Platinum Metals Review

PLATINUM METALS REVIEW

A quarterly survey of research on the platinum metals and oj developments in their application in industry

VOL. 40 JANUARY 1996 NO. 1

Contents

Rustenburg and Johnson Matthey, an Enduring Relationship 2

Platinum Metals Complex Catalysts for Liquid-Phase Hydrogenations 8

Activity of Platinum-Containing Electrodes Enhanced 18

Second European Congress on Catalysis 19

Platinum Group Metal Fullerenes 23

Platinum Nanochannel Replica Membranes 25

Increased Catalytic Activity 25

The Development of Molecular Wires 26

Small-Particle Platinum Catalysts 35

Hydrogen Treatment of Materials 36

Alkane Oxidation by Encapsulated Ruthenium Complexes 37

Palladium Alloy Mechanical Properties 37

Abstracts 38

New Patents 46

Communications should he addressed to The Editor, Susan V. Ashton, Platinum Metals Revim Johnson Matthey Public Limited Company, Hatton Garden, London ECl N 8EE Rustenburg and Johnson Matthey, An Enduring Relationship SIXTY-FIVE YEARS OF CONTINUOUS COMMITTED DEVELOPMENT By J. Todd Bruce Marketing and Planning Director, Anglo American Platinum Corporation Limited, Johannesburg, South Africa

The background and history of the connection between the world’s largest platinum producing group, the South African company Anglo American Platinum Corporation, and the United Kingdom company Johnson Matthey, is explained. The commitment of Amplats to meet the expected growth in demand for the six platinum group metals in the future and the role of Johnson Matthey in marketing these metals, and in contributing towards the development of advanced technological applications for them, will ensure that the needs of the industrial platinum users throughout the world will continue to be satisfied.

Prior to 1st January, 1995, Johannesburg als and base metals produced from the mining Consolidated Investment Company Limited, operations at Rustenburg. “JCI”, one of the leading mining finance houses The fledgling South African platinum indus- in South Africa, controlled and managed three try suffered a severe blow in 1932 with the platinum group metals producing companies: depression-induced collapse of the platinum Rustenburg Platinum Holdings Limited, price on international markets. As a result, min- Lebowa Platinum Mines Limited and ing operations at Rustenburg were suspended Potgietersrust Platinums Limited. On 1st until the end of 1933 when they were recom- January, 1995, the Anglo American Corporation menced on the advice of Johnson Matthey. of South Africa, the controlling shareholder of In 1938 Rustenburg’s first major expansion JCI, restructured JCI forming three separate programme, to 20,000 tons per month, was companies: a platinum mining operation, the completed and the iirst smelter furnace and con- Anglo American Platinum Corporation Limited, verter unit were commissioned. At this point “Amplats”; a gold, coal and base metals min- the material delivered to Johnson Matthey ing operation, “JCI Ltd”, and an industrial and changed from platinum group metal concen- property investment holding company, trates to the less bulky converter matte. “Johnnic”. Amplats is controlled by the Anglo During the Second World War years, 1939 American Corporation of South Africa. to 1945, mine production remained steady at Johnson Matthey’s links to the South African around 25,000 tons per month, but as a result platinum mining industry stretch back to the of improvements in Johnson Matthey’s pro- discovery of platinum-bearing deposits in the cessing and refining technology, production of Bushveld Igneous Complex in 1924. The sub- refined platinum increased to some 40,000 sequent founding of Rustenburg Platinum Mines ounces per annum. in 1931 to exploit the Merensky Reef marked After the war an upsurge in platinum demand, the start of an enduring relationship between initially from the chemical industry and later Rustenburg, the largest platinum producer in from other industrial sectors, resulted, over the the world, and Johnson Matthey as agent, cus- next 30 years, in an ongoing series of expan- tomer and refiner of the platinum group met- sions in production at Rustenburg. Platinum

Platinum Metals Rev., 1996, 40, (l), 2-7 2 Theo.1 shaft at Amandelbult Section output at Rustenburg doubled between 1947 reached with Johnson Matthey to form a jointly and 1949, in part by the acquisition in 1949 held company, Matte Smelters (Pty) Ltd, to of the operations of the Union Platinum Mining erect and operate a plant in South Africa to pro- Co. Ltd. A decision to double the output again duce saleable nickel and copper and a high grade was taken in 195 1 (at which time Rustenburg platinum group metals refinery feed Erom a por- was producing ore at a rate of about 70,000 tons tion of the matte produced by Rustenburg. The per month). At the same time agreement was balance of the Rustenburg matte continued to

Potgietersrust Platinum8 - the only open cast platinum mining project in South Africa

Platinum Merals Rev., 1996,40, (1) 3 be exported to Johnson Matthey in the United metals refinery, Matte Smelters and Johnson Kingdom for processing. The Matte Smelters Matthey’s smelting and refining operations at plant was commissioned during 1954/1955. Brimsdown and Royston in the U.K. The platinum requirements of the oil indus- The platinum market slumped severely in 197 1 try in the mid-1950s led to two hther expan- causing Rustenburg to cut production by almost sion programmes at Rustenburg, in 1955/56 50 per cent to some 550,000 ounces per annum. and 1956157. At this time it was also decided Fortunately, the successful development of auto- by the Board of Johnson Matthey, with the catalyst technology by Johnson Matthey and encouragement of the Directors of Rustenburg, Engelhard during the early 1970s represented to compile technical and scientific informa- the beginning of a major new application for tion on all the forms of platinum and the other platinum in 1975. In 1972, to meet this chal- platinum group metals. As part of this initiative lenge, Rustenburg decided to expand produc- the quarterly journal, Platinum Metals Review, tion beyond the previous 1 million ounces per was founded, and the first issue duly appeared annum level, by developing its Amandelbult in January 1957. Section, some 120 km north of the Rustenburg In 1958 the market experienced a sudden mining operations. Rustenburg’s production downturn attributable to a sharp reduction in capacity was further increased in 1977, when offtake by the oil industry. Production at Union the company acquired the mining operations of Section was temporarily suspended, and the Atok Platinum Mines (Pty) Ltd, situated on the output at Rustenburg was halved. However, eastern limb of the Bushveld Complex. increased industrial demand for platinum Due to the expansion in Rustenburg’s plat- emerged again during the early 1960s and inum output during the 197Os, Rustenburg and Rustenburg responded by undertaking another Johnson Matthey decided to replace the 23-year series of production expansions from about old Matte Smelters plant with a new MRR 1963 onwards, with platinum output eventu- base metals refinery which would process ally reaching 1 million ounces by 1970. These Rustenburg’s entire matte output into saleable expansions included the exploitation, under nickel, copper, cobalt and a high grade platinum tribute, which is a form of royalty agreement, group metals refinery feed. The new base met- of the mineral rights held by Brakspruit als refinery became operational in 1981/82. Platinum (Pty) Ltd, adjacent to the Rustenburg property. The assets and mineral rights of Extraction Technology Brakspruit Platinum were eventually acquired In 1980 Johnson Matthey concluded the suc- by Rustenburg in 1972. cessful testing of a pilot platinum group met- In 1969 a platinum group metals refinery, als extraction plant based on Johnson Matthey’s financed 80 per cent by Johnson Matthey and proprietary new solvent extraction, “Solvex”, 20 per cent by Rustenburg, was commissioned technology. The success of the pilot plant at Wadeville in South Africa to treat a portion prompted Johnson Matthey and Rustenburg to of Rustenburg’s platinum group metal output build a pre-production scale Solvex plant at from the Matte Smelters plant. The balance Royston. Construction began in 1981 and the of the Rustenburg material continued to be plant was commissioned in 1983. refined by Johnson Matthey at Royston in the In 1984 it was agreed by Johnson Matthey and U.K. In 1972 Rustenburg and Johnson Matthey Rustenburg that Rustenburg should take over formed a jointly held company, Matthey sole responsibility for the crucial stages of pro- Rustenburg Refiners (Pty) Ltd, “MRR, to cessing and refining. Accordingly, Rustenburg acquire and operate the platinum group metals purchased the Wadeville platinum group met- processing facilities owned and operated by als refinery and the new base metals refinery Johnson Matthey and Rustenburg. Accordingly, from MRR. Rustenburg contracted MRR to MRR acquired the Wadeville platinum group manage the Wadeville refinery and MRR

Platinum Metals Rev., 1996, 40, (1) 4 Tapping matte from the furnace at the Waterval smelter complex, Rustenburg Section

continued to own and operate the platinum Rustenburg with the necessary increased capac- group metals refinery in Royston. Rustenburg ity to refine the additional platinum group met- decided in 1986 to erect a new platinum metals sourced from two additional expansion pro- als refinery in South Africa at Rustenburg jects begun in the late 1980s. These were the Section using Johnson Matthey’s Solvex tech- Amandelbult expansion project and the devel- nology. In 1987 Rustenburg acquired a con- opment of Potgietersrust Platinums Limited, trolling share in MRR and contracted MRR the only open-cast platinum mining venture in to manage the new refinery upon completion. South Mica. The new platinum group metals In 1988 Johnson Matthey purchased the refinery was commissioned in May 1989 and Royston platinum group metals refinery from the refining of Rustenburg’s platinum group MRR. The new platinum group metals refin- metals at Wadeville and Royston ceased during ery, apart from employing the state-of-the-art the latter half of that year. Solvex refining technology, also provided Over the 65 years that Rustenburg and Johnson

Installing rock supports at Rustenburg Section

Platinum Metals Rev., 1996,40, (1 ) 5 Matthey have been associated, the business rela- closely in platinum jewellery market develop- tionship between the two companies has been ment, with Johnson Matthey concentrating on governed by numerous Marketing and Refining the manufacturing and technical side of the jew- Agreements. An important milestone in the rela- ellery industry and Amplats - through its involve- tionship was reached in 1992, when the 1972 ment with the PGI - providing support for the Marketing Agreement was renegotiated and sup promotion of platinum jewellery to manufac- plemented by a new Principal Sales Agreement. turers, retailers and consumers. This joint The term of these two agreements ensures the approach has had considerable success, par- continuation of the Rustenburg/Johnson ticularly in the United States, where platinum Matthey relationship (including the two other jewellery demand has more than trebled since producers in the Amplats stable) well into the 199 1. The huge potential of the Chinese market future. has not gone unrecognised by Johnson Matthey In addition to the purchase of services pro- and Amplats. Several market research studies vided by Johnson Matthey under the Marketing have been commissioned and Johnson Matthey Agreement (Market Research for example) has taken the first steps to establish a viable pres- Rustenburg also jointly funds certain research ence for the sale of platinum jewellery in China. and development programmes for technical applications with Johnson Matthey. These activ- Platinum Supplies Will Meet ities are performed at the various Johnson Expected Demand Matthey Technology Centres. Given the likelihood that the platinum market will continue to expand in the future - largely Development of New Applications in response to Amplats’ market development The development of new technical applica- initiatives via the PGI and those undertaken tions for platinum and the expansion of the exist- in collaboration with Johnson Matthey - Amplats ing platinum jewellery markets are vital for the has already taken steps, in the form of the expan- long-term prosperity of the platinum produc- sions undertaken in 1989, to ensure that plating and fabrication industries. Rustenburg has inum supplies from the group’s mining and pro- recognised the importance of funding market cessing operations will be able to meet the support and development programmes since expected growth in demand. Furthermore, a the early 1970s. smelter refurbishment and expansion pro- In 1975 Rustenburg supported the founding of gramme, started in 1990, has recently been com- the Platinum Guild International, “PGI”, specif- pleted at Rustenburg and various new mine ically to promote platinum jewellery in Japan. expansion options are currently being assessed. The tremendous success of this operation is These include low-cost expansions at the shown by an estimated demand for platinum jew- Potgietersrust open-cast operation (currently ellery in Japan of 1.49 million ounces in 1995, the lowest cost producer in the industry), expan- the twelfth year of continuous growth in the sion of UG2 production at the Amandelbult Japanese platinum jewellery market. PGI subse- Section and possible new mines at Boschkoppie quently established offices to develop markets for and Kruidfontein, located between Rustenburg platinum jewellery in Germany (1976), Italy and Union Sections. In addition, a programme (1986) and theunited States ofAmerica (1992). is already in place to increase output gradually In 1986 PGI opened an office in the U.S.A. to at Lebowa Platinum Mines. promote platinum investment products. The proposed expansion of productive capac- In the 21 years since PGI was founded the ity at all the Amplats’ group mining operations Amplats group of producers have invested will be done in such a manner as to enable a cumulative R 562.5 million in platinum Amplats not only to take full advantage of jewellery and investment market development. favourable market conditions but also, if mar- Amplats and Johnson Matthey co-operate ket conditions prove temporarily adverse, to

Platinum Metals Rev., 1996, 40, ( 1) 6 Making palladium grain at the precious metals refinery

enhance the group’s competitiveness by reduc- make-up, structure and fortunes of the platinum ing production from relatively high-cost areas. market over the past 65 years. As the 2 1st The mutually beneficial relationship between Century approaches there is every reason to Rustenburg and Johnson Matthey has success- believe that this fitfi.~Iassociation will continue fully weathered the numerous changes in the to flourish.

Feeddiseohrereaetors in Bay 2 at the precious metals refinery

Platinum Me& Rm., 1996,40, (1) 7 Platinum Metals Complex Catalysts for Liquid-Phase Hydrogenations NOVEL CATALYSTS UTILISING ALIPHATIC AMINES AND RELATED SYSTEMS By Professor Y M. Frolov A. V. Topchiev Institute of Petrochemical Synthesis, Russian Academy of Sciences, Moscow

Results of the syntheses and applications of platinum metals complex catalysts, which are uniquely active for the liquid-phase hydrogenation of unsaturated organic compounds, such as olefins, dienes, acetylenes and aromatics, are described. The platinum metals complex catalysts are synthesised by the interaction between platinum metals compounds and aliphatic amines with sufficiently long alkyl groups (C, and higher). Similarities are shown in the production of palladium-, platinum-, and rhodium-based catalysts, which involves the formation of hydride ligands, using the hydrogen atoms of the alkyl groups, and the specific catalytic behavwur of each metal is described. Examples of synergistic effectsfor these platinumgroup metal catalysts and some of their related systems are discussed.

In spite of the considerable amount of work pound, since the usual methods of catalyst regen- that has been undertaken on the hydrogenation eration cannot be applied to such systems. of unsaturated organic compounds, it is still the In recent years a new approach to catalytic hydro- subject of intensive investigations, with the plat- genation, based on using complexes of platinum inum group metals continuing to be the most metal compounds with aliphatic amines containing common components in hydrogenation cata- eight or more carbon atoms in alkyl radicals, has lysts, as well as in catalysts of other processes. been developed at our Institute. As numerous As an example of this, at the first European metal complex catalysts good for hydrogenation Congress on Catalysis, “EUROPACATI”, held contain phosphines or phosphites, bonded to the in September 1993, nine out of the fifteen sym- metal with a considerable contribution of the back posia featured catalysis using the platinum met- donation using the d-orbitals of phosphorus, the als to some extent, and thirteen of the fifteen initial purpose of this work was to determine to papers at the symposium on metallic and what extent replacing traditional phosphorus con- bimetallic systems described the activities of taining ligands by nitrogen containing ligands, for platinum group metals (1). Metal complexes which this type of bonding is impossible, would proved to be very successful in the construction affect the catalytic properties. From a practical of promising new systems that are capable of standpoint, the selected amines looked more suit- operating under much milder conditions than able, since they are less toxic than the usual phos- traditional heterogeneous catalysts. phorus containing ligands. Strictly speaking, the only platinum metal complex systems which are of interest are those Interactions between Components whose high specific activity, stability and length of the Catalyst System of operation, as well as high selectivity, com- The general outline of the synthesis is given pensate for the additional cost needed to recover in Figure 1. The interaction in toluene between the noble metal and synthesise the initial com- the initial platinum metals compounds, which

Placinum Metals Rev., 1996, 40, (l), 8-18 8 Fig. 1 A general outline of the PdC12 H2PtC16 PdC12 (n- CjHsPdC1)2 svnthesis of the catalvsts. R = ~~(OCOCHJ)~Rh2(OCOCH3)4 Pd(OC0CHj)z I RuCII pic14 ikyl C,-C,,; i-Bu = Lo-bntyl. ptc12 Pt(OC0CHj)kPt(C€OCHj)& The temperature of interactioninteraction RhClj'4H20 between thethe startingstarting compounds compounds and aliphatic amines is 20 toto and aliphatic aminea is 20 RNHlRNHl R3N R3N RNHz 90°C; thethe solventsolvent isis toluenetoluene v SOLUTION OF A COMPLEX

AI(I-Bu)j. HAlti- BU)a

I AI~O~,A1203, Si02, zeolites. eiceic. SUPPORTED CATALYSTS

are insoluble in aromatic media, and the aliphatic with an increase of the turnover frequency) (14, amines under an argon atmosphere for tens of 18-20). Here, we have used conventional val- hours resulted in a gradual transfer of metal ues of turnover frequency, calculated as the num- species into solution, due to the high affinity ber of moles of the substrate that reacted per of long alkyl groups for the solvent. In certain one g-atom of the metal per hour. cases (on the left side of the scheme which is Mared and NMR spectral studies of the inter- shown above as Figure 1) the solution which action of the initial palladium, platinum and was produced did not show catalytic properties, rhodium compounds with aliphatic amines in but hydrogenation activity appeared after treat- an aromatic solvent showed the formation of ing the complexes which are formed with a rather hydride ligands on the metal during the first strong reducing agent (usually an organoalu- stage of the reaction. It is of interest that the minium compound). Because of the high affin- source of the hydrides on the metal is both from ity of the reduction products for the solvent, the hydrogen atoms in the amino groups of the these catalytically active species also remain sol- primary or secondary amines and from the uble. In this way efficient palladium- (2-5), plat- hydrogen of the alkyl groups of tertiary amines. inum- (6, 7), rhodium- (8), and ruthenium- For the reaction between palladium chloride based (8, 9) catalysts have been obtained. and a tertiary amine, the spectral data indicate In the most interesting cases (on the right in the formation of a bridged hydride (v,,,~,, = Figure l), it is the interactions of the initial plat- 1590 to 1600km) and co-ordination bonding inum metals compounds with aliphatic amines between palladium and nitrogen (v,,, = that lead to the formation of highly active homo- 490km) (9). At the same time double bonds geneous catalysts (the systems: palladium salts arise in one of the alkyl groups as a result of a (10-12), rhodium trichloride (8, 9, 12, 13) or hydrogen transfer to the metal (vc=c= 161 Okm, platinum compounds (1 2,1416) with tertiary 'H NMR signal for -CH=CH- at 5.3 x 10 6, amines, and sr-ally1 palladium chloride with &scale (9)). primary amines (17)). The simultaneous formation of hydride lig- An important property of all these systems is ands on the metal and a double bond in an alkyl that they can be readily heterogenised, by the group of the amine has also been observed in direct contact of a solution of the homogeneous the platinum tetrachloride-tri-n-octylamine catalyst with the outgassed surface of a mineral system (Figure 2). It can be seen from this Figure support, without activity decrease (in most cases that the participation of a second amine

Platinum Metals Rev., 1996, 40, (1) 9 water of crystallisation, with tri-octylamine has hydride ligands on rhodium and a C=C double bond in one of the alkyl groups of the tertiary amine, according to IR spectroscopic data, see PtCIL + 2NR3 -T~CI + [NHR3]+Ci Figure 3. According to NMR data, the double CI NR2 bond is located at the second carbon atom of C5H11-C H-CHCHZ the alkyl group (13). Similar data were obtained for ruthenium sys- Fig. 2 Interaction between platinum tetrachloride and tri-n-octylamine, based on IR tems. Thus, based on these results it can be con- evidence cluded that the formation of hydride ligands on the metal during the interaction between the Type of bond cd I initial compound and the aliphatic amine, using vibration the hydrogen of an alkyl group of the amine, is v~-~,(terminal) 340 a general feature typical for all the platinum met- v,,,-~(terminal) 470-560 v~-~(terminal) 2000 als studied. However, we do not think that the vc=c 1550-1600 hydride, formed at an early stage of the inter- 6,.c=c 1420,750,895,950 action between the components, can react with Group of bands a multiple bond of the substrate to start a cat- of substituted ammonium salt 2-2700 alytic cycle. Instead, it initiates a chain of reactions that finally results in the formation of metal complex species (also perhaps of hydride character) which are capable of activating mol- molecule helps to link a proton being abstracted ecular hydrogen. from the first amine molecule (simultaneously Further interactions between the components with the hydride) to form a salt of the substi- of the catalyst system are accompanied by more tuted ammonium. profound changes, the details of which are so A primary product of the interaction of far still not clear. However, there is some rhodium trichloride, having four molecules of indirect evidence in favour of the formation

R HH\/ \/R 0 H N-CH~-CH=CH-CSH~~

C'\jh /Cl\dh/ // I 'CI/ I'CI CSHii-CH=CH- CH2-N H 0 /\ /\ HH RR

Fig. 3 A hypothetical primary produet of the interaction between RhC1,.4H20 and hi-n-octylamine, aceording to lR spectra. R = C,H,, Type of bond vibration I cm-' I I vm." (terminal) 1860,1970,1990 1635,1595 970,750 250-280 320 570 470 34Qo

Platinum Metals Rev., 1996,40, (1) 10 Fig. 4 Dependence of the hydrogenation rate ratio (W/W,) on 1 o the amount of carbon monoxide admitted to the reactor. The metal is palladium or platinum: 1 PdCI2-(C9H,JaN, isoprene, 2 08 20°C 2 PdC12-(C9H19)3N/~-AI,0al 2- isoprene, 20°C 2 0.6 3 Pt(OCOCH,),-(C,H,,),N, E 1-hexene, 20°C 3

a W g 02 L,\ \\\ > I \ \\_\\ \ \

I I I 5 10 15 CARBON MONOXIDE: METAL, mole per cent of polynuclear or cluster structures. active in liquid-phase hydrogenation (2 1,22). During the final stages of the interaction of A feature very characteristic of the platinum platinum tetraacetate with mi-n-nonylamine, we group metal catalysts prepared by our method could not detect the presence of co-ordinated is their exceptionally high catalytic activity, which amine molecules or acetate groups. However, sometimes attains tens of thousands of catalytic absorption bands were observed which are char- acts per one metal atom per hour. acteristic of both terminal and bridged hydride groups, and may suggest that plane polynuclear Palladium-Based Catalysts structures are formed. The most active catalysts are palladium-based Data on the inhibition of the hydrogenation and their field of application is for the selec- reaction by carbon monoxide, see Figure 4, show tive hydrogenation of conjugated dienes and that complete blocking of the active sites takes acetylenes into olefins. Analysis of kinetic data place at relatively low ratios of carbon monox- on the hydrogenations (23) -zero order in sub- ide:palladium and carbon monoxide:platinum strates and selectivities attaining 100 per cent (less than 20 per cent). These values were at conversions close to 100 per cent - allows a obtained by extrapolating the linear plots to the conclusion to be made about complete cover- zero hydrogenation rate. The results agree with age of the active sites by the co-ordinated sub- the concept that the formation of active sites strates under equilibrium conditions of co-ordi- occurs within the polynuclear or cluster struc- nation (chemisorption).A quantitative criterion tures. of the reaction selectivity is the factor R = However, we have never observed any broad- k,K,/k&, where k,and k, are the rate constants ening in the NMR signals due to the formation for the hydrogenation of a substrate and an olefin of metallic particles suspended in the aromatic product (both in the co-ordination state); and solvent (even for rhodium species), although there K, and K, are the corresponding equilibrium are indications in the literature that the interac- constants of co-ordination on the active sites (or tion between RhCl, and N(C,H,,),B(C,I-&),H in adsorption coefficients in the case of supported tetrahydrofuran leads to the formation of col- catalysts). It follows from the analysis that a loidal particles of metallic rhodium protected by selectivity of 98 per cent can be attained at a tetraalkylammonium groups, which are very conversion of 98 per cent if R is as high as 150

Platinum Metals Rev., 1996, 40, (1) 11 Table I Activities of Catalysts at 2OUC,Based on the System PdCI,-(C,H,,),N/Carrier (0.05% Pd by weight)

Substrate Solvent Carrier Turnover frequency, h ' x atm ' 1I I Isoprene Hexane 121,000 Isoprene Hexane 137,000 Isoprene DMFA 49,000 Isoprene 94,000 Cyclopentadiene Toluene 38,000 Cyclopentadiene Hexane 57,000 Cyclopentadiene 45,000 3-Heptyne To1 uene 32,000 3-Heptyne Hexane 49,500 R-CH(0H)-CFCH Toluene 13,100 R-CH(OH)-CECH Heptane NaX zeolite 8,800 NaX zeolite

All onetic runs with platinum metal systems were carr eo OL~at constant nvdrogcn pres,t.re in il sn ny ny reactor "naer conailions where an increase in the swinging frequencv 010no1 affect tne rate 01 nydroyen coris.mipt6on DMFA (1 methylformamide. R 2-letranydr~f~ry

(23). Dilution of a diene with olefins reduces upon fine powders of mineral carriers consid- the selectivity but, nevertheless, selectivity was erably increases their stability and makes it pos- still found to be high (94 per cent) even when sible to hydrogenate functional derivatives of butadiene was hydrogenated as a 4 per cent conjugated dienes and acetylenes; for example, impurity in a mixture of butenes up to conver- acetylenic alcohols into olefinic ones (25). In sions close to 100 per cent (24). contrast to traditional Lindlar's catalysts (metal- Homogeneous catalysts are sensitive to lic palladium on calcium carbonate partially poi- hydroxyl-containing substances and can be used soned by quinoline or lead salts), our catalysts only for the hydrogenation of unsaturated hydro- proved to be more active by almost two orders carbons. Supporting palladium-based systems of magnitude.

