scope of this problem. On the other hand, limited crystallinity is taking shape as signal peak broadening in the diffraction diagram which, in turn, leads to difficulties in interpretation and structure determination. The diffraction diagram is not as pronounced and resolved as it would be in a "perfect" crystal and, thus, does not supply sufficient data to deduce an unambiguous crystallographic model. Consequently, a concrete idea regarding a model is necessary beforehand, which is done in the convolution of known models of starting material and other related structures, such as successfully interlayer expanded and topotactically condensed zeolites structures. The question as to why the diffraction method is applied if it is not serving to unambiguously identify the chemical structure, as it does in many other cases, is simple. There is no other approach powerful enough to deliver univocal information. The complexity of the material necessitates the combination of the available analysis methods. The complementarity is essential for the understanding of the novel material as each applied method has its own limitations. Nevertheless, the utilised methods served to successfully and productively deliver data on the regarded materials that resulted in satisfactory solutions. The investigated materials exhibit a high degree of conformity with a few small exceptions. Successful syntheses runs have been observed for Me cations Co, Ti, V and Zn. However, reports in recent literature have listed fruitful application of the Me interlayer expansion process to Fe and Sn. As a synthesis specification with a high success rate has not been found, even for the successfully synthesised materials, it is prudent to assume that the creation of Me-IEZ-RUB-36 is extendible to any Me cation and even to other HLSs, provided the appropriate synthesis conditions are specified. The synthesis runs with 0 % success rate may, then, be only lacking in terms of correct and stable synthesis parameters rather than an impossibility of formation. Thus, a generalisation of the reaction and synthesis principle is successfully postulated. This leads to the conclusion that the procedure does not represent an isolated case but can be regarded as a general principle, whose individual experimental parameters require some adjustments.

Compared to literature ﬁndings, the catalytic activity and number of acid sites as measured by NH3-TPD was found to be impaired for the three tested samples, whereas the Zn

156 sample exhibited limited crystallinity compared to later synthesised samples. Nonetheless, similar materials reported on have been tested using CO-TPD, H2O- and Argon-sorption, alkylation and acylation reactions of bulky molecules as well as FTIR spectroscopy with pyridine and acetonitrile as probe molecules to monitor the presence of LEWIS and BRØN- STEDT acidity. Thus, the analysis of microporous functionality is not exhaustively completed for the presented materials and leaves room for future considerations.

An interesting feature is hypothesised by the extension to an incorporation of a combination of various Me cations for the optimisation of functionality. The successfully synthesised Ti sample showed great potential as a microporous material, however, a suitable amount of sample was not available at the time of NH3-TPD analysis, as well as catalysis test reactions. Therefore, future work will emphasise on the further analysis of this material and its applicability as catalyst material, with a focus on epoxidation reactions.

157

❆♣♣❡♥❞✐①

❆✳ ▲✐ ♦❢ ❋✐❣✉❡

1.1. Concept and aim of this work...... 1

2.1. First mention of zeolites by AXEL FREDRIK CRONSTEDT...... 9 2.2. Graphical representation of FER framework type in a projection along ~c. . . . 11 2.3. Schematic representation of different types of shape-selectivity in zeolites. . 16 2.4. Acid sites important in zeolites...... 19 2.5. Post-synthesis modiﬁcations of layered zeolite precursor RUB-36...... 24 2.6. Materials derived from layered zeolite precursor RUB-36...... 25

3.1. Common SBUs identiﬁable in zeolite frameworks...... 32 3.2. Building scheme for different zeolites...... 33 3.3. Materials and synthesis procedure for RUB-36...... 35 3.4. Teﬂon container and stainless steel autoclave for the hydrothermal synthesis. 36 3.5. Materials and synthesis process for the interlayer expansion of RUB-36. . . . 37 3.6. Materials and synthesis process for the Me interlayer expansion of RUB-36. . 37 3.7. PXRD diagrams of samples RUB-36 and Zn-082 to Zn-087...... 39

4.1. SEM picture and photograph of FERRIERITE...... 44 4.2. [5 1] SBU and [5 4] PerBU...... 48 ~ 4.3. fer-type layer viewed along ~c axis, along b axis and along ~a axis...... 49 4.4. Scheme of the possible stacking procedures of the fer-type layer...... 50 ~ 4.5. As-made RUB-36 viewed along b-axis and along ~c-axis...... 52 4.6. Sheets of fer stacked to create CDO and FER-type framework...... 54 4.7. Schematic crystal structures illustrating the σ fault models...... 55 4.8. PXRD diagrams of DIFFaX calculated series between CDO and FER...... 57 4.9. Exemplary faulted sequence of CDO and FER type stacking...... 58

5.1. General information content of a PXRD pattern...... 61

159 Appendix

5.2. Visualisation of the BRAGG equation...... 63 5.3. Different types of PXRD set-ups...... 64 5.4. Sample holder for PXRD experiments...... 69 5.5. PXRD diagrams of as-made RUB-36 and Me-IEZ-RUB-36 samples...... 70 5.6. PXRD diagrams of as-made and simulated RUB-36...... 71 5.7. Visualisation of RIETVELD refinement for as-made RUB-36...... 72 5.8. Different simulation approaches for Zn-IEZ-RUB-36 generated with DIFFaX. 75 5.9. Visualisation of RIETVELD refinement for as-made Co-IEZ-RUB-36...... 77 5.10. Visualisation of RIETVELD refinement for as-made Ti-IEZ-RUB-36...... 77 5.11. Visualisation of RIETVELD refinement for as-made V-IEZ-RUB-36...... 78 5.12. Visualisation of RIETVELD refinement for as-made Zn-IEZ-RUB-36...... 78 5.13. Structure plot of sample materials...... 80 5.14. SEM sample holder and SEM pictures of sample materials...... 84 5.15. SEM pictures of unsuccessfully post-treated sample materials...... 85 5.16. ADT graphical representation of reciprocal space of Ti-IEZ-RUB-36...... 88 5.17. ADT graphical projection of reciprocal space of Zn-IEZ-RUB-36...... 89 5.18. Three different stacking variations...... 89 5.19. ADT simulation and record for Ti and Zn material...... 90

5.20. NH3-TPD of sample materials and commercial ZSM-5...... 98 5.21. IUPAC classiﬁcation of adsorption isotherms and hysteresis loops...... 101

5.22. N2 sorption experiments on sample materials Zn-080 and Zn-080-calc. . . . 101

5.23. N2 sorption experiments on sample material Zn-080-calc...... 102

5.24. N2 sorption experiments on Co-029-calc, Ti-001, V-025-calc and Zn-085. . . 103 5.25. DTA and TG analyses of Co-029, V-025, Zn-080 and RUB-36...... 106 5.26. Q-notation of the different Si connectivities and DMFit modelling of Zn-085. 110 5.27. 29Si MAS spectra of Me-IEZ-materials...... 116 5.28. 13C CP MAS spectra of Me-IEZ-materials...... 119 5.29. 1H MAS spectra of Me-IEZ-materials...... 120 5.30. FTIR spectra of RUB-36 and Me-IEZ materials...... 126 5.31. UV-vis spectra of Me-IEZ materials...... 131

6.1. Chemical structure of a generic epoxide...... 136 6.2. Chemical structure of peroxy acid and carboxylic acid...... 137 6.3. Generalised epoxidation equation with transition state...... 137 6.4. Epoxidation of 1-hexene reaction...... 138 6.5. Schematic overview of catalytic cracking of petroleum hydrocarbons. . . . . 142

160 A. List of Figures

6.6. The compacting equipment and sieves for catalyst preparation...... 143 6.7. Reactor with Zn-080-calc before and after 1-octene reaction...... 144 6.8. Experimental set-up of 1-octene reaction...... 145 6.9. Conversion of 1-octene, selectivity of light oleﬁns and 1-octene isomers. . . . 145 6.10. PXRD diagrams before and after the 1-octene reaction...... 147

161 Appendix

❇✳ ▲✐ ♦❢ ❚❛❜❧❡

3.1. Synthesis conditions and starting chemicals of RUB-36...... 35 3.2. Synthesis conditions and starting chemicals of Me-IEZ-RUB-36...... 38

4.1. Most important properties of framework type FER...... 46 4.2. Classiﬁcation of SBUs with exemplary materials...... 47 4.3. SDAs and layer type fer...... 48 4.4. Most important properties of framework type CDO...... 51

5.1. PXRD experimental conditions and crystallographic data for Me-IEZ-RUB-36. 79 5.2. Atom content as determined by EDX analyses...... 85 5.3. BRAVAIS lattice of different Me-IEZ-RUB-36 materials...... 87 5.4. Me content as determined by ICP-AAS analyses...... 92 5.5. Me content as determined by AAS analyses...... 93 5.6. Me content as determined by XRF analyses...... 95

5.7. Sample preparation for NH3-TPD experiments...... 97

5.8. Results from N2 sorption experiments...... 104 5.9. Initial weight and weight loss during TG/DTA experiments...... 108 5.10. Experimental NMR conditions...... 114 5.11. 29Si CP MAS integrated relative signal intensities for IEZ materials...... 117

6.1. Results of the epoxidation reaction of 1-hexene with Zn-080...... 139 6.2. Amount of coke as calculated from TG measured weight loss...... 148

7.1. Synthesis protocol...... 170 7.2. Atomic positions for Co-IEZ-RUB as derived from RIETVELD analysis. . . . . 173 7.3. Atomic positions for Ti-IEZ-RUB as derived from RIETVELD analysis...... 176 7.4. Atomic positions for V-IEZ-RUB as derived from RIETVELD analysis...... 179 7.5. Atomic positions for Zn-IEZ-RUB as derived from RIETVELD analysis. . . . . 182

