VOL. 19 JANUARY 1975 NO. 1 - Platinum Metals Review · A Honeycat Diesel Exhaust Purijier unit forming part of the exhaust train of a Ford- Stamford 40 kVA diesel alternator set assembled

UK ISSN 0032-1400

PLATINUM METALS REVIEW

A quarterly survey of research on the platinum metals and of

developments in their application in industry

V O L . 1 9 J A N U A R Y 1 9 7 5

Contents

Exhaust Purifiers for Compression Ignition Engines

Organometallic Chemistry of Platinum

The Production of Acetic Acid

Superconductivity in Palladium-Hydrogen Alloys

Heavy Platinum Plating from a Molten Salt Bath

The Production of Heavy Water

Photocatalytic Properties of Materials

Trifluorophosphine Complexes of the Platinum Metals

An Age-hardenable Palladium Based Spring Alloy

Abstracts

New Patents

NO. 1

2

11

12

14

1.5

16

21

22

29

30

37

Communications should be addressed to The Editor, Platinum Metals Review

Johnson Matthey & Co Limited, Hatton Garden, London EClP 1 A E

Exhaust Purifiers for Compression Ignition Engines CATALYTIC CONTROL OF DIESEL EXHAUST GASES

By E. J. Sercombe Research Laboratories, Johnson Matthey & Co Limited

A new platinum catalyst system has been developed at the Johnson Matthey Research Laboratories for the OxidatiorL of hydrocarbons and carbon monoxide emitted by compression ignition internal combustion engines. The catalyst was evaluated during tests on a direct injection diesel engine using the 13- mode cycle devised by the California Air Resources Board, thereby assisting the design of catalyst systems to meet specijc emission control targets in particular industrial applications. The new catalyst combined with retardation of injection timing can provide overall control of exhaust emissions, including the nitrogen oxides, from diesel engines.

Compression ignition engines using diesel oil as fuel are widely used as motive power in road, rail, or sea transport and for haulage or lifting equipment in mines and factories. They range in size from small air cooled industrial units of less than I litre cylinder displacement volume to large marine engines of over 1500 1. The performance of these engines is highly dependent on the efficiency of the combustion process and considerable effort has been applied to the development of different types of combustion chamber in order to balance the need for fuel economy with the requirement for high power output. The small high speed diesel engines used in taxis, cars and other light duty vehicles are frequently based on an indirect injection (IDI)

Platinum Metals Rev., 1975, 19, (l), 2-11 2

systcm in order to give acceptable efficiencies over a wide speed range. These can compete with petrol fuelled spark ignition engines. The larger commercial vehicles are usually fitted with direct injection (DI) engines where adequate power is available without excessive fuel consumption. Both types of engine are highly reliable and can be operated for long periods without needing major servicing.

In some of these applications, such as mining, or inside factory and warehouse areas where engines are operating in confined spaces, it is necessary to ensure that exhaust emissions are not hazardous to health or to general safety. In contrast, emissions from engines used in marine applications can be freely discharged to the atmosphere without causing an immediate nuisance or health hazard. However, there is increasing public awareness of the direct and indirect harmful effects of all forms of environmental pollution. Therefore, extensive effort is being applied to develop practicable and economic methods for the control of pollution emanating from industrial manufacturing processes and from the combustion of fuel in engines used on mobile or stationary applications.

The pollution from internal combustion engines is due to the chemistry of the reactions taking place between fuel vapour and air mixtures during high temperature combustion and to the effects that engine design and engine operating conditions have on these reactions. Although this article is primarily concerned with diesel engines it is important to remember that there is no fundamental difference from the analogous pollution prob-

A Honeycat Diesel Exhaust Purijier unit forming part of the exhaust train of a Ford- Stamford 40 kVA diesel alternator set assembled by John S. Allen & Son Limited. This stationary generator is powered by a Ford model 2712E four cylinder diesel engine, which is coupled to a Stamford brushless alternator giving a 415 volt three-phase 50 €Iz output. The set will be used within a building

lem for petrol fuelled engines. Therefore the principles governing application of catalysts to the control of engine emissions and some of the legislation are common to both spark and compression ignition engines.

Engine Exhaust Emissions Exhaust gases contain the oxidation pro-

ducts from combustion of the hydrocarbon fuel and, if chemical equilibrium was reached, these products would consist almost entirely of carbon dioxide and water vapour. This would OCCLU at high temperatures provided the fuel vapour plus (at least) the stoichiometric quantity of air was homogeneously mixed and the residence time was sufficiently long. In practice the combustion processes in an engine are extremely complex as fuel: air ratios and temperature can vary considerably according to the position in the combustion zone. Therefore the composition and the

concentration of individual components in the combustion products will vary considerably according to engine type and engine operating conditions. Typical exhaust from a petrol engine may contain up to 10 per cent carbon monoxide-due to the combustion process taking place at, or near to, stoichiometric air/fuel ratios-together with about 1000 p.p.m. hydrocarbons from unburnt fuel or partially oxidised products. In contrast a diesel engine operates with a large excess of air, which is sometimes increased by turbo- charging, so combustion is more complete. Concentrations of 0.1 per cent carbon monoxide and 300 p.p.m. hydrocarbons are typical. Some sulphur dioxide may be present due to combustion of organic sulphur compounds in the fuel, particularly for diesel oils.

Diesel exhaust may contain up to 0.5 g/m3 particulate matter, which becomes very obvious as a dark smoke. This is due to

Platinum Metals Rev., 1975, 19, (l), 3

incomplete combustion, and smoke formation is favoured by high pressures, high temperatures and low oxygen availability. Black smoke due to presence of carbonaceous material must be distinguished from the white smoke caused by unburnt fuel droplets and from the blue smoke due to combustion of lubricating oil. Smoke formation does not normally occur to any significant amount in a properly maintained petrol engine.

The temperature of combustion in both compression and spark ignition engines is high enough to cause formation of nitrogen oxides (NO,) from the nitrogen and oxygen present in the air used for combustion, and up to 4000 p.p.m. NO, may be present in exhaust gases. In a direct injection engine the formation of NO and smoke is highly dependent on the conditions in the vicinity of the fuel injection nozzle and on the degree of &/fuel mixing in the swirling action caused by the geometry of the combustion chamber. Con- ditions which favour minimum smoke formation tend to promote NO formation and, therefore, design of the combustion zone and fuellair inlet arrangements has to be a com- promise. Until recently emphasis has been placed on minimising smoke formation.

The distinctive obnoxious odour of diesel exhaust gases is a well know-i nr?;sance. I t should not be considered as a separate emission because it is entirely due to the presence of oxygenated compounds produced by partial oxidation of certain fuel fractions and is, therefore, included with hydrocarbon emissions. Thus any method that reduces these emissions or promotes complete oxidation to carbon dioxide and water will help eliminate odour.

Legislation The United States, Canada, Japan, South

Africa, and many European countries, including the United Kingdom, have introduced legislation designed to limit the emission of smoke from diesel engines used on road vehicles. Precise limits, test procedures, and methods of enforcement vary considerably. Experience in the United Kingdom has shown that although it is possible to ensure that new engines, as delivered from the manufacturer, meet the regulations there are very obvious failures under actual use conditions, particularly when heavy transport vehicles are working under maximum load. Until relatively recently no country has

American Legislation for Exhaust Emissions

Regulation

f

California, heavy duty vehicles

California, light duty vehicles

California, light duty trucks

U.S. Federal, heavy duty vehicles

U.S. Federal, l ight duty vehicles

U.S. Federal, light duty trucks

DateX

1973-74 1975-76 1977

1975

1975

1974

1975 1976

1976-77

Test Method

CARB CARB CARB

cvs cvs CARB

cvs cvs cvs

Emission Limits

HC I CO

- 40 - 30 - 25

0.9 9.0

2.0 20.0

- 40

0.41 3.4 0.41 3.4

2.0 20

- - - 2.0

2.0 - 3.1 0.4

3.1

HC+ I Units

16 g/bhp/h 10 g/bhp/h

- g/mile

- g/mile

16 g/bhp/h

- g/mile - g/mile

- g/mile

NO*

5 g/bhp/h

* Some of these regulations are no t yet finalised but have been proposed for the dates shown


Table I

The elimination of noxious emissions from equipment used in tunnel construction i s obviously necessary to safeguard the health of those engaged in the work. This dump truck owned hy Southdown Plant Limited has been Jitted with a Honeycat DEP unit before use by Tube Headings Limited in driving a tunnel beneath a main road in north London

attempted to limit other emissions by legislation but pollution in the United States, particularly in CaIifornia, has caused that country to consider the overall pollution problem in considcrable detail and to propose regulations (some of which are now becoming legally operative) for all types of road vehicle. Table I shows the emission limits defined in U.S. Federal and California State regulations for various types of vehicle. For heavy duty vehicles (which usually use diesel engines to supply motive power) the total brake specific emissions for a 13-mode steady state cycle are determined by means of a weighted sum- mation of mass emissions determined for each mode. This cyclc has been defined by the California Air Resources Board and is conveniently referred to as the CARE cycle. U.S. Federal regulations for heavy duty

diesel and petrol powered vehicles over 6000 lb. (approx. 2.7 tonnes) gross vehicle weight use the same test cycle with slight modification of experimental conditions. Federal limits for diesel light duty vehicles are based on a constant volume sampling (CVS) cycle as used for the I972 petrol engine regulations.

It may be possible to meet all these targets for road vehicles by engine modifications (and much development effort has been applied by manufacturers to achieve this) but it is believed that the very low combined figure of 5 g/bhp/h for HC and NO, may be quite difficult to obtain and maintain under actual service conditions. In this and other special cases, such as when engines are used in confined spaces where ventilation may be inade- quate, additional means of control may be necessary. Catalytic oxidation is a proven


system (I) that is being applied to the analogous problem on petrol engined vehicles which are now becoming subject to stringent exhaust regulations in certain countries. Similar systems developed (2) in these laboratories have also already been used in diesel engine applications but lack of effective legislation has not given users sufficient incentive to abate the pollution from this source.