Table II Effect of Poisons on the Catalyst System PdC1,-(C,H,,),N as a Homogeneous System or Supported on y-Alumina during the Hydrogenation of 3-Heptyne into 3-Heptene at 20°C

- Turnover frequency, h ' x atm ' Inhibitor Inhi bitor/Pd, Homogeneous Supported mole/mole

None 0 25,800 32,500 Water 20 1,200 32,000 Triphenylphosphine 40 23,900 32,500 Thiophene 50 20,400 30.800 Dihexylsulphide 1 18,000 30,100 Dihexylsulphide 50 0 3,500 Hexylrnercaptan 1 0 3,200

Platinum Metals Rew., 1996, 40, (1) 12 8 Fig. 5 The effect of heating for 0,000 2 hours on the activity of sup- - 1 ported catalysts in hydrogena- 'E a tion reactions: - 1 PdCI,-(C,H,,),N/~-AI20,, 64000 isoprene *u- 2 PdCI,-(%H,,),N/NaX zeolite, :: diphenylacetylene t 3 Pt(OCOCH,),-(C,H,,),N/y- t 40,000 AI,O,, 1-hexene Y 8 n n 20,000 w 6 rr +3

50 100 150 200 250 300 TEMPERATURE OF HEATING, 'C

Hydrogenation of disubstituted acetylenes is mediates during the production of vitamins, and stereoselective: diphenylacetylene and 4-octyne in the hydrogenation of vegetable oils. yield cis-stilbene (95 per cent) and cis-4-octene For sunflower seed oil, it is necessary to hydro- (99 per cent), respectively. genate one double bond of the linoleic acid frag- Activities of supported catalysts in various sol- ments in the corresponding glycerides. Double vents are given in Table I. It can be seen that bonds in linoleic acid are not conjugated. the best results have been obtained either in sat- Nevertheless, it was shown that rapid isomeri- urated hydrocarbons or without using solvent. sation occurred at first on our palladium cata- Table I1 summarises data on poisoning homo- lysts, resulting in the formation of a system of geneous and supported catalysts (26).It can be conjugated double bonds, and this was followed seen that water and triphenylphosphine do not by selective hydrogenation to produce a frag- affect the activity of supported catalysts; thio- ment of oleic acid and some of its isomers. phene slightly suppresses their activity at a molar Compared to modern industrial nickel catalysts ratio poison:metal = 50. Other poisons have a it is possible to use 0.1 per cent of the amount much more pronounced effect, and the sup- of metal and to decrease the reaction temper- ported systems are more resistant to poison- ature by almost 100°C (27). ing than the homogeneous ones. The supported catalysts retain their activity Platinum- and Rhodium-Containing after heating at up to 150 to 200"C, as is shown Catalysts in Figure 5 (curves 1 and 2). Due to the Platinum-containing catalysts are to some chemisorptive nature of the support, an upper extent even more interesting than the palladium- limit in the percentage of metal on the carrier based ones. The reason is that unlike the large is observed. Usually this value does not exceed number of palladium systems described in the 0.2 per cent by weight. literature, only a relatively small number of plat- For practical purposes palladium-containing inum systems have been reported, and most catalysts are of interest for use in such liquid- of them have serious disadvantages. They are phase processes as the hydropurification of unstable towards molecular oxygen and mois- olehs to remove traces of dienes and acetylenes, ture, they have low activity, they can hardly be for the hydrogenation of acetylenic fragments heterogenised and they catalyse migration of into olefinic fragments in a number of inter- C=C double bonds during hydrogenation.

Platinum Metals Rev., 1996, 40, (1) 13 Table 111 Hydrogenation of 1-Hexene at 20°C in the Presence of Platinum-Based Catalysts: Homogeneous or Supported on y-Alumina (0.06 % Pt by weight)

System Turnover Frequency, h-' x atm-' Homogeneous Supported

H,PtCI,-( C~H&N-HAI(/-BLI)~ 17,000 20,500 PtCI,-( CaHI,),N- H2 12,000 12,000 PtCI2 -(CaH,,),N H - HAl(i-Bu), 2,900 6,500 PtCI, - CaH I,NH,- HAl(i-Bu), 2 1,400 32,600 Pt(OCOCHJ,-(CgH1g),N-H, 10,600 11,600 Pt(OCOCHJ,-( C,H,,),N H 3,000 4,600

In our studies, however, the use of the inter- Table III shows the effect that a y-alumina sup- action of platinum compounds, particularly the port has on catalyst activity. Most supported acetates of bi- and tetravalent platinum, with systems are more active, in terms of turnover aliphatic amines allowed catalysts to be prepared kequency, than homogeneous systems. For some which were stable to dioxygen and water, and catalysts a preliminary treatment with molec- which were capable of carrying out the com- ular hydrogen was necessary to attain high activ- plete hydrogenation of unsaturated substrates, ity, otherwise kinetic curves had induction such as olefins, dienes and acetylenes. For exam- periods with a subsequent slow increase in the ple, the platinum tetraacetate-trinonylamine hydrogenation rate. system did not show any decrease in hydro- An important property of the platinum-based genation activity for 1-hexene when the molar catalysts is their relatively high activity, not only ratio waterplatinum was increased to 200. This in hydrogenating a-olefins but also in hydro- last catalyst could be synthesised and stored genating olefins with internal double bonds. We in air. now have some evidence that this property can As was the case with the palladium-based cat- be used for the hydrogenation of unsaturated alysts, supporting the platinum-containing polymers and attains quite good rates. It is note- species on the surface of mineral carriers (y-alu- worthy that the hydrogenation of a-olefins is mina, silica, zeolites) increases their stability. In zero order with respect to the substrate, whereas Figure 5 (curve 3), the activity of the supported the first order law is typical for olefins with inter- platinum-based catalyst drops only after heat- nal double bonds (14). The latter case may ing up to 200°C. reflect a much lower coverage of the active sites.

Table IV Hydrogenation of Olefins in the Presence of Rhodium-Based Catalysts

Catalyst system Substrate Turnover frequency, I I h-' x atm-' R hC1,.4H,O -( CaHl,),N I-Hexene 26,000 RhCl,.4H,O-(C,Hl,),N/r-Al,O, I-Hexene 52,400 R hC1,.4H20 -(C,H,,),N/SiO, I-Hexene 50,200 R hCI,.4H,O-(CaH,,),N/Nd,O, 1-Hexene 60,300 R hCl~.4H~O-(C~H~~)~N/IcAI,o, Cycl o hexane 20,100 R hC13.4H2O-(C,H,,)3N/yAI203 Cyclopentene 37,000

Platinum Metah Rev., 1996, 40, (1) 14 ~~ ~ ~ 90 Fig. 6 Effect of the composition of a mixed system RuCI,-PdCI,- 8o - (C,H,,),N reduced with HAI(I- Bu), on the activity during the - 70. hydrogenation of toluene into ‘5 methylcyclohexane, temperature -m 60 - I 20°C r 50 - 1 Homogeneous catalyst >- 2 Catalyst supported on y-Al,O, ” 40- 2 30i LL :201 0 f 10- 3I-

I 10 20 30 40 50 60 70 80 90 1 1OOx Pdl(Rh+Pd), per cent

Very active rhodium-based catalysts (Table both homogeneous and supported catalysts. IV) could also be synthesised by this method. A comparison between the activity of our cat- The activities of the systems studied during the alyst with data from the literature for a ruthe- hydrogenation of 1-hexene and cyclohexene are nium hydride complex with a triphenylphos- several times higher than those of “classical” phine ligand, [RuHC1(q-CJ4e6)(PPh,)], which catalysts - based on tris(tertiary phosphine)- is active for the hydrogenation of benzene into chlororhodium (28-30). The catalysts are not cyclohexane (32), showed that its turnover fie- of interest for the actual hydrogenation of lin- quency, according to our estimate, was 50hour ear olefins, since that reaction is accompanied at 50°C and 50 atm. However, in our case, a by migration of the double bond in the sub- turnover frequency of 80hour was attained at strate, but for their surprising ability of being 20°C and 1 am, which demonstrates the advan- considerably activated upon treatment with tages of our approach. A ten-fold increase in the dioxygen and water (13). hydrogen pressure up to 10 atm resulted in a proportional enhancement of the activity. Ruthenium-Containing Catalysts The synthesis of ruthenium-based systems has Synergistic Effects Caused by the made it possible to obtain highly active catalysts Presence of a Non-Noble Metal for the hydrogenation of aromatic rings. After As the promotion effects of non-noble met- reduction with di-iso-butylaluminium hydride, als to catalysts are of most interest we have the ruthenium systems revealed unique catalytic undertaken a search for a suitable bimetallic sys- properties for the hydrogenation of toluene into tem which might be able to demonstrate the methylcyclohexane (31). It was established that necessary type of synergistic effect. Unfor- additions of small amounts of palladium exerted tunately, palladium-nickel systems with tertiary a pronounced promoting effect, see Figure 6, amines proved to be useless because they did whereas the palladium complex itself was totally not display the superadditivity effect; the spe- inactive. cific activity of this system was directly pro- The superadditivity of catalytic properties (a portional to the mole fraction of the palladium “synergistic effect”) for the mixed system was complex. characterised by a rather sharp maximum which The solution to this problem was found by corresponded to an additive of 17 mole per cent using homogeneous binary palladium-nickel palladium. Surprisingly, this was the case for complex systems, prepared by the interaction

Platinum Metals Rev., 1996, 40, (1) 15 of monomeric and linear oligomeric forms of DMA). Similarly, no bands characteristic of a x-alkenyl complex of palladium were visible in the spectrum. As a hypothesis it could be suggested that a complex of palladium with a dimer of DMA, containing a four-member ring, was formed. Upon oxidation of the sample in air for 15 to 30 seconds, the intensity of the bands at 820, 1068, and 1136/cm sharply decreased; ,.. to ;o 30 40 50 60 7b 80 90 100 these were not bands for aluminium acetylace- loox NtI(Pd+Nd. per cent tonate. We suggest that these bands referred Fig. 7 Synergistic effect in the system to a hypothetical palladium n-complex with a Ni(acac),-Pd(acac),-DMA reduced with tri-iso-butylaluminium for hydrogenation of cyclic dimer of DMA. The bands above are not isoprene into isopentenes, 20°C; acac = acetyl- unlike those observed experimentally for a acetonate similar lithium complex. The IR spectrum of the four-component system Ni( acac) ,-Pd (acac) ,-DMA-A1 (i-Bu) did of a mixture of the acetylacetonates of these met- not contain any bands characteristic of acetyl- als with allene or 1,l-dimethylallene (DMA) acetonate ligands and free acetylacetone. Almost and the subsequent treatment of the product, all the bands that are characteristic of Al(i-Bu), which has oligoallene ligands, with tri-iso-butyl- were present, but they were greatly changed. aluminium (33). The presence of the oligoal- A number of bands at 350 and 470/cm rapidly lene ligands caused the "floatation effect", sim- disappeared in air, indicating the presence of ilar to that of higher amines, which provides the both palladium-carbon and nickel-carbon bonds. solubility in hydrocarbon media. These systems The above-mentioned bands of the palladium were also very active in the selective hydro- complex at 820, 1068 and 1 136/cm, hypothet- genation of conjugated dienes into olefins. ically referring to a palladium n-complex with The dependence of the catalytic activity of the a dimer of DMA, were present in the spectrum binary system on its composition during the of the mixed complex at 815, 1065 and hydrogenation of isoprene into isopentenes is shown in Figure 7. The plot shows the activity, based on the sum of both metals. It is clearly of superadditive character, the maximum activity being approximately three times as large as the activity of the pure palladium complex. The R- \ C-CHz pure nickel complex was inactive. CH Infrared spectroscopic data were used to /\ CH) CHJ explain some details of the interaction mechanism of the components in mono and bimetal- Fig. 8 Probable structure of a mixed palla- lic systems. The spectrum of the Pd(acac),- dium-nickel complex formed in the Pd(aeac),- Ni( acac),-1,l-dimethylallene (DMA)-AI( i- DMA-Al(i-Bu), system did not contain any Bn), system, R = iso-butyl: absorption bands characteristic of Al(i-Bu),, but No bands of acetylacetonate ligands; all bands that are typical of aluminium acetyl- Bands of isobutyl groups are shifted and split ("A,.,? 6," u, 6," ); acetonate were present in the spectrum. The A numbegof b&ds at 350-470/cm disappear absence from the spectrum of relatively inten- rapidly in air (Pd-C and Ni-C bonds); sive bands at 1130, 980 and 910/cm indicated A n-alkenyl ligand on Ni: 1490, 910,55O/cm; A cyclic dimer of DMA as a ligand on Pd: 815, that there was a great change in the DMA in the lO65,1120/cm complex (there were no bands characteristic

Platinum Metals Rev., 1996, 40, (1) 16 1120/cm. However, there were also bands at a well-determined specificity inherent in each 1490,910 and 550/cm which could be assigned metal. It appears that the “drawbacks” of to a n-alkenyl bonding with nickel in the hypo- aliphatic amines, caused by their inability to par- thetical structure shown in Figure 8. ticipate in building up multiple bonds with the Consequently, the presence of a second tran- metal of a complex (unlike phosphines and phos- sition metal crucially changed the picture of the phites) are well compensated for by the high interaction between the components, and might reactivity of the hydride complexes that are result in the formation of active sites that are formed during the interaction between the com- much more active than monometallic ones, due ponents of the catalyst system. As a result of the to their mixed structure. The fact that an exam- interaction to form hydride complexes, rather ple of such a bimetallic system was found complicated catalytically active polynuclear (although not with amine containing systems) structures may arise, under conditions which is very encouraging for a future search to find favour the solubility of these species. highly active catalysts involving a complex of a Although most of our results were only non-noble metal as a second component. This obtained on a laboratory scale, the very high approach, which is often used for heterogeneous activities, selectivities, and relative inertness catalysis, is usually overlooked for use with metal to poisons of these platinum group catalyst sys- complex systems, because very efficient ways of tems make them promising for commercial use. affecting catalytic properties already exist, such Extending the scope of the catalysts, by using as the appropriate choice of ligand. It is inter- bimetallic systems to find synergistic effects, esting that results similar to ours were obtained and of substrates involving organic compounds with palladium-nickel alloy films for the cat- with functional groups to be hydrogenated, is alytic hydrogenation of ethylene (34), although one of the main aims for the future. the observed effects differ mechanistically. Acknowledgements Conclusions The author is indebted to his colleagues who per- The data that have been presented show that formed the experimental work and took part in numerous discussions: 0. P. Parenago, L. P. Shuikina, A. V. interactions between compounds of the plat- Novikova, G. M. Cherkashin, A. I. Elnatanova, E. G. inum group metals and aliphatic amines with Kliger, E. Ya. Mirskaya, N. G. Bazhirova, K. K. sufficientlylong alkyl groups lead to a new type Turisbekova, E. M. Kharkova, L. E. Rozantseva, L. I. Parshina, N. V. Komarov and M. P. Filatova. The of hydrogenation catalysts, which have a num- participation of G. N. Bondarenko who registered and ber of common features in their production and interpreted the IR spectra is gratefully acknowledged.

References 1 G. C. Bond, Platinum Metals Rev., 1994,38, (l), 8 K. K. Turisbekova, L. P. Shuikina, 0. P. Parenago 16 and V. M. Frolov, Kinet. Katal., 1988, 29, (4), 2 V. M. Frolov, 0. P. Parenago and L. P. Shuikina, 1023 Kinet. Katal., 1980, 21, (4), 1085 3 L. P. Shuikina, A. I. Elnatanova, L. S. Kovaleva, 9 V. M. Frolov, 0. P. Parenago, L. P. Shuikina, A. 0. P. Parenago and V. M. Frolov, Kinet. Katal., V. Novikova, E. G. Kliger and K. K. Turisbekova, 1981,22, (l), 177 Nefrekhimzya, 1991, 31, (2), 197 4 L. P. Shuikina, G. M. Cherkashin, 0. P. Parenago and V. M. Frolov, Dokl. Akad. Nauk SSSR, 1981, 10 V. M. Frolov, 0. P. Parenago, G. N. Bondarenko, 257, (3), 655 L. S. Kovaleva, A. I. Elnatanova, L. P. Shuikina, 5 V. M. Frolov, 0. P. Parenago, L. P. Shuikina and G. M. Cherkashin and E. Ya. Mirskaya, Kinet. G. M. Cherkashin, React. Kinet. Cad.hn., 1981, Katal., 1981, 22, (9,1356 16, (2-3), 115 6 E. G. Kliger, L. P. Shuikina, 0.P. Parenago and 11 V. M. Frolov, 0. P. Parenago, L. S. Kovaleva, A. V. M. Frolov, Kinet. Katal., 1986, 27, (2), 521 V. Novikova, A. I. Elnatanova, E. Ya. Mirskaya 7 E. G. Kliger, L. P. Shuikina and V. M. Frolov, and E. G. Kliger, US.S.R.Authors Cernx No. SU Kinet. Katal., 1995, 36, (2), 319 1,066,975 A; 1983

Platinum Metals Rev., 1996, 40, (1) 17 12 V. M. Frolov, 0. P. Parenago, L. P. Shuikina, A. 22 H. Bonnemann, W. Brijoux, R. Brinkmann, E. V. Novikova, A. I. Elnatanova, G. M. Cherkashin, Dinjus, R. Fretzen, T. Joussen and B. Korall, 3. E. G. Kliger and E. Ya. Mirskaya, in Mol. Catal., 1992, 74, 323 “Homogeneous and Heterogeneous Catalysis. 23 V. M. Frolov and 0. P. Parenago,J. D. I. Mena!ekev Proc. 5th Int. Symp. on Relations between All-Union Chem. SOC.(in Russian), 1989,34, (6), Homogeneous and Heterogeneous Catalysis”, 659 Novosibirsk, 1986, VNU Science Press, Utrecht, 24 P. S. Ivanov, A. V. Novikova, 0. P. Parenago, Kh. the Netherlands, 1986, p. 587 Dimitrov and V. M. Frolov, Neftekhimiya, 1988, 13 V. M. Frolov, L. P. Shuikina, K. K. Turisbekova 28,(3), 320 and G. N. Bondarenko, Kinet Catal., 1994, 35, 25 V. M. Frolov, R. A. Karakhanov, 0. P. Parenago, (6), 800 (transl. into English from Kinet. Katal., M. M. Vartanyan, E. Ya. Mirskaya, T. Yu. 1994, 35, (6), 867) Solovieva, A. I. Elnatanova and L. S. Kovaleva, 14 E. G. Kliger, L. P. Shuikina, 0. P. Parenago and React. Kinet. Catal. Lett., 1985,27, (2), 375 V. M. Frolov, Izv. Akad. Nauk SSSR, Ser. Khim., 26 A. V. Novikova, G. M. Cherkashin, A. I. 1988, (l), 2420 Elnatanova, E. Ya. Mirskaya, 0. P. Parenago and 15 E. G. Kliger, L. P. Shuikina and V. M. Frolov, V. M. Frolov, Neftekhimiya, 1989, 29, (3), 323 Kinet. Katal., 1990, 31, (2), 510 27 N. G. Bazhirova, A. V. Novikova, N. V. Komarov, 16 E. G. Kliger, L. P. Shuikina and V. M. Frolov, R. I. Ter-Minasyan, 0. P. Parenago and V. M. Kinet. Katal., 1995,36, (4), 546 Frolov, Manuscript deposited in the Russian 17 0. P. Parenago, V. M. Frolov, G. M. Cherkashin Institute for Scientific Information (“V.I.N.I.T.I.”), and L. P. Shuikina, in “The 6th International NO. 3042-V89; 1989 Conference on Organometallic Chemistxy”, Riga, 28 L. Horner, H. Biitze and H. Siegel, Tetrahedron Latvia, 1985, p. 117 Lett., 1968, (37), 4023 18 E. Ya. Mirskaya, A. I. Elnatanova, L. S. Kovaleva, 29 S. Montelatici, A. van der Ent, J. A. Osborn and 0. P. Parenago and V. M. Frolov, Dokl. Akad. G. Wilkinson,J. Chem. SOC.(A), 1968, (5), 1054 Nauk SSSR, 1984,276, (6), 1407 30 J. A. Osborn, F. H. Jardine, J. F. Young and G. 19 G. M. Cherkashin, L. P. Shuikina, 0. P. Parenago Wilkinson,J. Chem. SOC.(A), 1966, (12), 1711 and V. M. Frolov, Kinet. Katal., 1985, 26, (3, 31 V. M. Frolov, Neftekhimiya, 1995,35, (3), 198 1110 32 M. A. Bennett, Tai-Nang Huang, A. K. Smith 20 V. M. Frolov, 0. P. Parenago, A. V. Novikova and and T. W. Turney,J. Chem. SOC.,Chem. Commun., L. S. Kovaleva, React. Kinet. Catal. Lett., 1984, 1978,582 25, (3-4), 319 33 E. M. Kharkova, A. V. Novikova, L. E. Rozantseva 2 1 H. Bonnemann, W. Briioux, R. Brinkmann, E. and V. M. Frolov, Kinet. Katal., 1993,34, (5), 866 Dinjus, T. Joussen and B. Korall, Angem Chem., 34 R. L. Moss, D. Pope and H. R. Gibbens,J. Cad., 1991,103, 1344 1977,46,204 Activity of Platinum-Containing Electrodes Enhanced The extraction of zinc from its ores by elec- alloys containing 1 per cent platinum group trolysis in aqueous solution provides a high metal, and other elements, display enhanced purity product and is the method used for win- activity for anodic sulphite oxidation in a neu- ning a substantial proportion of world zinc out- tral borate buffer solution. Now the same inves- put. The process is energy intensive, but energy tigators at the Institute for Materials Research efficiency was not a consideration in the design at Tohoku University, Sendai, Japan, have of existing electrowinning plants, which are gen- reported on their evaluation of the effect of erally sited close to sources of cheap hydro- cathodic reduction on the catalytic activity for electricity. Now, however, various attempts are anodic oxidation of sulphite on electrodes pre- being made to develop more efficient processes. pared from amorphous nickel-valve metal-plat- In conventional electrowinning of zinc oxygen inum group metal alloys (T. Mori, A. gas is evolved in the cell, as an unnecessary Kawashima, E. Akiyama, H. Habazaki, K. by-product, and this accounts for a substan- Asami and K. Hashimoto,J. Appl. Electrochem., tial part of the cell voltage. In a new process this 1995, 25, (lo), 953-961). oxygen evolution is replaced by the anodic oxi- After immersion in hydrofluoric acid and sub- dation of sulphur dioxide produced during the sequent cyclic voltammetry in sulphuric acid, smelting process, or by the anodic oxidation their electrodes were subjected to galvanostatic of hydrogen. For this new process to be feasi- cathodic reduction before assessment. Addition ble the anode has to have high electrocatalytic of platinum, together with rhodium, iridium or activity for the oxidation of sulphurous acid. ruthenium, to amorphous nickel-40 niobium Previous work has demonstrated that after suit- was found to be particularly effective in improv- able activation amorphous nickel-valve metal ing the catalytic activity for sulphite oxidation.

