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PLATINUM METALS REVIEW

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

VOL. 41 APRIL 1997

Contents Electrodes Based on Noble Metals By G. K. Chandler, 3. D. Genders and D. Pletcher

A Rhodium Solvated Molecular Wire

Gas-Powered Co-Generation By H. Winduwi, R. Guntrum and3. Kempf

Platinum Catalysts Used in the Silicones Industry By L. N, Lewis, J. Stein, Y. Gao, R. E. Colborn and G. Hutchins

New Platinum-Based Lean NOx Conversion Strategy By A. P. Walker

Emission Control Technology at Detroit ByM. V. Twigg

Aspects of Co-ordination Chemistry By S. M. Godfey

Monodispersed Nanostructured Ultrafine Platinum

P1atinum:Platinum-Rhodium Thermocouple Wire By Baoyuan Wu and Ge Liu

The Metallurgy of Iridium

Bertrand Pelletier, Master Pharmacist By W. A. Smeaton

Abstracts

New Patents

NO. 2

54

63

64

66

75

76

79

80

81

85

86

89

96

Communications shouM be addressed to Tha Editor, Susan V. Ashton, Platinum Me&& Review

Johnson Matrhey Publie Limited Company, Hatton Garden, London ECl N 8JP

Electrodes Based on Noble Metals ESSENTIAL COMPONENTS FOR ELECTROCHEMICAL TECHNOLOGY

By G. Kim Chandler

J. David Genders

and Derek Pletcher

Johnson Matthey, Precious Metals Division, Royston

The Electrosynthesis Co. Inc., Lancaster, New York, U.S.A.

The Department of Chemistry, University of Southampton, England

Electrochemical technology is playing an increasingly important role in modern society and especially in the chemical industry, see Table I. Major reasons for the shift towards electrochemical technology include: (a) the unique ability of electrolysis to bring about selective chemical change without the use of toxic reagents or hazardous conditions; (b) the myriad possibilities for the recycling of metals, chemicals and process streams; (c) the need for clean and efficient energy sources, especially for transport systems; and (d) the many opportunities for designing small and portable sensors which use electrochemical detectors.

The key components of all electrochemical cells are the electrodes and, in some cases, the separators. There is little doubt that developments in both electrode materials and ion permeable membranes during the last quarter of a century have allowed the successful imple- mentation of many novel concepts. In fact, in almost all cases where process economics require the optimisation of cell performance, electrodes made from noble metals or noble metal oxides are the components of choice. Although noble metals are expensive, their properties are such that the overall costs of the process are reduced through their use.

Common features which recur in the development of materials for electrodes, with many diverse applications are:

the use of platinum group metals and their oxides as coatings on inert substrates

the niinimisation of the platinum metal loading

the use of platinum group metal alloys or mixtures of oxides to enhance electrode stability, to improve product selectivity and/or to minimise overpotentials

the fabrication of membrane/electrode com- binations to reduce interelectrode gaps and hence energy inefficiencies.

In this review some of the roles of the platinum group metals, in particular platinum, iridium and ruthenium, in present and potential applications of electrochemical technology will be highlighted.

Dimensionally Stable Anodes The late 1950s saw an event of great impor-

tance for electrochemical processing - the development of dimensionally stable anodes (2). These introduced a new approach to the manufacture of coated electrodes and increased expec- tations of the performance of electrodes. The first examples of dimensionally stable anodes consisted of ruthenium dioxide (RuOz) coatings on titanium and these were prepared very simply by repeatedly spraying or painting a pre- treated titanium surface with a solution of ruthenium trichloride, followed by thermal decomposition in air. These electrodes found rapid application in the chlor-alkali industry because of a unique combination of properties - a very low overpotential for chlorine evolution and a very long service life -both in stark contrast to graphite, the previous anode of choice, see Table 11. Moreover, this coating technique could be used on titanium substrates which had been fabricated into almost any shape. Hence,

Platinum Metals Rev., 1997, 41, (2), 54-63 54

I Table I

Typical Applications of Electrochemistry (1)

Anode

Graphite Pt+ Ru02TTi

The Manufacture of Inorganic Chemicals including CI2/NaOH, KOH, CIO;. CIO;, BrOY, H2, 02, Fz, 03, H202, MnOz, Cu20, Mn04, CrZO,?., Sz082-, N205, NH20H, SnO,'-, Ce", AsH3

The Synthesis of Organic Compounds typically monomers, fine chemicals, pharmaceutical and agrochemical intermediates

The Extraction of Metals including Al, Na, K. Mg, Li, Cu, Zn, Ga

The Recycling of Chemicals and Process Streams metal recovery and refining, recycling of redox reagents, salt splitting, electrodialysis for stream concentration and purification

salt removal, treatment with CIO-, H20z and 03, the removal of metal ions to < 1 ppm, and the removal of organics, nitrate and radioactive ions

such as the destruction of contaminated waste from the nuclear industry, and the destruction of polychlorinated biphenyls

in processes such as electroplating, anodising, electropainting and surface modification

including printed circuit boards, deposition of metal contacts and semiconductor layers

in processes such as electrochemical machining, electroforming and electrogrinding

by, for example, anodic and cathodic protection, sacrificial anodes

such as batteries for electronic devices, household and portable devices, fuel cells for vehicles and on site power generation

for monitoring atmospheres, toxic hazard warning, optimisation of engine/furnace performance, monitoring water quality, process streams, medical applications and others

Water and Effluent Treatment

The Total Destruction of Toxic Materials

Metal Finishing

The Manufacture of Electronic Components

Metals Fabrication

Corrosion Control

Batteries and Fuel Cells

Sensors

CIz overpotential, mV Anode weight loss

= 400 2-3 kg/tonne C12 = 200 0.4-0.8 g/tonne CI2 z 50 < 0.03 g/tonne C12

Platinum Metals Rev., 1997, 41, (2) 55

Table I 1 Performance of Anode Materials in Cells

Used for the Manufacture of Chlorine and Sodium Hydroxide Reaction conditions: 25 per cent brine a t 363 K; current density 3 kA m-*

Platinum anodes can also passivate leading to a substantial further increase in overpotential

these coated titanium anodes made possible the construction of sealed cells with a range of electrode configurations; thereby introducing a new flexibility into cell design. The result was a new generation of improved performance cells including the highly successful membrane cells for chlor-alkali production.

Coating Compositions Dimensionally stable anodes rapidly became

more complex in composition (2-5). It became apparent that for some applications it was advantageous to have an undercoat. This could be a titanium dioxide (TiOz) layer, a mixture of RuOz and TiOz, or a layer with a gradient in composition. It also became customary to include other platinum group metals, valve metals, tin and/or transition metals in the coating, with the objec- tives of:

reducing the chlorine overpotential even further

increasing the resistance of the coating to damage during electrolysis

further enhancing the lifetime or reducing the catalyst loading

improving the current efficiency for chlorine (that is, decreasing the oxygen content of the chlorine by increasing the overpotential for the competing water oxidation reaction) or just

establishing a stronger patent position for

Fig. 1 Scanning electron micrograph of a modern oxide coated titanium anode for a chlor-alkali cell. Scale: 1 cm represents 20 pm Photograph reproduced e ~ u n e s y of ICI Chemicals & Polpets Ltd.

a technology which had become both highly successful and very profitable.

Variations in the coating composition are easily achieved by changing the composition of the spray/paint solution. Such oxide coatings usually have the “cracked mud” appearance when examined by scanning electron micro- scopy, see Figure 1.

Modern coatings for the anodes used in mer- cury, diaphragm and membrane cells in the chlor-alkali industry differ in composition, to allow for differences in the operating conditions and the environment close to the anode surface. Anodes for membrane cells are now generally a mixture of RuOz and iridium oxide (11-0’) and, with a platinum group metal loading of 10-20 g m-’, have a guaranteed operating life of five to eight years. Such coatings give a very stable, low chlorine overpotential and a low oxygen content in the chlorine. In common with other cell components, the anodes are also now asked to operate at higher current densities. For many years the accepted current density was 2 to 3 kA m-’ and the emphasis was on reducing the energy consumption of the cell. However, the recent trend is towards using further improvements in cell performance to lower the capital cost of the plant, and it would be advantageous for the anodes to operate at 4 to 5 kA m-? without significant loss in performance.

Platinum Metals Rev., 1997,41, ( 2 ) 56

Such developments clearly demonstrated the possibilities for modifying the electrocatalytic properties of coatings on titanium by changing the composition of the oxide. This is well illustrated by two examples. Dimensionally stable anodes for oxygen evolution are now widely used for applications including cathodic protection, electrogalvanising and electrowinning of metals from aqueous acid (5, 6). For these anodes, the coating is based upon IrOz which gives a low overpotential for the oxidation of water to oxygen. Minor changes to the coating composition haye led to a substantial improvement in oxygen anode performance, particularly the wear rate. Perhaps the most spectac- ular application of these electrodes is in electrogalvanising where steel strip is coated with zinc on a reel-to-reel system at high speed and the coated anodes operate at 7 to 10 kA m-’.

Another type of anode has been developed for the production of chlorate. In this process the anode reaction is again the oxidation of chloride ions, but the reaction is carried out a t a higher pH (pH > 6, compared with a pH of 3-4 in a chlor-alkali cell). The chlorine is immediately hydrolysed to hypochlorite which then dis- proportionates in solution to chlorate and chloride. The higher pH leads to a greater loss of current efficiency due to oxygen evolution and also to higher rates of dissolution of the RuOz layer. In attempting to overcome these problems, the Canadian company Chemetics International developed coatings based on Ti02/Ru02/A1Sb04 (or RhSbOa) with a low RuOz content (7). These compositions exhibit better catalytic activity, higher selectivity (with less oxygen production) and lower wear rates compared with Ru02 or RuOz/Ti02 anodes. They also permit operation at a higher temperature, which significantly reduces the plant capital and operating costs.

Cathodes for Hydrogen Evolution The overpotential for the cathode reaction in

a chlor-alkali cell is, of course, also critical to the process energy consumption. Perhaps sur- prisingly, it has proved more difficult to elimi- nate the significant overpotential for this

electrode reaction: the reduction of water to hydrogen and OH- in strong caustic soda solution (usually > 30 per cent). The primary literature contains descriptions of many studies of the hydrogen reaction and many non-noble metal catalysts have been proposed. Even so, many chlor-alkali producers still rely on cathodes coated with noble metals, which are available from most electrode suppliers.

While their exact compositions are not dis- closed, many are believed to be related to the platindruthenim coatings described by Grove (8). Nickel is used as the substrate, to ensure stability against corrosion, and the coatings contain 3.0 to 3.5 g m-’ of platinum and 1 .O to 1.5 g m-’ of ruthenium. The coatings are prepared by immersion plating. After appropriate surface preparation, the nickel substrate is simply dipped into a solution of the noble metal chlorides and left to stand at room temperature until the required loading of noble metal is obtained. The nickel metal is the reducing agent in this cemen- tation reaction. Once again, uniform coatings on complex surface shapes are easily obtained, for instance on expanded metal mesh and slat- ted louvres, as well as on flat surfaces, all of which are found in modern cell designs.

Typically the overpotential for hydrogen evolution is 100 mV with a current density of 3 kA m-’ in 35 per cent NaOH at 363 K and this performance can be maintained for more than 2 years. The major reason for loss of performance is due to coverage of the active catalyst surface by base metals, which have a high overpotential for hydrogen evolution. Hence, it is advantageous to operate with a catholyte which is free of metal ions, such as iron(I1). However, some tolerance to iron poisoning has been claimed for noble metal cathodes and an upper limit of 60 ppm has been proposed (9).

Platinised Titanium Electrodes Platinum electrodes are the workhorses of

many laboratories, especially for the study of oxidations. They are regarded as being stable to anodic dissolution, and it is assumed that platinum coated titanium, either plated or as a cladding of thin platinum foil, will be a cost

PIannum Metals Rev., 1997,41, (2) 57

fine porous layer with dispersed catalyst e g P t on C

Fig. 2 Schematic diagram of a gas diffusion electrode and

hydrophobic layer with of a single pore showing the coarse pores e g PTFE f C three phase interphase

gaseous - between gas, electrolyte and aqueous

electrolyte reactant mm __c catalyst < 1 pm

catalyst

carbon

electrolyte

mesh current collector

carbon

Single pore

layer to give li maximum three

phase contact catalystlelectrolytelgas

thin electrolyte f i lm over catalyst OR MORE LIKELY hlgh area Of

effective, industrially useful alternative to bulk platinum metal; unfortunately, neither is entirely true.

On the longer timescale of pilot plant operation, platinum is often found to corrode significantly (5). There are only limited studies, but the available data suggest that platinum cor- rodes more rapidly in the presence of organics and certain anions. For example, in a scale-up of the conversion of methyl adipate to dimethyl sebacate, loss of platinum from the anode was found to be a significant factor in the process economics (1 0). Moreover, platinised titanium can have significantly different properties from platinum itself, presumably because of its higher surface area and perhaps also because of the poor adhesion of platinum to the titanium substrate.

Platinised titanium anodes however, have cer- tainly found applications in electrochemical technology. They have been used in the electrosynthesis of several inorganic compounds, including persulfates and perchlorates, in electrochlori- nation plants and electroplating processes, for example, for chromium and gold. They are widely employed as the anodes for cathodic protection in sea water environments (for example, sea water intakes and heat exchangers, and for oil rigs) because their resistance to abrasion is superior than that of other anode coatings. At present, modern platinised titanium anodes are manufactured with an undercoating layer of platindiridium or noble metal oxide, and covered with a dense layer of platinum by electroplating. For cathodic protection in sea water,

such anodes have a wear rate of 1 to 2 pg/A h. Platinised titanium anodes were the fist coated

electrodes to be marketed, and in many applications they have been displaced by dimensionally stable oxide coatings that have been highly optimised for the particular electrolyte. However, there remains a market for anodes which can be used in relatively small scale processes and this could be met by high performance, platinised titanium anodes. Indeed, the number of such applications in electrosynthesis and environmental processing is expanding. It may be timely, therefore, to re-examine the manufacture and performance of platinised titanium anodes and to consider using platinum alloys for non- specific applications; for example, platindiridium coatings on titanium are known to have superior properties in some applications.

Gas Diffusion Electrodes Gas difFusion electrodes are porous structures,

where the gas is fed to the back of the electrode away from the electrolyte, and a three-phase interphase between the gas, electrolyte and electrocatalyst is formed close to the electrode/solution interface. Most electrodes consist of a relatively thick layer of carbon and PTFE containing a current collector (such as a fine metal mesh) and a thinner layer of carbon containing the electrocatalyst on the solution side, see Figure 2.

The skill in the fabrication of electrodes is in selecting the appropriate catalyst, minimising the catalyst loading and designing a stable structure where the gaslsolution interface is formed

Platinum Metals Rev., 1997,41, (2) 58

2 C

concentrated NaOH dilute Na2COp

Fig. 3 Schematic diagram of the membrane cell process envisaged for the conversion of sodium carbonate to high purity, 35 per cent sodium hydroxide 1

co32-

diffusion t concentrated

anode

Cation permeable membrane

I I I

Cathode

CATHODE

I dilute NaOH

2H,O + 2e'- .?OH'+ H2 ANODE Na2COp

H2-2e--2H' 2H'+ CO:-- CO2+ H20

at the catalyst site. Such electrodes can be operated with almost insoluble gases at current densities in the range of 1-10 kA m-'.

Fuel Cell Uses Gas diffusion electrodes were originally

developed for fuel cells where hydrogen and oxygen (from the air) are reacted at the anode and cathode to give water and a significant energy output. One such type of fuel cell is the proton exchange membrane fuel cell (PEMFC) which employs a perfluorinated membrane as a solid electrolyte (1 1-13). Due to their intrin- sic simplicity and high power density, PEMFCs are suitable for both stationary and transportation applications. Major progress towards com- mercialisation has been made with these fuel cells, especially by Ballard Power Systems in collaboration with Johnson Matthey. Test units of up to 250 kW, as well as whole buses, have completed extensive trials ( 12).

The catalysts used for PEMFCs are typically platinum for the air cathode and platinum or platinum based alloys or mixed metals, such as platindruthenium, for the anode. Optimisation of electrode structure - to improve catalyst utilisation - and better catalyst dispersion have led

to noble metal loadings of typically 3 g m-'. Substantial developments have also occurred

recently in direct methanol fuel cells (DMFCs) (14). Organic fuels have advantages over hydrogen in their relative ease and safety of transportation and distribution, and their lower cost. There are a number of factors responsible for the advances in performance. These include the use of solid polymer electrolytes, which allow the fuel cell to be operated at higher temperatures than is possible with traditional liquid electrolytes, and improvements in anode performance. For many years, the performance of DMFCs was poor due to poisoning of the platinum catalyst by intermediates in the oxidation of the fuel. One particular problem is carbon monoxide, which absorbs strongly and irreversibly onto the platinum surface, thus restricting the rates of methanol oxidation to 1 A m-'. The use of catalysts, such as platindruthenium materials often with additives, for example tidtungsten or tidzirconium, has reduced electrode poisoning, thus allowing the fuel cell to give a power output of 2 kW m-* at a discharge rate of 4 kA m-* (1 5, 16).

Gas diffusion electrodes have now become an accepted tool in electrochemical technology and


-1 0 -0.5 0.0 POTENTIAL vs SCE, volt5

E

E >. t z w

+ W LL LL 3

U

200-

n 100.

( b )

I

POTENTIAL vS SCE, V o l t 5

Fig. 4 Curredpotential curves for hydrogen oxidation at a platinum blacklPTFE gas diffusion electrode: (a) in three different electrolytes at 294 K; and (b) for 2 M sodium carbonate as a function of temperature

have found applications in batteries, sensors, metal recovery and synthesis. Processes for the reduction of oxygen to hydrogen peroxide at uncatalysed gas diffusion cathodes are being developed (1 7), and platinum catalysed gas diffusion electrodes find application in electrochemical processing as counter electrodes.

The replacement of hydrogen evolution by the 4e- reduction of oxygen, or oxygen evolution by hydrogen oxidation can lead to substantial decreases in energy consumption by the cell. Thus, oxygen cathodes have been used, for example, in cells for the production of ozone (for water treatment) (1 8, 19) and hydrogen anodes have been used in cells for zinc electrowinning (20) or the regeneration of redox reagents such as Ti3+ (used for organic synthesis) (21).

The hydrogen anode plays a more central role in a novel process for the conversion of sodium carbonate to sodium hydroxide. This is effectively an electrolytic version of the old Soda

Lime Process - which is both energy efficient and benign to the environment (22). From the scheme of the cell chemistry, Figure 3, it can be seen that the cathode chemistry and catholyte are identical to those in a chlor-alkali membrane cell. The hydrogen formed at the cathode is, however, piped around to a noble metal catalysed gas diffusion anode in an anolyte stream consisting of aqueous 2 M Na2C03. The chemistry which occurs at the anode is:

H? - 2e- ---. 2H' 2H' + CO,' ---. C 0 2 + H 2 0

and the overall chemical change in the cell is

NalCOl + H2O + 2NaOH + CO,

where the carbon dioxide is found in the anode gas stream. The Gibbs energy change associated with the cell reaction is only z +54 kJ (compared to = +420 kJ in a chlor-alkali cell), leading to the possibility of a very low cell voltage and low energy consumption. It should be noted that the process uses available and successful membrane cells, cathode coatings, membranes and the hydrogen oxidation anode. Moreover, with the exception of the anode, all the components are used in environments almost identical to those for which they were developed and optimised.

Hence, the key to success lies in the performance of the gas diffusion anode. Currentholt- age characteristics for a preferred anode in three different electrolytes, are shown in Figure 4(a). Each characteristic shows the expected equilibrium potential for the pH concerned and is linear due to the voltage drop at these high currents. The response in sodium carbonate shows a much lower slope and this may arise partly from the higher resistance of this solution. However, the dominant factor is thought to be the local pH within the pores which decreases with increasing current density. Figure 4(b) shows the influence of temperature for the sodium carbonate electrolyte, and it can be seen that increasing the temperature is very beneficial to the process performance.

Using a flow cell operating at 363 K, with electrode areas of 7.5 cm', a Nafion 902 membrane

Platinum Metals Rev., 1997, 41, ( 2 ) 60

Process

Chlor-alkali membrane cell

Na2S04 splitting 3 compartment cell 2 compartment cell 2 compartment cell with H2 anode bipolar membrane cell

_ _ _ _ ~ ~

1 100 (target 800) I Na2C03 4 2NaOH

Energy consumption, kWh ton-’ NaOH

2500

4700 3600 2800 1800

and a catalytic cathode (see above), it has proved possible to produce very pure 13M NaOH with a current efficiency of over 98 per cent and a cell voltage of 1.6 V at 2.5 kA m-’. This gives an energy consumption of 1100 kWh ton-’ of NaOH, which is much lower than is achievable by competing technologies, see Table 111. Moreover, the energy consumption should be reducible to about 800 kwh ton-’. The economics of the process depend on the balance of the markets for chlorine and NaOH, as well as on the value given to the liquid carbon dioxide recovered from the anode gas stream. Future work will focus on the long term stability of the anode and the influence of impurities in the sodium carbonate feedstock.