Properties of Oxidation Catalysts Recent work in these laboratories has led

to the development of an improved type of platinum group metal catalyst which can be supported on a refractory monolith and can be applied to the oxidation of diesel exhaust gases. The supported catalyst module is contained inside a sheet metal box similar in external appearance to a standard automobile silencer box. The overall system is known as the Honeycat” Diesel Exhaust Purifier (DEP).

A standard DEP unit taken from routine production was evaluated for control of emissions from a Perkins 4.236 (-4 litre) direct injection engine mounted on a dynamometer test bed. Emissions before and after the catalyst were measured by standard pro- *Johnson Matthey Chemicals registered trade name


cedures (3). The essential properties of the catalyst are illustrated in Fig. I which shows the effect of variations in engine speed (and therefore volume of exhaust gases) and exhaust temperature on the conversion of hydrocarbons and carbon monoxide. Obviously the key factor which determines whether the catalyst will be effective is whether the temperature of the exhaust gases is above the ignition temperature (usually defined as tS0 per cent) of the catalyst. Values as low as 150°C for carbon monoxide to about 225°C for hydrocarbons are typical of this catalyst. Therefore it is necessary to examine how exhaust temperature varies with operating mode on typical engines.

Diesel Exhaust Gas Temperatures Exhaust temperatures vary considerably

with engine loadjspeed combinations and with engine type. Values shown in Figs. 2 (a) and 2 (6) for direct and indirect injection engines illustrate the general trend. Increasing the load at a constant speed increases the temperature up to a maximum of 500-600°C. The isotherms also represent lines of equal conversion which may be predicted from the conversion data of the type shown in Fig. I

for particular catalysts.

Effect of the Catalyst on Engine Operation

The effect of fitting a DEP unit into the exhaust system on fuel consumption, engine power, and smoke production is negligible, as shown in Fig. 3. The effect on exhaust back pressure will obviously alter with the cross-sectional area and volume of the catalyst chosen to meet particular emission control targets but the system used for these experiments doubled the back pressure.

Control of Carbon Monoxide and Hydrocarbons

The volume and composition of exhaust fume varies with engine operating condition. Hydrocarbon emissions show concentrations between 500 and 750 p.p.m. over the major part of the working range of the engine in the ex-works con-


Effect of the Cataiyst on Engine Operalion

T h e effect of fitting a DEP unir into rhe exhaust system on fuel ciinsumptim, engine power, and 5rnrikt. pruduction is negligible, as shown in Fig. 3. The effect on exhaust back pressure will obviously alter Lvith the cross-sectional area and volume of thc catalyst chosen LO meet particular emission conrrol targets but tht. system used for these experiments doubled the back pressure.

Control of Carbon Monoxide and Hydrocarbons

Thc volume and compositiun of cxhaust fume varies with engine opcrating condition. Hydrocarbon crnissions show conccntrations between 500 and 750 p.p.m. Over the major part of the working range of tlic cnginc in the ex-works con-

TTable II Catalytic Oxidation of Hydrocarbons and Carbon Monoxide during CARB Cycle

Emissions, gjh Per cent

Full Power

Hydrocarbons Carbon Monoxide Engine Mode

iefore Catalysi 2fterCataiyst ,efore Catalyst 4fter Catalyst

Idle* 0

2 25 50 75

100

I00 75 50 25 2

24

70 59 51 46 44

62 93 97

115 151

18

56 24 11

5 2

6 14 21 31 48

22

57 68 67 78 403

489 31 8 252 291 21 2

21

11 9 6

12 57

14 17 17 23 17

intermediate Speed (1680 r.p.m.)

Rated Speed (2800 r.p.m.)

0.7 Brake specific emissions, g/bhp/h 2.52 I 0.78 I 6.8

* Average over the three idle periods for 13-mode cycle. Data obtained on 4.236 D.I. engine fitted wi th standard Honeycat Diesel Exhaust Purifier

dition, and less than 250 p.p.m. after cat- proportional to speed. There is only a limited alytic treatment during the load/speed range area at virtually zero load where the catalyst where the catalyst is operating above igni- is not able to operate due to insufficient tem- tion temperature. The absolutc amount of perature. Similar data is available for carbon emissions obviously increases with increase in monoxide and shows that, as expected, con- engine speed and will be approximately version efficiencies for this easily oxidised

Table Ill Emissions before and after Catalytic Oxidation for Direct and Indirect

Injection Engines

I Brake Specific Emissions, CARB Cycle, g/bhp/h Engine Catalyst

Geometry H C I C O injection Type

NO*

Before I After

10.5 10.3 10.3 10.5

4.4 4.6 4.3 4.6

3.4 3.4

Timing I Before I After IBefore I After

Direct

D i rec t

Indirect

2.5 2.2

5.3 4.9

2.4

0.8 0.8

2.7 2.3

1 .o

6.8 6.8

14.0 10.6

11.0

0.7 0.9

1.7 1.4

2.0

Type B elliptical cross-section


Type B elliptical cross-section Type L circular cross-section; catalyst volume approximately 14 per cent smaller than Type B

HC+NO,

Standard

12" retard

Standard

Standard

12" retard

Standard

Standard

12" retard

Standard

Before After

molecule are higher than for hydrocarbons at corresponding temperature. Overall performance for hydrocarbon and carbon monoxide oxidation is demonstrated by emission measurements on exhaust gas samples taken before and after the catalyst installation during operation of the engine through the CARB 13-mode cycle referred to previously. Table I1 shows values for the 4.236 engine using a standard Honeycat catalyst. Table I11 summarises the CARB cycle specific emission data for DI and ID1 engines using two catalysts of identical composition but with slightly different volumes chosen as convenient to fit commonly used round and elliptical cross section silencer boxes.

Control of Nitrogen Oxides Table I11 shows that the catalyst has no

significant effect on NO, emissions. Any small apparent increase across the catalyst is not a real effect but is due solely to experimental error in sampling and analysis. It also shows that the NO, value is a major contributor to the combined HC +NO, limit value specified in certain American legislation. (Although NO is used as a convenient method for expressing total NO, emission, it should be noted that NO is the major component.) However, it is known that retarding injection timing will reduce NO, formation. Un- fortunately, as mentioned earlier, and shown in Fig 5, the conditions which help to prevent NO, synthesis will lead to decreased combustion efficiency and, therefore, to an increase in the amounts of oxidisable components in the exhaust.

This technique of altering timing therefore suggests a method of NO, emission control provided that catalytic systems are used to control the increased quantities of hydrocarbons and CO. Although a minimum value for HC 4 NO, occurred at about 8' retard the value of 12' retard, corresponding to minimum NO, formation, was chosen to evaluate the catalyst system because this could only affect HC and CO. Comparison of the CARB cycle data of Table I11 for the diesel engine

in standard and retarded timing shows that the catalyst will cope very efficiently with the increased emissions.

Odour Control Accurate quantitative data on odour control

is difficult to obtain as it is usually necessary to use organoleptic methods of assessment. The use of odour panels is expensive and time consuming but independent measurement of the efficiency of the Johnson Matthey catalyst using specially constructed air sampling cells and a trained panel of observers has demonstrated that the catalyst is an extremely effective method of odour control. Similar work, using successive dilution of exhaust samples taken by hypodermic syringe to determine odour threshold values (4), was done in our own research programme.


EXHAU V0LUI.I

300

1 oc

0 0 .? m a a I L ~

n n n w w w

G A S ftyrnin

100 2 0 0 3 0 0 400 500 IN3

STANDARD CATALYST BOX SIZE EN G I N € DISPLACE M E N 1

Fig. 6 Chart used to estimate the size of catalytic exhaust purijier required for a particular application. Most engines operate within the range shaded on the right-hand side. Reading across, the y axis gives the exhaust gas volume and the lejbhand shaded portion gives the size of catalyst system from the x axis

Measurements of odour threshold were made during runs arranged as a 2 x2 factorial experimental design (s), with centre point, in order to determine the amount of odour control possible for various load/speed engine conditions. These confirmed that the catalyst made a significant contribution to odour control at all times when exhaust gas temperature was above about zooPC. Even at engine idle, when temperatures were too low for catalytic ignition, some observers reported an improvement in odour. Further work on this topic is planned in which organoleptic and instrumental methods of odour measurement will be used simultaneously.

Application to Diesel Engined Plant or Vehicles

Thus we have shown that by combining the measured properties of catalysts with the relevant engine emission data (exhaust gas

volume, composition, and temperature) it is possible to predict the emission control capabilities of commercially available units for specific applications. Honeycat Diesel Exhaust Purifiers are available in standard sizes (DEP 60, DEP 90, DEP 145) in which catalyst volumes are progressively increased. Choice of purifier will depend on both geo- metrical constraints for the particular engine installation and on the emission standards required. In general, it is convenient to use charts of the type shown in Fig. 6 to estimate the size of purifier required for the application under consideration. Most engines operate in the speed range shown on the shaded right- hand portion of the diagram and estimates of exhaust gas volume can be read directly on the y-axis for a given engine displacement size. By reference to the appropriate space velocity line, chosen on the basis of known performance and required emission target,


it is possible to choose the appropriate DEP. This is then installed on the automobile, fork lift truck or other equipment as near to the engine exhaust manifold as practicable.

Acknowledgement The majority of results reported in this article

were obtained during a Johnson Matthey research programme undertaken at Ricardo and Co. Engineers (1927) Ltd. Supplementary confirma- tory data has been obtained during confidential projects in cooperation with various Johnson Matthey Chemicals Ltd. customers and with other research laboratories. The author wishes to thank the staff of Ricardo Ltd. for helpful dis- cussions during the course of this work.