Platinum Metals Rev., 1996, 40, (1) 18 Second European Congress on Catalysis By Professor G. C. Bond Brunel University Uxbridge, Middlesex

The second European Congress on Catalysis (EUROPACAT-11) was held in the MECC Centre, Maastricht, The Netherlands,from 3rd to 8th September, 1995, and was attended by more than 750participants. There were 13 separate symposia, covering all aspects of catalysis, with three running simultaneously Two poster sessions contained a large number of presentations. This report covers aspects of the work presented featuring the platinum group metals.

As usual the metals of the platinum group was a time-delay before nitrogen appeared (3). featured prominently as catalysts in many of the There still remains some scope for improv- sections. In this short report the conmbutions ing the performance of the catalysts used for presented in the three most relevant symposia vehicle exhaust treatment by altering the nature are highlighted; and a few important papers of the support. Solid solutions of CeO, + ZrO, given in other symposia will be mentioned. are in some ways superior to ceria by itself, and in particular they have a very high oxygen stor- Catalysis and Catalytic Processes age capacity at low temperatures (4). to Abate Environmental Damage The continuing use of palladium as the active The reactions occurring in simulated vehicle component in exhaust gas treatment catalysts exhaust continue to excite considerable atten- has stimulated a comparison between the tion; however, in practice, the number of chem- decomposition of nitric oxide, and its reaction ical species present is such that for fundamen- with hydrogen and with carbon monoxide, on tal work it is necessary to use simpler systems. single crystal surfaces of palladium and of Thus, for example, for a Pt-Rh/Al,O, three-way rhodium. The decomposition of nitric oxide catalyst, the addition of 1 to 12 per cent water requires a higher temperature on palladium than vapour increases the rate of carbon monoxide on rhodium, and on palladium affords some oxidation by 2 to 6 times, respectively, and the nitrous oxide, whereas on rhodium the only presence of ceria also enhances the oxidation product is nitrogen (5). rate. By using isotopically-labelled oxygen ('*O,) A comprehensive study of the oxidation of a it was found, surprisingly, that the main source number of different hydrocarbons on a Pt/Al,O, of the oxygen used to form the carbon dioxide catalyst was reported (6). Alkyl-substitutedben- was in fact water, and not molecular oxygen (1). zenes are less easily oxidised than benzene itself, From a broadly-based kinetic modelling study because the substituents release negative charge of NO + CO and CO + 0, reactions, it was con- to the aromatic ring, which is consequently more cluded that nitrous oxide is formed as an inter- strongly adsorbed on the catalyst and less reac- mediate product in the former reaction (2). tive. Bicyclic C,,molecules, such as naphtha- Because of the continuously-changing condi- lene, decalin and tetralin, are less reactive than tions that the actual catalyst has to endure, the n-decane, again because of adsorption through transient-response technique is particularly suit- the ring structures. able for providing information on reaction kinetics. Consequences of the step-changes applied Catalysis of (Pseudo) Metals to a conventional three-way catalyst were The somewhat strange title of this symposia analysed on a time-scale of about 2 minutes, was intended as a short way to show that com- and showed that for the NO + CO reaction there pounds such as the carbides of molybdenum

Platinum Metals Rm., 1996, 40, (l), 19-22 19 and of tungsten, which show catalytic proper- were in the same range (4 to 6 nm) in each case. ties similar to those of metals, were within the An explanation was suggested based on a dif- remit of the symposium. Papers dealing with ference in binding energy of the palladium 3d them are not however covered here. core level (1 1). One factor that can affect the The reason for the enhancement of activity activity of palladium catalysts in hydrogenation during the hydrogenation of 2,4-dinitrotoluene reactions is the dissolved hydrogen content, on adding iron to Pd/SiO, was examined by which is known to decrease as the particle size studying the IR spectra of chemisorbed car- becomes smaller. There is, in fact, a linear rela- bon monoxide and nitric oxide. It was concluded tion between x in P-PdH, and dispersion, and that on chemisorption nitric oxide oxidises Feu between x and the temperature at which the to Fe”, which in turn can chemisorb nitric oxide, hydride decomposes (- 70°C). No hydride is but carbon monoxide is only adsorbed on pal- formed when the dispersion exceeds 80 per cent, ladium surface atoms; the two species are inter- for then the particles have almost no middle. spersed at an atomic level (7). However, for dispersions over 45 per cent (where The structures and properties of some other XRD ceases to be effective) the decomposi- bimetallic systems were reported. A series of tion temperature can be used to estimate the alumina-supported RuGe catalysts were degree of dispersion ( 12). described: Ge’ is not incorporated in the ruthenium particles except at the highest germa- Ruthenium for Ammonia Synthesis nium:ruthenium ratio; however, according to Carbon-supported ruthenium catalysts pro- EXAFS spectra, it exists as GeO, ‘molecules’ moted with barium or caesium are effective cat- on the surface (8). alysts for ammonia synthesis. Systematic stud- One of the best methods for investigating the ies are in progress, aimed at understanding how surface composition of bimetallic catalysts is ruthenium differs from iron, and to this end the low-energy ion scattering (LEIS), which is a ruthenium (0001) surface, polycrystalline ruthe- strictly surface-sensitive technique. By its use it nium and ruthenium on magnesia and on alu- was shown that platinum-palladium particles mina, both unpromoted and promoted by potas- on alumina are enriched in platinum after a treat- sium and caesium, are being examined by a ment in hydrogen at 300°C, while at lower tem- variety of techniques. It appears that the peratures bulk and surface compositions were Ru(OOO1) surface has a very low sticking coef- about the same (9). A number of different types ficient for nitrogen, and that in the supported of metallic particles are formed by platinum and catalysts only a small fraction of the surface is copper on and in the zeolite ZSM-5; the com- active; the active sites in the caesium-promoted bined use of EXAFS, of FTIR using carbon Ru/MgO catalyst are associated with the pres- monoxide, and of XPS, leads to the identifica- ence of the alkali (13). tion of five different kinds of particle or sur- Finally, two contributions of a more funda- face (10). mental kind will be mentioned from this sym- Straightforward methods of catalyst prepara- posium. Many of the most important catalytic tion are still capable of producing surprises. The reactions of the platinum group metals involve use of acetylacetonates in non-hydroxylic sol- hydrogen, and detailed studies of its chemisorp- vents as impregnating solutions is well estab- tion on EUROPT-1 (PdSiO,), and on Rh/Al,O, lished; however, it could not be predicted that and Pd/SiO,, show that under all conditions of the hydrogenation activity of the catalyst result- measurement it is the change in Gibbs free ing from using palladium acetylacetonate in ben- energy, G, and not kinetic factors, that controls zene depended on whether (i) there were mul- what takes place (14). tiple impregnations with dilute solutions or (ii) The importance of equilibrium constants for there was a single impregnation with a con- the adsorption of reactants was also stressed, centrated solution, although the particle sizes using alkane hydrogenolysis on Ru/Al,O,

PZatinum Metals Rev., 1996, 40, (1) 20 catalysts as the example: differences in activity It is now possible to monitor catalytic reac- caused by changing the particle size or surface tions on single crystal metal surfaces over a wide morphology have been naced to thermodynamic pressure range, and, although such surfaces factors, rather than to geometric (that is the do not precisely mimic technical catalysts, the ensemble size) factors (15). added advantages - in terms of the applicable techniques for study - more than compensate Research on Model Catalysts for this limitation. So, for example, the cause of In recent years interest has grown in the prepa- the oscillatory behaviour in carbon monoxide ration of ‘model’ catalysts that simulate the struc- oxidation on Pd(ll0) and Pt(210) surfaces is ture and properties of supported metals, but suggested to be subsurface oxygen (20). This because they are made on flat surfaces under form of adsorbed oxygen also features in the UHV conditions, they can be investigated by interpretation of the results of the NO + CO methods of characterisation that are not usually reaction on iridium (2 1). Oscillation is also suitable for powdered materials. In a careful shown in the reaction of NO + H,on the stepped study of ethene oxidation on platinum foils, thick Rh(533) surface at 470 K and mbar, but platinum films and model Pt/SiO, catalyst, it not on Rh(100) (22). was found that the oxidation rates were pro- A new technique in the study of adsorbed portional to the metal area only when the species is Temperature Programmed Static ethene:oxygen ratio was low. It was concluded Secondary-IonMass-Spectrometry (TPSSIMS), that the support takes an active part in the reac- which together with the more traditional TPD tion when the platinum surface is covered by has been used to investigate the conversion of hydrocarbon species (1 6). chemisorbed ethene to ethylidyne, and its fir- Another example of support involvement is ther decomposition at higher temperatures, on provided by the sulphur dioxide-assisted oxi- the Rh(ll1) surface (23). dation of propane catalysed by the Pt( 11 1) sur- Another novel and powerful method for exam- face, which when partially covered by a disor- ining adsorbed species, Sum Frequency dered aluminium oxide layer gives a rate that Generation Vibrational Spectroscopy, was is much greater than on the uncoated metal sur- described by G. A. Somorjai in his plenary lec- face. It is thought that adsorption of SO:- groups ture. It has the advantage over copventional on the support allows an increased uptake of i&ared spectroscopy by having no interference hydrocarbons ( 17). from gaseous molecules.

Characterisation of Model Catalysts Contributions to Other Symposia New and sensitive techniques, such as scan- It is not only the metallic states of the plat- ning tunnelling microscopy (STM) and atomic inum metals that are catalytically active. force microscopy (AFM), as well as EXAFS, However, few of the platinum group metal com- are being applied to the characterisationof model pounds are stable under the conditions that are catalysts. The rate and selectivity shown in the required for use in industrial processes; the sul- hydrogenation of 1,3-butadiene depend on the phide may be such a compound. Ruthenium microstructure of palladium-graphite films: the sulphide displays very high activity for structure of which can be changed by altering hydrotreating processes, especially for hydro- the hydr0gen:hydrocarbon ratio (18). These desulphurisation (HDS) and can moreover be observations are relevant for understanding the prepared in various states of dispersion depend- strange behaviour of palladium catalysts pre- ing on whether it is supported or not (24). pared from acetylacetonate, as mentioned above Metals of the platinum group are also highly (1 1). Particle growth of IrFe/SiO, bimetallic effective oxidation catalysts. The use of Pd/AI,O, model catalysts after oxidation has been followed for the catalysed complete oxidation of methane both by EXAFS and TEM (1 9). allows heat generation at a lower temperature

Platinum Metals Rev., 1996,40, (1) 21 than does non-catalysed combustion, and after which it reacts with either carbon diox- thereby reduces the extent of nitrogen oxides ide or with water: formation. Water, being a product, does how- CH, + H,O + CO + 3H, ever act as an inhibitor (25) (see also (16) and (1 7)). The possibility of reforming methane with Concluding Remarks carbon dioxide, that is The arrangement of three parallel sessions, together with the very large number of posters CH, + CO, + 2CO + 2H, available for inspection, made it virtually impos- has recently attracted attention, and alumina- sible to absorb and retain all the information. supported ruthenium, rhodium, iridium and This however reflects the healthy state of the platinum catalysts all show comparable behav- subject, and the great effort that European sci- iour for this process (26). In the partial oxida- entists are devoting to its development. Platinum tion of methane to synthesis gas, that is group metals retain their foremost position in the field of metal catalysis, from which they are CH, + 1/2 0, + CO + 2H, unlikely to be moved in the foreseeable future. the methane is in fact initially oxidised non- EUROPACAT-III will take place in Cracow selectively until all the oxygen has disappeared, in 1997. It is a beautiful city: try to be there. Speakers 1 M. A. J. Campman, J. H. B. J. Hoebink and G. B. 13 M. Miihler, F. Rosowski, 0. Hinischen and G. Marin, Emdhoven University of Technology, The Ertl, Fritz-Haber Institut, Berlin Netherlands 14. A. Frennet and C. Hubert, Universite libre de 2 G. Leclercq, P. Granger, J. J. Lecomte, C. Dathy, B-elles, Belgium L. Leclercq, G. Mabilon and M. Prigent, Universite des sciences et ~~~hn~l~gi~~de ~11~15 G. C. Bond and J. C. Slaa, Brunei University, and Institut FranCais du Peuole, France Uxbridge, U.K. 3 J. Ahola, T. Maunula, H. Haario, T. Salmi, M. 16 L.-G. Petersson, I- R Wallenberg and u. AckW Harkonen, M. Luoma and V. J. Pohola, Kemira Linkoping University, and Chemical Center, Metalcat and Abo Akademi, Finland Lund, Sweden 4 J. Kaipar, P. Fornasiero, G. Balducci and M. 17 K. Wilson, C. Hardacre and R. M. Lambert, Graziani, Universita di Trieste, Italy Cambridge, University M. Bowker and m,hdW u~mi% 18 K. Catani, K.-H. Lee and E. E. Wolf, University 6 F. Deihl, G. Mabilon and I. Guibard, Institut of Notre Dame. Indiana. USA Frangais-du Peuole, France 19 R. Zanoni, M. Bellaueccia, R. Psaro, C. Dossi, 7 F. Boccuui, E. Guglielminotti, F. Pinna and M. S. Calmom, R. Della Pergola, S. Bertoni and S. Signoretto, Universita di Torino and Universita Marengo, Universita di Milano and Istituto G. di Venezia, Italy Donegani, ENICHEM, Novara, Italy 8 B. S. Clausen, C. V. Ovensen, J. Schietz, J.K. 20 M. Berdau, S. Moldenhauer, A. Hammoudeh, K. Nerskov and H. Topsee, Haldor Topsee Research Christmann and (the late) J. H. Block, Fritz-Haber Labs., Lyngby, Denmark Institut and Freie Universitat, Berlin. 9 L. C. A. van den Oetelaar, 0. W. Nooij, A. W. Denier van der Gon, H. Brongersma, A. G. 21 A. I. Boronin, V. I. Elokhin and E. A. Ivanov, Rosenbrand and J. A. R. van Veen, Eindhoven Boreskov Institute of Catalysis, Novosibirsk, Russia University of Technology and Koninklijke/Shell 22 N. M. H. Jassen, P. D. Cobden, B. E. Laboratorium, Amsterdam, The Netherlands Nieuwenhuys, M. Ikai and K. Tanaka, 10 E. S. Shpiro, 0. P. Tkachenko, R. W. Joyner, M. Rijksuniversiteit Leiden, The Netherlands, and R. H. Siddiqi, N. I. Jaeger and G. Schulz-Ekloff, University of Tokyo Zelinksy Institute of Organic Chemistry, Moscow, 23 H. J. Borg, R. M. van Hardeveld and J. W. University of Liverpool and Universitat Bremen, Niemantsverdriet, Eindhoven University of Germany Technology, The Netherlands 11 J. Goetz, M. A. Volpe, A. M. Sica, C. E. Cigola and R. Touroude, Universite Louis Pasteur, 24 M. Lacroix, M. Breysse, H. Jobic, V. Kougionas and J. L. Portefaix, Institut de Recherches sur la Strasbourg, and U.N.S.-Conicet, Bahia Blanca, Catalyse, Villeurbanne, France Argentina 12 G. Fagkmzzi, A. Benedem, S. Polizzi, A. di Mario, 25 J. C. van Giezen, A. J. van Dillen and J. W. Geus, F. Pinna, M. Signoretto and N. Pernicone, Utrecht University, The Netherlands Universita di Venezia and Montecatini- 26 H. Papp and Q. Zhuang, Universitat Leipzig, Technologie, Novara, Italy Germany

Platinum Met& Rw., 1996, 40, (1) 22 Platinum Group Metal Fullerenes SOME RECENT STUDIES ON SYSTEMS CONTAINING C, By D. T. Thompson Consulting Chemist, Reading, England

The C,, molecule, named 'buckminster- Addition of Pt(q2-C,H4)(PPh3),to C,, in fullerene', is very stable physically, and its poten- toluene under nitrogen gave the C,, platinum tial as a source of a number of useful materials complex indicated in Equation (i) as black has been suggested. For example, nonhydro- microcrystals in 85 per cent yield; Pt($- static compression of C, transforms it into bulk C,)(PEt,), could be prepared by reaction with polycrystalline diamond at room temperature Pt(PEt,), (1 1). The triethylphosphine complex (1); and when doped with alkali metals C, gives was obtained in 68 per cent yield after purifi- the highest temperature organic superconduc- cation by column chromatography on silica gel. tors seen to date (2-4). The soot deposits from The triphenylphosphinecomplex is also formed arc evaporation contain near perfect nanotubes when fullerene-60 reacts with a binuclear het- with potentially outstanding electronic and erometallic compound with a mercury-platinum mechanical properties, and encapsulated pal- bond, trans-Ph2CHCH,HgPt(PPh3),Br,or cis- ladium can act as the seed for the growth of a (CF,),CFHgPt(PPh,),CH=CPh,(1 2). worm-like nanostructure (4,5). The biological [60]Fullerene complexes have now been activity of unsubstituted buckminsterfullerene reported for all the platinum group metals. The is also being investigated using C,labelled with reaction of C, with excess Cp*Ru(CH,CN),+X radioactive carbon-1 4 (6, 7). Potential biolog- (Cp* = q5-C5Me,;X- = 0,SCFJ proceeds as ical applications for fullerenes are being sought follows ( 13) : in areas ranging from drug metabolism to agro- Cp*Ru(CH,CN),'X- + C, + chemicals. (excess) { [Cp*Ru(CH,CN),],C,} '+(XJ3 (ii) In spite of its physical robustness, C,, readily undergoes chemical reactions and its organic The first ruthenium carbonyl derivative of chemistry has been widely investigated. In recent fullerene, (T~-C,)RU(CO),,was prepared by the years there have also been reports of its reac- reaction between Ru(CO), and C, in toluene tions with inorganic species, including platinum solution under nitrogen. The product is more group metals systems. These have given rise stable than the equivalent iron compound (14). to the preparation of a number of platinum The synthesis of a [60]fullerene derivative cova- group metals complexes, the first such com- lently linked to a ruthenium(II) tris(bipyridine) pound being: C,,(OsO,) (4-Bu'C,H4N),, an complex has been reported (15). [Ru(bpy),lZ' osmate ester with C-0-0s bonds, which was complexes are photoactive (2),known to trans- reported by Hawkins and co-workers (8,9). The fer energy in the excited state, and [60]Mlerene first example of a compound with a direct metal- has a high electron affinity and can reversibly c60 bond, Pt(qz-C,,) (PPh,), was described in accept up to six electrons in solution. Due to 1991 (lo), see Equation (i), below. solubility problems, however, the reaction of

Platinum Me& Reet., 1996,40, (l),23-25 23 Me f: -0-c

Ru(bpy),(bpy-5-COCl) (PF,), with the parent Ir(qz-Cb,)Cl(CO)(PPh,), which readily disso- N-H fulleropyrrolidine gave a very insoluble ciates into C,, and IrCl(CO)(PPh,),. ‘Naked stone-like material which could not be charac- metal’ complexes M(C,,) have been prepared terised (1 6); but when the fulleropyrrolidine(1) for a number of metals including rhodium - the was synthesised and treated with general approach involves the formation of M’ Ru(bpy),C1,.2H20 in refluxing 1,2-dichloro- ions from pure metal targets by laser desorp- ethane, in the presence of NH,PF,, compound tion, followed by interaction with C,, in the (11) was produced, see Equation (iii), above. vapour state (20). Compound (11) is now being studied as a Ir(q2-C,,)Cl(CO)(PPh,),.5C,H,,was obtained model for long-lived charge separated states, as brown-black crystals when a purple solution and is being compared with compounds which of C,, in the dangerous solvent, benzene, was have conventional rigid spacers less flexible than added to a yellow benzene solution of the triethylene glycol chain. IrC1(CO)(PPh3),(21). The indenyl C,, com- A number of isomers of the bis-complex plex Ir(q5-C9H,)(qz-Cbo)(CO) was obtained by C,,[OsO,(py),], have been prepared (17); and refluxing the indenyl cyclooctene complex Ir(q5- C,, triosmium cluster compounds have been C,H,) (qz-C8Hl.,)and C,, in dichloro-methane obtained from the reaction between a toluene (22). C,,[IrCl(CO)(PMe,Ph),], has been solution of Os,(CO),,(NCMe) and one equiv- obtained in two conformational isomers (20, alent of C,, by heating at 80°C for 5 minutes. 23), and C,,~,C1,(1,5-COD),],.2C,Hbhas been The products have the formulae (q2- prepared by mixing solutions of C,, and ~60)~~3(~~)11,(~’-c~)os3(co),0(NCMe), (qz- Ir~C12(l,5-COD)~in benzene (24). C,O)O~~(CO)IO(PP~~)and (~2-~~0)~~3(~~)9- Pd(qz-C,,) (PPh,), has been reported (25) and (PPh,), (9). the reaction between C,, and M(PEt,),, where A C,, rhodium complex Rh(qz-C,,)H(CO)- M is nickel, palladium or platinum, gives (q2- (PPh,),, which is a dark green powder, has been C,,)M(PEt,), compounds. Addition of Pt(PEt,), prepared by the addition of one equivalent of to a solution of C,, in benzene produced RhH(CO)(PPh,), in toluene to C,, in toluene C,,[Pt(PEt3),], (26), and analogous compounds (18). This rhodium complex may also be pre- of nickel and palladium have also been prepared pared in dichloromethanesolution and obtained (27). In the palladium product the molecule has and isolated as green-black crystals (19). This a C,, core bearing six octahedrally-disposed product is more stable in solution than Pt(PEt,), groups (26).

