Platinum Metals Review

VOLUME 55 NUMBER 3 JULY 2011

Platinum Metals Review is published by Johnson Matthey Plc, reﬁ ner and fabricator of the precious metals and sole marketing agent for the six platinum group metals produced by Anglo American Platinum, South Africa.

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JULY 2011 VOL. 55 NO. 3 Contents

The PGM 2011 Industrial Commercialization Competition 153 A guest editorial by Michael Joseph

Carbon Nanotubes as Supports for Palladium and Bimetallic Catalysts 154 for Use in Hydrogenation Reactions By R. S. Oosthuizen and V. O. Nyamori

6th International Conference on Environmental Catalysis 170 A conference review by Noelia Cortes Felix

9th International Frumkin Symposium 175 A conference review by Alexey Danilov

“Heterogenized Homogeneous Catalysts for Fine Chemicals 180 Production: Materials and Processes” A book review by Raghunath V. Chaudhari

Phase Diagram of the Rhenium-Rhodium System: State of the Art 186 By Kirill V. Yusenko

“Ruthenium Oxidation Complexes: Their Uses as 193 Homogenous Organic Catalysts” A book review by Peter Maitlis

The Early Life of Smithson Tennant FRS (1761–1815) 196 By David G. Lewis

“Platinum 2011” 201

Publications in Brief 203

Abstracts 206

Patents 209

Final Analysis: Is Gold a Catalyst in Cross-Coupling Reactions 212 in the Absence of Palladium? By Madeleine Livendahl, Pablo Espinet and Antonio M. Echavarren

Editorial Team: Jonathan Butler (Publications Manager); Sara Coles (Assistant Editor); Ming Chung (Editorial Assistant); Keith White (Principal Information Scientist) Platinum Metals Review, Johnson Matthey Plc, Orchard Road, Royston, Hertfordshire SG8 5HE, UK Email: [email protected]

Guest Editorial The PGM 2011 Industrial Commercialization Competition

Anglo American Platinum, the world’s largest The unique qualities of pgms make them a vital primary platinum miner, is a proud partner component in many technological inventions and of the 2011 SA Innovation Summit. This aims a part of our everyday lives – in applications as to provide opportunities for innovators and diverse as transport, industrial processes, electronic inventors to communicate their ideas, including device manufacture and medicine. Their catalytic new applications for the platinum group metals properties make them a signifi cant contributor to (pgms) mined by Anglo improving the environment by American Platinum. Access to providing cleaner, more effi cient these opportunities is promoted energy. Research and development through the PGM Industrial into the applications of the pgms Commercialization Competition. has brought signifi cant technical South Africa is home to 77% of the world’s and commercial success in all of these areas. platinum reserves, and Anglo American Platinum Together with their ability to be recycled, pgm use accounts for about 42% of newly mined production is also increasingly sustainable. globally, with its operations primarily based in Innovation and economic growth are integrally South Africa. Benefi ciation of South Africa’s mineral linked. This competition should help promote wealth before export has huge potential for major innovative, commercially viable technology that fi nancial growth with many opportunities for job will add value to the pgm economic chain. creation in the country. South Africa’s strengths include technical and production expertise as MICHAEL JOSEPH well as comprehensive research and development Anglo American Platinum, South Africa activities. Anglo American Platinum launched the PGM Email: [email protected] Development Fund in 2009 with the specifi c objective of providing capital for future pgm More Information market development and benefi ciation. The Fund To download an entry form, visit the PGM seeks to invest primarily in early stage or start-up Development Fund website: activities with commercial viability. The Industrial www.pgmdevelopmentfund.co.za Commercialization Competition for the best new For more information on the Innovation Summit, application for pgms or an improvement on a visit: www.innovationsummit.co.za current commercialised product will be a platform for funding consideration by the PGM Development The Author Fund. Michael Joseph is the Manager: Industrial Development and The competition is open to researchers, Beneﬁ ciation at Anglo American Platinum, and leads the PGM institutions, manufacturers, designers or teams Industrial Commercialization Competition. resident in South Africa and must be submitted by 30th November 2011.

Carbon Nanotubes as Supports for Palladium and Bimetallic Catalysts for Use in Hydrogenation Reactions doi:10.1595/147106711X577274 http://www.platinummetalsreview.com/

By R. S. Oosthuizen‡ and V. O. Nyamori* Carbon nanotubes (CNTs) possess unique properties which make them competitive with conventional catalyst School of Chemistry, University of KwaZulu-Natal, supports. This short review collates fi ndings from many Westville Campus, Private Bag X54001, Durban 4000, research groups on the benefi ts of palladium/carbon South Africa nanotubes in hydrogenation reactions. The effects of ‡ Email: [email protected]; *[email protected] modifi ed CNTs and bimetallic platinum group metal (pgm) catalyst/CNT systems for hydrogenation reactions are also discussed.

Introduction The need to optimise industrially important processes and new technologies, and to create a sustainable society and environment, drives the search for better energy sources and better materials. Coupled with this is the need for economic development and competi- tiveness in the global market. Worldwide trends are towards greener chemistry, greener energy and a decrease in our reliance on fossil fuels. Catalysis plays an important role in this and two recent papers have discussed how it has shaped, and will continue to shape, society (1, 2). Progressive research into novel catalytic systems is a part of this endeavour. Palladium is one of the most versatile metal catalysts used in industry. Two of the main reasons for its importance are its ability to catalyse the formation of carbon–carbon bonds and the insensitivity of many Pd catalysts to water or oxygen. Pd is particularly effi - cient as a catalyst in hydrogenation reactions. Metal catalysts reach a much greater potential when supported. This is because metal catalyst particles can be dispersed to a greater degree, and therefore are exposed to a larger number of substrate molecules. Up to 75% of hydrogenation reactions are currently carried out over Pd/C catalysts. A variety of carbon supports for precious metal catalysts have, for several decades, been used in heterogeneous catalysis (3). Emerging carbonaceous supports, such as the newly discovered carbon allotropes and shaped carbon nanomaterials (SCNMs), including CNTs (4), see Figure 1(a), carbon microspheres (5),

(a) (b) (c)

40 nm 40 nm 50 nm Fig. 1. TEM image of: (a) Pd/MWCNTs used for heterogeneous hydrogenation of trans- stilbene (76); (b) Pd/microspheres before a hydrogenation reaction (5); (c) Pd/CNFs used for the heterogeneous hydrogenation of cinnamaldehyde (6) (Reproduced by permission of The Royal Society of Chemistry and Elsevier) see Figure 1(b), and carbon nanofi bres (CNFs) (6), This article covers a wide range of literature on Pd/ see Figure 1(c), are gaining more interest. The CNT systems. The examples chosen for this review remarkable properties of CNTs, such as being rela- mainly involve some current studies of Pd/CNT sys- tively light in weight and strong in nature, make them tems for hydrogenation reactions. Specifi cally, exam- worthwhile to investigate as supports for Pd metal ples based on cinnamaldehyde (Figure 2(a)), which catalysts. Although the existence of fi lamentous car- has useful applications such as a fl avouring, fungicide, bon nanomaterials (7) has been known for decades, antimicrobial agent or anticancer agent among others, it is only since the report in 1991 by Iijma (8) that are provided. The reduction of this organic compound many researchers have devoted much time and effort in is interesting because it has more than one functional developing new strategies for the synthesis of SCNMs. group that can be reduced. The useful products that Trends in technological and scientifi c progress in are obtained include cinnamyl alcohol (Figure 2(b)), catalysis lean towards the production of more effi - 3-phenylpropionaldehyde (Figure 2(c)) and 3-phenyl- cient catalysts, smaller particle sizes and more fi nely propan-1-ol (Figure 2(d)), among others, depending dispersed particles to optimise yields and decrease on chemoselectivity. Hence, this compound, as an reaction times. For this reason, nanosized catalytic example, could form the basis for the comparison of particles have received much attention and they are conversions and the effect or infl uence of the support known to display higher catalytic activity (9). Hybrid on Pd chemoselectivity. metal-CNT systems have been shown by theoretical calculations to have altered properties compared to Synthesis of Carbon Nanotubes unmodifi ed CNTs (10). The results of hydrogenation CNTs and other SCNMs can be made by a variety of reactions on various supports suggest that the interac- procedures and these include numerous variations tion between the metal catalyst and the support greatly of arc discharge (14, 15), laser ablation (16, 17) and infl uences the catalytic activity in a hydrogenation chemical vapour deposition (CVD) processes (18– reaction (11–13). Hence, this review addresses the 21). In the arc discharge and laser ablation methods, issue of catalyst support use with the aim of broadly the catalysts required for synthesis are generally answering the following questions: made from metals or metal salts. Both of these meth-  How do CNTs compare with other traditional car- ods produce relatively pure CNTs but are currently bonaceous supports for catalysts and in what not easy to scale up to industrial levels of production. cases are CNTs superior as Pd supports in hydro- The CVD processes, by contrast, allow for easy scale- genation reactions? up.  How do chemically modifi ed CNTs infl uence the There are two main approaches to the CVD synthe- activity of Pd nanoparticles (NPs), especially in sis of CNTs. The fi rst method entails passing a gas hydrogenation reactions? phase carbon source over a supported catalyst. The  What effect does a secondary metal have on the catalyst used can be derived from any metal source catalytic activity of the Pd/CNT system? including an organometallic complex (22). In the sec- Lastly, we look at a few literature examples involving ond method, both the catalyst and the carbon source the use of Pd/CNT hybrids in hydrogenation reactions. are in the gas phase and the CNTs are formed in the

Fig. 2. Structure of: (a) cinnamaldehyde; (b) cinnamyl alcohol; (c) 3-phenylpropionaldehyde (hydrocinnamaldehyde); (d) 3-phenylpropan-1-ol gas phase. This latter process is called the ‘fl oating well as industrial hydrogenation catalysts for liquid catalyst’ method and typically requires volatile organo- (41–43) and gas (44) phase processes. metallic complexes. Many studies have attempted to rationalise the The Advantages of Carbon Nanotubes as mechanism of catalytic synthesis of CNTs. There is Catalyst Supports now a consensus as to the mechanism involved in A host of supports for Pd catalysts are available, from the synthesis of CNTs over supported catalysts (23–27). metal oxide supports such as alumina, silica and In this process, small catalyst (metal) particles are zeolites, to the traditional carbonaceous supports deposited on a support and the carbon from the gas such as activated charcoal or activated carbon (AC), phase deposits onto, or dissolves in, the catalyst parti- carbon blacks, graphites and the emerging carbon cle. For metals like iron and cobalt, growth of the nanomaterials (3). CNT then arises from the precipitation of the carbon Oxide supports are often mechanically and thermally out of the metal. If the catalyst–support interaction is unstable. In the case of alumina, at high temperatures strong then the carbon tubes grow away from the the ions of the catalytically active phase can interact support surface (‘base-growth’ mechanism), but if the with the support in such a manner as to lower the cata- catalyst–support interaction is weak, then the metal lyst availability and catalytic activity (45). In transition particle is displaced from the surface by the carbon aluminas, conversion to -alumina at temperatures (‘tip-growth’ mechanism) (27). The mechanism has near 1100ºC can occur, resulting in a lowered surface been further simplifi ed by Moisala et al., who pro- area (46). Heat dispersion in certain oxide supports, posed that the metal catalyst particles act as nuclei for such as alumina, is not always uniform, due to the insu- the growth of CNTs in the gas phase (28). lating nature of this material. Thus, under oxidising Another type of CVD approach to CNT synthesis conditions, so called ‘hot-spots’ can form, resulting in involves the reactions taking place in a closed con- alteration of both the support and catalyst metal (47). tainer (for example, an autoclave or a sealed quartz There are a variety of AC products that differ in tube) at elevated temperatures. Typically, in this certain key properties such as porosity, pore size and method, organometallic complexes (at times contain- particle size distribution, surface area, resistance to ing an external carbon source) are used as starting attrition and content of ash, depending on the pro- materials (29–39). cess of manufacture. AC is commonly used in liquid phase processes and remains the popular choice of Catalytic Applications of Carbon Nanotubes support for hydrogenation reactions. This is due to its CNTs exhibit extraordinary properties which are ease of separation from the reaction mixture, resist- required for several potential applications (40). ance towards aggressive media such as high pH, and Among these applications, the use of CNTs as catalyst the relative ease of metal recovery after use. Carbon supports seems to be one of the most promising fi elds, black, which is produced from acetylene under high with large economic implications. CNTs can be used temperatures, is more suitable for use as a support as synthesised (‘pristine’) or can be modifi ed, func- than conventional carbon black made from other tionalised, doped or used as a part of a composite. petroleum fractions. However, carbon black in general Many applications involve hybrids or composites of has a relatively low ash content (3). CNTs with precious metal NPs. It is predicted that In order to overcome some of the disadvantages of such composites will fi nd uses in modern materials as the common commercial supports, there is a need to

research and develop new nanodimensional sup- mechanically taxing catalytic environments such as ports such as CNTs or CNFs. These nanostructured vigorously stirred liquid phase reactions. On more carbon-based materials display good physical and conventional supports, high levels of friction may chemical properties which are ideal for catalyst sup- lead to attrition, effectively altering the surface area ports. The two main types of CNT considered here are of the exposed metal catalyst (47). Moreover, the rela- the single-walled carbon nanotube (SWCNT) and the tively lower mechanical stability of common com- multiwalled carbon nanotube (MWCNT) (Figure 3). mercial carbon-based supports initiates the formation of fi ne particulates during operation. The existence of Electronic Properties a large amount of micropores can reduce the full The arrangement of carbon atoms determines the sur- accessibility of the reactant particles to the active face and electronic properties of CNTs. According to site. theoretical predictions, the geometry of the ring struc- The high strength of CNTs results from the covalent tures imparts either a metallic or semi-metallic nature sp² bonds, which form a honeycomb lattice between to CNTs (48, 49). This naturally has an effect on the the individual carbon atoms. In 2000, a MWCNT was properties of metals loaded onto the support. Duca tested and found to have a tensile strength of 63 GPa et al. studied the combined properties of graphite (51). A SWCNT has been shown to be the strongest

versus SWCNTs with Pd9 clusters by means of compu- material synthesised to date with a Young’s modulus tational methods (50). Their fi ndings showed that Pd9 of ca. 1 TPa (52). clusters may have a stronger interaction with a CNT than with traditional fl at graphite sheet bilayers due to Reactivity and Stability the curvature of the nanotube which has an effect on Carbon supports are often unreactive and stable in metallic properties. many acidic and basic media, and consequently fi nd use in a wide range of industrial applications (3, 53) Mechanical Strength while many other supports are rendered useless after The high mechanical strength of CNTs makes them reaction. However, traditional carbon-based supports not only favourable in composites (47, 48), but also in have limitations not only when it comes to mechanical stability but also in terms of resistance to oxidising atmospheres at high temperatures (47). Oxidation and hydrogenation processes can result in gasifi cation when the temperature is above 500ºC and approximately 700ºC, respectively (5). The order of ease of oxidation is: amorphous carbon > MWCNTs > SWCNTs. SWCNTs are generally more structured and have fewer surface defects than MWCNTs, and hence are more stable under most conditions (4). AC is more easily oxidised than CNTs (4), and CNTs are more easily oxidised than graphite. Chiang et al. showed by thermogravimetric analysis (TGA) that acid oxidised MWCNTs were more thermally stable than

AC fi bres or C60 fullerene (54). However, impurities in carbonaceous supports, such as metal residues from CVD processes, as well as defects in the structure, may not only limit the temperature at which hydrogenation 3 nm takes place, but may also poison the active metal catalyst, such as Pd, and lower the temperature at which carbon oxidises (4). CNTs have good thermal conductivity and therefore reactions catalysed by metal/carbon Fig. 3 Micrograph of a systems need to be carefully controlled, especially if MWCNT, with cross-section they are exothermic. Temperature can affect the per- showing ﬁ ve carbon layers (8) (Reproduced by permission of formance of the catalyst on the carbon support and Nature Publishing Group) more research is needed to explore this aspect.

The effect of microwave irradiation on MWCNTs catalysts. One reason for this is the high surface-to- has been studied by Olivier et al. (55). The authors volume ratio of SWCNTs compared to other supports. prepared 10 wt% Pd on MWCNTs with metal particles They also have high surface areas, 1587 m2 g–1 (57) found only on the outer walls. Microwave irradiation (see Table I) after purifi cation and tube end opening. was used to drive the hydrogenation of cinnamate The SWCNT structure is such that every atom is esters with ammonium formate as a reductant. Chem- exposed to not one but two surfaces – both the inner oselective C C bond hydrogenation occurred for all and outer surfaces of the nanotube. Table I shows the substrates and the catalyst could be recycled more approximate surface areas of various carbon supports. than fi ve times without loss of activity. The same In the case of AC, the micropores are large in quantity reaction carried out under the same conditions with and their size may actually slow the progress of sub- Pd/AC generated a variety of other products due to strate molecules into the pores (47). The ACs can microwave degradation of chemical species, demon- have macro-, meso- and micropores, which can strating that Pd/AC is less regio- and stereoselective decrease the reproducibility of metal loading. Surface than 10 wt% Pd on MWCNTs. areas can range from 800–1200 m2 g–1 (3). However, Liang et al. investigated the hydrogenation of car- the loading of Pd on the SWCNTs has been found to bon dioxide catalysed by supported palladium/zinc be lower than that obtained on MAXSORB® AC for oxide catalysts (56). Pd/ZnO on MWCNTs proved hydrogen sorption studies (58). The authors of that more favourable than Pd/ZnO on either alumina or AC, study suggest that this is due to the larger pore vol- with the MWCNTs providing a promoting effect. Also, umes and surface area of the AC, and thus the corre- herringbone-type MWCNTs had a greater promoting spondingly larger number of sites on which nucleation activity than parallel-type MWCNTs in these studies. can occur. However, smaller Pd crystallites were The high conversion and selective formation of metha- formed on SWCNTs than on AC. nol from CO2 by the MWCNT-supported catalysts was It has been shown that Pd’s activity for the hydro- due to their favourable ability to reversibly adsorb a genation of ,-unsaturated aldehydes is high, but greater amount of hydrogen, thus increasing the rate of its selectivity remains challenging and many times it surface hydrogenation reactions. has been boosted by the addition of promoters (59). A much researched model compound of this class of Surface Area and Selectivity aldehydes is cinnamaldehyde. Pd’s selectivity for SWCNTs, which are inherently microporous, are con- cinnamyl alcohol is low when compared to Pt or sidered by some to be very suitable supports for metal ruthenium, however, using CNTs as supports seems to

Table I Comparison of the Surface Areas of Carbon-Based Supports

Support Typical surface Reference area, m2 g1

Activated carbon 800–1200 (3) Conventional 100–1500 (3) Carbon black Graphitised 60–300 (3) Graphite 10–50 (3) SWCNTs 1587a (57) CNTs Shaped carbon MWCNTs 400b (62) nanomaterials Carbon nano- and 10 (117) Other microspheres a After (i) debundling with DMF/EDA; (ii) acid treatment; (iii) wet oxidation b After basic treatment

provide advances in overcoming this challenge. conditions. They showed that benzene conversion to Corma et al. compared Pd/SWCNTs with Pd/AC pre- cyclohexane approximates 100% at the highest load- pared by the same method (60). They showed that Pd/ ing (12.0 wt%) Pd/MWCNT. An intermediate loading AC had higher activity for the hydrogenation of cinna- (8.0 wt%) yielded nearly double the conversion of maldehyde to 3-phenylpropionaldehyde than Pd/ benzene compared to that achieved using the AC- or SWCNTs. However, there was a wider range of particle zeolite-supported catalysts. This was despite the fact sizes for Pd/AC than for Pd/SWCNTs. This was thought that the specifi c surface area of the MWCNTs was to be due to the larger variety of functional groups lower than those of the zeolite and AC as determined on AC. This may cause Pd2 ions not to be uniformly after acid treatment. It was also shown that diluted deposited in the beginning stages of deposition, Pd salt solutions yielded smaller Pd particles inside resulting in bigger agglomerates over time, and hence tubes and more concentrated solutions yielded larger a larger range of sizes. particles, which would infl uence catalytic rates. MWCNTs are inherently mesoporous structures. The In a study on the partial hydrogenation of phenyl- pore sizes of MWCNTs allow for diffusion, reaction and acetylene, CNT, AC and carbon black were used as desorption of chemical species and thus are good supports for Pd (65). Although all active phases supports for catalysts (61). They also possess high achieved over 95% conversion to styrene, the selectiv- surface areas, reaching up to approximately 400 m2 g–1 ity was highest for the Pd/CNT catalyst, with fi ve after basic treatments (62). These supports sometimes runs maintaining the activity and selectivity. The AC give better activity than microporous supports such support showed agglomeration of the Pd NPs. as AC. Janowska et al. showed that selectivity for the Pd/CNFs (5 wt% Pd) and Pd/AC were used in the C C bond hydrogenation product of cinnamaldehyde liquid phase hydrogenation of the C C bond in can exceed 80% when performed over Pd/CNTs (63). cinnamaldehyde by Pham-Huu et al. (6). Both the The explanation given was the lack of micropores as surface area:volume ratio and thus catalytic activity well as the high surface area of the CNTs. Lack of were higher for the CNF-supported catalyst. This was micropores affects the time spent by reactants and assumed to be due to the large number of micropores products on the support surface as well as affecting on AC leading to diffusion problems which affect the the manner in which desorption occurs. Also, Pd catalytic rate. This cannot occur in CNFs because crystallites and CNTs may interact to alter the they have no micropores. Pd/CNFs produced almost adsorption and selectivity properties. exclusively (98%) hydrocinnamaldehyde and negligible In other research, Pd NPs inside MWCNTs and on AC amounts of cinnamyl alcohol and 3-phenylpropanol, both achieved complete conversion of cinnamalde- showing that the selectivity of the catalyst for C C hyde, although the completion times for the former hydrogenation under these conditions was good. were slightly faster (64). In this work it was shown that The AC catalyst produced a mixture of all products. at a higher hydrogen fl ow rate, the rate of hydrogena- However, the nature of the carbon support was shown tion increased, but more so for the AC support than to have negligible effect on the hydrogenation of a for the MWCNTs. The MWCNT-supported catalyst variety of polar aromatic compounds in a recent arti- hydrogenated predominantly the C C bond, rather cle by Anderson et al. (66). They showed that the than the C=O bond, with only about 10% of the totally nature of the solvent is a bigger factor in selectivity. hydrogenated product forming. The AC-supported Graphite has a comparatively low surface area catalyst showed an equal selectivity for both products. (10 to 50 m2 g–1), although grinding processes can Neither catalyst showed any selectivity for cinnamyl increase it up to approximately 300 m2 g–1 (3). The alcohol. It was concluded that the MWCNT-supported capacity for adsorption of volatile organic compounds catalyst was superior in terms of selectivity for hydro- onto MWCNTs and CNFs is lower than for high surface cinnamaldehyde and that the MWCNTs had a higher area graphite (67). surface area (some micropores on the traditional support being inaccessible to some substrates), resulting Recovery and Recycling of Precious Metals in a higher catalytic activity. The high price of precious metals makes the recovery Zhang et al. used MWCNTs with different Pd load- and reuse of such catalysts economically important. ings for benzene hydrogenation (43). They then com- Carbon supports make recovery more economical pared the results with those from Pd/zeolite (SiO2: compared to metal oxide supports as they can be