Three Dimensional Electrodes Some electrolytic processes inevitably take

place at low current densities because: (a) the objective of the process is to remove a low level toxic component from an effluent (b) the reactant for a synthesis has only a low solubility, or (c) the rate of conversion is kinetically controlled. For such processes, scale-up may be achieved using a three dimensional electrode, fabricated, for example, from a bed of spheres or particles, a foam or a felt (23). Such structures made solely from noble metals are not available, and in any case, would be prohibi-

tively expensive. Hence, three dimensional electrodes using the platinum group metals must again be based on coated titanium.

The Olin Corporation has recently started to market a titanium felt type material called TySARTM which is manufactured by welding together titanium fibres of thickness 50 to 60 ptn (24). The material is 85 to 90 per cent porous, has a specific surface area of 6000 to 9000 mz m-’ and is available in sheets of size 0.5 m x 1.0 m with a thickness of 3.2 mm. Hence, in many respects it is similar to the metal and carbon foams which can be purchased. Although there is little data in the open literature, TySARTM should be an excellent three dimensional electrode material, allowing reactions with accept- able space-time yields to be carried out in cells at low current densities. TySARTM EP is a form supplied with an electroless metallic platinum coating of sub-micron sized, hemispherical platinum particles, giving a 60 to 95 per cent coverage of the titanium surface. The total platinum loading in a 1.0 m x 1.0 m x 3.2 mm electrode would be = 80 g. Although this is still costly, TySARTM offers one route to achiev- ing a three dimensional platinum electrode. Expanded titanium mesh is a standard material suitable for coating with platinum group metals or oxides. Indeed, electrodes based on coated expanded titanium mesh are widely available.

Therefore, stacked coated titanium meshes


Table 111

Energy Consumption for Various Electrochemical Technologies for the Manufacture of Sodium Hydroxide

n l - . 0 2 03 04 05 06 07 08 09 1 0

POTENTIAL V S SCE, volts

Fig. 5 Current, I, versus potential, E, curves for a solution comprising 5 mM

and 0.5 M Na2S04 at pH 11, in a cell containing an anode made up of 8 fine expanded, SnO, mated titanium meshes. The potential scan rate is 5 mV s-’ and the temperature is 298 K. The mean linear velocities of the electrolyte are: (a) 0.007 rn s-’, (b) 0.04 m s-l, (c) 0.07 m s-’, (a) 0.14 m E-’, (e) 0.28 m s-l

K b F e ( c N ) 6 , 2 5 mM K3Fe(cN)6

provide a second convenient way to fabricate three dimensional electrodes where the active surface may be a platinum group metal, an alloy or an oxide. Stacks of fine meshes also make excellent three dimensional electrodes because they lead to high values of the mass transfer coefficient as well as moderate specific electrode areas (25).

Voltammograms of a solution of 5 mM ferrocyanide at a stack of 8 fine, coated titanium meshes are shown in Figure 5 (the coating is SnOz although the data for a mass transport controlled reaction is independent of the coating). It can be seen that very high limiting currents are obtained even for such a low reactant concentration (42 mA cm-’ mM-’). In practice, limiting currents are about twice as high as at a metal foam anode for the same flow rates of solution; this would allow the design of very compact cells for high, single-pass, conversions. Unfortunately, with a loading of 10 g m-’ on the titanium surface and a stack of 8 fine meshes of total area 1 mz, the platinum group metal content of such an electrode structure would contain approximately 50 g of metal.

Thus, it can be seen that high performance, three dimensional electrodes are very achievable; however, there is a great commercial ben- efit in minimising the thickness of the platinum group metal coating.

Conclusions Electrochemical technology is now clearly

identified as a “clean technology” for the manufacture of chemicals. It also finds application in processes for recycling chemicals and materials, treating effluents, destroying toxic materials, soil remediation and other diverse technologies. All this technology depends on stable electrode materials and, frequently, only platinum group metal materials fulfil this requirement. The objective of electrodekatalyst design is often, therefore, to place the noble metal in a stable matrix and to achieve the required performance with a minimum noble metal loading. Platinum group metals, their alloys and oxides used as coatings on inert substrates of titanium, nickel and carbon, have already found many applications, and further advances are sure to be a feature of the early 21st century.

References 1 D. Pletcher and F. C. Walsh, “Industrial 3 “Electrodes of Conductive Metallic Oxides, Parts

ELectrochemisay”, ChapmanandHall,London, 1990 A and B”, ed. S. Trasatti, Elsevier, Amsterdam, 2 D. L. Caldwell, in “Comprehensive Treatise of 1980/1981

Elecuochemisay”, Volume 2, eds. J. O’M. Bockris, 4 S. Trasatti, in “The Electrochemistry of Novel B. E. Conway, E. Yeager and R. E. White, Plenum, Materials”, eds. J. Iipkowski and P. N. Ross, VCH, New York, 1981, p. 122 Boca Raton, 1994


5 E. N. Balko, Studies Inorg. Chem., 1991, 11, 267 6 C. Comninellis and G. P. Verceri, J. Appl.

Electrochem., 1991, 21, 335 7 A. P. Bacon, 2. Twardowski and N. Tam, in

“Modern Chlor-Alkali Technology”, Volume 6, ed. R. W. Curry, R. SOC. Chem., 1995, p. 258

8 D. E. Grove, in “Modern Chlor-Alkali Technology”, Volume 3, ed. K. Wall, Ellis Horwood, 1986

9 D. S. Cameron, R. L. Phillips and P. M. Willis, in “Modern Chlor-Alkali Technology”, Volume 4, eds. N. M. Prout and J. S. Moorhouse, Elsevier Applied Science, 1986

10 Y. B. Vassiliev, E. P. Kovsman and G. N. Freidlin, Electrochim. Acta, 1982, 21, 937 and 953

1 1 D. S. Watkins, in “Fuel Cell Systems”, eds. L. Blomen and M. Mugerwa, Plenum, New York, 1993,493

12 K. B. Prater,J. Power Sources, 1996, 61, 105 13 S. Srinivasan, 0. A. Velev, A. Parthasarathy, D. J.

Manko and A. J. Appleby, J. Power Sources, 199 1, 36,299

14 M. P. Hogarth and G. A. Hards, PZutinum Metals Rev., 1996,40, (4), 150

15 M. S. Wilson, J. A. Ben, T. A. Zawodzinski, J. A. Valerio and S. Gottesfeld, Electrochem. SOC. Spring Meeting, San Francisco, 1994, Abstract no. 626

16 A. S. Arico, 2. Poltarzewski, N. Giordano and V. Antonucci, Electrochem. SOC. Spring Meeting, Reno, 1995, Abstract no. 484

17 P. C. Foller and R. T. Bombard, J. Appl. EZectrochem., 1995, 25, 613

18 A. M. Couper and S. Bullen, Inst. Chem. Eng. Symp. Series, Rugby, 1992, 127, 49

19 P. C. Foller and G. H. Kelsall, 3. Appl. Electruck., 1993,23, 996

20 R. J. Allen, P. C. Foller, R. J. Vora, R. T. Bombard and M. Demarinis, J. O.M., 1993,45, (3), 49

21 P. C. Foller, R. J. Allen, R. T. Bombard and R. Vora, Proceeding of the Fifth Int. Forum on Electrolysis in the Chemical Industry, Fort Lauderdale, November, 199 1, The Electrosynthesis Co. Inc., Lancaster, New York

22 J. D. Genders, E. F. Spiegel, D. Pletcher and N. L. Weinberg, J. Appl. Electrochem., submitted

23 D. Pletcher and F. C. Walsh, in “Electrochemistry for a Cleaner Environment”, eds. J. D. Genders and N. L. Weinberg, The Electrosynthesis Co. Inc., Lancaster, New York, 1992

24 Olin Corporation, US. Patent 5,294,319 25 L. Lipp and D. Pletcher, EZectrochim. Acta, 1997,

42, 1101

A Rhodium Solvated Molecular Wire One-dimensional inorganic compounds have

been investigated for a number of years because of their interesting electrical properties and their predicted high temperature superconductiv- ity; indeed the square-planar platinum cyano- complex ion, [Pt(CN)4]2, has been one of the commonest materials examined (1). Recently, there has been increased attention paid to molecular structures which can form molecular wires and act as connectors in molecular-scale electric devices (2). The controlling factors for the formation of these structures have been the ligands, which effectively govern the closeness between the metal atoms, and the electronic properties of the metals, which need incom- pletely filled bands to allow electron movement. However, there have been few infinite metal- metal bonded chains, because the ligands typically used in co-ordination compounds do not allow direct approach of the metal atoms along the axial direction.

Now, however, scientists from Michigan State University and Siemens in the U.S.A. and the Institut de Ciencia de Materials de Barcelona in Spain, have succeeded in converting a discrete rhodium-rhodium bonded dimer into an infinite one-dimensional “polymer” array, { [FUI(M~CN)~] (BF4)l.5}=, by the one-electron reduction of [Rhz(MeCN)lo] (BF&, in a cell also containing [(nC4H9)4N]BFd in MeCN, with platinum electrodes and an applied current of 2 pA.

The unbridged rhodium compound was used in the investigation because it possessed only small, linear MeCN ligands, whose steric effects are minimal (3).

This rhodium polymer is the first, mixed valence, one-dimensional compound of rhodium, and is the only example of an infinite metal-metal bonded chain synthesised from a dinuclear precursor. The ligands are neutral donors, thus there is cationic charge on the chains which form the backbone. This contrasts with the partially oxidised tetracyanoplatinates which are anionic. The ligands may also be tailored, so it might be possible to produce insulating sheaths around the central chain of rhodium atoms, leading perhaps to liquid crys- tallinity, and allowing small changes in properties by varying the organic groups.

This novel rhodium chain polymer will enable the theory of one-dimensional materials to be tested, and using different ligands, will give insights into structures and transport properties.

References 1

2

A. E. Underhill, Platinum Metals Rev., 1974, 18, (11221 V. Grosshenny, A. Harriman, M. Hissler and R. Ziessel, Platinum Metals Rew., 1996, 40, (l), 26; op. cit., 1996, 40, (2), 72

3 G. M. Finniss, E. Canadell, C. Campana and K. R. Dunbar, Angew. Chem., Int. Ed. Eng., 1996, 35, (23/24), 2772

Plarinum Metals Rev., 1997, 41, (2) 63

Gas -Powered Co - Generation PLATINUM METALS MAXIMISE EMISSION CONTROL AND HEAT GENERATION FOR RESIDENTIAL USE

An engine powered by natural gas has been developed by the Sachs Special Motor Division of Fichtel & Sachs AG of Schweinfurt, Germany, to co-generate heat and electricity for both residential and commercial use. The power unit is a 0.583 litre single cylinder gas engine designed to run for a minimum of 60,000 hours or 15 years. It has an electrical output of 5.5 kW, together with 12.5 kW equivalent heat which is produced with the help of an oxidation catalyst.

The Environmental Products Group of Johnson Matthey’s Catalytic Systems Division has worked with Fichtel & Sachs on an extensive programme which involved the evaluation of various configurations of the catalyst so as to optimise the system. The catalyst is required to perform two different functions:

to reduce emissions of hydrocarbons and carbon monoxide in the engine exhaust, in order to meet environmental emissions control requirements, and at the same time

to promote catalytic combustion of any unburnt gases in the exhaust, to ensure that heat generation and recovery are optimised.

Specifically, the primary requirements of

the dual purpose platinum metals catalyst are: (i) High efficiency for the reduction of methane, ethane, propane and other volatile organic compounds in the exhaust: this is because the light hydrocarbons - particularly methane - are relatively hard to combust. New catalyst technology has been developed to meet this requirement. (ii) Maximum heat generation and recovery in order to optimise the heat output: thus the catalyst is coated on a honeycomb metallic substrate so that heat transfer is enhanced. (iii) Minimised impact on the engine performance: t h i s is achieved by the use of a thin walled metallic substrate which reduces the back pressure to the engine. (iv) Meet life-cycle requirements with little or no maintenance: thus, the catalyst needs to have a high durability of performance. As this is determined by the composition of the catalyst materials, they must possess long-term thermal stability under the harsh exhaust environments encountered. The durability characteristics of the catalyst over thousands of hours of operation have been demonstrated.

The combined heat and power eo-generation unit oecupiea the same space a standard heating unit. Systems can easily be linked together to heat larger buildings. The system, which UE- natural gas, produces over 5 k W of electricity and the heat it produces can supplement an existing furnace or heat domestic water. With the catalyst, the unit produces lees NOx and carbon dioxide emissions, and I.equiree less fuel than conventional heating systems. Maintenance is minimal and silencers ensure it complies with local requirements

Plarinurn Metals Rev., 1997,41, (2), 64-65 64

For these reasons, the highly durable catalyst consists of platinum metals on a washcoated thin-walled metal substrate, which ensures optimum gas flow, high heat transfer and high thermal durability with good adhesion of the platinum metals catalyst to the metallic substrate.

The catalyst is positioned in a compartment attached to the engine through a uniquely designed water-cooled heat exchanger. The complete system is packaged in a compact unit that can be installed much like any other residential heating unit. The heat can be directly utilised or transferred to neighbouring buildings, while the electric power can either be inte- grated directly into the residential electricity supply or transmitted to a local power utility.

Compared to separate heat and power units, this new development reduces NOx emissions by 25 per cent and emissions of carbon dioxide by 47 per cent. In fact, looking at the total balance of energy input, the new SenerTec co-generation unit requires 3 1 per cent less fuel input than conventional heating systems.

Once the technical concept was proven, which included durability tests lasting for in excess of 10,000 hours, Fichtel & Sachs established an independent joint venture - SenerTec GmbH - to manufacture, market and sell these novel co-generation units. The units are already on sale in Germany, the Netherlands, Austria, Switzerland, Denmark and Sweden. Following

Engine performance data generated after the sseembly of a unit as a quality control measure prior to shipment of the unit. The data in the upper figure show the performance characteristics of the engine, while in the lower figure the characteristics of the engine emissions are shown

The co-generation unit showing the control eonsole and the water-cooled heat exchanger where the emission control catalyst is situated

the successful collaboration between the groups, Johnson Matthey have been appointed exclusive supplier of catalysts for these SenerTec engines.

H. WINDAWI, R. GUNTRUM AND J. KEMPF

Phtinum Metals Rm., 1997,41, (2) 65

Platinum Catalysts Used in the Silicones Industry THEIR SYNTHESIS AND ACTIVITY IN HYDROSILYLATION

By Larry N. Lewis, Judith Stein, Yan Gao, Robert E. Colborn and Gudrun Hutchins GE Corporate Research & Development Center, General Electric Company, Schenectady, New York

Hydrosilylation i s a reaction widely used in the silicones industry for the preparation of monomers, containing silicon-carbon bonds, and for crosslinking polymers, and results in a variety of products. Hydrosilylation reactions are catalysed by highly active plat inum catalysts, such as the silicone-soluble Karstedt's catalyst, which is prepared by the reaction of chloroplatinic acid, H,PtCl,, with vinyl-silicon containing compounds, such as diuinyltetramethyl- disiloxane, A f ' i V f . Inhibitors are widely used during hydrosilylation reactions to prevent premature crosslinking of polymers at ambient temperature, but permit rapid platinum-mediated crosslinking reactions at higher temperatures. Platinum colloids are formed at the end of the reaction and were identvied by analysis. T h i s paper discusses the mechanism of the hydrosilylation reaction, catalyst formation, characterisation, the effects of inhibitors and the range and complexity of the end products.

The silicones industry extensively uses the platinum-catalysed hydrosilylation reaction, in which a silicon-hydrogen (Si-H) bond is added across the unsaturated carbon-carbon double bond (C=C) of an olefin, Equation (i), resulting in the formation of a silicon-carbon (Si-C) bond (1-8).

R S H + HzC=CHR a RISiCHzCH2R (i)

Hydrosilylation can be used for the synthesis of monomers; for example, in Equation (ii) the addition of a methyl dichlorosilane to an alkene gives a monomer, a methyldichlorosilyl-

substituted compound, which upon hydrolysis gives a polymer, a polysiloxane with hydrocarbon functional groups.

Hydrosilylation is used to a much greater extent in industry to produce crosslinking reactions (9-1 1). The crosslinked network shown in Equation (iii), for example, is created by the addition of platinum to a mixture composed of a difunctional vinyl-containing polydimethylsiloxane and the multifunctional Si-H- containing copolymer of polydimethylsiloxane and methylhydrogen siloxane.

Here, to show the crosslinking in the polymer

Platinum Metals Rev., 1997,41, (2), 66-75 66

chain which has been catalysed by platinum, the M, D, T and Q notation is used, where My D, T and Q refer to mono, di, tri and quaternary oxygen substitution at silicon and where a super- script is used to describe substitution at silicon other than methyl as in M", which refers to vinyldimethylsiloxane, D is dimethylsiloxane and DH is methylhydrogen siloxane.

Crosslinked silicones such as these are used for: automotive gaskets, paper release coatings, pressure sensitive adhesives, baby bottle teats, and many other applications. So-called liquid injection molding (LIM) applications employ hydrosilylation for curing and LIM finds application in computer key pads, to name just one current use.

Hydrosilylation Catalysts One class of platinum compounds used as

hydrosilylation catalysts are Pt(0) complexes containing vinyl-siloxane ligands ( 12, 13). An example of such a catalyst is Karstedt's catalyst, Pt.(M"M"),, formed by the reaction of divinyltetramethyldisiloxane (MnM") with chloroplatinic acid, H2PtCla, Equation (iv).

Karstedt's catalyst is a Pt(0) complex which contains both bridging and chelating di-vinyl ligands (14, 15). The designation of Pt(M"M"), and M"D,M" as "solution A" is taken from the work of Lappert's group and is used to describe

Platinum Metals Rev., 1997, 41, (2)

the mixture of products containing platinum and vinyl- siloxane oligomers (1 6, 17).

In the late 1960s and early 1970s, Willing of Dow Coming ( 18) and Karstedt of GE (1 5) described the reaction of chloroplatinic acid and vinyl-containing siloxane monomers to make silicone- soluble platinum complexes.

Little was then known (1 9) about the structure of the platinum complexes which resulted from the reaction shown in Equation (iv) until the work of Lappert and co-workers (16, 17). The Lappert group reported that the platinum product, 1, of Equation (v):

2Pt(COD)2 + 3M"M"- Pt2(M"M"), (V)

1

I COD = 1.5syclwctadtene

contained a bridging MnMn and each platinum had a chelating M"Mn group. '95Pt NMR spectroscopic analysis of "solution A" showed the presence of two resonances which Lappert suggested was due to two isomers of 1. We proposed that the two 195Pt NMR resonances were caused by the presence of 1 and 2, see Equation (vi) (20).

2Pt(MnMv')2 $ Pt2(M"Mn)3 + MnMn 2 1 (vi)

Pt(MnMn)2 + 3MnDxMn =+ Pt(MnD,MV'), + 2M"M"

#en "solution A" was combined with vinyl- stopped polydimethylsiloxane oligomers, a single lP5Pt resonance was observed. Furthermore,

67

analysis of "solution A" by field desorption mass spectroscopy (FDMS) showed the presence of 2 and vinyl-stopped oligomers, as shown in Equation (iv). .

The reduction of Pt(1V) to Pt(0) by a silicon-vinyl group, in Equation (iv), appeared to be a new reaction. When M"M" was the reducing agent, some of the silicon vinyl functionality was converted to a silicon-oxygen group. The net result was the conversion of an M" group into a D (dimethylsiloxane) group. The vinyl group was changed primarily into either butadiene or ethylene. Water was the source of the new oxygen bond to silicon. Similarly, when D" is the source of reducing agent, as in the reaction of Equation (vii), a D" group is converted into a T group.

The overall platinum conversion occurring in Equation (iv), is from Pt(IV) to Pt(0); the platinum in "solution A" being in the zero oxidation state. We attempted to observe the imputed P t O intermediate from this vinyl-silicon-mediated reduction in Equation (iv). Typically, in this reaction, chloroplatinic acid is reacted with MnM" in the presence of some ethanol, which aids in the dissolution of &PtC16. Sodium bicar- bonate was added to remove chloride. Both ethanol and NaHC03 may aid the reduction. A

Pt NMR spectrum of "solution A" showed the previously mentioned resonances at -6200

However, when the reduction was carried out without ethanol or NaHC03, a broad 1 9 T t resonance was observed at -3470 ppm, which may be due to a Pt(II) intermediate. In order to char- acterise further the potential Pt(I1) intermediates and to improve understanding of the mech-

195

ppm.

anism of the reduction process, HzPtCls was reacted with several silicon-vinyl-containing species. The product of the reaction of HZPtCl6 and dimethyldivinylsilane, (CH3)zSi(CH=CHz)2, gave two products, see Equation (viii), a Pt(I1) complex, 3, and a Pt(0) structure, 4. Complex 3 was isolated and a single crystal X-ray

structure, see Figure 1, showed it to be a dinuclear complex with two bridging chlorine atoms and a bridging (CH3)2Si(CH=CH2)2 lig- and. Additionally each platinum atom in 3 contained a q':qZ-(CH&Si(CH=CH2)(CH2CH3) ligand. Compound 3 had a "'Pt N M R resonance at -3603 ppm, while the Pt(0) product, 4, had a 195Pt NMR resonance at 4 152 ppm. Although the structure of 4 was not determined directly, addition of PPh, to solutions containing 4 produced (M"M")Pt(PPh3) suggesting that 4 was Ptz(M"M'i).((CH3)2Si(CH=CH2)z), (20).

