DOCSLIB.ORG

Thesis Final

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Thesis Final TRANSITION METAL CONTAINING SILICO- AND GERMANOTUNGSTATES BY BASSEM S. BASSIL A thesis submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Chemistry Approved, Thesis Committee: Prof. Dr. Ulrich Kortz (chair, Jacobs University, Germany) Prof. Dr. Horst Elias (Technische Universität Darmstadt, Germany) Prof. Dr. Emmanuel Cadot (Université de Versailles, France) Dr. Michael H. Dickman (Jacobs University, Germany) Date of defense: 27 th of June 2008 School of Engineering and Science Abstract Polyoxotungstates (POTs) are anionic tungsten-oxide clusters with a wide structural variety and interesting properties. Thus, POTs exhibit potential applications in diverse areas such as catalysis, magnetism, bio- and nanotechnology, and materials science. POTs are usually synthesized via condensation reactions in aqueous, acidic solution. These reactions can be influenced by careful variation of the synthesis conditions, e.g. ratio and concentration of reagents, solvent, pH, counter cations, and temperature. Having identified the proper synthesis conditions, POTs usually form quickly in what is often described as a self- assembly process. This work focuses on the interaction of the versatile dilacunary silicotungstate [γ- 8- SiW 10 O36 ] with different metal cations leading to novel compounds interesting for magnetic and catalytic applications. Also this work reports two new lanthanide containing polytungstates, a sandwich type silicotungstate and a dimeric-pentameric germanotungstate. The 15-cobalt-substituted polyoxotungstate [Co 6(H 2O) 30 {Co 9Cl 2(OH) 3(H 2O) 9(β- 5- SiW 8O31 )3}] (1) has been characterized by single crystal XRD, elemental analysis, IR, electrochemistry, magnetic measurements and EPR. Single-crystal X-ray analysis was carried β out on Na 5[Co 6(H 2O) 30 {Co 9Cl 2(OH) 3(H 2O) 9( -SiW 8O31 )3}]·37H 2O, which crystallizes in the hexagonal system, space group P6 3/m , with a = 19.8754(17) Å, b = 19.8754(17) Å, c = 22.344(4) Å, α = 90 °, β = 90 °, γ = 120 °, and Z = 2. The trimeric polyanion 1 has a core of nine Co II ions β - encapsulated by three unprecedented ( -SiW 8O31 ) fragments and two Cl ligands. The highly β 17- symmetrical ( D3h ) assembly [Co 9Cl 2(OH) 3(H 2O) 9( -SiW 8O31 )3] is surrounded by six antenna- II like Co (H 2O) 5 groups resulting in the satellite-like structure 1. Synthesis of 1 is accomplished in 2 II 8- a simple one-pot procedure by interaction of Co ions with [ γ-SiW 10 O36 ] in aqueous, acidic NaCl medium (pH 5.4). 22- The 6-cobalt-substituted [{Co 3(B-β-SiW 9O33 (OH))( B-β-SiW 8O29 (OH) 2)}2] (2) has been characterized by IR and UV-vis spectroscopy, elemental analysis, magnetic studies, electrochemistry and gel filtration chromatography. Single-crystal X-ray analysis was carried out on K 10 Na 12 [{Co 3(B-β-SiW 9O33 (OH))( B-β-SiW 8O29 (OH) 2)}2]·49H2O ( KNa-2), which crystallizes in the monoclinic system, space group P2 1/n , with a = 19.9466(8) Å, b = 24.6607(10) Å, c = 34.0978(13) Å, β = 102.175(1) °, and Z = 2. Polyanion 2 represents a novel class of asymmetric sandwich-type polyanions. It contains three cobalt ions which are encapsulated between an unprecedented (B-β-SiW 9O34 ) fragment and a ( B-β-SiW 8O31 ) unit. Polyanion 2 is composed of two sandwich species via two Co-O-W bridges in the solid state and almost certainly also in solution as based on gel filtration chromatography. 