Al2O3  5.1) and Pd/AC prepared under the same burnt off the metal catalyst and the catalyst recovered

from a small volume of ash. The solid waste is mini- either using less catalyst for the reaction or decreas- mal. The metal can then be dissolved and recovered ing the Pd metal loading. from acidic solutions. Pristine CNTs are considered to be relatively inert, Oxidation of AC over long periods of time can allowing for only low levels of Pd deposition (4) at decrease its usefulness as a support (3). The inert- defect sites such as Stone-Wales defects, dangling ness of CNTs, on the other hand, enables them to bonds at open tips and vacancies (77). The CNTs do resist oxidation over long periods of time and allows not contain many functional groups on their surfaces them to be recycled many times. CNT-metal hybrids and thus need to be activated to create anchoring sites can be dispersed to a fairly uniform degree by stirring for better Pd metal deposition. Many of these tech- in organic solvents. After use, the hybrid CNT-NPs niques are similar to the pretreatment of other carbon can be recovered by gravitational sedimentation. supports and are primarily used to remove metallic Hence, as a support, CNTs are economical and stable impurities, such as iron derived from the CNT synthe- when it comes to the processes of recovery and reuse sis, and generate surface groups in the process. Func- of catalysts. tionalisation can be done through ball milling (78) or by chemical or electrochemical means. Chemical Loading Techniques and Considerations means often incorporate the use of highly oxidising A fair amount of research has gone into mechanisms conditions such as sulfuric or nitric acid (79–81) or suitable for attaching Pd NPs to the walls of SWCNTs molecular oxygen (79). Sometimes sonication is used and MWCNTs (68). Common loading techniques for in conjunction with a chemical means (82). Plasmas Pd include impregnation (42, 43, 64), deposition pre- can also be employed (79, 83, 84). Covalent functional cipitation (69), electroless deposition (70, 71) and groups such as alcohols (–OH), carbonyl groups electrochemical deposition (72, 73). Less commonly (–C O) and carboxylic acids (–COOH) form. used methods include CVD (74) and microemulsion In general, more oxygen groups aid higher disper- techniques (75). Supercritical CO2 has been used sion of Pd, although some authors maintain that instead of conventional solvents to effect a greener oxygen-containing groups are not sites onto which the approach to Pd loading techniques (76). However, metals anchor, but rather that they merely increase the Pd NP size, crystal structure and distribution wetting. Enhanced wetting allows for better dispersion cannot be accurately manipulated by many of these in aqueous deposition solutions. Unger et al. achieved processes. very low loadings of Pd (1 wt%) on pre-oxidised CNTs Considerations for choosing a loading technique (85). They suggest that covalent bonding does not include the desired level of Pd loading, required occur between the oxide groups and the metal, and particle size and/or size distribution ranges, and the that Pd therefore cannot attach in large quantities. macroscopic distribution of particles on the support. However, Guo et al. suggested that more Pd particles The higher the Pd loading, in general, the greater the form at positions where –COOH groups would prefer- rate of product formation, since more Pd catalyst ably form, for example at the end of SWCNTs (86). particles are exposed to substrate molecules. Most Most reports discuss Pd NPs decorated on the exte- methods yield heterogeneously dispersed particle rior of CNT surfaces. However, some state that certain sizes, although controlling the size of metal particles Pd metal catalysts loaded on the inside of nanotubes is still being investigated. Typically, the smaller the exhibit a higher catalytic activity than the same particle size, the larger the surface area of Pd metal amount on more conventional supports (43, 87). and the higher the catalytic activity. Pore structure and Figure 4 shows a transmission electron microscopy accessibility of the substrate to the metal in the pores (TEM) image of such a system. The supposition is also infl uences the macroscopic distribution. The that the partial pressure of the substrates inside the most common types of supported catalyst structure tubes is increased, altering the rate of catalysis. are eggshell, uniform distributions or intermediates of Factors affecting the placing of Pd particles inside the two (3). Typically, uniform distribution of small tubes include the hydrophobicity of tubes, the inner metal NPs is ideal for hydrogenations. However, uni- diameter, the concentration of the Pd in the precursor formly impregnated catalysts are more likely to lose solution and the surface tension of the Pd deposition part of the Pd metal loading through leaching (3). solution. Pd particles found near the tips of tubes were This can be minimised by improving the availability probably deposited there due to the fast rate of evapo- of hydrogen in the liquid reaction medium and by ration of water out of the tubes. The strong interaction

Pd(PPH3)4 as the Pd source. Different precursor Pd compounds were also found to infl uence the loading on CNTs and AC in the same studies.

Modiﬁ ed CNTs as Supports Besides modifi cation with oxide groups, other means of functionalisation can produce further benefi ts. Functionalisation can be covalent (91) or non- covalent (92). CNTs have the ability to attach a wide range of chemical species at active sites, such as their sidewalls, tubular tips or defect areas. Exohedral and endohedral functionalisation can also provide an opportunity to create unique catalyst supports for Pd. Agglomeration of NPs reduces the surface area of catalytically active metal particles. Some loading techniques, such as modifi cation of the support 10 nm with a surfactant or an an ionic liquid (IL) before metal deposition, can be employed to control the for- Fig. 4. TEM image of Pd NPs located primarily on the mation of larger nanoclusters on the surface of CNTs. inside of MWCNTs with the arrowheads indicating Surface moieties are thought to aid stabilisation of the the presence of some highly faceted Pd particles (87) crystallites during sintering (3). Chun et al. functional- (Reproduced by permission of Elsevier) ised MWCNTs with an imidazolium bromide followed by Pd (93). They effectively formed an IL catalytic sys- between Pd particles and the tube could give rise to tem rendering the functionalised MWCNTs soluble in the faceted nature of the catalyst particles (87). It has water, and thereby successfully prevented CNT been suggested that this interaction may affect disper- agglomeration and aided dispersion in the aqueous sion (43). Tessonnier et al. suggest that the morphology phase ready for Pd deposition. Following this, hydro- of the inner wall may alter the electronic nature of the genation of trans-stilbene was performed with turnover adsorbed metal and thus modify the adsorption of the frequency (TOF) values up to 2820 mol h–1, which is substrate and selectivity for the product (64). They considered to be high. Varying the anion was shown stated that the nature of the precursor solution seemed to infl uence the catalytic activity in this hydrogena- to have a negligible effect on dispersion. tion reaction. Pd/IL-f-MWCNTs (where f indicates Factors infl uencing the properties of the nanometal- functionalised; IL is [1-butyl-3-methylimidazolium] lic particles include size, shape and crystalline geom- [hexafl uoroantimonate]) remained active after 10 cycles etry (88). Computational calculations indicated that and were then used in olefi n hydrogenations. Only

CNT-supported Pd9 clusters would have a higher after 50 runs did the activity signifi cantly decrease.

activity than the unsupported cluster for H2 bond break- Sodium dodecyl sulfate (SDS) (94) and sodium ing in hydrogenation reactions, (89). Franklin et al. bis(2-hexylethyl)sulfosuccinate (AOT) (75) also aid in reported the fi rst controlled decoration of SWCNTs the homogenous distribution of Pd particles on the with Pd particles of a consistent morphology (90), support by acting as surfactants. Agglomeration of Pd and Ansón et al. found that the mass ratios of the Pd: particles is prevented. Figures 5(a) and 5(b) show support (SWCNTs or MAXSORB® AC) directly deter- Pd/CNTs prepared with and without AOT, respectively mined the percentage of Pd loaded (58). These latter (75). The fairly even distribution of NPs in Figure 5(a) authors suggested, from their results, that a threshold is apparent, whereas Figure 5(b) shows signifi cant for Pd saturation is reached when the mass ratio of agglomeration. SDS (95) and sodium n-tetradecyl support:Pd is 1:4. Also, the crystallite size was larger at sulfate (SC14S) (96) also induce reduction of the Pd higher Pd loadings. These authors demonstrated that precursor. Karousis et al. used Pd/MWCNTs with SDS the quantity of Pd loaded onto the SWCNTs was not to hydrogenate a variety of olefi ns (97). Four olefi ns altered in runs that used oxidative pretreatments, were successfully hydrogenated. The Pd/MWCNTs although their Pd wt% loading values decreased were then compared to Pd/AC for the hydrogenation slightly after a nitric acid treatment in the case of of methyl-9-octadecenoate and 2-methyl-2-pentenal.

(a) (b) Fig. 5. TEM image of Pd/MWCNTs prepared: (a) with a surfactant, showing fairly uniform distribution of Pd NPs; and (b) without a surfactant, resulting in agglomeration of Pd NPs (75) (Reproduced by permission of the American Chemical Society) 50 nm 200 nm

The molar ratio of Pd:substrate was kept constant. isorption with doped SWCNTs as opposed to pristine TOF values for Pd/MWCNTs for both compounds were SWCNTS. B-doped CNTs gave the most enhanced 3 to 5 times higher than for Pd/AC. Large amounts of binding. Amadou et al. carried out experiments in the Pd precursor also cause agglomeration. Thus it is which the dispersion of Pd was found not to be signifi - important to control the amounts of both the precur- cantly different on doped or undoped tubes (42). sor and the SDS added to the reaction mixture for opti- However, it was interesting to note that no Pd NPs were mal dispersion (94). found inside the N-doped tubes. This was thought to In another paper, Pd was loaded onto SDS-stabilised be due to compartmentalisation as shown in Figure 6. MWCNTs and SWCNTs and then used in successful The Pd/N-doped CNTs were compared with Pd/CNTs hydrogenations of the same four olefi ns as well as and Pd/AC for the liquid phase hydrogenation of cin- 3-phenyl-2-propenal (98), although a detailed com- namaldehyde. Pd/AC, with the highest specifi c surface parison of the two supports was not given. The area, displayed the highest activity. Pd/N-doped CNTs Pd/MWCNTs were then compared with Pd/AC for had an activity nearly equal to that of Pd/AC, but the hydrogenation of methyl-9-octadecanoate and almost double that of the undoped Pd/CNTs. This 2-methyl-2-pentenal. TOF values for Pd/MWCNTs indicated a signifi cant infl uence of the N incorpora- approximated 3 to 5 times higher than for the conven- tion on the activity of the catalyst for C C bond hydro- tional catalyst. Even after 7 cycles of the Pd/MWCNTs genation. In terms of selectivity, the doped support there was little to no leaching of Pd off the support. was best for hydrocinnamaldehyde production while Doping of CNTs has been fairly extensively the Pd/AC catalyst was the least selective. researched for N- and B-dopants (99–101) resulting in modifi ed properties. Many properties such as elec- Bimetallic Catalysts – Effect of tronic properties (102) and even the strength with Secondary Metal which other species adsorb (103) are affected by dop- Research has shown that bimetallic catalysts can infl u- ing. Most CNT doping studies have been carried out ence the catalytic activity of a system (107) and some- for MWCNTs, with a few on SWCNTs for applications times have higher catalytic performance in certain such as fi eld emission devices. Generally, CNTs are reactions than a single metal catalyst (108). The inert, but the incorporation of heteroatoms into their additional metal(s) can improve the size and structure can give rise to a more chemically active material. Disadvantages include the fact that often N-doped counterparts are less thermally stable and more prone to oxidation (104). The nitrogen incorporation can greatly alter the morphology of the CNTs (104, 105), although in some cases no morphology change was observed (101). Graphitisation was found to be enhanced in B-doped MWCNTs (106). An and Turner studied the binding between transition metals and CNTs by making use of 20 nm density functional theory (DFT) calculations for individual metal atoms on N- or B-doped SWCNTs at chosen sites (103). These initial studies showed, among Fig. 6. TEM showing the ‘bamboo’ cross-structures in a Pd loaded N-doped MWNT without Pd NPs other things, that a range of commercially important incorporated inside the cavities (42) (Reproduced by transition metals, including Pd, undergo higher chem- permission of Elsevier)

morphology of active particles as well as the catalyst 10 atm. Pd/CNT needed 24 h at 50ºC and 10 atm to selectivity (108). achieve a near 50% conversion of benzene to the The activity of palladium-platinum is superior to that saturated product. Pd-Rh/CNT was shown to be recy- of other commercial bimetallic catalysts in the hydro- clable multiple times. genation of aromatic compounds, a pre-step in the Functionalised MWCNTs in a water-in-hexane micro- desulfurisation of fuels. Noble metals are susceptible emulsion with a surfactant were loaded with Pd, Rh or to poisoning by sulfur. Use of acidic supports or Pd-Rh (75). Arene hydrogenation tests revealed that bimetallic Pd-Pt catalysts has proven to enhance the Pd-Rh/CNTs (see Figure 7) were more active than the resistance to poisoning by sulfur (109). Pawelec et al. monometallic systems for anthracene hydrogenation. studied Pd-Pt/MWCNTs in the hydrogenation of tolu- However, the detailed morphology of this bimetallic ene and naphthalene in the presence of dibenzothio- catalyst system was not studied or confi rmed. phene in the gas phase to monitor, simultaneously, It has also been shown that the molar ratio of the the hydrodesulfurisation of the sulfur-containing com- two metals in a bimetallic oxide catalyst, such as pound (110). A Pd-Pt/zirconium phosphate–silica zeo- Pd/ZnO, has infl uence on the catalytic activity of CO2 lite and a Pd-Pt/amorphous SiO2–Al2O3 (ASA) catalyst hydrogenation (56). were also prepared for comparison although different loading techniques were used. The results suggested Hydrogenation on Palladium/CNT Catalysts that all catalysts were more active for toluene hydro- Palladium on CNT supports is effective as a catalyst for genation than for the polyaromatic compound. the reduction of a variety of functional groups. Below Pd-Pt/MWCNTs had the lowest loading and BET spe- are specifi c examples for carbon–carbon multi-bond cifi c areas but the highest activity for toluene hydro- and nitrogen-containing group hydrogenations. genation. However, Pd-Pt/ASA was the best catalyst for naphthalene hydrogenation and the hydrodesulfurisa- Alkene and Alkyne Hydrogenation tion of dibenzothiophene. The combined effect of Pd/CNTs grown and supported on carbon microfi bres the Pd-Pt alloy may be a factor, coupled with the loca- were used as catalysts in the gas phase hydrogenation tion of these NPs on the MWCNTs, since a marked lack of cyclooctene (74). Initial studies showed the system of steric hindrance for the substrate would be found to be active for the reduction of this alkene. on the outer surfaces of MWCNTs as compared to the The fi rst report of the use of Pd/CNT to hydrogenate other catalysts. However, the bimetallic effect is still not C C discussed the successful hydrogenation of yet well understood. tolane, phenylacetylene and 1-heptyne with 5% Pd on Qiu et al. observed that the conversion and selectiv- CNTs (113). The results showed that only 0.02 mol% ity towards cinnamyl alcohol was highest for a Pd-Ru Pd/CNT was needed to convert all the starting materi- bimetallic catalyst on CNTs than for either of the two als to products, indicating that this catalytic system monometallic catalysts under identical conditions had a high activity towards C C hydrogenation. This (111). This fi nding was attributed either to Ru’s pro- catalytic activity was higher than that found in earlier moting effect on Pd or to a combined enhanced effect work by the same authors for the hydrogenation of from Pd and Ru together. toluene over Pd complexes supported on fullerenes Arene hydrogenation is important in industry, for (114). The ratio of the two reaction products was example, for diesel fuels with low aromatic contents. found to be determined largely by the temperature and Heterogeneous catalysis with metals at high tempera- length of time of hydrogenation. The lower the hydro- tures is the traditional method for arene hydrogena- genation time, or the higher the temperature (within tion. Yoon et al. hydrogenated benzene at room the range 22–60ºC), the greater the conversion to a temperature under 1–20 atm over palladium-rhodium/ CNTs (112). A high activity for benzene reduction, Fig. 7. TEM image with no solvent, was found. Commercially available of Pd-Rh/MWCNTs (75) (Reproduced by Pd/ C and Rh/C cannot do this under these conditions permission of the yet. Pd/CNT had very low or no activity at room tem- American Chemical perature, whereas the Pd-Rh/CNT had a catalytic activ- Society) ity much higher than either of the monometallic systems. A conversion of 98% of benzene to cyclo- 100 nm hexane occurred after 24 h at room temperature and

saturated product. Further reactions with the Pd/CNT Pd/CNT showed that such systems can take up hydro- catalyst showed the same catalytic performance. All gen effectively in signifi cant amounts. This may also be three acetylenic hydrocarbons underwent complete of interest to the hydrogen storage industry. CNTs with- conversion to a mixture of ethylenic and saturated out a metal additive were hydrogenated to a far lesser compounds. Reapplication of the catalyst at 60ºC for extent. Subsequent addition of NO caused reduction 7 h yielded 100% selectivity for the saturated product. of this gas in only the Pd/hydrogenated CNTs. Jung et al. studied Pt on CNFs and CNTs for cinna- Many examples of Pd/CNTs and bimetallic pgm/ maldehyde hydrogenation and Pd on CNFs for 1-octyne CNTs as hydrogenation catalysts are found in the liter- hydrogenation (115), amongst other supports. They ature. Table II summarises some of this research. used a colloidal microwave process to load metals onto supports. This method makes pretreatment Conclusions unnecessary and yields a high dispersion of the cata- This survey of the literature has shown that the catalyst. Unloaded supports (CNFs, CNTs, AC and Al2O3) lytic activity of nanosized Pd metal particles in hydro- were tested for cinnamaldehyde catalysis but no activ- genation reactions is greatly infl uenced by the support ity was found. Pd is possibly the most selective catalyst on which this metal is loaded. CNTs may be highly for the semi-hydrogenation of alkynes. Previous stud- advantageous as supports compared with the more ies had shown the hydrogenation of cinnamaldehyde traditional carbonaceous supports. CNTs do not dis- over Pt/CNTs to be poorer than over Pt/CNFs, thus only play many of the disadvantages that the more com- CNFs were used in the 1-octyne studies. Conversion of mon commercial supports possess. In particular, CNTs 1-octyne by Pd on two types of CNFs yielded the semi- have very high mechanical strength and thus are pref- hydrogenated product 1-octene, which had a slow erable over other supports in mechanically taxing conversion to the saturated product. stirred batch reactions. In terms of surface area, SWC- NTs, in particular, have very high surface areas and are Conversion of Nitro to Amino Group via inherently microporous. Their high surface areas also Hydrogenation allow for more reproducible loading compared to Pd/AC is a common catalyst for the selective hydrogen- some of the currently used ACs. CNTs lower the rate of ation of nitrobenzene and derivatives thereof. In one metal NP agglomeration, due to the strong metal– study, nitrobenzene was hydrogenated in the liquid support interaction arising from the unique curvature phase by using Pd deposited on the inside of MWCNTs of the CNTs, thereby enhancing the lifespan of the (87). This reaction was compared with a Pd/AC system. catalyst and ensuring its high level of activity. The The activity of the Pd/MWCNT catalyst hybrid was chemical stability of CNTs makes them less easily oxi- superior to that of the Pd/AC catalyst system, even dised than ACs, and they are economical and stable though the surface area of the AC was higher than that when it comes to the recovery and reuse of catalysts. of the MWCNTs. The observed results were explained In many cases the chemoselectivity of Pd/CNTs in in terms of the lack of micropores in the MWCNTs. It hydrogenation reactions has been shown to be superior was also suggested that convection in the liquid phase to Pd/AC systems. One study showed that surfactant- in the MWCNTs increased the rate of substrate collision modifi ed Pd/MWCNTs gave higher TOF values for with H2 molecules and thereby increased the activity. hydrogenation than the equivalent Pd/AC hybrids. Jiang et al. hydrogenated the nitro group of Almost double the activity and a superior selectivity o-chloronitrobenzene to provide an amine derivative for a specifi c product was found for Pd/N-CNTs com- using Pd supported on three different supports: CNTs, pared to undoped Pd/CNTs and a Pd/AC catalyst,

-Al2O3 and SiO2 (116). Both the activity and selectiv- respectively, in a study on hydrogenation reactions. ity for the formation of the amine product were Studies of bimetallic Pd systems on CNTs revealed favoured by the CNT-based catalyst. These results may that selectivity and conversion for the hydrogenation be infl uenced by the geometric and electronic effects of selected bonds, as well as activity towards hydro- of CNTs on the catalytic process as well as the textures genation of certain substrates, is enhanced by the pres- and properties of the CNTs. ence of a secondary metal. In summary, evidence exists for the superior activity Hydrogenation of Nitric Oxide and selectivity of Pd/CNTs in a range of hydrogena- Wang et al. used pre-hydrogenated Pd/CNTs to reduce tion reactions. There is also evidence for improved NO (44). The reducing action of the hydrogenated catalytic performance in certain cases by the use of

Table II

Examples of Palladium and Platinum Group Metal Bimetallic Catalysts Supported on Carbon Nanotubes Used in Hydrogenation Reactions

Metal-catalyst system Substrate for hydrogenation References

Monometallic catalyst Pd/CNTs Pd/SWCNTsa Cinnamaldehyde (60) Pd/MWCNTsb NO (44) Benzene (43) Cinnamaldehyde (47, 63, 64) trans-Stilbene (76) Cyclooctene (74) Nitrobenzene (87) Phenylacetylene (65) Cinnamate esters (55) Tolane, phenylacetylene, 1-heptyne (113) o-Chloronitrobenzene (116) Pd/CNFsc Cinnamaldehyde (6) 1-Octyne (115) As-synthesised CNTs Benzoic acid, benzaldehyde, acetophenone, (66) Platinum MetalsRev benzamide, phenylacetic acid, cinnamic acid, 4-hydroxybenzoic acid

Pd-Ru/CNTs Cinnamaldehyde (111) ., 2011, Pd-Pt/MWCNTs Toluene/naphthalene/dibenzothiophene (110)

Pd-Rh/MWCNTs Benzene (112) 55 , (3)• (Continued) 166 doi:10.1595/147106711X577274 •

Table II (Continued)