162 C. List of crystallographic symbols

❈✳ ▲✐ ♦❢ ❝②❛❧❧♦❣❛♣❤✐❝ ②♠❜♦❧

Symbols Meanings ~ ~a,b,~c crystallographic axes ∗ ~∗ ∗ ~a ,b ,~c reciprocal crystallographic axes |~a| = a0 ~ b = b0  ~  ¯|c¯| = c0  ¯ ¯ ~  lattice parameters α¯ =¯ b ∧~c   β = ~a ∧~c ~ ~  γ = a ∧ b   θ  angle of diffraction  λ radiation wavelength Å Ångström = 10 – 10 m ø diameter ∼ average, roughly V volume of the UC [u v w] indices denoting a direction in the direct lattice [101] Example for [u v w] 〈u v w〉 indices denoting a set of directions in the direct lattice 〈101〉 Example for 〈u v w〉 (h k l) Miller indices describing a single plane (101) Example for (h k l) {h k l} Miller indices describing a set of all planes that are equivalent to (h k l) {101} Example for {h k l}

163 Appendix

❉✳ ❉❡❛✐❧❡❞ ❙②♥❤❡✐ ♣♦♦❝♦❧

The detailed synthesis protocol includes all synthesised materials during the course of this work and is listed by corresponding Me cation rather than chronologically. Successful syntheses are marked by X, whereas unsuccessful syntheses are indicated by ×.A X in brackets hints to an ambiguous outcome. Three samples have been indicated by an additional to mark samples stemming from syntheses that yielded sufﬁcient material for catalyticL experiments. A full sample denotation would be AB-Me-IEZ-RUB-36-XXX, with AB as initials for the scientist that prepared the material, Me for the corresponding cation and XXX as the consecutive number in this synthesis route. For convenience, the sample notation is shortened to the cation and the number, as everything else remains the same or is of no importance for the understanding of the work.

cation notation RUB-36 acac H2O HCl time temp. success g g ml ml d K Co Co-001 0.2041 0.1489 0.8 0.05 1 433 × Co Co-002 0.2070 0.1153 0.8 0.05 1 433 × Co Co-003 0.2075 0.1155 0.8 0.05 1 433 × Co Co-004 0.2078 0.1150 0.4 0.40 1 433 X Co Co-005 0.2053 0.1155 0.5 0.30 1 433 × Co Co-006 0.2073 0.1151 0.6 0.20 1 433 × Co Co-007 0.2061 0.1155 0.7 0.10 1 433 × Co Co-008 0.2077 0.1164 0.4 0.40 1 433 × Co Co-009 0.2077 0.1172 0.5 0.30 1 433 × Co Co-010 0.2074 0.1161 0.6 0.20 1 433 × Co Co-011 0.2086 0.1165 0.7 0.10 1 433 × Co Co-012 0.2090 0.1147 0.4 0.40 1 433 × Co Co-013 0.2095 0.1159 0.5 0.30 1 433 × Co Co-014 0.2071 0.1161 0.6 0.20 1 433 × Co Co-015 0.2079 0.1168 0.7 0.10 1 433 × Co Co-016 0.2071 0.1150 0.4 0.40 1 433 × Co Co-017 0.2086 0.1155 0.4 0.40 1 433 × Co Co-018 0.2068 0.1163 0.4 0.40 1 433 × Co Co-019 0.2084 0.1150 0.4 0.40 1 433 X Co Co-020 0.2071 0.1146 0.4 0.40 1 433 × Co Co-021 0.2073 0.1179 0.4 0.40 1 433 × Continued on next page

164 D. Detailed Synthesis protocol

Table 7.1 – Continued from previous page cation notation RUB-36 acac H2O HCl time temp. success g g ml ml d K Co Co-022 0.2070 0.1165 0.4 0.40 1 433 × Co Co-023 0.2081 0.1167 0.4 0.40 1 433 × Co Co-024 0.2073 0.1517 0.4 0.40 1 433 × Co Co-025 0.2071 0.1545 0.4 0.40 1 433 × Co Co-026 0.2070 0.1515 0.4 0.40 1 433 × Co Co-027 0.2068 0.1530 0.4 0.40 1 433 × Co Co-028 1.0354 0.5771 0.2 0.20 1 433 × Co Co-029 1.0371 0.5759 0.4 0.40 2 433 X X Co Co-030 0.6214 0.3479 1.2 1.20 1 433 L Co Co-031 0.6209 0.3480 1.2 1.20 1 433 X Co Co-032 0.6249 0.3459 1.2 1.20 1 433 × Co Co-033 0.6233 0.3457 1.2 1.20 1 433 × Cu Cu-001 0.2000 0.2001 0.8 0.05 3 423 × Cu Cu-002 0.2011 0.1989 0.8 0.00 3 423 × Cu Cu-003 0.2001 0.1006 0.8 0.05 3 433 × Cu Cu-004 0.1999 0.0991 0.8 0.00 3 433 × Cu Cu-005 0.2000 0.1008 0.8 0.05 3 443 × Cu Cu-006 0.2001 0.0994 0.8 0.00 3 443 × Fe Fe-001 0.2013 0.1004 0.8 0.00 2 433 × Fe Fe-002 0.1008 0.0527 0.4 0.00 2 433 × Fe Fe-003 0.2010 0.1014 0.8 0.00 2 433 × Fe Fe-004 0.2010 0.1015 0.8 0.00 2 433 × Fe Fe-005 0.2018 0.1015 0.8 0.00 2 433 × Fe Fe-006 0.2043 0.1014 0.8 0.00 2 433 × Fe Fe-007 0.2017 0.1071 0.8 0.00 2 433 × Fe Fe-008 0.2027 0.1212 0.8 0.00 2 433 × Fe Fe-009 0.2095 0.1521 0.8 0.05 2 433 × Fe Fe-010 0.1957 0.0682 0.8 0.00 2 433 × Ga Ga-001 0.2009 0.0700 0.8 0.05 1 423 × Ga Ga-002 0.2014 0.0697 0.8 0.00 1 423 (X) Ga Ga-003 0.2000 0.0695 0.8 0.05 1 433 (X) Ga Ga-004 0.2016 0.0711 0.8 0.00 1 433 × Continued on next page

165 Appendix

Table 7.1 – Continued from previous page

cation notation RUB-36 acac H2O HCl time temp. success g g ml ml d K Ga Ga-005 0.2018 0.0720 0.8 0.05 1 443 × Ga Ga-006 0.2012 0.0697 0.8 0.00 1 443 × Ga Ga-007 0.2008 0.0700 0.8 0.05 2 423 (X) Ga Ga-008 0.2008 0.0699 0.8 0.00 2 423 × Ga Ga-009 0.2009 0.0699 0.8 0.05 2 433 × Ga Ga-010 0.2003 0.0710 0.8 0.00 2 433 × Ga Ga-011 0.2008 0.0720 0.8 0.05 2 443 × Ga Ga-012 0.2003 0.0696 0.8 0.00 2 443 × Ga Ga-013 0.2002 0.0708 0.8 0.05 3 423 × Ga Ga-014 0.2003 0.0698 0.8 0.00 3 423 × Ga Ga-015 0.2005 0.0699 0.8 0.05 3 433 × Ga Ga-016 0.2004 0.0699 0.8 0.00 3 433 (X) Ga Ga-017 0.2008 0.0712 0.8 0.05 3 443 × Ga Ga-018 0.2014 0.0713 0.8 0.00 3 443 (X) Sn Sn-001 0.1911 0.1669 1.4 0.05 2 433 × Sn Sn-002 0.2208 0.1607 1.4 0.05 2 433 × Ti Ti-001 0.6029 0.3991 2.7 0.05 1 433 X Ti Ti-002 0.6073 0.4036 2.7 0.05 1 433 × Ti Ti-003 0.6004 0.3949 2.7 0.05 1 433 × Ti Ti-004 0.6078 0.3985 2.7 0.05 1 433 × V V-001 0.2016 0.1498 0.8 0.05 2 433 × V V-002 0.2000 0.1530 0.8 0.05 2 433 × V V-003 0.2008 0.1519 0.8 0.05 2 433 × V V-004 0.1998 0.1524 0.4 0.40 2 433 × V V-005 0.1999 0.1535 0.5 0.30 2 433 × V V-006 0.2000 0.1550 0.6 0.20 2 433 × V V-007 0.2005 0.1509 0.7 0.10 2 433 X V V-008 0.1998 0.1520 0.4 0.40 2 433 × V V-009 0.2004 0.1514 0.4 0.40 2 433 × V V-010 0.2000 0.1517 0.4 0.40 2 433 X V V-011 0.2015 0.1510 0.4 0.40 2 433 × V V-012 0.2001 0.1515 0.4 0.40 2 433 × Continued on next page