References I G. J. K. Acres and B. J. Cooper, Platinum

2 G. J. K. Acres, Platinum Metals Rev., I970,14,

3 California Exhaust Emission Standards, Test and Approval Procedures for Diesel Engines in 1973 and Subsequent Model Year, Vehicles over 6,001 Ib. gross Weight, Proposed Nov. 18th, 1970, State of California Air Resources Board

4 D. P. Potter, J. Wignall, and M. L. Windsor, J. Environmental Planning Pollution Control, 1972, 2, (2),47-52

5 See any standard textbook on statistical design of experiments, e.g. “Experimental Designs”, W. G. Cochran and G. M. Cox, 2nd edn., publ. John Wiley Ltd.

Metals Rev., 1972, 16, (3), 74-86

(31, 78-85

Organometallic Chemistry of Platinum ORGANOMETALLIC AND COORDINATION CHEMISTRY OF PLATINUM BY UMERTO BELLUCO, Academic Press, London and New York, 1974,701 pp. k17.50

This volume is a recent addition to the series of monographs on Organometallic Chemistry which includes P. M. Maitlis’ “The Organic Chemistry of Palladium”. It is the first hook to be devoted entirely to the chemistry of platinum complexes and supplements F. R. Hartley’s “The Chemistry of Platinum and Palladium”.

Dr Belluco and his colleagues do not claim to have comprehensively covered the literature, especially in the section on coordination complexes. They have, however, provided the most up-to-date compilation of informa- tion necessary for a full appreciation of reactivity and bonding in the organometallic chemistry of platinum. A total of 1400 references, up to August 1973, are quoted in the text, in addition to a list of reviews on the subjects covered by each chapter.

The book opens with a chapter on coordination compounds which is sub-divided into the chemistry of platinum in its various oxidation states. Each section contains details of the physical and spectral properties of the relevant complexes. Specific descrip- tions of preparative methods have been omitted for the sake of brevity and the discussion is limited to general procedures and selected compounds. There is an additional section on oxidative addition to platinum(I1) complexes.

There follows a discussion on the mechanism of substitution reactions with particular reference to the effect on reactivity of entering and leaving groups, cis and trans ligands, and the nature of the solvent.

Platinum Metals Rev., 1975, 19, (l), 11-1 1 11

There is also a very brief comparison with the reactivities found in other dB square planar systems.

The organometallic chemistry of the element is treated according to the nature of the ligands, with chapters on hydride complexes, metal-Group IV 0-bonded complexes, and compounds formed with unsaturated hydrocarbons. Each chapter is sub-divided as for the coordination compounds of a given oxidation state, but with particular emphasis on the preparative chemistry. In the five chapters on the complexes of platinum, extensive use has been made of tabulated nuclear magnetic resonance, infrared and Raman spectral data, and there are numerous illustrations of the molecular structures of significant complexes.

The final chapter is on homogeneous catalysis, where the emphasis is on the hydrogenation and isomerisation of olefins by platinum(I1) complexes. However, the inclusion of short sections on homogeneous catalysis by other ds metal complexes appears rather incongruous when details of the in- dustrially viable homogeneous hydrosilation catalyst, trans-Pt(Et,S),Cl,, have been omitted.

There is an adequate subject index, but the reviewer regrets the absence of author and formula indices which are found most useful in W. P. Griffith’s “The Chemistry of the Rarer Platinum Metals”.

Overall, the book is a welcome addition to the literature and will be valued by students and practical chemists alike. P. C. H.

The Production of Acetic Acid RHODIUM CATALYSED CARBONYLATION OF METHANOL

By James F. Roth Monsanto Co., St. Louis, Missouri

The new Monsanto Company acetic acid process employs a rhodium- based homogeneous liquid-phase catalyst which promotes methanol carbonylation in high selectivity and at low pressures. This article describes some of the chemistry involved in this process, with particular emphasis on the role played by rhodium complexes in the catalytic cycle.

The new acetic acid plant built by the Monsanto Company at Texas City is designed to operate at lower pressures than previous plants. The output of 300 million pounds per year of acetic acid derived from methanol is the result of the successful development of a homogeneous catalyst based on rhodium. This new catalyst was reported recently ( I , 2) for the low pressure liquid-phase synthesis of acetic acid from methanol and carbon monoxide.

Previously, workers at B.A.S.F. described a commercial acetic acid process, based on methanol carbonylation and an iodine- promoted cobalt catalyst, that employs carbon monoxide pressures of about 7500 lb/in2 and gives a molar selectivity to acetic acid of about go per cent (3). The new rhodium catalyst can be used at much lower pressures and affords reaction rates essentially independent of carbon monoxide partial pressure in the range between 200 and 1800 lb/in2. I t effects methanol carbonylation in 99 per cent selectivity and displays similar selectivity even when the carbon monoxide feed contains as much as 50 per cent hydrogen.

Catalyst Composition The carbonylation catalyst is comprised of

two components, a soluble rhodium complex and an iodide promoter. The catalytic species is believed to consist of a coordination complex of rhodium with carbon monoxide and

Platinum Metals Rev., 1975, 19, (l), 12-14

halogen ligands. A wide variety of rhodium compounds and iodine compounds have been found to give similar reaction rates and product distribution. This suggests that these tend to form the same active catalytic species. Solvent effects, e.g. faster rates in more polar solvents, indicate that the active species may be ionic.

Kinetics of Methanol Carbonylation The overall stoichiometry of the acetic

acid synthesis is represented simply by

CH,OH 1 CO-rCH,COOH

The results of kinetics studies of the rhodium-catalysed homogeneous reaction have been reported (2) and have several interesting and unusual features. The reaction was found to be zero order with respect to both reactants-methanol and carbon monoxide. An obvious consequence of the zero order dependence on carbon monoxide pressure is the ability to obtain high reaction rates at low reaction pressures. With respect to catalyst components, it was found that reaction rate was directly proportional to both the rhodium and iodide concentrations. Another key observation made relates to the fate of the methyl iodide (formed via reaction of CH,OH+HI) concentration during the reaction. This was determined by analysis of timed liquid samples removed during the course of the reaction. I t was observed that

12

The Monsantu Co. acetic acid plant at Texas City uses a new proress bused on a rhodium homogeneons liquid- phase catalyst which g ims higher selectivity ,for the carbonylation of methanol ut lower pressures than earlier processes

methyl iodide reached a steady-state concentration very rapidly, that this concentration remained constant over most of the reaction, and that the rate of formation of acetic acid was constant during the same period.

Mechanism of the Reaction

All of the kinetics results can be rationalised by as- suming that the reaction proceeds in a stepwise manner, as follows :

The initial step in the catalytic cycle consists of a rapid conversion of methanol to methyl iodide, for example, via :

CH,OH+HI%CH,I +H,O

the rhodium-alkyl acyl-rhodium(II1)

(1)

bond occurs to yield an complex. This is ac-

companied by subsequent or simultaneous replacement of co in the rhodium coordination sphere.

Then, an oxidative addition of methyl iodide to a Rh(1) complex (d8 square planar) occurs [Equation (z)]. This results in formation of a six-coordinate alkyl-rhodium( I1 I) (d6) complex.

slow CH,I + [Rh complex]

Rapid insertion of carbon monoxide, Finally, the d6 acyl-rhodium(II1) complex reacts to produce acetic acid and to regenerate present as a ligand in the Rh complex, into


the original d8 rhodium(1) complex. Several different reaction modes can be proposed to describe this step. These include a direct hydrolysis of the acyl-rhodium(II1) complex by water, a specific methanol-assisted sol- volysis of this complex, or reductive elimination of acetyl iodide from the complex followed by immediate hydrolysis of the acetyl iodide to yield acetic acid, the: starting rhodium(1) complex and HI. Of these possibilities, we favour the latter, as shown:

1 CH, 0

I 1 +[Rh complex] + CH,C-I (4)

I I

I Rh complex i Hzo

CH,COOH +HI . i _I This overall reaction scheme is cclnsistent

with the observed reaction order depen- dencies and with the observed conslancy of CHJ concentration during most of the reaction, if one assumes that reaction (2) is the rate-determining step. Accoxding to this scheme, the role played by rhodium complexes is threefold, consisting of the rate- determining oxidative addition step, which

results in introduction of the methyl group into the coordination sphere and two subsequent rapid steps involving first an exceptionally facile carbon monoxide insertion reaction and then a facile reductive elimination step. This sequence leads to the estab- lishment of a catalytic cycle. This multiple step process all occurs with a degree of selectivity that is remarkable even for a homogeneous catalytic reaction.

It has been shown (4) that a heterogeneous analogue of the homogeneous catalyst can be prepared and that the kinetics of methanol carbonylation are identical for the solid supported rhodium complex and the homogeneous liquid-phase catalyst systems. This suggests that, in spite of the obvious physical differences between these catalysts, a similar reaction mechanism is probzbly operative.

References I F. E. Paulik and J. F. Roth, J. Cherrr. SOC.,

Chem. Commwz., 1968, 1578 2 J- F. Roth, J. H. Craddock, A. Hershman and

F. E. Paulik, Chem. Techno!., 1971, 600-605 3 H. Hohenschultz, N. von Kutepow and W.

Himmele, Hydrocarbon Proces., 1966, 45, 141 4 K. K. Robinson, A. Hershman, J. H. Craddock

and J. F. Roth, J. Caralysis, 1972,27, (3 ) , 389

Superconductivity in Palladium-Hydrogen Alloys Superconducting properties have not gen-

erally been associated with the platinum group metals. However, in I972 T. Skoskiewicz of the Polish Academy of Sciences reported that palladium enriched with hydrogen possesses superconductivity, with a transition temperature T, of -5 K when H:Pd=o.g.