10- The new, monometal substituted silicotungstates [Mn(H 2O) 2(γ-SiW 10 O35 )2] (3), 10- 10- [Co(H 2O) 2(γ-SiW 10 O35 )2] (4) and [Ni(H 2O) 2(γ-SiW 10 O35 )2] (5) have been synthesized and isolated as the potassium salts K 10 [Mn(H 2O) 2(γ-SiW 10 O35 )2]·8.25H 2O ( K-3), K 10 [Co(H 2O) 2(γ- SiW 10 O35 )2]·8.25H 2O ( K-4) and K 10 [Ni(H 2O) 2(γ-SiW 10 O35 )2]·13.5H 2O ( K-5), which have been characterized by IR spectroscopy, single-crystal X-ray diffraction, elemental analysis and cyclic voltammetry. Polyanions 3-5 are composed of two ( γ-SiW 10 O36 ) units fused on one side via two W-O-W’ bridges and on the other side by an octahedrally coordinated trans-MO 4(OH 2)2 transition metal fragment, resulting in a structure with C 2v point group symmetry. Anions 3-5 8- 2+ 2+ were synthesized by reaction of the dilacunary precursor [ γ-SiW 10 O36 ] with Mn , Co and Ni 2+ ions, respectively, in 1M KCl solution at pH 4.5. 3 8- Reaction of ZrCl 4 with [γ-SiW 10 O36 ] in potassium acetate buffer results in two different products depending on the reactant ratios. The trimeric species [Zr 6O2(OH) 4(H 2O) 3(β- 14- SiW 10 O37 )3] (6) consists of three β23 -SiW 10 O37 units linked by an unprecedented Zr 6O2(OH) 4(H 2O) 3 cluster with C 1 point group symmetry. The dimeric species 10- [Zr 4O2(OH) 2(H 2O) 4(β-SiW 10 O37 )2] (7) consists of a β22 - and a β12 -SiW 10 O37 unit sandwiching a Zr 4O2(OH) 2(H 2O) 4 cluster and has also C 1 symmetry. We have also synthesized and structurally characterized the unprecedented peroxo- 18- zirconium(IV) containing [Zr 6(O 2)6(OH) 6(γ-SiW 10 O36 )3] (8). Polyanion 8 comprises a cyclic 6- peroxo-6-zirconium core stabilized by three decatungstosilicate units.. Polyanion 8 represents the first structurally characterized Zr-peroxo POM with side-on, bridging peroxo units. The simple, one-pot synthesis procedure of 8 involving dropwise addition of aqueous hydrogen peroxide could represent a general procedure for incorporating peroxo groups into a large variety of transition metal and lanthanide containing POMs. We have also synthesized and structurally characterized the mono-lanthanide containing 13- polyanions [Ln( β2-SiW 11 O39 )2] (Ln = La ( 9), Ce ( 10 ), Sm ( 11 ), Eu ( 12), Gd ( 13 ), Tb ( 14 ), Yb (15 ), Lu ( 16 )). Synthesis was accomplished by reaction of the respective lanthanide ion with the 8- monolacunary, chiral, Keggin-type precursor [ β2-SiW 11 O39 ] in a 1:2 molar ratio in 1M KCl medium at pH 5. Polyanions 9-16 were isolated as potassium salts and then characterized by IR, single-crystal X-ray diffraction and elemental analysis. The structures of 9-16 are composed of 3+ 3+ an eight-coordinated Ln center sandwiched by two chiral ( β2-SiW 11 O39 ) units. Larger Ln ions appear to favor an R,R (or S,S) configuration (point group C 2) of the Keggin units, with an increasing amount of R,S (or S,R) configuration (point group C 1) found in the solid state as the 4 Ln 3+ ion decreases in size. Evidence for this trend is also given by solution 183 W NMR results for the diamagnetic La 3+ and Lu 3+ derivatives. Finally, The gigantic 20-cerium(III) containing 100-tungstogermanate 56- III [Ce 20 Ge 10 W100 O376 (OH) 4(H 2O) 30 ] (17 ) has been synthesized using Ce ions and [ α- 10- GeW 9O34 ] in aqueous acidic medium at pH 5.0. Polyanion 17 represents the first lanthanide substituted tungstogermanate and it is one of the largest polytungstates reported to date. 5 Acknowledgements I thank Jacobs University, in the person of Dean Prof. Dr. Bernhard Kramer, for supporting this project by providing me a research opportunity and a stipend as a PhD student for three years. I also thank Prof. Ulrich Kortz for being a patient and guiding supervisor during my research in his group at Jacobs University. He also collected the crystal structure of some polyanions described here at Florida State University Chemistry Department (USA). I also wish to thank the entire Kortz group for all the help and in particular Dr. Michael H. Dickman for his XRD work and guidance. I would also like to express my gratitude and thanks Prof. Emmanuel Cadot and Prof. Horst Elias, for accepting to part of my thesis and defense committee. I also appreciate all the help from the undergraduate students Anca Tigan, Alexandra Dumitriu, Shibani De Silva and Marie Asano in the experimental work done in the lab. Last but not least I thank my parents for supporting me all the way till the top of the educational ladder. 