References 1 M. N. Regueiro, P. Monceau and J.-L. Hodeau, 3 P. F. Henry, M. J. Rosseinsky and C. J. Watt, 3 Nature, 1992,355,2372 Chem. Soc., Chem. Commun., 1995,2 13 1, and ref- 2 J. T. S. Irvine, A. Mills, “Insights into Speciality erences therein Inorganic Chemicals”,ed. D. T. Thompson, The 4 E. Konecny, C. P. Quinn, K. Sachs and D. T. Royal Society of Chemistry, Cambridge, U.K., Thompson, “Universities and Indushial Research”, 1995, pp. 275,457 Royal Societyof Chemisny, Cambridge, U.K., 1995

Platinum Metals Rw., 1996, 40, (1) 24 5 Y. Wang,J. Am. Chem. Soc., 1994,116, 397 16 M. Maggini, G. Scorrano and M. Prato, 3 Am. Chem. Soc., 6 W.A. Scrivens and J. M. Tour,J. Am. Chem. SOC., 1993,115, 9798 1994,116,4517 17 J. M. Hawkins, A. Meyer, T. A. Lewis, U. Bunz, R. Nunlist, G. E. Ball, W. Ebberson and K. R. Dagnani, Chem. Eng. News, June T. 7 13, 1994,7 Tanigaki,J. Am. Chem. SOC.,1992,114,7954 8 J. M. Hawkins, A. Meyer, T. A. Lewis, S. Loren 18 R. E. Douthwaite, M. L. H. Green, A. H. H. and F. J. Hollander, Science, 199 1,252, 3 12, and Stephens and J. F. C. Turner,J. Chem. SOC.,Chem. references therein Commun., 1993, 1522 9 J. T. Park, J.-J. Cho and H. Song, J. Chem SOC., 19 A. L. Balch, J. W. Lee, B. C. No11 and M. M. Chem. Commun., 1995, 15 Olmstead, lnorg. Chem., 1993, 32, 3577 10 P. J. Fagan, J. C. Calabrese and B. Malone, Science, 20 J. Bowser, Adv. Organomet. Chem., 1994,36, 57 1991,252,1160 21 A. L. Balch, V. J. Catalan0 and J. W. Lee, horg. I1 M.Iyoda, Y. Ogawa, H. Matsuyama, H. Ueno, Chem., 1991,30, 3980 K. Kikuchi, I. Ikemoto and Y. Achiba, Fullerene 22 R. S. Koefod, M. F. Hudgens and J. R. Shapley, Sci. Tech., 1995, 3, (l), 1; Platinum Metals Rev., J. Am. Chem. SOC.,1991,113,8957 1995, 39, (2), 81 23 A. L. Balch, J. W. Lee, B. C. No11 and M. M. 12 V. V. Bashilov, B. L. Tumanskii, P. V. Petrovskii Olmstead,J Am Chem. SOC.,1992, 114, 10984 and V. Sokolov, Izv. Akad. Nauk. Rossii, Ser. 24 M. Rasinkangas, T. T.Pakkanen, T. A. Pakkanen, Khim., 1994, (6), 1131; PZatinum Metals Rev., M. Algren and J. Rouvinen, J. Am. Chem. SOC., 1995, 39, (l), 38 1993.115.4901.. 13 P. J. Fagan, J. c. Calabrese and €3. Malone, Act. 25 B. Chase and P. J. Fagan,J. Am. Chm. SOC.,1992, Chem. Res., 1992,25, 134 114,2252 14 M. Rasinkangas, T. T. Pakkanen and T. A. 26 P. J. Fagan, J. C. Calabrese and B. Malone,J. Am. Pakkanen, J. Organomet. Chem., 1994,476, C6 Chem. SOC.,1991, 113, 9408 15 M. Maggini, A.Dono, G. Sconano and M. Prato, 27 P. J. Fagan, J. C. Calabrese and B. Malone, Acc. J. Chem. SOC.,Chem. Commun., 1995,845 Chem. Res., 1992,25, 134 Platinum Nanochannel Replica Membranes Nanoscale materials are widely used in elec- ing. The buffer layer is dissolved in sodium tronic and optical devices, and for filtration and hydroxide and the platinum replica membrane biological applications; so there is clearly a need floated off. Thin platinum membranes having for suitable production and patterning tech- a uniform, hexagonal pattern of voids as small niques, and some have been discussed here as 40 nm in diameter, and possibly less, have before, Platinum Metals Rm., 1993,37, (2), 101. been formed. The membranes, displaying good Researchers at the Naval Research Laboratory, mechanical properties, can be used as masks in Washington D.C., U.S.A., now report the prepa- pattern deposition onto substrates. This method ration of thin platinum membranes using is said to be an improvement on the usual lith- nanochannel glass replica membrane technol- ographic techniques and involves fewer steps. ogy (D. H. Pearson and R. J. Tonucci, Science, 1995,270, (5233), 68-70). Increased Catalytic Activity The thin membranes produced, which can be Clearly, it would be advantageous if the cat- fabricated from platinum, gold, tungsten and alytic activity and/or the selectivity of a het- molybdenum, contain uniform, nanometre- erogeneous catalyst could be varied by a sig- scale, patterned voids. The metal membranes nal given to the catalyst. are formed on nanochannel glass (NCG) wafer Recent studies by scientists at the Nagaoka substrates. The NCG material is fabricated by University of Technology, Japan, have lead them a draw process similar to the preparation of opti- to conclude that remarkable enhancements in cal fibres and the fibres are packed together in the catalytic activity of a thin film palladium cat- a hexagonal close-packed arrangement. The alyst supported on ferroelectric lead strontium fibres are then repacked and redrawn to achieve zirconium titanate and lithium niobate substrates the desired packing density and element size, can result from resonance oscillation of the mat- made into wafers, polished and etched. Other erial (Y. Inoue and Y. Ohkawara, J. Chem. SOC., packing schemes enable more complex void pat- Chem.Commun., 1995, (ZO), 2 101-2102). terns to be achieved. Using the resonance oscillations generated by The usual deposition techniques are employed low-frequency voltages of the ferroelectric sub- to deposit an easily dissolved buffer layer of alu- strates, remarkable 250 to 300 fold increases in minium onto the NCG, followed by a 75 nm activity of the catalyst surfaces were found thick layer of platinum by magnetron sputter- during ethanol oxidation. I.E.C.

Platinum Metals Rev., 1996, 40, (1) 25 The Development of Molecular Wires RUTHENIUM AND OSMIUM POLYPYRIDINE COMPLEX TERMINALS FOR FAST ELECTRON MOVEMENT ALONG POLYYNE BRIDGES By VI Grosshenny, A. Harriman, M. Hissler and R. Ziessel Ecole Europ6enne de Hautes Etudes des Industries Chimique de Strasbourg, Universit6 Louis Pasteur, Laboratoire de Chimie d’Electronique et de Photonique MolBculaires, Strasbourg, France

The growth in research in molecular sized electronic devices in the very recent past,for functions such as optical switches, fast recording devices, miniaturised sensors and molecular computers, has created a need for equally small connectors which comply with the stringent requirements of such structures to link them to the surrounding assembly. Among materials that are suitable for the terminal subunits are polypyridyl complexes of ruthenium(ZZ), osmium(ZZ) and rhenium(I), linked together by bridging polyynes. The triplet excited states of these complexes have long lives and are formed under visible-light illumination. Their metal-to-ligand charge-transfer character allows electron promotionfrom the metal centre to the bridging ligand, giving directional electron transfer. Complexes based on ruthenium( IZ) or osmium(ZZ) seem more promising due to their amenable absorption and emission spectral profiles and their facile oxidation-reduction processes. Thispaper looks at the development of the molecular materials and structures that are required to act as molecular-scale connectors enabling molecular-scale electronic devices to function successfully.

The advent of molecular-scale electronic devices nium(I1) polypyridine complexes, appear to be demands the availability of suitable molecular promising materials for use as the redox-active components that can be integrated into a terminal subunits, while polyenes (2), polyynes supramolecular assembly and subsequently con- (3), and poly-aromatics (4-6) may be consid- nected to a macroscopic support. Among the var- ered as potential bridging units. It is neces- ious components needed for fabrication of effec- sary, however, to determine the capability of tive devices are molecular wires (l), whose such bridges to function as electron carriers, purpose is to provide strong electronic commu- and this is the subject of intense current research. nication between spatially-remote, redox-active Due to the rigidity, relative chemical inertness, subunits. Such wires are intended to fulfil sev- resistance to isomerisation, and synthetic adapt- eral critical roles, including (i) maintaining smct ability of polyynes, we have concentrated our stereochemical integrity of the halassembly and efforts on exploring their potential application (ii) promoting unidirectional electron flow along as molecular wires. Such functionalities are ideal the molecular axis under appropriate external for the construction of linear, rod-like molecules stimulation. The latter impetus may be initi- with transition metal complexes as termini. ated by absorption of a photon, by application The terminal complexes, which are formed of a potential at an attached electrode, or by chem- from oligopyridine ligands, may be identical - ical means - the fastest response being attained giving rise to symmetrical systems (7),or dis- by photochemical triggering of the system. similar - resulting in asymmetrical systems (8). Transition metal complexes, especially those By careful selection of the central metal cation based on photoactive complexes of ruthe- and the overall ligand field, it becomes possible

Platinum MenLC Rev., 1996,40, (I), 26-35 26 Fig. 1 Pathways for the preparation of building blocks (top) and ethynyl bridged ditopic back-to-back terpyridine ligands (bottom)

to ensure that the complexes are photo- andor between the termini that occurs when the length redox-active, while, by incorporating several of the polyyne bridge is increased. This latter complexes into a single molecular array, a redox effect may be studied experimentally by mea- gradient can be established along the chain. suring rates of intramolecular electron- or For such multicomponent molecular systems, energy-transfer processes that take place via it is necessary to find out the exact role played bonding or antibonding molecular orbitals by the polyyne bridge and, in particular, to quan- localised on the bridging polyyne, see Panel 2. tify its ability to promote electronic coupling between the terminal complexes. Since one of Measurement of Attenuation in the ultimate objectives of such research (9) is to Electronic Coupling design systems comprisinginsulating lipid bilayer In order to perform such experiments, a series membranes capable of allowing light-induced of multidentate ligands was first prepared (10) electron flow, see Panel 1, it is especially impor- by a palladium(O)-catalysed cross-coupling reac- tant to establish the magnitude of any attenu- tion (a Heck-type reaction for the synthesis of ation in the degree of electronic coupling the ethynyl-bridged compounds, see Figure 1)

Fig. 2 Pathways for the preparation of butadiyne bridged ditopic back-to-back terpyridine ligands

Platinum Metals Rev., 1996,40, (1) 27 Panel 1

Photoinduced electron transfer across an insulating membrane might take place in one of three ways: First, see Diagram at (a), a photosensitiser (PS) dissolved in Water Membrane wate? the aqueous phase may initiate an electron-transfer reaction with an appropriate redox-active quencher (Q) present in the aqueous phase or at the membrane-water interface. The reduced form of the quencher (Q- '), together with its comple- mentary protonated form (QH'), may enter the membrane and thereby migrate to the opposite interface by a random diffusional process. Migration may involve electron exchange with similar species dissolved in the membrane. (C I Upon reaching the other interface, the reduced quencher may transfer its extra elec- A- tron to a water-bound electron acceptor (A) or enter the aqueous phase itself. Plasto- quinone molecules are believed to operate in this way in green plant photosynthetic organisms. Second, see Diagram at (b), PS might be located inside the membrane but close to the interface. Under illumination, the excited state of PS may transfer an electron to an appropriate electron acceptor (QJ held at the electron across the membrane it might a fixed site deeper inside the membrane. In be possible to use a highly conductive elec- competition to charge recombination, the tron channel to ferry the electron to an accep- reduced form of the acceptor may transfer tor (Q) sited at the opposite side of the mem- its extra electron to a different acceptor (Q2) brane. Thus, upon illumination of PS a giant positioned Weracross the membrane, pro- dipole is created comprising PS' and Q-. viding the reaction is energetically downhill. These species might undergo secondary elec- In this way, a cascade of electron-transfer tron transfer processes with appropriate steps, each event occurring over a fixed dis- redox-active species dissolved in the aque- tance and being driven by a certain ther- ous phase on either side of the membrane. modynamic driving force, provides a means Alternately, see Diagram at (d), the excited for achieving charge separation across the state of the PS might abstract an electron membrane. Subsequent reactions of the oxi- from a donor (D) in the aqueous phase, dised form of the donor (PS') and the forming PS-.. This extra electron can be reduced form of the ultimate acceptor transferred across the membrane to Q, and (Q1')with species dissolved in the aqueous subsequently to A. Such long-range electron phase result in transmembrane charge sep- transfer has been demonstrated in certain aration. This is the basic mechanism whereby modified enzymes, but the reactions are rel- bacterial photosynthetic reaction centres atively slow. operate. Whether or not it will become possible to Third, see Diagram at (c), PS might be held design artificial systems capable of rapid, inside the membrane but close to the aque- long-range electron transfer remains an unan- ous surface. Rather than use a series of swered question. The solution depends crit- exactly-positioned electron relays to shuttle ically on the development of molecular wires.

Platinum Metals Rev., 1996,40, (1) 28 Fig. 3 Molecular structures of the mononuclear ruthenium (11) and trinuclear Runz/M” I complexes. M is cobalt(II), irou(II) or ziuc(II) or a copper(II)-catalysed oxidative self-coupling to be in the region of 175 ns in deoxygenated reaction (Glaser-type homocoupling for the syn- acetonitrile solution at room temperature. thesis of the butadiyne-bridged compounds, see Figure 2). Systems with a Central Cobalt Complex The preparation of mononuclear ruthenium@) In contrast, the triplet lifetimes of the ruthe- complexes, by the selective complexation nium(I1) chromophores in the trinuclear com- of one appended terpyridine with plexes assembled around a central cobalt(I1) [Ru(terpy)(DMSO)CL] (where terpy is bis-terpyridyl complex were observed to be about 2,2’:6’,2”-terpyridine and DMSO is dimethyl- 7 ps. These vastly decreased triplet lifetimes can sulphoxide), allows a series of trinuclear com- be attributed to intramolecular electron trans- plexes to be isolated. These have terminal ruthe- fer from the central cobalt(I1) complex to the nium(I1) bis-terpyridyl complexes connected to triplet state of a terminal ruthenium(I1) com- a central metal (such as cobalt(II), iron(II) or plex; the rate constants for these reactions being zinc(I1)) bis-terpyridyl complex by one or two of the order of 1O”/s. Such reactions can be con- ethynyl groups, see Figure 3. The correspond- sidered to involve transfer of an electron from ing mononuclear ruthenium(II) complexes lack- a d-orbital localised on the cobalt(I1) centre to ing the central metal complex were used as a d-orbital localised on the ruthenium(II1) cen- reference compounds. tre, the latter species arising by way of a metal- to-ligand charge-transfer process associated Electron Transfer in Trinuclear with population of the triplet excited state of Systems the ruthenium(I1) complex, see Panel 4. Laser excitation of these mononuclear com- Conseque‘ntly, the reaction can be formally plexes (1 1) gave rise to the triplet excited state described as a hole-transfer process, and it is of the chromophoric Rum bis-terpyridyl com- important to note that no such reaction occurs plex, which allowed its lifetime to be measured in the dark, see Scheme 1. by transient spectroscopy, see Panel 3. The life- By comparing the measured rate constants for times of these triplet excited states were found hole transfer over one and two ethynyl groups,

Platinum Metals Rev., 1996,40, (1) 29 Panel 2 The rate constant (kb)for light-induced arating the two reactants, by the expression: electron transfer or for triplet energy transfer can be determined by measuring the triplet lifetime (q)of the appropriate mul- Here, k,, refers to the rate constant when ticomponent compound and comparing it the reactants are within orbital contact (that with that of the reference compound (z,) in is R = 0) and p is an attenuation factor (in deoxygenated solution: A-') that describes the electronic resistivity of the intervening medium. When the bridge k, (1ht) - (lh,,) = can be considered as a single chemical entity This method assumes that the difference (for example: an acetylenic function) or an in triplet lifetimes between the two com- homologous series of identical groups (for pounds arises solely from the quenching example: a polyyne chain), p is representa- process of interest, that is by electron or tive of the individual molecular functions that energy transfer. combine to form the bridge and can be Providing that this quenching process expressed in terms of groups, atoms, or bonds involves through-bond electron and/or hole rather than distance. If the bridge is formed transfer (in the case of triplet energy trans- by combination of several different func- fer this requires that the reaction occurs by tionalities, as is the case with protein matri- electron exchange rather than by dipole- ces, p cannot be assigned to individual dipole transfer), the derived rate constant, molecular segments but must be considered kb,can be related to the distance (R),sep- as representative of the whole structure.

it becomes possible to estimate the attenua- suggests that it may be possible to engineer mol- tion factor for hole transfer (P{h}) as being about ecular systems based on polyyne wires which 0.12 /A. This is a rather small attenuation fac- are capable of long-range hole transfer. In fact, tor when compared to other bridging units, and given that the inherent triplet lifetime of a

Panel 3 Excitation by a short duration laser pulse absorbed by the triplet state, giving rise to of the various compounds, at a wavelength a triplet-triplet absorption transition. The corresponding to a reasonably strong absorp- absorption spectrum can be recorded in the tion transition, results in rapid establishment same way as ground-state absorption spec- of the lowest-energy excited triplet state. This tra are measured, while kinetic measurements metastable species may luminesce in solu- can be made at fixed wavelength. tion, as is the case with most ruthenium(I1) This technique is also appropriate for and osmium(I1) polypyridine complexes, recording absorption spectra of other reac- and, if so, the triplet lifetime is conveniently tion intermediates and for determining their measured by he-resolving the luminescence lifetime under particular conditions. Such decay. measurements can be made on time scales This technique works very well provided as short as 100 fs, and other detection modes the triplet lifetime is not too short (that is z (for example, resonance Raman, infrared, > 100 ps) and that the luminescence can circular dichroism, or EPR) can be used. be properly resolved from background light. In this manner, it becomes possible to fol- In other cases, the triplet state can be detected low the course of a photochemical reaction, by transient absorption spectroscopy. Here, to monitor kinetic parameters for important a second photon, delivered by a delayed laser intermediates, and to idenufy major reaction pulse or from a continuous light source, is pathways.

Platinum Metak Rev., 1996,40, (1) 30 Panel 4 The primary reason for using transition ligand. Furthermore, conjugation between metal complexes such as ruthenium(I1) bis- the aromatic residues and the bridging terpyridyl as photosensitisers in these sys- polyyne provides an extended n*-orbital in tems concerns the realisation that their low- which the electron can reside. In this respect, est energy excited states are of metal-to-ligand the MLCT transition can be considered to charge-transfer (MLCT) character. In fact, be vectorial. the singlet excited states tend to be extremely short lived and photochemistry is restricted to the triplet manifold. Under illumination with visible light, an electron is transferred from the metal centre to one of the co-ordinated ligands, resulting in the transient formation of a ruthenium(II1) centre and the n-radical anion of the ligand, see Diagram. W For symmetrical complexes, there is no preference as to which ligand becomes reduced and the electron may be delocalised over the entire ligand field. However, for !IhV asymmetrical complexes there will be pref- erential reduction of the most-easily reduced ligand and the electron will be localised at this ligand. This is the case with ethynyl-substituted terpyridyl ligands, which are reduced pref- erentially to the correspondingunsubstituted

terminal ruthenium(I1) complex is

I I about 175 ns and that P{h} - 0.12/A,we can calculate that light- induced hole transfer could occur hvl over a distance of 85 A with an efficiency of 50 per cent, in such systems. The redox products formed dur- <={ >-<= ing this reaction have been detected by transient absorption spectroscopy and their lifetimes were Scheme 1 found to be around 130 ps (1 1). Decay of these species occurs by way of intramolecular charge recombination in which the electron, resident in a n*-orbital on the terpyridyl ligand of the ruthenium@) complex, is transferred to the cobalt(I1I) centre, see Scheme 1. Formally, such reactions can be described as electron-transfer processes taking place via LUMOs

Platinum Metals Rev., 1996,40, (1) 31 Panel 5 It is convenient to consider the various reactions in terms of frontier molecular orbital (MO) dia- - grams. The energy levels of the LUMO (lowest unoccupied) and HOMO (high- ...+ est occupied) states for hv each of the metal com- +t plexes, together with those of the polyyne bridge, can 4- be derived for the ground- tt state subunits by electro- L Rull L -x L Rulll (L-X]: chemistry. Selective excitation of the ruthenium@) complex, see Chart A Chart A, adjacent, gener- ates the corresponding triplet excited state, the energy levels of which usually referred to as a "virtual state": differ from those of the ground-state complex by the amount of the excitation energy (ET).Since the triplet state possesses MLCT character, it is useful to describe the triplet as consisting of a ruthenium(II1) centre and with the displaced electron residing in a n*- orbital localised on the ethynyl-substituted terpyridyl ligand. In the cobalt(I1)-containing molecular system, it is energetically favourable for an electron to move from the HOMO localised on Here, we consider that the ruthenium(II1) the cobalt(I1) centre, thereby forming a centre abstracts an electron from the bridge cobalt(II1) site, to the ruthenium(II1) cen- (Y). The resultant positive charge can migrate tre, hence restoring the starting ruthenium@) along HOMOs localised on the bridge by species, see Chart B. This electron-transfer way of individual ethynyl groups. Electron step takes place via HOMOs situated on the abstraction from the cobalt(I1) centre gives bridge and, consequently, may be termed as rise to the final state. For this "superex- "hole transfer". change" mechanism to operate, it is impor- The reaction can be written in terms of the tant that the energy of the bridge is less than following (hypothetical) intermediate state, that of the metal-centred reactants, so that

Platinum Metals Rev., 1996,40, (1) 32 Panel 5. continued the proposed Y' species does not appear as bridge. The electron can migrate along the a real redox intermediate. In the systems bridge until it is transferred irreversibly to described, the overall thermodynamic dri- the cobalt(II1) centre. As for the hole-trans- ving force (AG,")for light-induced electron fer process, LUMOs situated on the bridge transfer from the ruthenium(I1) complex must be at higher energy than those on the to the cobalt(I1) centre is about -0.37 eV. metal complexes, such that Y-does not fig- Subsequent electron transfer from the x- ure as a real redox intermediate. radical anion of the ethynyl-substituted ter- In the corresponding osmium(I1)- and pyridyl ligand co-ordinated at the ruthe- iron(1I)-containing molecular systems, light- nium(I1) centre to the cobalt(II1) site is induced electron transfer between the metal thermodynamically very favourable (AG; = complexes does not take place because of -1.75 eV). This reaction takes place by way unfavourable positioning of the various of LUMOs localised on the bridge and can energy levels. However, the triplet energy be formally described as "electron transfer". gaps for the osmium(I1) and iron(I1) bis-ter- As an extreme approximation, we can express pyridyl complexes are significantly smaller the mechanism as involving the following than that for ruthenium(I1) bis-terpyridyl, virtual state: allowing triplet energy transfer to take place. In this latter process, an electron moves from the osmium(I1) or iron(I1) centre to the ruthenium(II1) cation present in the MLCT triplet state by way of hole transfer through HOMOS localised on the bridge. Simul- taneously, the electron resident in the x*- orbital localised on the ethynyl-substituted terpyridyl ligand is transferred along the bridge to the second (covalently-linked) terpyridyl ligand. This process occurs by way Here, the x-radical anion of the ruthe- of LUMOs localised on the bridge, see below. nium(I1) bis-terpyridyl complex can donate The net result is the formation of the triplet its extra electron, located in a ligand-centred excited state of the osmium(I1) or iron(I1) x*-orbital, to the LUMO associated with the bis-terpyridyl complex.