Metal-catalyst system Substrate for hydrogenation References

Modiﬁ ed CNTs with Pd/SDS-MWCNTsf Methyl-9-octadecanoate, 2-methyl-3-buten-2-ol, (97) monometallic catalyst 3,7-dimethyl-2,6-octadien-1-ol, 2-methyl-2-pentenal Methyl-9-octadecanoate, 2-methyl-3-buten-2-ol, (98) 3,7-dimethyl-2,6-octadien-1-ol, 2-methyl-2-pentenal, 3-phenyl-2-propenal Pd/SDS-SWCNTs Methyl-9-octadecanoate, 2-methyl-3-buten-2-ol, (98) 3,7-dimethyl-2,6-octadien-1-ol, 2-methyl-2-pentenal, ed CNTs ﬁ 3-phenyl-2-propenal Pd/imidazolium salt-MWCNTs trans-Stilbene (93) Modi Pd/sodium bis(2-hexylethyl)- Anthracene (75) sulfosuccinate-MWCNTs Bimetallic-surfactant Pd-Rh/sodium bis(2-hexylethyl)- Anthracene (75) composite sulfosuccinate-MWCNTs Doped Pd/N-MWCNTs Cinnamaldehyde (42) Platinum MetalsRev

a SWCNTs  single-walled carbon nanotubes b MWCNTs  multiwalled carbon nanotubes

p  parallel-type ., 2011, f SDS  sodium dodecyl sulfate 55 , (3)• doi:10.1595/147106711X577274 •Platinum Metals Rev., 2011, 55, (3)•

modifi ed or bimetallic Pd/CNT systems. Such fi nd- 16 A. Thess, R. Lee, P. Nikolaev, H. Dai, P. Petit, J. Robert, ings will, hopefully, spur on research in this fi eld. C. Xu, Y. H. Lee, S. G. Kim, A. G. Rinzler, D. T. Colbert, However, ACs are still widely chosen as hydrogena- G. E. Scuseria, D. Tománek, J. E. Fischer and R. E. Smalley, Science, 1996, 273, (5274), 483 tion supports due to their ease of preparation and 17 J. Liu, A. G. Rinzler, H. Dai, J. H. Hafner, R. K. Bradley, low cost. The challenge remains of improving the P. J. Boul, A. Lu, T. Iverson, K. Shelimov, C. B. Huffman, cost-effectiveness of CNT synthesis to make them an F. Rodriguez-Macias, Y.-S. Shon, T. R. Lee, D. T. Colbert economically viable alternative to ACs as Pd supports and R. E. Smalley, Science, 1998, 280, (5367), 1253 for hydrogenation reactions. 18 M. José-Yacamán, M. Miki-Yoshida, L. Rendón and J. G. Santiesteban, Appl. Phys. Lett., 1993, 62, (6), 657 Acknowledgements 19 A.-C. Dupuis, Prog. Mater. Sci., 2005, 50, (8), 929 We extend a grateful acknowledgement and thanks to 20 S. Amelinckx, X. B. Zhang, D. Bernaerts, X. F. Zhang, the National Research Foundation (NRF) Nanotech- V. Ivanov and J. B. Nagy, Science, 1994, 265, (5172), 635 nology Flagship Programme ‘Nano-architecture in the 21 J.-B. Park, G.-S. Choi, Y.-S. Cho, S.-Y. Hong, D. Kim, Benefi ciation of Platinum Group Metals’ through the S.-Y. Choi, J.-H. Lee and K.-I. Cho, J. Cryst. Growth, grant holder, Dr Leslie Petrik (University of the Western 2002, 244, (2), 211 Cape) for funding. We are also grateful to Professor 22 V. O. Nyamori, S. D. Mhlanga and N. J. Coville, Neil Coville (University of the Witwatersrand) for his J. Organomet. Chem., 2008, 693, (13), 2205 advice in the construction of this review and Professor 23 R. Saito, G. Dresselhaus and M. S. Dresselhaus, “Physical Bice Martincigh (University of KwaZulu-Natal) for Properties of Carbon Nanotubes”, Imperial College Press, London, UK, 1998 assisting in proof reading and comments during the 24 G. Cao, “Nanostructures and Nanomaterials: Synthesis, manuscript development. Properties and Applications”, Imperial College Press, London, UK, 2004 References 25 M. S. Dresselhaus, G. Dresselhaus and P. C. Eklund, 1 C. Adams, Top. Catal., 2009, 52, (8), 924 “Science of Fullerenes and Carbon Nanotubes”, 2 G. Centi and S. Perathoner, Catal. Today, 2008, 138, Academic Press, San Diego, California, USA, 1996 (1–2), 69 26 “Carbon Nanotubes: Properties and Applications”, ed. 3 E. Auer, A. Freund, J. Pietsch and T. Tacke, Appl. Catal. M. J. O’Connell, CRC Press, Boca Raton, Florida, USA, A: Gen., 1998, 173, (2), 259 2006 4 P. Serp, M. Corrias and P. Kalck, Appl. Catal. A: Gen., 27 M. Endo, T. Hayashi, Y. A. Kim, M. Terrones and M. S. 2003, 253, (2), 337 Dresselhaus, Phil. Trans. R. Soc. Lond. A, 2004, 362, 5 K. C. Mondal, L. M. Cele, M. J. Witcomb and N. J. (1823), 2223 Coville, Catal. Commun., 2008, 9, (4), 494 28 A. Moisala, A. G. Nasibulin and E. I. Kauppinen, 6 C. Pham-Huu, N. Keller, L. J. Charbonniere, R. Ziessel J. Phys.: Condens. Matter, 2003, 15, (42), S3011 and M. J. Ledoux, Chem. Commun., 2000, (19), 1871 29 V. O. Nyamori and N. J. Coville, Organometallics, 2007, 7 I. Martin-Gullon, J. Vera, J. A. Conesa, J. L. González 26, (16), 4083 and C. Merino, Carbon, 2006, 44, (8), 1572 30 D. Jain, A. Winkelm and R. Wilhelm, Small, 2006, 2, 8 S. Iijima, Nature, 1991, 354, (6348), 56 (6), 752 9 R. Schlögl and S. B. Abd Hamid, Angew. Chem. Int. Ed., 31 J. Liu, M. Shao, Q. Xie, L. Kong, W. Yu and Y. Qian, 2004, 43, (13), 1628 Carbon, 2003, 41, (11), 2101 10 E. Durgun, S. Dag, S. Ciraci and O. Gülseren, J. Phys. 32 M. Laskoski, W. Steffen, J. G. M. Morton, M. D. Smith Chem. B, 2004, 108, (2), 575 and U. H. F. Bunz, J. Am. Chem. Soc., 2002, 124, (46), 13814 11 A. Yu Stakeev and L. M. Kustov, Appl. Catal. A: Gen., 1999, 188, (1–2), 3 33 B. El Hamaoui, L. Zhi, J. Wu, U. Kolb and K. Müllen, Adv. 12 A. Chambers, T. Nemes, N. M. Rodriguez and R. T. K. Mater., 2005, 17, (24), 2957 Baker, J. Phys. Chem. B, 1998, 102, (12), 2251 34 L. Zhi, T. Gorelik, R. Friedlein, J. Wu, U. Kolb, W. R. 13 C. Park and R. T. K. Baker, J. Phys. Chem. B, 1998, 102, Salaneck and K. Müllen, Small, 2005, 1, (8–9), 798 (26), 5168 35 J. Wu, B. El Hamaoui, J. Li, L. Zhi, U. Kolb and K. Müllen, 14 T. W. Ebbesen and P. M. Ajayan, Nature, 1992, 358, Small, 2005, 1, (2), 210 (6383), 220 36 S. Liu, X. Tang, Y. Mastai, I. Felner and A. Gedanken, 15 H. Huang, H. Kajiura, S. Tsutsui, Y. Hirano, M. Miyakoshi, J. Mater. Chem., 2000, 10, (11), 2502 A. Yamada and M. Ata, Chem. Phys. Lett., 2001, 343, 37 C. Wu, X. Zhu, L. Ye, C. OuYang, S. Hu, L. Lei and Y. Xie, (1–2), 7 Inorg. Chem., 2006, 45, (21), 8543

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6th International Conference on Environmental Catalysis

PGM-based technologies for NOx, CO, HC and PM abatement

doi:10.1595/147106711X582575 http://www.platinummetalsreview.com/

Reviewed by Noelia Cortes Felix The 6th International Conference on Environmental Johnson Matthey Technology Centre, Blounts Court, Catalysis (ICEC) was held in Beijing, China, from 12th Sonning Common, Reading RG4 9NH, UK to 15th September 2010. It was organised by the Email: [email protected] Research Centre for Eco-Environmental Sciences (RCEES), Beijing, of the Chinese Academy of Sciences (CAS). The topics of this conference covered fi ve important fi elds: automotive exhaust catalysis; clean air and water; clean energy; reducing greenhouse gases; and green chemistry. Around 500 people from around the world attended. The organisers selected 16 keynotes, 119 oral presentations and 322 posters. This review solely focuses on automotive exhaust catalysis. The talks have been divided depending on their application, including: particulate matter (PM) control; three-way catalysts (TWCs); ammonia-selective

catalytic reduction (NH3-SCR); hydrocarbon-selective catalytic reduction (HC-SCR); and lean nitrogen oxides (NOx) traps.

Particulate Matter Control The fi rst keynote talk was presented by Atsushi Satsuma (University of Nagoya, Japan) and titled ‘Combustion of Carbon Using Ag/Ceria Prepared by Self-Dispersion of Ag Powder into Nano-particles’. Satsuma and coworkers presented an innovative method of preparing silver/ceria. This preparation process consisted of mixing silver powder with ceria, followed by calcination at 500°C. Upon calcination, the activity of the prepared catalyst improved, due to redispersion of the silver metallic particles, the reverse of what occurs when the catalysts are prepared by wet impregnation. The same experiment was tried with other metals: copper, gold and platinum, but no improvements in the activity were seen. The effect of the support was also studied; it was found that ceria was the best, with others following the order: ceria  titania  zirconia  zinc oxide  tin(II) oxide  niobia, however ceria is not very thermally stable. To improve thermal stability alumina was added to the ceria prior to mixing with silver. Yasutake Teraoka (University of Kyushu, Japan) focused on the effects of supported metals and

support oxides on PM combustion activity in his talk (SpaciMS). To demonstrate the high accuracy of ‘Catalytic Activity of Supported Metal Catalysts for SpaciMS, carbon monoxide oxidation over platinum- Diesel Particulate Combustion’. In their experiments, rhodium/alumina was studied. The technique is carbon black (CB) and hexadecane were used as non-invasive and non-conductive, and it is therefore substitutes for soot and for the soluble organic fraction possible to resolve kinetic oscillations and their (SOF), respectively. Comparing different precious met- dependence on local reaction conditions (1). als supported on titania, platinum showed the greatest The effect of doping palladium/ceria-zirconia activity for SOF oxidation (Pt  Pd  Ag); however, (Pd/CZ) materials was presented by Guangfeng Li the silver catalyst was by far the best for soot oxidation (University of Zhejiang, China) in ‘The Infl uence of (Ag  Pt ~ Pd). The effect of the support was only Iron Doping on the Physicochemical Properties of

studied for soot oxidation. As silver was the most Ce0.67Zr0.33O2 and the Catalytic Behaviour of Pd-Only active metal, this was impregnated on different sup- Three-Way Catalyst for Automotive Emission Control’. port oxides. It was concluded that the chemical nature Li and colleagues showed that the introduction of iron of the oxide is more important than the physical char- into CZ replaces cerium atoms, creating a more homo- acteristics of the catalyst. Cobalt(II,III) oxide (Co3O4) geneous Ce-Zr-Fe-O ternary solid solution. This substi- was the best support for soot oxidation, with others fol- tution enhances the surface area of the catalyst as lowing the order: cobalt(II,III) oxide  titania  ceria  well as the average pore diameter and broadens the lanthanum cobalt oxide  -alumina  lanthanum range of pore distribution. 1% Fe showed the maximum manganese oxide  -alumina. improvement (Figure 1) (2). As a result of the structural changes, the order of activity followed: Pd/CZFe Three-Way Catalysts (1%) > Pd/CZFe (2.5%) > Pd/CZFe (5%) > Pd/CZFe Sarayute Chansai (Queen’s University Belfast, UK) pre- (0.5%) > Pd/CZ. Unfortunately, the results shown here sented the work of his colleagues Alexandre Goguet were for fresh catalysts. The experiments with their et al. (Queen’s University Belfast; Universidade de aged counterparts are ongoing. Li stated that for the Aveiro, Portugal; and Oak Ridge National Laboratory, moment the results with iron-doped CZ are still better USA). The presentation was titled ‘Spatial Resolution than the undoped catalysts. of Kinetic Oscillations within a Catalytic Monolith’. The following lecture, presented by Naoki Takahashi Due to the lack of techniques available to study in situ (Toyota Central R&D Labs Inc, Japan), focused on the reactions inside a monolith, the group from Queen’s improvement of the stability of TWCs using platinum/ University Belfast worked on a technique called ceria-based supports. The talk was titled ‘Increasing spatially resolved capillary-inlet mass spectrometry the Lifetime of Automotive TWC Thanks to Pt-O-Ce

Fig. 1. Oxygen storage 720 150 complete capacity (OSCC) and

surface area (SBET) of doped 660 palladium/ceria-zirconia samples as a function of iron 140 loading (2) 600 –1 g S 2 BET

540 , m 130 mol O 2 g  –1 480 OSCC, 420 120

360 110 0 1 2 3 4 5 Fe loading, %

Bonds’. The CZ support was calcined at 1323 K NH3-SCR catalyst they incorporated it to the actual before impregnation of platinum to avoid support catalyst as a lower layer. The problem found with sintering later on. During ageing, reducing and oxi- this catalyst was the diffi cult diffusion of ammonia dising conditions were alternated at 1223 K. The cata- to the platinum layer, emphasising the need to opti- lysts were then regenerated in air at 1073 K for mise the thickness of the washcoat layer. 30 minutes and treated in a reducing atmosphere at 773 K for 10 minutes. Carbon monoxide adsorption Hydrocarbon-Selective Catalytic Reduction experiments showed that at low platinum loading The presentation entitled ‘A Mechanistic Study of the

(0.25 wt%) it was possible to inhibit platinum sinter- H2-Assisted Reduction of NOx by Octane on Ag/Al2O3 ing and to redisperse the agglomerated platinum. Using SSITKA-DRIFTS-MS Technique’, was given by This is believed to be due to platinum anchoring on Sarayute Chansai (Queen’s University Belfast, UK). specifi c surface sites (Pt-O-Ce) that act as the driving They presented work on the role of hydrogen in the force for the redispersion (3, 4). HC-SCR reaction (5–7), fi nding the intermediates involved and differentiating between spectator and Ammonia-Selective Catalytic Reduction active forms of the same surface species. Using iso- Chen Xu (Cummins Inc, USA) focused on the issue of topic transient kinetics they could see that, under full ammonia slip in SCR catalysts. Xu’s talk ‘New Insights steady state conditions, the intermediates found were into Reaction Mechanism of Selective Ammonia Oxi- isocyanates and cyanides. However, experiments using dation Catalyst in Diesel Aftertreatment Applications’ steady state isotopic transient kinetic analysis presented an ammonia slip catalyst (ASC) based on (SSITKA) and fast transient diffuse refl ectance fourier platinum that is positioned in front of the SCR catalyst. transform infrared spectroscopy-mass spectrometry The ASC controls ammonia oxidation to NOx when (DRIFTS-MS) with pulses of hydrogen revealed that running under lean conditions. This catalyst was under non-steady state conditions the isocyanates are hydrothermally aged at 650°C for different periods of the active intermediates, and the cyanides are only time. It was seen that ammonia conversion was unaf- spectator species (Figure 2) (8). fected by the ageing time. However, the selectivity Mingli Fu (South China University of Technology, changed towards undesired byproducts with longer China) incorporated rhodium into silver/ceria-zirconia/ ageing times. A. Scheuer (Technische Universitat alumina (CZA), fi nding a positive synergistic effect Darmstadt, Germany) presented a similar work in their between silver and rhodium in their presentation talk ‘Design of Dual Layer Catalysts for NH3 Oxidation ‘DRIFTS Study of the Selective Catalytic Reduction of in Automotive Exhaust’. In this case, instead of posi- NO by C3H6 under Lean-Burn Conditions over Ag-Rh/ tioning a platinum-based catalyst in front of the CZA’. Having rhodium and silver together make it

Fig. 2. Evolution of 1.2 (a) the DRIFTS spectra of 14N-containing species and (b) the MS intensity of gas 14 1.0 phase N2 over a Ag/Al2O3 HC-SCR catalyst (8) 0.8

0.6

0.4 a 0.2 b Relative intensity, arbitrary units Relative intensity,

0 2 4 6 8 10 Time after switch to 14NO, min

possible to have a wider activity window (300–500°C) conditions could have a signifi cant impact on the and higher NO conversion with propene. selectivity of the purge: purge length; reductant concentration; temperature; reductant type; and the state Lean NOx Traps of the catalyst (fresh or aged). One of the most interest- The fi rst talk about NOx storage and reduction (NSR) ing parts of the talk was the infl uence of using hydro- catalysts was presented by Roberto Matarrese gen or propene as a reductant. When using hydrogen (Politecnico di Milano, Italy), and was entitled ‘Inter- the selectivity towards ammonia would mainly depend play between NOx and Soot Removal over Pt-Ba NSR on the H2:NOx ratio. In contrast, when using propene Catalysts’. Matarrese focused on the infl uence of soot the selectivity increases with increasing temperature. on the NOx storage process, studying the stability of This is due to the conversion of propene to hydrogen stored NOx in the presence and absence of soot in the via steam reforming. The catalyst used for the study system. They concluded that the presence of 10 wt% was a fully formulated catalyst based on Pt-Rh-BaO- soot during the storage process at 350ºC decreases [La-stabilised CeO2]-[La-stabilised Al2O3] (9). the NOx storage capacity by nearly 30%. The reduc- Do Heui Kim presented ‘Effect of the Reductive tion part was not seen to be affected. The stability of Treatments on Pt Dispersion and NOx Storage in the stored nitrates was also lower in the presence of Lean NOx Trap Catalysts’. Do Heui Kim (Institute for soot, indicating a possible interaction between the Interfacial Catalysis, USA) discovered that the loss of stored nitrates and soot particles. Matarrese concluded available platinum after a reductive treatment in that there is evidence supporting the oxidation of soot hydrogen (300–800°C) on a Johnson Matthey catalyst with NOx by direct participation of the adsorbed NOx (Pt-BaO/Al2O3) was not due to platinum sintering as and/or releasing NO2 and O2, both of which actively originally thought (Figure 3) (10). Characterisation oxidise soot. tests showed that the loss of platinum active surface One ideal system for NOx abatement would be to area was due to platinum being covered with mobile use a NSR catalyst with an NH3-SCR catalyst in order to barium and not as a result of platinum sintering. The increase conversion to nitrogen and avoid ammonia reoxidation of the samples resulted in barium mov- slip. The diffi culty of controlling the selectivity ing back to the support, thus increasing the accessible towards ammonia during the regeneration of the NOx platinum area. trap and the different temperatures in both systems makes this a diffi cult process. Mark Crocker (University Concluding Remarks of Kentucky, USA) focused on the optimisation of the More groups from academia than from industry ammonia selectivity during the regeneration process attended the 6th ICEC. The poster sessions were a in his talk titled ‘The Effect of Regeneration Conditions great opportunity for discussions, allowing people to on the Selectivity of NOx Reduction in a Fully Formu- share ideas. A major focus of the conference were the lated Lean NOx Trap Catalyst’. They found that several mechanistic studies of the reactions that take place on

Fig. 3. Change in the H:Pt ratios and NOx 0.4 65 uptake (%) as a function of reduction temperature for a model Pt-BaO/Al2O3 A catalyst. Region A shows the uptake of 60 0.3 NOx increasing, in contrast to the decreasing NOx uptake, % accessible Pt surface area. In region B where reduction temperatures exceed 600ºC, the b 55 decrease of NOx uptakes may be explained 0.2 B by multiple factors. Point a is the NOx 50 uptake of the fresh sample without any H:Pt ratio reduction treatment; point b is the NOx a uptake after a reduction treatment at 350ºC 0.1 45 (10)

0 40 300 400 500 600 700 800 Temperature, ºC

autocatalysts. Several groups have developed new 2003, 217, (1), 47 techniques such as SpaciMS to study these reactions, 7 K. Eränen, F. Klingstedt, K. Arve, L.-E. Lindfors and D. Y. although many reactions remain poorly understood. Murzin, J. Catal., 2004, 227, (2), 328 Much work has been carried out on applications 8 S. Chansai, R. Burch, C. Hardacre, J. Breen and F. Meunier, using platinum group metals (pgms), although most of J. Catal., 2010, 276, (1), 49 the talks mentioned the high cost of these catalysts. 9 Y. Ji, C. Fisk, V. Easterling, U. Graham, A. Poole, M. Crocker, Several studies into possible substitutes for the pgms J.-S. Choi, W. Partridge and K. Wilson, Catal. Today, 2010, were presented, but despite some benefi ts these alter- 151, (3–4), 362 natives are still far away from competing with the pgms. 10 X. Q. Wang, D. H. Kim, J. H. Kwak, C. Wang, J. Szanyi Overall, ICEC 2010 provided high quality work and and C. H. F. Peden, Catal. Today, 2011, in press proved once more to be one of the most important conferences specialising in environmental catalysis. The Reviewer Noelia Cortes Felix studied Chemical Science at the Autonoma University References of Barcelona, Spain. As a student she 1 P.-A. Carlsson, V. P. Zhdanov and M. Skoglundh, Phys. followed an Erasmus programme at Chem. Chem. Phys., 2006, 8, (23), 2703 Twente University, The Netherlands, studying the impregnation of 2 G. Li, Q. Wang, B. Zhao, M. Shen and R. Zhou, J. Hazard. platinum and palladium on carbon Mater., 2011, 186, (1), 911 nanoﬁ bres for their use as catalysts. Following this, she carried out 3 Y. Nagai, T. Hirabayashi, K. Dohmae, N. Takagi, T. Minami, research into novel precious metal H. Shinjoh and S. Matsumoto, J. Catal., 2006, 242, (1), 103 catalysts for the control of NOx 4 Y. Nagai, K. Dohmae, Y. Ikeda, N. Takagi, T. Tanabe, emissions at the Johnson Matthey Technology Centre, Sonning N. Hara, G. Guilera, S. Pascarelli, M. A. Newton, O. Kuno, Common, UK. She is currently H. Jiang, H. Shinjoh and S. Matsumoto, Angew Chem. conducting research into three-way Int. Ed., 2008, 47, (48), 9303 catalyst technology, which she 5 J. P. Breen and R. Burch, Top. Catal., 2006, 39, (1–2), 53 combines with a PhD programme in the same subject within The Open 6 N. Bion, J. Saussey, M. Haneda and M. Daturi, J. Catal., University, UK.