Inhibitors Another important aspect of industrial hydrosi-

lylation is the use of inhibitors (21-23). The crosslinking reaction of Equation (iii) will usually occur with as little as 10 ppm platinum, at ambient temperature in a matter of minutes. The rapidity of this reaction leads to the need

04" I

? T is M e S i - 0 -

d\ =/ \ =J\

D;'T-TD?

t Higher oligomers

? (vii)


Fig. 1 The three dimensional structure of 3 produced by the reaction of H2PtC16 with (CX&)Si(CH=C€&)l. This dinuclear complex has two bridging chlorine atoms and a bridging (CH,)rSi(CH=CHz)z ligand. Each platinum atom in 3 contains a tl’:tl’-(~)Si(CH=CH,)(CHzCX&) ligand (20)

for inhibitors to give some control over the reaction. Typical industrial applications require long work times at low temperatures, followed by fast curing times at elevated temperature.

the reaction of “solution A” with one equivalent of PPh3, in the presence of 10 equivalents of MnM”. In effect the fumarate (or maleate) replaces the bridging, but not the chelating

Two inhibitors, dimethyl fumarate and dimethyl maleate, are commonly added to platinum-catalysed crosslinkable silicone formulations to permit 1ong.work life by the end user at ambient temperature with a rapid cure at elevated temperature. The reaction of “solution A” with four equivalents of dimethyl fumarate, relative to platinum, resulted in formation of a platinum-fumarate complex, 5, see Equation (ix). Complex 5 was characterised on the basis of its I3C NMR spectrum and by comparison of its spectrum with those of the maleate analog, 6, and the previously well characterised compound PPh3Pt(M”M”), 7. Compound 7 was prepared by

Solution A - + i s

2


/

\

' 6 7

MnMn ligand in Karstedt's catalyst. A comparison of the 13C NMR spectra for 5,

6 and 7 in the olefin-platinum region is shown in Figure 2. All the "C olefin resonances had

Pt satellites. The spectrum of 5 showed four overlapping triplets from 68 to 72 ppm. These four resonances derived from the four different olefinic carbons present in the chelating M"Mn ligand.

By contrast, the ''C NMR spectrum for 6 had two resonances for the olefinic carbons of the MnMn ligand because the two double bonds are chemically equivalent. The downfield triplet resonance at 69.2 ppm (JWC = 56 Hz) was assigned to the methylene carbon of the M"M"

195

ligand of 6, while the methyne carbon was the triplet upfield at 7 1.94 ppm (JPK = 42 Hz) . Both 5 and 6 showed peaks in the I3C NMR due to the olefinic carbons of fumarate and maleate, respectively, with large coupling constants: JP~-c = 89 and 104 Hz, respectively. Compound 7, where maleate or fumarate was replaced with PPh3 had two resonances for those of the olefinic carbons of M"M", but shifted

upfield relative to those in 6 due to the presence of the PPh3 ligand.

Platinum Colloid Formation The mechanism of the hydrosilylation reac-

tion at the molecular level has been studied for many years (1-8), and several reviews have been devoted to the reaction (24-28). The Chalk-Harrod mechanism, developed during the 1960s, is the most often cited mechanism for hydrosilylation and is based on fundamen- tal steps of organometallic chemistry (8); these include oxidative addition of a Si-H group to a metal-olefin complex, insertion steps and reductive elimination. However, a number of

Me

70 60 50

Fig. 2 Comparison of ''C NMR spectra in the "bound" olefin region for compounds 5 ,6 and 7 (23); 5 is the spectrum of the fumarate analogue, 6 is the speetrum of the maleate analogue and 7 is the spectrum of the eompound prepared from "solution A", w,ith PPh, and M"'M"'

Platinum Metals Rev., 1997,41, ( 2 ) 70

phenomena are not explained by the Chalk-Harrod mechanism and among these is the presence of an induction period (the time between the start of a chemical reaction and its observable occurrence), formation of coloured bodies and co-catalysis by oxygen. In the 1980s Lewis and co-work-

ers proposed a mechanism based on the intermediacy of platinum colloids (13, 14, 25, 26), which had been observed via transmission electron microscopic (TEM) analysis of reaction solutions following platinum-catalysed hydrosilylation (27).

Reaction solutions from a platinum-catalysed hydrosilylation reaction were originally analysed by first evaporating the reaction solutions

evaporation. Pt crystallitea

evaporation Pt crrjtallites

Karstedt's catalyst evaporation Pt crystallitei

(xiv) PtClL + (CH3)2(CH3CH20)SiH - D&

evaporation Pt crystallites

Note that D4 is cyclooctamethyltetrasiloxane

and then recording the TEM images (12-14, 22-25). TEM analysis showed, in some cases, that colloidal platinum had formed after the hydrosilylation reaction. More recently, Pt EXAFS of reaction solutions from hydrosilylation reactions has shown that the type of platinum species formed in solution at the end of a reaction depends on:

the ratio of Si-H to vinyl used (21), and the nature of the olefin (hydrocarbon or

silicon-vinyl) . The two types of platinum end products

observed are illustrated in Equation (x) where

M " M ~ MD"M

sin vinyl Pt

Karstedts catalyst

Sin vinyl pt-pt(i) z 85A

g I 8 was the species formed at high vinyl concentrations and 9 was the platinum product formed when the concentration of Si-H was greater than,

or equal to, that of vinyl. Compound 8 was the designation used for platinum species containing only Pt-C bonds (at a typical Pt-C:olefin distance of around 2.17 A and with a co-ordination number, number in parentheses, of six). Compound 9 was the species that contained both Pt-Pt and Pt-Si single bonds as determined by EXAFS.

Platinum species 9 could be converted to 8 in the presence of excess olefin (if the olefin was a silicon-vinyl compound, that is, ifmore MD"M was added). Compound 8 was formed when silicon-olefin was the olefin source, that is MD"M.

However, if a Si-H compound was reacted with an olefinic hydrocarbon, such as hexene, which does not contain silicon-vinyl, then 9 was formed regardless of the stoichiometry of olefin and Si-H. Similarly, with neo-hexene (3,3- dimethyl-1-hexene) platinum reaction product 9 is formed &om the platinum-catalysed hydrosilylation reaction between neo-hexene and a number of different Si-H compounds, even if'he concentration of Si-H:neo-hexene is 1 :2.

The reactions in Equations (xi) to (xiv), (where (xi) and (xii) describe the platinum catalysed hydrosilylation of triethylsilane with neo-hexene), all give dark-coloured solutions. TEM analyses of the reaction products from these


solutions after evaporation all show that platinum crystallites were present.

A representative TEM, from Equation (xiii), is shown in Figure 3; here individual crystallites can be seen, displaying diffraction fringes with spacing which matches that for the (1 1 1) plane in crystalline platinum. The diffraction pattern also could be indexed to that of platinum. Finally, energy dispersive X-ray spectroscopy of the spots confirmed that they were composed of platinum.

In the reactions shown in Equations (xi) and (xi;) , in situ studies showed that platinum of type 9 (from Equation (x)) formed in the reactions with neo-hexene. On evaporation, the type 9 platinum composition is converted to platinum crystallites. The effect of dilution with D, or

Equation Pt concentration, mg ml-'

(xi) 0.29 (xii) 0.3 (xiii) 0.3 (xiv) 0.46

Fig. 3 Transmission electron micrograph of the platinum colloids formed hy evaporation of the reaction product between (CH3)2(CHdXL0)SiH and Karstedt's catalyst solution, (Pt(CH3)z(H2C=CH)SiOSi(CH= CHz)(CH3)2)., Equation (xiii). The dark spots are platinum crystallites which reveal diffraction fringes corresponding to the platinum (111) lattice spacing

Number average

Mean, A Minimum, A Maximum, A Standard deviation

24.4 16 36.1 3.6 17.3 10.3 26.4 2.9 22.6 9.6 33.3 3.6 30.4 17.6 46.9 5.4

of running the reaction without solvent was examined together with the effect on platinum crystallite size. Reactions between dimethyl- ethoxysilane and either Karstedt's catalyst (Equation (xiii)) or PtCl, (Equation (xiv) (1 2)) were carried out under conditions where previous reports had shown that colloids formed. The Table shows the results of a statistical analysis of the particle sizes of the platinum crystallites formed from the reactions in Equations (xi) to (xiv).

The particle size of the crystallites may have been affected by the platinum concentration; it can be seen in the Table that the larger particles from Equation (xiv) are produced from a higher platinum concentration. The particles formed from Equations (xi) and (xiii) were

Statisties on Particle Sizes of Platinum Crystallites Formed in Equations (xi) to (xi.)


Fig. 4 Transmission electron darkfield image of the evaporated solution from Equation (xvii). Note the presence of moiC diffraction fringes due to slight mis- alignments of the thin crystalline sheets making up the material

similar in size and larger than those from Equation (xii). Equation (xii) did not use D4 diluent .

When hydrosilylation reactions were run with silicon-vinyl substrates, for example Equation (x) where platinum of type 8 is formed, TEM analyses of the resulting evaporated solutions were different from those obtained from Equations (xi) to (xiv). Note that all of these reactions were carried out in neat solutions and it is not known if the absence of diluent con- tributed to the observed TEM. TEM of evaporated solutions from Equations (xv) to (xviii) showed the complete absence of the platinum crystallites seen in Figure 3.

M"M + M ~ M P ~ -

M D ~ M + M D ~ M (xvii)

M"M" + (CH,CH2),SiH2 a (xviii)

A darkfield TEM micrograph, prototypical for the evaporated solution Erom Equations (xv) to (xviii) is shown in Figure 4. Energy dispersive X-ray spectroscopy confirmed the presence of platinum. However, the diffraction pattern did not match that of metallic platinum

or any platinum compound in the powder diffraction file. Electron diffraction analysis indicated the presence of a crystalline material which had formed in very thin crystalline sheets that were slightly misaligned with respect to one another. The moire diffraction fringes due to this misalignment are clearly visible in the micrograph.

Evaporation of the product solution from the reaction between PtCL and a siloxane-like Si- H source, M3TH, tris(trimethylsi1oxy)silane (MeSiO)SiH, gave a TEM similar to Figure 3, while evaporation of the product solution from the reaction between PtCL, MITH and M3T' gave a TEM similar to Figure 4. Further studies are underway to determine the structure of platinum species present during hydrosilylation under the various conditions discussed here. The species in Figure 4 may be explained by these analyses (29).

Summary and Conclusions Hydrosilylation is widely used industrially for

the preparation of monomers with silicon- carbon bonds and for producing crosslinked polymers.

Highly active, silicone-soluble platinum catalysts can be prepared by the reaction of chloroplatinic acid with vinyl-silicon containing compounds. The vinyl-silicon compounds, such as


divinyltetramethyldisiloxane (M”M”) reduce platinum(IV), in chloroplatinic acid, to platinum(0) with the concurrent conversion of the silicon-vinyl group to a silicon-oxygen group. A typical platinum catalyst is Karstedt’s catalyst, Ptx(M”M”),.

Inhibitors are widely used in industry to control the platinum-mediated addition reaction of curable systems. The addition of inhibitors pre- vents hydrosilylation (crosslinking) at low temperature while permitting rapid reaction at elevated temperature. Commonly used inhibitors include those with electron deficient double bonds, such as maleates and fumarates. Dimethyl maleate reacts with Karstedt’s catalyst to make a complex containing a chelating M”M” group and a maleate ligand.

Previous studies reported that formation of platinum colloids was a key step in hydrosilylation. It is now clear that colloid formation occurs as an end stage of the reaction. EXAFS analy-

sis has shown that molecular compounds are present during hydrosilylation. Colloidal platinum is observed by TEM after evaporation of solutions from several reactions which involve platinum, a Si-H compound and either poorly co-ordinating olefins or no olefin. However, in some cases where silicon-vhyl-containing species were present, the reaction product between platinum and a Si-H-containing compound did not give colloidal platinum species; and TEM analysis showed that the crystalline material present was not metallic platinum crystallites.

Further work is in progress to identify the structures of platinum intermediates formed during hydrosilylation and industry continues to search for more highly active catalysts and more effective inhibitors.

Acknowledgements

statistical analysis from the TEM images. I would like to thank Jim Grande for performing the

References

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New Platinum-Based Lean The introduction of increasingly stringent envi-

ronmental legislation brings benefits to our quality of life, and presents challenges to catalytic chemists, who are required to develop novel solutions to enable the new legislation to be met. Within the automotive area, new legislative lim- its to exhaust pollutants mean that it will soon be necessary for the catalytic convertors on diesel vehicles to additionally remove significant concentrations of nitrogen oxides, NOx, from the exhaust feed, besides the oxidation functions for carbon monoxide, CO, and hydrocarbon which they already perform.

Diesel engines are extremely fuel-efficient. This is achieved by ensuring that combustion occurs under highly oxidising conditions, and results in a strongly oxidising gas feed which needs to be treated using a catalytic convertor. Under such highly oxidising conditions the oxidation of the unburnt hydrocarbons to COZ and HzO and of the CO to COz is relatively straight- forward. However, reducing NOx to Nz under such conditions is very difficult.

The major breakthrough in automotive NOx control under very oxidising conditions was reported simultaneously by the Held group in Germany (1) and by the Iwamoto group in Japan (2). These workers independently showed that significant quantities of NOx could be reduced to Nz under highly oxidising conditions using a catalyst of copper incorporated into ZSM-5 zeolite. Others have characterised the mechanistic aspects of the reaction over CdZSM-5 (for example (3)), and have shown that the major role of the copper is to oxidise NO to NO,. This subsequently reacts with hydrocarbon-derived species activated by the surface of the zeolite.

The copper catalyst can only be used at relatively high temperature (350-550°C), and it is not particularly stable. The conversion of NO to NOz over copper is poor at the low temperature end of this range, so its performance here is nowhere near as good as that of platinum. At high temperature the NO to NOz reaction becomes limited by thermodynamics and both copper and platinum catalysts then become equivalent in their NO oxidation performance.

Now, Iwamoto has used the mechanistic

NOx Conversion Strategy - - information/approach to develop a highly efficient NOx conversion catalyst system capable of operating at low temperatures (4). The strategy uses two separate catalysts - one to oxidise the NO into NO, and the other to reduce this NOz into Nz. Iwamoto has shown that platinum incorporated into ZSM-5 zeolite is a highly efficient NO oxidation catalyst and t h i s catalyst is used to perform the first step in the conversion process. The second step is carried out using indium incorporated into ZSM-5 zeolite. Since there is only a small amount of unburnt hydrocarbon in the exhaust stream of a diesel vehicle, additional hydrocarbon needs to be injected to provide the reductant to achieve significant NOx conversions.

Position of Hydrocarbon Injection Platinum is an excellent oxidation catalyst,

which means that if the hydrocarbon were injected in front of the platinum catalyst, substantial quantities would be converted over the platinum, thereby lowering the hydrocarbon concentration reaching the indium catalyst. Iwamoto proposes that this additional hydrocarbon injection should instead occur between the two catalysts: that is, after the platinum catalyst and before the indium catalyst, thus ensuring that the indium reduction catalyst sees enough hydrocarbon to effect the reduction of the NO, generated over the platinum catalyst.

This approach is the latest in the long line of platinum-based strategies developed to remove NOx under highly oxidising conditions. Within industry and academia, platinum-based work is continuing to advance the technology further to ensure that future environmental legislation can be met. A. P. WALKER

Referencea 1

2

3

W. Held, A. Konig, T. Richter and L. Puppe, SAE Paper 900496,1990 M. Iwamoto, Proc. Catalytic Technology for Removal of Nitrogen Monoxide, Tokyo, 1990,17 G. P. Ansell, A. F. Diwell, S. E. Golunski, J. W. Hayes, R. R. Rajaram, T. J. Truex and A. P. Walker, Appl. CutuZ. B: Emiron., 1993,2, 81 M. Iwamoto, A. M. Hernandez and T. Zengyo, Chem. Commun., 1997, (l) , 37

4

PZuzinum Met& Rev., 1997,41, (2) 75

Emission Control Technology at Detroit A SELECTIVE REPORT FROM THE 1997 SAE ANNUAL CONGRESS

Traditionally, the main annual Congress of the Society of Automotive Engineers (SAE) takes place each year in Detroit during the last week of February. This year it was held from 24th to 27th February, inclusive, and the scale of the event can be judged from the 800 exhibit- ing companies in the “expo~ition” areas, and the 45,180 officially registered participants, drawn from all the countries concerned in the manufacture of cars or their components. In total 1008 papers were presented, covering all aspects of automobile technologies; each day there were sessions dealing with exhaust emission control. Within this area a wide range of topics was considered. Most of the papers are available in SAE “single publications” SP1227, SP1238, SP1246, SP1248 and SP1260.

Here, a selection of these papers has been chosen to illustrate the changing roles that platinum group metals have in the important area of exhaust aftertreatment, and the direction that catalyst technology is taking. The SAE reference numbers of the original papers are given in parentheses.

The main emphases in emissions control this year, as last year, included cold start strategies and three-way catalysts (TWCs) for conventional gasoline engines. Additionally, there was a high level of interest in the treatment of exhaust gases from diesel and other lean burn engines.

Cold Start Strategies Electrically Heated Catalysts

Last year several reports were presented on the use of electrically heated catalysts (EHC) for dealing with cold start emissions (1). This year Alpina, BMW and Emitec (970263) gave an update on the only European production car fitted with EHCs. Of the 100 vehicles produced, each was started on average four times per 100 km, and more than a third of them were cold starts where the coolant temperature was below 40°C. The EHCs worked well and had good mechanical durability during the first year of

service. However, with the present combination of a 110 Ali’ battery and 150 A alternator, the EHC system is not capable of dealing with low temperature starting, for example, at -7”C, mainly due to the high internal resistance of the battery under these conditions. Clearly, further developments are needed in this area before EHC technology is capable of being introduced more generally. A paper by the Polish company Bosmal(970740) emphasised that low ambient temperatures are common during winter in much of Eastern Europe and many parts of North America, and described the effects this has on the initial emissions.

A rich-start strategy with secondary air injection, and an EHC for rapid increase in the temperature of a low light-off catalyst, was discussed in a paper by Nissan (971022). Nissan noted that the volume of exhaust gas increases as the alternator load rises, which has the disadvan- tage of reducing the rate of the desired exother- mic reactions over the catalyst. It was concluded that it is preferable to supply electric power for the EHC from a battery, but no comments were made on low-temperature starting. Interestingly, a correlation between fuel distil- lation temperature and exhaust gas temperature was observed, which suggested that fuel composition could influence the performance of the cold start catalyst.

Hydrocarbon Traps Development of hydrocarbon trap technology

to minimise cold start emissions for ULEV (Ultra Low Emission Vehicles) applications continues, and Johnson Matthey (970741) described how in situ mass spectrometry techniques showed that hydrocarbon traps are effective for trapping aromatic species, C4 and higher alka- nes and alkenes, but ineffective for the very volatile methane, ethane and ethylene con- stituents. The trapping performance for C, to Cs hydrocarbons is improved when competition with water is minimised by using a “water trap”


upstream of the hydrocarbon trap. Hydrocarbon trapping efficiency then increases from about 40 to 60 per cent during the first 10 seconds of a cold start.

Three- Way Catalysts Promoters

Several papers discussed the roles of promoters, stabilisers and other components in auto- catalyst formulations containing platinum group metals; these included an explanation of the chemistry of the NOx trap. A highlight was two entire sessions devoted to the uses of zirconia in emissions control applications, ranging from oxygen sensors to autocatalysts. A contribution fkom MEL Chemicals (970460) provided a useful general overview. The chemical inertness and refractory properties of zirconia have been exploited in high temperature chemical process catalysts in the past, and over recent years zirconia has been used both as a support for platinum group metals in autocatalysts to impart improved thermal resistance, and in oxygen storage components in combination with other oxides. N. E. Chemcat (970466) reported on the effects of dopants on the thermal stability of the surface area of zirconia -barium, calcium and lanthanum being the most effective dopants. They measured the oxygen storage properties of various ceridzirconia mixed oxides. This was also a topic covered by other papers, for example, RhBne-Poulenc (970463) focused on the characterisation of cerium-rich ceria/zirconia mixed oxide phases.

A contribution from the University of Pennsylvania and W. R. Grace (970461) pointed out that conventional characterisation studies, such as X-ray diffraction, of these mixed oxides can result in misleading conclusions. This is because it is not the bulk structure of defective oxides that is important in controlling surface reactions, but rather local structure at the atomic level.