166 D. Detailed Synthesis protocol

Table 7.1 – Continued from previous page cation notation RUB-36 acac H2O HCl time temp. success g g ml ml d K V V-013 0.2009 0.1517 0.4 0.40 2 433 × V V-014 0.2002 0.1510 0.4 0.40 2 433 × V V-015 0.2009 0.1513 0.4 0.40 2 433 × V V-016 0.2005 0.1512 0.4 0.40 2 433 × V V-017 0.2007 0.1512 0.4 0.40 2 433 × V V-018 0.2004 0.1510 0.4 0.40 2 433 × V V-019 0.2001 0.1519 0.4 0.40 2 433 × V V-020 1.0015 0.7570 2.0 2.00 2 433 × V V-021 0.2001 0.1516 0.4 0.40 2 433 × V V-022 0.2004 0.1513 0.4 0.40 2 433 × V V-023 0.2007 0.1519 0.4 0.40 2 433 × V V-024 0.2008 0.1516 0.4 0.40 2 433 × V V-025 1.0005 0.7550 2.0 2.00 2 433 X V V-026 0.2004 0.1511 0.4 0.40 2 433 L× V V-027 0.2015 0.1514 0.4 0.40 2 433 × V V-028 0.2004 0.1520 0.4 0.40 2 433 X V V-029 0.2006 0.1533 0.4 0.40 2 433 × V V-030 1.0008 0.7569 0.4 0.40 2 433 X V V-031 0.6090 0.4555 1.2 1.20 2 433 × V V-032 0.5982 0.4496 1.2 1.20 2 433 × V V-033 0.5943 0.4596 1.2 1.20 2 433 × V V-034 0.6003 0.4544 1.2 1.20 2 433 × Zn Zn-001 0.2050 0.1160 0.5 0.05 2 433 × Zn Zn-002 0.2021 0.1146 0.8 0.05 2 433 × Zn Zn-003 0.2006 0.1399 0.8 0.05 2 433 × Zn Zn-004 0.2033 0.1127 0.8 0.05 2 433 × Zn Zn-005 0.2052 0.1109 0.8 0.05 2 433 × Zn Zn-006 0.2007 0.1155 0.4 0.40 2 433 × Zn Zn-007 0.1861 0.1145 0.4 0.40 2 433 × Zn Zn-008 0.1848 0.1195 0.4 0.40 2 433 × Zn Zn-009 0.1847 0.1190 0.4 0.40 2 433 X Zn Zn-010 0.2032 0.1266 0.4 0.40 2 433 (X) Continued on next page

167 Appendix

Table 7.1 – Continued from previous page

cation notation RUB-36 acac H2O HCl time temp. success g g ml ml d K Zn Zn-011 0.2027 0.1162 0.4 0.40 2 433 (X) Zn Zn-012 0.1842 0.1213 0.4 0.40 3 433 × Zn Zn-013 0.1848 0.1237 0.2 0.60 3 433 × Zn Zn-014 0.2023 0.1193 0.4 0.40 3 433 × Zn Zn-015 0.2023 0.1175 0.2 0.60 3 433 × Zn Zn-016 0.1841 0.1141 0.4 0.40 2 433 × Zn Zn-017 0.1840 0.1152 0.4 0.40 2 433 × Zn Zn-018 0.2020 0.1155 0.4 0.40 2 433 × Zn Zn-019 0.2016 0.1154 0.4 0.40 2 433 × Zn Zn-020 0.1844 0.1151 0.4 0.40 2 433 × Zn Zn-021 0.1843 0.1163 0.4 0.40 2 433 × Zn Zn-022 0.2010 0.1132 0.4 0.40 2 433 × Zn Zn-023 0.2053 0.1205 0.4 0.40 2 433 × Zn Zn-024 0.2014 0.1162 0.4 0.40 2 433 × Zn Zn-025 0.2045 0.1198 0.4 0.40 2 433 X Zn Zn-026 0.1841 0.1153 0.4 0.40 2 433 (X) Zn Zn-027 0.1860 0.1148 0.4 0.40 2 433 (X) Zn Zn-028 0.2011 0.1174 0.4 0.40 2 433 × Zn Zn-029 0.2025 0.1191 0.4 0.40 2 433 × Zn Zn-030 0.1850 0.1148 0.4 0.40 2 433 × Zn Zn-031 0.1849 0.1155 0.4 0.40 2 433 × Zn Zn-032 0.2035 0.1164 0.4 0.40 2 433 × Zn Zn-033 0.2021 0.1160 0.4 0.40 2 433 × Zn Zn-034 0.1856 0.1144 0.4 0.40 2 433 × Zn Zn-035 0.1844 0.1151 0.4 0.40 2 433 × Zn Zn-036 0.2042 0.1141 0.4 0.40 2 433 × Zn Zn-037 0.2013 0.1198 0.4 0.40 2 433 × Zn Zn-038 0.1841 0.1158 0.4 0.40 2 433 × Zn Zn-039 0.1843 0.1136 0.4 0.40 2 433 × Zn Zn-040 0.2003 0.1167 0.4 0.40 2 433 × Zn Zn-041 0.2042 0.1159 0.4 0.40 2 433 (X) Zn Zn-042 0.1833 0.1139 0.4 0.40 2 433 × Continued on next page

168 D. Detailed Synthesis protocol

Table 7.1 – Continued from previous page cation notation RUB-36 acac H2O HCl time temp. success g g ml ml d K Zn Zn-043 0.1848 0.1147 0.4 0.40 2 433 X Zn Zn-044 0.2012 0.1176 0.4 0.40 2 433 (X) Zn Zn-045 0.2024 0.1163 0.5 0.30 2 433 × Zn Zn-046 0.2024 0.1150 0.6 0.20 2 433 × Zn Zn-047 0.2038 0.1150 0.7 0.10 2 433 × Zn Zn-048 0.1853 0.1145 0.4 0.40 2 433 × Zn Zn-049 0.1869 0.1151 0.5 0.30 2 433 X Zn Zn-050 0.1845 0.1138 0.6 0.20 2 433 X Zn Zn-051 0.1857 0.1147 0.7 0.10 2 433 × Zn Zn-052 0.2023 0.1156 0.4 0.40 2 433 × Zn Zn-053 0.2021 0.1157 0.4 0.40 2 433 × Zn Zn-054 0.1843 0.1162 0.4 0.40 2 433 × Zn Zn-055 0.1880 0.1145 0.4 0.40 2 433 × Zn Zn-056 0.2018 0.1147 0.4 0.40 2 433 × Zn Zn-057 0.2020 0.1158 0.4 0.40 2 433 × Zn Zn-058 0.1844 0.1139 0.4 0.40 2 433 × Zn Zn-059 0.1856 0.1199 0.4 0.40 2 433 × Zn Zn-060 0.2022 0.1152 0.4 0.40 2 433 × Zn Zn-061 0.2035 0.1176 0.4 0.40 2 433 × Zn Zn-062 0.2061 0.1161 0.4 0.40 2 433 × Zn Zn-063 0.2041 0.1199 0.4 0.40 2 433 × Zn Zn-064 0.1887 0.1195 0.4 0.40 2 433 × Zn Zn-065 0.1869 0.1164 0.4 0.40 2 433 × Zn Zn-066 0.1851 0.1142 0.4 0.40 2 433 × Zn Zn-067 0.1849 0.1153 0.4 0.40 2 433 × Zn Zn-068 0.2011 0.1348 0.4 0.40 2 433 × Zn Zn-069 0.2012 0.1145 0.4 0.40 2 433 × Zn Zn-070 0.2019 0.1140 0.4 0.40 2 433 × Zn Zn-071 0.2012 0.1153 0.4 0.40 2 433 X Zn Zn-072 0.1840 0.1165 0.4 0.40 2 433 × Zn Zn-073 0.1854 0.1148 0.4 0.40 2 433 (X) Zn Zn-074 0.1838 0.1145 0.4 0.40 2 433 × Continued on next page

169 Appendix

Table 7.1 – Continued from previous page

cation notation RUB-36 acac H2O HCl time temp. success g g ml ml d K Zn Zn-075 0.1842 0.1151 0.4 0.40 2 433 X Zn Zn-076 0.2007 0.1237 0.4 0.40 2 433 X Zn Zn-077 0.2019 0.1145 0.4 0.40 2 433 X Zn Zn-078 0.1840 0.1157 0.4 0.40 2 433 X Zn Zn-079 0.1844 0.1165 0.4 0.40 2 433 X Zn Zn-080 0.9206 0.5745 2.0 2.00 2 433 X Zn Zn-081 0.9213 0.5709 0.4 0.40 2 433 L× Zn Zn-082 0.5530 0.3401 1.2 1.20 2 433 × Zn Zn-083 0.5686 0.3469 1.2 1.20 2 433 × Zn Zn-084 0.5556 0.3457 1.2 1.20 2 433 × Zn Zn-085 0.5505 0.3468 1.2 1.20 2 433 X Zn Zn-086 0.5509 0.3456 1.2 1.20 2 433 × Zn Zn-087 0.5503 0.3472 1.2 1.20 2 433 × Zn Zn-088 0.5530 0.3427 1.2 1.20 2 433 × Zn Zn-089 0.5527 0.3428 1.2 1.20 2 433 × Zn Zn-090 0.5568 0.3501 1.2 1.20 2 433 × Zn Zn-091 0.5179 0.3422 1.2 1.20 2 433 × Zn Zn-092 0.5579 0.3432 1.2 1.20 2 433 × Zn Zn-093 0.5607 0.3466 1.2 1.20 2 433 × Zn Zn-094 0.5571 0.3410 1.2 1.20 2 433 × Zn Zn-095 0.5560 0.3442 1.2 1.20 2 433 ×

Table 7.1.: Synthesis protocol.

❊✳ ▲✐ ♦❢ ❛♦♠✐❝ ♣♦✐✐♦♥

The atomic positions for each material are given in terms of atom type and label, fractional coordinates x, y, z, as well as isotropic temperature factor Biso, site occupation factor (Occ.) and Multiplicity (Mult.) with respective standard deviations in brackets. If the parameter has not been reﬁned, the standard deviation is 0. Since in all synthesis runs purely siliceous

170 E. List of atomic positions material was produced, only Si and O represent framework atoms. Layer bridging atoms are presented by Co, Ti, V and Zn respectively. EFPs, usually in the form of lone C atoms, are inserted due to encountered residue electron density during RIETVELD reﬁnement and subsequent FOURIER transformation and stem from the organic cation DEDMA from RUB- 36 synthesis or the corresponding acac in post-synthesis treatment.