9th International Frumkin Symposium

“Electrochemical Technologies and Materials for 21st Century”

doi:10.1595/147106711X579074 http://www.platinummetalsreview.com/

Reviewed by Alexey Danilov Introduction A. N. Frumkin Institute of Physical Chemistry and The 9th International Frumkin Symposium was held Electrochemistry of the Russian Academy of Sciences, at the Conference Hall of the Russian Academy of Moscow, Russia Sciences in Moscow, Russia, between 24th–29th Email: [email protected] October 2010. The event was organised jointly by the A. N. Frumkin Institute of Physical Chemistry and Elec- trochemistry of the Russian Academy of Sciences (IPCE RAS) and the Chemical Department of Lomono- sov Moscow State University. The Symposium was sponsored by the Russian Academy of Sciences and the International Society of Electrochemistry. The fi rst symposium of this series, held in 1979, was dedicated to the memory of Russian electrochemist Alexander Frumkin (1895–1976). Since then, the Sym- posia have been held every 3–5 years to discuss current understanding of fundamental electrochemistry and its applications. The 9th Frumkin Symposium included 4 plenary lectures, 112 oral and 131 poster presentations. Scien- tists from the Russian Federation, Ukraine, Belarus, the USA, Canada, Austria, the UK, Germany, Spain, Denmark, Poland, Serbia, Switzerland, Finland, France, Italy, Iran and Taiwan took part in fi ve ‘microsympo- sia’ which made up the conference, including ‘Electri- cal Double Layer and Electrochemical Kinetics’, ‘New Processes, Materials and Devices for Successful Elec- trochemical Transformation of Energy’, ‘Corrosion and Protection of Materials’, ‘Electroactive Composi- tion Materials’ and ‘Bioelectrochemistry’. Platinum group metals (pgms) are widely used by electrochemists as electrode materials for studies of adsorption, nucleation, electrodeposition, electrocatalytic reactions and many other electrochemical processes used in applications such as fuel cells. About 30 presentations focused on pgm studies at the Symposium. This short review highlights a selection of the work presented.

Electrochemistry of PGM Single Crystals The Symposium was opened with a plenary lecture by Juan Feliu (University of Alicante, Spain). He discussed models for the estimation of potential zero

total charge (pztc) and potential zero free charge The main problem in carbon monoxide displace- (pzfc), experimental results on anion adsorption and ment experiments (3) is oxygen interference. Without displacement of the adsorbed species by carbon this, the pztc and the pzfc almost coincide at 0.37 V vs. monoxide and the thermodynamic analysis of the reversible hydrogen electrode (RHE) for the Pt(111) temperature dependence of interfacial properties of electrode. The potential of the maximum entropy of platinum single crystal electrodes (basal faces and double layer formation, obtained from laser pulsed stepped surfaces). experiments, also coincides with this value (4). The For the three basal planes of Pt, both the entropy results of CO displacement experiments for stepped of formation of the interface and the entropy of surfaces Pt(S)[n(111)  (111)] (n atomic width (111) adsorbed hydrogen and hydroxyl species are struc- terraces separated by parallel steps of monoatomic ture sensitive magnitudes. These results can be ana- height with (111) orientation) are shown in Figure 1. lysed using statistical thermodynamic calculations, It can be seen that an increase in the step density revealing that adsorbed hydrogen is rather mobile leads to a negative shift in the pztc. on Pt(111) and Pt(100), while adsorbed hydroxyl is Several reports by Alexey Danilov and colleagues rather immobile. Interestingly, adsorbed hydrogen on (IPCE RAS and University of Alicante) were devoted Pt(110) is rather immobile at low coverages but to the kinetics and mechanism of nitrate anion reduc- becomes very mobile at near saturation coverage. tion on Pt single crystals and copper modifi ed elec- Using cyclic voltammetry (CV), it has also been shown trodes (5, 6). Modifi cation of the Pt surface with Cu that some anions are not adsorbed on Pt. For instance, adatoms or a small amount of 3D Cu crystallites was trifl uoromethanesulfonic acid and perchloric acid performed using potential cycling in solutions with a both show the same voltammetry on basal plane low concentration of Cu2 ions. This allowed the sur-

electrodes and no adsorbate bands were observed face coverage of Cu, Cu, to be varied smoothly. It was by spectroscopy (2). also found that nitrate reduction in sulfuric acid

200 200 j, Pt(n n n–2) Pt(10 10 9) Pt(554) Pt(S)[n(111)  (111)] 100 n = 20 n = 10 150  –2 Pt(S)[(n–1)(111) (110)]  0 100 A cm C cm  Pt(775) –2 –100 50 j,

–200 0 0.2 0.4 0.6 0.8 0.2 0.4 0.6 0.8 Pt(775) Pt(221) 100 150

q, n = 7 n = 4 –2  A cm

C cm 0 100  –2 –100 50

–200 0

q, 0.2 0.4 0.6 0.8 0.2 0.4 0.6 0.8 E, vs. RHE E, vs. RHE

Fig.1. Potential dependences of total charge and positive-going sweeps of cyclic voltammograms for stepped surfaces of platinum single crystals (Courtesy of Professor Juan Feliu)

solutions at E  0.05 V on Cu modifi ed electrodes was surface than for the disordered surface. This differ- hindered due to enhanced adsorption of sulfate ani- ence was attributed to the blocking of surface defect ons on a positively charged Cu adlayer. The effect sites by (bi)sulfate anions. However, at a low Cu con- was less pronounced for the Pt(100) surface where centration in the solution (1.2  106 M), the adsorption sulfate adsorption was weaker. of Cu adatoms occurred at lower potentials, where the In perchloric acid solutions, a strong catalytic effect interaction of anions with the Pt surface was weaker. In was observed at low potentials, due to induced this case the defects act as the preferential adsorption adsorption of nitrate anions. Nitrate reduction on Cu sites for UPD Cu. The Cu UPD process seems to be modifi ed electrodes was much faster as compared more sensitive to crystalline defects in the Pt(100) sur- to pure Pt; the current density was higher by 2 to 4 face than CO electrooxidation, and can be used as a orders of magnitude. Structure-sensitive competitive monitoring reaction to estimate the degree of order- adsorption of background electrolyte and nitrate ani- ing of a Pt(100) surface. ons largely determined the kinetics of nitrate reduction both on the faces of Pt single crystals and on the PGMs as Electrocatalysts epitaxial 2D and 3D deposits of Cu. The maximal rate Jean-Pol Dodelet (National Research Institute of of the process was observed for the Cu modifi ed Energy, Materials and Telecommunications, Varennes, Pt(100) electrodes. The origin of intermediate prod- Canada) in his plenary lecture compared the behav- ucts of the nitrate reduction was discussed on the iour of platinum- and iron-based electrocatalysts basis of CV and Fourier transform infrared (FTIR) for the reduction of oxygen in proton exchange spectroscopy data. membrane (PEM) fuel cells. The catalytic activity of Results of electrochemical and in situ scanning new Fe/N/C electrocatalysts (Figure 2) was signifi - tunneling microscopy (STM) studies of the Pt(100) cantly improved by using a new synthesis procedure surface structure as dependent on the cooling atmos- (10). Cell current densities were comparable to those phere after fl ame annealing were presented by Alex- of Pt catalysts in the kinetic region and in the mass ander Rudnev (IPCE RAS) and Thomas Wandlowski transport region of the polarisation curve. However, all (University of Bern, Switzerland). The following cool- Fe/N/C catalysts produced thus still lack necessary sta- ing conditions were applied: a mixture of hydrogen bility. The catalyst should be stable at least for 5000 and argon (reducing atmosphere), argon (inert gas) hours at the current density and potential practically and air (oxidising atmosphere). Previous in situ STM used in fuel cells. Solving this problem is in progress. experiments revealed that a Pt(100) surface as pre- A highly active catalyst based on organometallic pared by fl ame annealing and subsequent slow cool- clusters was designed and tested for low temperature ing in a H2 fl ow exhibits atomically fl at terraces (7). fuel cells, as reported by Vitaly Grinberg and col- Cooling in an Ar atmosphere led to a reconstructed leagues (IPCE RAS and Kurnakov Institute of General Pt(100)-hex-R0.7° surface, where R0.7° means rotated and Inorganic Chemistry, RAS, Moscow). A new by 0.7°. However, the reconstruction was lifted after approach to the synthesis of electrocatalysts has been electrosorption of H2 and/or in the presence of traces suggested. Individual heterometallic clusters were sub- of O2 in the electrochemical system (8). Because of jected to thermal destruction on highly dispersed car- the excess of Pt surface atoms originating from the bonaceous supports at the temperatures of 250–500ºC. lifting of the hexagonally reconstructed Pt(100)-hex- The distinguishing feature of these catalysts was their R0.7° electrode, a (1  1) surface with many islands of good reproducibility with respect to composition, as monatomic height was generated (9). Cooling in air well as uniformity of the catalyst distribution over the led to a disordered surface structure characterised by support, which results in stability and reproducibility a large number of defects. of the catalyst characteristics (11). A bimetallic plati- The infl uence of defect density and of long range num-tin catalyst (Pt:Sn atomic ratio in the surface surface order of the Pt(100) electrode on the kinetics layer 2:1) and fl uoro-containing nickel-ruthenium cat- of CO electrooxidation and Cu underpotential deposi- alyst (Ni:Ru atomic ratio in the surface layer 8.6:1) tion (UPD) was demonstrated. A Pt(100) electrode were synthesised by deposition on highly dispersed cooled in Ar displayed a slightly higher activity with carbon black from clusters of the corresponding met- respect to the CO oxidation reaction than that cooled als. These catalysts (Pt3Sn and Ni12RuF5) were character- in an Ar and H2 mixture. On the other hand, the Cu ised by X-ray diffraction and energy dispersive X-ray adsorption rate was higher for the 2D ordered Pt(100) (EDX) analysis, laser mass spectrometry and transmis-

Fig. 2. Schematic presentation Fe/N/C catalytic site for O2 reduction of new iron/ nitrogen/carbon ~ 13 Å electrocatalysts (Courtesy of Professor Jean-Pol Dodelet)

N N Crystallite 1Fe Crystallite 2 Fe/N/C N N

Micropore

2.46 Å

Carbon particle ~ 30 nm

sion electron microscopy (TEM). The mean size of best operating characteristics for many electrochemi- these catalyst particles was in the range 1–12 nm. cal applications.

According to voltammetric data, the synthesised Pt3Sn The abstracts of oral and poster presentations and Ni12RuF5 catalysts are superior to the Pt-Sn and given at this conference are available by contacting Ni-Ru catalysts described in literature for ethanol oxi- the organisers (1). The next Frumkin Symposium is dation and for sodium borohydride oxidation, planned to be held in October 2015 in Moscow, Russia. respectively. It was also shown that the specifi c catalytic activity of these catalysts exceed those of Pt-Sn References and Ni-Ru bimetallic systems prepared from simple 1 9th International Frumkin Symposium: www.phyche. salts by impregnation of carbon black. ac.ru/frumkinsymp/ (Accessed on 13th May 2011) 2 A. Berná, J. M. Feliu, L. Gancs and S. Mukerjee, Concluding Remarks Electrochem. Commun., 2008, 10, (11), 1695 This Symposium made it very clear that the pgms 3 J. M. Feliu, J. M. Orts, R. Gómez, A. Aldaz and J. Clavilier, remain very popular for electrochemical studies of J. Electroanal. Chem., 1994, 372, (1–2), 265 the electric double layer structure and of electro- 4 V. Climent, N. García-Araez, E. Herrero and J. Feliu, Russ. catalytic reactions. Although much research is being J. Electrochem., 2006, 42, (11), 1145 carried out to attempt to replace pgms by other 5 A. V. Rudnev, E. B. Molodkina, M. R. Ehrenburg, R. G. materials for use in fuel cells and other electro- Fedorov, A. I. Danilov, Yu. M. Polukarov and J. M. Feliu, catalytic processes, the pgms currently provide the Russ. J. Electrochem., 2009, 45, (9), 1052

6 E. B. Molodkina, M. R. Ehrenburg, Yu. M. Polukarov, 11 V. A. Grinberg, A. A. Pasynskii, T. L. Kulova, N. A. Maiorova, A. I. Danilov, J. Souza-Garcia and J. M. Feliu, Electrochim. A. M. Skundin, O. A. Khazova and C. G. Law, Russ. Acta, 2010, 56, (1), 154 J. Electrochem., 2008, 44, (2), 187 7 K. Sashikata, T. Sugata, M. Sugimasa and K. Itaya, Langmuir, 1998, 14, (10), 2896 The Reviewer 8 A. Al-Akl, G. A. Attard, R. Price and B. Timothy, Alexey I. Danilov completed his PhD studies in the ﬁ eld of J. Electroanal. Chem., 1999, 467, (1–2), 60 electrochemical metal nucleation and growth at the Institute of Physical Chemistry and Electrochemistry of the Russian Academy of 9 L. A. Kibler, A. Cuesta, M. Kleinert and D. M. Kolb, Sciences (IPCE RAS) of Moscow, Russia, in 1985. He obtained his J. Electroanal. Chem., 2000, 484, (1), 73 Dr Sci (Physical Chemistry) in 2002. Most of his studies have been devoted to processes of adsorption, nucleation and electrocatalysis 10 M. Lefèvre, E. Proietti, F. Jaouen and J. P. Dodelet, on pgms. He is currently the Head of the Laboratory of Surface Layer Science, 2009, 324, (5923), 71 Structure at the IPCE RAS.

“Heterogenized Homogeneous Catalysts for Fine Chemicals Production: Materials and Processes”

Edited by Pierluigi Barbaro and Francesca Liguori (Istituto di Chimica dei Composti Organo Metallici, Firenze, Italy), Springer, Dordrecht, The Netherlands, 2010, 459 pages, ISBN: 978-90-481-3695-7, £126.00, €139.95, US$189.00 (Print version); e-ISBN: 978-90-481-3694-4, doi:10.1007/978-90-481-3696-4 (Online version) doi:10.1595/147106711X581350 http://www.platinummetalsreview.com/

Reviewed by Raghunath V. Chaudhari Introduction The Center for Environmentally Beneﬁ cial Catalysis, “Heterogenized Homogeneous Catalysts for Fine The University of Kansas, Lawrence, KS 66047, USA Chemicals Production” is Volume 33 of the series Email: [email protected] “Catalysis by Metal Complexes”, edited by Claudia Bianchini (Institute of Chemistry of Organometallic Compounds, Sesto Fiorentino, Italy), David J. Cole- Hamilton (University of St Andrews, UK) and Piet W. N. M. van Leeuwen (Institute of Chemical Research of Catalonia, Tarragona, Spain). One of the book’s co- editors, Pierluigi Barbaro, is a permanent researcher at Instituto di Chimica dei Composti Organo Metallici (ICCOM), Firenze, Italy, and has research interests in homogeneous and asymmetric catalysis with a focus on supported and nanostructured catalysts for sustainable production processes. The other co-editor, Francesca Liguori, is also at ICCOM and specialises in the chemistry of heterocycles and carbohydrates, organometallic chemistry and the synthesis of heterogenised homogeneous catalysts. There are 13 chapters by a total of 29 authors, with many years of research experience and expertise in their respective fi elds. Most of the contributors are from academic institutions or universities, with just one chapter by authors from an industrial background. The aim of this book is to review the current state of the art on the ‘heterogenisation’ (or ‘immobilisation’) of homogeneous catalysts for fi ne chemicals production, low to medium volume high-value products which are often diffi cult to separate and purify by conventional techniques such as distillation or extraction. Heterogenisation is a useful technique for developing advanced technologies and green chemical synthesis, as is pointed out in the foreword by David J. Cole- Hamilton and in the introduction to Chapter 1, written by Duncan Macquarrie (University of York, UK). A number of examples of heterogenised catalytic complexes involving different transition metals are

given, but this review will focus on the platinum group properties for the development of heterogenised metals (pgms). These are grouped by topic. 10 out of homogeneous catalysts is highlighted with a number the 13 chapters include pgm examples, with the most of examples. The chapter starts with a general over- commonly used metals being ruthenium, rhodium view of the different materials that have been used and palladium, although platinum- and iridium-based classically for immobilisation of metal complex cata- catalysts are also mentioned. lysts, followed by the introduction of some new sup- The topics covered are: the synthesis of ‘hetero- ports consisting of metal oxide nanoparticles, carbon genised’ catalysts; asymmetric catalysis; oxidation nanotubes, graphite materials and composite matri- reactions; polymerisation reactions; reaction engi- ces. The chapter is well divided into sections with dif- neering; and instrumental techniques for the charac- ferent solid catalysts categorised according to the type terisation of catalytic materials. The design and of interaction between the support and the active development of ‘heterogenised’ catalysts is of great catalyst, for example, support–metal or support– practical signifi cance as it has implications for catalyst– ligand interactions. Synthetic strategies, characteri- product separation, recycling and the effi cient use sation techniques and applications for several of pgm catalysts. immobilised pgm and other transition metal complex catalysts are reviewed. The infl uence of the nature of Synthesis Methods for Heterogenised the support matrices and other conditions are also Catalysts discussed. Several newer strategies are described, The synthesis of ‘heterogenised’ catalysts is reviewed including the silylation of oligo(methylsilane) (OMS) in 8 out of the book’s 13 chapters. Chapters 2–5 are materials to build encapsulated complex catalysts mainly focused on catalyst preparation, with some within large mesoporous cages, previously thought illustrative examples of model reaction systems. Chap- possible only with microporous matrices. Concepts ters 3–5 describe catalysts based on pgms, mainly Pd, such as immobilisation by adsorption and supported Rh and Ru with a few Pt catalysts. Chapter 2, by David liquid phase catalysis (SLPC) are also discussed in Xuereb et al. (University of Southampton, UK), intro- detail with several applications showing prospective duces biomimetic single site heterogeneous catalysts research directions for fi ne chemical applications. consisting of non-pgms, although the approach may Several novel Rh-, Ru- and Pd-based catalysts with uses also be useful for pgm catalysts. in fi ne chemicals are included. For example, hydro- Chapter 3 by José Fraile et al. (Universidad de genation of (Z)-N-acetamidocinnamic acid deriva- Zaragoza, Spain) presents a very comprehensive tives using Rh complexes with proline derived ligand review of synthesis methods and applications for on ultrastable Y (USY) zeolite (Figure 1). heterogenised catalysts, mainly focusing on the use of In Chapter 4, an extensive review of the synthesis of inorganic supports such as silica, alumina, mixed immobilised asymmetric catalysts on polymers and metal oxides, layered solids (clays and layered double nanoparticle supports is presented by Ciril Jimeno hydroxides), crystalline solids (zeolites including et al. (Institute of Chemical Research of Catalonia mesoporous materials) and nanoparticles, for exam- (ICIQ), Spain). The catalytic performance of a selec- ple gold nanoparticles and carbon nanotubes. The tion of Pd, Rh and Ru complexes with immobilised importance of inorganic supports and their structural ligands is compared for a range of reactions. An

Fig. 1. Immobilisation of rhodium complexes with proline derived ligand on USY zeolite

Catal. A

Homogeneous Silica USY zeolite Catal. A 54% ee 58% ee 94% ee Catal. B Catal. B 34% ee 84% ee 53% ee

inte resting new approach using functional nanoparti- In Chapter 6, the preparation and application of cles such as gold and magnetic iron(II, III) oxide membranes for the separation of catalysts is addressed.

(Fe3O4) as supports for the immobilisation of pgm com- Although this chapter mainly gives non-pgm examples, plexes is presented, which may lead to wider applica- the approach is generic and has scope for expansion tions. This chapter will help researchers to identify to pgm-catalysed reactions. different materials for the innovative and rational design of improved immobilised catalysts. Applications to Fine Chemicals and Chapter 5 reviews the immobilisation of metal com- Speciality Polymers plex catalysts on dendrimer supports. These large Asymmetric Catalysis by Heterogenised molecules enable easy separation of the supported Chiral Metal Complexes catalyst complex by membrane fi ltration. The design Chapter 7 by Benoît Pugin and Hans-Ulrich Blaser of dendrimers with different functionalisation on the (Solvias AG, Switzerland) is an important contribu- periphery and at the core has opened new horizons tion addressing industrial aspects of fi ne chemicals for immobilisation using several different functional production with examples of commercialised pro- moieties in a single structure. The synthesis and appli- cesses. The authors have extensive experience in the cations of these materials for epoxidation, coupling industrialisation of asymmetric catalytic processes. and hydrosilylation reactions is well presented in this They give examples of industrial enantioselective chapter and there is scope for expansion into other catalysis using a number of immobilised pgm cata- fi ne chemicals applications. Examples of dendrimer lysts which include: supported pgm complexes include: (a) [Ir(COD)Cl]2 on chiral Josiphos (a proprietary

(a) A dendrimer supported [Rh(nbd)2](ClO4) (ndb = ligand from Solvias AG) immobilised on function- 2,5-norbornadiene) complex for the asymmetric alised silica on polystyrene supports (Figure 3) hydrogenation of dimethyl itaconate, which gives for the manufacture of a herbicide, (S)-metola- high activity, enantioselectivity and stability; and chlor, which is produced at >20,000 tonnes per (b) The asymmetric transfer hydrogenation of aceto- year; and

phenone using [RuCl2(p-cymene)]2 immobilised (b) Rh diphosphine and Ru-BIPHEP (2,2-bis(di- on a core-functionalised dendrimeric ligand phenylphosphino)-1,1-biphenyl) immobilised on (Figure 2). silica for asymmetric hydrogenation reactions.