Recent research in this field has been briefly summarised by R. Taylor (New Scientist, 1974, 64, (923, Nov. 14), 473), who comments on work by B. Stritzker et al. of the Nuclear Research Centre at Julich aimed at raising T, ( Z . Physik, 1974, 268, (z), 261-264) and by C. A. Mackliet et al. at the Naval Research Laboratory at Washington, D.C., on the specific heat of superconducting Pd-H alloys (Solid State Commun., 1974, 15, (t), 207-210).

The Julich team, which had first raised T, to 9.4 K by H+ ion bombardment to increase

the H:Pd ratio on the surface of palladium foils to more than I, had also shown that the substitution of deuterium for hydrogen can raise T, to 11 I<. It is suggested that these additions may be modifying the lattice vibrations, or phonons, in the solids, thereby changing their coupling to the electrons, since it is the electron-phonon interaction which is believed to lead to superconductivity. Stritzker has now shown that alloying of suitable amounts of copper, silver or gold to Pd-H can raise T, still more (to 16.6 K for 45 per cent Cu-Pd when H:Pd-0.7; the optimum silver and gold concentrations are smaller).

Mackliet and his co-workers have dis- covered that, whereas the peaks in the specific heat of superconductors usually drop sharply above T, to the normal state, i.e. the superconducting state is more ordered, in Pd-H the drop is less marked. F. J. S.


Heavv Platinum Plating from a J

Molten Salt Bath The electroplating of platinum from con-

ventional aqueous electrolytes is readily achieved on to a number of basis metals but, as with other coatings, is extremely difficult on to refractory metals owing to the presence of oxide layers. Some success has been achieved with metals such as titanium but the maximum thickness of deposit has usually been of the order of 2.5 microns and a com- plicated sequence of pre-treatment operations has been necessary.

A molten salt electrolytic process has now been developed in the Metals Research Department of Degussa at Wolfgang near Frankfurt for the deposition of highly ad- herent and ductile coatings of platinum on to a range of refractory metals such as titanium, tantalum, niobium, molybdenum, and tungsten, and even on to graphite.

The process uses a bath of molten cyanides, operating at a temperature of around 55o"C, and thick-

Examples of the applications of platinum deposition from the Degussu molten salt electrolytic process, including ex- panded metal anodes, tubes, rods, andJinished components. The rod in the lower right hand corner of the illustration was bent over a radius of 20 mm after deposition without failure

nesses of roo or 150 microns can be achieved. High tensile and shear strength values have been determined on these deposits, ranging from four to eight times the values obtained with normal electrodeposits, together with high ductility, with fracture occurring under test in the basis metal rather than at the interface.

The process offers the possibility of obtain- ing the desirable electrochemical properties of platinum on refractory metals in such applications as anodes for cathodic protection, for chlorine production, for the purification of toxic waste water, and for insoluble anodes in electroplating baths.


The Production of Heavy HYDROGEN-WATER DEUTERIUM EXCHANGE PLATINUM METALS ON CARBON SUPPORTS

By N. H. Sagert and R. M. L. Pouteau Atomic Energy of Canada Limited, Pinawa, Manitoba

Water OVER

Catalysts using suitably supported platinum show promise for the commercial production of heavy water. Carbons are potential primary supports for the platinum and metal-support interactions have been observed in this system. These interactions lower the chemical activation energy and increase the rate of reaction under conditions where it seems likely that the support donates electrons to the metal.

The Canadian nuclear power system, the so-called CANDU system, is based on the use of natural uranium oxide fuel. To use this fuel, a very efficient moderator is required, and the only practical moderator is heavy water, D,O. The present generation of heavy water-moderated, pressurised, heavy water-cooled reactors use about I Mg of D,O per MW (electrical). Thus, at current prices, the heavy water in a 400 MW(e) unit costs L1.3 x IO', so there is considerable incentive to produce it more cheaply.

The current commercial process for making heavy water uses a dual temperature exchange between the deuterium in water and hydrogen sulphide, H,S. The process i s highly developed but suffers from a number of short- comings including the inability to extract more than 20 per cent of the deuterium from water of natural deuterium abundance, and the necessity of dealing with Mg quantities of H,S at pressures of 2 MPa. An alternative process is the dual temperature exchange between hydrogen and water. However, this exchange reaction requires an efficient catalyst. Supported platinum and chromia- promoted nickel are good catalysts in the vapour phase but lose their activity rapidly in the liquid phase. Fortunately, Stevens (2, 3) recently demonstrated that supported

platinum catalysts would retain their activity in the presence of liquid water if they were protected from wetting by a permeable hydrophobic film. The exchange reaction then takes place in the vapour state in the interior of the catalyst, which is surrounded by liquid water. This process is much more likely to be economic.

Various charcoals have often been used as primary supports for the platinum, and vapour phase rates over carbon-supported catalysts have often been higher than over alumina- or silica-supported platinum (I).

However, it is only recently that methods have been developed for measuring metal surface areas in the presence of a support (4). Therefore it is not clear from the earlier work whether there is a true metal support interaction with the carbon supports or whether the platinum is merely better dispersed on these supports. It seemed desirable to learn whether the specific rates (rates per unit metal surface area) were, in fact, higher with the carbon supports. Also, since the electronic properties of carbon are easily altered by heat treating (5 ) , it might be possible to find optimum electronic properties for the support and at the same time to learn something about the mechanism of the exchange reaction.


Fig. 1 Research workers at Atomic Energy of Canada Limited have found that the mass spectrometer is an indispensable tool for the study of isotopic exchange reactions. This instrument monitors the deuterium content of hydrogen from the catalytic reactor

Support Effects Rates for the H,-HDO exchange were

measured in the vapour phase using platinum black and platinum on carbon catalysts (6). The carbon was graphitised at various heat treatment temperatures before the platinum was deposited on it. The results are shown in Fig. 2, where the specific rate, r,, is thenumber of moles of HD that would be initially produced if static experiments could be done using pure HDO and H,. In actual fact, rates were measured in a flow system using H, with its natural abundance of deuterium and water containing about 4 per cent deuterium (8 per cent HDO). Rates are given in terms of the platinum surface area. Obviously, graphitising the support lowers the apparent activation energy (makes it more negative) and increases the rate at lower temperatures. Since the rates are calculated from plots of the logarithm of the conversion against reciprocal flow, we do

not think that external diffusion is important. Since varying the particle size did not change the rates, neither do we think that pore diffusion is causing these effects.

Over a relatively small range of pressures, the rate of a catalytic reaction may often be adequately represented by a power law

Under these conditions, and with surface exchange rate controlling (7), the true activation energy for the surface exchange (8) is given by:

E, iEapp + a AH,O t b AH, (2)

where Eapp is the apparent activation energy, and the A’s are the heats of desorption of water and hydrogen. Since a and b can be obtained experimentally and values of A are available, then E, can be calculated, and E, values are shown in the Table overleaf. Clearly, graphitisation of the support leads to


a considerable lowering of E,. Since the work function of well graphitised carbon is less

I 1 Activation Energies for Hydrogemwater

Deuterium Exchange over Platinum Catalysts

than that of platinum, it was suggested that electron transfer to the platinum might be responsible for this effect.

Noble Metals on Graphon In the above section, we suggest that

electron transfer from the graphitised carbon might be responsible for the lowering of E, as the graphitising temperature of the support is changed. Since all the Group VIII noble metals catalyse the hydrogen-water exchange, we measured specific rates, orders and apparent activation energies over all six platinum group metals, supported on Graphon (8). For comparison, data were obtained over unsupported metal powders (10). The work


A1 &'a

SiOI

None

Thermax

Graphon

Thermax (2100)

Support Reference

functions of these metals cover the range 4.5 to 5.7 eV whereas the work function for Graphon is probably somewhere above that for well crystallised graphite (4.4 eV). Therefore we would expect electron transfer effects to be minimal with metals of lower work function and to become more pro- nounced as the work function of the metal increases.

Over the unsupported powders, the true activation energies (E,) were within the range 61 f 6 kJ/mol for all six metals. How- ever, when the same metals were supported on Graphon, the E, values varied from 103 kJ/mol for Ru to 36 kJ/mol for platinum.

Figure 3 shows the ratio of E, over supported catalysts to E, over unsupported powders, plotted as a function of the themionic work functions selected by Bouwman and Sachtler (I I). A good correlation was obtained and the slope suggests that for each kJ/mol that the work function is raised, E, is lowered by 0.67 kJ/mol. The quantitative aspect of the correlation may be somewhat suspect, as the reported values of work functions vary considerably. However, we did use a consistent set measured recently.

The observed orders of reaction were best explained by a mechanism involving exchange between chemisorbed hydrogen atoms


and physically adsorbed water (6, 7). Since hydrogcn chemisorption is not hindered by the presence of water vapour (IZ), it is thought that hydrogen and water are adsorbed on separate types of sites and do not interfere with each other. This leads to a rate expression of the form

r =k, OH,O @H (3)

If a Freundlich isotherm is assumed, k, can be identified with the k, of equation (I). Thus, writing k, in its Arrhenius form,

(4)

where C, and CH2, are the surface concentrations in molim? which can be calculated from the reaction orders. Relative frequency factors for supported and unsupported catalysts are shown in Fig. 3b. There seems to be some compensation between the frequency factor and the activation energy, but fortunately this compensation is not complete and the actual specific rates at 433K are always increased by supporting the metal on Graphon.

If our proposed mechanism holds, the observed lowering of E, is associated with a lowering of the activation energy for the exchange step where a deuterium atom is exchanged between physically adsorbed water and a chemistorbed hydrogen atom. Since the water is weakly bonded, it is most reason- able to assume that the major way in which the activation energy can be lowered is by a change in the Pt-H bonding.