(lowest unoccupied molecular orbitals) on the therefore, such electron-transfer reactions might bridge and, as outlined above, the attenuation be expected to occur over very large distances. factor for electron transfer (p {e})was estimated to be about 0.04 /A.This is a particularly small Systems with a Central Iron Complex value, indicating that there is a very low bar- In the corresponding trinuclear systems that rier for electron tunnelling through the bridge have a central iron(I1) bis-terpyridyl complex in these systems. In fact, this is the smallest (Figure 3) the triplet lifetimes of the terminal attenuation factor reported for electron tun- ruthenium@) complexes were found to be about nelling through any organic medium; for exam- 10 ps, see Scheme 2. Here, light-induced elec- ple, the protein matrix that surrounds the bac- tron transfer does not take place, instead the terial photosynthetic reaction centre complex triplet state of the chromophoric ruthenium(II) is characterised by p {e} - 1.4/A (12). Clearly, bis-terpyridyl complex transfers its excitation

Platinum Met& Rev., 1996, 40, (1) 33 14+ Fig. 4 Molecular structures of the ethpyl-substituteddinuclear Ru(II)lOs(II) complexes 4 PFg-

energy to the appended iron(I1) complex. This through-bond electron exchange, see Figure 5. intramolecular triplet energy-transfer process As mentioned above for the iron(I1)-contain- takes place via electron exchange and may be ing trinuclear complexes, the attenuation fac- considered to involve molecular orbitals localised tor for triplet energy transfer (P{t}) was esti- on the polyyne bridge. Formally, electron mated to be about 0.17/A. These reactions are exchange corresponds to simultaneous transfer among the fastest yet reported for triplet energy of both an electron and a hole, see Panel 5. It transfer between spatially-remote reactants. is interesting to note that the measured atten- Identical processes take place in an ethanol glass uation factor for triplet energy transfer @{t} - at 77 K and, at both temperatures, triplet energy 0.17/A) corresponds almost exactly to the transfer is quantitative. At room temperature, sum of attenuation factors for electron and hole the magnitude of the electronic coupling matrix transfers. element (VDA)that quantifies the level of elec- The resultant triplet state of the central iron0 tronic coupling between the terminal metal com- bis-terpyridyl complex survives for about 3 ns plexes, was calculated to be about 7/cm for the at room temperature but does not luminesce. case when a single ethynyl group was the bridge. This is a reasonable value, given that the sepa- Ethynyl Group Connections ration distance between metals is about 14 A, Similar studies (8) were made with asymmet- being only a fraction of the available thermal rical binuclear complexes having terminal ruthe- energy at 25°C (210/cm). This value is clearly nium(I1) and osmium(I1) bis-terpyridyl com- sufficient to promote very fast intramolecular plexes connected via ethynyl groups, see Figure electron exchange. 4. In this case, very fast intramolecular triplet These various experiments serve to indicate energy transfer OCCLUS from the ruthenium(I1) that polyynes are very effective bridges for the bis-terpyridyl complex to the covalently-linked promotion of through-bond electron-transfer osmium(1I) bis-terpyridyl complex. Triplet life- and hole-transfer processes between terminal times, measured for the ruthenium(I1) and metal complexes. In particular, the attenuation osmium(I1) bis-terpyridyl subunits in aceto- factor for electron transfer (O.O4/A) is remark- nitrile solution at room temperature are about ably small, even when compared to polyenes 20 ps and 75 ns, respectively. and polyphenyls (8). The observed rates of energy transfer (k - 5 The reason for such efficient electron tun- x lO''/s) are approximately 5,000-fold faster nelling becomes apparent when the photo- than the rates calculated for a through-space physical properties of the corresponding zinc@)- process and are therefore most likely due to containing trinuclear complexes are examined

Platinum Metah Rev., 1996, 40, (1) 34 Fig. 5 Schematic representation of ET through space energy transfer, ET, across one (k = 7.1 rs100ns x 1Yo/.9)and two (k = 5 x 10%) &yne subunitr, at room temperature. The rate of energy transfer through spaee (k = 1 x 107/s)is calculated from the Forster expression for a single ethynyl spaeer

ET through brldge 5 c25ps

(Figure 3). In this case, the energy levels of 4 M. J. Crossley and P. L. Burns, J. Chem. SOC., Chem. Comm., 1991,1569; H. L. Anderson, Inox. the various components are situated such that Chem., 1994,33,972 energy- and electron-transferreactions are ther- 5 P. Binerle, Adv. Maw., 1992,4, 102; S. Hota and modynamically unfavourable. Instead, the triplet K. Waragai, Adv. Mazer., 1993, 5, 896 lifetimes of the terminal ruthenium(I1) bis-ter- 6 J.-P. Collin, P. Laink, J.-P. Launay, J.2Sauvage and A. Sour,J. Chem. SOC.,Chem. Comm., 1993,434 pyridyl complexes (z - 175 ns) are seen to be 7 A. C. Benniston, V. Grosshenny, A. Harriman and markedly enhanced relative to that of the R. Ziesse1,Angew. Chem., 1994,106,1956; Angew. mononuclear complexes (z - 0.56 ns) in deoxy- Chem., Int. Ed. Engl., 1994,33, 1884 8 V. Grosshenny, A. Harriman and R. Ziessel, genated acetonitrile solution. There is also a Angew. Chem., 1995, 107, 121 1; Angew. Chem., substantial lowering of the mplet energy and an Int. Ed. Engl., 1995, 34, 1100 increase in the luminescence yield upon incor- 9 J. M. Lehn, in “Supramolecular Chemistry” VCH, poration of an ethynyl substituent into one of Weinheim, 1995 10 V. Grosshenny and R. Ziessel, Tetrahedron Lett., the co-ordinated terpyridyl ligands. 1992,33,8075;3 Chem. SOC.,Dalwn Tmns., 1993, Such effects are entirely consistent with selec- 8 17; J. Organomet. Chem. 1993,453, C 19 tive promotion of an electron from the ruthe- 11 V. Grosshenny, A. Harriman and R. Ziessel, Angew. Chem., 1995, in press nium(I1) centre to the ethynyl-substituted ter- 12 C. C. Moser, J. M. Keske, K. Warncke, R S. Farid pyridyl ligand within the metal-to-ligand and P. L. Dutton, Nature, 1992, 355, 796 charge-transfer triplet manifold. Conjugation Small-Particle Platinum Catalysts between the ethynyl substituent and the ter- The highly uniform mesoporous aluminosil- pyridyl ligand might enable this electron to reside icate (MCM-4 1) has excellent catalytic prop- in an extended x*-orbital that encompasses both erties but has only recently been studied as a the ethynyl-substitutedterpyridyl ligand co-ordi- support material. nated to the ruthenium centre, and the bridg- Now, however, researchers from Germany have ing alkyne. synthesised platinum-containing MCM-4 1 catalysts via different techniques and tested their The concluding part of this paper is scheduled catalytic performance during the oxidation of to appear in the April 1996 issue of this journal. carbon monoxide in air u. Chem. SOC.,Chem. Commun., 1995, (22), 2283-2284). References Catalyst performance depended on the prepa- 1 D. Gust, Nature, 1994,372, 133 ration method. The best performance was 2 A. C. Benniston, Goulle, A. Harriman, J. M. V. achieved over platinum-MCM-4 1 prepared by Lehn and B. Marczinke, J. Phy. Chem. 1994,98, 7798 incipient wetness, giving platinum particles of 3 A. E. Steigman, V. M. Miskowski, J.W. Perry and size around 2 nm, and 50 per cent carbon monox- D. R Coulter,J. Am. Chem. SOC.,1987,109,5884 ide conversion at temperatures as low as 360 K.

Platinum Metals Rev., 1996,40, (1) 35 Hydrogen Treatment of Materials PALLADIUM STUDIES REPORTED AT A DONETSK CONFERENCE Technological interest in the results of inter- tageous significance, concerned macroscopic actions of hydrogen with metals and with vari- fracturing and powdering together with subse- ous other materials has been concerned with quent reformulation. This topic was introduced both destructive and advantageous structural with particular emphasis on the treatment of alterations. This has been demonstrated by the titanium, titanium alloys and analogous mate- contributions presented at the series of con- rials. However it was also discussed in terms ferences held over recent years in Wyoming, of the beneficial incorporation of hydrogen treat- U.S.A., organised by A. W. Thompson, N. R. ments during the processing of intermetallic and Moody and I. M. Bernstein. electronic materials. These may have relevance The programme of studies pursued by to the solution of problems associated with Professor V. I. Goltsov and his colleagues in hydrogen storage and energy generation, such Donetsk, Ukraine, has tended to concentrate as hydrogen batteries and shape memory devices. on the advantageous consequences resulting Improvements in kinetic parameters, including from the interaction of hydrogen with various those of diffusion processes, order-disorder materials. Thus at the recent conference on transformations and the formation of specifi- Hydrogen Treatment of Materials, held from cally selected products, resulting from hydro- 20th to 22nd September, 1995, at the State gen treatment were also discussed. Technical University in Donetsk, Professor Goltsov, in a keynote introductory address, high- Further Studies with Palladium lighted the advantages of hydrogen treatment. and Palladium Alloys In many instances this can provide competi- Contributions dealing with studies on palla- tive alternatives to straightforward mechanical dium and palladium alloys were still focused treatment or to other means of processing largely upon their use as hydrogen purifica- materials. tion membranes and in particular chemical Considering the rather specific subject matter processes where their specific catalytic advan- of this conference, there was an encouraging tages are utilised. In both of these areas the attendance of approximately 100 participants, technological research had two objectives: including representatives from France, Spain, improving the composition of membrane mate- Poland, China, Japan, South Korea, United rials used for various combinations of experi- Kingdom and United States of America, mental conditions, and avoiding the develop- together with representation from ten of the ment of irreversible lattice dimensional and Confederation of Independent States, with most dislocation structural network damage, result- contributors being from Ukraine and Russia. ing from the a * P-phase hydride transitions. In the historically-centred review by Professor The possibility of unwanted dimensional Goltsov, mention was made of various areas changes taking place within membranes during where advantageous results occurring after sequences of hydrogen absorption and desorp- hydrogen treatments had either been initiated tion was again addressed. R. V. Kotelva and col- or further developed. These included improve- leagues from the Technical University in Donetsk ments achieved in some well investigated top- described changes in the shape of a palladium ics, such as in specific cases of structural dam- plate and discussed experimental procedures in age and distortion, embrittlement and even some detail. A further report from Donetsk, pre- softening of metals and alloys. sented by T. A. Ryumishina and colleagues, con- Another previously quite well investigated cerned the evolution of stresses during hydro- research area, included to emphasis its advan- gen diffusion processes in palladium. Associated

Platinum Metals Rev., 1996, 40, (l), 36-37 36 problems of kinetic and morphological pecu- iour to bulk lattice hydrogen diffusion processes, liarities occurring during hydride phase trans- as shown by Gorsky and Diffusion Elastic Effect formations were reported by Yu. A. Artemenko related phenomena, was reported in a paper by and co-workers of Donetsk, while allied mea- R. V. Bucur, Uppsala, Sweden, K. Kandasamy, surements of changes in the mechanical prop- Jafha, Sri Lanka, Y.Sakamoto, Nagasaki, Japan, erties of the palladiudhydrogen system were together with X. Q. Tong and F. A. Lewis, presented by A. P. Kusin and colleagues, also Belfast, Northern Ireland, with particular ref- from the same university. erence to apparent changing trends in the hydro- Further quantitative and theoretical conse- gen diffusion coefficient, D,, with the initial val- quences of the effects of hydrogen expansion ues of the hydrogen content. were discussed. The modelling of hydrogen- Lastly, results of hydrogen isotope structure induced non-elastic deformations was reported analyses by powder X-ray diffraction, for com- by V. N. Madudin and co-workers, Chelyabinsk, positions approximating to PdHo6) PdDo.5and Russia. A paper by Young-sui Cho, University PdTo.s6were reported by T. A. Beiter and J. S. of Kangwon, South Korea, considered the kinet- Cantrell, of Miami University, Oxford, Ohio. ics of hydrogen absorption - determined from A number of the papers presented at this measurements of changes in the electrical resis- Donetsk conference will be published in a spe- tivity of thin palladium films. cial issue of the Znmnatiund3ournd of Hydrogen The importance of stress/straingradient behav- Energy. F.A.L.

Alkane Oxidation by Encapsulated Ruthenium Complexes- The oxidation reaction of alkanes by the usual Encapsulation prevented dimerisation of the metal complex catalysts eventually results in complex and enhanced the activity. Even though deactivation or catalyst degradation. Catalysts, the catalyst now contained less metal, it had over such as porphyrin- or phthalocyanine-based ten times the activity of the homogeneous cat- complexes, can acquire improved stability by alyst. Cyclohexane was oxidised primarily to the a halogenation treatment. However, these sys- ketone at a rate of almost 3000 turnoverdday tems still eventually degrade. Encapsulating cat- and no deactivation was seen after over 20,000 alytic materials within other structures is now turnovers. Placing the RuF16Pcinto the zeolite a routine operation, and has resulted in many increased its selectivity towards cyclohexanone, interesting properties (see, for example, Platinum compared with the homogeneous catalyst. The Metals Rev., 1994, 38, (2), 59) including peroxide efficiency was also improved. enhanced catalytic activity. Therefore, isolating This system may be one of the best low-tem- the phthalocyanine catalyst, to remove it from perature peroxide-based oxidation catalysts. outside attack, by encasing it within zeolite pores was tried as a way to improve its lifetime. Palladium Alloy Mechanical Properties However, there are still drawbacks caused by The mechanical properties of three structural the peroxide and iodosylbenzene oxidants. forms of palladium-manganese alloy, contain- Recent work has involved encapsulatingan iron ing 10 to 25 atomic per cent manganese, have phthalocyanine, FePc, catalyst in zeolite within been examined (D. Jonsen, A. MOSS,J. Shenk, a polymer matrix, and this has been successful K. Rebeiz, S. Nesbit, R. Foley and A. Craft, in producing a more active and stable catalyst. Muter. Sci. Eng., 1995, A199, (2), 131-138). A perfluorinated FePc complex catalyst, how- One form, with L1 structure, produced by the ever, was as sensitive to the oxidant as FePc. presence of hydrogen during heat treating the Based on this researchers at the University alloy, had markedly different properties to the of Texas at Dallas, U.S.A., (K. J. Balkus, M. other two forms; these included enhanced Eissa and R. Levado,J. Am. Chem. Soc., 1995, strength and hardness, reduced ductility and 117, (43), 10753-10754) prepared a fluorinated fatigue life. The differences are thought due to ruthenium phthalocyanine catalyst, RuFI6Pc, the formation of the L1 structure and a hydride and encapsulated it in zeolite NaX. It was used phase in this alloy whose decomposition signif- together with tert-butyl hydroperoxide oxidant icantly affects the properties. The hydrogen- for the oxidation of cyclohexane and cyclo- induced lattice rearrangement may be a way of hexanol at room temperature. manipulating the mechanical properties of alloys.

Platinum Metals Rev., 1996, 40, (1) 37 ABSTRACTS of current literature on the platinum metals and their alloys

PROPERTIES Synergistic Alloying Behaviour of Pd,Cu, Single Crystals upon Adsorption and Co- Magnetic Properties and Co-operative Domain adsorption of CO and NO Structures in Early Stages of Ordering of Y. DEBAUGE, M. ABON, J. C. BERTOLINI, J. MASSARDIER Cobalt-Platinum Single Crystals under and A. ROCHEFORT, Appl. sut$ sci., 1995, 90, (I), Compressive Loading 15-27 N. I. VLASOVA, G. S. KANDAUROVA, N. N. SHCHEGOLEVA, The surface reactivity of Pd,,,Cu,o(1 11) and (1 10) v. v. MAYKOV and A. E. ERMAKOV, Fiz. Metal. Metalh., single crystals was studied during adsorption and co- 1995, 80, (l), 2740 adsorption of CO and NO at low temperatures. CO Magnetic properties and the magnetic domain struc- and NO were more tightly bound to Cu and less tightly ture in various stages of atomic ordering were stud- bound to Pd than to the pure metals. The calculated ied under compression in Copt single crystals. A rela- NO coverages on Pd-Cu were about four times lower tionship between the magnetic properties and the than for CO due to the dissociation of a fraction of domain structure of Copt, which has monocrystalline NO on the surfaces. Presaturation with NO leads to characteristics, is established. A detailed description molecular adsorbed states and irreversible dissociated of the newly discovered magnetic domains in PtCo species not removed during exposure to CO. single crystals is given. Superconductivity and Magnetism in the Specific-Heat Study of Nanocrystalline La,,Nd,Rh,Si, System Palladium N. G.PA% K. GHOSH and s. RAMAKRISH", Phys. Rew. Y. Y. CHEN, Y. D. YAO, S. S. HSIAO, S. U. JEN, B. T. LIN, H. B, 1995,52, (13), 9679-9690 M. UN and C. Y.TuNG, Phys. Rev. B, 1995, 52, (13), The bulk superconductivity in La2Rh,Si,was estab- 9364-9369 lished below 4.4 K together with bulk antiferromag- Studies of the low temperature specific heat for T = netism in Nd,Rh,Si, below 2.7 K, from resistivity, 0.7-20 K and magnetic susceptibilityfor T=1.6-300 susceptibility and heat capacity studies. The super- K of Pd nanocrystals with average particle size 84 A conducting transition temperature of La,Rh,Si, showed an enhancement at T>3.5 K, which is related decreased with Nd substitution for La. The temper- to both the softening and the size effect on the pho- ature dependence of the upper critical field of Nd- tons. The linear temperature coefficient of specific doped La,Rh,Si, alloys was also analysed. heat decreases to a lower value compared to that of bulk Pd. An estimated surface coefficient of the spe- Structure and Magnetic Properties of cific heat is - 30% that of the bulk. Srz+4Jr04 (A= Ca and Ba) T. SHIMURA, Y. INAGUMA, T. NAKAMURA, M. ITOH and Y. Nanoscale Ag-Pd and Cu-Pd Alloys MORII, Phys. Rev. B, 1995,52, (13), 9143-9146 H. N. VASAN and c. N. R. RAO, Mater. Chem., 1995, Substitutions of Ca and Ba for Sr in SrJrO, resulted 5, (lo), 1755-1757 in an increase in the Ir-O(2)-Ir bond angle in the 110, Nanoparticles of Ag-Pd and Cu-Pd alloys with diam- plane. However, the IrO(2) distance was unchanged eters of 5-40 nm were prepared by heterogeneous reac- by Ba substitution, but was decreased by Ca substi- tion of dry MeOH or EtOH with intimate mixtures tution. Semiconductive behaviour of the resistivity of AgNO, + PdO, and CuO, + PdO,, respectively. was displayed by all compounds with increase in acti- The nanoscale alloys have f.c.c. structure. AU the alloy vation energy above 200 K. particles could be obtained in bulk quantities. Deposition and Characterization of Crystalline Synthesis and Hydrogen Permeation Conductive RuO, Thin Film Properties of Ultrathin Palladium-Silver Alloy Q. X. &4, S. G. SONG, S. R. FOLTYN and X.D. W, 3 Mater. Membranes Res., 1995, 10, (lo), 2401-2403 V. JAYARAMANand Y. s. m, J. Membrane Sci., 1995, Highly conductive RuO, thin films were grown on 104, (3), 251-262 (1 00) yttria-stabilised ZrO, (YSZ) substrates by pulsed Ultrathin (250- 500 nm) Pd-Ag alloy films were effi- laser deposition. Epitaxial growth of RuO, thin films ciently deposited on porous ceramic supports by sput- with electrical properties similar to those of bulk sinter deposition. At 250"C,the ceramic-metallic mem- gle crystal RuOz was obtained. The crystalline RuO, brane showed a H:N separation factor of 5.69, which thin films, deposited at 500-7OO0C, had a room increases with permeation temperature. Under suit- temperature resistivity of 35 f 2 acm,and residual able preparation conditions, a pinhole-free y-Al,O, resistance ratio of - 5. The RuO, films have much support ensures the gas-tightness and high selectiv- lower resistivity and a higher residual resistance ratio ity of the coated Pd-Ag membrane. than polycrystalline ones.

Platinum Metals Rev., 1996, 40, (l), 3845 38 CHEMICAL COMPOUNDS Iridium Complexes with a-Diimines:Catalytic Hydrogen Transfer from Isopropanol to The First Reported Structure of a Cyclohexanone Platinum( IV) Complex Containing M. BIKRANI, L FWAEO and M. A. GARRALDA, polyhedmn, Deprotonated Amide Ligands - A Model for 1996, 15, (l), 83-89 Platinum(IV)-PeptidelProtein Interactions Ir complex [Ir(COD)Cl], (COD = 1,5-cyclooctadi- C. J. CAMPBELL, A. CASTINEIRAS and K. B. NOLAN, J. ene) reacting with a-diimines (LL) derived from gly- Chem. SOC.,Chem. Commun., 1995, (19), 1939-1940 oxal (GLL) or biacetyl (BLL) gave different types of Unexpected product cis-Pt(LH-,)Cl, and also compounds depending on the ligand and on the sto- H,L[PtCl,] were formed by reaction of 1,2-diamino- ichiometric ratios used; [Ir2(COD),C12(GLL)]or ethane-N,N,N’,N-tetra(N-methy1acetamide)L with IrCl(COD)(LL) were formed when the ratio K2[PtC1,]in aqueous solution. This Pt(IV) complex, [Ir(COD)Cl],:GLLis 1:l or 1:2, respectively. In the which contains deprotonated amide ligands, is novel presence of bulky anions, cationic [Ir(COD)(LL)]A and is used as a model for Pt(1V)-peptide/protein species, which had high activity, were formed. interactions. The formation of Pt(IV) complexes from the corresponding Pt(I1) systems, even when two or New Homoleptic Metal Carbon7 I Cations: the more deprotonated amide groups are present, is new. Syntheses, Vibrational and C MAS NMR Spectra of Hexacarbonyl-Ruthenium(II) and A Strongly Fluorescent Organoplatinum -Osmium(II) Undecafluorodiantimonte(V), Complex [Ru(CO)~][SbzFll]z and [os(co)6][SbzFll]z K.-T. AYE and R. J. PUDDEPHATT, Inorg. Chim. Acta, C. WANG, B. BUY, G. BALZER-JOLLENBECK, A. R. LEWIS, 1995,235, (1-2), 307-310 s. c.SIU, H. WILLNER and F. AUBKE,~ Chem. SOC.,Chem. A novel organo PtOcomplex, [PtBrMe,(4-CHZ-7- Commun., 1995, (20), 2071-2072 MeO-coumarin)(phen)], where phen = 1,lO-phenan- In a simple, one-step procedure, new homoleptic car- throline, was prepared and characterised. The bony1 cations [RU(CO),]~’and [Os(CO),]” were coumarin substituent causes the complex to fluoresce obtained as [Sb,F,,] salts by the reductive carbony- strongly in fluid solution at room temperature. The lation of M(SO,F)? (M = Ru, Os), under very mild emission appears to originate from the excited state conditions of 1 atm CO and at 60-90°C. These which is centred on the coumarin substituent. [M(CO),] [Sb,F,,], salts are thermally stable. Structure of Polynuclear Hydroxo Complexes of Palladium(I1) Formed by Alkaline ELECTROCHEMISTRY Hydrolysis of Its Chloride Complexes Formation and Reduction of Hydrous Oxide S. YU. TROITSKII, A. L. CHUVILIN, D. I. KOCHUBEI, B. N. Films on Platinum in Aqueous Solution at NOVGORODOV, v. N. KOLOMIICHUK and v. A. 273 K LIKHOLOBOV, Izv. Akad Nauk Rossi, Set Khim., 1995, L. D. BURKE and D. T. BUCKLEY, J. Appl. Electrochem., (lo), 1901-1905 1995, 25, (lo), 913-922 The structure of polynuclear hydroxo complexes of Studies of Pt hydrous oxide deposits, produced by Pd” (PHC) formed by alkaline hydrolysis of Pd” chloro potential cycling, with a lower limit of 0.2 V, in acid complexes was studied. The PHC particles were found solution at 273 K, showed two reduction peaks which to be filaments containing - 100 Pd atoms which were were attributed to the presence of the two oxide com- curled into a ball. The filaments consist of square- ponents, H01 and H02. Thick hydrous oxide films planar PdO, units linked via one or two 0-bridges, were formed at 273 K, with - 0.25 V lower limit, giv- the latter increases in number with PHC ageing. The ing a nearly pure H02 deposit, but thinner deposits interatomic distances around the I’d atoms, the size of either HO 1 or mixtures of HO 1 + H02 were formed distribution of the PHC, and photomicrographs of using a value of > - 0.45 V for the lower cycling limit. the PHC particles adsorbed on graphite were obtained. In Situ FTIR Spectroscopy Characterization Selectivity in the Aliphatic Palladation of of the NO Adlayers Formed at Platinum Single Ketone Hydrazones. An Example of Crystal Electrodes in Contact with Acidic Palladium-PromotedIntramolecular Addition Solutions of Nitrite of a N,N-Dimethylhydrazone to an Alkene A. RODES, R. G6MEZ, J. M. ORTS, J. M. FELIU, J. M. PkREZ D. J. ChENASand A. M. ECHAVARREN, &gUfZOmetdkCS, andA. ALDAZ, Langmuz’r, 1995,11, (9), 354-3553 1995, 14, (9), 44274430 Adsorbed NO was formed on the Pt(100), Pt(ll1) A y,&unsamrated dimethylhydrazone reacted with and Pt(ll0) basal planes of Pt single crystal electrodes Pd(PPh,)2ClZto yield a palladacycle which resulted from acidic nitrite solutions. The effect of the elec- from the addition of the imino group to a (@-alkene)Pd trode potential on the N-0 stretching frequency was complex. The nucleophilicity of the hydrazone imino lower for NO adsorbed on the Pt( 110) electrode than N diminishes the efficacy of the aliphatic pallada- for Pt(ll1) and Pt(100). N,O was detected as an inter- tion giving no benzylic or allylic C-H activation. This mediate during the reduction of nitrous acid at 0.6-0.4 is the first example of intramolecular attack of the V on Pt( 100). At potentials of > 1.10 V, both adsorbed imino N of a hydrazone to an alkene promoted by Pd. NO and nitrous acid in solution oxidised to nitrate.