Sulfur Poisoning In meeting emission requirements, high con-

versions of pollutants take place over modern TWCs, but even small changes in performance can affect tail-pipe emissions. Factors such as

catalyst poisoning are therefore important. In fact, two papers from Johnson Matthey were concerned with poisoning due to sulfur. One paper (970739) concluded that the performance of standard palladium-only catalysts is more sensitive to sulfur poisoning than platinum/ rhodium, palladiudrhodium, or platindpal- ladidrhodium catalysts. Also, controlling interactions between the palladium and cerium-containing components in the washcoat is critical for the achievement of high catalyst activity at high sulfur levels. However, optimised palladium-only catalyst is more active than standard palladium-only catalysts in the presence of relatively high sulfur levels, and recovers activity more quickly as sulfur levels are lowered.

This paper, and a second one (970737) showed, as expected, that palladium-only catalysts generally have superior hydrocarbon performance under all conditions, and that sulfur affects carbon monoxide and NOx conversions more adversely over palladium-only catalysts, than over formulations containing rhodium. A paper from the University of Dundee and MEL Chemicals (970468) suggested that the addition of zinc to palladium-only TWC formulations can have advantages when operating in the stoichiometric to lean-burn range.

NOx Traps The main engine exhaust component of

“NOx” is nitric oxide (NO) and, although ther- modynamically it is unstable compared with nitrogen and oxygen, its dissociation is virtually impossible under normal engine exhaust conditions. Therefore, NO is most conveniently treated by reducing it catalytically to nitrogen, and water or carbon dioxide, depending on the reductant concerned. One of the most demand- ing challenges for catalytic emission control is thus the removal of NOx under lean conditions. Such conditions exist in diesel engine exhaust, and will become increasingly commonplace as lean-burn gasoline engines are introduced for improved fuel efficiency.

One means of treating NOx under lean conditions is to adsorb it in a “NOx trap” as a surface nitrate species. When the trap is saturated


it is purged with a short, concentrated pulse of reductant to reduce the adsorbed NOx. All of the NOx traps so far described contain platinum and rhodium, and the main objective of this technology is to remove NOx without deterio- ration of vehicle driveability, or significant fuel penalty. In a paper from N. E. Chemcat (970745), the thermodynamics of the processes involved in NOx traps were discussed. Under lean conditions NO is oxidised to NOz over platinum, which then reacts with alkaline metal carbonate in the trap to form nitrate species. When conditions are reducing, the nitrate species are unstable, and decompose to the metal oxide and NOz. The latter is reduced to nitrogen over plat- indrhodium, and the metal oxide reacts with carbon dioxide to reform the carbonate. In a joint paper, Mercedes-Benz, Daimler-

Benz and Degussa (970746) concentrated on the modes of deactivation of NOx traps. They stressed the need for low sulfur fuel to prevent sulfate formation, and showed that high temperature treatment can even improve stoichiometric three-way performance, but NOx storage features are irreversibly lost. This was identified as being due to the NOx absorption components reacting with washcoat components to form stable compounds, such as aluminates, zirconates and titanates. A second deactivation mode involves sintering of the platinum and rhodium (as well as the absorbent species) and leads to loss of surface area, thus significantly reducing the interface between these two materials, with the result that the rate of NOz spillover from the active metal, where it is formed, is markedly lowered.

Diesel Aftertreatment In an update of global trends in diesel emis-

sions control, Michael Walsh (970179) pointed out that the number of diesel engined light duty vehicles is steadily increasing in many parts of the world. This can result in positive environmental benefits: lower fuel consumption (reduced COz emissions), reduced hydrocarbon and carbon monoxide emissions (enhanced by using platinum oxidation catalysts) , and very low evap- orative hydrocarbons, when compared to their

gasoline counterparts. However, diesel engines have relatively high NOx and particulate emissions, but new advanced engine design and catalytic aftertreatment strategies are improving the situation. A related paper from Mitsubishi (970753) reviewed the global situation with heavy duty diesel vehicles, and had similar conclusions.

Sun Electric (970748) described a potentially versatile 90" backscatter measurement of particulates using a red laser that could be developed and refined for on-board applications using small solid state devices. Comparisons were made with opacity methods, and the advantages and disadvantages were discussed. Soot is a problem, with heavy duty diesel engines in buses and other vehicles used in inner cities for delivery and collection duties. A joint paper fkom Engine Control Systems, Environment Canada and the Ontario Ministry of Transportation (970186) reported the results of retrofitting platinum oxidation catalysts on heavy duty diesel vehicles. They concluded that oxidation catalysts can reduce particulate matter - mainly soluble organic fraction - and can significantly lower carbon monoxide and hydrocarbon emissions without increasing fuel consumption.

A joint paper from Johnson Matthey, HJS Fahneugtechnik, Eminox, Swebus and PESAG (970 182) described extensive successful expe- riences of Continuously Regenerating Traps (CRTs) in heavy duty applications. The CRT removes a high proportion of carbon monoxide and hydrocarbons, and eliminates soot emissions by using the NOz formed over a special platinum catalyst to burn soot retained in a fil- ter; this is a combustion process that takes place at relatively very low temperatures (2).

Conclusions The Detroit conference this year has again

shown that the platinum group metals have key roles to play in the technologies that enable vehicles to comply with increasingly stringent legislative demands. M.V. TWIGG

References 1

2

M. V. Twigg, Platinum Metab Rm., 1996,40, (3), 110 P. N. Hawker, Platinurn Metals Rev., 1995,39, (I), 2

Platinum Metals Rea, 1997, 41, ( 2 ) 78

Aspects of Co-ordination Chemistry Synthetic Coordination Chemistry: Principles and Practice

World Scientific Publishing Co. Pte. Ltd., Singapore, 1996, 452 pages, BY J. A. DAVIES, C. M. HOCKENSMITH, V. YU. KUKUSHKIN AND YU. N. KUKUSHKIN,

ISBN 981-02-2084-7, E77.00

This book comprehensively covers all aspects of synthetic co-ordination chemistry, drawing together the rich wealth of research undertaken, but little known, from the former Soviet Union, and work performed in the West. It contains several very interesting chapters covering the more esoteric synthetic procedures, which are not normally readily accessible from the chemical literature, but are of great value. For example, Chapters 8 and 9 describe non-traditional oxidants and reductants in preparative co-ordination chemistry and constitute a fascinating review of the diverse synthetic techniques employed to produce novel co-ordination compounds. With such a broad scope, the book will prove valuable to most synthetic co-ordination chemists and be particularly useful when the synthesis of a specific metal complex is required and existing preparative methods either prove inadequate, non cost-effective or perhaps even impossible for the project concerned. Probably the greatest strength of the book lies in its being a ‘idea provider’ for those working in research.

Theoretical considerations for the synthesis of co-ordination compounds are described in Chapter 1 , and the platinum group metals, especially platinum, are extensively featured. Although the majority of the material is available in currently established texts, it neverthe- less provides a very helpful summary and reminder of the theory behind co-ordination chemistry. The style of writing together with extra material and examples covered, make this chapter an interesting read and a very useful teaching aid.

The solubility of co-ordination compounds and the relationship of solubility to composition and structure are investigated in Chapter 2. This is an ambitious and helpful contribution to the book, as no rigorous theory exists of the solubility of chemical compounds. The addi-

tion of hydrophilic counterion effects for ionic complexes and macrocyclic compounds are all described. Tabulated data and examples are also provided by the Authors.

Solvento-Complexes Chapters 3 and 4 relate to the generation and

subsequent use of solvento-complexes (a compound containing co-ordinated solvent molecules as well as other co-ordinated ligands) as starting materials for preparative co-ordination chemistry. Chapter 3 has an informative introduction on such complexes. Halide abstraction reactions of platinum complexes and the synthesis of homoleptic solvento-complexes of palladium, platinum and ruthenium are all described. The synthesis of bridged hetero- and homopolynuclear complexes of gold, indium and ruthenium are included. Chapter 4 features an extensive Table concerning the synthesis of a wide variety of solvento-complexes, which is well referenced and describes all the platinum group metals.

Methods available for ion exchange and their implications for synthetic co-ordination chemistry are outlined in Chapter 5. Palladium complexes containing ‘non-co-ordinating’ anions as ligands and the generation of platinum-main group metal bonds are discussed.

The synthesis of bridged complexes and ring closures is considered in Chapter 6. The principal methods centre around the removal of an anionic ligand from a metal cluster to fuse two unsaturated fragments. The chapter, although short, is interesting and is almost solely concerned with the platinum group metals, especially palladium and platinum.

An overview of the electrosynthesis of co-ordination compounds is provided in Chapter 7. While this topic has received a fair amount of attention previously, this Chapter, in contrast


to many other reviews, focuses on the use of electrosynthesis for preparative chemistry and is therefore very useful. The use of inert electrodes, as well as sacrificial anodes and cathodes is considered, as is the solvent employed. Electrochemical synthesis of platinum and ruthenium complexes are described.

Novel Oxidants and Reductants The use of non-traditional oxidising and reduc-

ing agents in synthetic co-ordination chemistry is described in Chapters 8 and 9. These two chapters constitute a significant proportion of the book and are fascinating to read. Although some of the reagents may be familiar to synthetic co-ordination chemists, many may not be, and the use of such reagents offers valuable possibilities for the synthesis of novel materials as well as facile synthesis of established metal complexes. Oxidising agents, such as aryl- diazonium salts, tropylium salts, metal salts, non-metal halides and aminoxides are all considered in detail. The modification of such reagents for utilisation in aqueous media is also described. An extensive collection of novel reducing agents is also provided. The range of unusual products obtained, described by the use of the reagents employed, make these chapters of interest both to academic and industrial chemists. This information is not readily available, except by a lengthy and detailed search of the chemical literature. While more metals

are considered here than in other chapters, the platinum group metals still receive much attention.

The use of boron and aluminium hydrides in preparative chemistry is reviewed in Chapter 10, while the book concludes with features on molecular rearrangements of co-ordination compounds (Chapter 11) and some interesting possibilities for the solid state thermal synthesis of co-ordination compounds (Chapter 12). Many of these reactions are concerned with the expulsion of water or hydrogen halide from metal complexes to produce new species. The platinum metals again feature extensively.

Overall, the book is a welcome addition to the chemical literature and has much to recommend it. The platinum group metals receive excellent and thorough consideration, with roughly over 50 per cent of the book concentrating on them, the remainder being principally concerned with the 3d transition metals. The style, clarity and readability of the book are excellent and the book is well referenced and has sensibly con- structed indexes. Most of the chapters deal with interesting research matters informatively, which is particularly important since many of the topics covered in the book are not covered in existing texts. I, therefore, consider this book to be a useful purchase for anyone seeking novel synthetic methodologies for academic or industrial application and I recommend it highly.

S . M. GODFREY

Monodispersed Nanostructured Ultrafine Platinum - Nanostructured metal particles with interest-

ing properties due to their quantum size effects, and with uses as advanced materials, have mostly been studied as isolated particles; while platinum monolayers have been little examined because of the difficult preparation of monodispersed ultrafine platinum particles.

However, a method has now been developed to control the size of polymer-protected ultrafine platinum particles (T. Teranishi, M. Hosoe and M. Miyake, Adv. Mater., 1997, 9, (l), 65-67). Ultrafine platinum particles, of different diameters, protected by poly(N-vinyl-2- pyrrolidone) (PVP), were prepared by heating H,PtCl, under reflux in aqueous alcohol with PVP, and varying the reaction conditions.

Higher alcohol concentrations gave smaller particles of narrower size distribution; particle size reduced as: methanol > ethanol > 1-propanol. Thus nucleation rate is the principal factor in determining particle size and distribution. Electro- phoresis produced monolayers dependant on platinum concentrations, voltages and times.

Industrial Platinum Metals Chemistry Please note that the following change should be

made in “Industrial Platinum Metals Chemistry Towards the Year 2000”, which appeared in Platinum Metals Rev., 1997, 41, (1) 8-11.

On page 10, in Figure 4, the molecule involved in the palladium-catalysed Heck reaction should have been dihydrofuran and not furan.


P1atinum:Platinum-Rhodium Thermocouple Wire IMPROVED THERMAL STABILITY ON YTIRlUM ADDITION TO PLATINUM

By Baoyuan Wu and Ge Liu Shenyang Institute of Gold Technology, Liaoning, l? R. China

A new type of p1atinum:platinum-rhodium thermocouple wire which incorporates traces ofyttrium in the platinum limb has been developed and tested in some typical working environments. This thermocouple possesses good thermal stability and mechanical strength at high temperatures, and a long service life, compared with conventional p1atinum:platinum-rhodium thermocouples. The thermocouple meets the output requirements of the Type S standard for thermocouples - those made of Pt:Pt-lO%Rh - whose manufacturing tolerances are prescribed by the International Electrotechnical Commission ( I . E .C . ) ( I ) . The life of thermocouples made from this wire is increased by around 1.5 to 2 times and they display a greater resistance to contamination.

Large amounts of p1atinum:platinum-rhodium (Pt:Pt-Rh) thermocouple wire are used each year in China, for monitoring temperature in the iron and steel industries, during melting, annealing and metal forming processes. Other industries also utilise these materials. Platinum, however, is costly (around $380/troy ounces in March 1997) and as China produces only a small amount of platinum each year, with about 90 per cent of the total requirement being imported, there is a need for a less costly device.

Pt:Pt-Rh thermocouples are normally used in temperature regions above 1000°C. For instance thermocouples in the glass industry are used at temperatures of 1000 to 1200°C and last for 5 to 7 years. At these temperatures the grain size of the platinum negative limb will increase; creep will occur and the material will become weak. When the temperature reaches about 1400°C, continuous oxidation will occur on the surface of the platinum wire, causing it to increase in size at a rate of approximately 39 x lo-’ mg cm-* h-I.

The physical properties of platinum and platinum-rhodium are different; for example, at 1200°C the tensile strength for the pure platinum negative limb is 3.9 MPa, but it is 11 MPa for the platinum-10 per cent rhodium alloy

positive limb (2). This adversely affects the thermal stability and service life of the thermocouple. Therefore, in order to overcome the effects these differences cause, a new type of dispersion hardened Pt:Pt-1 O R h thermocouple has been developed (3).

Dispersion Hardened Thermocouple Wire

Since the 1970s, in countries outside China, dispersion hardened platinum has widely replaced pure platinum, especially for high temperature usage, but not for thermocouple applications, and this has resulted in improved technical and economic performance (4). In China, research into dispersion hardened platinum has also been undertaken and a new type of dispersion hardened platinum crucible was developed at the Institute of Precious Metals in Kunming (5). This crucible has twice the mechanical strength at high temperatures, compared with previously used crucibles, resulting in a longer service life and improved corrosion resistance.

At the Shenyang Institute of Gold Technology, a dispersion hardened Pt:Pt- 1 O R h thermocouple has been developed and put into commercial


Table I

Thermoelectric Potential Test Results for the New Pt:Pt-1ORh Thermocouple

Temperature, I.E.C. Type S Gradient for Thermocouples used OC Reference Table, Type S. in the experiment

mV CIVPC No. 2 No. 3

800 7.345 10.87 7.347 7.334 850 7.892 11.10 7.912 7.898 900 8.448 11.20 8.447 8.442 950 9.012 11.40 9.013 9.026

1000 9.585 11.53 9.582 9.587 1050 10.165 11.70 10.177 10.160 1100 10.754 11.83 10.773 10.754 1150 11.348 11.90 11.365 11.314 1200 11.947 12.02 11.965 11.945 1250 12.550 12.10 12.580 12.572 1300 13.155 12.12 13.169 13.155

P Thermocouples No 2 and No. 3 are typical of the thermocouples

production. Its physical properties were tested at the Liaoning Institute of Testing Technology and at the Anshan Iron and Steel Company, where it was found to meet the requirements of the Type S standard (1). It has also attained the International Electrotechnical Commission standard. The thermocouple has good stability, well balanced tensile strength between the two limbs and doubled service life. With this new material the diameter of the thermocouple wire can

8.911

14.463

14.402

14.442

be reduced, resulting in less material usage and lower cost.

Experimentally determined thermoelectric potentials for dispersion hardened Pt:Pt- 1 O R h thermocouples are listed in Table I.

From Table I it can be seen that the thermoelectric potential can meet the needs of the International Electrotechnical Commission Type S standard. Using the new type of dispersion strengthened Pt:Pt-1 O R h thermocouple, the

8.911 8.915

14.464 14.462

14.400 14.400

14.441 14.441

~~

Table II

Thermal Stabilities for a Standard Thermocouple and for Three Experimental Thermocouples (at 1400°C for 200 h)

8.915

14.461

14.394

14.442

Test number"

Standard** thermocouple Thermocouple

Thermocouple

Thermocouple N0.3

N0.4

8.901

14.461

14.395

14.443 - ** Standard Pt:Pt-lORh

Thermoelectric potential, mV

3

8.936

14.464

14.408

14.440

- -24 hours mnocouple

4

8.912

4.462

14.402

14.440

-

5 1 6 1 7

The thermocouples are the same ones used

8 1 9

oughout the experiments

82 Platinum Metals Rev., 1997, 41, ( 2 )

1

8.952

14.464

14.41 0

14.437

2

8.946

14.462

14.407

14.436

Item

Table 111

Thermocouple

Before experiment After experiment

1 Change in Thermoelectric Potential (at 1400°C for 200 h) I

No. 1 No. 2 No. 4

10.588 10.567 10.587 10.589 10.565 10.589

I Item I Thermoelectric potential at the copper freezing point, mV

need to make changes to other instruments is avoided. The thermal stability of the thermocouple is demonstrated by the very small change in the thermoelectric potential at the freezing point of copper before and after the experiment.

Table II shows the test results for three thermocouples obtained by the Local Metrological Bureau of Liaoning Province, using the same limb and the double limb method, which, according to the Chinese standard, are a fixed point and a comparison method, respectively.

After thermal stability tests at temperatures of 1400°C for 200 hours, the change in the thermoelectric potential for the conventional Pt:Pt- 1 OF& thermocouple at the copper freezing temperature is normally about 30 pV, approximately 3"C, but for the new thermocouple the change is only approximately 1-2 FV, which is 0.15"C, as shown in Table 111.

From the data obtained by the Local Metrological Bureau of Liaoning Province, it is apparent that the thermal stability has clearly improved and that the thermocouple performed well. The thermocouple is more stable than a conventional one at high temperatures and for long periods of time, and has initially met the I.E.C. Class 2 tolerance.

Yttrium Additions One of the major methods for dispersion hard-

ening, which was applied to the new thermocouple, was to add traces of the rare earth metal yttrium to the 99.9 per cent platinum. The resul- tant hardening can be seen in Figures 1 and 2. For the conventional Pt:Pt-1 O R h thermocouple, the ratio of tensile strength between the two limbs is 15:3 1 at room temperature and 4: 1 1 at

high temperature (1 200°C) (6). Due to the large variation in the physical parameters between the two limbs, the strain will differ considerably, resulting in internal stresses. This will adversely affect the precision of the thermocouple measurements and shorten its service life. However, the tensile strength on the platinum limb of the new thermocouple was approximately doubled by dispersion hardening, giving a ratio for the tensile strengths between the two limbs of 29:31 at room temperature and 5:6 at high temperature (1200°C). In addition, the ratio of yield stress between the two limbs is about 6.8:7, which is an improvement over the conventional thermocouple. When the physical parameters are well balanced on the two limbs, the precision of the measurements and the thermal stability are obviously improved, and the service life is doubled.

Thermocouple in Use Data obtained by the Anshan Iron and Steel

Company, Anshan in Liaoning Province, illustrate the beneficial effects of the new thermocouples. [a] Environmental data. Six new dispersion hardened Pt:Pt-1 O R h thermocouples were used in the soaking pits of a cogging mill at the Anshan Iron and Steel Company. The combustion media were carbon monoxide and air. The temperature inside the soaking pit was approximately 1330 to 1360°C and about 20 to 80°C outside. There are generally 50 to 60 ton ingots in the pit to be heated and production is continuous.

When an ingot is put into or taken out of the pit by crane, there are arduous mechanical


The IPTS-68 value is 10.571 rnV

0.02 0.04 0.06 O < YTTRIUM, "/a

Fig. 1 Relationship between tensile strength of platinum and its yttrium content at room temperature

6 4 wl 0

0 50

TIME, hours

Fig. 2 Relationship between the yield strength and time for platinum and platinum alloys

conditions and much dust, resulting in a very poor working environment. The cogging mill has 53 pits, and 6 pits in which to perform the experiments were chosen at random. The new thermocouple was found to satisfy production needs. [b] Data from the results show that the service life of conventional Pt:Pt-Rh thermocouples in the soaking pits is about 20 to 25 days. After prolonged use brown spots occur on the surface, and in some places the thermocouple wire sticks to the protecting sleeve.