6 Table of Contents Chapter 1: General Introduction 15 I- Polyoxotungstates 16 II- Keggin Ion 20 III- Lacunary Keggin Silico- and Germanotungstates 24 8- A- [β2-SiW 11 O39 ] 26 8- B- [γ-SiW 10 O36 ] 28 10- C- A-[α-GeW 9O33 ] 30 IV- Nomenclature of β-dilacunary Keggin units 32 V- Instrumentation 34 8- Chapter 2: Results with [ γ-SiW 10 O36 ] 35 8- 2+ I- Interaction of [ γ-SiW 10 O36 ] with Co 36 A- Introduction 36 B- The Satellite-Shaped Co-15 Polyoxotungstates, 5- [Co 6(H 2O) 30 {Co 9Cl 2(OH) 3(H 2O) 9(β-SiW 8O31 )3}] 37 C- Cobalt Containing Silicotungstate Sandwich Dimer 22- [{Co 3(B-β-SiW 9O33 (OH))( B-β-SiW 8O29 (OH) 2)} 2] 43 D- Conclusion 51 7 12- II- Formation of the fused [γ-Si 2W20 O70 ] unit 53 A- Introduction 53 B- Transition Metal Containing Decatungstosilicate Dimer 10- 2+ 2+ 2+ [M(H 2O) 2(γ-SiW 10 O35 )2] (M = Mn , Co , Ni ) 54 C- Conclusion 61 8- 4+ III- Interaction of [ γ-SiW 10 O36 ] with Zr 63 A- Introduction 63 B- Synthesis and Structure of Asymmetric Zirconium-Substituted 14- Silicotungstates, [Zr 6O2(OH) 4(H 2O) 3(β-SiW 10 O37 )3] and 10- [Zr 4O2(OH) 2(H 2O) 4(β-SiW 10 O37 )2] 64 C- 6-Peroxo-6-Zirconium Crown Embedded in a Triangular Polyanion: 18- [Zr 6(O 2)6(OH) 6(γ-SiW 10 O36 )3] 70 D- Conclusion 75 Chapter 3: Results with lanthanides 76 I- Introduction 77 8- II- Interaction of lanthanides with [ β2-SiW 11 O39 ] 79 A- Introduction 79 B- The Mono-Lanthanide Containing Silicotungstates 13- [Ln( β2-SiW 11 O39 )2] (Ln = La, Ce, Sm, Eu, Gd, Tb, Yb, Lu), a Synthetic and Structural Investigation 79 C- Conclusion 94 10- III- Interaction of Cerium(III) with [A-α-GeW 9O34] 96 8 A- Introduction 96 56- B- The Tungstogermanate [Ce 20 Ge 10 W100 O376 (OH) 4(H 2O) 30
Load more

Recommended publications
  • Conversion of Synthesis Gas to Oxygenates by Using Keggin-Type Structure Heteropoly Compound-Based Catalyst Compositions
    (19) TZZ _T (11) EP 2 627 445 B1 (12) EUROPEAN PATENT SPECIFICATION (45) Date of publication and mention (51) Int Cl.: of the grant of the patent: B01J 37/03 (2006.01) B01J 37/08 (2006.01) 07.01.2015 Bulletin 2015/02 B01J 37/02 (2006.01) B01J 27/188 (2006.01) C07C 29/158 (2006.01) C07C 29/157 (2006.01) (2006.01) (2006.01) (21) Application number: 11768222.9 C07C 29/16 C07C 31/04 C07C 31/08 (2006.01) C07C 31/10 (2006.01) (22) Date of filing: 26.09.2011 (86) International application number: PCT/US2011/053202 (87) International publication number: WO 2012/050806 (19.04.2012 Gazette 2012/16) (54) CONVERSION OF SYNTHESIS GAS TO OXYGENATES BY USING KEGGIN- TYPE STRUCTURE HETEROPOLY COMPOUND-BASED CATALYST COMPOSITIONS UMWANDLUNG VON SYNTHESEGAS IN OXYGENATE MITTELS VERWENDUNG VON KATALYSATOREN AUF DER BASIS VON HETEROPOLYVERBINDUNGEN MIT KEGGIN- STRUKTUR CONVERSION DE GAZ DE SYNTHÈSE EN OXYGÉNATS À L’AIDE DE COMPOSITIONS DE CATALYSEUR À BASE D’UN COMPOSÉ HÉTÉROPOLY À STRUCTURE DE TYPE KEGGIN (84) Designated Contracting States: • RAO, Sreenivasa AL AT BE BG CH CY CZ DE DK EE ES FI FR GB Pune 411007 (IN) GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO • BARTON, David, G. PL PT RO RS SE SI SK SM TR Midland, MI 48642 (US) (30) Priority: 11.10.2010 US 391739 P (74) Representative: Beck Greener Fulwood House (43) Date of publication of application: 12 Fulwood Place 21.08.2013 Bulletin 2013/34 London WC1V 6HR (GB) (73) Proprietor: Dow Global Technologies LLC (56) References cited: Midland, MI 48674 (US) US-A- 4 210 597 US-A- 6 127 432 US-B1- 6 278 030 (72) Inventors: • MANIKANDAN, Palanichamy Pune 411014 (IN) Note: Within nine months of the publication of the mention of the grant of the European patent in the European Patent Bulletin, any person may give notice to the European Patent Office of opposition to that patent, in accordance with the Implementing Regulations.