Co-IEZ-RUB

label type x y z Biso occ. Mult. Si1 Si 0.5607(40) 0.0000(0 ) 0.3975(124) 1.041 0.5(0 ) 1 Si2 Si 0.4333(49) 0.5000(0 ) 0.8787(136) 1.041 0.5(0 ) 1 Si3 Si 0.0876(46) 0.0000(0 ) 0.1332(137) 1.041 0.5(0 ) 1 Si4 Si 0.9774(47) 0.5000(0 ) 0.6283(139) 1.041 0.5(0 ) 1 Si5 Si 0.4631(50) 0.0000(0 ) 0.1129(132) 1.041 0.5(0 ) 1 Si6 Si 0.5350(49) 0.5000(0 ) 0.6008(133) 1.041 0.5(0 ) 1 Si7 Si 0.9830(57) 0.0000(0 ) 0.4188(126) 1.041 0.5(0 ) 1 Si8 Si 0.0739(50) 0.5000(0 ) 0.9199(133) 1.041 0.5(0 ) 1 Si9 Si 0.3735(40) 0.6994(70 ) 0.8772(136) 1.041 1.0(0 ) 2 Si10 Si 0.6313(37) 0.8077(73 ) 0.3818(142) 1.041 1.0(0 ) 2 Si11 Si 0.1697(39) 0.8262(75 ) 0.1177(141) 1.041 1.0(0 ) 2 Si12 Si 0.9129(38) 0.6954(75 ) 0.6190(136) 1.041 1.0(0 ) 2 Si13 Si 0.4856(51) 0.0000(0 ) 0.6990(133) 1.041 0.5(0 ) 1 Si14 Si 0.5206(52) 0.5000(0 ) 0.1832(138) 1.041 0.5(0 ) 1 Si15 Si 1.0111(52) 0.0000(0 ) 0.8219(138) 1.041 0.5(0 ) 1 Si16 Si 0.0718(48) 0.5000(0 ) 0.3426(140) 1.041 0.5(0 ) 1 Si17 Si 0.4395(42) 0.7962(72 ) 0.1890(128) 1.041 1.0(0 ) 2 Si18 Si 0.5530(40) 0.7062(73 ) 0.6916(130) 1.041 1.0(0 ) 2 Si19 Si 0.0982(39) 0.7045(71 ) 0.8313(138) 1.041 1.0(0 ) 2 Si20 Si 0.9921(40) 0.7905(72 ) 0.3171(130) 1.041 1.0(0 ) 2 Si21 Si 0.4414(42) 0.7917(70 ) 0.5903(130) 1.041 1.0(0 ) 2 Si22 Si 0.5548(42) 0.7159(69 ) 0.1042(132) 1.041 1.0(0 ) 2 Si23 Si 0.1126(44) 0.7159(68 ) 0.4085(128) 1.041 1.0(0 ) 2 Si24 Si 0.9794(42) 0.7833(69 ) 0.9140(130) 1.041 1.0(0 ) 2 Co1 Co 0.2974(95) 0.7982(201) 1.1191(337) 41.187 2.0(5 ) 2 Co2 Co 0.7856(70) 0.7931(242) 0.4653(538) 21.624 1.2(4 ) 2 O1 O 0.5469(49) 0.0000(0 ) 0.6047(128) 1.000 0.5(0 ) 1 Continued on next page

171 Appendix

Table 7.2 – Continued from previous page (Co-IEZ-RUB)

label type x y z Biso occ. Mult. O2 O 0.4603(55) 0.5000(0 ) 0.0782(149) 1.000 0.5(0 ) 1 O3 O 0.0702(50) 0.0000(0 ) 0.9225(133) 1.000 0.5(0 ) 1 O4 O 1.0140(59) 0.5000(0 ) 0.4499(172) 1.000 0.5(0 ) 1 O5 O 0.1237(48) 0.9070(62 ) 0.1648(196) 1.000 1.0(0 ) 2 O6 O 0.9448(53) 0.5972(56 ) 0.6549(218) 1.000 1.0(0 ) 2 O7 O 0.5955(50) 0.0953(57 ) 0.3452(208) 1.000 1.0(0 ) 2 O8 O 0.4031(54) 0.4029(56 ) 0.8337(214) 1.000 1.0(0 ) 2 O9 O 0.5079(64) 0.0000(0 ) 0.2701(202) 1.000 0.5(0 ) 1 O10 O 0.4826(62) 0.5000(0 ) 0.7334(202) 1.000 0.5(0 ) 1 O11 O 1.0309(68) 0.0000(0 ) 0.2591(208) 1.000 0.5(0 ) 1 O12 O 0.0206(63) 0.5000(0 ) 0.7952(190) 1.000 0.5(0 ) 1 O13 O 0.1086(55) 0.5940(52 ) 0.8688(242) 1.000 1.0(0 ) 2 O14 O 0.9789(95) 0.9047(52 ) 0.3166(217) 1.000 1.0(0 ) 2 O15 O 0.4262(54) 0.9075(52 ) 0.1462(235) 1.000 1.0(0 ) 2 O16 O 0.5681(53) 0.5936(50 ) 0.6628(234) 1.000 1.0(0 ) 2 O17 O 0.4891(81) 0.0000(0 ) 0.9140(104) 1.000 0.5(0 ) 1 O18 O 0.5130(84) 0.5000(0 ) 0.3978(99 ) 1.000 0.5(0 ) 1 O19 O 1.0140(87) 0.0000(0 ) 0.6092(105) 1.000 0.5(0 ) 1 O20 O 0.0560(79) 0.5000(0 ) 0.1289(95 ) 1.000 0.5(0 ) 1 O21 O 0.3088(44) 0.6979(150) 0.9137(276) 1.000 1.0(0 ) 2 O22 O 0.6958(37) 0.8168(181) 0.4046(366) 1.000 1.0(0 ) 2 O23 O 0.2271(42) 0.8782(111) 0.1052(351) 1.000 1.0(0 ) 2 O24 O 0.8481(43) 0.7006(159) 0.5762(331) 1.000 1.0(0 ) 2 O25 O 0.3850(51) 0.7732(102) 0.7105(184) 1.000 1.0(0 ) 2 O26 O 0.6138(47) 0.7443(107) 0.2063(175) 1.000 1.0(0 ) 2 O27 O 0.1609(51) 0.7583(105) 0.2819(163) 1.000 1.0(0 ) 2 O28 O 0.9249(47) 0.7476(114) 0.8073(155) 1.000 1.0(0 ) 2 O29 O 0.4056(67) 0.7390(111) 0.0439(169) 1.000 1.0(0 ) 2 O30 O 0.5969(65) 0.7573(117) 0.5475(182) 1.000 1.0(0 ) 2 O31 O 0.1400(66) 0.7605(111) 0.9563(187) 1.000 1.0(0 ) 2 O32 O 0.9516(62) 0.7468(122) 0.4682(184) 1.000 1.0(0 ) 2 O33 O 0.1053(64) 0.5991(54 ) 0.3743(242) 1.000 1.0(0 ) 2 O34 O 0.9844(69) 0.9004(53 ) 0.8870(235) 1.000 1.0(0 ) 2 Continued on next page

172 E. List of atomic positions

Table 7.2 – Continued from previous page (Co-IEZ-RUB) label type x y z Biso occ. Mult. O35 O 0.4594(56) 0.9038(60 ) 0.6139(182) 1.000 1.0(0 ) 2 O36 O 0.5471(69) 0.5984(55 ) 0.1319(236) 1.000 1.0(0 ) 2 O37 O 0.4236(65) 0.7720(118) 0.3883(90 ) 1.000 1.0(0 ) 2 O38 O 0.5630(72) 0.7362(111) 0.8915(90 ) 1.000 1.0(0 ) 2 O39 O 0.1190(67) 0.7290(118) 0.6265(91 ) 1.000 1.0(0 ) 2 O40 O 0.9726(92) 0.7547(107) 0.1210(94 ) 1.000 1.0(0 ) 2 O41 O 0.5079(31) 0.7840(96 ) 0.1838(217) 1.000 1.0(0 ) 2 O42 O 0.4862(32) 0.7165(91 ) 0.6592(219) 1.000 1.0(0 ) 2 O43 O 1.0299(31) 0.7209(101) 0.8291(215) 1.000 1.0(0 ) 2 O44 O 0.0583(33) 0.7782(109) 0.3563(273) 1.000 1.0(0 ) 2 EF1 C 0.5856(0 ) 0.0000(0 ) 0.8244(0 ) 7.870 3.3(9 ) 1 EF2 C 0.6876(0 ) 0.5000(0 ) 0.5548(0 ) 41.498 4.4(16) 1 EF3 C 0.1491(0 ) 0.2961(0 ) 0.8073(0 ) 13.686 8.0(15) 2 EF4 C 0.3832(0 ) 0.5000(0 ) 0.4259(0 ) 1.000 2.6(9 ) 1 EF5 C 0.6399(0 ) 0.2342(0 ) 0.3568(0 ) 7.800 5.6(17) 2 EF6 C 0.4101(0 ) 0.0000(0 ) 1.0363(0 ) 2.385 2.1(9 ) 1 EF7 C 0.6403(0 ) 0.2443(0 ) 0.8557(0 ) 0.879 4.2(10) 2 EF8 C 0.8726(0 ) 0.3952(0 ) 0.7418(0 ) 17.960 3.1(13) 2 EF9 C 0.6121(0 ) 0.2019(0 ) 0.2394(0 ) 2.855 3.2(18) 2 EF10 C 0.7454(0 ) 0.0000(0 ) 0.0028(0 ) 13.939 2.3(11) 1 EF11 C 0.2385(0 ) 0.0000(0 ) 0.6586(0 ) 9.463 2.4(10) 1 EF12 C 0.2685(0 ) 0.5000(0 ) 0.9109(0 ) 20.994 2.9(13) 1 EF13 C 0.2755(0 ) 0.4319(0 ) 0.4268(0 ) 13.764 4.8(10) 2

Table 7.2.: Atomic positions for Co-IEZ-RUB as derived from RIETVELD analysis.