The six new thermocouples, Number 3 having a diameter of 0.5 mm, and the others having a diameter of 0.38 mm, were used for 45 days (1080 hours). One of them developed a dark area about 300 mm from the cold end due

to a crack on the protecting sleeve. The other five thermocouples continued to work well and retained a clean surface.

Compared with the conventional, 0.5 mm diameter, Pt:Pt-Rh thermocouple, the service life of the new one is 1.5 to 2 times longer and can withstand contamination.

The Dispersion Hardening Mechanism

Some of the characteristics of platinum can be improved by the usual alloy hardening method of adding a metal to the platinum base, followed by heat treatment. However, problems can occur after alloying. For example, when a high concentration of any alloying element is added to the platinum base, the electrical properties of the resulting platinum limb become inferior; at the same time the hardening phase will partially or totally dissolve into the base at high temperatures, thus the effects of the hardening action will be reduced.

The addition of traces of yttrium to platinum as a dispersion phase markedly increases the tensile strength of the platinum at high temperature, prolongs the service life and improves the thermal stability. Yttrium additions prevent the growth in the grain size and help retain the stable fine grain structure, as the dispersed particles of high melting point resist movements of dislocations and make the material harder. The strength of a material is related to the movement and number of the dislocations.

In order to harden metals, the movement of the dislocations needs to be restricted either by the production of internal stress or by putting particles in the path of the dislocation. After the melting and annealing process, the majority of the trace yttrium (in the dispersion phase of the platinum) becomes yttrium oxide, which has a much higher melting point than platinum. When the temperature is near the melting point, dispersion hardened particles fuc the dislocations, thus hardening the platinum and increasing its strength.

At the same time the grain structure becomes stable after dispersion hardening and there is also microstructural hardening. The dispersed


particles affect the recrystallisation dynamics, inhibit rearrangement of the dislocations on the grain boundaries and prevent the movement of the grain boundaries. Therefore, this dispersion hardened platinum possesses a stable fine grain structure at high temperature.

Conclusions [ 11 The cold forming properties of the dispersion hardened platinum are between those of pure platinum and Pt-lORh, thus it is easy to form wire at room temperature. [2] The technology of melting dispersion hardened platinum is more complicated than that of pure platinum, since the melting equip- ment requires a better vacuum system and the incorporation of magnetic stirring. [3] The thermal stability of the conventional Pt:Pt-Rh thermocouple is affected by the loss of oxide (platinum oxide and/or rhodium oxide) which forms at high temperatures, by diffusion,

and by the chemical action between the thermocouple wire and the surrounding insulating material. The chemical action is limited by the following factors: (a) the afFmity between platinum and contaminants from the insulating ceramic; (b) the surface area; (c) the rate of diffusion of oxygen and the metal vapour from the area in which they react (7). Thus, when the thermocouple is used at high temperatures for a long time, a difference will occur between the real temperature and the recorded values. This difference was overcome by the new dis-

persion hardened Pt:Pt-1 O R h thermocouple, due to the dispersion phase inhibiting the growth in the grain size in the hot environment. The thermocouple has a stable fine grain structure at high temperature, improved resistance to creep and a long service life. Additionally, the diameter of the wire could be reduced from 0.5 mm to 0.38 mm, making such thermocouples more economic.

References 1 Xiangjian Chen, Noble Metals, 1983,4, (l), 13 2 K. Schwarz, Neue Hum, 1980,25, (4), 145 6 Yukui Zhang, “Non-Ferrous Metals and the 3 Chinese Patent 85/100,658 Applitzzion of Rare Earth Metals”, 1983, No. 1, pp. 4 G. L. Selman, J. G. Day and A. A. Bourne, 33-36

Platinum Metals Rev., 1974, 18, ( l ) , 46; G. L. 7 Zhexi Huang, “The Recent Development of Selman and A. A. Bourne, op. cit., 1976,20, (3), Thermocouple Materials”, The Chongqing 86; R. B. McGrath and G. C. Badcock, op. cit., Institute of Instrumental Technology, 1984, pp.

C . W. Corti,Pkztinum MetnlsRev., 1988,32, (2), 72 5

1987, 31, ( l) , 8 8-14

The Metallurgy of Iridium Metallurgy and Mechanical Behaviour of Iridium

Urals Branch of Russian Academy of Science, Ekaterinburg, Russia, 1996, 119 pages, (in Russian), BY N. I. TIMOFEEV, A. V. YERMAKOV, V. A. DIMITRIEV AND P. E. P A ” ,

ISBN 5-76914673-5, $25.00 This book selectively reviews papers published

over the past 30 years, with a few earlier texts, on the metallurgical and mechanical properties of iridium; roughly half the papers are Russian.

The book is in two sections, the first covering iridium refining, and pyrometallurgical methods for purification of this high melting point metal. This includes remelting scrap in an oxidising environment and electron beam melt- ingialloying. Iridium recovery after refining and the production of massive single crystals are described. The behaviour of impurities and alloying additions to iridium, in an inert atmosphere, as a function of atmosphere, pressure and temperature is analysed.

The second section examines the mechani-

cal properties of iridium single crystals, including the mechanisms of deformation and frac- ture, with emphasis on the growth of cracks on the surface of massive single crystals and in thin crystalline iridium foils. Basic methods for working iridium, its alloys and their properties are described. There is discussion of grain structure development and the recrystallisation that occurs during iridium annealing. Finally, a range of applications of iridium, such as use as a con- tainer material, particularly for crucibles, and rolled sheet production are briefly mentioned.

The book may be purchased from Dr Sergei M. Pirogov, Ekaterinburg Non-Ferrous Metal Processing Plant, Lenin Ave., 8, 620014 Ekaterinburg, Russia, Fax: +7-3432-58-0739.


Bertrand Pelletier, Master Pharmacist HIS REPORT ON JANETY’S PREPARATION OF MALLEABLE PLATINUM

By W. A. Smeaton Ely, Cambridgeshire, England

Bertrand Pelletier (1761-1797) was born in Bayonne, in south-west France, on 3 1 July 176 1. He was apprenticed to his father, a master pharmacist, from 1775 to 1778 and then to a pharmacist in Paris, where he became the protege of Jean d’Arcet, Professor of Chemistry at the College de France. D’Arcet appointed Pelletier as his assistant and encouraged him to do research in the laboratory that was attached to the pharmacy in the Rue Jacob, near the Abbey of Saint-Germain-des-Pres, which Pelletier bought on qualifying as a master pharmacist in 1784 (1,2).

Pelletier’s main interest was in inorganic chemistry, and in 1788 a long investigation of metallic phosphides, few of which had been previously known, led him to discover a new method for the preparation of malleable platinum (3). Native platinum containing base metals was heated strongly with phosphorus pentoxide and charcoal to yield a brittle button and a glassy material, which contained the impurities. The button was considered by Pelletier to be a compound or ‘alloy’ of platinum and phosphorus. When the button was heated again for several hours phosphorus was expelled, leaving platinum which he assumed to be pure. Marc Eti- enne Janety (1739-1820) the royal goldsmith who had been producing and working with malleable platinum for two years, made some balance pans from this platinum (4). Pelletier believed that his process might replace Janety’s, which involved the use of arsenic and thus not only exposed the workers to dangerous fumes but also might deter the public from buying platinum ware for domestic use. However, Pelletier conceded that his process was more expensive, which is probably why it was not adopted.

For several years Pelletier was registered as a medical student in the prestigious University of

Paris, but in 1790 he graduated as a physician at the University of Reims, which he had visited only twice. As his chemical research kept him fully occupied, and he had already installed his brother Charles as manager of the pharmacy, he did not immediately practise medicine, though presumably he hoped to do so later. After 1789, however, the French Revolution changed the direction of his career and led him to become involved in the application of chemistry to various technical problems.

The French Revolution A shortage of copper coinage led to a sug-

gestion in the National Assembly that copper might be obtained from the bells of churches made redundant by the reorganisation of parishes. The alloy from which bells are made contains copper and tin, so in 1791 several chemists developed methods for removing the more easily oxidised tin. Pelletier’s method involved heating molten bell metal with manganese dioxide, a powerful oxidising agent, but as manganese dioxide was not plentiful, a less expensive method was found by Antoine Franqois de Fourcroy (1755-1809) who oxidised the tin in the molten alloy with atmos- pheric oxygen. Fourcroy also acknowledged that Janety, in collaboration with the chemist M. J. J. Dize (1764-1852), had independently solved the problem in a similar way (5). Janety had previously worked only with precious metals, but because many of his wealthy clients probably left France early in the Revolution, he may have been seeking an alternative occupation.

In fact, copper was not extracted from bells on a large scale until 1793, when it was required for the manufacture of cannons (6). However, by then, Janety was working in Marseilles, making parts for clocks, and took no part in the operation.


Before the Revolution, royal grants and pen- sions were given to manufacturers and crafts- men chosen by the King’s advisers, often on the recommendation of the Academy of Sciences. This secret procedure was unacceptable in these new democratic times, so in 1791 the National Assembly established the Bureau de Consul- tation des Arts et Metiers (Consultative Board for Arts and Trades, originally called Bureau de Consultation pour les Arts). This comprised fifteen members of the Academy of Sciences and fifteen representatives of other societies, and was responsible for distributing awards (7). The Bureau had at its disposal 300,000 livres (about El 2,500) for the ‘useful arts’ and 100,000 livres for the ‘fine arts’. Pelletier was a member, at first representing the Society for Natural History and later the Academy of Sciences to which he was elected on 17 March 1792.

Janety’s Award for Malleable Platinum

When Janety sought an award for his method of making malleable platinum, the Bureau de Consultation appointed Pelletier and Claude Louis Berthollet (1 748-1 822), a senior chemist in the Academy, to examine his claim. Berthollet’s name appears first in their report, but as Pelletier was already acquainted with Janety and his work, and had himself done research on platinum, it can be assumed that his contribution was substantial.

The file concerning Janety’s application has survived and its contents have been published (8). On 16 March 1792, Janety wrote to the local government of Paris, asking how to claim an award and on 5 April, presumably following the advice given, he applied to the Minister of the Interior, enclosing a certificate showing that he had lived in the Rue de 1’Arbre Sec in Paris for fifteen years, a memoir of about 2000 words on ‘Platinum and the means of obtaining it in a massive and malleable form’ and another certificate from the local government confirming that there were no objections to his application.

Berthollet and Pelletier submitted their report to the Bureau de Consultation on 18 April 1792. They noted that Janety was not the first to purify

Bertrand Pelletier 1761-1797

Frontispieee of “MCrnoires et observations de chirnie de Bertrand Pelletier”, volume 1, see Ref. 11

platinum by heating with arsenic, but that his predecessors had only worked on a small scale, while he had produced very large objects for the Academy of Sciences. These included a ball weighing 8 marcs (2 kg), two bars of length 19 feet (6.2 m) and a concave mirror weighing 12 marcs (3 kg). He had also made small objects, such as snuff boxes, crucibles and a coffee pot. They showed some of Janety’s products to the Bureau and recommended that Janety should receive the maximum permitted award of 6,000 livres (about E250). The other members agreed to this and pointed out that his work opened up a new branch of commerce of the greatest utility to society. Janety received the payment a few days later, four months before the overthrow of the monarchy led to a financial crisis.

Most reports to the Bureau de Consultation were seen only by its members, but Berthollet and Pelletier published their report in July 1792 in the monthly journal Annales de Chimie; both


were members of its editorial board (9). After summarising earlier attempts to prepare malleable platinum, they described Janety’s process using his words from his submission to the Bureau de Consultation, only altering his idio- syncratic spelling. According to his account, Janety melted 24 ounces (730 g) of native platinum with 48 ounces (1460 g) of arsenious oxide and 16 ounces (490 g) of potassium carbonate in a crucible and, after cooling, removed a metallic button h m beneath the slag. The button was magnetic, showing that some iron had remained, so the procedure was repeated a second and sometimes a third time until all the iron was removed. The platinum now contained metallic arsenic, which was expelled as vapour by heating under controlled conditions for twelve hours, leaving a spongy metal, considered by Janety to be pure platinum, which he hardened by repeated heating and hammering. The reactions leading to the formation of metallic arsenic have been discussed previously (1 0).

Although Berthollet and Pelletier published in full Janety’s account of his procedure, they omitted the iirst half of his manuscript in which he speculated at some length about the reason why native platinum was not malleable. His experience with silver alloys had convinced him that the brittleness of an alloy was related to the differences in expansion and fusibility of its con- stituents, and since platinum differed so much from other metals in these properties, it had to be completely freed of impurities if it was to become malleable. Janety provided no experimental evidence in support of his theory, and Berthollet and Pelletier may have served him well by not publishing it.

Pelletier’s Wartime Reports Pelletier wrote other reports for the Bureau de

Consultation, but in 1793 he began to contribute to other reports, concerning processes that were

soap, rapidly tanning leather, repulping waste paper and extracting copper from bells (1 1).

A shortage of engineers, urgently required by the army and navy, led to the foundation in 1794 of a new college, the Ecole Polytechnique, to which Pelletier was appointed as a professor of chemistry. In 1795 he became a member of the Institut National, the successor to the Academy of Sciences. He served on a commit- tee of the Institut which was examining methods of improving gunpowder production, but he had already contracted pulmonary tuber- culosis and died on 21 July 1797, before the task was completed. His son, Pierre Joseph Pelletier (1788-1842), also became a pharmacist and professor and achieved fame by isolating qui- nine and other alkaloids in collaboration with J. B. Caventou (1795-1877). The pharmacy remained in his possession until 1836, on the site of the present building at 45 Rue Jacob. A later proprietor moved it to 48 Rue Jacob, where it is still named ‘Pharmacie Pelletier’ (12).

References 1 P. Dorveaux, “Bertrand Pelletier”, Rev. Hist.

Pharm., 1937,6,5-24 2 W. A. Smeaton, “Bertrand Pelletier”, in

“Dictionary of Scientific Biography”, ed. C. C. Gillispie, Scribner’s Sons, New York, Vol. 10, 1974, pp. 496-497

3 B. Pelletier, Observatiomsutla Physique, 1789,34, 195-197 (read to the Academy of Sciences in 1788)

4 For an account of Janety see D. McDonald and L. B. Hunt, “A History of Platinum and its Allied Metals”, Johnson Matthey, London, 1982, pp. 78-86md180-181

5 A. F. Fourcroy, Ann. Chim., 1791,9,305-352 6 W. A. Smeaton, “Fourcroy, Chemist and

Revolutionary”, London, 1962, pp. 120-121 7 D. de Place, ‘2e Bureau de Consultation pour les Arts,

8 Op. cit., (Ref. 7), pp. 169-176 9 C. L. Berthollet and B. Pelletier, Ann. Chim., 1792,

10 Op. cit., (Ref. 4), p. 85 (where it is erroneously stated that Berthollet and Pelletier submitted their report to the Academy of Sciences)

Paris, 1791-1796”, Hin. T a M , 1988,5,139-178

14,20-33

important to a country at war, Cut off from its 1 1 These reports were reprinted with Pelletier’s other traditional SOUTCeS of essential materials. The publications and some unpublished works, in

“Mkmoires et observations de chimie de Bertrand reports were requested by the government, Pelletier”, eds. C. Pelletier and J. Sedillot, which published them as pamphlets, Pelletier Crodleboisy vols.~ 1798 was a co-author of reports on instructions for 12 C. Warolin, “Les variations du numkrotage de la

pharmacie de Joseph Pelletier, rue Jacob”, Rev. preparing soda from sea salt, manufacturing Hisf. Pharm., 1989,36, 196201


ABSTRACTS of current literature on the platinum metals and their alloys

PROPERTIES Properties of PdCu(ll0) Single Crystal Alloy Surfaces: Temperature-Induced Processes in the Surface Microstructure J. LOBODA-CACKOVIC, %uUm, 1996, 47, (12), 1405-1411 PdCu(ll0) alloy single crystal surfaces, with atomic concentration ratio Cu:Pd of 1:l in the bulk, were prepared with a Cu:Pd ratio of 0 . S 2 in the - 4 layers deep, surface region. The PdCu(ll0) surface consists of small crystalline domains containing -10-20 lattice cells depending on preparation. Two temperature-induced surface processes change the surface microstructure: surface roughening and partial surface disordering, starting at - 550 and - 700 K, respectively.

S t u d y of the Reactions I- + Id&= and Fe(CN)F + Sz08” in Micellar Solutions

F. SANCHEZ and P. L~PEZ-CORNEJO, hngmuir, 1997,

The kinetics of the reactions 1- + =I,” and Fe(CN)dc + S,O.Z- were studied in anionic micelles of Na dode- cylsulfate at 298.2 K. The present work and the results in Na bis-2-ethylhexyl sulfosuccinate/decane/HzO microemulsions and aqueous Na nitrate were explained by using as a starting point the Bronsted equation.

R M U , M. M. GRACIANI, A. RODRfGUEZ, M. L MOYA,

13, (2), 187-191

CHEMICAL COMPOUNDS Chloride Anion Recognition by Neytral Platinum(I1) and Palladium(I1) 5,5 -bis- amide Substituted Bipyridyl Receptor Molecules P. D. BEERN. C.FLETCHER,M. G.B.DREWandT.J.WEAR, Polyhedron, 1997,16, (3,815-823 A series of new acyclic neutral Pt@) and Pd@) 53’- bis-amide substituted 2,2’-bipyridyl receptors have been synthesised and the X-ray structures of two receptors determined. Proton NMR anion binding studies in deuterated dimethylsulfoxide solution reveal that these neutral receptors complex the halide anion via favourable amide C@NH- - -CT H bonding interactions.

Self-Assembly of Tetraalkylammonium Salt- S t a b i i Giant Palladium Clusters on Surfaces M. T. m, M. W I N T E R ~ ~ ~ B . TESCHE, Chem. Commun.,

N a n o s t r u d Pd clusters, stabilised by a monomole- cular coat of surfactants N(CaH17),Br or N(ClJ337),Br, self-assembled on C surfaces in an ordered manner to form h.c.p. structures. These structures self-organ- ised into two-dimensional films and three-dimensional superlattices, controlled by varying the length of the alkyl chains on the ammonium ions.

1997, (2), 147-148

Synthesis and Structural Characterisation of [Pda(p-Br)2(PBu‘3)2], an Example of a Palladium( I) -Palladium( I) D’ uner R D. M. P. ~ 1 ~ ~ 0 s a n d c . j . CARD IN,^,^. Chem. Soc., Dalton Tram., 1996, (23), 4313-4314 The synthesis, spectroscopic characterisation and, when X = Br, the single-crystal structure, of the novel Pd’-Pd’ dimers [Pd2(p-X)z(PBu’,),] (X = Br or I) are described. Preliminary results on their reactions with CO, H,, CNC6H3Mez and C2Hz are also reported. When dissolved in toluene, [P~,(~-X),(PBU’,)~] were good initiators for the polymerisation of acetylene; with X = I the dimer was catalytic.

Formation of Zerovalent Palladium from the Cationic Complex Pd(PPh,),(BF,), in the Presence of PPh3 and Water in DMF c. AMATORE, A. JUTAND and M. J. MEDEIROS, New J.

Stable Pd(0) complexes were spontaneously and slowly generated in situ from the cationic Pd(I1) complex Pd(PPh,),(BF& in the presence of mphenylphosphine (PPh,) and H,O. The generated (PPhJ oxide shows that (PPh,) can reduce the Pd(I1) to Pd(O), probably via a Pd(I1) hydroxy-containing intermediate.

Large Second-Order Nonlinear Optical Properties of Novel Orgauometallic (a-Aryl- enyny1)Ruthenium Complexes

M. P.GAMASAandJ.GIMEN0, @ ~ a m e d & s , 1996,15, (25), 52665268 A series of novel Ru a-acceptor aryl-enynyl complexes, including homo- and heterobimetallic complexes, have been synthesised and their nonlinear properties evaluated. The effects upon the hyperpolarisability of chain length, configuration of the metal donor group, and nature of the metal acceptor group are reported. These complexes are found to possess the largest quadratic hyperpolarisabilities, reported to date, for bimetallic compounds.

A Novel Route to Butahicmylidene Complexes: Stabilisation of :C=C=C=CH, on Ru, Clusters c. J. ADAMS, M. I. BRUCE, B. w. SKELTON and A. H. WHITE, Chm. Commun., 1996, (23), 2663-2664 The addition of Cz(Sih4e3)z to [Ru,~C,)(p-PPhz),O.- SMe)2(CO)II] gave [Ru,(p,-CCCCH(SiMe,)} (p- PPh2),(p-SMe)(p3-SMe)(CO),,](1) as a mixture of geometrical isomers in 94% yield. Alkaline hydrolysis of (1) resulted in the first stable buramenylidene complex [Ru5(pr-CCCCH2)(p-PPhn),(p-SMe)(p,- SMe)(CO),,,] (2) in 84% yield. The spiked-rhom- boidal pentanuclear complex [Ru,&-CCCCH2) (p- PPh,),(pSMe),(CO),,] was isolated in 62% yield &om the carbonylation of (2).