With platinum on Graphon, electron donation from the Graphon to the metal occurs because of the difference in work function. Because both phases are conductors, complete equilibrium should be achieved. Now at room temperature and above, the polarisation of the platinum- hydrogen bond is Pts'--HS- (13). Thus, charging the platinum negatively will weaken the platinum-hydrogen bonds. Indeed, in hydride-platinum complexes, it has been shown that adding ligands which withdraw electrons from the platinum strengthens


the platinum-hydrogen bond (14). Adding electrons to the platinum should therefore weaken this bond. Weakening the platinum- hydrogen bond should lead to a lower activation energy. In the case of metals with lower work functions, the bonding seems to be changed in the opposite direction, leading to higher E, values. Figure 3 suggests that the effective work function of Graphon is about 5.2 eV.

We think that the donation of electrons to the metal affects the platinum-hydrogen bond but other explanations are possible. Levy and Boudart (IS) suggested recently that the following equilibrium may exist on the platinum surface in the presence of hydrogen and water

PtH 7 H,O+iPt- + H,O+ (5)

This reaction provides a mechanism for exchange between chemisorbed hydrogen and physically adsorbed water. The work function of the metal would be involved directly in the thermochemistry of this exchange.

The frequency factor for supported platinum divided by the frequency factor for platinum black is less than unity. This suggests that there are relatively fewer active sites produced by electron transfer to the metal than were present in its absence. Similarly, the ratios of frequency factors for the other metals are greater than unity, suggesting that more of the metal surface participates in the reaction.

In summary, we have noted a metal support interaction in the hydrogen-water deuterium exchange. The evidence suggests that the activation energy for surface exchange is lowered when the work functions of the metal and the support are such as to allow electrons to be donated to the metal. This evidence may be sumrnarised as follows :

(i) Graphitising the carbon support lowers the chemical activation energy for hydrogen-water exchange.

(ii) When different noble metals are used on graphitised carbon supports, a

correlation is obtained between the chemical activation energies and the work functions of the metals. Metals with lower work functions have the highest chemical activation energies.

(iii) When these noble metals are not supported, the chemical activation energies are constant, which means that the correlation observed in (ii) is not a property of the metals them- selves.

This type of chemical, or electronic, promotion may well be of more importance than is generally realised. I t has already been noted in the alkali metal promotion of supported ruthenium catalysts for the synthesis of ammonia (16).

References I “Production of Heavy Water”, ed. 6. M.

Murphy, hlcGraw-Hill, New York, 1955, 145-260

2 W. H. Stevens, Canadian Patent 907,292,

3 Can. Chem. Process., 1972, 56, ( I Z ) , 22 4 M. Boudart, Adw. Catal. Rel. Subj., 1969,

5 S . Mrozowski, Carbon, 1971, 9,97 6 N. H. Sagert and R. M. L. Pouteau, Can. J.

7 J. H. Rolston and J. W. Goodale, Can. J .

8 N. H. Sagert and R. M. L. Pouteau, Can. J .

g N. H. Sagert and R. M. L. Pouteau, Can. J .

10 N. H. Sagert and R. M. L. Pouteau, Can. J.

r r R. Bouwman and W. M. H. Sachtler, Surface Sci., 1971, 24, r4o

12 E. S. J. Tomezsko and G. T. Furukawa,J. Cuta2ysis, 1967, 8, 386

13 J. C. P. Mignolet, J . Chim. Phy., 1957, 54, I9

14 A. P. Ginsberg, “Transition Metal Chem- istry”, Vol. I, ed. R. L. Carlin, Marcel Dekker, New York, 1965, 21.5

15 R. B. Levy and M. Boudan, J . Catalysis, 1974, 32, 304

16 K. I. Aika, H. Hori and A. Ozaki,J. Catalysis, 1972~27, 424

I972

20, I53

Chenz., 1972, 50, 3686

Chem., 1972, 50, 1900

Chem., 197% 51, 4031

Chem., 1971, 49, 3411

Chem., 1974,52,2960

Photocatalytic Properties of Materials THE PHOTOREDUCTION OF PALLADIUM IONS ON TITANIUM DIOXIDE

The predominant position occupied by the metal silver in photographic processes often obscures the fact that other metals and materials possess photographic properties. Both scientific and economic reasons have prompted recent studies of these alternatives with varying degrees of success.

I t has been known since 1920 that titanium dioxide TiO, exhibits photocatalytic properties, since it is darkened by ultra-violet radiation. Both electrons and holes produced by light excitation may be involved. More recently, the photoreduction of palladium ions Pd+ at TiO, has been studied as an initial step towards a photographic process with TiO,. Photoreduction of a few metal ions forms the initial image in a photographic process and this image has subsequently to be developed during a second stage to make it visible and to retain it. Any photocatalytic reduction of Pd+ ions on TiO, is, of course, accompanied by a corresponding oxidation process at the TiO,.

Simultaneous studies of the photocatalytic reduction of Pdf and of the electrochemical

properties of TiO, have now been reported by F. Mollers, H. J. Tolle and R. Memming of Philips Forschungslaboratorium Hamburg G.m.b.H. (J . Electrochem. Soc., 1974, 121, (9), I 160-1 167). They carried out electrochemical and photocurrent measurements on vapour-deposited TiO, films on conducting substrates (SnO, on glass, or titanium sheet).

It was shown that the primary step in this process is the generation of an anodic photocurrent, i.e. evolution of oxygen, which catalyses the cathodic deposition (reduction) of palladium under open-circuit conditions.

The nature of the photocatalytic deposition of palladium on TiO, was interpreted on the basis of the photovoltaic effect of the semiconducting TiO,. Further studies included an examination of the various parameters affecting the phenomenon, e.g. space charge effects, film thickness and doping. The results are clearly illustrated by a series of graphs depicting the various electrochemical data and the whole is presented as a useful and stimulating paper.

F. J. S.


Trifluorophosphine Complexes of the Platinum Metals A REVIEW OF RECENT DEVELOPMENTS

By John F. Nixon and J. Richard Swain School of Molecular Sciences, University of Sussex, Brighton

The chemistry of the trijluorophosphine complexes of the transition metals, and of the platinum metals in particular, is of increasing importance. This article describes some of the more recent developments in trifluorophosphine complexes of the platinum metals, including their syntheses, structures, reactions, and potential as homogeneous catalysts.

The rapid development of transition metal carbonyl chemistry originated with the dis- covery of Ni(CO), in 1890. About the same time the first trifluorophosphine coordination complex [PtF,(PF,)], was synthesised by Moissan, but its true identity was not recognised at the time. It was only following the synthesis of the complexes cis-PtC1, (PF,), and [PtCI,(PF,)], by Chatt and Williams in 1950 that attention was drawn to the similarity of trifluorophosphine and carbon monoxide as ligands towards transition metals. I t was proposed that the dative sigma bond formed by donation of the lone- pair of electrons on phosphorus to the metal was supplemented by a symmetry allowed x-bond involving back donation of transition metal d-electrons into empty phosphorus #-orbitals. The 0- and x-components were

considered to operate in the same “synergic” fashion as that already suggested for the analogous metal carbonyls. The n-component was expected to be favoured in trifluorophosphine-metal complexes because of the presence of the highly electronegative fluorine atoms attached to phosphorus (I).

A large number of trifluorophosphine- transition metal complexes are now known and their chemistry has been extensively studied (2, 3, 4).

Binary Compounds Pl.atinum metal complexes in which tri-

fluorophosphine is the only ligand present are listed in Table I. It is interesting to note that the corresponding carbonyl complexes M(CO)4, (M =Pd, Pt) and M’B(CO)B, (M’= Rh, Ir) are unstab1,e. As yet there is no

Table I Platinum Metal - Trifluorophosphine Complexes

Rh*(PF3)8 (yellow, m.p. 92.5”C)

RU(PF3)5 (colourless, m.p. 30°C)

I [Rh(PF3),], (x=3 or4) (red crystals)

IrdPF3h yellow, m.p. 113-116°C)

OS(PF3, (colourless crystals)

Pd (PF,), (colourless, rn.p. -4O”C,

dec -20°C)

(colourless, Pt(PF3L m.p. -15OC)

b.p. 86”C/730 dec 130°C)


Pt(PFJ4 (colourless, m.p. -15°C) b.p. 86"C/730 dec 130°C)

extensive chemistry of polynuclear metal trifluorophosphine complexes.

Methods of Preparation The main synthetic route developed by Th.

Kruck and co-workers in Germany involves “reductive fluorophosphination”. In this method the platinum metal halide is heated in an autoclave with copper or zinc in the presence of high pressures (5c-500 atm) of trifluorophosphine (2, 5, 6).

; 400 atm

150-250°C M’CI, 3Cu 5PF,-M‘ (PP,) 3CuCl

(M”- Ru, 0 s )

250 am 2RhC1, I GCu I BPI.,-Rh,(PF,), GCuCI

> 150°C

Interestingly, when IrC1, is heated with PF, and copper only small amounts of the orange red crystalline p,-phosphido-nonaks -(trifluorophosphine) tri-iridium Ir,P(PF,) are formedrather than Ir,(PFJ8 (7). The latter can be obtained in good yield from the reaction between K[Ir(PF,),] and IrCl(I?F,), (8) or by U.V. irradiation of IrH(PF,), (9). It is thermally stable up to 200°C. The rhodium analogue, on the other hand, evolves two moles of PF, per dimer at 170°C to afford a red volatile solid, [Rh(PF,),],, whose identity is not yet fully established (8).

The platinum and palladium complexes M(PF,),, which are readily available by reductive fluorophosphination of the appropriate metal halide (10) can also be obtained in the absence of any reducing metal since PF, can act as its own reducing agent (11, ~z),viz.

100-150 am

100°C PtCI, : jPF,-Pt(PF,), : PF,CI,

Other synthetic routes using milder reaction conditions involve displacement of ligands (e.g. CO, x-allyl) already coordinated to the platinum metal (13, 14), e.g.

PF,

(x -5 4, 3:

Rua(C0),zw RuPFXCO), x

Pd(PF,), can also be obtained by the direct reaction between palladium powder and trifluorophosphine at high temperature and pressure (15).