173 Appendix

Ti-IEZ-RUB

label type x y z Biso occ. Mult. Si1 Si 0.5629(65 ) 0.0000(0 ) 0.3975(184 ) 1.041 0.5(0 ) 1 Si2 Si 0.4351(65 ) 0.5000(0 ) 0.8757(189 ) 1.041 0.5(0 ) 1 Si3 Si 0.0837(62 ) 0.0000(0 ) 0.1367(190 ) 1.041 0.5(0 ) 1 Si4 Si 0.9756(64 ) 0.5000(0 ) 0.6295(193 ) 1.041 0.5(0 ) 1 Si5 Si 0.4626(67 ) 0.0000(0 ) 0.1150(181 ) 1.041 0.5(0 ) 1 Si6 Si 0.5362(65 ) 0.5000(0 ) 0.6005(185 ) 1.041 0.5(0 ) 1 Si7 Si 0.9828(78 ) 0.0000(0 ) 0.4158(173 ) 1.041 0.5(0 ) 1 Si8 Si 0.0703(68 ) 0.5000(0 ) 0.9266(184 ) 1.041 0.5(0 ) 1 Si9 Si 0.3735(54 ) 0.6949(98 ) 0.8797(188 ) 1.041 1.0(0 ) 2 Si10 Si 0.6339(50 ) 0.8078(104) 0.3841(195 ) 1.041 1.0(0 ) 2 Si11 Si 0.1669(53 ) 0.8274(98 ) 0.1396(194 ) 1.041 1.0(0 ) 2 Si12 Si 0.9115(52 ) 0.6992(105) 0.6151(190 ) 1.041 1.0(0 ) 2 Si13 Si 0.4854(69 ) 0.0000(0 ) 0.6997(185 ) 1.041 0.5(0 ) 1 Si14 Si 0.5193(70 ) 0.5000(0 ) 0.1812(191 ) 1.041 0.5(0 ) 1 Si15 Si 0.0087(71 ) 0.0000(0 ) 0.8246(190 ) 1.041 0.5(0 ) 1 Si16 Si 0.0707(64 ) 0.5000(0 ) 0.3473(194 ) 1.041 0.5(0 ) 1 Si17 Si 0.4408(55 ) 0.7988(99 ) 0.1864(182 ) 1.041 1.0(0 ) 2 Si18 Si 0.5550(54 ) 0.7072(103) 0.6843(183 ) 1.041 1.0(0 ) 2 Si19 Si 0.0998(54 ) 0.7077(101) 0.8481(185 ) 1.041 1.0(0 ) 2 Si20 Si 0.9939(53 ) 0.7906(102) 0.3212(183 ) 1.041 1.0(0 ) 2 Si21 Si 0.4416(57 ) 0.7919(96 ) 0.5950(183 ) 1.041 1.0(0 ) 2 Si22 Si 0.5560(57 ) 0.7162(96 ) 0.1064(183 ) 1.041 1.0(0 ) 2 Si23 Si 0.1128(58 ) 0.7132(95 ) 0.4240(183 ) 1.041 1.0(0 ) 2 Si24 Si 0.9796(58 ) 0.7851(95 ) 0.9208(181 ) 1.041 1.0(0 ) 2 Ti1 Ti 0.2927(135) 0.7924(551) 0.1361(1236) 42.518 1.4(17) 2 Ti2 Ti 0.7855(110) 0.7383(892) 0.3309(2425) 30.320 0.7(16) 2 O1 O 0.5465(65 ) 0.0000(0 ) 0.6087(177 ) 1.000 0.5(0 ) 1 O2 O 0.4609(75 ) 0.5000(0 ) 0.0748(206 ) 1.000 0.5(0 ) 1 O3 O 0.0684(66 ) 0.0000(0 ) 0.9214(183 ) 1.000 0.5(0 ) 1 O4 O 1.0132(76 ) 0.5000(0 ) 0.4526(239 ) 1.000 0.5(0 ) 1 O5 O 0.1198(65 ) 0.9070(88 ) 0.1815(289 ) 1.000 1.0(0 ) 2 O6 O 0.9443(72 ) 0.5984(76 ) 0.6580(299 ) 1.000 1.0(0 ) 2 O7 O 0.5951(67 ) 0.0969(81 ) 0.3469(288 ) 1.000 1.0(0 ) 2 Continued on next page

174 E. List of atomic positions

Table 7.3 – Continued from previous page (Ti-IEZ-RUB) label type x y z Biso occ. Mult. O8 O 0.4044(73 ) 0.4027(77 ) 0.8279(281 ) 1.000 1.0(0 ) 2 O9 O 0.5085(87 ) 0.0000(0 ) 0.2701(284 ) 1.000 0.5(0 ) 1 O10 O 0.4851(82 ) 0.5000(0 ) 0.7354(279 ) 1.000 0.5(0 ) 1 O11 O 0.0294(89 ) 0.0000(0 ) 0.2605(285 ) 1.000 0.5(0 ) 1 O12 O 0.0181(87 ) 0.5000(0 ) 0.7962(265 ) 1.000 0.5(0 ) 1 O13 O 0.1070(73 ) 0.5936(74 ) 0.8865(333 ) 1.000 1.0(0 ) 2 O14 O 0.9832(127) 0.9058(72 ) 0.3124(301 ) 1.000 1.0(0 ) 2 O15 O 0.4253(69 ) 0.9082(71 ) 0.1424(329 ) 1.000 1.0(0 ) 2 O16 O 0.5700(70 ) 0.5931(70 ) 0.6554(330 ) 1.000 1.0(0 ) 2 O17 O 0.4886(110) 0.0000(0 ) 0.9155(143 ) 1.000 0.5(0 ) 1 O18 O 0.5127(111) 0.5000(0 ) 0.3964(137 ) 1.000 0.5(0 ) 1 O19 O 0.0121(122) 0.0000(0 ) 0.6086(147 ) 1.000 0.5(0 ) 1 O20 O 0.0537(104) 0.5000(0 ) 0.1351(131 ) 1.000 0.5(0 ) 1 O21 O 0.3096(55 ) 0.6910(203) 0.9184(428 ) 1.000 1.0(0 ) 2 O22 O 0.6983(49 ) 0.8179(266) 0.4065(520 ) 1.000 1.0(0 ) 2 O23 O 0.2243(59 ) 0.8749(170) 0.1014(507 ) 1.000 1.0(0 ) 2 O24 O 0.8504(59 ) 0.7091(222) 0.5628(469 ) 1.000 1.0(0 ) 2 O25 O 0.3883(68 ) 0.7692(149) 0.7188(249 ) 1.000 1.0(0 ) 2 O26 O 0.6133(63 ) 0.7423(153) 0.2093(241 ) 1.000 1.0(0 ) 2 O27 O 0.1651(63 ) 0.7574(150) 0.3155(238 ) 1.000 1.0(0 ) 2 O28 O 0.9251(65 ) 0.7551(159) 0.8064(213 ) 1.000 1.0(0 ) 2 O29 O 0.4059(91 ) 0.7363(157) 0.0526(239 ) 1.000 1.0(0 ) 2 O30 O 0.5995(85 ) 0.7610(165) 0.5532(249 ) 1.000 1.0(0 ) 2 O31 O 0.1398(89 ) 0.7676(155) 0.9792(251 ) 1.000 1.0(0 ) 2 O32 O 0.9525(81 ) 0.7488(170) 0.4717(252 ) 1.000 1.0(0 ) 2 O33 O 0.1037(87 ) 0.5993(78 ) 0.3849(342 ) 1.000 1.0(0 ) 2 O34 O 0.9829(94 ) 0.9003(74 ) 0.8955(321 ) 1.000 1.0(0 ) 2 O35 O 0.4571(97 ) 0.9029(82 ) 0.6332(312 ) 1.000 1.0(0 ) 2 O36 O 0.5482(94 ) 0.5997(76 ) 0.1302(326 ) 1.000 1.0(0 ) 2 O37 O 0.4217(83 ) 0.7756(170) 0.3883(126 ) 1.000 1.0(0 ) 2 O38 O 0.5651(96 ) 0.7355(156) 0.8915(124 ) 1.000 1.0(0 ) 2 O39 O 0.1209(89 ) 0.7253(171) 0.6412(125 ) 1.000 1.0(0 ) 2 O40 O 0.9711(118) 0.7520(149) 0.1271(132 ) 1.000 1.0(0 ) 2 Continued on next page