C h m . , 1996,20, ( l l ) , 1143-1148

S. HOUBRECHTS, K. CLAYS, A. PERSOONS, V. CADIERNO,


Synthetic, Structural, Electrochemical and Electronic Characterisation of Heterobimetallic bis(acety1ide) Ferrocene Complexes M. C. B. COLBERT, J. LEWIS, N. J. LONG, P. R. RAITHBY, A. J. P. WHITE and D. J. WILLIAMS, 3 Chem. SOC., Dalton Trans., 1997, (l), 99-104 A series of novel heterobimetallic bis(acety1ide) ferrocene complexes of the form [(C,H,)Fe"(C,H,)C= CRu"(dppm),(CrCR)] (dppm = 1,2-bis(diphenyl- phosphin0)methane) are reported. Incorporation of donor-substituted aromatic acetylide ligands causes a cathodic shift in the Ru""" redox potential, while electron-withdrawing substituents lead to an anodic shift. The structure of nans-[Ru(dppm), (C=C(C,H& Fe(C,H,)},] shows the Ru centre linearly bound to 2 ferrocene units by rigid rod-like acetylene linkages.

Thermal Decomposition of the bis(dihydr0- gen) Complex R U H ~ ( H ~ ) ~ ( P C Y ~ ) ~ in the Solid State B. CHAUDRET, P. DAGNAC, D. LABROUE and s. SABO- ETIENNE, N e w 3 Chem., 1996,20, (1 I), 1137-1 141 Temperature programmed decomposition studies of RuH,(H2),(PCy3), (1) were performed under a flow of He. Study of the H, evolution revealed a two-step process. In the first step, (1) was reversibly trans- formed into a mixture of RuH,[(q3-CaHs)PCy,] (PCyJ and RuH(q3-CaHs)PCy,] [(qz-C6Hp)PCy2]. In the second step, C,H, was lost and the Ru complexes trans- formed into unidentified species. Under H,, C,H, was converted into cyclohexane, thus demonstrating the catalvtic Dronerties of the Ru comnlexes.

Temperature Independent Ru + 0s Electronic Energy Transfer in a Rodlike Dinuclear Complex with a 2.4 nm Intermetal Separation L. HAMMARSTROM, F. BARIGELLETTI, L. FLAMIGNI, N. ARMAROLI, A. SOUR, J.-P. COLLIN and J.?. SAUVAGE, 3. Am. Chem. Soc., 1996,118, (47), 11972-11973 Energy transfer is studied in a rodlike dinuclear complex, (ttp)Ru(tpy-ph-bco-ph-tpy)Os(tpp)" (tpy = 2,2':6',2"-terpyridine, tpp = 4'-ptolyl-tpy, ph = 1,4- phenylene and bco = bicyclo[2.2.2]octane), which has a rigid, linear geometry. The Ru + 0s energy transfer rate was found to be 5.2 X lo6 s ' (& 20%) at 90-200 K. Energy transfer is therefore unaffected by the temperature changes and state of the solvent.

ELECTROCHEMISTRY Kinetic Study of the Hydrogen Oxidation Reaction on Platinum and Nation@ Covered Platinum Electrodes R. M. Q. MELLO and E. A. TICIANELU, Electrochim. Acta,

Hydrogen oxidation at Pt and Pdpolymer electrolyte interfaces in contact with solutions of H S O , and K,S04 at pH 0.2-7.5 was studied using cyclic voltam- metry, rotating disk electrode and potential step chronoamperometry. The solubility and the diffusion coefficient of H, gas in the solutions and the perme- ability in the polymer electrolyte were determined.

1997,42, (6), 1031-1039

Electrocrystallization of a Halogen-Bridged Mixed-Valence Platinum Complex H. AWANO, T. KUMAZAWA and K. KASWA, Electrochim. Acta, 1997, 42, (3), 483488 Electrocrystallisation of [Pt(en),] [PtCl,(en),] (C104), ( l ) , a halogen-bridged mixed-valence Pt complex with Pt" ... X-Pt"-X... chains, is reported. Electrochemical reduction of tranr[PtCl,(en),]Clz in a solution of per- chloric acid at -1.5 to -1.6 V vs. a Pt counter electrode gave red needle crystals of (1) several mm long, on a Sn-doped In oxide substrate. No crystals formed during electrochemical oxidation of a Pt" complex.

On the Nature of the Interaction of H2PdCI, with the Surface of Graphite-Like Carbon Materials

MOROZ, A. I. BORONIN, A. L. CHWILIN and v. A. LIKHOLOBOV, Carbon, 1997, 35, ( l ) , 73-82 The adsorption of H2PdCI, from aqueous solutions onto the surface of graphite-like C materials proceeded through two competitive pathways: (1) reduction, giving rise to I'do particles of 6-100 nm in size localised near the exterior surface of the porous C particles and (2) formation of n-complexes of PdCI, with >C=Cc fragments of the C matrix, which takes place on the whole surface of the particles. The ratio, dispersion and morphology of the adsorbed Pd" and Pd" species are found to be dependent upon many factors.

Effect of a Graphite Pad on the Adsorption and the Electrocatalytic Activity of Microdeposits of Rhodium E. HOROZOVA, z. JORDANOVA and M. VELKOV, Electrochim. Acta, 1997, 42, (3), 369-376 The effect of a graphite pad on the adsorption and electrocatalytic activity of Rh microdeposits electro- chemically dispersed on graphite was studied with regard to H, and electrocatalysis towards cathodic Hr evolution. The type of graphite affects adsorptivity and the energy spectrum of H, adsorption, and has some effect on the specific currents and kinetic parameters of the cathodic liberation of H,. Electron microscopic studies of rhodanised graphite electrodes showed that the role of the graphite pad is in the formation of Rh deposits of different structure.

Supramolecular Electrode Materials Derived from Pyrrole-Substituted Ruthenium(I1) Bipyridyl Calix[4] arenes H. c.-Y. BETTEGA, M. HISSLER, J.-C. MOUTET and R. ZIESSEL, Chem. Muter., 1997, 9, (l), 3-5 Electropolymerisation of calixarenes bearing pendant Ru complexes, to produce poly(calixarene-[Ru(bpy)J'*) (bpy = 2,2'-bipyridine) (1) modified electrodes is reported. Pyrrole-substituted (1) were prepared by heating the bipyridyl mono- and disubstituted calixarenes with Ru(L),Cl, (L = 4-(pyrrol-l-yl)-4'-methyl- 2,2'-bipyridine) at 60°C in EtOH, followed by pre- cipitation as hexafluorophosphate salts. Electrodes were coated by oxidative homo- and copolymerisation, with N-methylpyrrole, of the monomer complexes.

P. A. SIMONOV, A. V. ROMANENKO, I. P. PROSVIRIN, E. M.


PHOTOCONVERSION Photocatalytic Transfer Hydrogenation of Schiff Bases with Propan-2-01 by Suspended Semiconductor Particles Loaded with Platinum Deposits B. OHTANI, Y. GOTO, s.-I. NISHIMOTO and T. INUI, J. C h . Soc., Faraday Trans., 1996,92, (21), 42914295 Photoirradiation at >300 nm of a propan-2-01 solution of Schiff bases (N-benzylidenebenzylamine and N-benzylideneaniline) containing platinised TiO, (Ti0,-Pt), or CdS loaded with PtO,, gave the corresponding secondary amines (dibenzylamine and N- benzylaniline, respectively) via catalytic transfer hydrogenation. The most efficient catalyst has small Pt deposits dispersed uniformly on each TiO, particle.

Photocatalytic Hydrogen Production by Dye- Sensitized PtlSnO, and Pt/Sn02/Ru02 in Aqueous Methyl Viologen Solution

SASTFZI, Int. J. Hydrogen Energy, 1997,22, (l), 57-62 H, photoproduction by a wide band gap SnOl semiconductor in powder form loaded with Pt and RuO,, and sensitised by Ru(bpy),2’ and organic dyes or with low band gap CdS semiconductor, was studied. Acriflavin, Eosin Blue, Rhodamine B, Rose Bengal and Fluorescein were used as photosensitisers in the presence of methyl viologen (MV”), with or without EDTA as a sacrificial agent. The maximum rate of H, production was observed at [Ru(bpy),z’] = 3.75 x mol dm-’ and [MV”] = 2.5 x mol dm-’.

Femtosecond Dynamics of Excited-State Evolution in [Ru(bpy),]” N. H. DAMRAUER, G. C E R U O , A. YEH, T. R. BOUSSIE, C. v. SHANK and J. K. MCCUSKER, Science, 1997, 275, (5296), 54-57 The earliest events associated with excited-state relax- ation in tris(2,2‘-bipyridine)Ru(II) were monitored by time-resolved absorption spectroscopy on the femtosecond time scale. The data revealed dynamics associated with the temporal evolution of the Franck- Condon state to the lowest energy excited state of this molecule, which was completed in - 300 femtosec- onds after the initial excitation.

Hydrogen Generation Using Water-Insoluble Polymer-Bound Ruthenium(I1) Complexes M. SUZUKI, s. KOBAYASHI, M. KIMURA, K HANABUSA and H. SHIRAI, Chem. Commun., 1997, (2), 227-228 Water-insoluble free-standing films of partially quater- nised poly( 1-vinylimidazo1e)-bound Ru(II) complexes were prepared and used as polymer-solid photosensitisers for H, generation. When an aqueous solution containing the polymer-bound Ru(I1) complex film, methyl viologen ( M T ) , triethanolamine and bis (2,2’-bipyridine)Pt(II) was irradiated with light (h > 440 nm) HZ was generated. Electron transfer from the photoexcited Ru(I1) complex to the M T species on the polymer surface forms MV“ species which diffuse into the bulk solution and react with Pt giving H,.

K. GURUNATHAN, P. MARUTHAMUTHU and M. V. C.

Excited State Properties of bis-Tetraaza- phenanthrene-Ru(I1) Diad Complexes with a Ferrocenyl Unit S . CHOUA, A. KIRSCH-DE MESMAEKER, L. JACQUET, C. =IN and N. CHABERT, J. Phowchem. Photobiol., A: Chem., 1996,99, (2-3), 127-136 The excited state properties of the diad complexes R~(tap),(ppFc)~’ and Ru(bpy),@pFc)” (tap = 1,4,5,8- tetraazaphenanthrene and bpy = 2,2’-bipyridine), bearing a reducing ferrocenyl (Fc) centre on a deriva- tised (pyridine)pyrazole (pp) ligand, were compared with those of the corresponding complexes lacking a Fc unit. Intermolecular photoelectron transfer with ferrocene was favoured when bpy was replaced by tap. The different excited state behaviour in the absence of reducing agent was explained on the basis of pho- tophysical data available for other tap complexes.

ELECTRODEPOSITION AND SURFACE COATINGS Epitaxial Growth of Thin Films of SrTil-xRuxOa by Pulsed Laser Deposition A. GUPTA, B. w. HUSSEY and T . M. SHAW, Muter. Res.

Pulsed laser deposition is used to epitaxially grow SrTil-xRuxO,d (0 s x s 1) thin films on (100)-orien- tated SrTiO, substrates. The films are grown in a low pressure 0, ambient with in situ characterisation of the surface using MEED. The solid solution films are potentially useful as latticed-matched buffer layers for heteroepitaxial growth, or as barrier layers in tunnel junctions with controlled resistive properties.

B d . , 1996,31, (12), 1463-1470

APPARATUS AND TECHNIQUE Amperometric Determination of Nitrite via Reaction with Iodide Using Microelectrodes M. BERTOTTI and D. PIETCHER, Anal. Chim. Acm, 1997, 337, (l), 49-55 The measurement of steady state currents at Pt microdisk electrodes (radii 2.5-10 pm), generated fiom the quantitative conversion of iodide to miodide by nitrite in 0.1 M H,SO,, is the basis of a method for the determination of nitrite in H,O. This rapid and simple procedure can be used to reliably determine levels 2 0.1 pM in natural H20 and human saliva.

Glucose Detection at Bare and Sputtered Platinum Electrodes Coated with Polypyrrole and Glucose Oxidase P. J. H. J. VAN os, A. BULT, c. G. J. KOOPAL and w. P. VAN BENNEKOM, Anal. Chim. Acm, 1996,335, (3), 209-216 Glucose sensors have been fabricated by the gal- vanostatic polymerisation of 0.3 M pyrrole in 4-(2- hydroxyethy1)- 1 -piperazine-ethane sulfonic acid buffer (PH 7.0) with 200 U ml-’ glucose oxidase using a current of l fl at bare and sputtered Pt electrodes. Addition of flavine adenine dinucleotide did not increase the glucose response. The selectiviv for other sugars (lactose, galactose and fructose) was good.


Development of a Novel Manganese Oxide- Clay Humidity Sensor K. m m , M. HIEDA and T. KATO, Ind. Eng. Chem. Res., 1997, 36, (l), 88-91 Clay materials, such as kaolinite (l), muscovite (2), etc., were used as components in a potential-type humidity sensor, Pt/EMD/M, where EMD is electrolytic MnO,, and M is Cu or Al. With (1) and (2), the humidity-sens- ing characteristics of EMD were enhanced, giving good linearity and fast response. A mechanism for this enhancement was proposed, based on the role of inter- layer H20 molecules in the EMD-additive system.

Fluorescence-Based Thin Plastic Film Ion- Pair Sensors for Oxygen A . M I L L s ~ ~ ~ M . T H O M A S , A ~ ~ ~ ~ ~ ~ , 1997,122, (l), 6 M 8 Thin-film sensors for 0,) which incorporate the dye ion-pair, ais(4,7diphenyl-l, 10-phenanthroline) R u m ditetraphenylborate in a variety of thin film poly- medplasticiser matrices, have been prepared. When poly(methy1 methacrylate) was used as the polymer and ni-n-butyl phosphate as the plasticiser, the sen- sitivity of the film towards 0, increased markedly with increasing level of the plasticiser, but was largely independent of tempera- and age. An O2 sensor exposed to alternating O2 and N2showed a &90% response and recovery times of 0.4 and 4.4 s, respectively.

HETEROGENEOUS CATALYSIS Transient and Resonant Behavior for NO Reduction by CO over a Pt/AI,O, Catalyst during Forced Composition Cycling R R. SADHANKARandD. T. LYNCH, Can. 3 chem. Eng., 1996,74, (5), 674-682 The reduction of NO by CO over a Pt/A120, catalyst was studied in an isothermal recycle reactor at 485 K. Maximum time-average CO and NO conversions of 66 and 78%, respectively, were achieved from out- of-phase feed concentration cycling at a frequency of 5.5 mHz, compared with the steady-state conversions of 2 and 3.8%, respectively. The difference in the CO and NO conversions was due to the formation of N20. Higher NO conversions were obtained by decreasing the NO phase lead to below 180".

Catalytic Testing of TiOJPlatindSilicalite- 1 Composites N. VAN DER PUIL, E. J. CREYGHTON, E. C. RODENBURG, T. S. SIE, H. VAN BEKKUM andJ. C. JANSEN, 3 C h . SOC.,

Furaday Trans., 1996,92, (22), 4609-4615 The synthesis, characterisation and testing of composite Ti0,-supported Pt catalyst particles, covered with a 0.S1.3 pn thick silicalitel layer, are described. The composite shows mass transport selectivity giving high ratios of the initial conversion rates (35 at 100°C) in the competitive hydrogenation of a linear and a dibranched alkene. Steric constraints observed at the catalytic sites lead to regioselectivity in the hydrogenation of long-chain alkenes. A linear alkene with a terminal double bond is converted preferentially over an isomer with an internal double bond.

Hydrodesulfwization over PdMoMY Zeolite Catalysts

F. ZUGAZAGA, M. B. G~JEMEZ and^. L. ARIAS, Fuel, 1997,

A series of binary PdMo/HY zeolite catalysts has been prepared by a two-step impregnation procedure and tested in the hydrodesulfurisation (HDS) of diben- zothiophene and diesel oil (1.1 wt.% S). Pd/HY was more active than PdMo/HY, suggesting an inhibitory effect of Mo on activity, due to the formation of H.MoSz and S[PdH'] hydride-type sulfides in the PdMo zeolites. The initial S conversion in HDS of gas oil over PdMY was similar to that on a CoMo/Al,O, catalyst, but both PdMY catalyst and the blank HY zeolite deactivated rapidly at short times on-stream.

The Semihydrogenation of Acetylenes over Pd Catalyst on BER in the Presence of CSI N. M. YOON, K. B. PARK, H. J. LEEandJ. CHOI, Tezrahedron

Pd(OAc), on borohydride exchange resin (BER) in 95% ethanol, in the presence of CsI, was found to be a highly selective catalyst for the semihydrogenation of acetylenes. Terminal acetylenes were converted to the corresponding terminal olefins and internal acetylenes to the corresponding &-olefins in virtually quantitative yield at room temperature.

B. PAWELEC, R. NAVARRO, J. L. G. FIERRO, 1. F. CAMBRA,

76, (l), 61-71

Lett., 1996, 37, (47), 8527-8528

Polymer-Supported Palladium and Rhodium Species as Hydrogenation Catalysts P. c. SELVARAJ and v. MAHADEVAN, 3 Polymer Sci., A: Polymer Chem., 1997,35, (l), 105-122 New copolymers containing amino and heterocyclic ligands were prepared and used to anchor Pd(OAc), and RhCl,.xH20 to give highly active catalysts for the hydrogenation of alkenes, dienes, alkynes and nimben- zene under very mild conditions. Relative reactivities and the effects of substrate structure, solvents, catalyst loading, anchoring ligands, metal species and particle size on the hydrogenation rates were determined. Recycling efficiencies of the catalysts were very good.

Fullerene-Based Ruthenium Catalysts: A Novel Approach for Anchoring Metal to Carbonaceous Supports. I. Structure. 11. Hydrogenation Activity T. BRAUN, M. WOHLERS, T. BELZ, G. NOWITZKE, G. WORTMA", Y. UCHIDA, N. P F m E R and R. SCHLOGL, Catal. Len., 1997,43, (3, 4), 167-173; 175-180 The effect of fullerenes and related carbonaceous support materials on the structural and catalytic properties of Ru was studied. Catalysts based on C,, raw fullerene black, extracted fullerene black, cathode deposit and graphite were prepared by a combined impregnatiordactivation reaction based on the ther- mally induced decomposition of Ru,(CO),,. The catalysts were studied using low-temperature CO hydrogenation and liquid-phase hydrogenation of 2-cyclohexenone. The role of non-six-membered C rings in the support materials on the stability and catalytic performance of the Ru particles is discussed.


Ruthenium Porphyrin Encapsulated in Modified Mesoporous Molecular Sieve MCM- 41 for Alkene Oxidation c.-J. LIU, s.-G. LI, w.-Q. PANG and c.-M. CHE, Chem. Commun., 1997, (l), 65-66 [RuL(CO)(EtOH)] ( where H,L is meso-tetrakis(4- chloropheny1)porphyrin) encapsulated in MCM-41, modified with 3-aminopropyltriethoxysilane, is reported as a stable catalyst for the oxidation of akenes by m-butyl hydroperoxide. When 0.1 wt.% Ru/MCM- 41 catalyst was used, significantly higher turnovers and longer catalyst lifetimes were achieved for a range of alkenes, than with free [RuL(CO)(EtOH)].

The Nature of Ruthenium Sulfide Clusters Encaged in a Y Zeolite B. MORAWECK, G. BERGERET, M. CATTENOT, V. KOUGIONAS, C. GEANTET, J.-L. PORTEFAIX, J. L. ZOTM andM. BREYSSE,J Catd., 1997,165, (I), 45-56 Catalysts of RuS, supported in a dealuminated KY zeolite were prepared by ion exchange and subsequent sulfidation by H,S/H,. They were characterised by HREM, EDX, TPR and EXAFS. The activity for the hydrogenation of tetralin, carried out in the presence of excess H,S (1.85%), was very high and roughly 300 times that (expressed per metal atom) of an industrial NiMo/Al,O, hydrotreating catalyst. The active phase was found to consist of clusters of < 50 Ru atoms of a RuS,-like phase with very small domains of Ru metal.

HOMOGENEOUS CATALYSIS Hydration of Alkynes by a PtCI,-CO Catalyst W. BAIDOSSI, M. IAHAV andJ. BLUM,J m. chem., 1997,

The treatment of PtCI, with CO at 40-1 10°C forms a HPtCI(CO), complex, which acts as a highly efficient and selective catalyst for the hydration of aliphatic and aromatic acetylenes. The catalyst operates both under homogeneous conditions in wet THF and under phase-transfer conditions in (CHCl,),/HzO in the presence of tricaprylmethylammonium chloride (Aliquat 336). This system is more environmentally fiiendly than the conventionally used Hg-based process and more efficient than other transition metal-catalysed processes.