    [Show full text]
  • Equilibrium and Structure Studies of Aqueous Vanadophosphates and Molybdovanadophosphates
    Equilibrium and structure studies of aqueous vanadophosphates and molybdovanadophosphates by Anna Selling <5 °< c/> ■O • V AKADEMISK AVHANDLING som med tillstånd av rektorsämbetet vid Umeå Universitet för erhållande av filosofie doktorsexamen framlägges till offentlig granskning vid Kemiska instutitionen, Sal C, LuO, Naturvetarhuset, fredagen den 7 juni 1996, kl. 13.00. Fakultetsopponent: Dr. Atsushi Yagasaki, Kwansei Gakuin University, Japan. U m eå 1996 Title: Equilibrium and structure studies of aqueous vanadophosphates and molybdovanadophosphates. Author: Anna Selling Address: Department of Inorganic Chemistry, Umeå University, S -901 87 Umeå, Sweden. Abstract: This thesis comprises a summary and discussion of four papers, where heteropolyanions containing phosphorus as heteroatom and molybdenum and/or vanadium as addenda atoms have been studied. The ultimate goal was to study the equilibrium spéciation in the reduced molybdovanadophosphate system. The latter is a good catalyst in the selective oxidation of olefins to carbonyls. The studies were been performed in 0.6 M Na(Cl) medium at 25 °C. The main techniques employed included potentiometry, NMR- and ESR spectrometry, complemented with FTIR, X-ray diffraction and cyclic voltammetry. Experimental data were treated with the computer program LAKE, which is capable of simultaneously handling multimethod data. Before the reduced molybdovanadophosphate system could be studied, the subsystems needed to be known. Since the spéciation in most of the oxidised subsystems has been reported earlier in the same ionic medium, only the binary phosphate and the ternary vanadophosphate systems had to be studied. These are reported in this thesis. All three pXa values for the phosphate system have been determined with high precision. In the vanadophosphate system, equilibrium species with the formula [HzPVi40 42](9 z) and the trans-bicapped Keggin structure were formed.
    [Show full text]
  • Location of Protons in Anhydrous Keggin Heteropolyacids H3pmo12o40 and H3PW12O40 by 1H{31P}/31P{1H} REDOR NMR and DFT Quantum Ch
    Published on Web 06/11/2002 Location of Protons in Anhydrous Keggin Heteropolyacids 1 31 31 1 H3PMo12O40 and H3PW12O40 by H{ P}/ P{ H} REDOR NMR and DFT Quantum Chemical Calculations S. Ganapathy,†,‡ M. Fournier,§ J. F. Paul,§ L. Delevoye,⊥ M. Guelton,§ and J. P. Amoureux*,‡ Contribution from the National Chemical Laboratory, 411 008 Pune, India, LCPS, CNRS-8012, UniVersite´ de Lille1, 59655 VilleneuVe d’Ascq, France, Laboratoire de Catalyse, CNRS-8010, UniVersite´ de Lille1, 59655 VilleneuVe d’Ascq, France, and Bruker-France, 67166 Wissembourg, France Received December 21, 2001 Abstract: HeteroPolyAcids (HPA’s) are a class of solid acids that have broad applications in many fields of science and technology, including catalysis and chemical engineering. The proton locations within the thermally stable and commonly known Keggin unit, which is the primary structure building unit/block, has remained undetermined in anhydrous HPAs, despite numerous theoretical and experimental efforts. However, Rotational Echo DOuble Resonance (REDOR) NMR and Density Functional Theory (DFT) quantum chemical calculations offer a new opportunity to determine the exact locations of protons within the Keggin unit. The crucial experimental evidence is provided for the basic and very extensively studied n+ acidic form of H8-nX M12O40,X) Si, P and M ) Mo, W, belonging to the Keggin structure. While showing that the acidic protons are located in the bridging oxygen positions (RP-H ) 520 ( 20 pm) in H3PMo12O40 and in the terminal oxygen positions (RP-H ) 570 ( 20 pm) in H3PW12O40, REDOR measurements also provide for the first time the structural basis to consistently rank the acid strength for the important class of Keggin solid catalysts.