Platinum Metals Rev., 1996, 40, (1) 39 Electrochemical Deposition of Hydrogen on The Electrochemical Permeation of Hydrogen Platinum Single Crystals Studied by Infrared- in Palladium: Boundary Conditions during Visible Sum-Frequency Generation a Galvanostatic Chargingunder Low Charging A.PEREWS andA.TADJEDDINE,J Chm. &JS.., 1995, Current Densities 103, (16), 7197-7203 P. MANOLATOS, c. DURET-THUAL, J. LE COZE and M. Vibrational patterns of the hydride surface were mon- JEROME, Corros. &i., 1995, 37, (11), 1797-1807 itored during under- and overpotential deposition The electrochemicalpermeation of H in Pd was stud- of H, on polycrystalline Pt, Pt( loo), Pt( 1 10) and ied and was easier than H permeation in steel. Total Pt( 111) surfaces in H,SO, by IR-visible sum-frequency oxidation of the H diffusing through the I'd sample generation (SFG). For Pt(100) and Pt(l1 l), the occurred, giving H efficiency of - 100%. The diffu- observed double SFG resonance was most consistent sion coefficient was evaluated as 7 x 10 ' cm'ls. Using with a bonding configuration in which HzO dimers electrochemical H permeation in Pd, the metal sur- are each bonded to three H atoms adsorbed on the face phenomena can be controlled and stationary con- relaxed substrate. Significant H adsorption was ditions and good reproducibility can be obtained. detected on Pt(ll1) in H2S04electrolyte at under- potentials as high as 0.35 V/NHE. Oxygen Evolution and Reduction on Iridium Oxide Compounds Kinetics of Dissociative Adsorption of Formaldehyde on a Pt(ll1) Electrode in M. V. TEN KORTENAAR, J. F. VENTE, D. J. W. IJDO, S. M-R and R. KOTZ, J. Power sources, 1995, 56, (l), 51-60 Sulphuric Acid Solutions Studied Using a Studies of the electrochemical properties of twelve Programmed Potential Step Technique and Ir oxide compounds during the 0-evolution reac- Time-Resolved Fourier Transform IR tion (OER) and the 0-reduction reaction (ORR) Spectroscopy showed that Pb,(Pb,Ir, 30, and Nb,IrO, compounds S.-G. SUN, G.-Q. LU and Z.-W. TIAN,J Electroanal. Chem., had the highest activity for both reactions. Steady- 1995,393, (1-2), 97-104 state current-potential curves were measured in 45% Quantitative studies of the kinetics of the dissociative KOH. The catalytic activity of pyrochlores towards adsorption of HCHO on a Pt( 1 1 1) electrode showed the ORR is more dependent on the presence of a Pb the initial rate was around 10 "mol/cm2s, and pro- or Bi cation than is the catalytic activity towards OER. ceeded as follows: HCHO adsorption onto the Pt(ll1) surface; interaction of adsorbed HCHO with the Electrochemical Promotion of IrO, Catalyst Pt(ll1) surface; breaking of chemical bonds and for the Gas Phase Combustion of Ethylene the formation of the final products. The products con- E. VARKARAKI, J. NICOLE, E. PLATITER, C.C0M"ELLI.S sisted of linear and bridge bonded CO. At -0.25 to and C. G. VAYENAS, J. Appl. Electrochem., 1995, 25, 0.25 V, the rate of dissociative adsorption of HCHO (lo), 978-981 on Pt(ll1) displayed a volcano curve with two max- An increase by up to a factor of 10 in the catalytic halocated at -0.06 and 0.15 V, respectively. activity of IrO, catalyst films for the gas phase combustion of ethylene was achieved via anodic polari- Preparation and Chemical Reduction of sation of the IrO, catalyst relative to a Au electrode, Pt(1V) Chloride-GICs: Supported Pt vs Pt both deposited on Y,O,-stabilised ZrO, solid elec- Inclusion Graphite Compounds trolyte. The steady state increase in the catalytic reac- J:Y. T!J@UIN, R COT$., G. VEILLEUX, D. GUAY, J. P. DODELET tion rate was 200 times higher than the expected and G. D&S, Carbon, 1995, 33, (9), 1265-1278 rate increase of ethylene combustion, calculated from Pt(1V) chloride-graphite intercalation compounds Faraday's law. This is the first example of the effect (M-GICs) were prepared from pm sized graphite pow- of non-faradaic electrochemical modification of cat- der and were subsequentlychemically reduced. PtO alytic activity (NEMCA) using a metal oxide catalyst. chloride-GIC was obtained by isothermal vapour transport of PtClnat 350-500°C under C1, gas pres- Mass Transport Study of Nafion'@Coatings sure in a very slow process. PtCl, or PtCl, is also Saturated with [O~(bpy)~]" by an intercalated in graphite after the reaction of H,PtCl, Electrochemical Quartz Crystal Microbalance with graphite in SOCl, for 2 days under Ar. M. SHIN, E.-Y. KIM,J. KWAK and I. C. EON, 3 Electroanal. Chem., 1995,394, (1-2), 87-92 Electro-Oxidationof D-Sorbitol on Platinum Studies of mass transport behaviour in [O~(bpy)~]~'- in Perchloric Medium: A Voltammetric Study saturated Nafion coatings on an electrode showed that I. FONSECA, M.I. S. LOPES, J. L. SANTOS and L. PROENCA, the mass of the electrodes varies with the number of Electrochim. Acta, 1995,40, (17), 2701-2706 cycles, during cyclic voltammetry, after the start of The electrocatalytic oxidation of D-sorbitol on a poly- the potential scan and approaches a steady state. The crystalline Pt electrode, in perchloric aqueous medium, first cyclic voltammogram showed an anodic peak was studied by cyclic voltammetry under different at - 0.85 V vs. Ag/AgCl, corresponding to ejection sweep rates, potential limits, stirrings, temperature, of [O~(bpy),]~+complexes, while the frequency change- pH and D-sorbitol concentrations. A value of - 50 potential curve showed an increase in mass on the first kJ/mol was obtained for the apparent activation positive scan. This is explained by the H,O and the enthalpy of the oxidation reaction at 0.1 V. [Os(bpy)J" complexes moving in opposite directions.

Platinum Metals Rev., 1996, 40, (1) 40 PHOTOCONVERSION Photo-Splitting of Water to Dihydrogen and Hydroxyl Radicals Catalysed by Rhodium- Photocatalytic Hydrogenation by Using Deposited Perfluorinated Poly@-phenylene) Platinized Titanium Dioxide for Carbon- T. KITAMURA, K. MARUO, Y. WADA, K. MURAKOSHI, T. Carbon Double Bonds of Linoleic Acid AKANO and S. YANAGIDA, 3. Chem. soc., Chem. A. A. WIDODO, K. MINE, T. KATO and Y. BUTSUGAN, Denki Commun., 1995, (7), 2189-2190 Kagaku, 1995,63, (7), 678-679 Perfluorinated poly(p-phenylene) (1) with colloidal The hydrogenation of linoleic acid using WiO,pho- Rh metal deposited on it catalysed the photosplitting catalyst had oleic acid as an intermediate. Pt was pho- of HzO under W irradiation to H,and hydroxyl rad- todeposited onto TiO, to increase the H, evolution icals which were scavenged by benzene to give phenol. rate. Hydrogenation on the Pt occurred smoothly in Rh was an effective mediator for irreversible electron the presence of H, in the dark. A 100% yield in stearic transfer from (l), and benzene as hydroxyl scavenger acid formation from oleic acid was detected, after using was also important in the heterogeneous photocat- Pt/TiO, in EtOH. The irradiation time was 20 h. alytic H,O-splitting reaction. Effect of Platinum Loading on the Photooxidation of Ru(bpy)(CN)l- and Photocatalytic Activity of Cadmium(I1) Ru( DMbpy )(CN),2- Sulfide Particles Suspended in Aqueous Amino A. OLmCZKY and A. HORVATH, Inorg. Chim. Acta, 1995, Acid Solutions 236, (1-2), 173-176 B. OHTANI, J. KAWAGUCHI, M. KOZAWA, Y. NAKAOKA, Y. The photophysical and photochemical properties of NOSAKA and s. NISHIMOTO,J. Phowchem. Photobiol. A: Ru(bpy)(CN)," (1) and Ru(DMbpy)(CN)," ,where Chem., 1995, 90, (l), 75-80 bpy = 2,2'-bipyridine and DMbpy = 4,4'-dimethyl- Loading small amounts of Pt by colloidal deposition 2,2'-bipyridine, are reported. The luminescencequan- or PtO, by mechanical mixing, onto CdS particles tum yields of the lowest energy d-A* state are (8 ? inhibited the photocatalytic racemisation of L-lysine 1) x 10 ' and (7 2 1) x for the bpy and DMbpy in aqueous suspension at ambient temperature under complexes, respectively, in aqueous solution at ambi- deaerated conditions, but promoted deamino-N-cycli- ent temperature. Lifetimes are 125 and 115 ns, respec- sation of L-lysine into pipecolinic acid. Less than tively, and luminescence lifetimes increase - 3-fold in 0.3 wt.% of colloidally deposited k is needed to sep- DzO.Photolysis of (1) was also studied in chloroform. arate the surface reaction sites, but a larger amount of mechanically deposited PtO, is needed. Laser Flash Photolysis and Matrix Isolation Studies of Ru[R,PCH~CH,PR~]~H,(R = C,H,, Cadmium Sulfide with Iridium Sulfide and C,H,, C,F,): Control of Oxidative Addition Platinum Sulfide Deposits as a Photocatalyst Rates by Phosphine Substituents for the Decomposition of Aqueous Sulfide L. CRONIN, M. C. NICASIO, R. N. PERUTZ, R. G. PETERS, D. I. B. RUFUS, B. VISWANATHAN, v. RAMAKRISHNAN and J. M. RODDICK and M. K WHlTTLESEY, 3 Am. Chem. soc., c.KURIACOSE,J. Phwchem. Phwbiol. A: Chem., 1995, 1995,117, (40), 10047-10054 91, (l), 63-66 The primary photoproducts of the title Ru hydrides, Studies of the effect of the in situ deposition of Pt and Ru(drpe),H, (drpe = depe, dppe and dfepe), respec- Ir on CdS during photocatalytic decomposition of tively, are the 4-coordinate complexes Ru(drpe),, and aqueous sulphide showed the formation of a very effec- their multiband UV-visible spectra are characterisuc tive bifunctional photocatalyst MStCdStM, where MS of a structure close to square planar for Ru(dmpe),, is Pt or Ir sulphide and M is Pt or Ir. The order of Ru(depe), and Ru(dppe),. The reactivity of the com- reactivity for the metallisauon of CdS by the above plexes increased in the order: Ru(dfepe)z< Ru(dppe), method is: Rh > Pt > Pd > Ru = Ir > Co= Ni = Fe. < Ru(depe), < Ru(dmpe)?. The rate constant of each This method avoids oxidation of the metals by air. Ru(drpe), complex increased with substrate, in the order C,H, < CO < HZ,but the selectivity toward sub- Hydrogen Production from Water by Visible strates was greater for Ru(depe), and Ru(dppe),, than Light Using Zinc Porphyrin-Sensitized for Ru(dmpe),. Platinized Titanium Dioxide Photoelectrochemical Properties of RuS2- E. A. MALINKA, G. L. KAMALOV, S. V. VODZINSKII, V. I. MELNIK and z. I. ZHILJNA, J. Photochem. Phowbwl. A: Coated Ti0, Electrodes Chem., 1995, 90, (2-3), 153-158 M. ASHOKKUMAR,A. KUDO and T. SAKATA, Bull. Chem. The rate of H, evolution from aqueous suspensions SOC.Jpn., 1995,68, (9), 2491-2496 of Pt/TiO, with deposited Zn porphyrin in the pres- RuS,-coated TiO, electrodes displayed semiconduc- ence of an electron donor, EDTA, uiethanolamine, tor sensitisation by RuS, fine particles on TiO, dur- etc., during visible-light irradiation was optimised ing photoelectrochemical studies. The electron-trans- with respect to the concentrationsof Pt, Zn porphyrin fer efficiency from RuS, to TiO, was affected by the and electron donor. H, production increased sharply number of RuS, colloid coatings and the prepara- in alkaline solutions when triethanolamine molecules tion temperature of the RuS, colloids. A band-gap were deprotonated. Photostability is increased on the value of around 2.8 eV was evaluated for the RuS, semiconductor. particles with high sensitisation efficiency.

Platinum Metals Rev., 1996,40, (1) 41 ELECTRODEPOSITION AND Palladium-Doped Screen-Printed Electrodes SURFACE COATINGS for Monitoring Formaldehyde J. WANG, M. PEDRERO and x. CAI, Analyst, 1995, 120, Some Experiences with a Platinum-Plated (7), 1969-1972 Titanium Anode for Chromium Electro- Disposable amperometric sensors for HCHO detec- deposition tion were fabricated by screen printing Pd-doped C R M. KRISHNAN, S. SRIVEERARAGHAVAN, S. JAYAKFUSHNAN strips. These sensors rely on the strong electrocatalytic and s. R NATARAJAN, Met. Finkh., 1995,93, (9), 4648 action of the dispersed Pd particles in reducing the The behaviour of Pt-plated Ti anodes was studied HCHO. The low detection limit of 2 x 10 ' mom was in three different Cr electroplating solutions. A Ti accompanied by a wide linear range and high selec- sample was Pt plated in a dinitrito platinous acid bath tivity. These single-use sensor strips allow on-site envi- at a pH of 1.&1.5,70"C, current density of 5 Mcm', ronmental and industrial HCHO monitoring. using a Pt wire as an anode, to a thickness of 5 pm. H2-InducedSurface and Interface Potentials The Pt/Ti electrode is most suitable for use in on Pd-Activated SnOz Sensor Films conventional Cr plating baths. J. MIZSEI, Sens. Actuators B, 1995, 28, (2), 129-133 Novel Preparation of PdNycor Composite The surface and interface potentials of an SnOr gas- Membranes sensor film were studied by vibrating capacitor and K. L. YEUNG, J. M. SEBASTIAN and A. VARMA, Catal. To*, other methods. Ultra thin, 2-5 nm, Pd films were 1995,25, (3-4), 231-236 sputtered as activators onto the Sn02layer. The work Pd film plated onto porous Vycor glass was prepared function of the Pd particles affects the charge-car- by electroless plating from typical hydrazine-based rier concentration directly at the Pd-SnO, Schottky and formaldehyde modified baths. Two methods of barriers, and indirectly by capacitive coupling between improving the Pd Nm quality by modlfylng the plat- the Pd surface and Pd-free areas. The work-func- ing solution and by osmosis were tested. The elec- tion change of the Pd surface layer controls the car- troless Pd film obtained from the modified bath has rier concentration change, and thus the specific resis- a higher lustre and density, and smaller grain size. By tivity change in the whole layer. combining electroless plating and osmosis, the Electrocatalytic Oxidation and Amperometric microstructure of the Pd film can be manipulated to Detection of Aliphatic and Furauic Aldehydes give both porous and dense films. at a Mixed-Valent Ruthenium Oxide- Ruthenium Cyanide Film on Glassy Carbon APPARATUS AND TECHNIQUE Electrodes Performance of Platinum-Based Spherical T. R. I. CATALDI, c. CAMPA and D. CENTONZE, Anal. Mercury Microelectrodes in Cyclic Chem., 1995,67, (20), 3740-3745 Voltammetry and Stripping Analysis A chemically modified glassy C electrode, with a mixed M. A. BALDO, s. DANIELE, M. CORBETTA and G. A. valent RuO-RuCN inorganic film was constructed MAZZOCCHIN, Electroanalysas, 1995,7, (1 0), 980-985 and tested for the electrocatalytic oxidation of aliphatic and furanic aldehydes, such as 2-furaldehyde, etc., in The cyclic voltammetric (CV) and anodic stripping acidic media. Such electrodes were used in cyclic voltammetric performance of spherically shaped Hg voltammetry and flowing streams amperometricdetec- microelectrodes, formed by electroreduction of Hg tion, and could catalyse the slow electrode reaction onto an inlaid Pt microdisk of radius r, and charac- of the aldehydes. Low levels of RuC1, and &Ru(CN), terised by different Hg drop heights h, with h:r ratios in the mobile phase improved the response stability. of 0.1-2, were tested in solutions containing Pbz+and Cd" in NaCl and NaCIO, + HCIOl as supporting electrolytes. For CV the results depend on h:r. The HETEROGENEOUS CATALYSIS thickness of the Hg deposit on the Pt microelectrodes affected the analysis of low Cd levels in H,O. The Hydrogenation of Naphthalene with PlatinumlAlumina- Aluminum Phosphate Measurement of Pt Electrode Surface Area of Catalysts Automotive ZrO, Oxygen Sensors T.-C. HUANG and B.-c. KANG, Ind. Eng. Chem. Res., R. K. USMEN, E. M.LOGOTHETIS and M. SHELEF, Sens. 1995, 34, (9), 2955-2963 Ac~u~~o~sB, 1995,28, (2), 139-142 A WAAF'x catalyst, where AAP is Al,O,-AI phosphate The application of a very sensitive CO methanation and x is the Al:P atomic ratio, was used as a hydro- method is described for measuring Pt loading and dis- genation catalyst to reduce the aromatic content in persion on the outer sensing electrode of commer- diesel fuels. It showed better activity but lower cis- cially heated exhaust-gas 0, sensors. The Pt disper- Decalin selectivity than Pt/y-Al,O,, due to the higher sion was determined using the methanation of acidity of the AAPx support. The catalysts with 6 < adsorbed CO with H, by measuring the amount of x < 10 displayed the highest hydrogenation activity CH, formed using a flame ionisation detector. In all and the lowest &-Decalin selectivity of all the WAAPx sensors, the Pt dispersion was very low, with only 1-3 catalysts. For x = 3 a large pore size catalyst with good atoms in 10' directly accessible to the gas phase. hydrogenation activity is obtained.

Platinum Metals Rev., 1996,40, (1) 42 The Thioresistance of Platinum/Aluminum Total Combustion of rn-Xylene over Palladium Borate Catalysts in Aromatic Hydrogenation Catalysts Supported by Stainless Steel Flakes T.-C.HUANGandB.-c.KANG,JMol. cad., 1995,103, L. BORK~,z. SCHAY and L. GUCZI, Appl. Catal. A: Gen., (3), 163-174 1995,130, (2), 157-174 PtlABx and PtlBx-Al,O, catalysts, where AB is A1 The ignition temperature of the combustion of m- borate, have higher hydrogenation activity and S tol- xylene mixtures over metdlic Pdktainless steel flakes erance than Ptly-Al,O, (1) due to the higher acidity catalyst was lowered by - 330"C, compared to that of of the supports. The addition of B to (1) improved thermal oxidation, in order to study the total com- the catalyst hydrogenation activity and S tolerance of bustion of m-xylene. High and low activity states were the catalyst due to the increasing acidity of the sup- observed during ignition at 20WEO"C and - 400°C, ports. The Pt metal distribution affects the S toler- respectively. Combustion in the high activity state was ance of (1). These studies were performed during initiated by the catalyst, this was followed by a chain naphthalene and benzothiophene dissolution in n- reaction which propagated into the gas phase. Active hexadecane to simulate the aromatics and S com- species which accumulated on the surface during the pounds in diesel fuels. induction period before combustion, were thought to be responsible for this process. Study of Pt-Promoted cobalt CO Hydrogenation Catalysts Ruthenium Catalysts on Fullerene C, for D. SCHANKE,S. VADA, E. A. BLEKKAN, A. M.HILMEN, A. Ammonia Synthesis HOFFandA.HOLMEN,J Caral., 1995,156, (I), 85-95 Y. IZUMI, s. HIKAZUDANI and K.-I. m,Shokubai, 1995, The effect of small amounts of Pt on supported Co 37, (6), 466469 catalysts was studied on samples prepared by co- NH,synthesis was performed over Ru,-CsrCs+/SiO, impregnation of 9 wt.% Co and 0 or 0.4 wt.% Pt on (1) catalysts prepared by the reaction of Ru,(CO),~ Al,O, or SO,. At 483 K, 1 bar pressure and H,: CO with CG0followed by impregnation on Cs'/Si02. The = 7, CO hydrogenation rates for Pt-modified cata- rate of NH,synthesis was a maximum at the ratio Cs' lysts were 3-5 times higher than those on the unmod- : Ru, = 1.5 for (l), containing 2.7 wt.% Ru and 9.8 ified ones. The Pt strongly affected the reducibilityof wt.% C, and was higher by a factor of 7.0 than the the catalysts; this was most pronounced on the AL0,- maximum rate for C, free (1) (Cs': Ru, = 20). The supported catalysts due to the reduction of highly dis- promotion mechanism is discussed in terms of the persed surface co oxides. The dispersion of metal- structural effect of C, to bind the smaller Ru active lic Co on Pt modified catalyst also increased. species, particle size < 10 A, and of the electronic effect of C, as the electron transport medium for (1). Hydrocarbon Synthesis from CO and H, on (Fe + Pt)/SiO, Catalysts HOMOGENEOUS CATALYSIS v. I. KOVALCHUK and B. N. KUZNETSOV, J Mol. Catal. A: Chem., 1995, 102, (2), 103-110 A Novel PtCl,-Catalyzed Cyclorearrangement Catalytic and adsorption properties of (Fe + Pt)/SiO, of Ally1 Propynyl Ethers to 3-Oxabicyclo catalysts were studied on catalysts prepared by co- [4.1.0] Heptenes impregnation of SiO, with aqueous solutions of FeCI, J. BLUM, H. BEER-- and Y.BADRIEH, 3 &g. chem., and H,PtCL. Fe-Pt particles of size 5-36 nm and b.c.c. 1995, 60, (17), 5567-5569 or f.c.c. crystal lattice were formed during reduction of the catalysts by flowing Hz. Bimetallic cata- A one-pot synthesis of 3-oxabicyclo[4.1 .O]hept-4-enes lysts had higher specific activity for the CO hydro- (1) by cyclorearrangement of ally1 propynyl ethers (2) genation reaction than monometallic ones, and the using a catalytic amount of PtCl, in O,-free benzene increased activity of the Fe-Pt particles was shown by during brief treatment at room temperature is reported. increased formation of C,, olefins. The transformation of (2) to (1) involves formation of Pt-allene intermediates. With [(CO,)Rh(p-Cl)], the Promoter Effect of Pd in Hydrogenation of oxabicycloheptenes give cyclopropane-ring cleavage. 1,3-Butadiene over Co-Pd Catalysts Asymmetric Hydroformylation of Styrene A. ShKhY,Z. ZSOLDOS, G. STEFLER,J. W.HIGHTOWER with ptc1,(Atropoisomeric Diphosphine)/SnC12 and^. GUCZI,~Catal., 1995, 157, (l), 179-189 Systems The effect of adding 0.1-1.0 wt.% Pd to 5 wt.% Co/Al,O, was studied during the hydrogenation of A. SCRIVANTI,s. ZEGGIO,v. BEGHETTO and u. pure 1,3-butadiene and butadiene in a mixture with MATTEOLI,J Mol. Card., 1995, 101, (3), 217-220 1-butene at room temperature. The presence of Pd A Pt chiral complex [PtCl,,{(S)-(-)-MeOBIPHEP}] increased the reducibility of the Co, and separate alu- (l), where MeOBIPHEP is the ampoisomeric diphos- minate, Co, and Pd-Co bimetallic surface phases were phine 2,2'-bis(diphenylphosphino)-6,6'-dimethoxy- identified. Increasing the Co : Pd ratio decreased the 1,l'-biphenyl, was produced and its catalytic activ- formation of n-butane at room temperature relative to ity was examined. In the presence of SnCl,, the Pt the rate of butadiene conversion. The improved selec- chiral complex was an efficient catalyst for the asym- tivity was achieved at the expense of increased olefin metric hydroformylationof styrene. The effects of CO isomerisation and deactivation caused by the accu- and HI partial pressures on the catalytic activity of the mulation of carbonaceous residues on the surface. (l)/SnCl, system were also studied.