Fig. 2. Asymmetric transfer hydrogenation with ruthenium on dendrimer catalyst. G3 = 1% 1, [RuCl2(p-cymene)]2 generation 3 dendrimer 5% iPrOK, RT

Fig. 3. A process for the preparation of (S)-metolachlor Ir catalyst

MEA imine 4 stereoisomers 4 stereoisomers metolachlor

This chapter is unique in this book with a brief includes recent strategies involving the use of but useful discussion of practical aspects such as cata- designed ionic liquids and/or multiphasic liquid sys- lyst reuse, availability, development time, costs and tems, envisioning lower catalyst loss and better recy- opportunities for process engineering, which are clability, activity and selectivity. A specifi c example of often diffi cult to accomplish with immobilised catalysts. the heterogenisation of a Ru-BINAP (2,2-bis(diphenyl- It is also the only chapter written by authors working phosphino)-1,1-binaphthyl) catalyst via a spacer is in industrial research and development. It is evident shown (Figure 4). from the references that a more detailed version of the issues addressed in this chapter is available in another Oxidation Reactions book coedited by Hans-Ulrich Blaser (1). Chapter 10 summarises a selection of Ru- and Pd-based Chapter 9 by Agnes Zsigmond et al. (University of heterogenised catalysts for oxidation reactions. How- Szeged, Hungary) provides a very well written and ever, there is limited information about the synthesis comprehensive review of the chemoselective and and structural characterisation of the complexes. The enantioselective hydrogenation of alkenes, aldehydes, initial part of the chapter sums up general method- diketones and imines using a number of immobilised ologies to immobilise metal complex catalysts, and pgm catalysts, which include some chiral complexes. there is a good selection of references on oxidation Different aspects of strategic catalyst design and syn- reactions, although there is a much broader spec- thesis are described, including characterisation, appli- trum of exciting applications of oxidation in fi ne cations, recyclability and stability aspects, involving chemicals which is not covered here. mostly Ru- or Rh-based catalysts. The historical development of industrial technology for enantioselective Polymerisation Reactions hydrogenation reactions is reviewed. Topics such as In Chapter 11, polymerisation reactions using novel polymer bound and inorganic solid supported Ru or immobilised Ru catalysts are reviewed by Matthew D. Rh complexes are thoroughly discussed, with empha- Jones (University of Bath, UK) with applications in sis on stability and recyclability. The chapter also specialty polymers although these are not strictly

Support (e.g. alumina, zeolites, silica)

HPA = heteropolyacid

Fig. 4. Heterogenisation approaches for ruthenium-BINAP with spacer

defi ned as fi ne chemicals. Immobilising metal com- Chapter 13 by John Evans and Moniek Tromp (Uni- plex polymerisation catalysts is a useful strategy for versity of Southampton, UK) is a very general intro- the development of more sustainable processes and duction to the characterisation of catalytic materials ‘green technology’. Special emphasis is placed on by spectroscopic methods. The characterisation of polymer degradation; the proposed single site cata- Pd, Rh, Os and Ru catalysts are described, and the lysts are particularly useful for synthesis of specialty chapter will be useful as a reference source. How- polymers with biodegradable properties, which is sig- ever the coverage of different techniques is limited, nifi cant to the goal of sustainable and green techno- considering the vast progress made in this area in logy. One example of a major breakthrough is the recent years. heterogenised Grubb’s catalyst (a Ru complex on a silica support) for olefi n metathesis (Figure 5) which Conclusions has insignifi cant leaching. Other examples discussed This book presents a comprehensive review of recent in this chapter relate to non-pgm catalysts. developments in the ‘heterogenisation’ of metal complex catalysts with a focus on synthetic methodology, Reaction Engineering and Instrumental characterisation and applications in fi ne chemicals. Techniques Many different synthetic approaches are covered, In Chapter 8, Albert Renken (École polytechnique although most of the examples are illustrative rather fédérale de Lausanne, Institute of Chemical Sciences than real processes used in the fi ne chemicals industry. and Engineering (EPFL-ISIC), Lausanne, Switzerland) It is, however, evident from this book that the pgms presents an excellent overview of reaction engineering have wide ranging applications in fi ne chemicals and involving heterogenised molecular catalysts, which is emerging technologies. useful as an introduction to the subject for chemists The chapters in this book are well written by highly and engineers working in this area who are not familiar qualifi ed authors and will provide an excellent with the fundamentals of reactor design. The well resource for postgraduate and doctoral students as developed concepts of mass transfer coupled with well as researchers working in the areas of metal com- chemical reactions are described in the context of het- plex catalysis, asymmetric catalysis and catalytic pro- erogenised catalytic systems, which generally fall into cess development. A number of known applications the class of multiphase catalytic reactions. using heterogenised metal complex catalysts in com- A selection of relevant examples such as biphasic mercially relevant hydroformylation, carbonylation hydroformylation catalysed by a water soluble Rh com- and oxidation reactions are not adequately covered plex with triphenylphosphine trisulfonate (TPPTS) (see also (2–8)) and more comparison of the perfor- ligand, and SLPC reactions catalysed by RhCl(CO) mances of heterogenised catalysts and their homoge-

(PPh3)3 dissolved in dioctyl phthalate containing free neous counterparts would also have been of value.

PPh3 supported in porous materials are given. The arti- Overall, the book reads well and covers a subject cle also provides a very useful reference source for of interest to both academic and industrial research- reaction engineering concepts. In Chapter 12, a brief ers. It should inspire many young researchers to but essential introduction of molecular simulation is develop novel catalytic materials and make progress presented which is very timely for understanding towards more sustainable and green chemical molecular interactions in heterogenised catalysts. processes.

Fig. 5. Heterogenisation of Grubbs oleﬁ n metathesis ruthenium catalyst Silica surface

“Heterogenized Kamer, M. Lutz, A. L. Spek and P. W. N. M. van Leeuwen, Homogeneous Catalysts Angew. Chem. Int. Ed., 1999, 38, (21), 3231 for Fine Chemicals 7 B. R. Sarkar and R. V. Chaudhari, J. Catal., 2006, 242, Production: Materials and (1), 231 Processes” 8 R. V. Chaudhari and A. N. Mahajan, Council of Scientiﬁ c and Industrial Research, ‘Novel Catalytic Formulation and its Preparation’, US Patent 7,026,266; 2006

The Reviewer Raghunath V. Chaudhari is the Deane E. Ackers Distinguished Professor at the Department of Chemical and Petroleum Engineering, University of Kansas (KU), Lawrence, USA. He worked at the National Chemical Laboratory, Pune, India, for 30 years as Head, Homogeneous Catalysis Division References before joining KU in 2007. His research 1 “Asymmetric Catalysis on Industrial Scale: Challenges, experience covers interdisciplinary ﬁ elds Approaches and Solutions”, 2nd Edn., eds. H.-U. Blaser of homogeneous and heterogeneous catalysis, chemical reaction engineering and H.-J. Federsel, Wiley-VCH Verlag GmbH & Co KGaA, and modelling of multiphase systems Weinheim, Germany, 2010 with current activities focused on biomass conversion processes and 2 G. A. Ozin and C. Gil, Chem. Rev., 1989, 89, (8), 1749 the design and development of novel 3 J. M. Andersen, Platinum Metals Rev., 1997, 41, (3), 132 catalytic materials. He has authored or co-authored a number of research 4 K. Mukhopadhyay, B. R. Sarkar and R. V. Chaudhari, papers, review articles and two books, J. Am. Chem. Soc., 2002, 124, (33), 9692 the most recent one being on “Trickle Bed Reactors”, published in 2011 by 5 K. Mukhopadhyay, A. B. Mandale and R. V. Chaudhari, Elsevier. He also teaches kinetics, reaction Chem. Mater., 2003, 15, (9), 1766 engineering and chemical engineering thermodynamics at graduate and 6 A. J. Sandee, L. A. van der Veen, J. N. H. Reek, P. C. J. undergraduate levels at KU.

Phase Diagram of the Rhenium-Rhodium System: State of the Art doi:10.1595/147106711X579966 http://www.platinummetalsreview.com/

The available experimental data for metallic solid By Kirill V. Yusenko solutions in the rhenium-rhodium binary metallic solid-chem GmbH, Universitätsstr. 136, D-44799 Bochum, system are incomplete. This paper reviews recent data Germany on the Re-Rh system which enables the solidus parts Email: [email protected] of the equilibrium phase diagram to be constructed. Experimental data for solid solutions prepared by different techniques and theoretical modelling show that the single phase regions are wider than previously reported. The maximum solid phase solubility of Re in Rh is 15 at%, and that of Rh in Re is 75 at%. In this paper, a phase diagram for the Re-Rh system which serves as a reliable model for the representation of the available experimental data is proposed.

Introduction Polymetallic compositions containing platinum group metals (pgms) and rhenium are widely used in industry as high-temperature materials, in superalloys and as catalysts (1). Re-Rh solid solutions are used in high- temperature thermocouples (2), as coatings with high thermal, mechanical and chemical stability (3) and in applications where high hardness is required (4). The properties of solid solutions depend on the composition, the preparation conditions and particularly on the presence of impurities in the alloy. Metallic phase behaviour is most commonly predicted using the relationship between composition or temperature and properties. However, the information currently available about the Re-Rh system is poor and contradictory due to the diffi culties that arise during the preparation of solid solutions. This, together with the high cost of the materials, limits the practical applications of Re-Rh solid solutions and composites. Construction of the correct equilibrium phase diagram would provide a fi rm foundation for future investigations of chemical, physical and material properties of Re-Rh solid solutions and could enable their usefulness to be extended. Comprehensive knowledge of two-component systems is also essential for the construction of ternary and quaternary phase diagrams. The collection of equilibrium data is made

diffi cult by the extremely high melting points of the Kaufman later calculated the two-component phase metal components. The present paper aims to criti- diagrams for Re with all pgms, using the regular cally analyse recent experimental data on Re-Rh solution model (6). Further measurements of mixing solid solutions and calculate the equilibrium phase volumes and formation enthalpy for high melting diagram for the Re-Rh system using the regular solu- point metallic systems confi rmed the accuracy of this tion model. model. Although Kaufman’s calculations were partly based on non-validated thermodynamic data, they The Rhenium-Rhodium System were in tolerable concordance with the experimen- In the early 1960s, the fi rst experimental data on the tal diagrams. The calculated and experimentally Re-Rh system was obtained using high-temperature obtained phase diagrams were adequate for the melting and annealing of fi ne metallic powders in majority of metallic systems, but not for Re-Rh. This vacuum. The fi rst phase diagram was constructed may be explained by the inapplicability of the model based on the analysis of bimetallic solid solutions or by the inaccuracy of the corresponding experimen- prepared at a wide range of concentrations (5). As tal data. Direct thermodynamic measurements for a shown in Figure 1, the peritectic phase diagram has binary Re-Rh system could help to improve the use- three regions in the solid state: face-centred cubic fulness of the model in this case. This information is (fcc) solid solutions in the Rh part, hexagonal close- available for pure pgms and pure Re (7–10), and for packed (hcp) solid solutions in the Re part and a some of the bimetallic solid solutions. The criteria for two-phase region between the single phase sections. analysing the accuracy of data used to construct According to published data, this two-phase region is experimental and calculated phase diagrams were wide. The maximum solubility at 1000ºC of Re in Rh discussed by Schmid-Fetzer et al. in 2005 (11). Based has been estimated as 15 at% and that of Rh in Re as on these criteria, the available experimental phase 24 at%, and the peritectic temperature was determined diagram for the binary Re-Rh system (5) seems to be to be 2620ºC. incorrect, at least in the liquidus part (hcp liquid).

Key 3000 Experimental (5)

Kaufman (6) 2500 Calculated (this study)

2000

1500 Temperature, ºC Temperature,

1000

500 0 10 20 30 40 50 60 70 80 90 100 Re Composition, at% Rh Rh

Fig. 1. Proposed phase diagram for the rhenium-rhodium system according to data from experiment (5), Kaufman (6) and the present study. A two-phase sample with 80 at% Rh is shown as a black circle. Other compositions and preparatory temperatures are given in Table I

Korenev and coauthors developed the ‘single be incorrect since the atomic volume is less than source precursor strategy’ for the preparation of solid that of pure Rh. This solid solution was therefore not solutions of pgms under mild conditions using considered in the present study. The V/Z depend- bimetallic double complex salts as precursors (12). ence can be fi tted by the second-order polynomial This approach allows the reproducible preparation of (Equation (i)): a broad range of pgm solid solutions with precise 3 5 2 compositions. Heating the obtained metallic solid V/Z  14.75  15.4  10  XRh  5.45  10  XRh (i) solutions up to the melting point does not change the phase composition and cell parameters; in other where XRh is the at% of Rh in a binary solution. The words, the phases prepared are thermodynamically phases were prepared by melting and the thermal stable and in equilibrium. The working temperatures decomposition of bimetallic compounds follows a are usually below 800ºC. This approach has also been standard curve, indicating that solid solutions pre- applied to the preparation of Re-Rh solid solutions pared by thermal decomposition of single source pre-

(13–18). For example, the Re0.50Rh0.50 solid solution cursors are nearly in equilibrium. This polynomial can be obtained by thermal decomposition of curve can be used for estimating the composition of

[Rh(NH3)5Cl][ReCl6] in a hydrogen or argon stream at Re-Rh solid solutions with known cell parameters. 600ºC (16). The variation of the precursor composi- A powerful tool for understanding the properties tion and preparatory conditions results in different of metals with extremely high melting points is the metallic materials based on polymetallic nanoparti- thermodynamic modeling of the binary phase dia- cles, which can be also prepared on porous supports grams in equilibrium, which gives information about for catalytic applications (19). To improve the accu- the possible solubility limits and peritectic tempera- racy of the data used to construct the phase diagrams, ture. The technique can also be used for materials Re-Rh solid solutions were also synthesised by heating design and industrial process optimisation. For the fi ne powders of the highly pure metals at 1000–1100ºC present study, the phase diagram was calculated under vacuum for 100–200 h (20, 21) as well as using using the PANDAT 8 software (27) based on the the thermobaric treatment (2000ºC, 4 GPa) (22). The CALPHAD method (28) and using the Scientifi c Group solid solutions obtained were characterised by pow- Thermodata Europe (SGTE) v. 4.4 thermodynamic der X-ray diffraction (XRD), elemental analysis and database (29). Figure 1 shows that the calculated scanning electron microscopy (SEM), with the meas- solid solubility limits are inconsistent with the exist- urements of the cell parameters and atomic volumes ing experimental phase diagram (5). However, there taken for all phases. The crystallographic characteris- is good compatibility between the theoretical phase tics and preparatory conditions for all known Re-Rh diagram and recently obtained experimental data for solid solutions are summarised in Table I. Accord- the Re-Rh solid solutions. The comparison clearly ing to the data obtained, the two phase region in the shows that the previous experimental phase diagram Re-Rh phase diagram at 1000ºC should be placed for the Re-Rh system should be reconsidered and cor- between Re0.15Rh0.85 (fcc) and Re0.25Rh0.75 (hcp), indi- rected below the peritectic temperature. The Rh part cating that the maximum solid phase solubility of Re (fcc solid solutions) of the experimental phase dia- in Rh is 15 at%, and that of Rh in Re is 75 at%. gram seems to be accurate, whereas the Re part (hcp To analyse the hcp-fcc bimetallic system, the atomic solid solutions) requires correction. volume, V/Z (where V is the volume of the elemental cell and Z corresponds to the number of atoms in the Conclusion and Further Work elemental cell, with Z  6 for hcp and Z  4 for fcc), In conclusion, the proposed phase diagram for the is plotted against the composition of the obtained Re-Rh system serves as a reliable model for repre- metallic phase according to Zen’s law (25, 26). All senting the experimental data which are available solid solutions in the Re-Rh system show a nearly to date. Further thermodynamic studies of solid solu- linear dependence of V/Z on composition, with a neg- tions derived from high purity metals are recom- ative defl ection of no more than 2% (Figure 2), which mended in order to improve the phase diagram. roughly refl ects the idealness of the system. Reported A critical analysis of the available experimental data values for the cell parameters of the cubic solid solu- on the solid solutions of pgms and rhenium should be 3 tion Re0.12Rh0.88 (a  3.64 Å, V/Z  12.06 Å ), prepared carried out to construct a consistent set of thermody- by melting the pure metals at 2500ºC (5), appear to namic data and phase diagrams for these systems.

Table I. Crystallographic Data on Known Phases in the Rhenium-Rhodium System

Composition (Reference) Cell parameters, Cell Space Density, Atomic Preparation conditions

a, Å parameters, group Dx, volume, c, Å c/a g cm–3 V/Z, Å3

Re (23, No. 5-702) 2.760 1.615 P63 / mmc 21.026 14.705 Melting point 3180ºC 4.458

Re0.75Rh0.25 (20, 21) 2.753(1) 1.597 P63 / mmc 19.098 14.43(2) Annealing in vacuum 4.396(2) (1250ºC, 80 h)

Re0.75Rh0.25 (13) 2.749(2) 1.599 P63 / mmc 19.094 14.38(4) Thermal decomposition in He of

4.395(3) [Rh(NH3)5Cl]2[Re6S8(CN)6] · 3H2O (1200ºC, 1 h)

Re0.67Rh0.33 (20, 21) 2.746(1) 1.598 P63 / mmc 18.380 14.34(2) Annealing in vacuum 4.387(2) (950ºC, 450 h)

Re0.67Rh0.33 (14) 2.746(1) 1.598 P63 / mmc 18.398 14.32(2) Thermal decomposition in H2 of

4.387(2) [Rh(NH3)5Cl](ReO4)2 (950ºC, 400 h)

Re0.60Rh0.40 (15) 2.7473(2) 1.597 P63 / mmc 17.704 14.34(4) Thermal decomposition in H2 of

4.3886(4) [Rhpy4Cl2]4[Re6S8(CN)6] · 1.5H2O Platinum MetalsRev (850ºC, 1 h)

Re0.50Rh0.50 (20, 21) 2.730(1) 1.595 P63 / mmc 17.082 14.05(2) Annealing in vacuum

Re0.50Rh0.50 (16) 2.733(5) 1.597 P63 / mmc 17.006 14.11(8) Thermal decomposition in H2 of

4.364(6) [Rh(NH3)5Cl][ReCl6] ., 2011, (600ºC, 1 h) 55

(Continued) , (3)• 190 doi:10.1595/147106711X579966 •

Table I. (Continued)

Composition (Reference) Cell parameters, Cell Space Density, Atomic Preparation conditions

a, Å parameters, group Dx, volume, c, Å c/a g cm–3 V/Z, Å3

Re0.50Rh0.50 (16) 2.727(5) 1.596 P63 / mmc 17.128 14.01(8) Thermal decomposition in Ar of

4.352(6) [Rh(NH3)5Cl][ReBr6], (550ºC, 1h)

Re0.50Rh0.50 (16) 2.730(5) 1.595 P63 / mmc 17.078 14.05(8) Thermal decomposition in H2 of

4.355(6) [Rhpy4Cl2]ReO4, (470ºC, 1 h)

Re0.33Rh0.67 (20, 21) 2.721(1) 1.598 P63 / mmc 15.533 13.94(2) Annealing in vacuum 4.348(2) (1200ºC, 145 h)

Re0.33Rh0.67 (18) 2.722(5) 1.598 P63 / mmc 15.514 13.96(8) Thermal decomposition in H2 of

4.350(6) [Rh(NH3)5Cl]2[ReCl6]Cl2 (700ºC, 1 h)

Re0.30Rh0.70 (20, 21) 2.721(1) 1.599 P63 / mmc 15.257 13.94(2) Annealing in vacuum 4.348(2) (1100ºC, 200 h) a Re0.20Rh0.80 (20, 21) 2.716(1) 1.599 P63 / mmc – 13.89(2) Annealing in vacuum 4.350(2) (1200ºC, 75 h) Platinum MetalsRev – 3.814(1) – Fm3m – 13.86(1) – Re Rh (20, 21) 3.810(1) – Fm3m 13.358 13.83(3) Annealing in vacuum © 2011Johnson Matthey 0.10 0.90 (1100ºC, 200 h) – Rh (23, No. 5-685) and (24) 3.8031 – Fm3m 12.425 13.752 Melting point 1960ºC ., 2011,

aMixture of hcp and fcc solid solutions 55 , (3)• doi:10.1595/147106711X579966 •Platinum Metals Rev., 2011, 55, (3)•

14.70

14.55

14.40 3 , Å

V/Z 14.25

14.10 Atomic volume, 13.95

13.80

0 10 20 30 40 50 60 70 80 90 100 Re Composition, at% Rh Rh

Fig. 2. Atomic volumes for known hcp (hexagons) and fcc (squares) Re-Rh solid solutions. The corresponding compositions and atomic volumes, V/Z, are given in Table I

Improved data on binary systems will enable ternary 5 M. A. Tylkina, I. A. Tsyganova and E. M. Savitskii, Russ. J. and quaternary phase diagrams to be predicted with Inorg. Chem., 1962, 7, (8), 990 greater accuracy. Investigation of the physical proper- 6 L. Kaufman, in “Phase Stability in Metals and Alloys”, ties of Re-Rh solid solutions such as their hardness, eds. P. S. Rudman, J. Stringer and R. I. Jaffee, McGraw- Hill, New York, USA, 1967, p. 125 electrical and thermal conductivity and thermoelec- tric characteristics will improve the practical useful- 7 J. W. Arblaster, Platinum Metals Rev., 1996, 40, (2), 62 ness of this system. 8 J. W. Arblaster, Platinum Metals Rev., 2010, 54, (2), 93 and references therein Acknowledgement 9 J. W. Arblaster, CALPHAD, 1995, 19, (3), 357 The author is grateful to Dr Maria V. Yusenko (Ruprecht- 10 J. W. Arblaster, CALPHAD, 1996, 20, (3), 343 Karls University of Heidelberg, Germany) for helpful 11 R. Schmid-Fetzer, A. Janz, J. Gröbner and M. Ohno, Adv. discussions. Eng. Mater., 2005, 7, (12), 1142 12 S. V. Korenev, A. B. Venediktov, Yu. V. Shubin, S. A. References Gromilov and K. V. Yusenko, J. Struct. Chem., 2003, 44, 1 A. V. Naumov, Russ. J. Non-Ferrous Met., 2007, 48, (1), 46 (6), 418 13 S. A. Gromilov, K. V. Yusenko and E. A. Shusharina, 2 A. Naor, N. Eliaz, E. Gileadi and S. R. Taylor, The J. Struct. Chem, 2007, 48, (5), 899 AMMTIAC Quarterly, 2010, 5, (1), 11 14 Yu. V. Shubin, E. Yu. Filatov, I. A. Baidina, K. V. Yusenko, 3 P. Stevens and G. R. Lurie, Oxy Metal Industries Corp, A. V. Zadesenetz and S. V. Korenev, J. Struct. Chem., ‘Method and Electrolyte for Electroplating Rhodium- 2006, 47, (6), 1103 Rhenium Alloys’, US Patent 3,890,210; 1975 15 E. A. Shusharina, K. V. Yusenko, N. V. Kuratieva, I. A. 4 K. Ruthardt, W. C. Heraeus GmbH, ‘Spinnerette’, US Baidina and S. A. Gromilov, J. Struct. Chem., 2008, 49, Patent 2,967,792; 1961 (2), 375

16 S. A. Gromilov, S. V. Korenev, I. A. Baidina, I. V. 26 W. B. Pearson, “The Crystal Chemistry and Physics of Metals Korolkov and K. V. Yusenko, J. Struct. Chem., 2002, and Alloys”, Wiley-Interscience, New York, USA, 1972 43, (3), 488 27 S.-L. Chen, S. Daniel, F. Zhang, Y. A. Chang, X.-Y. Yan, 17 A. V. Belyaev, S. V. Korenev, V. I. Lisojvan and S. A. F.-Y. Xie, R. Schmid-Fetzer and W. A. Oates, CALPHAD, Gromilov, Nikolaev Institute of Inorganic Chemistry, 2002, 26, (2), 175 SB RAS, Novosibirsk, Russia, ‘Method for Producing 28 L. Kaufman and H. Bernstein, “Computer Calculation Rhenium-to-Rhodium Alloy’, Russian Patent 1,410,378; of Phase Diagrams”, Academic Press, New York, USA, 1994 1970, p. 334 18 K. V. Yusenko, S. A. Gromilov, I. V. Korol’kov, I. A. 29 A. T. Dinsdale, CALPHAD, 1991, 15, (4), 317 Baidina, G. V. Romanenko and S. V. Korenev, Russ. J. Inorg. Chem., 2004, 49, (4), 511 19 P. V. Snytnikov, K. V. Yusenko, S. V. Korenev, Yu. V. Shubin The Author and V. A. Sobyanin, Kinet. Catal., 2007, 48, (2), 276 Kirill Yusenko studied chemistry at 20 E. Yu. Filatov, Yu. V. Shubin and S. V. Korenev, the Novosibirsk State University, Z. Kristallogr. Suppl., 2007, 26, 283 Russia, and received his PhD in 2005 at the Nikolaev Institute of 21 E. Filatov, ‘Preparation and X-Ray Diffraction Study of Inorganic Chemistry, Novosibirsk, the Nanodimensional Bimetallic Powders Containing Russia, in the area of coordination of Platinum Group Metals’, PhD Thesis, Nikolaev Institue and material chemistry of platinum group metals (pgms). After a year of Inorganic Chemistry, Russia, 2009 as a postdoctoral researcher at the 22 S. A. Gromilov, Yu. V. Shubin, E. Yu. Filatov, T. V. University of Hohenheim, Stuttgart, Germany, he spent 3 years as a D’yachkova, A. P. Tutunnik and Y. G. Zainulin, J. Struct. researcher at the Ruhr-University Chem., 2011, 52, (3), 520 Bochum, Germany. Since 2011 he 23 “Powder Diffraction File, Alphabetical Index, Inorganic holds a position of the leader of the analytical laboratory at solid- Phases”, Joint Committee on Powder Diffraction chem GmbH based in Bochum, Standards (JCPDS) International Centre for Diffraction Germany. His scientific interests Data, Pennsylvania, USA, 1983 are focused on the chemistry of pgms and nanomaterials based on 24 J. W. Arblaster, Platinum Metals Rev., 1997, 41, (4), 184 metallic particles, thin films and 25 A. R. Denton and N. W. Ashcroft, Phys. Rev. A, 1991, 43, porous coordination polymers as well as solid-state chemistry of (6), 3161 pharmaceutical materials.