62, (3), 669-672

Palladium-Catalyzed Additions of Terminal Alkynes to Acceptor Alkynes B. M. TROST, M. T. SORUM, c. CHAN, A. E. HARMS and G. RUHTER,J Am. Chem. Soc., 1997,119, (4), 698-708 The addition of the C-H bond of terminal alkynes to either terminal alkynes (self-coupling) or activated internal alkynes (cross-coupling) to produce conjugated enynes, in the presence of a catalytic amount of Pd acetate and the electron-rich sterically encumbered lig- and, ms(2,6-dimethoxyphenyl)phosphine, is reported. This system gives excellent yields of both 1:l homo- and cross-coupled products. The extraordinary chemc- selectivity suggests that any functionality will be com- patible with this reaction. The chemoselectivity and excellent regio- and diastereoselectivity make this a very valuable reaction in organic synthesis.

A New Approach to the Solid-Phase Suzuki Coupling Reaction s. R. PIETTRE and s. BALTZER, Tetrahedron Len., 1997,

The reaction of polymer-bound aryl halides with a pinacol ester of diboron under a catalytic Pd(0) system gave the corresponding polymer-bound boronates. The Suzuki coupling reaction was then carried out with a variety of aryl halides under the most eff- cient system, Pd(PPh3),/K,P04/DMF, at 80°C. Cleavage from the support with trifluoroacetic acid gave the expected products in unusually good yields and with high purity (> 98%).

RhCI(PPh,), and RhH(PPh,), Catalyzed Hydrogenation of Acrylonitrile-Butadiene Copolymers J. s. PAFENT, N. T. MCMANUS and G. L. REMPEL, Ind. Eng. Chem. Res., 1996, 35, (12), 44174423 Both RhCI(PPh,), (1) and RhH(PPh& (2) are efficient catalytic systems for the selective hydrogenation of acrylonitrile-butadiene copolymers under severe reaction conditions. Detailed kinetic and selectivity data and the effect of varying process conditions upon the rate of hydrogenation are reported. Dilute solution viscosity data are used to show the uniform selectivity of (1) and (2) catalysed hydrogenations. A prob- able reaction mechanism for the RhCl(PPh,), system

38, (7), 1197-1200

was derived using analysis of variance model Chirality Transfer via the Palladium-Catalyzed discrimination procedures. Cross-Coupling Reaction of Optically Active 2-Cyclohexenylsilane: Stereochemical and Isomerization of Hexene Using Mechanistic Aspects Dihydridorhodium Complex in Dimethyl T. HIYAMA, H. MATSUHASHI, A. FUJITA, M. TANAKA, K. Sulfoxide HIRABAYASHI, M. SHIMIZU and A. MOM, Organometallics,

The cross-coupling of the optically active silane (3- (2-cyclohexenyl)difluorophenylsilane (1) with aryl halide or d a t e , catalysed by Pd(PPh,),, in the presence of fluoride ion proceeds stereospecifically, strongly depending upon the nature of the reactants. The reaction of (1) with 4-iodoacetophenone and tetrabuty- lammonium fluoride gave the product with retention of configuration, but the reaction with the corresponchg triflate using CsF gave the inversion product.

1996,15, (26), 5762-5765 N. KAMEDA and R S A N G O , Nippon f i g d m fiishi, 1996, (12), 101P1018 The isomerisation of 1-hexene with a dihydrido( 1,3- diphenyltriazenido)bis(triphenylphosphine)Rh(III) (dihydridoRh complex)-dimethyl sulfoxide system was studied under 1 a m pressure of H2 or N, at 30°C. Under H,, the isomerisation and hydrogenation of 1- hexene decreased in the order: mans-2-hexene > cis-2- hexene > hexane, whereas under N,, isomerisation was slower and the reaction products were initially found to be in the order: cis-2-hexene > mans-2-hexene.


Phosphoramidites: Novel Modifying Ligands in Rhodium Catalysed Hydroformylation A. VAN ROOY, D. BURGERS, P. c. J. KAMER and I? w. N. M. VANLEEUWEN, Recl. Trav. Chim. Pays-Bas, 1996,115, (1 1/12), 492498 Several monodentate and bidentate phosphoramidites were prepared and tested as ligands in the hydroformylation of oct-1-ene and styrene using Rh(CO),Acac as catalyst precursor. The monodentate ligands are probably too bulky to give satisfactory results. The diphosphoramidite ligands, especially those that co-ordinate bis-equatorially in the mgonal bipyra- midal Rh complexes, give hydroformylation catalysts with good rates and selectivities, With modification, chiral phosphoramidites can be readily obtained, which may be suitable for enantioselective catalysis.

Hydroformylation of 2,4,4-Trimethyl-l-pentene Catalyzed by the Hiqh Nuclearity Carbonyl Cluster [Rh,,(CO),]

and^. REPOSSI, J. Mol. Catal. A: Chem., 1997, 115,

The hydroformylation of 2,4,4-trirnethyl- 1-pentene in tetrahydrofuran was catalysed by the precursor Na,[Rh,,(CO),,], which readily fragmented to give derivatives of lower nuclearity, under high pressures of CO/H, (20-120 atm) at 300-400 K. The reaction is highly chemioselective, approaching 100% selectivity to 3,5,5-trimethylhexanal. Typical turnover numbers are 100-1000 mol olefidmol cluster. The order of the reaction with CO was positive.

A Novel Water-Soluble Rhodium-Poly(eno1ate- co-vinyl alcohol-co-vinyl acetate) Catalyst for the Hydroformylation of Olefins J. CHEN and H. ALPER, J. Am. Chem. SOC., 1997, 119,

The water-soluble polymer, poly(eno1ate-co-vinyl alcohol-co-vinyl acetate) ( P E W is reported as a valuable ligand for the Rh biphasic catalytic hydroformylation of olefins, especially aliphatic olefins. The average turnover frequency for the catalytic hydroformylation of 1-octene was 5.46 X lo-' kmol (kg(Rh)s)-' at 90°C and of 1-dodecene was 2.36 ~ 1 0 ' kmol (kg(Rh)s)-'

R. DELLA PERGOLA, L. GARLASCHELLI, S. MARTINENGO

(2), 265-27 1

(5), 893-895

Ruthenium-Catalyzed Dimerization of Terminal Alkynes Initiated by a Neutral Vinylidene Complex c . SLUGOVC, K. MEREITER, E. ZOBETZ, R. SCHMID and K. KIRCHNER, Organometallics, 1996, 15, (25),

The complexes RuTp(PPh,),Cl, RuTp(PPh,) (py)Cl and RuTp(PPh,),H (Tp = trispyrazolylborate, py = pyridine) catalyse the dimerisation of HC=qR (R = Ph, SiMe,, n-Bu and t-Bu) to give 1,4- and 2,4-disubstituted butenynes. The conversion depends upon the choice of solvent, and both the conversion and selectivity depend strongly upon the nature of the alkyne substituent.

5275-5277

FUEL CELLS CO-Stabilized Supported Pt Catalysts for Fuel Cells: Radiolytic Synthesis B. LE GRATIET, H. REMITA, G. PICQ and M. 0. DELCOURT, J. Catul., 1996, 164, (l), 36-43 K2PtC1, was radiolytically reduced in a CO-saturated HzO/2-propanol mixed solvent, either into molecular carbonyl clusters of the [PtJ(C0)6]:- series or into colloidal metal particles by changing the CO:Pt ratio. The colloidal Pt and also the molecular clusters can be easily impregnated on C black, giving catalysts which are efficient for MeOH or H, electrooxidation and 0, electroreduction. These particles, 2-3 nm in size, are independent of the catalyst loading and support surface area, even for high loadings.

Analysis of the Electrochemical Characteristics of a Direct Methanol Fuel Cell Based on a Pt-RdC Anode Catalyst A. S. ARICO, P. CRETi, H. KIM, R MANTEGNA, N. GIORDANO and v . ANTONUCCI, J. Electrochem. SOC., 1996, 143, (12), 3950-3959 A vapour-feed DMFC based on a Nafion 1 17" solid polymer electrolyte was studied using Pt-Ru/C (1) and Pt/C (2) catalysts for MeOH oxidation and 0, reduction, respectively. Crystalline f.c.c. phases were found in the Pt and Pt-Ru catalysts, but the alloy composition in the latter differed from the nominal composition. An increase in the average particle size and

at 60°C. Selective hydroformylation of styrene and its derivatives pave UD to 97% of branched-chain alde-

particle agglomeration was observed in (1) compared to (2). The electrochemical performance of a DMFC

hyde using &-PEW under biphasic reaction conditions but at low conversions.

Catalytic Dehydrogenation of Cycloalkanes to Arenes by a Dihydrido Iridium P-C-P Pincer Complex M. GUPTA, c. HAGEN, w. c. KASKA, R E. CRAMER and c. M.JENSEN,J. Am. Chem. Soc., 1997,119, (4), 840-841 The Ir P-C-P pincer complex IrH,{ CaH,-2,6-(CHz- PBu',),} is reported as a highly active, completely catalytic homogeneous system for the transfer dehydrogenation of cycloalkanes to arenes. The unique reactivity is due to the P-C-P ligand, which renders the metal centre reactive with saturated hydrocarbons, but resmcts its access to the ligand P-C bonds.

was thus enhanced and output power density of- 150 mWcm-' was achieved with low Pt loadings.

Electrooxidation of CO and COIH, Mixtures on a Pt-Sn Catalyst Prepared by an Implantation Method N. M. MARKOVI~, A. WIDELOV, P. N. ROSS, 0. R. MONTEIRO andl.~.~Rom, C a d Len., 1997,43, (3,4), 161-166 A novel ion implantation technique is used to create a non-equilibrium Pt-Sn(1MP) (IMP is implanted) near surface alloy with - 8.6 at.% Sn. The kinetics of the electrooxidation of CO and 2% CO/H, mixtures on Pt-Sn(IMP) are nearly identical to those of Pt3Sn( 110). This method may lead to a new Pt-Sn alloy fuel cell catalyst with a unique surface composition of Sn.


Five Percent Platinum-Tungsten Oxide-Based Electrocatalysts for Phosphoric Acid Fuel Cell Cathodes 0. SAVADOGO and P. BECK, 3 Electrochem. Soc., 1996,

A Pt-W oxide-based electrocatalyst was produced by an inexpensive chemical route for use as an 0, cathode in 99% H,P04 at 180°C. The electrocatalytic properties for the 0, reduction reaction (ORR), such as exchange current density and mass activity, of a 5% Pt-40% W0,-based electrode (1) were twice as high as those of 10% Pt, due to an increase in its elec- trochemically active surface. The performance of (1) for ORR was compared to that for a 2% Pt- 1 % H,WO,-based electrode, and found to be lower.

143, (12), 3842-3846

CORROSION PROTECTION Hot Corrosion Behavior of Pt-A1 Coating in Molten Sulphate or Mixed Salts Y. PANG, H. GUAN, x. SUN and x. JIANG, Corros. Sci. Prot. Technol., 1997,9, (l), 3 4 3 7 The hot corrosion behaviour of a Pt-modified alu- minide coating on superalloys in the presence of molten Na,SO,, or NazSOl + NaCI, salts was studied in air at 900°C. The coating displayed good hot corrosion resistance in molten sulfate, forming only a protec- tive Al,O, layer on the surface. The addition of NaCl into the Na,SO, strongly decreased this resistance and the Pt-AI coating suffered from internal oxidation and sulfidation, while its inner NiAl phase showed even greater corrosion.

Corrosion Resistance of Titanium-Platinum Alloy Prepared by Spark Plasma Sintering J. ONAGAWA, T. GOTO, 0. ISE, N. ISHII, T. HOFUKAWA and K. SAWADA, Mater. Trans. JIM, 1996, 31, (11),

The corrosion resistance and microstructure of Ti- Pt alloys, prepared from Ti and Pt powders using spark plasma sintering, were studied by SEM and XRD. The Pt phases were dispersed throughout the Ti matrix, and some Ti-Pt intermetallic compounds were formed around the Pt phases. The corrosion resistance of Ti was improved by the addition of maces of Pt and by annealing, which created a eutectic state between the Pt and TiPt phases.

1699-1703

CHEMICAL TECHNOLOGY Purification of Rhodium-Filled Carbon Nanotubes Using Reversed Micelles J. COOK, J. SLOAN, R. J. R. HEESOM, J. HAMMER and M. L.

A non-invasive, external washing method for RhCI, filled nanotubes used a reversed micelle medium formed from dodecylammonium propionate (dap)- solubilised water in benzene. Treatment with H, at 500°C for 5h gave nanotubes filled with discrete crystals of Rh metal, but with no crystals on the exterior of the structures. These materials may find uses as nanowires, composites and catalysts.

H. GREEN, Chem. Commun., 1996, (23), 2673-2674

ELECTRICAL AND ELECTRONIC ENGINEERING Thermal Reliability and Characterization of InGaP Schottky Contact with TilPtlAu Metals C.-T. LEE,H.-P. SHIA0,N.-T.YEH, C.-D.TSAI,Y.-T. LYUand Y.-K. TU, solid-State Electron., 1997, 41, (l), 1-5 The characteristics of Ti/Pt/Au Schottky contacts on wide bandgap InGaP semiconductors, with surface pretreatment before Schottky contact deposition, and the effect of post heat treatment on Schottky diodes (1) are presented. Predeposition surface etching by dilute HC1, dilute NROH, or buffer oxide etchant greatly improved the performance of (1). After annealing (1) at 500"C, a drastic degradation of the barrier height and the ideality factor occurred. This may be due to the interdiffusion and peneuation of metals into the semiconductor.

AdGelPd Ohmic Contacts to n-GaAs with the Momi Diffusion Barrier

Y.-J. CHAN and H.-C. CHENG, 3 Electron. Mater., 1996,

Three different barrier structures, AdGeIPdGaAs, AwTi/GeiPdGaAs and Au/MoTTi/Ge/FdGaAs were studied to determine the effects of the As-outdiffusion and Au-indiffusion on their performance. The smoothest surface and the lowest specilic contact resistivity were found on Au/Mo/Ti/GeiPdn-GaAs sam- ples, at the widest annealing temperature range. MoTTi was an efficient diffusion barrier, retarding Au-indiffusion and As-outdiffusion against thermal annealing.

The Effects of Processing Conditions on the Resistivity and Microstructure of Ruthenate- Based Thick Film Resistors F. JOHNSON, G. M. CROSBIE and W. T. DONLON, 3 Mater. Sci., Mater. Electron., 1997, 8, (l), 29-37 Resistances were measured in situ during firing of blended resistors having a nominal sheet resistivity of 56 kQ/Uand TCR < f 100 ppm R'. XRD showed Pb ruthenate, A120, and Zr silicate in the resistors with the ruthenate lattice parameters increasing with increasing firing temperature and time. Resistance changes are attributed to increased separation of ruthenate particles by coarsening.

C.-Y. CHAI, ].-A. HUANG, Y.-L. W, 1.-W. WU, C.-Y. CHAh'G,

25, (12), 1818-1822

MEDICAL USES Kinetics of Nitric Oxide Scavenging by Ruthenium(II1) Polyaminocarboxylates: Novel Therapeutic Agents for Septic Shock N. A. DAVIES, M. T. WILSON, E. SLADE, S. P. FRICKER, B. A. MURRER, N. A. POWELL and G. R. HENDERSON, Chem. Commun., 1997, (l), 47-48 Two R u m polyaminocarboxylates, K[Ru(Hedta)CI], JM1226, and ~u(Hedta)(HzO)], JM6245, have been shown to rapidly bind NO (rate constant > 10' M-'s-') tightly (binding constant = 10' M-I) at physiological pH to form a stable 1 : 1 Ru(II) mononitrosyl. They have potential as NO scavengers in NO mediated diseases.


NEW PATENTS ELECTRODEPOSITION AND SURFACE COATINGS Metal Coated Amino Resin Polymer Particles

British Appl. 2,30 1,117A Metallic coated amino resin polymer particles (1) are manufactured by activating the surface of hollow or solid micropamcles by treatment with a solution containing ions of Pd, Au or Ag, preferably PdC12, H,PdCI,, or a tetrachloropalladate salt and H,SO,. The metallic coating is deposited by chemical met- allisation on the activated particles in colloidal form or as an enclosed metal layer. (1) are used in catalytic processes, as finely particulate anode materials, etc.

Production of Permanent Magnets

FRAUNHOFER GES FOERDERUNG ANGEWANDTEN

VACUUMSCHMELZE G.m.b.H. European Appl. 736,884A

A process for producing a permanent magnet containing rare-earth metals and protected against corrosion by an electrolytic coating is described. This involves coating the permanent magnet with a Pd alloy using an alkali Pd-containing electrolyte and a current yield > 85%. This coating avoids or minimises any surface damage which could result in loss of magnetic properties.

Forming Iridium Film Patterns on Electrodes

Japanese Appl. 81277,473 An Ir or Ir oxide film pattern is formed from a composition containing a specified amount of Ir, a cyclopentadienyl complex and an organic solvent. This is applied onto a matrix, followed by exposing the pattern to radioactive rays, removing unexposed parts by rinsing with a solvent, then heat treating in a reducing or oxidising atmosphere.

MITSUBISHI MATERIALS C O W .

APPARATUS AND TECHNIQUE Lead Frame for Semiconductor Devices TEXAS INSTR. INC. US. Patent 5,561,320 A lead frame for a semiconductor device consists of a metal layer of Pd or Pd/Ni plated on the lead frame, spot plating Ag on portions of the leads and Cu plating between the Ag and the Pd or Pd/Ni. I t has good solderability and allows low temperature processing.

High Temperature Sensor SIEMENS A.G. German Appl. 1/95/23,301 A heater for a high temperature metal oxide sensor has current flowing through Pt heating wires at 600-10OO0C, and measures the voltage drop across the Pt measurement wires. The heating wire tracks, measurement tracks and the heating structure all include Pt, with a thickness of 5 pm. The sensor is used in vehicle exhausts to measure the temperature of the heating element, while minimising heat loss.

HETEROGENEOUS CATALYSIS High Selectivity Platinum Metal Catalyst BAYER A.G. European Appls. 736,324-25A A catalyst carrier contains 0.01-15 (preferably 0.05-10) wt.% of a Pt group metal, compound or complex, and a co-catalyst of one or more oxides of Ti, V, Mn, Cr, Fe, Co, Ni, Cu, La, Nb, Mo, Pb, rare earth metal or actinide. Diary1 carbonates are produced with high activity and selectivity, by reacting aromatic hydroxy compounds with CO and O2 at 30-200°C and 1-150 bar using the above catalyst carrier, in the presence of the co-catalyst, a quaternary ammonium or phosphonium salt and a base.

Production of Aromatic Carbonates MITSUBISHI CHEM. C O W . European Appl. 736,5 12A Aromatic carbonates, for use in polycarbonate production, are manufactured by reacting aromatic hydroxy compounds with CO and O2 in the presence of Pd andlor Pd compounds; trivalent andlor tetrava- lent Ce compounds; and at least one inorganic halide which can be an alkali metal chloride or bromide, or an alkali earth metal chloride or bromide. This reaction proceeds in high yield and with good selectivity.

Alkyne Hydrogenation Catalysts PHILLIPS PETROLEUM CO. European Appl. 738,540A Alkyne hydrogenation catalysts, resistant to deactivation by S-containing impurities, contain Pd, one chemically bound alkali metal (preferably K), F and an inorganic support, preferably A1,0,. The atomic ratio of F:alkali metal is 1.3-4: 1. The catalyst additionally contains 0.01-10 wt.% Ag in a weight ratio of Ag:Pd of 2-1 0: 1. These catalysts are useful for the selective hydrogenation of feeds containing one 2-1 OC alkyne to form one alkene and find use in the conversion of small amounts of acetylene contained in ethylene streams from thermal alkane crackers.

Purification of Crude Pentafluoroethane ELF ATOCHEM S.A. European Appl. 742,192A A process for the purification of crude pentafluoroethane (F 125) containing chloropentafluoroethane (F 11 5) uses catalytic vapour phase hydrogenolysis over a Pd/AlF, catalyst. The catalyst is stable under the required conditions and can be used when the molar content of F 11 5 in the mixture 5 10%.

Preparation of 2-Pyrrolidones BAYER A.G. European Appl. 745,589A 2-Pyrrolidones (1) are prepared in high space-time yields by hydrogenating a mixture of maleic anhydride and a primary amine at 150-330°C and 10-300 bar in a liquid phase over a supported catalyst of 0.5-15 wt.% Pd, 0.5-10 wt.% Re, with a total Pd+Re content of 2-15.5 wt.%. Foreign solvent addition to the system is avoided. Little y-butyrolactone by-product is formed and no over-hydrogenation to THF occurs. (1) are polar solvents for polymers, extractants, etc.

Platinum MetulsRev., 1997,41, (2), 96-100 96

Purification of Polluted Air BCP SRL World Appl. 96132,182A An apparatus for the purification of air polluted by C, N and S oxides, ozone, unburned hydrocarbons, particulates, dust and exhaust fumes from 1.C.E.s consists of several sections, active for reducing one or more pollutants, which incorporate transition metal oxides, Pt or other Pt group metals as catalysts. The apparatus can be installed on a moving transport unit or in fixed sites. This system provides neghgible energy expenditure with respect to the amount of air treated and the process can be modified according to the pollutants present.