Platinum MeraLF Rev., 1996,40, (1) 43 New Synthetic Applications of Water-Soluble Hydroformylation with Water- and Methanol- Acetate PdlTPPTS Catalyst Generated in Soluble Rhodium CarbonyVPhenyl-Sdfonato- Situ. Evidence for a True Pd(0) Species alkylphosphine Catalyst Systems. A New Intermediate Concept for the Hydroformylationof Higher C. AMATORE, E. BLART, J. P. GENET, A. JUTAND, S. Molecular Olefins LEMAIRE-AUDOIRE and M. SAVIGNAC, J. Org. Chem., s. KANAGASABAPATHY, z. m,G. PAPADOGIANAKIS and 1995,60, (21), 6829-6839 B. FELL,J. Frakt. Chem., 1995, 337, (6), 446450 The H,O-soluble catalyst, prepared in situ from A Rh carbonyl/tertiary phosphine complex catalyst Pd(OAc), and P(C&-m-SO,Na),, is an efficient cat- system, soluble both in MeOH and H,O, was used alyst for sp-sp and s~’-spcoupling reactions without for the homogeneous catalytic hydroformylation of Cu(I) promoter, in a homogeneous acetonitrile-H,O olefins in methanolic solution. After the reaction, the system. Diynes are produced in moderate yields, and product mixture was heterogenised by adding H,O indolic and furanic products are formed from 2- to form an aqueous phase containing the catalyst sys- iodophenols or 2-iodoanilines and terminal alkynes, tem. The hydroformylation of n-tetradecene-1 with respectively, in good yields. A Pd(0) complex is formed the Rh carbonyl/phenylsulphonatoalkyl-phosphine spontaneously in the reaction mixture. catalyst system illustrated that this system could be used in the 0x0 reaction of high molecular olefms. Synthesis of Bie(a-Amino Acids) by Palladium- Catalyzed Allylic Double Substitution CyclopropanationCatalysed by RuCl,( PPh,), A. MAZ~N,c. NAJERA, J. EZQUERRA and c. PEDREGAL, and OsCI,(PPh,), Tetrahedron Ln., 1995,36, (42), 7697-7700 A. DEMONCEAU, C. A. LEMOINE, A. F. NOELS, 1. T. The reaction of Li enolate, derived &om glycine ben- CHLZHEVSKYand P. v. SOROKIN, Tetrahedron Lea., 1995, zophenone imine ester, with allylic dihalides, in the 36, (46), 8419-8422 presence of a catalytic amount of Pd(Ph,P), (5% mol) The cyclopropanation of ethyl diazoacetate with olefins yielded the corresponding bis(imino-esters) (1). to isoelectronic complexes was catalysed using Subsequent hydrolysis of (1) gave the correspond- RuCI,(PPh,), (1) and OsCI,(PPh,), (2) catalysts. ing bis(a-amino acids). This methodology was used Catalyst (2) was less active than (1) for the decom- to synthesise a,a’-diaminosuberic acid. position of the diazo reagent and the subsequent cyclopropanation. Using the above Ru and 0s based cat- Asymmetric Hydroformylation of Styrene alysts, the cyclopropanation reactions remained limited Using Dithiolato Bridged Dirhodium Catalyst to activated olefins, especially styrenes and isoprene. with BDPP as Chiral Ligand Hydroxylation of Alkanes with Molecular A. M. MASDEU-BULTO, A. OREJON, S. CASTIL~Nand C. CLAVER, Tetrahedron: Asymmetry, 1995, 6, (8), Oxygen Catalyzed by a New Ruthenium- 1885-1888 Substituted Polyoxometalate, ~ZnRuzm(OH)- Asymmemc hydroformylationof styrene is performed (HzO)(ZnW90&] ‘I- using dinuclear thiolato bridged complexes [Rh,(p- R. NEUMANN, A. M. KHENKIN and M. DAHAN, Angew. dithiolate)(COD),] with BDPP, where COD is cyclooc- Chem., Int. Ed. Engl., 1995, 34, (15), 1587-1588 tadiene and BDPP is (-)-(2S,4S)-2,4-bis(diphenyl The title diruthenium-substituted polyoxometalate phosphino) pentane, as the chiral auxiliary ligand. The was used as a catalyst for the hydroxylation of alka- optical yields depend upon the starting organometal- nes, such as adamantane, with 0,at atmosphericpres- lic complex. When (+) and (-) dithiolate bridged com- sure and under mild conditions. Hydroxylation plexes and (+) and (-) diphosphine were combined, occurred almost exclusively at the tertiary C positions. one pair could enhance enantioselectivity. Styrene Highly selective aerobic hydroxylation of tertiary C hydroformylation had a regioselectivity in 2-phenyl- centres in alkanes was achieved via 0, activation. The propanal of 5 94 % and ee of I43 %. regioselectivityshowed that the Ru-substituted polyoxometalate activated 0,in a non-radical way. The Influence of the Aqueous Phase Composition on the Catalytic Properties of FUEL CELLS RhCI, Modified by Polycation in the Hydroformylation of Hexene-1 Platinum Utilization in a Phosphoric Acid N. V. KOLESNICHENKO, M. V. SHARIKOVA, T. KH. Fuel Cell MURZABEKOVA, N. A. MARKOVA and E. v. SLIVINSKII, IZV. J. ARAGANE, H. URUSHIBATA and T. MURAHASHI, Denki Akad. Nauk Rosii, Ser. Khim., 1995, (lo), 1943-1945 Kagaku, 1995,63, (7), 642-647 Studies of H,O-soluble catalytic systems based on RhCl, Geometrical and electrochemical studies of Pt cov- and polyelectrolytes, poly-N,N-diallyl-N,N-dimethy- erage in a gas diffusion electrode of a phosphoric acid lammonium chloride, etc., showed that the hydro- fuel cell showed only - 50% utilisation of the Pt sur- formylation rate increased with increasing pH of the face area compared with the nominal Pt surface area. aqueous phase. Stable hydroformylation of hexene- 1 The impregnation procedure was found to be of more at pH 2 5 was achieved by substitutionof the akyl group importance than PTET content and heat treatment at the N atom for H. Increasingthe charge of the anion temperature. The corrosion reaction of the C support of the salt used for varying the pH increased stability. is suppressed to improve the cell performance.

Platinum Metak Rev., 1996, 40, (1) 44 A Novel Cell Design for Simplifying SOFC Structural Design of CoCrPt(Ta,B)/Cr System Magnetic Thin Film Media for Ultra High T. HIBINO, K. USHIKI, T. SATO and Y.KUWAHARA, Solid Density Longitudinal Magnetic Recording State lonics, 1995, 81, (1, 2), 1-3 P. GLIJER, K. SIN, J. M. SIVERTSEN and J. H.JUDY, Scr. A new design for the solid oxide fuel cell is reported Metal. Muter., 1995,33, (lO/ll), 1575-1584 by attaching the Pd and Au electrodes to the same CoCrPt(Ta,B) thin films with Cr underlayers were face of the BaCe,sGd,,O,, electrolyte. A mixture of studied as ultra-high density magnetic recording media CH, and O2 (CH, : 0,mole ratio = 2 : 1) is fed to for data storage at 10 Gbitshch'. Changes in struc- the cell at 950°C and electric power is generated. The ture and composition altering magnetic and noise ohmic resistance of the cell was lowered by reducing properties were found. In-plane coercivities of 2700 the distance between the two eiectrodes, and the unit Oe were obtained in CoCrPt films containing < 20 cells can be connected in series and parallel with at.% Pt; in CoCrPtTa with < 12% Pt and in CoCrPtB one another on the same electrolyte. with < 11% Pt. Improvements to the noise characteristics, grain size and surface roughness are shown. ELECTRICAL AND ELECTRONIC Thermally Stable, Low-Resistance PdGe- ENGINEERING Based Ohmic Contacts to High-Low Doped n- Barrier-Height Non-Uniformities of PtSilSi GaAs (111) Schottky Diodes J. S. KWAK,H. N. KIM, H. K. BAIK, J.-L. LEE, H. KIM, H. M. PARK and s. K.NOH, Appl. phys. Len., 1995,67, (1 7), P. LAHNOR, K. SEITER, M. SCHULZ, w. DORSCH and R. 2465-2467 SCHOLZ, Awl. Phys. A, 1995,61, (4), 369-375 The development of low resistance, thermally stable The forward I-V characteristics of PtSi Schottky con- PdGe-based ohmic contacts on high-low doped n- tacts on epitaxial n-type Si(ll1) were analysed at GaAs substrates is described. The lowest resistance 100-300 K, and an excess current was found. This obtained was two times lower than for prior reported was caused by a few thousand patches of reduced PdGe ohmic contacts. The contacts were thermally Schottky barrier height. The patch radius is - 70-250 stable even after isothermal annealing for 5 h at 400°C nm. The size of the patches correlates with the size of at atmospheric pressure. agglomerates that lead to bumps in the surface. The number of patches observed, which is a measure of RuOJTiN-Based Storage Electrodes for (Ba, the quality of the Schottky barrier, is reduced upon Sr)TiO, Dynamic Random Access Memory increasing the silicidation temperature, to I 550°C. Capacitors Platinum Bottom Electrodes Formed by K. TAKEMURA, S. YAMAMICHI, P.-Y. LESAICHERRE, K.

Electron-Beam Evaporation for High- TOKASHIKI.~ ~~~~~~ H. MIYAMORO. H. ONO. Y. MIYASAKA and Dielectric Thin Films M. YOSHIDA, 3pn. Appl. Phys., 1995, 34, (9B), 5224-5229 s. Y. CHA, H. c. LEE, w. J. LEE and K. G. KIM, 3pn. J. Appl. Phys., 1995, 34, (9B), 5220-5223 Sputtered (Ba, Sr)TiO, (BST) thin film capacitors were produced with thick RuO,/Ti-based storage Pt bottom electrodes were formed on SiOJSi sub- electrodes and poly-Si contact plugs. The electrode strates at various deposition temperatures by electron- height was > 450 nm and the contact size was 0.8 x beam evaporation, followed by the growth of 0.8 pm'. With increasing BST deposition tempera- (BaosSr,,)TiO, (BST) films under the same condi- ture, the oxidised TiN thickness in the Ru02/TiN tions by r.f. magnetron sputtering. The crystallinity electrode increases, raising electrode resistance. The of BST thin films is strongly dependent on the crys- resistance can be lowered by inserting a Ru layer at tallinity of the Pt films. The surface morphology of the Ru02/TiN interface, by a TiN/TiSidSi junction BST films appeared to be closely related to the change or by rapid thermal annealing of the TiN layer in N,. in the stress of Pt films during BST deposition; the stress affects the electrical properties. MEDICAL USES Novel Technique to Form Pt-Silicided Shallow p+n Junctions Using Low-Temperature Crystal Structure of Double-Stranded DNA Processes Containing the Major Adduct of the K.2. MA, C.-T. LIN and H.-C. CHENG, m.3 A@I. PhYS., Anticancer Drug Cisplatin 1995,34, Part 2, (9A), L1100-Ll102 P. M. TAKAHARA,A. c. ROSENZWEIG, c.A. FREDERICK and Excellent Pt-silicided p'n junctions were formed at s. J. UPPARD, Nature, 1995, 377, (6550), 649-652 low temperatures by implanting BF,' ions into poly- Most cisplatin-DNA adducts are intrasuand d(GpG) crystalline Si films on Si substrates. The samples and d(ApG) crosslinks and structural knowledge of implanted at 100 keV/5 x 10'5/cm2showed a leakage cisplatin-DNA adducts was limited to short single- of 7 nA/cm2and a junction depth of - 0.05 p after stranded deoxyoligonucleotides, such as ciS-~(NH,)z- 500°C annealing. The mtleakages further decreased {d@GpG)}].The X-ray structure at 2.6 resolution to - 2 &an2 when the annealing temperaturereached of a double-stranded DNA dodecamer containing the 550°C. Implant energy was the most important fac- adduct is described here. This should aid design of tor for obtaining excellent junction characteristics. new Pt and other metal crosslinking antitumour drugs.

Platinum Metals Rev., 1996,40, (1) 45 NEW PATENTS METALS AND ALLOYS Electrolytically Ionised Water KOBE STEEL LTD. Japanese Appl. 71171,571 Magnetic Alloy An electrode for the electrolytic ionisation of H20 KOMAG INC. European Appl. 669,610A consists of Ta or Nb base material coated with at least A magnetic alloy with good magnetic properties and 50 vol.% of Pt, Ir02,PtO or Rh,O,. The electrolysis excellent corrosion resistance comprises, in at.%: I is carried out by controlling the anode potential or 20 Pt, 5 10 Ni, 2 75 Co, I 10 Ta and I 10 Ti. This the voltage between the anode and cathode. The elec- is incorporated in recording media consisting, in order: trode can produce electrolytic ion HzO, alkaline H20 a substrate, a plated layer, a nucleation layer, a mag- from a cathode room and acidic H,O of pH 1-2 from netic alloy layer, a protective overlayer and a top lubri- an anode room. It has a longer operating life so that cant layer. The media are used in rigid disk drives for production is continuous over a long time. computer data storage. Manufacture of Silver-PalladiumAlloys ELECTRODEPOSITION AND E.I. DU PONT DE NEMOURS & CO. SURFACE COATINGS US.Patent 5,429,657 Palladium Alloy Plating Solution Finely divided particles of Ag-Pd alloy are manufactured by aerosol decomposition of an aqueous solu- S. S. MOON British Appl. 2,287,717A tion containing nitrates of Ag and Pd at a tempera- A Pd alloy plating composition comprises (in dl): ture below the melting point of the alloy but above 4-20 Pd ion, 0.3-2 Au ion, 5-100 conductive salt and the decomposition temperature of the nitrates. The 0.5-20 complexing agent. The Pd source is prefer- powders are not hollow, are of high purity and are ably a Pd(I1) diammonium, diamine, diammonium spherical. The alloys are used in electronics and den- or tetramine dichloride, diamine dinitride, oxide, tistry, in particular in electrode materials for multi- nitrate or cyanide. The composition may also contain layer ceramic capacitors and in printed circuits. 0.3-5 g/l Ni, Co, Cu, Sn, Se, W, Mo and/or Ti ions as alloying metal. The plated metal has excellent stabil- Silver-PalladiumPowder Manufacture ity, solderability and flexibility. Pd-Au alloy can be DAIDO TOKUSHUKO K.K. Japanese Appl. 7/150,206 electroplated onto lead frames, PCBs and connectors. A Ag-Pd powder is made by regulating the pH of a Lustrous Noble-Metal Decorations Ag-Pd solution in HNO, acid by adding a base, an aromatic reducing agent as the fist reducing process, CERDEC A.G. European Appl. 668,265A and a non-aromatic reducing agent as the second Mono-noble metal dithiolates contain a noble metal reducing process. The powders are used for electro- of Pt(II), Pd(II), Rh(III), Au(1) or Ag(I); a tetrava- conductive paste electrodes for hybrid ICs, multilayer lent 2-1OC organic group; an hydrophilic group, and ceramic capacitors and chip resistors. a mineral acid or carboxylic acid anion. Decals based on these compounds provide highly lustrous noble ELECTROCHEMISTRY metal decoration. The decorated substrates of glass, porcelain or ceramic can be baked. The decoration is Hydrogen Peroxide Production non-porous, stain-free and has good adhesion. KEMIRA CHEM. O.Y. European Appl. 672,6 17A Protective Coating for Lead Frames H202is produced by the anthraquinone process by NAT. SEMICONDUCTOR COW. World Appl. 95118,464 feeding H1or an H,-containing gas into the top part of a fixed bed reactor, flowing the H, downwards to A protective coating comprises, in sequence, layers of hydrogenate the anthraquinone derivative over a sta- Ni, Cu, Ag and Pd. Also claimed is the method for tionary catalyst of supported Pd catalyst mesh, and forming the coating by electrolytic deposition. removing the hydrogenatedworking solution from the Preferably the layers are pure metal or alloys of thick- reactor. The process is highly efficient, with good ness (in pm): 1.25-2.5 Ni, 0.08-0.38 Cu, 0.13-1.0 yields; catalyst regeneration problems are much Ag and 0.08-0.63 Pd. The finish is bondable, sol- reduced and a steadv- suuulv-- - flow into the reactor is derable, free of lead and corrosion resistant. achieved. A dense, almost foam-like dispersion is plating of precious-~~~~l~ obtained in the catalyst bed. TANAKA KIKINZOKU KOGYO K.K. Iridium Electrode Base Material Japanese Appl. 71157,879 mP0N STEELCOW. Japanese APPl. 7/166~350 Plating of Pt, Pd, Rh, Ir, Os, Au, Ag, Cu, Pb, Ni Ir is ion-implanted onto the surface of a base mater- and Co on a matrix surface is achieved by allowing ial which has a Ti metal layer on Ti metal. The Ir Hzto occlude into the manix by circulationor by pres- oxide coated electrode has high durability and no flak- sure. The matrix is then dipped into the metal-con- ing occurs, even under heavy usage. The electrode taining aqueous solution and metal is deposited onto is used as an insoluble electroplating electrode. its surface by reduction.

Platinum Metals Rev., 1996, 40, (l), 46-52 46 Platinum-CoatedLayer Formation HETEROGENEOUS CATALYSIS TANAKA KIKINZOKU KOGYO K.K. Hydrogenation of Aromatic Hydrocarbons Japanese Appl. 71188,934 MITSUBISHI CHEM. cow. European Appl. 659,718A Pt-coated layers are formed by mixing aqueous chloro- platinic acid solution and propargyl alcohol, coating A cycloolefin is produced by partial hydrogenation of onto a base material and baking. Grains of Pt metal a monocyclic aromatic hydrocarbon in the presence are heat-decomposed, deposited and baked onto the of H,O and a RdSiO, catalyst, modified by Zr oxide base at 20O-25O0C, which is a relatively low tem- to improve Ru dispersion and catalyst life, opuon- perature. Such a Pt-coated layer has - 1.6 times the ally in the presence of a metal salt. The catalyst has specific surface of a usual Pt-coated layer. The method good selectivity for cycloolefin, - 60-80% at - 30% is used to form a Pt-coated layer for an insoluble elec- conversion. Cycloolefinsare important intermediates trode, etc., used in electrochemical reactions. for lactams and dicarboxylic acids, etc. Anti-AllergicNoble Metal-Coating Exhaust Gas Cleaner SEIKO INSTR. INC. Japanese Appl. 71188,945 RIKEN COW. European Appl. 661,089A A noble metal coated ornament comprises a Cu-Sn An exhaust gas cleaner, for removing NOx by reduc- alloy coating containing 30-60% Sn as the primary tion and removing unburned CO and hydrocarbon layer at 0.5 pn thickness and a top coating of Pd, not components by oxidation from exhaust gas contain- containing Ni, at a thickness of 0.1-5 p.As an exam- ing NOx and 0, in an amount above stoichiomemc is ple, a wrist watch casing made of bronze was coated claimed. It comprises a first catalyst of 0.2-15 wt.% with 3 pm of Cu-Sn alloy and then coated with Pd Aglporous inorganic oxide support, optionallyin com- to a thickness of 3 pn. The coating is anti-allergic. bination with I 1 wt.% Pt, Pd, Ru, Rh, Ir and/or Au, or 5 5 wt.% W, V, Mn, Mo, Nb and/or Ta; and a second catalyst of a porous inorganic oxide supporting mp!TusAND TECHNIQUE I 5 wt.% Pt, Pd, Ru, Rh, Ir and/or Au and optionally < 10% W, V, Mn, Mo, Nb and/or Ta. The cleaner Silicone Coated Base Material is placed in the flow path of the exhaust gas. Reducing SHINETSUCHEM.CO. LTD. APPl. 6699419A agents- are added to the upstream side of the cleaner. A flame resistant, silicone coated base material for automotive air bags comprises an organopolysilox- Hydrogenation of Carboxylic Acids ane, an organohydrogen polysiloxane, an organic Si BP CHEM. LTD. European Appl. 662,343A compound containing an epoxy or a trialkoxysilyl A catalyst for hydrogenation of carboxylic acids to group metal oxide powder and catalyst. The catalyst alcohols or esters comprises an alloy of at least one is Pt on a C, NiO,, FeO, FeO,, Fe,O,, COO,, CeO, or Group VIII metal, such as Pd, Rh and Ru, and at least TiO, support. The air bag base material is formed on one other metal, such as Ag, Au and Cu, on a sup- a fibrous base material, such as polyamide fibres, poly- port of high surface area graphitised (HSAG) C, ester fibres and their woven or non-woven fabrics. graphite or activated C. A preferred catalyst comprises Oxygen Concentration Detecting Element an alloy of Pd-Ag and Re supported on HSAG C. UNISIAJECS cow. Japanese Appl. 71128,276 Three-Way Exhaust Gas Catalyst An oxygen concentration detecting element consists E. G. PAPADAKIS et a1 Eurqpean Appl. 665,047A of a ZrO, tube having an inner and an outer electrode, A three-way catalyst, for treating car exhaust gas, with a vapour deposited Pt layer on the outside sur- industrial and power station waste gases, involves oxi- face of the tube, which covers the outer electrode. A dation of CO and light hydrocarbons and NOx reduc- sintering-prevention agent is adhered to the Pt layer. tion, and comprises dispersed Rh, Pd and Pt each on Deterioration of the catalytic activity of the Pt cata- a different monolithic honeycomb-type support. The lyst layer is prevented during prolonged use. metal/support pairs are macroscopicallyuniform catalyst in the form of pellets or are applied as a wash- Treatment Process for Oxidant coat in three layers on the monolithic substrate. NIPPON SHOKUBAI co. LTD. Japanese Appl. 712 14,078 An oxidant in sea- and fresh-water is treated bv con- Catalyst for Treatment of ICE Exhaust Gases tact with a Pt/TiO,-ZrOz catalyst. The oxidant is INST. FRANCAIS DU PETROLE decomposed by contact with the solid catalyser. European Appl. 665,048A Garnet Crystal A catalyst for exhaust gas treatment comprises a support with a porous refractory inorganic oxide layer NAMIKI SEIMITSU HOSEKI K.K. and an active phase of: 0.3-4.4 % Ce, 0.1-3.5 % Japanese 7/2153799 Fe, 0.003-0.04 % Pt and balance of at least one refix- A garnet crystal for a magnetic-bubble or magneto- tory inorganic oxide. The formation of sulphates and optical device, is grown using a liquid-phase epitax- sulphites upon oxidation of SO2is prevented. The cat- ial device, which has a Pt-based crucible, a substrate alyst has good thermal stability and resistance to age- binder and a non-magnetic garnet substrate, which ing and is used to treat the exhaust gases from com- has a crystal growing face. No cracks are formed pression ignition (diesel) engines, especially for and reproducibility is good. commercial vehicles with a total weight of 2 3.4 tonne.

Platinum Metals Rat., 1996,40, (1) 47 Exhaust Gas Purification Catalyst Carbon Monoxide and Hydrogen Preparation CATALER IND. CO. LTD. European Appl. 666,103A SHELL CANADA LTD. World Appl. 95/18,063A An exhaust gas purification catalyst comprises a porous CO and/or H2are prepared from gaseous hydrocar- support loaded with a NOx storage component of bon feedstock, such as CH, or natural gas, by par- alkali, alkaline earth and/or rare earth element; and tial oxidation of the feedstock using an 0,-containing an adjacent catalyst of Pt, Pd and/or Rh, and CeO, gas, which also contains N, by a catalyst containing positioned away from the Pt group metal. The sup- Rh, Ir or Pt. At least part of the products is subjected port is Al,O,, zeolite, SiO,, ZnO, and/or Si0,/A1203. to a second stage process to remove NH,andor HCN. Oxidation of hydrocarbons and CO is controlled by Only small amounts of HCN and/or NHr are pro- the release rate of O2fiom CeO,, thus giving enhanced duced by this method and are thus easily removed NOx reduction in fuel-rich atmospheres. at the second stage. Preparation of Hydroxy-Benzaldehyde Production of Propylene RHONE POULENC CHIM. European Appl. 667,331A DOW CHEM. CO. US. Patent 5,430,215 A hydroxy-benzaldehydeis produced by oxidation of Hydrodechlorinationof 1,2,3-mchloropropane (TCP) the corresponding hydroxy-benzylic alcohol using 0, to produce propylene, in preference to propane, in in an aqueous medium containing an alkaline agent, 2 10% yield, comprises reacting TCP and Hz in the in the presence of a Pt-based catalyst, such as PdC, presence of a supported catalyst consisting of Pt in and of a B and a Bi derivative as co-catalyst. The elemental or compound form. Propylene is produced process is particularly applicable to the preparation in 2 20% yield, such as 42% yield with 47% selec- of salicyl-aldehyde from saligenol. The joint presence tivity. The process allows extension of the C value, of B and Bi derivatives, with the Pt-based catalyst, which would otherwise be lost during incineration gives greatly increased reaction yields. The final prod- of TCP. The propylene can be recycled to produce uct is obtained without isolating the intermediates. extra ally1 chloride for the epichlorohydrin process. Production of Fluoroaniline Compounds Dehydration of Lower Alkanes HOECHST A.G. European Appl. 667,337A PHILLIPS PETROLEUM CO. Us. Patent 5,430,220 Fluoroanilines (1) are produced by the reaction of A process for dehydrogenating a 2-8C alkane to an (chloro- or bromo)fluoronitrobenzene with H, in the alkene, in the presence of steam and a catalyst of Pt, presence of a Pd catalyst, such as 5 wt.% PdC, and Sn and a Zn aluminate-containing support, is improved a H,O-insoluble amine which forms a H,O-insoluble by impregnating the support with a solution formed hydrohalide, and optionally, in an inert solvent. The by combining aqueous solutions of a Pt compound method produces (1) in good to very good yields and and oxalic acid, and a Sn compound and an inorganic purity; (1) are plant protectants and pharmaceutical acid. This method of catalyst preparation increases intermediates. The process can be operated on a plant activity and selectiviv (especially to monoolefins), and scale, being readily reproducible, non-corrosive and decreases the rate of deactivation. not producing environmentallyharmful by-products. Catalyst for Synthesis of Chlorine Dioxide Catalyst Support for Fluidised Bed DEGUSSA CORP. US. Patent 5,435,984 STANDARD OIL CO. OHIO. European Appl. 672,453A C10, is generated by contacting a precursor in an Supports for the manufacture of vinyl acetate cata- aqueous medium with a catalyst consisting of a sup- lysts comprise a mixture of inert, microspherical SiO, port comprising a-Al,O,, y-Al,O1 or SO,, and con- particles of pore volume 0.24.7 cmJ/g,of surface area taining La,O, and/or Nd,O,, which is impregnated on 100-200 m2/gwith 2 50 % of the particles being < the outer surface with Pd, or Pd and another Pt group 100 pm. The support is impregnated with Pd and Au metal, or Pd and a Group IB metal. Preferably, the salts and alkali metal salts. Vinyl acetate is produced reaction temperature is 5-80°C, pH is 1-8, and by this catalyst by reaction of ethylene, acetic acid and contact time between catalyst and precursor is 0, in a fluidised bed. Continuous addition of the cat- 0.01-20 s. The rate of deactivation of the catalyst is alyst maintains peak performance and almost elimi- slower than for prior catalysts. nates the need for catalyst changes. Generation of Carbon Monoxide and Hydrogen Exhaust Gas Purification Catalyst PRAXAIRTECHNOLOGY INC. us. Patent 5,441,581 KEMIRA O.Y. World Appl. 95/17,249A CO and H, atmospheres for heat treating ferrous and A catalyst for the purification of gasoline engine non-ferrous metals, alloys and ceramic and/or metal exhaust gases comprises a catalyst body with numer- powders are obtained by an endothermic generation ous through-flow channels for exhaust gas. The cat- process. Input gases are passed through a conduit and alyst body material is coated with Al,O, slurry and La onto a catalyst comprising a noble metal, such as Pt oxide or soluble salt, and with Pd. The support addi- and particularly Rh, loaded on a porous ceramic car- tionally comprises oxides or soluble salts of Eu and/or rier, at 750-900°C. Output gases, of CO and H,, with Sm. The Pd content is 2-1 5 gA of catalyst honeycomb. space velocity of 2 10,000 unitsh are produced. The Also claimed is the catalyst preparation. The cata- reactor operates autothermally at very high space lyst has a maximum uniform surface and gives velocities and provides a buffered atmosphere to allow improved conversion of CO, hydrocarbon and NOx. the introduction of N, into the reducing furnaces.