Structures Vibrational spectroscopic studies suggested

that the M(PF,), complexes, (M=Pd, Pt), have perfectly tetrahedral structures and this has been subsequently confirmed in the case of the platinum complex (16). In contrast to the very short metal-phosphorus bond length found for Ni(PF,), (2.116 A), the platinum-phosphorus distance in Pt(PF,), (2.230 A) is not substantially different from that in other platinum-phosphine complexes. This may reflect the decreased importance of metal-phosphorus =-bonding for the heavier platinum metals.

T h e pentakis(trifluorophosphine)ruthenium and osmium complexes, M”(PF,),, almost certainly have trigonal bipyramid structures. Detailed 19F and 31P nuclear magnetic resonance studies show that these molecules are “fluxional” even at temperatures as low as - 160”C, the barrier to intramolecular ligand exchange between equatorial and axial positions being less than 5 kcal/mole (17) (Fig. 1).

Fig. 1 Possible intramolecular ligand exchange mechanism in M“( PF3)5 complexes


ally1 chloride

The structures of the M’,(PF& complexes (M’=Rh, Ir), are not yet known, but pre- sumably consist of two staggered trigonal bipyramid M’(PF,), units held together by a metal-metal bond. Ir,P(PF,), is thought to have the structure shown below (7).

(colourless, m.p. -40°C, b.p. 89Ti725)

(colourless, m.p. -39°C. b.p. 95“C/730)

Hy drides The hydrides M’H(PF,), (M‘=Rh, Ir)

and M”H,(PF,), (MN=Ru, 0s ) listed in Table I1 are obtained in high yields by heating a mixture of the metal chloride and copper under high pressures of trifluorophosphine and hydrogen (IS, IS).

RhCI,+SCu+ 4PF, iH, ---+RhH(PF,), 3CuCI

The rhodium and iridium hydrides can also be obtained by acidification of the metallates [M’(PF,),]- which are available from alternative low pressure synthetic routes. All the hydrides are very volatile liquids and, except for RhH(PF,),, exhibit considerable thermal stability.

The binuclear complex Rh,(PF,), is readily cleaved by hydrogen gas to yield RhH(PF,), quantitatively, while Ir,(PF,)* forms IrH(PF,), in the presence of moisture (2 ) . When a mixture of HIr(PF,), and HCo(PF,), is subjected to U.V. irradiation, the interesting bridged complex shown below is obtained as a red oil (7).


All the trifluorophosphine metal hydrides exhibit acidic properties, readily forming the metallates [M’(PF,),]-, (M‘ -Rh, Ir), [M”H(PF,),]- and [M”(PF,),]2-, (M”=Ru, Os), with bases or potassium amalgam (IS, IS).

The M’H(PF,), complexes react with triphenylphosphine to produce the salts [Ph,PH]+[M‘(PF,),]- while the substituted products RhH(PF,)(PPh,), and &H(PF,), (PPhJ2 have recently been obtained by reaction of the stoichiometric quantities of PF, and RhH(PPh,), (20). The complexes RhH(PF,)(PPh,), and RhH(PF,),(PPh,), exhibit high activity as homogeneous catalysts. For example, RhH(PE3)(PPh,), catalyses the hydrogenation of terminal olefins (at 25”C, I atm H,) while RhH$’F,),(PPh,), has been found to bring about rapid isomerisation of terminal olefins (20). The ruthenium complexes RuH,(PPh,), (PF,) and RuH,(PPh,),(PF,)2 have been obtained very recently from RuH,(PPh,),, but are not as catalytically active as their rhodium counter- parts (21).

Fig. 2 The struetiire of R h H ( P F , ) , US

determined i n the gas phase by electron diffraction

Table I I Trifluorophosphine Platinum Metal

Hydrides

Ru H d P F 3 , (colourless, m.p.

- 76T)

(colourless, m.p. -72°C)

OsHAPF,),

RWPF,), (colourless, m.p.

-40°C, b.p. 89Ti725)

IrH(PF3, (colourless, m.p.

-39°C. b.p. 95"C/730)

Structures The structure of RhH(PF,), (Fig. 2),

which has recently been determined by electron diffraction (22), may be considered to be pseudo-tetrahedral, i.e. based on a distorted trigonal bipyramid in which the hydrogen atom occupies an axial position. The rhodium-phosphorus distance is shorter than that in RhH(PPh,),and of the same order of magnitude as that found for Rh(NO) (PF3), (Rh-P-2.245 A) (23). It is not, however, the shortest rhodium-phosphorus bond length known. In the analogous cobalt complex, CoH(PFJ,, the cobdt-phosphorus bond is exceptionally short (24).

Variable temperature n.m.r. studies on M’H(PFJ4 (M=Co, Rh, Ir) establish that all these complexes are stereochemically non-rigid (fluxional) and it has been proposed that the phosphorus environments are interchanged by a “tetrahedral tunnelling” rearrangement mechanism (17).

A recent X-ray crystallographic study (25) of the catalytically active complex RhH

(PF3)(PPh3), has confirmed the basic trigonal bipyramidal structure proposed earlier on the basis of its IH, lDF, and 31P n.m.r. spectra (20) (Fig. 3). The rhodium-trifluorophosphine distance (2.15 a) is very much shorter than the rhodium-triphenylphosphine distances (average 2.33 A), which is consistent with the stronger n-bonding ability of PF,.

There is n.m.r. evidence that in complexes of the type M”H,(PF,)~ (M”=RU, 0 s )

(PPh,), (21), the hydrides occupy cis- positions in a distorted octahedron,

Halides The colourless complex cis-PtGl,(PF,),

and the orange dimeric compound [PtCl, (PF3)I2 mentioned above are both obtained by passing PF, through a plug of platinous chloride at 200-220°C.

Passage of PFz over heated rhodium trichloride in the presence of copper powder gives very low yields of the red crystalline,

volatile, chlorine bridged

but this complex has subsequently been conveniently synthesised in high yield by reaction of PF, with [RhCI(L,)] (L =ethylene, cyclo-octene, CO, etc.) under mild conditions (8, 26, 27).

(191, RuHz(PF,)(PPhJ, and RuHd’Fd,

dimer, [RhCI(PF,),I, (2)J

Fig. 3 The structure of RhH(PF,)(PPh,), (inner coordination sphere only). The H position i s not shown (Rh-H distance -1.6 A)


The complexes [RhX (PF3)Jt (X=Br, I) have been prepared similarly and are also obtained from halogen exchange reactions of [RhCl(PF,),], with LiBr or NaI (27). Treatment of ~MW8HIJ2 l2 GH14 =

cyclo-octene) with trifluorophosphine yields the rather

unstable IrCl(PF,), which readily decomposes to the dimeric [IrCl(PF,),], on warming (8). It is interesting that the corresponding carbonyl complex has the composition IrCl(CO),. The very volatile IrI(PF3)4 has been made by treating the metallate salt KJr(PF,), with iodine at -80°C (28).

The yellow crystalline complexes RhX(PF,), (X-Cl, Er, I) are stable at room temperature only under a pressure of PF,, rapidly reverting to the red [RhX(PF,),], compounds on removal of the trifluorophosphine pressure (27).

- lJP3 RhX(PFd,,Z====3 [RhX(PF&],

ycllow -1 PF, red

The synthetic utility of the dimeric [RhC1(PF,)J2 complex is summarised in Fig. 4. The complex trans-RhCl(PPh,),(PF,)

formed by treating the dimer with an excess of triphenylphosphine has been shown to undergo fast ligand exchange reactions with traces of trifluorophosphine or triphenylphosphine (26).

No structural data are available at present on any of the above halide complexes, but [RhCl(PF,),], probably has a similar structure to that found for [RhCl(CO),], with two chlorine bridges between the metal atoms and possibly some degree of metal-metal interaction in the solid state.

Organometallic Compounds Some typical complexes are listed in

Table 111. Rh,(PF,), reacts with a variety of acetylenes to give volatile compounds of the type Rh,(PF,),(acetylene). The structural

Table 111 Some Organometallic Compounds of the Platinum Metals Containing Trifluorophosphine


Fig. 4 Scheme showing some of the reactions of the haEide compound [RhCI( PF,),]

analogy between these compounds and the better known, related Co,(CO) ,(acetylene) complexes has been confirmed by an X-ray diffraction study of Rh,(PF,),(PPh,),(PhC r C P h ) (29) (Fig. 5). The rhodium-trifluorophosphine distances (average 2.216 8) are a g a i n s igni f icant ly shorter than the rhodium triphenylphosphine distances (average

A series of volatile, ii-allylic complexes Rh(x-allylic)(PF,), have been obtained by insertion of various dienes into the metal-hydride bond of RhH(PF,), (30, 31). These complexes react with hydrogen chloride to produce ul- timately [RhCl(PF,),],

2.391 8).

Fig. 5 The structure of Rh,( PF,)c(PPh,),(PhC_CPh). lhe Ph,P ligands have been deleted for clarity

The intermediate x-ally1 rhodium(II1) hydride complex has been detected by a low temperature n.m.r. study and this observation is important in providing support for the involvement of this type of intermediate during the isomerisation of olefins catalysed by transition metal complexes (32). A novel thermal isomerisation of Rh(i-t-I,r-dimethylaUyl)O, to the 1,2-

isomer has been observed (33) and a diene metal-hydride intermediate postulated (Fig. 6) .

The x-ally1 group in IUZ(X-C~H~)(PF~)~ is readily displaced by hydrogen and trifluorophosphine to yield RhH(PF,), quantitatively

H hlc / A , p e ..

Fig. 6 Thermal isomerisationof Rh(r-C,H,) (PF,), by way of a diene metal-hydride intermediate


and an olefin, e.g.

(34), and treatment with nitric oxide affords the volatile liquid nitrosyl Rh(NO)(PF,),, (2, 34), whose structure has been determined by electron diffraction (23).