Hydroquinone Dehydrogenation Catalyst MARATHON OIL CO. World Appl. 96133,015A A catalyst system for the dehydrogenation of hydro- quinones to the corresponding quinones and H, is manufactured by placing a rare earth metal oxide on a SiO, or ALO, support to reduce its acidity, and then applying a catalyst selected from Ni, Co and/or Pt group metals. The manufacture of S and H, from H,S gas is also claimed. The selection of optimum system parameters, including the use of less acidic supports and pretreatment by calcination, gives this catalyst improved selectivity.

Oxidative Dehydrogenation UNIV. MINNESOTA World Appl. 96133,149A A process for the oxidative dehydrogenation of organic compounds involves reaction with a Pt, Rh, Ni or Pt- Au catalyst on a particulate support, in a fluidised bed in the presence of 0,-containing gas. A similar oxidative dehydrogenation for hydrocarbons involves feed- ing a saturated hydrocarbon stream and 0,-containing gas to a reactor comprising the fluidised bed and a catalyst, at a flow rate sufficient to fluidise the bed. No build-up of C was observed on the catalyst and there was no deactivation over several davs.

Reduction of Nitro to Amino Groups CIBA GEIGY A.G. World Appl. 96136,588A Substituted aromatic amino compounds containing CN or CO multiple bonds, or halo atoms(s) on the aromatic ring and/or on a side chain, are prepared by the catalytic hydrogenation of the corresponding nitro compounds in the presence of a Pt catalyst. The catalyst is modified with Pb, Hg, Bi, Ge, Cd, As, Sb, Ag or Au and optionally a Fe, Ru, Co, Cu or Mn compound as a promoter, and ion pairs or salts soluble in organic solvents as co-promoters. The product is obtained with high purity and in good yields, and the reaction is accelerated by addition of the co-promoter.

Vapour-Phase Manufacture HOECHST CELANESE cow. World Appl. 96137,294A A catalyst for the vapour-phase manufacture of vinyl acetate from acetic acid, ethylene, and 0, comprises 2-14 gl-' Pd, 1-8 &' Au and at least one metal selected from 0.5-4 gl ' Zr and 1-8 gl ' Re deposited on a porous support, preferably SOz. The addition of alkali metal acetates is also favoured.The catalyst exhibits high activity and selectivity and has a long life.

Ethyl-Benzene Preparation KOREA KUMHO PETROCHEMICAL CO. LTD.

World Appl. 96137,449A The preparation of ethyl-benzene from 4-vinyl-cyclo- hexene, obtained from 1,3-butadiene, involves the catalytic transfer hydrogenation of 4-vinyl-cyclohex- ene in a H, donor solvent with an oxidising agent in the presence of a Pdactive C catalyst. The catalyst can be easily recovered and recycled for re-use and the solvent can be HzO, which reduces environmental problems. Non-polluting oxidising agents and low temperatures and pressures can be used. High yields of 86% are obtained for ethylbenzene and 100% for aniline with only 13% by-products.

Exhaust Gas Treatment Catalyst ASEC MFG. CO. World Appl. 96/40,4 17A A catalyst for treating the exhaust gas of a natural gas fuelled engine comprises a first washcoat support of AlzO,, a second of CeO, and lanthana promoted with Al,O,, and Pd, and optionally with Rh impregnated into the two washcoat supports. This catalyst improves the conversion of CH,, CO and NOx in lean, stoichiometric and rich airlfuel environments.

Catalyst for Treating Diesel Exhaust Gas ASEC MFG. CO. World Appl. 96/40,4 19A A catalyst for treating diesel exhaust gas comprises an effective amount of at least one Pt group metal selected from Pt, Pd, Rh and/or Ir dispersed on a two-part support which consists of a major amount of a zeolite and a minor amount of AlzO,, ZrO, and/or Sn oxide. A process for removing CO, hydrocarbon and NOx, while minimising production of SO,, involves contacting the gas with the above catalyst which is washcoated onto a flow-through monolithic carrier.

Platinised Microporous Nanoparticle Catalyst WISCONSIN ALUMNI. RES. FOUND.

World Appl. 96/40,43OA A platinised microporous nanoparticulate metal oxide ceramic catalyst is prepared by adsorbing the Pt precursor H2PtCI6 at s 200°C without photo-illumina- tion to achieve steady-state adsorption onto a microporous nanoparticle ceramic metal oxide with a surface area of 50-500 m'g-' and interior pores < 100 A. The precursor is then reduced to Pt metal and dried without affecting the structure of the material. This catalyst has a very high surface area with a highly dispersed Pt coating throughout, thus avoiding the aggregation of earlier products.

Selective Destruction of Formaldehyde MONSANTO CO. World Appl. 96140,592A The selective destruction of formaldehyde and formic acid in aqueous streams involves adding O2 to the stream and contacting with a Group VIII supported metal catalyst, preferably Pt, Pd or Rh at 50-90°C. The catalyst contains 0.1-10 wt.% Pt loaded on pow- dered C and the reaction is carried out in a reactor at s 200 psi. The formaldehyde is converted first to formic acid, then to CO, and H,O. This process is rapid and efficient, and avoids generation of bio-sludge.


Reforming a Naphtha Feed Stream EXXON RES. & ENG. CO. US. Patent 5,562,817 A process for reforming a naphtha feedstream to obtain improved 5C+ liquid yields takes place in a series of reactors. The lead reactor contains a catalyst of 0.1-1 wt.% Pt and 0.02-0.07 wt.% Re on an inorganic oxide support. The tail reactor contains a catalyst comprising 0.1-1 wt.% Pt and 0.1-1 wt.% Re uniformly dispersed throughout a particulate solid support. This process provides efficient and selective naphtha reforming and is used especially to improve the octane rating of naphthas or straight run gasolines.

4-H ydroxyphenyl-Methyl-Carbinol HOECHST CELANESE cow. US. Patent 5,563,300 A process for preparing 4-hydroxyphenyl-methyl- carbinol(4-HPMC) involves the hydrogenation of 4- hydroxyacetophenone in the presence of a Pd catalyst, such as 5%PdlC, Pd/Al,O,, PdlSiO, and PdCaCO,, and 2 25 ppm of a base. Also claimed is the manufacture of a carbinol from a ketone or a substituted ketone under the above conditions. 4-HPMC

Alkylmethyl Siloxanes DOW CORNING C O W . U S . Patent 5,578,692 Triorganosiloxy end-capped alkylmethyl siloxanes (1) are produced by reacting a linear triorganosiloxy end- capped methylhydrogen polysiloxane containing < 0.2% branch sites with an a-olefin in the presence of a Pt catalyst, such as 5%PtlC, until ( I ) , containing < 200 ppm H as residual =SiH, is formed. (1) have high molecular weights and very few branching sites.

Uniformly Plated Microsphere Catalysts J. A. PAlTERSON US. Patent 5,580,838 Uniformly plated microsphere catalysts with increased H, occlusion, for use in catalytic and electrical applications, comprise non-conductive cores with suc- cessive uniform layers of Cu, Ni, Pd and Ni. Pd-plated microspheres exhibit a marked improvement in both the speed and amount of H, absorbed. The uniform size and density of the microspheres result in a plating of uniform thickness. The layer of Ni over the Pd layer stabilises the Pd without inhibiting diffusion of H2 to the Pd.

is an intermediate in the production of polyhydro- xystyrene which is used in adhesives, coating compositions, photoresists, etc. ICT K.K. Japanese Appl. 81229,350

Decomposition Of Nitrogen Oxide

Vinyl Acetate Production

Vinyl acetates are prepared by the vapour phase reaction of ethylene, acetic acid and 0, or 0,-containing gases in the presence of a supported catalyst containing Pd, Cd and alkali metal compounds and, at most, one Ru and/or Zr compound. Higher space- time yields are obtained at the same or higher selectivity (such as 98.4%) with slower deactivation (such as 0.7:l) compared with catalysts without Ru or Zr.

Arylamine Compounds

HOECHST CELANESE COW. U s . Patent 5,576,457

MASSACHUSETTS INST. TECHNOLOGY U S . Patent 5,576,460

Arylamine compounds are prepared by reacting an amine with an activated aromatic compound at < 120°C in the presence of a catalyst selected from complexes of Pt, Pd, Fe, Ni, Ru and Rh, and a base. The catalyst complexes may include chelating ligands, alkyl and aryl derivatives of phosphines and bisphosphines, etc., such as PdCl,(P(o-tolyl),),. Mixtures of arylamines can be used in screening for pharmaceutical and biological activity and to prepare polyanilines.

Glyphosate Production MONSANTO CO. U S . Patent 5,578,190 The herbicide N-phosphonomethylglycine (1) is produced by the one-pot condensation of aminomethyl- phosphonic acid in an aqueous medium at pH 5-1 1 with glyoxylic acid, or its hemiacetals, acetals or hydrate, followed by electrochemical reduction (A), or catalytic hydrogenation (B), at 20-90°C. Process (B) uses a catalyst selected from Pt, Pd, Os, Ir, Rh, Ni and/or Co and their salts or oxides, especially Pt or Pd. (1) is obtained with a 35% current efficiency from method (A) and in yields of 90-96% from (B).

A catalyst for the decomposition of NO consists of a fireproof three-dimensional structure coated with a catalyst consisting of a Pt holding fireproof inorganic oxide powder and a second fireproof inorganic oxide powder. The content of Pt in the inorganic oxide powder is 5-50 wt.%. CO can be burned and removed.

Exhaust Gas Purification NISSAN MOTOR CO. LTD. Japanese Appl. 81229,355 A catalyst for the purification of exhaust gases contains at least one metal selected from Pt, Rh and Pd, and a perovskite oxide of La, .A.BO,, where 0 < x < 1; A = Ca or Ba; and B = Co, F, Mn or Ni, held on a fireproof inorganic carrier. NOx purification under a lean atmosphere can be improved over this catalyst.

Recovery Mesh for Ammonia Oxidation w. c. HERAEUS G.m.b.H. German Appl. 1/95/43,102 A Au-free mesh, used especially as a recovery mesh for NH, oxidation to HNO,, consists of a wire mesh made of Pd and other Pt group metals with preferably 10-20 wt.% Pt, and possibly also s 5 wt.% Rh. The mesh has high mechanical stability and good catalytic activity, and is effective both as a recovery and a catalytic mesh for the oxidation of NH,.

Exhaust Gas Purification Catalyst MAZDA MOTORCORP. German Appl. 1196117,123 A n exhaust gas purification catalyst consists of a support with an undercoat containing Ba andlor La, a top coat containing an adsorbent for H,O in the gas and a catalyst, containing a Pt group metal, in one or both coats. The weight ratio of top coat:both coats is 3:40-34:40. The catalyst can reduce NOx, hydrocarbons and CO into N2, H,O and CO,. The catalyst also inhibits poisoning of La and Ba by S and/or H,O, so that efficient emission control is maintained.


HOMOGENEOUS CATALYSIS 2-Hydroxy -4-methyltetrahydrofuran KURARAY CO. LTD. European Appl. 747,373A 2-Hydroxy-4-methyltetrahydrofuran (l), a useful intermediate in the production of various fine chemicals, is produced by reacting 2-methyl-2-propen-1-01 with H, and CO in the presence of a Rh compound and a tris(substituted aryl) phosphite with an electronic parameter (v-value) of 2080-2090 cm-l and a steric parameter (&value) of 135-190'. This process produces (1) economically, with 1 10-1000 moles of phosphite used per gram atom of Rh, and in high yield.

Production of Acetic Acid BP CHEM. LTD. European Appl. 752,406A The production of acetic acid by carbonylation of MeOH and/or reactive derivatives uses a liquid reaction composition containing an Ir carbonylation catalyst, methyl iodide co-catalyst, H20, acetic acid, methyl acetate and promoters, preferably Ru or 0 s . The concentration of H,O is maintained at s 6.5 wt.%, methyl acetate at 1-35 wt.% and methyl iodide at 4-20 wt.%. The increased carbonylation rate at this low HzO concentration allows the use of a lower concentration of Ir catalyst. The production of by-products is also reduced.

Aralkanoic Acid or Ester Preparation ALBEMARLE COW. World Appl. 9 6137,453A The preparation of an aralkanoic acid or ester involves reacting an aralkene and an alcohol with CO at 25-200°C and a pressure of a 1 atm, in the absence of Oz and in the presence of a Pd catalyst mixture. An acidic medium is not required for the process and the acid or ester products are obtained in good yield. This method is useful in the preparation of ibuprofen or naproxen derivatives.

Hydrosilation of Alkynes DOW CORNING COW.

U S . Patents 5,563,287 and 5,565,596 A process for the hydrosilation of alkynes involves contacting the alkyne at 40-150°C with a hydrosilane in the presence of a Pt catalyst and a 6-20C cycloalkadiene in the ratio 0.1-5 mol (6-20C) per g-atom of Pt. A related process using hydridosilanes and a 6-20C cycloalkene is also described. The Pt catalyst is selected from Pt halides and their reaction products with organosilicon compounds containing terminal aliphatic unsaturation. The cycloalkadiene and cycloalkene reduce formation of bis-silylated and bis-silated adducts, respectively.

Formation of Monosilanes DOW CORNING COW. US. Patent 5,567,837 Monosilanes are formed by reacting a mixture of a disilane, preferably hexamethyldisilane, with an organic halide, such as ally1 chloride, over a disubstituted Pd catalyst, such as PdC1, or bis-acetoacetyl Pd. This process gives monosilanes with alkenyl substitution and can convert the high boiling disilane-containing fraction from the direct process into monosilanes.

Preparation of 3-Aryl-1-butene HOECHST A.G. German Appl. 1195149,334 The production of 3-aryl-1-butenes (1) involves codimerising an optically substituted styrene with ethene in the presence of a Pd complex catalyst containing a monodentate P-chiral phosphinite ligand, preferably the menthyl ester of a r-butyl-phenyl-, methyl-phenyl-, etc., phosphinic acid. The preferred complex catalyst is (C,H,R)Pd(t-butylphenyl-o-menthyl)PSbF, (where R = H or 1-4C alkyl). (1) are obtained in an optically active form with high selectivity and are used as precursors for 2-aryl-propi- onic acids, used as non-steroidal anti-inflammatories.

FUEL CELLS Fuel Cell Electrodes BALIARD POWER SYSTEMS INC.

European Appl. 736,921A An anode or cathode electrode (1) has a first and second catalyst component active at gas phase and electrochemical reaction sites, respectively. For an anode, the first and second components are in physical contact. The electrode is formed by mixing a catalyst, such as 20 wt.% Pt/C black, with Nafion solution, and then coating it onto a C fibre substrate. When used in fuel cells (1) have better tolerance to poisons, such as CO and CO,, in the reactant fuel and oxi- dant streams and have high activity and durability.

Platinum- Aluminium Alloy Catalyst DEGUSSA A.G. European Appl. 743,092A A Pt-Al alloy catalyst on a conducting C carrier, where the atomic ratio of Pt:AI is 8&60:20-40, is described. The alloy particles are present in a carbided form, Pt&Cos. This catalyst is used in phosphoric acid and polymer electrolyte membrane fuel cells and has higher activity and improved ageing stability.

Lowering Carbon Monoxide and Methanol TOYOTA JIDOSHA K.K. European A@/. 743,694A An apparatus for lowering CO and MeOH levels in Hz-rich gases is incorporated into a fuel reforming system. It has an Oz introduction device and selective oxidising units, for both CO and MeOH, containing a Pt-Ru alloy catalyst. The reformed gas, containing H, and very low concentrations of MeOH and CO, is then fed to a polymer electrolyte fuel cell stack or to a phosphate fuel cell.

Cathodic Current Collector MTU FRIEDRICHSHAFEN G.m.b.H.

German Appl. 1/95/32,791 A cathodic current collector, for a fused carbonate fuel cell, has a base material of a highly corrosion resistant metal or its alloy (preferably a high Cr or Al-containing alloy). This is covered with thin layers of a highly conductive inert metal, such as Pt, Au or Ag, at the contact points between the collector and the cathode. A separator is optionally included when the collector is assembled in the cell. The collector has high corrosion resistance with low junction electrical resistance at the contact faces with the cathode.


CHEMICAL TECHNOLOGY High Density Magnetic Recording HITACHI LTD. Japanese Appl. 8/22 1,7 14 A high density magnetic recording and reproducing apparatus is composed of an antiferromagnetic film configured h m an alloy of Mn, Co and Pt. This apparatus has a magnetic head with magnetoresistive properties which is made to traverse the upper surface of the magnetic disc medium to detect magnetic field leaks. This technology reduces noise while achiev- ing sufficient reproduction and increased operational reliability.

Opto-Magnetic Recording Medium SANYO ELECTRIC co. LTD. Japanese Appl. 81227,541 This medium has, as the recording layer, a magnetic layer made of alternate Pt and Co layers formed on a substrate. The thickness of the Pt layer is 0.86-1.73 nm, while the Co layer is 0.27-0.55 nm. A foundation layer made of SiN has a thickness of 0.44-0.55 nm, and is formed between the recording layer and the substrate. C:N characteristics of the layered Pt and Co layers are saturated with sufficient low magnetic field, of - 280 oersteds.

Conductive Paste SUMITOMO METAL CERAMICS INC.

German Appl. 119611 1,239 A conductive paste for connections in ceramic electronic devices, which can be fired at 800-1000"C, comprises by weight: 100 pts. flake-like andor spher- ical Ag-based powder; 0.1-2 pts. of Sb,O, (or SUE- cient material combustible to give the required amount of Sb,O,) andor Rh powder; and at least 3 pts. of 2- tetradecanol. This composition shows little viscosity change when under pressure and is suitable for use with glass substrates also containing Al oxide.

Hydrogen Preparation KANSAI NETSUKAGAKU K.K. Japanese Appl. 81239,201 Hi is produced from reforming CH, by reacting CHI with 0, over a highly active Rh modified (Ni-Ce0,)Pt catalyst to give H, and CO. Heat produced from the combustion of CH, is partially used in the reforming reaction on the catalyst along with extra heat needed to maintain CH, reforming. The combustion products C 0 2 and HzO can also be used for the production of HZ and CO.

ELECTRICAL AND ELECTRONIC ENGINEERING Magneto-Optical Recording Medium MITSUBISHI D E W K.K. European Appl. 750,295A A recording medium capable of direct overwriting by light intensity modulation comprises a number of adjacent magnetic layers, where each has vertical magnetic anisotropy and any two adjacent layers are bound by an exchange force between them. A zeroth magnetic layer adjacent to the first, into which a light beam is first admitted, contains a Nd-containing rare earth elemendtransition metal alloy film or alternate films of Pt or Pd and Co in superposition. This medium has good reproduction output at 400 nm, which is half the currently used operating wavelength.

Magnetic Recording Medium HOYA COW. European Appl. 751,501A A magnetic recording medium comprises non-magnetic underlayer(s), a Copt magnetic layer and a substrate. The non-magnetic layer, in contact with the magnetic layer, contains Cr and Mo. A medium where at least the non-magnetic layer containing Cr and Mo and the Copt layer are formed by sputtering at 25M25"C and 0.510 mTorr Ar is claimed. The media are used in magnetic disks and have high magnetic coercive force, squareness ratio and low noise.

Piezoelectric Element PHILIPS ELECTRONICS N.V. World Appl. 971538A A piezoelectric element, useful as an actuator or a sensor for detecting mechanical or acoustic signals, has a number of piezoelectric layers of ceramic alternately stacked with Ag/Pd electrode layers with external electrical connections. A piezoelectric multilayer is made by screen-printing electrode layers on a ceramic foil using a Ag/Pd paste. The piezoelectric elements can be sintered at a lower temperature, < 1 150°C, and have a relatively high Curie temperature, > 250°C.

Multilayer Magneto-Optic Recording Medium EASTMAN KODAK CO. US. Patent 5,563,000 A magneto-optical recording medium consists of a substrate, a seed layer structure including a first layer of IT0 or ZTO 0.2-20 nm thick, a metal layer 0.2-3.2 nm thick and a recording multilayer of alternate layers of Pt and Co or Pd. The seed layer improves the squareness and coercivity of the recording layer.

MEDICAL USES Dental Impression Composition DENTSPLY MT. INC. World Appl. 96132,088A A dental impression material consists of a vinyl group containing resin, linear vinyl-terminated polydimethylsiloxane fluid, organo Pt catalyst, polymerisation retarder, filler and surfactant. The contact angle of the composition with H,O after 3 minutes is < 50". Compared with prior polyorganosiloxane materials, tear strength and wettability are improved, while adequate working time is provided.

Treatment of Tumours NEXSTAR PHARM. INC. World Appl. 96138,460A Modification of nucleosides is performed by reacting a nucleoside containing a leaving group with a nucle- ophile and CO, in the presence of a Pd catalyst. The resulting compounds inhibit viral activity and are useful for treating virus disease, especially cytomegalo- virus, as well as acting as antiviral, antibacterial, anti- fungal and antineoplastic agents.

The New Patents abstracts have been prepared from material published by Denvent Information Limited.


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