“Ruthenium Oxidation Complexes: Their Uses as Homogenous Organic Catalysts”

By W. P. Grifﬁ th (Imperial College, London, UK), Springer, Dordrecht, The Netherlands, 2011, 258 pages, ISBN: 978-1-14020-9376-0, £117.00, ¤129.95, US$159.00 (Print version); e-ISBN: 978-1-4020-9378-4, doi:10.1007/978-1-4020-9378-4 (Online version) doi:10.1595/147106711X580072 http://www.platinummetalsreview.com/

Reviewed by Peter Maitlis Professor William P. (Bill) Griffi th is the world expert Research Professor Emeritus, Department of Chemistry, on the chemistry of the heavier platinum group The University of Sheffi eld, Western Bank, metals (pgms), and has written defi nitive papers Sheffi eld S10 2TN, UK and review articles on many aspects of the chemis- Email: p.maitlis@sheffi eld.ac.uk try of complexes of platinum, palladium, rhodium, iridium, osmium and ruthenium (1–5). Most of his professional life has been spent teaching and researching at Imperial College, London, UK. An early and abiding interest has been the use of vibra- tional spectroscopy, in conjunction with other techniques, to defi ne structures of new complexes. His interests in their reactivity patterns and in the catalytic potential of the complexes grew out of this and, with his colleague Professor Steven Ley, he developed methodologies now widely used for the catalytic oxidation reactions of organic compounds (6, 7). These have been instrumental in helping workers in organic synthesis to devise new and useful catalytic oxidation reactions based on the chemistry of ruthenium and osmium. In addition Bill Griffi th has a strong interest in the history of chemistry, especially of the pgms (8, 9), and thus he is able to put the various discoveries into context. Much of his expertise he has distilled into this book, which is an immensely detailed and learned monograph despite its relatively small size. Although much of the readership of this book will be synthetic organic chemists, scientists of other back- grounds will also fi nd much useful material in it.

Ruthenium Complexes and Oxidation Reactions The literature is ordered fi rst by the reactions that are promoted and then by the types of ruthenium complexes that are used to carry them out. Within this latter category, the complexes are discussed in order of decreasing oxidation state of the ruthenium, starting

with the tetroxide (RuO4), Ru(VIII) in the 8 state, and solution. The author’s own classic (Griffi th) proce- going right down to the zerovalent carbonyls (Ru(0)), dure for making the very widely used reagent, tetra- emphasising the versatility of the metal. This section n- propylammonium perruthenate (TPAP reagent) is then brings discussions of the syntheses, the struc- also referenced (6). tures and the reactivities of the compounds which cause the oxidations together with some information Concluding Remarks on how the oxidations can occur. The book contains nearly 2000 references spanning The book begins with a brief history of the develop- the time from the discovery of ruthenium in Russia in ment of ruthenium chemistry in Chapter 1 and also 1844 (10) right up to the present explosion of interest describes the more important ruthenium complexes. arising from its employment as a catalyst. Thus the As the title of the book indicates, the main emphasis is literature cited deals with all aspects of oxidations on the many and varied oxidations of organic com- involving ruthenium compounds. Many of these pounds that are catalysed, mostly by higher oxida- involve reactions directed to the syntheses of complex tion state ruthenium compounds in solution; thus organic products and details are provided of their use there are very helpful sections dealing with the in natural product and pharmaceutical syntheses, detailed use and properties of these compounds. including the oxidations of carbohydrates, amines, For example, although the most active oxidant is gen- amides, ethers and thioethers. erally believed to be RuO4, since that material is a The text is well illustrated with formulae to clarify strong oxidant and not easily handled as such, it is the various reactions described. Inorganic and physi- normally prepared in situ from standard starting mat- cal chemists will also fi nd material to interest and to erials such as hydrated ruthenium chloride, available inspire them to learn more about the transformations from commercial sources. that ruthenium can promote. It is a book that is Chapter 2 covers oxidations of alcohols, carbohy- warmly recommended for synthetic organic chem- drates and diols, while the oxidations of alkenes, ists and will also interest researchers of other persua- arenes, alkynes and alkanes are discussed in Chapters sions too. 3 and 4; Chapter 5 collects together oxidations of amines, amides, ethers, sulfi des and organic com- References pounds containing other hetero-linkages. 1 W. P. Griffi th, “The Chemistry of the Rarer Platinum The oxidation reactions discussed include the con- Metals (Os, Ru, Ir and Rh)”, Wiley Interscience, London, versions of primary alcohols into aldehydes or car- 1968 boxylic acids, and of secondary alcohols into ketones 2 W. P. Griffi th, H. Jehn, J. McCleverty, Ch. Raub and S. D. or lactones. Alkenes are also oxidised, this can occur Robinson, ‘Rhodium’, in “Gmelin Handbook of Inorganic Chemistry”, eds. W. P. Griffi th and K. Swars, Springer- with C C cleavage, giving ketones and carboxylic Verlag, Berlin, 1982, Vol. 64, Suppl. Vol. B1; W. P. Griffi th, acids. Alternatively, under different conditions, alkene J. McCleverty and S. D. Robinson, ibid., 1983, Vol. 64, oxidation occurs without completely breaking the Suppl. Vol. B2; W. P. Griffi th, J. McCleverty and S. D. C—C link, to give cis-diols. In addition to the well- Robinson, ibid., 1984, Vol. 64, Suppl. Vol. B3 known reactions, many other oxidations, of pri- 3 W. P. Griffi th, J. McCleverty, S. D. Robinson and K. Swars, mary amines to nitriles, of tertiary amines to N-oxides, ‘Palladium’, in the “Gmelin Handbook of Inorganic Chemistry”, eds. W. P. Griffi th and K. Swars, Springer of ethers to esters, and of sulfi des to sulfones and Verlag, Berlin, 1989, Vol. 65, Suppl. Vol. B2 sulfates, are also described. 4 W. P. Griffi th and Ch. J. Raub, ‘Osmium’, in the “Gmelin A large number of the reactions can be run so that Handbook of Inorganic Chemistry”, ed. K. Swars, they are stoichiometric in the co-oxidant but catalytic Springer-Verlag, Berlin, 1978, Vol. 68, Suppl. Vol. 1 in ruthenium: that way they use only small amounts 5 W. P. Griffi th and Ch. J. Raub, ‘Iridium’, in the “Gmelin of the ruthenium compound in the presence of a Handbook of Inorganic Chemistry”, ed. K. Swars, less expensive co-oxidant such as sodium periodate Springer-Verlag, Berlin, 1978, Vol. 67, Suppl. Vol. 2

(NaIO4) or bromate (NaBrO3). 6 W. P. Griffi th, S. V. Ley, G. P. Whitcombe and A. D. White, A useful touch that the author offers is the inclu- J. Chem. Soc., Chem. Commun., 1987, 1625 sion of some actual recipes such as details of a 7 W. P. Griffi th, Platinum Metals Rev., 1989, 33, (4), 181 classic Sharpless procedure for the oxidation of an 8 W. P. Griffi th, Platinum Metals Rev., 2003, 47, (4), 175 olefi n, using ruthenium chloride hydrate and NaIO4 9 W. P. Griffi th, Platinum Metals Rev., 2004, 48, (4), 182 to generate RuO4 in situ, in aqueous acetonitrile 10 V. N. Pitchkov, Platinum Metals Rev., 1996, 40, (4), 181

“Ruthenium The Reviewer Oxidation Professor Peter Maitlis FRS is an Emeritus Professor at the Complexes: Their Department of Chemistry, University of Shefﬁ eld, UK. He holds Uses as Homogenous a number of honours from UK, US, Canadian, Australian and Organic Catalysts” European universities, institutions and learned societies. His research interests have been focused on synthetic and mechanistic organometallic chemistry, particularly relating to the catalysis of processes important to the chemical industry. One example is the rhodium-catalysed carbonylation of methanol to acetic acid and of methyl acetate to acetic anhydride. His group has also synthesised complexes of rhodium or ruthenium and investigated their reactions as models for stages in Fischer-Tropsch reactions.

The Early Life of Smithson Tennant FRS (1761–1815)

250th anniversary of the birth of the discoverer of iridium and osmium doi:10.1595/147106711X581710 http://www.platinummetalsreview.com/

By David G. Lewis Introduction Groundwork North Yorkshire, Civic Centre, Smithson Tennant’s name is well known to those who Portholme Road, Selby YO8 4SB, UK work with platinum group metals (pgms). He discov- Email: [email protected] ered both iridium and osmium in 1804, and his work with William Hyde Wollaston has been described in this journal (1). The unveiling of a plaque to note his birthplace in Selby, North Yorkshire, has also been recorded in Platinum Metals Review (Figure 1) (2). Tennant was elected a Fellow of the Royal Society (FRS) in 1785 at the remarkably early age of 23. Prior to his isolation of the two pgms, he had researched the nature of diamond and carbon dioxide, the agricultural importance of limestones and qualified as a medical doctor from Emmanuel College, Cambridge. The 250th anniversary of Tennant’s birth falls on 30th November 2011, and this article follows on from the 2006 paper in Platinum Metals Review (2) in providing more information on Tennant’s upbringing in Selby and his path towards the isolation of iridium and osmium.

Fig. 1. The blue plaque commemorating the birth of Smithson Tennant FRS, discoverer of iridium and osmium, located in Finkle Street, Selby, UK

Family Roots Calvert may also have moved to Selby due to the Smithson’s family came from Wensleydale in North status of Selby Abbey. At the time it remained one of Yorkshire, England. His father, Calvert Tennant, grew the major ecclesiastical foundations of the North of up either at Mount Park Farm (Figure 2) in the dale England, and provided a busy living for the then vicar itself, or at Park House (Figure 3), in the grounds of of Selby, Marmaduke Teasdale. There were insuffi cient Bolton Hall, seat of local landowner Lord Bolton. clergy to service the needs of the congregation and The forename ‘Calvert’ means ‘cowherd’, emphasising the thought of a further living attracted Calvert most the family’s farming links. probably during the 1750s. The Tennant family was fairly affl uent, having gained Calvert married Mary Daunt in Selby Abbey on Mid- land and position by many years of advantageous mar- summer’s Day, 1759. Mary was the only daughter of riage and property dealings. However, Calvert was local apothecary William Daunt, a Selby landowner not the eldest son, so was unlikely to inherit the ten- who had family links with the town of Beverley. ancy of the farm, and was therefore encouraged to William had died the year before, effectively leaving seek his fortune elsewhere. Calvert went into the his house at 12 Finkle Street and all his property to clergy, was ordained in 1741 and made a Fellow of Mary on the death of her mother in 1761. Finkle St John’s College, Cambridge, in 1743. He became Street, Selby, misnamed ‘Pinkhill’ on a 1792 survey curate in Castleford and rector of Great Warley in Essex. (Figure 4), is within 100 yards of the Abbey (Figure 5) Wensley is over 60 miles (100 km) from Selby, and and number 12 survives today as the ‘Elizabethan’ pub seemingly quite remote. However, the 1750s were an (Figure 6). era of rapid expansion of the turnpike road system, part of which linked the Wensleydale area to the major trade route between Leeds and Selby.

Fig. 4. Map of Selby drawn in 1792 with ‘Pinkhill’ rather than ‘Finkle’. Selby Abbey is approximately 100 m from Tennant’s house Fig. 2. Mount Park Farm, Wensley, 2011

Fig. 3. Park House, Wensley, 2000 (Photo courtesy Fig. 5. View of Selby Abbey in 2011 from upper of Liz Kirby) storey of ‘The Elizabethan’

50 students, a master and an usher, with a strong link to the church, and a strong emphasis on the classics. Smithson’s fi rst school was at Scorton, near Rich- mond, only a few miles from the family’s home in Wensleydale. This was “a free school for all persons after being qualifi ed to enter upon learning the Latin tongue” (4), and had over the years sent 14 pupils to Cambridge University. Scorton’s geographical position and academic record may have persuaded Mary to send Smithson there. Unfortunately, Smithson “left home with singular reluctance” and did not take to life at Scorton where he “gave the appearance of being indolent and dispir- ited and rarely joined the amusements of the rest of the boys” (4). Smithson’s interest in science began early. As medical books and chemicals were readily available at home due to his grandfather’s profession as an apothecary, it is perhaps not surprising that he prepared gunpowder for his own amusement. When attending his next school nearer Selby, at Tadcaster, he experi- Fig. 6. Smithson Tennant’s birthplace, now the enced the public lectures of Mr Walker, an itinerant ‘Elizabethan’ pub, currently being redecorated, with the blue plaque of 2005 (see Figure 1) visible to the “teacher of popular philosophy”. His intelligent ques- right tioning of Mr Walker led to him being invited to attend all the lectures, and is the fi rst external report of his Early Life and Education interest in science. The vicar, Marmaduke Teasdale, recorded Smithson However, Smithson did not remain long at Tennant’s birth on 3rd December in the Selby Abbey Tadcaster, but went instead to Beverley Grammar baptismal list for 1761 (Figure 7). His unusual fore- School (Figure 8), possibly as a result of his mater- name seems to have no family antecedents, and is nal grandfather’s family infl uence. said to mean ‘son of a (black)smith’, yet smithing was At this time, the Beverley Grammar School buildings not part of either family’s heritage. were in the grounds of Beverley Minster, and the staff His early education was at his father’s knee (3), were entirely ecclesiastical. Founded in the year learning Latin and Greek from the age of fi ve. Follow- 702 AD, and the oldest non-public school in England, ing Calvert’s death, in 1771 Mary sought to further her it was an institution that had an air of privilege. son’s education at various Yorkshire grammar schools. Instruction was in Latin and Greek with the expec- In the 18th century, these were predominantly tation that the boys would take an active part in the boys-only boarding establishments, with perhaps life of the church, and sing in Beverley Minster on

Fig. 7. Extract from baptismal list of Selby Abbey for 1761. Smithson Tennant is listed as the ﬁ fth name down (Courtesy of Borthwick Institute for Archives, University of York)

Fig.8. Beverley Grammar School ca. 1775 (Lithograph by R. Martin, courtesy of Beverley Grammar School)

Sundays. No record of Smithson’s vocal talent sur- oxygen, but Priestley’s other commitments made vives, but under the enlightened headmastership of this impossible. Instead, he planned to study with Dr George Croft he was encouraged to read widely. Dr Joseph Black at Edinburgh University, whose Amongst the volumes he studied was Newton’s treatise fame lay in the characterisation of carbon dioxide and on optics (5) which may have led to the experiment the outlining of physical concepts such as specifi c and he is alleged to have carried out concerning the focus- latent heat. Unfortunately, further domestic tragedy sing of moonbeams in an attempt to melt butter (6). precluded this. Tennant’s mother died in 1781 follow- At the end of his time at Beverley, Smithson, like all ing a fall whilst riding out with him. other leavers, was asked to sign a copy of a library This sad accident left Tennant alone in the world, book. The school still has some volumes going back with neither parents nor siblings. However, being a to the 18th century, but unfortunately not Smithson’s. scion of a wealthy family in Wensleydale, and owner Beverley Grammar School takes a pride in Smithson of property and land in Selby, the disposal of these Tennant’s achievements, as a plaque on a recent assets afforded him fi nancial security for the rest of his extension to the school’s buildings show (Figure 9). life. He seems not to have visited the town after 1788. He studied at Christ’s College, Cambridge, ostensi- Academic Successes Before the bly in medicine but also with a strong interest in Discoveries of Osmium and Iridium chemistry and botany. He matriculated in 1784 and in By the time his schooling came to an end in 1780, 1786 moved to Emmanuel College where he gained Tennant had gained a wide knowledge of classical his Bachelor of Medicine in 1788 and graduated as languages, a working understanding of French and a Doctor of Medicine in 1796. grounding in ‘Natural Philosophy’, as scientifi c mat- He also travelled widely in Europe. In Sweden he ters were referred to at the time. met Carl Scheele (also a researcher for new elements) Tennant had expressed a desire to extend his stud- and Jöns Berzelius (who helped develop a system of ies under Joseph Priestley, the well-known English chemical nomenclature). In France he met Claude- academic usually credited with the discovery of Louis Berthollet (who also worked on chemical nomenclature) and possibly Antoine Lavoisier (discoverer of oxygen, hydrogen and the metric system). For a very short time after matriculation in 1796 Tennant did practise medicine but he quickly concluded that he was not temperamentally suited to it and thereafter devoted himself to chemical research. He published a number of papers dealing with inter alia the composition of carbon dioxide (or “fi xed air” as it was known at that time) and the nature of diamond.

The Discovery of Iridium and Osmium Fig. 9. The plaque to commemorate Smithson Tennant on the science block of the current In 1801 Tennant worked with Wollaston on a 186 kg Beverley Grammar School buildings mass of Columbia platinum ore (‘platina’) (3). In

outline, platinum is soluble in aqua regia, a mixture Minster and permission from Lord Bolton and John of concentrated nitric and hydrochloric acids. When Loudon to visit the former Tennant family farm prop- platina is dissolved in aqua regia, a highly coloured erties in Wensleydale, along with permission to repro- solution and a black residue are obtained, indicating duce a document in the custody of the Borthwick the impurities in the ore. Institute and advice from Liz Kirby, a Wensleydale Tennant fused the insoluble residue with alkali at genealogist, are all gratefully acknowledged. high temperature and dissolved the resulting cooled solid in water, producing a further black solid and a References yellow solution. The yellow solution was probably a 1 W. P. Griffi th, Platinum Metals Rev., 2004, 48, (4), 182 basic form of osmium tetroxide, OsO4. The black 2 W. P. Griffi th, Platinum Metals Rev., 2006, 50, (2), 77 solid was further treated with hydrochloric acid, the 3 P. Milsom, “Smithson Tennant FRS”, Selby Civic Society, solid produced was fused with caustic soda and fur- 2005 ther treatment with acid obtained red crystals. These 4 Anon (probably J. Wishaw), Ann. Phil., 1815, 6, 1; Ann. Phil., 1815, 6, 81 are most likely to have been Na2[IrCl6]•nH2O. On heating these, a white powder of an unknown element 5 I. Newton, “Opticks: Or, A treatise of the Refl ections, was obtained, which was later identifi ed as iridium. Refractions, Infl exions and Colours of Light. Also Two The Royal Society’s Copley Medal was awarded to treatises of the Species and Magnitude of Curvilinear Figures”, Sam. Smith and Benj. Watford, Printers to the Tennant on his 43rd birthday, 30th November 1804, to Royal Society, London, 1704 mark the intricate experimentation that lay behind 6 D. McDonald, ‘Smithson Tennant, F.R.S. (1761–1815)’, these isolations. Notes Rec. R. Soc. Lond., 1962, 17, (1), 77

Appendix The Author Smithson Tennant’s life will be commemorated, A chemistry graduate from the 250 years after his birth, by a schools’ lecture at Selby University of York, David Lewis has, for the last three years, been Town Hall, a public lecture and an academic sympo- investigating the ‘Hidden Heritage’ sium concerning iridium and osmium chemistry to be of Selby for the educational charity, Groundwork North Yorkshire. On held at the University of York, UK. For further informa- realising that Smithson Tennant, who tion on these, please contact Dr Annie Hodgson at: ﬁ rst isolated the platinum group metals, iridium and osmium, was born [email protected]. in the town in 1761, David has been looking into Tennant’s early years. This article is part of a more detailed Acknowledgements work due to be published to mark the Information from Chris Goodwin and Nigel Young of 250th anniversary of Tennant’s birth, Beverley Grammar School, from the staff of Beverley on 30th November 2011.

“Platinum 2011”

Johnson Matthey’s latest analysis of the platinum group metal (pgm) markets, “Platinum 2011”, was released on 16th May 2011. The trends in supply and demand and the short term outlook on the status of the pgm market are reported.