    [Show full text]
  • POM@MOF Hybrids: Synthesis and Applications
    catalysts Review POM@MOF Hybrids: Synthesis and Applications Jiamin Sun 1, Sara Abednatanzi 1 , Pascal Van Der Voort 1,* , Ying-Ya Liu 2 and Karen Leus 1 1 COMOC—Center for Ordered Materials, Organometallics and Catalysis, Department of Chemistry, Ghent University, Krijgslaan 281, Building S3, 9000 Ghent, Belgium; [email protected] (J.S.); [email protected] (S.A.); [email protected] (K.L.) 2 State Key Laboratory of Fine Chemicals, School of Chemical Engineering, Dalian University of Technology, Dalian 116024, China; [email protected] * Correspondence: [email protected]; Tel.: +32-(0)9-264-44-42 Received: 4 May 2020; Accepted: 19 May 2020; Published: 21 May 2020 Abstract: The hybrid materials that are created by supporting or incorporating polyoxometalates (POMs) into/onto metal–organic frameworks (MOFs) have a unique set of properties. They combine the strong acidity, oxygen-rich surface, and redox capability of POMs, while overcoming their drawbacks, such as difficult handling, a low surface area, and a high solubility. MOFs are ideal hosts because of their high surface area, long-range ordered structure, and high tunability in terms of the pore size and channels. In some cases, MOFs add an extra dimension to the functionality of hybrids. This review summarizes the recent developments in the field of POM@MOF hybrids. The most common applied synthesis strategies are discussed, together with major applications, such as their use in catalysis (organocatalysis, electrocatalysis, and photocatalysis). The more than 100 papers on this topic have been systematically summarized in a handy table, which covers almost all of the work conducted in this field up to now.
    [Show full text]
  • Ii ION-PAIR BEHAVIOR BETWEEN POLYOXOMETALATES ANION
    ION-PAIR BEHAVIOR BETWEEN POLYOXOMETALATES ANION AND ALKALI METAL CATION A Thesis Presented to The Graduate Faculty of The University of Akron In Partial Fulfillment of the Requirement for the Degree Master of Science Songtao Ye May 2018 ii ION-PAIR BEHAVIOR BETWEEN POLYOXOMETALATES ANION AND ALKALI METAL CATION Songtao Ye Thesis Approved Accepted: ______________________________ ____________________________ Advisor Dean of the College Dr. Tianbo Liu Dr. Eric Amis ______________________________ ____________________________ Committee Member Dean of the Graduate School Dr. Toshikazu Miyoshi Dr. Chand Midha ______________________________ ____________________________ Department Chair Date Dr. Colleen Pugh iii ABSTRACT Ion-pair behavior describes the partial association of oppositely charged ions in electrolyte solutions. Previous study mainly focused on the ion-pair behavior between simple ions, such as ion pairing in NaCl solution as well as ion-pair interactions in supramolecular complexes and biological associations. However, very few attentions have been placed on the solution system with particle sizes in between. Recently, a group of well-defined, huge anionic cluster named polyoxometalates (POMs) have been synthesized and well characterized. The size of POMs is around nanometer scale, which is exactly between simple ions and large colloids. The solution behavior for POMs is much different form simple electrolyte solutions or large colloids. As a result, it is interesting to study the ion-pair behavior for POMs in solution. Herein, ion-pairs between Lacunary Keggin type POMs and alkali metal cations are investigated. The result showed that ion-pairs are formed between alkali cations and the “pocket” area on the surface of Lacunary Keggin type POMs – K7PW11O39. Electrostatic interaction and the entropy gain during the solvation shell lost were considered major driving forces during the ion-pair formation.