175 Appendix

Table 7.3 – Continued from previous page (Ti-IEZ-RUB)

label type x y z Biso occ. Mult. O41 O 0.5072(42 ) 0.7854(138) 0.1823(312 ) 1.000 1.0(0 ) 2 O42 O 0.4887(43 ) 0.7165(125) 0.6519(312 ) 1.000 1.0(0 ) 2 O43 O 0.0314(42 ) 0.7234(143) 0.8418(302 ) 1.000 1.0(0 ) 2 O44 O 0.0590(45 ) 0.7763(151) 0.3667(384 ) 1.000 1.0(0 ) 2 EF2 C 0.6951(0 ) 0.5000(0 ) 0.5423(0 ) 19.969 2.8(42) 1 EF3 C 0.1534(0 ) 0.3010(0 ) 0.7971(0 ) 8.422 7.5(46) 2 EF4 C 0.3785(0 ) 0.5000(0 ) 0.4301(0 ) 2.653 3.2(27) 1 EF5 C 0.6516(0 ) 0.2248(0 ) 0.3791(0 ) 1.094 2.2(43) 2 EF6 C 0.4158(0 ) 0.0000(0 ) 0.9914(0 ) 4.264 2.6(31) 1 EF7 C 0.6518(0 ) 0.2528(0 ) 0.8667(0 ) 8.482 3.6(37) 2 EF1 C 0.5819(0 ) 0.0000(0 ) 0.8171(0 ) 2.339 4.0(26) 1 EF8 C 0.9008(0 ) 0.3601(0 ) 0.6832(0 ) 1.796 1.5(32) 2 EF9 C 0.6237(0 ) 0.2019(0 ) 0.2162(0 ) 1.983 6.8(44) 2 EF10 C 0.7428(0 ) 0.0000(0 ) 0.0035(0 ) 0.541 2.8(35) 1 EF11 C 0.2285(0 ) 0.0000(0 ) 0.6254(0 ) 3.283 4.8(29) 1 EF12 C 0.2695(0 ) 0.5000(0 ) 0.8808(0 ) 15.242 5.2(38) 1 EF13 C 0.2870(0 ) 0.4114(0 ) 0.3953(0 ) 1.966 2.1(35) 2 EF14 C 0.2695(0 ) 0.5000(0 ) 0.5870(0 ) 1.000 -0.9(22) 1

Table 7.3.: Atomic positions for Ti-IEZ-RUB as derived from RIETVELD analysis.

176 E. List of atomic positions

V-IEZ-RUB label type x y z Biso occ. Mult. Si1 Si 0.5588(50 ) 0.0000(0 ) 0.3999(153 ) 1.041 0.5(0 ) 1 Si2 Si 0.4322(61 ) 0.5000(0 ) 0.8871(170 ) 1.041 0.5(0 ) 1 Si3 Si 0.0905(59 ) 0.0000(0 ) 0.1445(169 ) 1.041 0.5(0 ) 1 Si4 Si 0.9752(59 ) 0.5000(0 ) 0.6386(173 ) 1.041 0.5(0 ) 1 Si5 Si 0.4614(64 ) 0.0000(0 ) 0.1139(164 ) 1.041 0.5(0 ) 1 Si6 Si 0.5324(64 ) 0.5000(0 ) 0.6029(165 ) 1.041 0.5(0 ) 1 Si7 Si 0.9902(72 ) 0.0000(0 ) 0.4296(158 ) 1.041 0.5(0 ) 1 Si8 Si 0.0742(62 ) 0.5000(0 ) 0.9257(170 ) 1.041 0.5(0 ) 1 Si9 Si 0.3762(53 ) 0.6992(88 ) 0.8933(170 ) 1.041 1.0(0 ) 2 Si10 Si 0.6324(48 ) 0.8163(96 ) 0.4080(173 ) 1.041 1.0(0 ) 2 Si11 Si 0.1709(48 ) 0.8256(94 ) 0.1230(176 ) 1.041 1.0(0 ) 2 Si12 Si 0.9047(49 ) 0.7047(94 ) 0.6265(179 ) 1.041 1.0(0 ) 2 Si13 Si 0.4860(66 ) 0.0000(0 ) 0.7067(168 ) 1.041 0.5(0 ) 1 Si14 Si 0.5194(62 ) 0.5000(0 ) 0.1849(175 ) 1.041 0.5(0 ) 1 Si15 Si 1.0081(64 ) 0.0000(0 ) 0.8336(172 ) 1.041 0.5(0 ) 1 Si16 Si 0.0702(63 ) 0.5000(0 ) 0.3444(172 ) 1.041 0.5(0 ) 1 Si17 Si 0.4444(53 ) 0.7975(88 ) 0.1995(166 ) 1.041 1.0(0 ) 2 Si18 Si 0.5537(50 ) 0.7062(90 ) 0.6951(168 ) 1.041 1.0(0 ) 2 Si19 Si 0.0979(50 ) 0.7089(90 ) 0.8284(169 ) 1.041 1.0(0 ) 2 Si20 Si 0.9915(50 ) 0.7903(94 ) 0.3310(164 ) 1.041 1.0(0 ) 2 Si21 Si 0.4401(54 ) 0.7969(87 ) 0.6029(163 ) 1.041 1.0(0 ) 2 Si22 Si 0.5618(54 ) 0.7103(86 ) 0.1232(166 ) 1.041 1.0(0 ) 2 Si23 Si 0.1136(53 ) 0.7089(86 ) 0.4111(167 ) 1.041 1.0(0 ) 2 Si24 Si 0.9794(53 ) 0.7879(87 ) 0.9157(166 ) 1.041 1.0(0 ) 2 V1 V 0.2941(186) 0.8976(265) 0.8770(1812) 36.798 4.8(25) 2 V2 V 0.7744(186) 0.8666(708) 0.6948(2921) 21.241 1.1(10) 2 O1 O 0.5472(61 ) 0.0000(0 ) 0.6101(159 ) 1.000 0.5(0 ) 1 O2 O 0.4598(68 ) 0.5000(0 ) 0.0839(186 ) 1.000 0.5(0 ) 1 O3 O 0.0670(67 ) 0.0000(0 ) 0.9405(177 ) 1.000 0.5(0 ) 1 O4 O 1.0132(77 ) 0.5000(0 ) 0.4593(223 ) 1.000 0.5(0 ) 1 O5 O 0.1263(61 ) 0.9068(77 ) 0.1904(247 ) 1.000 1.0(0 ) 2 O6 O 0.9391(66 ) 0.5999(70 ) 0.6636(290 ) 1.000 1.0(0 ) 2 O7 O 0.5925(63 ) 0.0948(73 ) 0.3468(240 ) 1.000 1.0(0 ) 2 Continued on next page

177 Appendix

Table 7.4 – Continued from previous page (V-IEZ-RUB)

label type x y z Biso occ. Mult. O8 O 0.4009(69 ) 0.4025(67 ) 0.8388(249 ) 1.000 1.0(0 ) 2 O9 O 0.5061(81 ) 0.0000(0 ) 0.2728(255 ) 1.000 0.5(0 ) 1 O10 O 0.4822(81 ) 0.5000(0 ) 0.7435(254 ) 1.000 0.5(0 ) 1 O11 O 1.0386(90 ) 0.0000(0 ) 0.2812(265 ) 1.000 0.5(0 ) 1 O12 O 0.0177(75 ) 0.5000(0 ) 0.8090(233 ) 1.000 0.5(0 ) 1 O13 O 0.1076(70 ) 0.5963(67 ) 0.8799(300 ) 1.000 1.0(0 ) 2 O14 O 0.9846(121) 0.9056(63 ) 0.3321(270 ) 1.000 1.0(0 ) 2 O15 O 0.4262(66 ) 0.9052(64 ) 0.1471(297 ) 1.000 1.0(0 ) 2 O16 O 0.5670(67 ) 0.5946(66 ) 0.6476(298 ) 1.000 1.0(0 ) 2 O17 O 0.4899(104) 0.0000(0 ) 0.9190(131 ) 1.000 0.5(0 ) 1 O18 O 0.5089(100) 0.5000(0 ) 0.3999(121 ) 1.000 0.5(0 ) 1 O19 O 1.0182(108) 0.0000(0 ) 0.6217(121 ) 1.000 0.5(0 ) 1 O20 O 0.0564(101) 0.5000(0 ) 0.1331(118 ) 1.000 0.5(0 ) 1 O21 O 0.3144(59 ) 0.7198(144) 0.9613(408 ) 1.000 1.0(0 ) 2 O22 O 0.6944(61 ) 0.8448(251) 0.4441(449 ) 1.000 1.0(0 ) 2 O23 O 0.2311(60 ) 0.8657(220) 0.0995(444 ) 1.000 1.0(0 ) 2 O24 O 0.8432(63 ) 0.7440(210) 0.5939(391 ) 1.000 1.0(0 ) 2 O25 O 0.3876(63 ) 0.7750(135) 0.7327(230 ) 1.000 1.0(0 ) 2 O26 O 0.6183(60 ) 0.7445(138) 0.2370(229 ) 1.000 1.0(0 ) 2 O27 O 0.1655(60 ) 0.7499(135) 0.2926(228 ) 1.000 1.0(0 ) 2 O28 O 0.9223(56 ) 0.7537(142) 0.8219(199 ) 1.000 1.0(0 ) 2 O29 O 0.4152(80 ) 0.7283(125) 0.0613(223 ) 1.000 1.0(0 ) 2 O30 O 0.5943(81 ) 0.7713(146) 0.5714(221 ) 1.000 1.0(0 ) 2 O31 O 0.1361(86 ) 0.7745(144) 0.9584(229 ) 1.000 1.0(0 ) 2 O32 O 0.9476(79 ) 0.7540(152) 0.4800(247 ) 1.000 1.0(0 ) 2 O33 O 0.1047(81 ) 0.5966(70 ) 0.3776(302 ) 1.000 1.0(0 ) 2 O34 O 0.9800(84 ) 0.9027(65 ) 0.8923(295 ) 1.000 1.0(0 ) 2 O35 O 0.4603(73 ) 0.9051(76 ) 0.6225(226 ) 1.000 1.0(0 ) 2 O36 O 0.5522(83 ) 0.5973(69 ) 0.1460(299 ) 1.000 1.0(0 ) 2 O37 O 0.4236(80 ) 0.7750(150) 0.3990(113 ) 1.000 1.0(0 ) 2 O38 O 0.5688(89 ) 0.7232(152) 0.9066(111 ) 1.000 1.0(0 ) 2 O39 O 0.1232(79 ) 0.7226(155) 0.6259(114 ) 1.000 1.0(0 ) 2 O40 O 0.9746(116) 0.7626(143) 0.1251(116 ) 1.000 1.0(0 ) 2 Continued on next page