The structure of the unusual bis-Tc-allylic ruthenium complex dichloro-2,7-dimethyl- octa-2,6-diene-1,8-diyl(trifluorophosphine) ruthenium, RUCI,(C,~H,,)(PF,), (35) i s shown in Fig. 7. This represents the first structural study of a trifluorophosphine complex of a metal in an oxidation state greater than one (25). I t is interesting to note that the ruthenium-phosphorus bond length (2.237 8) is still considerably shorter than in other rutheniuim phosphine complexes (typically

A new synthetic method which promises to have considerable general application involvcs transfer of PF, initially coordinated to nickel to other transition metals. Thus treatment of the pentamethylcyclopenta- dienyl complexes (Me,C,MCl,), (M =Rh, Ir) with an excess of the commercially available complex Ni(PF,), in boiling toluene gives good yields of the complexes z-(Me5C,)

2.30-2.37 8).

M(PF,), (36).

References I J. Chatt, Mature (London), 1950, 165, 637;

J. Chatt and A. A. Williams, J. Chem. SOC.,

2 Th. Kruck, Angew. Chem., International

3 J. F. Nixon, Advances Inorg. Chem. Radio-

4 J. F. Nixon, Endeavour, 1973,32, 19 5 Th. Kruck and A. Prasch, 2. Anorg. Allgem.

Chem., 1968,356, 118 6 Th. Kruck, N. Derner and W. Lang, Z.

Naturforsch., 1966, zIb, 1020

7 Th. Kruck, G. Sylvester and I.-P. Kunau, Z. ATaturforxch., 1973, 28b, 38

8 M. A. Bennett and D. J. Patmore, Inorg. Chem., 1971, 10, 2387

g Th. Kruck, G. Sylvester and 1.2. Kunau, Angew. Chem., International Ed. En., 1971,

10 Th. Kruck, and K. Baur, Angezu. Chem., International Ed. En., 1965, 4, 521

11 Th. Kruck and K. Baur, 2. Anorg. Allgem. Chem., 1969, 364,192

12 J. F. Nixon and M. D. Sexton,J. Chem. Soc., A, Inorg. Phys. Theor., 1970, 321

13 C. A. Udovich and R. J. Clark, J. Organo- metal. Chem., 1972, 36, 355

14 H. T. Dodd and J. F. Nixon,J. Organometal. Chem., I971,32, C67

15 Th. Kruck, K. Baur and W. Lang, Chem. Ber., 1961, 101, 138

16 J. C. Marriott, J. A. Salthouse, M. J. Ware and J. M. Freeman, Chem. Commun., 1970, 595

1951, 3061

Ed. En., 1967, 6, 53

chern., 1970, 13, 363

10, 725

Platinum Metals Rev., 1975, 19, (l),

2

8

Fig. 7 The structure of the complex RuCZ2(Cl,H,,)( PF,)

17 P. Meakin, E. L. Muetterties and J. P. Jesson, J . Am. Chem. SOC., 1972,95, 527r

18 Th. Kruck, W. Lang, N. Derner and M. Stadler, Chem. Ber., 1968, 101, 3816

19 Th. Kruck and A. Prasch, Z. Anorg. Al2gem. Chem., 1969, 371, I

20 J. F. Nixon and J. R. Swain,J. Organometal. Chem., 1974, 72, C I ~ - C I ~

21 R. A. Head and J. F. Nixon, to be published 22 D. W. H. Rankin, personal communication 23 D. M. Bridges, D. A. Clement, J. F. Nixon

and D. W. H. Rankin, Acta Cryst. A, 1972, 318, 1130

24 B. A. Frenz and J. A. Ihers, Inorg. Chem., 1970, 33 2403

25 P. Hitchcock, J. F. Nixon and J. Sinclair, submitted for publication

26 D. A. Clement and J. F. Nixon, 3. Chem. SOC., Dalton Trans., 1972,2553

27 J. F. Nixon and J. R. Swain, J. Chem. SOC., Dalton Trans., 1972, I044

28 Th. Kruck, A. Engelmann and W. Lang, Chem. Bm., 1966, 99, 2473

29 M. A. Bennett, R. N. Johnson, G. B. Robertson, T. W. Turney and P. 0. Whimp, 3. Am. Chem. SOC., 1972, 94,6540

30 D. A. Clement, J. F. Nixon and B. Wilkins, J . Organometal. Chem., 1972, 37, C43

31 J. F. Nixon, B. Wilkins and D. A. Clement, J . Chem. SOC., Dalton Trans., 1974, 1993

32 J. F. Nixon and B. Wilkins, J . Organometal. Chem., 1972, 44, C25

33 M. A. Cairns, J. F. Nixon and B. Wilkins, Chem. Commzm., 1973, 86

34 J. F. Nixon and B. Wilkins, J. Organometal. Chem., 1974,80,129

35 R. A. Head, J. F. Nixon, J. R. Swain and C. M. Woodard, J . Organometal. Chem., 19741 76,393

36 R. B. King and A. Efraty, J. Am. Chem. S0c.J 1971, 931 5260

An Age-hardenable Palladium Based Spring Alloy Strong, light and rigid structural com-

ponents are frequently produced by incor- porating strong fibres of high elastic modulus into a lighter and weaker matrix. Glass or graphite fibres can thus be used to reinforce synthetic resin matrices, while other types of glass fibres are being employed to strengthen fine concrete mixes. With metals, however, fibre reinforcement has met with little success because at high temperatures the matrix tends inevitably to react with the strengthening phase, which is either dissolved or seriously weakened.

D r K. H. Reiff of the Carl Haas spring factory has recently described (Metall, 1974, 28, (7), 686-690) an attempt to develop a fibre-strengthened spring alloy in which no degradation of the strengthening phase occurs because it is always in thermodynamic equilibrium with its weaker matrix. With this object in mind he selected eutectic alloys based on the ternary system palladium- copper-gallium, in which the lamellar phase was an intermetallic compound, strong but ductile enough to allow the alloy as a whole to be heavily cold worked. The working and annealing procedure adopted produced a highly aligned fibre structure in the wires drawn from chill cast ingots. The proportion of the reinforcing fibres appeared to vary with the copper rather than with the gallium content of the alloys, and similar considera- tions applied to the hardness and tensile strength.

Wires having an initial diameter of 1.75 mm were cold drawn without annealing to a diameter of 50 pn, the area reduction ratio being approximately 1000: I. The heavily cold worked wires were then aged, and tensile values peaking at 260 kp/mm2 or) rather more than 165 ton/in2) were obtained after one hour at 425°C. Such tensile values are remarkably high for a ductile non-ferrous alloy and are comparable to those of maraging steels or of hard drawn wires of tungsten or rhenium. The high tensile strength was, however, due simply to age-hardening, and over-ageing reduced strength values cata- strophically to the 80 ton/in' level, which was much below that of the hard drawn, un-aged wire.

These results, coupled with the fact that the elastic modulus of the fibrous wires was only marginally higher than that of pure palladium, show that the high strengths attained were a consequence of precipitation hardening alone and could not be attributed to fibre strengthening. Whatever the mechanism involved, however, a tensile strength approximately twice that of fully heat treated beryllium- copper is still impressive, and the heat treatment procedures required would seem well suited to the setting of hair springs. Certain applications might therefore be envisaged where economic justification could be found for the use of this strong but expensive palladium-based spring alloy.

A. S. D.


ABSTRACTS of current literature on the platinum metals and their alloys

PROPERTIES The Heat of Adsorption of Hydrogen on Platinum P. R. NORTON and P. J. RICHARDS, Surface Sci.,

UHV adiabatic calorimetric studies of the heat of adsorption (9) of H on clean polycrystalline Pt determined as a function of the coverage (0) and temperature showed that adsorption at 273 K resulted in a stepped shape q-0 curve with q (0=0)-24.7 kcal/mole. At 77 K the form of the curve depends on the temperature of pre- adsorption.

1974 44, (I), 129-140

Temperature-dependence of Resistivity of PtCr Alloys R. M. ROSHKO and G . WILLIAMS, Phys. Rev. B, 1974, 9, (111, 4945-4953 Studies of the electrical resistivity of s-Iz%Cr-Pt alloys at 1.4-300 K showed that the spin-fluctua- tion temperature increased from 52.5 to 85 K as Cr concentration increased from 5 to 12 at.:!;. No magnetic ordering occurs above 1.4 K for concentration <12 at.?(,; a rough calculation is performed which qualitatively accounts for the decreasing magnetic-ordering temperature across the series AuCr, PdCr and PtCr.

Magnetic Structure of Ordered Iron- Platinum Alloys A. z. MEN'SHIKOV, YU. A. DOROFEEV, v . A. KAZANTSEV and S. K. SIDOROV, Fiz. Metal. Metalloved., 1974, 38, (31, 505-518 Elastic scattering of neutrons and magnetic measurements on 10-75 at.O/,Fe-Pt alloys revealed five magnetic structures corresponding to Pt,Fe, Pt, ,5Fel.2SJ Pt,.,Fe,.,, PtFe, and Fe,Pt. Their magnetic properties vary from antiferromagnetic ordering in Pt,Fe and Pt2.75Fel 25 to ferro- magnetic in Pt, 5Fe,.j and Fe,Pt. FePt is believed to possess uncompensated antiferro- magnetism, i.e. ferrimagnetism. Experimental and theoretical values are in best agreement for atomic moments of Fe (3.O-2.75)pB and Pt (0.2- 0.3)VB.

The Reversible Martensite Transformation in Iron-Platinum Alloys near Fe,Pt s. KAJIWARA and w . s. OWEN, Metall. Trans., 1974,

A series of 25-27 at.q/,Pt-Fe alloys with ordering of the y phase varying from substantial disorder to nearly complete order were thermally cycled at 25-196°C. The kinetics of the y%cc trans-

5, (91,2047-2061

formations, the hysteresis revealed by electrical resistance/temperature plots, the thermoelastic growth and the reappearance of an identical microstructure after thermal cycling were studied as a function of the ordering of the y-phase.