    [Show full text]
  • The Effect of Cation Type and H+ on the Catalytic Activity of the Keggin Anion [Pmo12o40]3- in the Oxidative Dehydrogenation Of
    Journal of Catalysis 195, 360–375 (2000) doi:10.1006/jcat.2000.2987, available online at http://www.idealibrary.com on The Effect of Cation Type and H+ on the Catalytic Activity 3 of the Keggin Anion [PMo12O40] in the Oxidative Dehydrogenation of Isobutyraldehyde Ji Hu and Robert C. Burns1 School of Biological and Chemical Sciences, The University of Newcastle, Callaghan 2308, Australia Received March 23, 2000; revised July 4, 2000; accepted July 5, 2000 such as the oxidative dehydrogenation of isobutyric acid The oxidative dehydrogenation of isobutyraldehyde to metha- and the oxidation of methacrolein, both of which yield 3 crolein over [PMo12O40] -containing catalysts has been shown to methacrylic acid (1–5). Methacrylic acid is, in turn, reacted proceed through bulk catalysis-type II, which depends on the rates with methanol to yield methyl methacrylate, an extremely + of diffusion of the redox carriers (H and e ) into the catalyst bulk. important acrylic monomer, which is then polymerized to Variations in catalyst behaviour have been shown to change with give poly(methyl methacrylate). Heteropolyoxometalates the countercation and appear to be related to the polarizing abil- are also active acid catalysts, and processes based both on ity of the cation, which can be represented by the ionic potential their redox and acid–base properties have found commer- (charge/ionic radius). This, in turn, may indicate that the active 3 cial applications (3–5). site at the [PMo12O40] ion is close to an attendant countercation. For the alkali metal ions Li+,Na+,K+,Rb+, and Cs+ as well as the The study of heteropolyoxometalates as oxidation– (isoelectronic) ions of the series Cs+,Ba2+,La3+, and Ce4+, the stud- reduction catalysts has involved primarily Keggin-based 3 ies have shown that conversion generally decreases with increasing structures, principally [PMo12O40] , as well as substi- ionic potential, while selectivity to methacrolein is less affected by tuted species involving replacement of one or more changes in this property.
    [Show full text]
  • Structure and Functional Properties of Heteropolyoxomolybdates Supported on Silica SBA-15
    Structure and functional properties of heteropolyoxomolybdates supported on silica SBA-15 vorgelegt von Dipl.-Chem. Rafael Zubrzycki geb. in Berent von der Fakultät II - Mathematik und Naturwissenschaften der Technischen Universität Berlin zur Erlangung des akademischem Grades Doktor der Naturwissenschaften -Dr. rer. nat.- genehmigte Dissertation Promotionsausschuss Vorsitzender: Prof. Dr. rer. nat Thomas Friedrich Berichter/Gutachter: Prof. Dr. rer. nat. Thorsten Ressler Berichter Gutachter: Prof. Dr. rer. nat. Malte Behrens Tag der wissenschaftlichen Aussprache: 20. März 2015 Berlin 2015 Abstract Heteropolyoxomolybdates with Keggin structure (HPOM) were supported on SBA-15 and introduced as model catalysts for investigating structure-property correlations during selective propene oxidation. The chemical composition of the HPOM was varied by substituting molybdenum with vanadium or tungsten. Subsequently, the various heteropolyoxomolybdates were supported on nanostructured silica SBA-15. Additionally, unsubstituted HPOM were deposited on SBA-15 with different pore radii. Unsupported and supported heteropolyoxomolybdates were characterized by ex situ techniques yielding a detailed knowledge about structure and chemical composition of the model catalysts. Afterwards, the unsupported and supported heteropolyoxomolybdates were characterized by in situ techniques and tested for their catalytic properties in the partial oxidation of propene. HPOM supported on SBA-15 were investigated to elucidate the influence of addenda atoms, the silanol groups of SBA-15, the pore radii of SBA-15, and the HPOM loading on the resulting structures forming during propene oxidation conditions. The initial Keggin structure was retained after supporting HPOM on SBA-15. The removal of adsorbed water and a following dehydroxylation of silanol groups of SBA-15 lead to a destabilizing effect on the Keggin ion during propene oxidation conditions.