178 E. List of atomic positions

Table 7.4 – Continued from previous page (V-IEZ-RUB) label type x y z Biso occ. Mult. O41 O 0.5121(39 ) 0.7810(121) 0.1949(291 ) 1.000 1.0(0 ) 2 O42 O 0.4859(40 ) 0.7201(114) 0.6741(285 ) 1.000 1.0(0 ) 2 O43 O 1.0286(39 ) 0.7245(130) 0.8276(277 ) 1.000 1.0(0 ) 2 O44 O 0.0588(43 ) 0.7734(135) 0.3639(363 ) 1.000 1.0(0 ) 2 EF1 C 0.6951(0 ) 0.5000(0 ) 0.5423(0 ) 23.469 24.4(62) 1 EF2 C 0.1534(0 ) 0.3010(0 ) 0.7971(0 ) 8.842 37.9(77) 2 EF3 C 0.3785(0 ) 0.5000(0 ) 0.4301(0 ) 1.999 14.9(32) 1 EF4 C 0.4158(0 ) 0.0000(0 ) 0.9914(0 ) 1.000 19.6(46) 1 EF5 C 0.2285(0 ) 0.0000(0 ) 0.6254(0 ) 8.496 16.3(45) 1 EF6 C 0.2695(0 ) 0.5000(0 ) 0.8808(0 ) 19.184 10.4(59) 1 EF7 C 0.2870(0 ) 0.4114(0 ) 0.3953(0 ) 1.000 4.5(46) 2

Table 7.4.: Atomic positions for V-IEZ-RUB as derived from RIETVELD analysis.

179 Appendix

Zn-IEZ-RUB

label type x y z Biso occ. Mult. Si1 Si 0.5638(60 ) 0.0000(0 ) 0.3982(166) 1.041 0.5(0 ) 1 Si2 Si 0.4338(60 ) 0.5000(0 ) 0.8735(169) 1.041 0.5(0 ) 1 Si3 Si 0.0847(57 ) 0.0000(0 ) 0.1323(171) 1.041 0.5(0 ) 1 Si4 Si 0.9741(59 ) 0.5000(0 ) 0.6246(173) 1.041 0.5(0 ) 1 Si5 Si 0.4632(63 ) 0.0000(0 ) 0.1154(163) 1.041 0.5(0 ) 1 Si6 Si 0.5368(60 ) 0.5000(0 ) 0.5988(166) 1.041 0.5(0 ) 1 Si7 Si 0.9803(72 ) 0.0000(0 ) 0.4171(155) 1.041 0.5(0 ) 1 Si8 Si 0.0697(63 ) 0.5000(0 ) 0.9274(166) 1.041 0.5(0 ) 1 Si9 Si 0.3734(49 ) 0.6931(87 ) 0.8796(169) 1.041 1.0(0 ) 2 Si10 Si 0.6334(46 ) 0.8068(91 ) 0.3825(174) 1.041 1.0(0 ) 2 Si11 Si 0.1669(49 ) 0.8283(86 ) 0.1425(173) 1.041 1.0(0 ) 2 Si12 Si 0.9123(47 ) 0.6980(93 ) 0.6184(170) 1.041 1.0(0 ) 2 Si13 Si 0.4856(63 ) 0.0000(0 ) 0.7009(166) 1.041 0.5(0 ) 1 Si14 Si 0.5200(66 ) 0.5000(0 ) 0.1823(172) 1.041 0.5(0 ) 1 Si15 Si 1.0091(66 ) 0.0000(0 ) 0.8235(171) 1.041 0.5(0 ) 1 Si16 Si 0.0708(59 ) 0.5000(0 ) 0.3478(175) 1.041 0.5(0 ) 1 Si17 Si 0.4388(51 ) 0.8003(88 ) 0.1875(161) 1.041 1.0(0 ) 2 Si18 Si 0.5550(49 ) 0.7053(91 ) 0.6883(162) 1.041 1.0(0 ) 2 Si19 Si 0.1005(50 ) 0.7069(89 ) 0.8488(166) 1.041 1.0(0 ) 2 Si20 Si 0.9933(49 ) 0.7906(90 ) 0.3199(162) 1.041 1.0(0 ) 2 Si21 Si 0.4420(52 ) 0.7885(85 ) 0.5876(164) 1.041 1.0(0 ) 2 Si22 Si 0.5551(52 ) 0.7176(85 ) 0.1033(163) 1.041 1.0(0 ) 2 Si23 Si 0.1133(53 ) 0.7140(84 ) 0.4245(162) 1.041 1.0(0 ) 2 Si24 Si 0.9793(53 ) 0.7826(85 ) 0.9240(160) 1.041 1.0(0 ) 2 Zn1 Zn 0.2960(104) 0.7991(302) 0.1288(704) 42.518 1.1(5 ) 2 Zn2 Zn 0.7909(80 ) 0.7971(292) 0.4221(685) 30.320 1.2(4 ) 2 O1 O 0.5473(60 ) 0.0000(0 ) 0.6090(161) 1.000 0.5(0 ) 1 O2 O 0.4606(69 ) 0.5000(0 ) 0.0748(186) 1.000 0.5(0 ) 1 O3 O 0.0688(62 ) 0.0000(0 ) 0.9212(165) 1.000 0.5(0 ) 1 O4 O 1.0120(70 ) 0.5000(0 ) 0.4488(214) 1.000 0.5(0 ) 1 O5 O 0.1206(60 ) 0.9085(79 ) 0.1824(257) 1.000 1.0(0 ) 2 O6 O 0.9441(67 ) 0.5985(69 ) 0.6544(268) 1.000 1.0(0 ) 2 O7 O 0.5960(62 ) 0.0958(72 ) 0.3440(258) 1.000 1.0(0 ) 2 Continued on next page

180 E. List of atomic positions

Table 7.5 – Continued from previous page (Zn-IEZ-RUB) label type x y z Biso occ. Mult. O8 O 0.4039(67 ) 0.4032(70 ) 0.8289(251) 1.000 1.0(0 ) 2 O9 O 0.5091(80 ) 0.0000(0 ) 0.2681(254) 1.000 0.5(0 ) 1 O10 O 0.4835(76 ) 0.5000(0 ) 0.7301(250) 1.000 0.5(0 ) 1 O11 O 1.0282(82 ) 0.0000(0 ) 0.2574(255) 1.000 0.5(0 ) 1 O12 O 0.0181(81 ) 0.5000(0 ) 0.7962(237) 1.000 0.5(0 ) 1 O13 O 0.1072(68 ) 0.5940(67 ) 0.8880(298) 1.000 1.0(0 ) 2 O14 O 0.9777(117) 0.9048(65 ) 0.3149(269) 1.000 1.0(0 ) 2 O15 O 0.4251(64 ) 0.9081(64 ) 0.1480(294) 1.000 1.0(0 ) 2 O16 O 0.5703(65 ) 0.5928(63 ) 0.6567(297) 1.000 1.0(0 ) 2 O17 O 0.4895(103) 0.0000(0 ) 0.9161(130) 1.000 0.5(0 ) 1 O18 O 0.5134(104) 0.5000(0 ) 0.3963(124) 1.000 0.5(0 ) 1 O19 O 1.0110(114) 0.0000(0 ) 0.6093(133) 1.000 0.5(0 ) 1 O20 O 0.0536(97 ) 0.5000(0 ) 0.1352(118) 1.000 0.5(0 ) 1 O21 O 0.3080(50 ) 0.6907(177) 0.9100(375) 1.000 1.0(0 ) 2 O22 O 0.6985(45 ) 0.8218(227) 0.3969(450) 1.000 1.0(0 ) 2 O23 O 0.2247(54 ) 0.8794(148) 0.1081(444) 1.000 1.0(0 ) 2 O24 O 0.8476(55 ) 0.7069(194) 0.5724(407) 1.000 1.0(0 ) 2 O25 O 0.3873(63 ) 0.7651(131) 0.7138(220) 1.000 1.0(0 ) 2 O26 O 0.6135(58 ) 0.7434(135) 0.2104(216) 1.000 1.0(0 ) 2 O27 O 0.1651(58 ) 0.7579(131) 0.3158(212) 1.000 1.0(0 ) 2 O28 O 0.9255(60 ) 0.7473(140) 0.8084(190) 1.000 1.0(0 ) 2 O29 O 0.4049(84 ) 0.7387(140) 0.0516(214) 1.000 1.0(0 ) 2 O30 O 0.6005(77 ) 0.7561(145) 0.5511(222) 1.000 1.0(0 ) 2 O31 O 0.1405(82 ) 0.7628(138) 0.9812(224) 1.000 1.0(0 ) 2 O32 O 0.9534(74 ) 0.7478(151) 0.4727(223) 1.000 1.0(0 ) 2 O33 O 0.1042(80 ) 0.5984(70 ) 0.3851(305) 1.000 1.0(0 ) 2 O34 O 0.9835(87 ) 0.9009(66 ) 0.8964(287) 1.000 1.0(0 ) 2 O35 O 0.4566(89 ) 0.9035(73 ) 0.6282(280) 1.000 1.0(0 ) 2 O36 O 0.5468(87 ) 0.5995(69 ) 0.1304(292) 1.000 1.0(0 ) 2 O37 O 0.4212(77 ) 0.7789(150) 0.3879(114) 1.000 1.0(0 ) 2 O38 O 0.5640(89 ) 0.7366(138) 0.8903(112) 1.000 1.0(0 ) 2 O39 O 0.1210(82 ) 0.7257(151) 0.6411(113) 1.000 1.0(0 ) 2 O40 O 0.9695(108) 0.7512(132) 0.1272(119) 1.000 1.0(0 ) 2 Continued on next page