Platinum Platinum Market Close to Balance in 2010 In 2010, the platinum market was close to balance with a surplus of 20,000 oz. Gross demand for platinum increased by 16% to 7.88 million oz, however, supplies remained almost fl at at 6.06 million oz. Recycling of platinum also increased by In 2010, the demand for platinum in autocatalysts almost a third to 1.84 million oz. surged. A better-performing global automotive industry increased the demand for emissions Slight Rise in Supplies in 2010 control devices After a mixed year for producers, global supplies of platinum increased very slightly by 35,000 oz to of consumer electronics increased the level of 6.06 million oz in 2010. In South Africa, platinum demand. supplies remained fl at at 4.64 million oz. Refi ned production in South Africa increased very slightly, Fall in Platinum Demand for Jewellery however, not all of this metal had been shipped Manufacture by the year-end. Platinum shipments from Russia Demand for platinum jewellery dropped by 14% increased by 5% to 825,000 oz. There was a ramp-up following strong demand in 2009. Although the of expansion projects in Zimbabwe which resulted Chinese jewellery market remained robust, this in growth of almost a quarter to 280,000 oz. was considerably lower than in 2009 due to the higher metal prices and full stock levels. Autocatalyst Demand Surged Platinum demand increased by 30% in North Following poor demand in 2009, the global America and continued to gain popularity in automotive sector recovered and demand for India. Demand was slightly down in Japan and platinum in autocatalysts rose by 43% to 3.13 Europe. million oz. Vehicle production increased in all regions, therefore increasing the demand for Palladium platinum. Europe, where platinum was mainly used Palladium Market in Fundamental Deﬁ cit in in diesel autocatalyst formulations, had the largest 2010 increase in demand as the market share of diesel Palladium supplies increased by 3% to 7.29 vehicles increased. million oz, however, gross demand rose by 23% to 9.63 million oz after a strong performance Industrial Demand Rose in 2010 by the automotive sector and a large increase Gross industrial demand rose by 48% to 1.69 million in investment demand, leaving the market in a oz due to economic recovery in developed markets fundamental deficit of 490,000 oz. and strong growth in emerging ones. Production In 2010, open loop recycling of palladium in of electrical, glass and chemical products which the automotive, electrical and jewellery sectors use platinum either in the fi nished item or in reached 1.85 million oz, an increase of nearly a the manufacturing process soared. Higher sales third compared with 2009.

Autocatalyst Demand Increased Other Platinum Group Metals Gross demand for palladium in the autocatalyst Supply and demand data is briefl y discussed market grew by 35% to 5.45 million oz in 2010 for rhodium and the net demand for ruthenium due to economic recovery and stricter emissions and iridium is summarised. A strong recovery in legislation. Palladium is increasingly used as an purchasing of rhodium by the automotive industry alternative to platinum in autocatalyst formulations and glass and chemical markets led to a rise in gross despite a narrowing of the price difference between demand of 22% to 873,000 oz. There was a slight the two metals. In China, economic growth and tax decline in global supplies by 19,000 oz to 751,000 breaks from the government aided growth in the oz, due to a build-up of pipeline stocks in South market for light-duty vehicles and the demand for Africa. On the whole, the rhodium market tightened, palladium surged by 42% to 975,000 oz. however, it remained in surplus by 114,000 oz. Net demand for ruthenium rose by 79% to 1.03 Weaker Demand in the Jewellery Sector million oz. The biggest demand for ruthenium Gross demand for palladium in the jewellery came from the electrical sector which was driven market diminished by 20% to 620,000 oz. A fall by an increase in purchasing for hard disk drive in palladium jewellery manufacturing in China manufacture, where it is used together with contributed to this reduction, which counteracted platinum in perpendicular magnetic recording increases in Europe (increased by 40%) and North hard disk drives. America, which had grown in 2010 to 65,000 oz. Net iridium demand increased from 81,000 oz in 2009 to 334,000 oz in 2010. Strong sales of back- Rise in Industrial and Investment Demand lit LED televisions drove the demand for iridium for Palladium crucibles, used to make single sapphire crystal Gross industrial demand for palladium which is used as a substrate in LEDs. strengthened by 70,000 oz to 2.47 million oz in 2010. This was aided by increases in the chemical Special Features industry by 22% and a rise in gross purchasing from A special feature on fuel cells explains their the electrical market by 40,000 oz to 1.41 million potential and the importance of the pgms in the oz. Physical investment demand expanded by 74% catalyst layer. Fuel cells in the auxillary power, to 1.09 million oz in 2010 due to purchasing of combined heat and power (CHP) and materials Exchange Traded Funds (ETFs) in the USA. handling vehicle markets are summarised. A report on the use of pgms in glass manufacturing discusses the role of pgms in this process and reviews the current market conditions and prospects.

Availability of “Platinum 2011” Palladium demand in electronic components rose The book is available to download free of charge, during 2010 as a PDF fi le in English, Chinese or Russian by visiting the Platinum Today website at: http://www. Recycling of Platinum Group Metals platinum.matthey.com/publications/pgm-market- 2010 saw another rise in open loop recycling reviews/archive/platinum-2011/. Alternatively the (autocatalyst, electrical and jewellery) where the English version can be ordered in hard copy, by metal is sold back to the market after refi ning. fi lling in the form at: http://www.platinum.matthey. This contrasts with closed loop recycling where com/publications/pgm-market-reviews/request-a- the pgms are recycled and reused in the same copy/, by emailing a request to: ptbook@matthey. application. Open loop recycling fi gures for com, by writing to: Johnson Matthey, Precious Metals platinum, palladium and rhodium for the different Marketing, Orchard Road, Royston, Hertfordshire, applications are discussed. SG8 5HE, UK.

Publications in Brief

BOOKS of nanoalloy cluster structure and heterogeneous catalysis by bimetallic nanoparticles, and should “Advances in Fischer-Tropsch Synthesis, also be of interest to researchers working on other Catalysts, and Catalysis” applications of nanoalloys, including sensors, optics Edited by B. H. Davis (Center for Applied and magnetics. Energy Research, Lexington, Kentucky, USA) and M. L. Occelli (MLO Consulting, “Privileged Chiral Ligands and Catalysts” Atlanta, Georgia, USA), CRC Press, Boca Edited by Q.-L. Zhou (Nankai Raton, Florida, USA, 2010, 424 pages, University, Tianjin, China), Wiley- ISBN 978-1-4200-6256-4, US$236.95; VCH Verlag & Co KGaA, Weinheim, e-ISBN 978-1-4200-6257-1 Germany, 2011, 484 pages, ISBN This book focuses on catalyst 978-3-527-32704-1, £115.00, preparation and activation, €138.00, US$175.00; e-ISBN 9783527635207 reaction mechanism and process- related topics and is drawn from the proceedings at a This book is for chemists working symposium held during the 236th American Chemical in asymmetric catalysis and starts with the core structure of the Society Meeting in Philadelphia, Pennsylvania, USA, catalysts, explaining why a certain ligand or catalyst is in August 2008. Fischer-Tropsch technology holds so successful. It describes in detail the history, the basic promise in the area of renewable resources. The book structural characteristics, and the applications of these includes chapters on ‘Catalytic Performance of Ru/ “privileged catalysts”. Among the eleven ligands and Al O and Ru/Mn/Al O for Fischer-Tropsch Synthesis’ 2 3 2 3 catalysts used as examples, BINAP, DuPhos, Josiphos, and ‘Low-Temperature Water-Gas Shift: Assessing spiro ligands, BOX and PHOX are chiral ligands in Formates as Potential Intermediates over Pt/ZrO and 2 metal catalysts; Salen complexes are chiral metal Na-Doped Pt/ZrO Catalysts Employing the SSITKA- 2 catalysts; and cinchona alkaloids and proline are DRIFTS Technique’. generally used as organocatalysts. BINOL and TADDOL “Computational Studies of Transition Metal were used as chiral ligands in Lewis acid catalysts in Nanoalloys” earlier studies but recently they have also been used L. O. P. Borbón (Theory Department, as organocatalysts in various reactions. All six pgms Fritz-Haber-Institut der Max-Planck are covered in this book. Gesellschaft, Berlin, Germany), Springer Theses, Springer-Verlag, Berlin, Heidelberg, Germany, 2011, JOURNALS 180 pages, ISBN 978-3-642-18011-8, ACS Catalysis €106.95; e-ISBN 978-3-642-18012-5 Editor-in-Chief: C. W. Jones (Georgia The Springer Theses series Institute of Technology, USA); recognises outstanding PhD American Chemical Society; e-ISSN research. This thesis involves 2155-5435 the computational modelling of bimetallic gas- ACS Catalysis is a new phase nanoalloy clusters of palladium-platinum, journal from the American silver-platinum, gold-gold and palladium-gold. The Chemical Society dedicated author used a combination of global optimisation to publishing original techniques – coupled with a Gupta-type empirical research on heterogeneous many-body potential – and density functional catalysis, homogeneous catalysis and biocatalysis. theory (DFT) calculations to study the structures, Coverage includes life sciences, drug discovery bonding and chemical ordering, as well as & development, household products, polymer investigate the chemisorptions of hydrogen and discovery & production, environmental protection carbon monoxide on bimetallic clusters. The work and energy & fuels. The journal includes both is relevant to theoretical and experimental studies experimental and theoretical research and reviews

on molecules, macromolecules or materials that online, open access, primary research publication are catalytic in nature. New reactions and new covering all areas of the natural sciences: biology, approaches to synthesis involving known catalysts, chemistry, physics and earth sciences. Hosted on discovery or modification of new catalysts, novel nature.com, Scientific Reports is open to all and mechanistic and investigatory studies, practical publishes original research papers of interest to enhancements of known processes, and conceptual specialists within their field. advances will be featured. Contributions of Inorganic Chemistry to Energy Advanced Energy Materials Research Editorial Board Co-chairs: C. Brabec Dalton Trans., 2011, 40, (15), 3761– (Erlangen University, Germany) and M. 3996 Waidhas (Siemens, Germany); Wiley- With guest editors Duncan VCH; ISSN 1614-6832; e-ISSN 1614- Wass (School of Chemistry, 6840 University of Bristol, UK) and Wiley-VCH’s new journal Neil Robertson (School of Advanced Energy Materials is an Chemistry and EaStChem, interdisciplinary forum of original University of Edinburgh, UK), peer-reviewed contributions on materials used in all this themed issue of Dalton forms of energy harvesting, conversion and storage. Transactions focuses on the inorganic chemistry Topics include: of sustainable energy technologies such as solar (a) Organic and inorganic photovoltaics energy conversion, hydrogen storage, fuel cells, (b) Batteries and supercapacitors batteries, nuclear chemistry, biomass conversion, (c) Fuel cells CO2 conversion and other aspects of catalysis for (d) Hydrogen generation and storage energy. Interesting items include ‘Light-Induced (e) Thermoelectrics Charge Separation and Photocatalytic Hydrogen (f) Water splitting and photocatalysis Evolution from Water Using RuIIPtII-Based Molecular (g) Solar fuels and thermosolar power Devices: Effects of Introducing Additional Donor (h) Magnetocalorics and/or Acceptor Sites’ and ‘Purification-Free (i) Piezoelectronics Synthesis of a Highly Efficient Ruthenium Dye Catalysis Science & Technology Complex for Dye-Sensitised Solar Cells (DSSCs)’, Editorial Board Editors-in-Chief: C. Friend among others. (Harvard University, USA) and P. van Special Issue on Industrial Catalysis Leeuwen (Institut Català d’Investigació Química (ICIQ), Tarragona, Spain); Royal Catal. Today, 2011, 163, (1), 1–54 Society of Chemistry; ISSN 2044-4753; This special issue of Catalysis e-ISSN 2044-4761 Today is in honour of the industrial Catalysis Science & Technology is a chemist, Martin Lok, who retired new multidisciplinary journal from from Johnson Matthey in the Royal Society of Chemistry 2008. Details on his career are that focuses on both the fundamental science and highlighted by his colleague John technological aspects of catalysis. The journal aims Casci. The guest editors Sean A. to contain fundamental, applied, experimental Axon (Johnson Matthey Plc, UK) and computational work and will bring together and Aalbert Zwijnenburg (Johnson Matthey Chemicals research from the homogeneous, heterogeneous and GmbH, Germany) aimed in their selection to shed light biocatalysis communities. on some of the developments in catalysis that occurred Scientiﬁ c Reports during the span of Martin Lok’s career. Those articles Nature involving pgms include: ‘A History of Industrial Catalysis’, Publishing ‘Catalytic Control of Emissions from Cars’, ‘Oxidation Group; e-ISSN of Benzyl Alcohol Using Supported Gold--Palladium 2045-2322 Nanoparticles’ and ‘Vapour Phase Hydrogenation of Nature Publishing Group’s Scientific Reports is an Olefi ns by Formic Acid over a Pd/C Catalyst’.

Molecular Surface Chemistry and Its Applications Special Issue Langmuir, 2010, 26, (21), 16187– 16624 This special issue of Langmuir is a celebration of Professor Gabor A. Somorjai on the occasion of his 75th birthday. Professor Somorjai is recognised for laying the foundation of modern surface chemistry. One of his main contributions is in the area of heterogeneous catalytic chemistry which he converted into a quantitative science and enabled the catalytic site to be understood in terms of surface atomic structures and fundamental molecular properties. His pgm research has included the characterisation of particle size and size distribution of platinum nanoparticles on alumina catalysts and low energy electron diffraction (LEED) studies of platinum catalysts used in petroleum refi ning.

Abstracts

CATALYSIS – APPLIED AND PHYSICAL CATALYSIS – REACTIONS ASPECTS Catalytic Oxidation of Biomass Tar over Why is Metallic Pt the Best Catalyst for Platinum and Ruthenium Catalysts Methoxy Decomposition? S. J. Yoon, Y. K. Kim and J. G. Lee, Ind. Eng. Chem. Res., R. Ren, C. Niu, S. Bu, Y. Zhou, Y. Lv and G. Wang, J. Nat. Gas 2011, 50, (4), 2445–2451 Chem., 2011, 20, (1), 90–98 The catalytic oxidation of toluene was investigated

The decomposition of methoxy on Cu(111), Ag(111), using Pt and Ru on -Al2O3. As the reaction Au(111), Ni(111), Pt(111), Pd(111) and Rh(111) has temperature increased and the size of the catalyst been analysed by DFT calculations. The calculated decreased, the conversion of toluene increased. activation barriers were correlated with the coupling Usually, the higher content of Pt and Ru showed higher 2 matrix element Vad and the d-band center (d) for the conversion of toluene. The Pt catalyst showed a higher Group IB metals and Group VIII metals, respectively. toluene conversion effi ciency than the Ru catalyst at By comparison of the activation energy barriers of the the same temperature in the absence of syngas; while methoxy decomposition, Pt was found to be the best in the presence of syngas, the Ru catalyst showed a catalyst. better conversion effi ciency than the Pt catalyst. A temperature of >300ºC is required to oxidise tar The Atomic Structural Dynamics of -Al O 2 3 effi ciently. Supported Ir–Pt Nanocluster Catalysts Prepared from a Bimetallic Molecular Precursor: A Study Using Aberration-Corrected Electron EMISSIONS CONTROL Microscopy and X-Ray Absorption Spectroscopy Effect of Palladium Dispersion on the Capture M. W. Small, S. I. Sanchez, L. D. Menard, J. H. Kang, A. I. of Toxic Components from Fuel Gas by Frenkel and R. G. Nuzzo, J. Am. Chem. Soc., 2011, 133, (10), Palladium-Alumina Sorbents 3582–3591 J. P. Baltrus, E. J. Granite, E. C. Rupp, D. C. Stanko, B. Howard Deposition of [Ir Pt (μ-CO) (CO) ( -C Me ) ] on 3 3 3 3  5 5 3 and H. W. Pennline, Fuel, 2011, 90, (5), 1992–1998 -Al O , and its subsequent reduction with H , gave 2 3 2 The preparation method used for Pd/Al O sorbents highly dispersed supported bimetallic Ir-Pt NPs. 2 3 was found to infl uence their performance. When Pd Various characterisation techniques were combined is well dispersed in the pores of the support, Pd is less to show that Ir-Pt NPs supported on -Al O containing 2 3 susceptible to S poisoning, and the sorbent has better a 1:1 ratio of Ir:Pt adopt segregated structures in which long-term activity for adsorption of AsH and H Se, Ir occupies the core region. 3 2 but poorer adsorption capacity for Hg. As the contact Kinetics and Product Distribution Studies on interaction between Pd and the support is lessened Ruthenium-Promoted Cobalt/Alumina Fischer- the Pd becomes more susceptible to poisoning by S, Tropsch Synthesis Catalyst resulting in higher capacity for Hg, but poorer long- A. Tavasoli, A. Nakhaei Pour and M. G. Ahangari, J. Nat. Gas term performance for adsorption of As and Se. Chem., 2010, 19, (6), 653–659 HC production rates and distributions on Ru promoted FUEL CELLS Al2O3 supported Co Fischer-Tropsch synthesis catalyst were investigated by the concept of two superimposed Preparation of Ptshell–Pdcore Nanoparticle with Anderson-Schulz-Flory (ASF) distributions. The Electroless Deposition of Copper for Polymer characterising growth probabilities 1 and 2 are strongly Electrolyte Membrane Fuel Cell dependent on reaction conditions. By increasing the H2/ I. Choi, S. H. Ahn, J. J. Kim and O. J. Kwon, Appl. Catal. B: CO partial pressure ratios and reaction temperatures, Environ., 2011, 102, (3–4), 608–613 deviation from normal ASF distribution decreases and The title NP was prepared by an electrochemical the double--ASF distribution changes into a straight method (see the ﬁ gure). Pd/C was surrounded by Cu line. Based on the concept of double--ASF distribution, through electroless deposition which was followed by a a rate equation for the production of HCs was obtained. displacement reaction with Pt. The catalytic properties

I. Choi et al., Appl. Catal. B: Environ., 2011, 102, (3–4), 608–613

Oxidation of 2+ – reducing agent 2+ CuCu +2e 2e– Cu 4e–+Pt4+  Pt Pd Cu Pd Pd

Porous carbon support were investigated using RDE. The kinetics of the developed. The method was validated with Pt-Ru electrochemically-prepared Pt/Pd/C catalyst for O2 electrocatalysts. reduction were superior to a conventional Pt/C catalyst. The Ptshell–Pdcore NP contains small amount of Pt METALLURGY AND MATERIALS leading to high mass-specifi c activity. Stress Induced Deformation in the Palladium-Based Electrodes: A Way to Reduce Solidiﬁ cation of Undercooled Co80Pd20 Alloys Platinum Content in Polymer Electrolyte S. Zhou, R. Hu, J. Li, H. Chang, H. Kou and L. Zhou, Mater. Membrane Fuel Cells Sci. Eng.: A, 2011, 528, (3), 973–977 E. Antolini, S. C. Zignani, S. F. Santos and E. R. Gonzalez, The Co Pd alloys were undercooled by denucleation Electrochim. Acta, 2011, 56, (5), 2299–2305 80 20 of molten glasses combined with cyclic superheating. A Pd-based PEMFC was formed using a Pd96Pt4/C The highest undercooling achieved was 415 K. Dense- anode catalyst and a Pd49Pt47Co4/C cathode catalyst. regular fault ribbons were detected in high undercooling When the overall Pd:Pt:Co atomic composition of grains of Co80Pd20. It provided experimental evidence both electrodes (anode + cathode) was 72:26:2, of stress existed in solidifi cation process at high the cell performance at a current density of 1 A undercooling. cm–2 was 89% that of a conventional Pt/C-catalysed PEMFC. Of the performance loss, 6% was ascribed to The Effect of Fe Additions on the Shape the anode catalyst and 5% to the cathode catalyst. Memory Properties of Ru-Based Alloys The performance losses were thought to be due to A. Manzoni, K. Chastaing, A. Denquin, P. Vermaut, J. van the higher particle size of the Pd-based catalysts Humbeeck and R. Portier, Scripta Mater., 2011, 64, (12), compared to Pt. The maximum power density of the 1071–1074 Pd-based cell was 76% of that of a Pt/C-catalysed cell. Equiatomic RuNb and RuTa shape memory alloys exhibit a shape memory effect (SME) and transformation Rapid Optical Screening Technology for Direct temperatures >800ºC. Controlling the transformation Methanol Fuel Cell (DMFC) Anode and Related temperatures while retaining the SME could be Electrocatalysts achieved either by changing the alloy composition F. G. Welsch, K. Stöwe and W. F. Maier, Catal. Today, 2011, or by adding a ternary element such as Fe. Eight alloys 159, (1), 108–119 were investigated and compression testing and DSC An optical high-throughput screening method were carried out. The SME was found to decrease with for DMFC catalysts based on the fl uorescence decreasing Ru content. of protonated quinine generated during electrooxidation of MeOH has been developed. APPARATUS AND TECHNIQUE The working electrode allows the parallel quantifi cation of the fl uorescence development for Acetylene Sensor Based on Pt/ZnO Thick Films up to 60 materials. For the preparation of the working as Prepared by Flame Spray Pyrolysis electrode a coating routine was employed, which N. Tamaekong, C. Liewhiran, A. Wisitsoraat and S. allows the use of sol–gel derived materials. Due Phanichphant, Sens. Actuators B: Chem., 2011, 152, (2), to the required stability of the electrode catalysts 155–161 towards the acidic polymer membrane, a fast optical ZnO nanoparticles loaded with Pt were produced prescreening method for acid stable materials was by fl ame spray pyrolysis using Zn naphthenate

and Pt(II) acetylacetonate precursors dissolved in S. Takizawa, R. Aboshi and S. Murata, Photochem. Photobiol. xylene. Under the 5/5 (precursor/oxygen) fl ame Sci., 2011, 10, (6), 895–903 condition, ZnO nanoparticles and nanorods were Photooxidation of 1,5-dihydroxynaphthalene was obtained. The crystallite sizes of ZnO spherical and carried out in the presence of cyclometallated neutral 1 hexagonal particles were from 5 to 20 nm while ZnO and cationic Ir complexes as singlet oxygen ( O2) + + nanorods were 5–20 nm in width and 20–40 nm in sensitisers. [Ir(ppy)2(phen)] and [Ir(ppy)2(bpy)] 1 length. Pt NPs with diameter of ~1 nm were uniformly have high O2 generation quantum yields. The neutral deposited on the surface of ZnO particles. Acetylene complexes with lower oxidation potentials were sensing characteristics of ZnO NPs was signifi cantly considered to have a more effi cient charge-transfer improved as Pt content increased from 0 to 2 at%. A interaction with molecular oxygen, which decreased 1 low detection limit of 50 ppm was obtained at 300ºC the effi ciency of O2 formation. High yields of the operating temperature. oxidised product when using the cationic complexes indicated their excellent photosensitising durability. TG/DTA of Hydrogen Reduction Kinetics of TiO2 Supported PdO Chemochromic Pigments A Phosphorescent Material with High and N. Mohajeri, A. T-Raissi and J. Baik, Thermochim. Acta, 2011, Balanced Carrier Mobility for Efﬁ cient OLEDs 518, (1–2), 119–122 T. Peng, Y. Yang, Y. Liu, D. Ma, Z. Hou and Y. Wang, Chem. Commun., 2011, 47, (11), 3150–3152 TiO2-supported PdO chemochromic pigments were used in H2 sensing devices for detecting H2 leaks. A novel phosphorescent material (Fppy)2Ir(dipba) TG/DTA analysis was used to study the kinetics of was shown to possess superior hole and electron reduction of PdO/TiO2 by H2 gas and revealed a two- transporting properties. (Fppy)2Ir(dipba) performed step process. A colour change was associated with the as an effi cient phosphorescent emitter as well as an second step during which the adsorbed H2 reacts with excellent host for a yellow phosphorescent dopant PdOH species to form water. This step has fast kinetics to result in high-performance PHOLEDs. The results with reaction order of 0.55 and zero with respect to suggest that electroluminescence performance of [PdOH] and [H2], respectively. PHOLEDs based on doping strategy can be enhanced by using the phosphorescent complexes with the ELECTROCHEMISTRY improved charge carrier transporting property as the host. Molecular Adsorbates at Single-Crystal Platinum-Group Metals and Bimetallic Surfaces SURFACE COATINGS H. Baltruschat and S. Ernst, ChemPhysChem, 2011, 12, (1), 56–69 Electrodeposition of Al–Pt Alloys Using