    [Show full text]
  • Energetics of Heterometal Substitution in Ε-Keggin [Mo4al12(OH)24(OH2
    6/7/8+ 1 Energetics of heterometal substitution in -Keggin [MO4Al12(OH)24(OH2)12] ions 2 (Revision 2) 3 Dana Reusser1, William H. Casey2, and Alexandra Navrotsky1* 4 1Peter A. Rock Thermochemistry Laboratory and NEAT ORU, University of California at Davis, 5 Davis, California 95616, U.S.A. *E-mail: [email protected] 6 2Department of Chemistry, Department of Geology, University of California at Davis, Davis, 7 California 95616, U.S.A. 8 Abstract: Aluminum hydroxide ions in the -Keggin structure provide geochemical models for 9 how structure affects reactivity, and consequently, how aqueous ions evolve to bulk precipitates. 10 Here we report a systematic comparison of heterometal substitution into the MAl12 -Keggin 11 structure, where M = GaIII, AlIII, or GeIV. We use direct solution calorimetric techniques to 12 compare the energetics of these substituted structures and complement these measurements with 13 density functional theory, DFT, calculations to further examine this structure as a host to 14 alternative heterometals. The measured enthalpy of solution, ΔHsoln, at 28 °C in 5 N HCl for the 7+ 7+ 15 selenate salts of GaAl12 and AlAl12 , was measured as -869.71 ± 5.18 and -958.04 ± 2.79 -1 ° 16 kJ∙mol , respectively. The enthalpies of formation from the elements, ΔH f,el, for the selenate 7+ 7+ -1 17 salts of GaAl12 and AlAl12 , are -23334.18 ± 60.38 and -23075.02 ± 61.68 kJ∙mol , 18 respectively, supplanting previous values. We compare structural relationships to both 19 experimental and calculated energies to identify the driving forces that control these substitutions 20 and stability, and establish that tetrahedral M-O bond lengths are closely related to the strain and 21 stability of the structure.
    [Show full text]
  • Heteropolyacids As Effective Catalysts to Obtain Zero Sulfur Diesel*
    Pure Appl. Chem., Vol. 79, No. 11, pp. 1887–1894, 2007. doi:10.1351/pac200779111887 © 2007 IUPAC Heteropolyacids as effective catalysts to obtain zero sulfur diesel* Alberto de Angelis1,‡, Paolo Pollesel1, Daniele Molinari1, Wallace O’Neal Parker Jr.1, Alessandra Frattini2, Fabrizio Cavani2, Susie Martins3, and Carlo Perego1 1Eni, Refining and Marketing Division, via F. Maritano 26, San Donato Milanese, Italy; 2University of Bologna, viale Risorgimento 4, Bologna, Italy; 3UOP, 25 East Algonquin Road, Des Plaines, IL 60017, USA Abstract: This paper deals with the catalytic properties of different supported heteropolyacids (HPAs), both molybdenum- and tungsten-based, in the oxidative desulfurization process of diesel. We are jointly developing a new oxidative desulfurization process, aimed at reducing the sulfur content in diesel to less than 10 ppm (parts per million) using in situ produced per- oxides. In this new process, high-molecular-weight organosulfur compounds, such as 4,6-di- methyl-dibenzothiophene (DMDBT), difficult to be eliminated by conventional hydro- desulfurization, are oxidized to the corresponding sulfones and subsequently removed by adsorption. Molybdenum-based HPAs, with Keggin structure, proved to be the most active and selective catalysts for oxidizing DMDBT with on-stream lifetimes exceeding 1500 h time on stream (t.o.s.). Keywords: heteropolyacids; desulfurization; diesel; air pollution; molybdenum. INTRODUCTION The sulfur content in fuels is required, by regulations, to be progressively lowered. In diesel, it will have to be reduced to a value lower than 15 ppm (parts per million) in the United States, and to a value lower than 10 ppm in the European Union within the year 2009.
    [Show full text]
  • Isopoly and Heteropoly Acids and Salts
    CHAPTER 5 Isopoly and Heteropoly Acids and Salts: Isopoly and Heteropoly Acids and Salts of Mo and W: Structures of Isopoly and Heteropoly Anions The term polymetalate acid or simply poly acid may be defined as the condensed or polymerized form of the weak acids of amphoteric metals like vanadium, niobium, tantalum (VB group metals) or chromium, molybdenum, and tungsten (VIB group metals) in the +5 and +6 oxidation states. The anions of these poly acids contain several molecules of the acid anhydride and the corresponding salts are called as polysalts. Furthermore, if these polymerized acids contain only one type of acid anhydride, they are called as isopoly acids. However, these anhydrides can also condense with some other acids like phosphoric or silicic acid to form heteropoly acids. In other words, isopoly acids contain only one metal along with hydrogen and oxygen while heteropoly acids contain two elements other than hydrogen and oxygen. The corresponding salts of isopoly and heteropoly acids are called as isopoly and heteropoly salts, respectively. Consider the polymerization of chromate ion to form different isopoly chromates anions. CrO3 2– dissolves in an alkali to give yellow colored CrO4 ions solution. At very high pH, above 8, the chromate ions, 2– CrO4 , exist as the discrete entities but as the pH is lowered down, the protonation and dimerization take place. For instance: 2H2CrO4 ⟶ H2Cr2O7 – H2O and 3H2CrO4 ⟶ H2Cr3O10 – 2H2O and 4H2CrO4 ⟶ H2Cr4O13 – 3H2O 2– 2– 2– The polymeric anions Cr2O7 , Cr3O10 and Cr4O13 produced by the polyacids H2Cr2O7, H2Cr3O10 and H2Cr4O13, can successfully be isolated from their aqueous as sodium or potassium polysalts like K2Cr2O7, 5+ 5+ 5+ 6+ 6+ 6+ K2Cr3O10 and K2Cr4O13, respectively.