181 Appendix

Table 7.5 – Continued from previous page (Zn-IEZ-RUB)

label type x y z Biso occ. Mult. O41 O 0.5073(39 ) 0.7868(121) 0.1806(275) 1.000 1.0(0 ) 2 O42 O 0.4881(40 ) 0.7138(111) 0.6478(278) 1.000 1.0(0 ) 2 O43 O 1.0311(38 ) 0.7214(125) 0.8440(268) 1.000 1.0(0 ) 2 O44 O 0.0593(41 ) 0.7791(133) 0.3750(339) 1.000 1.0(0 ) 2 EF1 C 0.5819(0 ) 0.0000(0 ) 0.8171(0 ) 2.339 2.8(10) 1 EF2 C 0.6951(0 ) 0.5000(0 ) 0.5423(0 ) 19.969 4.0(15) 1 EF3 C 0.1534(0 ) 0.3010(0 ) 0.7971(0 ) 8.422 8.2(16) 2 EF4 C 0.3785(0 ) 0.5000(0 ) 0.4301(0 ) 2.653 2.1(11) 1 EF5 C 0.6516(0 ) 0.2248(0 ) 0.3791(0 ) 1.094 4.7(18) 2 EF6 C 0.4158(0 ) 0.0000(0 ) 0.9914(0 ) 4.264 2.4(13) 1 EF7 C 0.6518(0 ) 0.2528(0 ) 0.8667(0 ) 8.482 5.2(15) 2 EF8 C 0.9008(0 ) 0.3601(0 ) 0.6832(0 ) 1.796 3.2(13) 2 EF9 C 0.6237(0 ) 0.2019(0 ) 0.2162(0 ) 1.983 4.8(18) 2 EF10 C 0.7428(0 ) 0.0000(0 ) 0.0035(0 ) 0.541 2.6(11) 1 EF11 C 0.2285(0 ) 0.0000(0 ) 0.6254(0 ) 3.283 2.4(10) 1 EF12 C 0.2695(0 ) 0.5000(0 ) 0.8808(0 ) 15.242 1.8(13) 1 EF13 C 0.2870(0 ) 0.4114(0 ) 0.3953(0 ) 1.966 3.7(13) 2 EF14 C 0.2695(0 ) 0.5000(0 ) 0.5870(0 ) 1.000 0.6(8 ) 1

Table 7.5.: Atomic positions for Zn-IEZ-RUB as derived from RIETVELD analysis.

182 F. Curriculum Vitae

❋✳ ❈✉✐❝✉❧✉♠ ❱✐❛❡

Isabel Großkreuz place of birth: Herdecke Master of Science date of birth: 30.01.1986

❊❞✉❝❛✐♦♥

✵✶✴✷✵✶✸✕✵✶✴✷✵✷✵ Ruhr-University Bochum, Promotion Geosciences, Bochum

✶✵✴✷✵✶✵✕✶✷✴✷✵✶✷ Ruhr-University Bochum, M. Sc. Geosciences, Bochum Final grade: very good, 88%

✶✵✴✷✵✵✼✕✵✾✴✷✵✶✵ Ruhr-University Bochum, B. Sc. Geosciences, Bochum Final grade: good, 71%

✶✵✴✷✵✵✺✕✵✾✴✷✵✵✼ TU Dortmund, Faculty of Business and Economics, Dortmund

✶✵✴✷✵✵✹✕✵✾✴✷✵✵✺ Ruhr-University Bochum, Medical Faculty, Bochum

✵✽✴✶✾✾✻✕✵✻✴✷✵✵✹ Geschwister-Scholl-Gesamtschule, A-Level, Dortmund Final grade: 1,7

❲♦❦ ❊①♣❡✐❡♥❝❡

✵✶✴✷✵✶✸✕✵✻✴✷✵✶✽ Scientiﬁc Associate, Ruhr-University Bochum, Bochum

✵✾✴✷✵✶✻✕✶✵✴✷✵✶✻ Scientiﬁc Associate, Tokyo Institute of Technology, Yokohama

✵✾✴✷✵✵✾✕✶✷✴✷✵✶✷ Student Assistant, Ruhr-University Bochum, Bochum

183 Appendix

●✳ ❉❡❝❧❛❛✐♦♥ ✐♥ ❧✐❡✉ ♦❢ ♦❛❤

Last Name: Großkreuz First Name: Isabel Date of Birth: 30.01.1986

I herewith declare in lieu of oath that I have composed this thesis without any inadmis- sible help of a third party and without the use of aids other than those listed. The data and concepts that have been taken directly or indirectly from other sources have been acknowledged and referenced.

Other persons have not helped to produce this work as regards to its content or making. In particular, I have not used the services of any professional agencies in return for payment or those of other persons. Nobody has received payment in any kind – neither directly nor indirectly – from me for any work that is connected with the content of this master dissertation. This thesis has not been submitted, wholly or substantially, neither in this country nor abroad for another degree or diploma at any university or institute.

I declare in lieu of oath that I have said nothing but the truth to the best of my knowledge and that I have not withheld any information.

Before the above declaration in lieu of oath had been taken down, I was advised about the signiﬁcance of a declaration in lieu of oath as well as of the legal consequences of an incorrect or incomplete declaration.

Isabel Großkreuz Place and Date

184 H. Digital Appendage

❍✳ ❉✐❣✐❛❧ ❆♣♣❡♥❞❛❣❡

185

❘❡❢❡❡♥❝❡

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[225] R. C. Hansford, “Mechanism of Catalytic Cracking”, Industrial & Engineering Chem- istry 39.7 (1947), 849.

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206 ❆❝❦♥♦✇❧❡❞❣❡♠❡♥

I would like to express the deepest gratitude to all associates participating in the compilation and writing of my Ph. D. thesis. First and foremost, I want to thank Prof. Dr. HERMANN GIES, who has been a steady support during every step in the making of the thesis. Thank you for giving me the opportunity of writing my thesis in this interesting ﬁeld of work and your patience and advice during every aspect of it. Also, I want to thank Prof. Dr.-Ing. GUN- THER EGGELER for agreeing to support the compilation of this thesis. Additionally, I would like to thank Dr. BERND MARLER for his good-natured helpfulness regarding the high resolution PXRD, as well as the FTIR spectroscopy. Your interest and active participation during my work has been a great incentive.

My special acknowledgement goes to the scientific staff at the RUB. I am thanking scientific associate ALEXANDRA BRUNS for her patient support in every aspect regarding the practical work in the laboratory and her help in the execution of the thermal analysis plus the hydrothermal synthesis. Your self-evident cooperativeness never failed to astound me. In addition, I owe great gratitude to scientific associate SANDRA GRABOWSKI, who has been a steady and very patient help regarding many aspects of the practical work, only some of them being the IR and, especially the NMR spectroscopy. I also thank you for providing samples for PXRD refinement and always lending a helpful hand regarding the laboratory work. Another heartfelt thank you goes to ANTJE GRÜNEWALD-LÜKE for her helpfulness in the daily laboratory work, for giving advice and inspiring motivation. I am also much obliged to KIRSTEN KEPPLER and UTE GUNDERT for conducting the AAS analyses and their steady and welcoming presence at the RUB laboratory.

Many thanks to Prof. Dr. NOMURA JUNKO, Dr. TOSHIYUKI YOKOI and Dr. SUNGSIK PARK, as well as the whole team at the Tokyo Institute of Technology in Yokohama, Japan, for the opportunity to work at your facility, your friendly and devoted help and lessons regarding the special ﬁeld of zeolite catalysis. Your patience, kindness and camaraderie have made me feel at home at the other end of the world.

207 Acknowledgements

My gratitude also goes to Dr. UTE KOLB and HAISHUANG ZHAO from the Gutenberg- University in Mainz, Germany, who have been an important aid within the ﬁeld of Electron Diffraction. Thank you, HAISHUANG ZHAO for introducing and advising me to the ADT technique and guiding me into the right direction and for many amiable conversations and meetings.

I am much obliged to NOUSHIN ARSHADI from the Chair of Technical Chemistry at the RUB for conducting the BET-analyses.

Furthermore, I have to thank Dr. MALTE SOMMER a great deal for the help with the practical aspects of the writing of the thesis and the processing. Also, thank you for providing the LATEX template and your subsequent patient and selﬂess (on-line!) assistance in formatting. Thanks are also given to my editor WIEBKE WASSMUTH for the proof-reading, especially with regards to the English language and the moral support. It is due to both of you that I managed to format every part to my personal perfection.

The most special acknowledgement goes to my fellow colleagues Dr. MELANIE MÜLLER, SANDRINA MEIS,MARIAN HAPPEL and Dr. ANDREAS BÜRGER for many inspiring conversations and much needed motivation during my time at the RUB as well as the stimulating scientiﬁc debates during our Ph. D. meetings.

I especially thank BOJANA GROSSKREUZ, who has always been at my side during every step of the way, has never failed to motivate me or to give insight to arising problems. Special thanks also to KARIN SCHOLTKA-GROSSKREUZ and JENS HEINRICH, for the mental and moral support without which the studies and the compilation of this thesis would have never been possible.

Finally a big thank you to the whole working party of Prof. Dr. HERMANN GIES for the assistance and mentoring in every aspect of the thesis.

I would also like to thank the Ruhr University Research School PLUS, funded by Ger- many’s Excellence Initiative [DFG GSC 98/3], who have supported my international activities.

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