Fundamental studies of the molecule–surface Constant Potential Electrolysis in AlCl3–NaCl– interaction between organic species such as CO, C6H6 KCl Molten Salt Containing PtCl2 and C2H2 and Pt, Pd or their (sub)monolayers on Au M. Ueda, H. Hayashi and T. Ohtsuka, Surf. Coat. Technol., are reviewed. The surface orientation of the pgms was 2011, 205, (19), 4401–4403 found to determine the kind of organic species that Molten salt electrolysis with an AlCl3–NaCl–KCl molten would adsorb on them as well as the prevailing reaction salt containing PtCl2 at 448 K was used to form Al-Pt alloys channels. Pd was less active than Pt for oxidation or for high-temperature coatings. The voltammogram hydrogenation of the adsorbates. The experimental showed that cathodic reduction of Pt ions started at a results are of interest as models for more complicated potential of 1.4 vs. Al/Al(III) in the molten salt. Pure Pt adsorbates in the context of electrochemical sensors, was deposited at 1.2 V and there was co-deposition of Al electroorganic synthesis, corrosion inhibitors and and Pt at potentials <1.0 V. The co-deposit was a mixture brighteners for metal plating as well as electrocatalytic of intermetallic compounds of AlPt2 or AlPt3. The ratio processes. (Contains 107 references.) of Pt:Al (in at%) in the electrodeposits decreased from 100:0 at 1.2 V to 25:75 at 0.0 V. PHOTOCONVERSION Photooxidation of 1,5-Dihydroxynaphthalene with Iridium Complexes as Singlet Oxygen Sensitizers

Patents

CATALYSIS – APPLIED AND PHYSICAL C6H6, p-cymene or cyclooctadiene) and reacting ASPECTS this in an organic solvent at 40–120ºC with both the diphosphine ligand and diamine ligand added in Palladium Phosphine Complex excess of the reaction stoichiometry. Johnson Matthey Plc, World Appl. 2011/012,889 t PGM Catalyst for the Production of [Pd(P Bu3)(μ-Br)]2, 1, is prepared by mixing 0.05–2.5 –1 t Hydrocarbons mol l of Pd(diolefi n)Br2 and Bu3P in a solvent such as MeOH, the reaction mixture is then stirred at E. Harlin et al., US Appl. 2011/0,087,058 preferably –5–30ºC for ideally ~10 min to 1 h. The next A feedstock selected from fats and oils which originate step is the addition of an alkali hydroxide (preferably from plants, animals or other biomass is deoxygenated NaOH) to form the catalyst for cross-coupling reactions. by making contact with CO in the presence of a catalyst t The preferred molar ratios of Pd(diolefi n)Br2: Bu3P selected from Pt, Pd, Rh, Ir, Os, Ru, Re, Mn, Mo, Zn, Co or and Pd(diolefi n)Br2:alkali hydroxide are 1:1. Cu. This reaction is carried out in the presence of water, World Appl. 2011/012,889 under alkaline conditions at 150–350ºC under 0.1–150 bar to produce hydrocarbons which are suitable as tBu Br tBu biofuels. tBu P Pd Pd P tBu t Br tBu Bu EMISSIONS CONTROL 1 PGM Washcoat on Diesel Particulate Filter Int. Eng. Intellectual Prop. Co, LLC, European Appl. PGM Catalyst in Hydrogen Generation 2,290,203 (2011) Univ. Hong Kong, US Appl. 2011/0,059,378 A DPF includes a washcoat of at least one metal A catalyst is claimed with a tertiary metal composition, selected from Pt and Pd added to the surface and pore where the fi rst metal is either Pt or Ru, the second structure of the fi lter material. This washcoated fi lter metal is selected from Pt, Pd, Rh, Ir, Os, Ru, Au and/ material is a thin band located adjacent to the inlet. or Re and the third metal is Bi which is present as an The DPF should improve the distance between active oxide or a mixture of oxides and carbonates and is regenerations and may prevent HC/CO slip. in the +3 oxidation state. The catalyst is used in the Platinum and Palladium Three-Layered Catalyst dehydrogenation of small organic molecules such as Heesung Catal. Corp, US Patent 7,931,874 (2011) MeOH. A preferred embodiment, PtaRubBicOx, where 0.3 ≤ a ≤ 6.5, b = 1, 0.1 ≤ c ≤ 6.4 and 0.15 ≤ x ≤ 9.6 can A three-layered catalyst consisting of a substrate, a be in the form of a NP (2–100 nm in cross-section) lower layer of Pt, an intermediate layer of Pd and an upper layer of Pt, is used for purifying exhaust gases and the supporting material comprises C, TiO2, A l 2O3 of an internal combustion engine. The weight ratio or SiO2. of Pt in the upper and lower layers ranges from 60:40 to 80:20 and the substrate is selected from cordierite, CATALYSIS – REACTIONS -alumina and mullite. Osmium Complexes for Carbonyl Reduction Univ. Degli Studi Udine, World Appl. 2011/033,022 FUEL CELLS New Os complexes [OsX2(P2)(diamine)] (P = P atom of a diphosphine; X = anionic ligand) are prepared Iridium-Based Water Electrolysis Catalyst for catalysing the reduction of carbonyl compounds. Johnson Matthey Plc, World Appl. 2011/021,034 This catalyst is prepared by selecting an Os precursor A catalyst layer in a fuel cell includes an electrocatalyst

([OsX2(PAr3)3] (Ar = Ph, p-tolyl), [Os2X4(P(m-tolyl)3)5] (selected from the pgms, Au, Ag or a base metal) and and OsX2(“ligand”) where the ligand is selected from a water electrolysis catalyst, which consists of Ir or

IrO2 and one or more of Ti, Zr, Hf, Nb, Ta and Sn. At the ELECTRICAL AND ELECTRONICS anode, the ratio of the water electrolysis catalyst to the electrocatalyst is ideally from 0.75:1 to 5:1 and at the Platinum Complexes in Optical Data Storage cathode, this ratio is preferably from 0.5:1 to 1:5. The General Electric Co, European Appl. 2,290,408 (2011) electrocatalyst and the water electrolysis catalyst may A data storage medium consists of a polymer matrix, a exist as separate layers in the catalyst layer but are reactant able to undergo a photochemical change upon preferably a mixed layer. triplet excitation and a non-linear sensitiser comprising one or more Pt ethynyl complexes which are capable of Palladium and Iridium Electrode Catalyst absorbing actinic radiation at 405 nm and cause an upper Samsung Electronics Co, Ltd, US Appl. 2011/0,081,599 triplet energy transfer to the reactant. The Pt complexes An electrode catalyst containing Pd, Ir and one metal preferably consists of bis(tributylphosphine)bis(4-ethynyl- selected from Mn, Gd, In, Y, Zr, Sn, Cr and V or an oxide biphenyl)platinum and bis(tributylphosphine)bis(4-ethynyl- of these metals can be used in a fuel cell. At least one 1-(2-phenylethynyl)benzene)platinum or a combination metal is present in the range of 5–30 wt% relative to of both. Pd. This catalyst has a carbonaceous support selected from Ketjen black, carbon black, graphite, CNT and Platinum or Palladium in Motherboard carbon fi bre. Components Elitegroup Computer Systems Co, Ltd, US Appl. APPARATUS AND TECHNIQUE 2011/0,076,859 A motherboard includes a printed circuit board Platinum Coated Glass Melting Apparatus with connectors. Each connector has conductive Furuya Metal Co, Ltd, World Appl. 2011/027,813 terminals which consist of an electroplating layer A rod-shaped electrode which consists of Ir or Ir-based (containing Pt, Pd, Au or Ag) formed on the surface alloy is coated with Pt or Pt-Rh to prevent exposure to of a substrate layer (containing Cu and Ni or Cu-Ni). oxygen-containing gas atmosphere which can cause The thickness of the electroplating layer is between the oxidation of Ir. Electrolytic bubbles are prevented 0.128–1.28 μm. from being formed and higher quality of glass is produced. Joining PGMs to Carbon Nanotubes Ulvac Japan Ltd, Japanese Appl. 2011-014,598 Ruthenium Nanoparticles in Nitric Oxide Sensor A sulfur atom is introduced into a defect of a Cleveland State Univ., US Patent 7,914,664 (2011) growing CNT and metals selected from Pt, Pd, Rh, Ir, A composition of RuO2 NPs either dispersed within Os, Ru, Hg, Si, Ga, Au, Ag and As or their alloys can or on the surface coating of an electrode with an be joined to the CNT via the sulfur atom. This can electrically conductive powder selected from C, Pt, Au be used to form an electrode and provide a wiring or a combination and perfl uorinated oil is used in a NO structure using CNTs. sensor. A second coating of PEDOT and a third coating of RuO2 NPs may be added. The weight ratio of RuO2 NPs to electrically conductive powder is ~1:5 to ~1:7 ELECTROCHEMISTRY and the thickness of the surface coating is ~1 nm–1 μm. Platinum and Iridium Catalyst Layer Growing a Single Crystal Diamond Asahi Kasei Chem. Corp, US Appl. 2011/0,089,027

Shin-Etsu Chem. Co, Ltd, US Appl. 2011/0,081,531 A catalyst layer which consists of crystalline IrO2 A base material for growing a single crystal diamond (2= 34.70º), Pt and Pt-Ir is formed on a conductive consists of a MgO fi lm heteroepitaxially grown on base material and used in the cathode for H2 one side of a single crystal silicon substrate by a generation. The ratio of Pt:(Ir + Pt) is 20–50 at%. The sputtering or electron beam evaporation method. method for making this cathode includes applying An Ir or Rh fi lm is heteroepitaxially grown on the an Ir and a Pt compound onto a conductive base MgO fi lm. The thickness of the single crystal silicon material to form a coating, drying this to form a substrate is 0.03–20 mm and the thicknesses of the film, heating this film to decompose it and then MgO and the Ir or Rh fi lm are 5 Å to 100 μm. electrolysing the decomposed film.

MEDICAL AND DENTAL system. The alloy consists of (in wt%): 0.1–5 Au; 0–50 Pd; 25–50 In; 10–40 Ag; 0.1–0.3 Ir; and optionally 0.1–5 Linkage of Platinum Drug to Nanoparticles Pt. The advantages of this alloy are that it is corrosion Brown Univ., World Appl. 2011/031,478 resistant, fade resistant and biocompatible. A Pt drug is linked to a Au-Fe3O4 NP which acts as a targeting agent. This is prepared by dissolving the PHOTOCONVERSION L1 molecule (see Figure 1) in water, PEG or DMF. The solution formed is then mixed with Au-Fe3O4 Blue Light-Emitting Iridium Complex in OLED NPs in a ratio of ~1000:1 to ~10,000:1 for ≤ 6 h at Gwangju Inst. Sci. Technol., World Appl. 2011/019,179 ~4ºC under protection from light and all free L are 1 An OLED consists of two electrodes and a light-emitting removed. layer stacked between these electrodes. A blue light- Palladium Dental Alloys emitting Ir complex is situated in the light-emitting layer. Ceragem Biosys Co, Ltd, World Appl. 2011/046,274 This Ir complex contains ligands which have a low A dental casting alloy can be machined by a CAD/CAM electron density structure such as triazole or tetrazole.

Fig. 1. Schematic illustration of a World Appl. 2011/031,478 dumbbell-like Au-Fe3O4 nanoparticle L0 coupled with an antibody and Pt drug complex for target-speciﬁ c Pt drug L1 L0 delivery Au L1 L0 Fe3O4

O O H O H L0= N O N O N O n N Herceptin H O H O

O = CH2CH2C–O NH3 L1= –SCH2CH2– N Pt

CH2CH2= C–O NH3 O

FINAL ANALYSIS Is Gold a Catalyst in Cross-Coupling Reactions in the Absence of Palladium?

In the last decade gold has emerged as a kind of Moreover, only the most reactive iodobenzenes were “philosopher’s stone” in catalysis, being able to promote used as the coupling partners. Another group reported a bewildering variety of transformations, including that gold(I) iodide in the presence of mono- or diphos- cross-coupling reactions for the formation of carbon– phines as ligands acted as a catalyst for the Sonoga- carbon bonds. These highly useful transformations shira coupling of iodo- and activated bromobenzenes were developed in part by the 2010 Nobel Prize under similar conditions (130°C in toluene) (7). awardees Richard Heck, Ei-ichi Negishi and Akira A central argument behind the development of gold Suzuki (1) and with contributions from many other catalysts for cross-coupling chemistry was that “Au(I), research groups. Recently, there has been some ques- having the same d10 confi guration as Pd(0) can cata- tion over whether gold can catalyse these reactions lyse reactions typically catalysed by palladium” (2–6). which have been traditionally catalysed by palladium However, this is a rather simplistic argument, since complexes. even elements within the same group often behave In 2007, Corma’s research group published a paper very differently in catalysis. with the suggestive title ‘Catalysis by Gold(I) and The fi rst step in the catalytic cycle of haloarene cou- Gold(III): A Parallelism between Homo- and Hetero- pling reactions is the oxidative addition of aryl halides geneous Catalysts for Copper-Free Sonogashira Cross- (ArX) to the metal catalyst. Thus, for a gold-catalysed Coupling Reactions’ (2). This work stressed the similar reaction of ArX with a catalyst AuX(L) (L = ligand), behaviour of well-known homogeneous gold(I) com- a square planar Au(III) complex AuArX2(L) would be plexes such as AuCl(PPh3) with that of heterogeneous formed. There is no report for such oxidative addition. gold on ceria (Au/CeO2) as catalysts for the Sonogashira In fact, our preliminary results are pointing towards coupling reaction. In addition to AuCl(PPh3), a tri- high activation barriers for these types of transforma- nuclear Au(I) complex was also claimed to be a cata- tions and all our attempts to carry out the oxidative lyst for this reaction (Scheme I) (2–6). These homo- addition of a variety of iodobenzenes to AuCl(PPh3) geneous gold(I) catalysts were also reported to and other Au(I) complexes in a variety of solvents catalyse the Suzuki coupling of iodobenzenes with led to complete recovery of the staring materials (8). arylboronic acids (5, 6). This is in sharp contrast to the behaviour of PdL4 or

Pd2(dba)3  L systems, which react readily with aryl

Traces of Palladium halides to give complexes PdArX(L)2. Furthermore, Nevertheless, from a practical perspective, it is impor- we failed to observe any coupling reaction between tant to note that all these reactions proceeded only iodobenzene and phenylacetylene catalysed by gold under much harsher conditions (130°C in o-xylene) iodide and 1,2-(diphenylphosphino)ethane. Finally, (2–6) than those required with palladium catalysts. we examined a possible Sonogashira coupling

Homogeneous Au(I) catalyst

Scheme I. Can a homogeneous gold(I) complex catalyse the Sonogashira coupling reaction?

Scheme II. A gold(I) acetylide complex does not catalyse Sonogashira coupling

proceeding via a gold(I) acetylide (Scheme II), which (12–14). Thus, in the reaction between iodobenzene also met with failure. and phenylacetylene, long induction periods (145°C, It has been reported that as little as 50 ppb Pd 100 h) were required to detect the Sonogashira cou- present in commercially available sodium carbonate pling product in low yield. is able to catalyse the Suzuki coupling reaction (9). Corma’s group has recently published results that Since high purity gold often contains traces of palla- further confi rm the active role of gold nanoparticles dium, we suspected that palladium was actually in cross-coupling reactions, along with theoretical responsible for the success of the Au(I)-catalysed calculations that support the unlikeliness of a homo- ‘Pd-free Sonogashira reaction’. Indeed, low loadings geneous Au(I)-catalysed Sonogashira coupling reac- of palladium(0) were enough to carry out the couplings tion (15), in line with our own conclusions (8). in Schemes I and II (8). Therefore, we concluded that it was very unlikely that gold(I) complexes alone Conclusions could act as homogeneous catalysts for cross-coupling Taken together, all these results show that fundamen- reactions of aryl halides and closely related organic tal differences exist between heterogeneous and substrates (Csp2–X containing electrophiles) (8). homogeneous catalysts (10). In order to bridge the gap between these two fi elds, a deeper understand- Gold Nanoparticles ing of catalytic systems and their active species is All of the previous discussion here pertains to cou- required. pling reactions catalysed under homogeneous condi- Thus, while gold nanoparticles may play a role in tions. However, we should also consider the possibility catalysing cross-coupling reactions, homogeneous that the reaction proceeds via heterogeneous rather gold(I) complexes are unlikely to act as catalysts for than homogeneous catalysis. We have previously these reactions in the absence of palladium. shown that heterogeneous and homogeneous gold MADELEINE LIVENDAHL1, PABLO ESPINET2 AND catalysts activate small molecules such as alkynes ANTONIO M. ECHAVARREN1* and alkenes by totally different mechanisms (10). 1 Accordingly, it is not entirely surprising to fi nd that Institute of Chemical Research of Catalonia (ICIQ), Av. Països Catalans 16, E-43007 Tarragona, Spain; gold nanoparticles are effi cient catalysts for the Suzuki 2IU CINQUIMA/Química Inorgánica, Facultad de Ciencias, coupling reaction (11). The reaction catalysed by Universidad de Valladolid, E-47071 Valladolid, Spain gold nanoparticles prepared from hydrogen tetra- *Email: [email protected] chloroaurate and 2-aminothiophenol proceeded sat- isfactorily using chlorobenzenes as substrates, which References are less reactive than iodobenzene, under conditions 1 ‘Scientiﬁ c Background on the Nobel Prize in Chemistry (80°C, 4 h) much milder that those required with Au/ 2010: Palladium-Catalyzed Cross Couplings in Organic

CeO2 (150°C, 24 h) in o-xylene (2–6). Synthesis’, The Royal Swedish Academy of Sciences, In addition to contamination by palladium, which Stockholm, Sweden, 6th October, 2010: http:// will depend on the particular source of gold used for nobelprize.org/nobel_prizes/chemistry/laureates/2010/sci. html (Accessed on 18th May 2011) the preparation of the gold complexes, is there any other way by which complexes like AuCl(PPh ) could 2 C. González-Arellano, A. Abad, A. Corma, H. García, 3 M. Iglesias and F. Sánchez, Angew. Chem. Int. Ed., 2007, lead to species catalytically active in cross-coupling 46, (9), 1536 reactions? This issue was addressed last year by 3 C. González-Arellano, A. Corma, M. Iglesias and F. Sánchez, Lambert’s group, which demonstrated that gold Eur. J. Inorg. Chem., 2008, (7), 1107 nanoparticles were formed as the active catalysts by 4 A. Corma, C. González-Arellano, M. Iglesias, S. Pérez- the slow decomposition of the AuCl(PPh3) complex Ferreras and F. Sánchez, Synlett, 2007, (11), 1771

5 C. González-Arellano, A. Corma, M. Iglesias and F. Sánchez, 9, (11), 1624 J. Catal., 2006, 238, (2), 497 11 J. Han, Y. Liu and R. Guo, J. Am. Chem. Soc., 2009, 131, 6 A. Corma, E. Gutiérrez-Puebla, M. Iglesias, A. Monge, (6), 2060 S. Pérez-Ferreras and F. Sánchez, Adv. Synth. Catal., 2006, 12 G. Kyriakou, S. K. Beaumont, S. M. Humphrey, 348, (14), 1899 C. Antonetti and R. M. Lambert, ChemCatChem, 2010, 7 P. Li, L. Wang, M. Wang and F. You, Eur. J. Org. Chem., 2, (11), 1444 2008, (35), 5946 13 V. K. Kanuru, G. Kyriakou, S. K. Beaumont, A. C. 8 T. Lauterbach, M. Livendahl, A. Rosellón, P. Espinet and Papageorgiou, D. J. Watson and R. M. Lambert, J. Am. A. M. Echavarren, Org. Lett., 2010, 12, (13), 3006 Chem. Soc., 2010, 132, (23), 8081 9 R. K. Arvela, N. E. Leadbeater, M. S. Sangi, V. A. Williams, 14 S. K. Beaumont, G. Kyriakou and R. M. Lambert, J. Am. P. Granados and R. D. Singer, J. Org. Chem., 2005, 70, Chem. Soc., 2010, 132, (35), 12246 (1), 161 15 A. Corma, R. Juárez, M. Boronat, F. Sánchez, 10 M. García-Mota, N. Cabello, F. Maseras, A. M. Echavarren, M. Iglesias and H. García, Chem. Commun., 2010, J. Pérez-Ramírez and N. López, ChemPhysChem, 2008, 47, (5), 1446

The Authors

Madeleine Livendahl Pablo Espinet, born Antonio M. Echavarren, was born in Stockholm, in Borja (Zaragoza, born in Bilbao (Basque Sweden, in 1983. She Spain) is Professor of Country, Spain) is obtained her Master of Inorganic Chemistry Professor of Organic Science in Chemistry in the University of Chemistry and Group from Stockholm Valladolid, Spain. He is Leader in the Institute University. In 2009 she Director of the research of Chemical Research joined the research institute CINQUIMA of Catalonia (ICIQ) in group of Professor (Center for Innovation Tarragona, Spain. His Antonio M. Echavarren in Chemistry and research interests centre at the Institute of Advanced Materials). on the development Chemical Research His research covers the of new catalytic of Catalonia (ICIQ) experimental study of methods based on the in Tarragona, Spain, reaction mechanisms organometallic chemistry with a predoctoral of palladium-catalysed of transition metals as ICIQ fellowship. Her reactions and the well as the synthesis of research interests are synthesis of functional natural products and the discovery of new metal-containing polyarenes. transition metal- molecules. catalysed reactions.

Jonathan Butler Publications Manager Sara Coles Assistant Editor Ming Chung Editorial Assistant Keith White Principal Information Scientist

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