Platinum Metals Rev., 1996, 40, (1) 48 Hydrogenation of Acetylenic Glycols Exhaust Gas Purifying Catalyser AIR PROD. & CHEM. INC. US. Patent 5,444,170 NISSAN MOTOR CO. LTD. Japanese AppI. 711 36,5 18 The hydrogenation of acetylenic compounds obtained An exhaust gas purifying catalyser comprises Pd and by condensation of ketones or aldehydes with acety- a perovskite type combined oxide containing one of lene, comprises reaction with H, under suitable con- Co, Mn and one of Fe, Ni, Cu, V or Cr. A catalyser ditions to give paraffins, and uses a co-catalyst sys- was obtained by adding Pd(NO,), to the perovskite, tem containing Pd and Pt. The method completely and Pd(NO,), to y-Al,O,, followed by mixing, dry- hydrogenates the acetylene compounds, which are ing and burning at 400°C. The Pd catalyser has good contaminated with Pd catalyst poisons. The system NOx purifying ability for exhaust gas from the rich gives excellent rates of hydrogenation and remains side composition of the theoretical air-fuel ratio, and usable for a long time without deactivation. after high temperature usage for a long period. Hydrodehalogenation Catalyst Catalyser for Purifying Exhaust Gas E. I. DU PONT DE NEMOURS & CO. NISSAN MOTOR co. LTD. Japanese Appl. 71136,524 US. Patent 5,447,896 A catalyser consists of two catalyser layers: an inor- A hydrodehalogenationcatalyst is prepared by impreg- ganic layer of activated AlzO,containing Pt, I'd and nating a C support of ash content < 0.2 wt.% with a Rh, such as Pt-dinitrodiamine on a honeycomb car- combination of metals consisting of 5-95 wt.% Au rier, and a co-existing layer of Pt and S on a porous and 95.5 wt.% of at least one metal selected from Ru, carrier. The catalyser is used for punfymg exhaust gas Rh, Pd, Os, Ir and Pt, at - 350°C. The impregnated in ICE and retains good purifying capacity after expo- C is dried in air at 130-1 50"C, and heated in a reduc- sure to high temperatures from the stoichiometric ing atmosphere at - 350°C to provide metal in a to the lean range. reduced state. The addition of Au prevents sintering and increases the durability and mechanical Purification Apparatus for Exhaust Gas strength of the catalyst. MATSUDA K.K. Japanese Appl. 711 44,119 The apparatus is composed of m-dimensional cata- Preparation of Tercyclohexane from Benzene lyst, such as Pt-Rh/Al,O,, at the upper stream side; MOBIL OIL CORP. US. Patent 5,449,847 HC adsorbent, such as zeolite, mordenite, ferrierite The preparation of tercyclohexane involves passing and chabazite; and a ni-dimensional catalyst, such as Hzand benzene under suEcient conversion condi- PdAl,O,, at the downstream side. The activation tem- tions over a catalyst comprising an acidic solid of a perature for the upper stream side catalyst is higher Grodp IVB metal oxide, such as Zn; modified with than for the downstream side catalyst, but the acti- an oxyanion of Group VIB metal, such as W, and vation conditions for both catalysts are almost iden- an hydrogenation component of Group WImetals, tical. The purification ratio achieved for HC was 59%. such as Pt, Pd, Ir, Rh, 0sand Ru, preferably Pt. The catalyst has high activity and selectivity for the con- Material for Purifying Exhaust Gas version of benzene to tercyclohexanes. RIKEN CORP. Japanese Appls. 71148,435 and 71148,437 Removal of Oxygen-ContainingCompounds The purifying material is composed of 2 or 3 cata- AGENCY OF IND. SCI. & TECHNOL. lysts. The first catalyst contains Ag or Ag oxide, and Japanese Appl. 71136,461 at least one of Pt, Pd, Rh, Ru, Ir or Au, on a porous A gas mixture containing 0,-bearing compounds, inorganic oxide support, preferably Al,O,. The sec- such as methanol, aromatic compounds and O,, is ond catalyst comprises at least one of Pt, Pd, Ru, Rh, contacted with a Pt group metal catalyst, such as Pt, Ir or Au, on porous inorganic oxide or W andor V on on a ZSM-5, mordenite or Y-type zeolite support of porous inorganic oxide. The additional third catalyst regular structural micropores. The 0,-bearing com- contains at least one of Pt, Pd, Rh, Ir or Au on a porous pounds can be decomposed in exhaust gas which con- inorganic oxide. The material is used for removing tains aromatic compounds to suppress their oxida- NOx effectively, from excess 0, combustion exhaust tion. Methanol can thus be eliminated from the gas, over wide temperatures. Residual and non-react- exhaust gas of a methanoVgasoline engine. ing CO and hydrocarbons are also removed. Oxidising Catalyser Cleaning Exhaust Gas of Lean Burn Engines BABCOCK-HITACHI K.K. Japanese Appl. 711 36,5 13 NE CHEMCAT K.K. Japanese Appl. 71155,555 An oxidising catalyser for treatment of exhaust gas Exhaust gas from lean burn engines is contacted with comprises a base material carrier, such as A120,,which a crystalline Ir silicate catalyst on a carrier of metal contains at least one of Ba, Sr, La and Ce; Pt group carbide and metal nitride, and then with a Pt catalyst metal grains, such as Pt or Pd; and a covering TiO, made by depositing Pt on a porous carrier by a non- layer. The carrier is made of honeycomb or lattice electrolytic plating technique. The catalyst is effec- shaped ceramic or metal, ceramic or metal foam or tive for decomposing NOx in exhaust gas, at metal lath. The catalyser is used for combustion of 200-5OO0C, using HC as a reducing agent, and pre- inflammable components, and has high resistance vents the production of N20at 200-300°C. It is sta- to heat and poisoning. ble even in the presence of water vapour.

Platinum Metals Rev., 1996, 40, (1) 49 Improved Production of 1,4-Butanediol HOMOGENEOUS CATALYSIS MITSUBISHI KASEI cow. Japanese Appl. 71165,644 Bicyclic Ketoester Derivatives The production of 1,4-butanediol (BDO) andlor tetrahydrofuran (THF) by catalytic hydrogenation of MERCK & CO. INC. World Appl. 95119,979A maleic anhydride, maleic acid, succinic anhydride, A bicyclic ketoester derivative is prepared by cyclis- etc., involves using a catalyst which comprises com- ing a diazo compound in the presence of a Rh cata- ponents from Pt, Ru, and Rh and Sn supported on lyst and a catalytic amount of a Lewis acid, which is a carrier. BDO andor THF can be produced in high effective for reducing the formation of the 1-a methyl yields under comparatively mild reaction conditions. isomer. The process gives < 1% of 1-a methyl isomer, so requires no separation of the a- and p-isomers. Glyoxylic Acid Preparation MITSUI TOATSU CHEM. INC. Japanese Appl. 71173,099 Arylacetic Acid Ester Derivatives Preparation of glyoxylic acid comprises oxidation of CIBA GEIGY A.G. World Appl. 95120,569A an aqueous solution of glyoxal with 0, in the pres- Arylacetic acid ester compounds (1) are prepared ence of Pt and Pd, Pb, Sn, Bi andor their compounds by reacting boronic acid compounds with methoxy as a catalyst. The conversion rate of glyoxal is high imino-acetic ester, in the presence of a catalyst, such at 85-97% and the selectivity of glyoxylic acid is as Pt(OAc), and tetrakis(triphenylphosphine)Pd, etc. 8 1-82%, compared to 30-7 1% by other methods. Compounds (1) are useful as microbiocides, and can be prepared by this method simply and in high yield. Preparation of Diarylamine Derivatives NEW JAPAN CHEM. CO. LTD. Japanese &d.711 88,13 1 Silicon-Containing Pentacyclic Compounds Preparation of diarylamines comprises dehydro- AGENCY OF IND. SCI. & TECHNOL U S. Pazenr 5,449,800 genation of N-containing compounds in the presence A new Si-containing pentacyclic compound is pre- of a metal catalyst chosen from Pt, Pd, Ru, Cu, pared by reacting a 1,2-bis(hydrosilyl)benzene con- Cu-Cr and their oxides. Symmetric and asymmetric tainiig a monovalent group with a cyclic diene in the diarylamines can be produced in high yield under presence of a Pt compound. It is used as a raw mate- moderate conditions. rial for making Si-containing ladder polymers, for heat- and burn-resistant, electrically conductive and Preparation of Amino Alcohols non-linear optical materials, under mild conditions. BASF A.G. German Appl. 4,400,591 The preparation of amino alcohols comprises react- FUEL CELLS ing hydroxycarbonyl compounds with H, and NH, or a primary or secondary amine at 0-300°C and 1400 Perovskite Electrode bar in the presence of a catalyst of active mass 5&100 FORSHUNGSZENTRUM JUEUCH G.m.b.H. wt.% Ru. The process is a one-step synthesis, directly from the hydroxycarbonyl compounds, and gives WorldAppl. 95119,053A amino alcohols in high yields and purity. The amino An electrode, used as a cathode in a high tempera- alcohols have use as intermediates, etc. ture fuel cell, has perovskite material doped with Pt metal, such as a Pt metal additive based on La ferrite, Ruthenium Catalysts so as to reduce the reactivity between the electrode BAYER A.G. German Appl. 4,404,220 and the solid electrolyte of the fuel cell. The electrode Ru catalysts, which are used in the selective prepa- is based on ZrO, stabilised with Y20, and is doped ration of cycloaliphatic polyamine (1) by hydrogena- with Ir or Ru oxide at 10-1000 ppm. The solid tion of aromatic polyamine, additionally contain electrolyte fuel cell has improved electrochemical hydroxides andlor hydrated oxides of Ce and Mn characteristics. and/or their dehydrationproducts. The catalysts con- Direct Energy Conversion Device tain 0.1-10 wt.% Ru, and Mn:Ce in weight ratio 0.3-5.1 (as elements), and may additionally contain UNIV. CALIFORNIA World Appl. 95120,246A additives, auxiliaries and/or carriers. The catalyst has A direct energy conversion device, especially for a high selectivity and the reaction to (1) takes a short HJ'O, fuel cell, has a pair of C aerogel electrodes time at a high catalyst loading. The catalyst is easily (1) loaded with a Pt metal catalyst, such as Pt, Pd, prepared by using readily filtered precipitates. Rh, etc. (1) has density 0.3-1.2 g/cm' and a surface area of 400-1 200 m'lg. The fuel cell also includes cur- Tertiary Amino Production rent collector plates, gas manifolds and a separator. BASF A.G. German Appl. 4,407,466 Tertiary amines (1) are produced by reacting nitriles Battery for Electrical Energy Production with secondary amines and H, at 5C25O"C and 5-350 I. sEKINE Japanese Appl. 71176,311 bar in the presence of Pdoxide support catalyst. (1) A battery for the continuous production of electri- are useful as epoxy resin hardeners, polyurethane cat- cal energy in the home contains a fuel room within alysts, and intermediates for quaternary ammonium an auxiliary tank containing electrolyte which is pres- compounds, plasticisers, corrosion inhibitors, tex- sure operated, and a Pd plated steel electrode, which tile auxiliaries, dye, emulsifiers, etc. The process gives acts as a catalyser. The battery has a longer life and 83-93% yields in continuous operation. a safety valve for pressure adjustment.

Platinum Metals Rev., 1996, 40, (1) 50 Solid State Polymer Electrolyte Fuel Cell CHEMICAL TECHNOLOGY TOYOTAJIDOSHA K.K. Japanese A@[. 71201,346 A fuel cell comprises a cathode catalytic reaction layer, Hydrogen Cyanide Production which contains C particles and Pt, between an elec- E.I. DU PONT DE NEMOURS & CO. trolyte film and a cathode. A fire resistant layer con- World Appl. 95121,126A sisting only of C covers both sides of the catalytic layer. Hydrogen cyanide is produced using an induction 0, mixing with Hz causes combustion to take place heated Pt group metal catalyst at 0.5-30 MHz fre- in the presence of the Pt and the heat generated on quency to the reaction temperature and then con- the peripheral edge of the cathode side of the catalytic tacting with a mixture of NH3vapour and hydrocar- layer is dissipated by the C particles of the fire resis- bon gas to produce HCN, which is recoverable. The tant layer. Improved durability of electrolyte film is process is on a small scale, efficient and has low obtained. installation costs. Electrode Catalyst for Fuel Cell Production of cis-Substituted Cyclohexyl- FUJI ELECTRIC CO. LTD. Japanese Appl. 712 11,328 Amine Derivatives An electrode catalyst for fuel cells is manufactured HOECHST-SCHERING AGREVO G.m.b.H. hmPt particles supported on C which are heat mated German Appl. 4,405,728 at 1000°C in an inert gas. Pt is added to the dispersed C support from a Pt containing solution, is mixed, &-Substituted cyclohexylamine derivatives (1) are and a reducing agent is added to support the on prepared by reacting a cyclohexanone derivative with Pt and H, in the presence of a noble metal boride the C. The Pt is filtered, washed and dried to sepa- NH, rate solid and finally heat treated. The fuel cell has catalyst. The substituents may optionally be aliphatic, enhanced generating power and a longer life. Deposited alicyclic, aromatic or heterocyclic groups. Derivatives impurities are totally decomposed and scattered. (1) are useful as intermediates, for example for 4- amino- and 4-alkoxy-pyrimidines with insecticidal, Apparatus for Production of Chlorine acaricidal and fungicidal activity. The process gives yields (> 90%)with high selectivity (- 89-90%) MITSUI TOATSU CHEM. INC. Japanese ApPl. 7/21 6,570 high cis at relatively low pressures and is suitable for either Production of C1, from HCl acid in fuel cells com- continuous or semi-continuous operation. prises a Pt anode, a Pd cathode and an ion conductive membrane between two acid impregnated wool discs. Cl, is produced under mild conditions with- ELECTRICAL AND ELECTRONIC out yielding any by-products. The reaction energy can ENGINEERING be brought in from outside when required. Multilayer Magneto-Optic Recording Medium CORROSION PROTECTION EASTMAN KODAK CO. US. Patent 5,436,072 A magneto-optic recording medium has a seed layer Anticorrosion Coating Production of amorphous oxide Zn,Sn,O,, where x = 0.150.75, GENERALELECTFUC CO. Eumpean Appl. 671,486A and a recording multilayer of alternating layers of Modifying the initiation or propagation of cracks in Co and Pt on the seed layer. The seed layer is selected the surface of metal components in H,O-cooled to improve the coercivity and squareness of the mul- nuclear reactors and associated equipment, comprises tilayer. The medium is used for magneto-optic disks, injecting a solution or suspension of thermally decom- CDs and photo CDs and for cartridge use. posable Pd compounds into the reactor H,O. The Pd Photomagnetic Recording Medium decreases the electrochemical potential of the metal component surface, and Pd ions andlor atoms are HITACHI LTD. Japanese Awl. 71130,015 deposited or incorporated. The process reduces the A photomagnetic recording medium includes Pt/Co electrochemical potential of stainless steel below the multilayer film andor Pt/CoNi multilayer films. At critical threshold. Pd doping is also effective against least one layer of Co or CoNi, of thickness greater inter-granular stress corrosion cracking. than the transition metal element layer, in the multilayer film is formed, optionally in place of the mul- Hot Corrosion Protection tilayer film. The medium is suitable for high density SERMATECH. INT.INC. World Appl. 95123,243A recording using a short wavelength optical beam. It Hot corrosion protection for a Ni-base alloy is has improved magnetic field sensitivity. enhanced by enriching the surface by electroplating Printed Wiring Board Manufacture with Pt, heating to diffuse the Pt, and then diffusing molten Al and Si into the Pt-enriched substrate. This DAINICHI KOGYO K.K. Japanese 71147,478 gives a Pt-enriched Si-modified corrosion resistant A method for the manufacture of printed wiring board aluminide coating on the Ni-base alloy substrate. Also uses a Ni plating layer on the conductor pattern claimed is a Pt-enriched Si-modified aluminide coat- deposited on a substrate which is laminated with Cu. ing on a refractory-containingNi-base superalloy sub- Pd metal, in the form of an island, is deposited over strate. This coating is used for parts in gas turbine the Ni plating layer. This method provides inexpen- engines where temperatures are 2 12,OOO"C. sive soldering and reduces the wear effect.

Platinum Metals Rev., 1996,40, (1) 51 Semiconductor Chip Terminal Formation Magnetic Recording Medium WORLD METAL K.K. Japanese Appl. 711 83,327 TOSHIBA K.K. Japanese Appl. 71235,034 A semiconductor chip has input-output terminals A magnetic recording medium is formed by sand- formed from a base material, such as Al, which is first wiching vertically magnetised film containing Co-Pt ground processed, using a Pd chloride solution. A thin alloy between Co oxide, nitride or carbide layers. The Ni layer followed by a Pt group metal layer are then alloy is in crystallineform. The medium has increased deposited onto the terminals by chemical plating. The saturation magnetisation,vertical magnetic anisotropy terminals have enhanced solderability with improved and coercive force. Electrical resistance is raised. bonding. The mounting contains no solder bump. Conductive Paste for Through Hole Filling Perpendicular Magnetic Recording Medium NITSUKO K.K. Japanese Appl. 71235,215 SONY cow. Japanese Appl. 71192,224 Conductive paste is formed by adding 0.1-3 wt.% Rh A perpendicular magnetic recording medium com- powder to electrically conductive powder. Initially, prises laminations of a non-magnetic substrate, an the through hole is filled with ingredients, such as Ag undercoat layer and an alloy film based on CoICr. powder and then with Cu powder; the electrically con- The undercoat layer is Pt. The medium is suitable for ductive powder containing Rh powder is filled over high density recording and has improved writelread this. The paste is highly shape stable and reliable, does characteristics. The CoICr magnetic film has 3094 not heat shrink, and has electrical resistance typical cps peak intensity, since orientation and crystallisa- of small electric conductors. It does not crack and tion are improved by the Pt undercoat layer. gives improved wiring density. Structure of Opto-Magnetic Recording Medium MEDICAL USES KINSEISHA K.K. Japanese Appl. 71192,328 Precious Metal Dental Alloy An opto-magnetic recording medium has a substrate J. M. NEY CO. US. Patent 5,431,875 on which multiple recording film of varying thickness An alloy for dental restorations comprises (wt.%): is accumulated. The substrate has a first dielectric 60-95 precious metal(s) selected from: 60-85 Pd, film under a F't layer. A first recording layer is arranged 0-10 Pt, 0-5 Au, 0-12 Ag; 1-15 Sn; 2-7 Zn; between the Pt layer and a Cr film. A second dielec- 0.005-0.2 B; 0-2 Ga; 0-2 Co; 0-15 In; &0.2 deox- tric film with a laser beam reflecting coating layer is idant selected from Si, Ge, Mg, Al, Li and Ta; 0-1 .O provided on a second recording film which is irradi- grain refiners selected from Ru, Ir and Re. The alloy ated by a light beam of different wavelengths to write has a liquidus temperature of 2 14OO0C,a tensile yield or read out from the disk. The medium reproduces strength of 2 250 MPa, and an elongation of 2 2%. A information selectively and can simultaneously pro- claimed dental restoration method comprises casting duce two amounts of recorded information. the above metal alloy and firing a translucent porcelain coating upon it. The oxide film of the cast alloy Conductive Resin Paste does not discolour the translucent porcelain. SUMITOMO METAL MINING CO. Japanese Appl. 71192,527 Diamino Cyclohexane Platinum Complexes Conductive resin paste contains globular powdered UNIV. TEXAS SYSTEM US. Patent 5,434,256 Ag with an average grain diameter of 0.01-5 pm; pow- cis- 1,4-Diaminocyclohexane Pt(IV) complexes and dered Ru oxide of diameter 100-5000 & epoxy resin; 1,24iamino cyclohexane Pt(IV) complexes and their a hardening agent; and a solvent consisting of an ester stereoisomers, containing C1, propionate or butyrate; of a 6C or less monobasic acid and 6C or less primary acetate, trifluoroacetate, propionate, butyrate, pen- or secondary alcohol, and glycidyl ether. The weight tanoate, hexanoate or heptanoate, have been prepared. of the powdered Ru is 30-75 pts. wt.1100 pts. wt. of The compounds are antiturnour agents active against the resin-based material. The paste is used for con- leukaemia and solid tumours resistant to cis-platin necting semiconductor devices; it prevents malfunc- and tetraplatin. The compounds are non-nephrotoxic tion of a photo-transforming switch, including a pho- and have a high activity. tocoupler, and gives stable conductivity. Super-Elastic Spring Ceramic Wiring Board TOKIN COW. Japanese Appl. 71207,390 MATSUSHITA ELECTRIC WORKS LTD. A super elastic spring for catheter guide wires com- Japanese Appl. 712 12,009 prises a Ti-Pd shape memory alloy with a martensitic Ceramic wiring board, for mounting electronic com- transformation starting point of at least the service ponents, has a multilayer structure comprising a Cu temperatures and 2 60% of the deformed strain spon- layer and a Pd layer deposited by electroless plating. taneously being elastically recovered at the service temperatures. It is additionally used for wires for The thickness of the Pd layer is Z lpand is formed by electrolytic plating using current density of 1-20 straightening irregular teeth. A. The wiring board allows high resolution conduc- tion patterns to be deposited and improves bonding The New Patents abstracts have been prepared from properties. Heating up to 450°C prevents swelling. material published by Dement Publications Limited.

Platinum Metals Rev., 1996, 40, (1) 52