    [Show full text]
  • The Structure of Molybdenum-Heteropoly-Acids Under Conditions of Gas Phase Selective Oxidation Catalysis: a Multi-Method in Situ Study
    Applied Catalysis A: General, 256 (2003) 1-2, 291-317 The Structure of Molybdenum-Heteropoly-Acids under Conditions of Gas Phase Selective Oxidation Catalysis: A Multi-Method in situ Study. F.C. Jentoft, S. Klokishner, J. Kröhnert, J. Melsheimer, T. Ressler, O. Timpe, J. Wienold, R. Schlögl* Department of Inorganic Chemistry, Fritz-Haber-Institute of the MPG, Faradayweg 4-6, 14195 Berlin, Germany * Corresponding author: e-mail [email protected], phone +49 30 8413 4400, fax +49 30 8413 4401 Recieved 11 February 2003; accepted 25 March 2003 Abstract The present study focuses on the evidence about the existence of Keggin ions under various reactive conditions. The stability of the hydrated parent heteropoly acid (HPA) phases is probed in water, by thermal methods in the gas phase, by in situ X-ray diffraction and in situ EXAFS. An extensive analysis of the in situ optical spectra as UV-Vis-NIR in diffuse reflectance yields detailed information about the activated species that are clearly different from Keggin ions but are also clearly no fragments of binary oxides in crystalline or amorphous form. Infrared spectroscopy with CO as probe molecule is used to investigate active sites for their acidity. Besides –OH groups evidence for electron-rich Lewis acid sites was found in activated HPA. All information fit into a picture of a metastable defective polyoxometallate anion that is oligomerised to prevent crystallisation of binary oxides as the true nature of the “active HPA” catalyst. The as-synthesized HPA crystal is thus a pre catalyst and the pre- cursor oxide mixture is the final deactivated state of the catalyst.
    [Show full text]
  • Ammonia Adsorption on Keggin-Type Heteropolyacid Catalysts Explored by Density Functional Quantum Chemistry Calculations Billy B
    3556 J. Phys. Chem. B 2000, 104, 3556-3562 Ammonia Adsorption on Keggin-Type Heteropolyacid Catalysts Explored by Density Functional Quantum Chemistry Calculations Billy B. Bardin, Robert J. Davis, and Matthew Neurock* Department of Chemical Engineering, UniVersity of Virginia, CharlottesVille, Virginia 22903-2442 ReceiVed: September 13, 1999; In Final Form: January 26, 2000 Density functional quantum chemical calculations have been used to compare the acid strengths of phosphotungstic and phosphomolybdic acids by computing the adsorption energy of ammonia on model clusters of each heteropolyacid. The adsorption of ammonia on a phosphotungstic acid cluster was stronger than the adsorption on a phosphomolybdic acid cluster. The predicted adsorption energies were near -150 and -106 kJ mol-1 for phosphotungstic and phosphomolybdic acid, respectively. This compares well with the experimental heats of ammonia sorption determined from microcalorimetry. An analysis of different adsorption modes of ammonia on phosphotungstic acid showed that bidentate adsorption of ammonia on the heteropolyacid clusters aided in proton transfer and yielded stronger adsorption energies than did a monodentate adsorption mode. In addition, we report the computed adsorption energies of pyridine on a heteropolyacid cluster. Introduction introduce the long-range effect of the zeolite cage on simulations of acid chemistry.13,14 During these studies, various molecules The drive to develop environmentally friendly chemical have been used to computationally explore the acid chemistry processes has motivated a significant increase in research of zeolites. Most common among these molecules are water, activities that encompass understanding and designing solid acid ammonia, and methanol.15 catalysts. These materials offer the unique opportunity to replace the corrosive liquid acids currently used in many chemical Herein, we have modeled the class of materials known as conversion steps to provide “greener” processes.
    [Show full text]