Localised Enhancement Effects in Pd-Ag Alloys A. P. AIURANI, Phys. Rev. Lett., 1974,33, (2), 91-94 Low-temperature electrical resistivities of Pd-Ag alloys show a positive T2 temperature dependence in the concentration range above 60 at.O,:Ag. This behaviour supplements the well-known resistivity minima observed in alloys with lower concentrations of Ag, and strongly favours the model of scattering from localised exchange- enhanced Pd d states, as against s+d scattering in the rigid- or collective-band description of the alloys.

Surface Area Effects on the Sorption of Hydrogen by Palladium M. J. B. EVANS, Can.J. Chem., 1974, 52, (7), 1200- 1205 Pressure-composition isotherms for dilute solutions of H, in Pd were measured at 100-240°C and at up to 1000 Torr. For Pd foil the isotherms are consistent with data at lower temperatures, and with existing theoretical isotherms. With samples of appreciable surface area a higher sorptive capacity is found which may be due to the formation of a layer of adsorbed H, on the metal surface; appropriate correction may be made for this. The variation of partial molar enthalpy of adsorbed H2 with H,-content is also affected by this surface phenomenon.

Electrical Resistivity of Some Palladium- Silver Alloys Containing Hydrogen at 4.2 K R. J. SMITH and D. A. OTTERSON, NASA Tech. Note 0-7672, 1974, (May), 11 pp. The resistivities of the alloys of 50-900/oPd and go-roc)/Ag measured as a function of absorbed H at 4.2 K showed minimum and maximum values, except for IoO(,Ag-Pd, which had only a maximum, and so*GAg-Pd with only a minimum.

Effect of Pressure on the Curie Temperatures of PdFe, PdCo, PtFe and PtCo Alloys J. s. MEIER, c. w . CHRISTOE and G. WORTMANN, Solid State Commun., 1974, Is, (3), 485-488 The Curie temperatures of PdFe, PdCo, PtFe, and PtCo alloys with Fe or Co concentration of 1-10 at.o/, have been measured by thermal


scanning of the 67Fe Mossbauer resonance under pressures up to 170 kbar. The data are compared with models, which relate the variation of T, under pressure to changes in the impurity spin- conduction electron coupling parameter Ji and to changes of the pure host susceptibility Xh. The differences between the experimental data and these models are discussed.

High Pressure Magnetic Behaviour of Low Nickel Content Pd-Ni Alloys J . BEILLE, Phys. Lett. A, 1974, 49, (I), 63-64 The magnetic properties of disordered Pd-Ni alloys, with low Ni content were studied at high magnetic fields and at high pressures. The variation of the saturation magnetisation and Curie temperature with the concentration and pressure are described.

Defects in Glassy Pd-Si Alloys J. LOGAN, Scripta Metal., 1974, 8, (6), 727-732 X-ray diffraction and density studies on as- quenched and rolled Pd,,Si,, showed that X-ray diffracted intensities were identical for both as- quenched and rolled foils but the density of the as-quenched foils is -5% while the rolled foils vary by -0.3%. The increase in the density upon rolling is 0.5-5.8%.

The Glass Transition Temperature in Glassy Alloys: Effect of Atomic Sizes and the Heats

H. S. CHEN, Acta Metall., 1974, 22, (7), 897-900 The glass transition temperature T, of glassy systems (Pd,-,Mx)o B3jSio 165 for M=Cu, Ag, Au, Rh, Ni, Co and Fe and (Pd,-,Nx), ,,Po 2o

for N-Ni, Co and Fe was studied. The lowering of Tg on admixture of metals with different atomic radii results in the non-linearity in T, vs x curves (for small x) for (Pd1-,Mx), 835Sio.165 alloys and in the shift in peak positions of T, vs x curves of (Pdl-xNx)n.80 Po.,, alloys.

Effect of Palladium on the Oxidation Behaviour of Sintered Tungsten-Chromium- Palladium Alloys T. ITAGAKI and R. YODA, Nippon Icinzoku Gokkaishi,

The effect of Pd on sintering and oxidation behaviour of W-Cr alloys was studied on speci- mens containing ro-zoU/,Cr, 0.1-2%Pd and 0.1-2xNi and compared with that of Ni which is an effective activator for sintering of W. Both Pd and Ni accelerated the sintering of W-Cr as well as the sintering of W but Pd was more effective in activating the sintering than Ni.

Crystal Structure of the So-called R.E.,Pd, Compounds

Metals, 1974, 38, (I), 77-82 Single-crystal photographic data of the crystal

of Mixing

1974, 38, (6), 486-492

M. L. FORNASINI and A. PALENZONA,J. Less-common


structure of Dy,Pd, show that this compound is cubic with a=13.529& space group Fdjrn, and the elementary cell containing 68 Dy and 28 I'd atoms. The R.E.,Pd, compounds, where R.E. = Tb, Ho, Er, Tm, Lu, and Y , are isotypic with Dy,Pd,, and their lattice values are reported.

The Growth and Structure of Epitaxial Rhodium Films R. F. MILLER and J. KOSHY, J . Phys. D: Appl. Phys., 1974,7, (10, 1472-1474 Single-crystal Rh films were epitaxially grown by vacuum evaporation on the cubic, octahedral and dodecahedra1 planes of rock salt, and also on Ag. The structure of the films was investigated by electron microscopy as a function of substrate temperature and thickness of 28-600"C and 10-600 A, respectively.

Oxidation of Iridium R. T. WIMBER and H. G. KRAUS, Metall. Trans., 197455, (71, 1565-1.572 Ir wires heated by self resistance at r675-2260JC were oxidised in naturally convected O2 at 0.00132-1.32 atm. The experimental results were correlated by a theoretical rate equation based on control of the oxidation rates by diffusion of Ir(g), IrO,(g) and IrO,(g) through the gaseous boundary layer. Standard-state free-energies of IrO,(g) and Ir03(g) formation were obtained.

Phase Diagram of the Iridium-Zirconium System v. v. KUPRINA and G. I. KUPYACHAYA, Vest. Moskov. Univ., Ser. II , Khim., 1974~ 15, (3), 371-373 Studies of the Zr-Ir system detected the intermediate phases ZrIrs, ZrIr,, ZrIr, Zr,Ir, and ZrJr. ZrIr3, ZrIr, and ZrJr are formed by peritectic reactions. ZrIr is formed directly and undergoes the polymorphic conversion p-tr .

Investigation of the Character of the Interatomic Interaction in Alloys of the Ruthenium-Vanadium System v. K. YURTAEVA, G. P. MURAV'EVA, M. v. RAEVSKAYA, I. G. SOKOLOVA and E. M. SOKOLOVSKAYA, Vest. Moskov. Univ., Ser. 11, Khim., 1974, (4), 464-466 The probability of stacking fault formation in Ru-V alloys in the V solid solution range was studied and a relation between stacking faults and alloy hardness was detected.

Density of Molten Palladium, Platinum, and Iridium at the Melting Point P. S. MARTSENYUK and YU. N. IVASHCH~NKO, Ukr. Khim. Zh., 1974, 40, (41,431-433 Densities of molten Pd, Pt and I r measured at the melting point were found to be 10.52, 18.81 and 19.39 Mg/m3 for Pd, Pt and Ir, respectively. The impurity contents of the metals were o.ojo0,,Pd, o.02r0/,Pt and o.030°/,Ir.

CHEMICAL COMPOUNDS Structure-Activity Relationships for Anti- tuniour Active Platinum(I1) Complexes J. D. HOESCHELE, Abstr. Papers, 168th Nut. Mtg., Am. Ckem. SOC., 1974, (Sept.), INOR 16 At least three new major classes of antitumour active Pt(I1) complexes analogous to cis-Pt (NH,),C12 have been identified; [Pt(amine),X,], X, rmalonates, oxalate; cis-(PtA,Cl,], A = aliLyclic amines; and the “Platinum Blues” - an uncharacterised class of PtjNH,) ,-pyrimide complexes.

Chemistry and Antitumour Activity of “Platinum Blue” Complexes R. G. FISCHER and H. T. PERESIE, Abstr. PaDers, 168th Nut. Mtg., Am. Chem. SOC., 1974, (Sept.); INOR 17 The reaction of cis-diaquodiammine Pt(IX) with 2,4-dihydroxypyrimidines and primary amides leads to the formation of highly coloured complexes of Pt which are different in type from the classic “Platinum Blue” complexes. The results of chemical and spectral studies on these complexes are given and are related to possible structures for these complexes.

Potential Anti-cancer Activity of Platinum and Palladium Amine Complexes s. KIKSCHNER and A. MAURER, Abstr. Papers, 168th Nut. Mtg., Am. Chem. SOC., 1974, (Sept.), INOR 94 The preparation of Pd and Pt complexes with morpholine, piperazine and piperidine ligands, which show some biological activity but which do not exhibit anti-tumour activity in their own right, is reported. Complexes containing hydrazine as a ligand were also prepared and characterised before screening for anti-cancer activity.

Evidence for Ordered Layers of K+ in KCP

H. J. DEISEROTH and H. SCHULZ, Pkys. Reu. Lett.,

The crystal structure of K,[Pt(CN),] Cla.3.3H,0 was determined. It crystallises in space group P4mm, contrary to earlier assignments. The K t ions occupy ordered positions in layers with a periodicity of c=5.77 A which are perpendicular to the c axis. The same kind of superstructure was found for K,[Pt(CN),] BrO.,.3H,O.

Observation of Electromagnetic Resonances in Crystals of K,Pt(CN),Br, ,.3H,O at Microwave Frequencies R. C. JAKLEVIC and R. B. SAILLANT, Solid State Commun., 1974, 15, (2), 307-m Electromagnetic dielectric resonances in the range 8-11 GHz have been observed in I mm sized crystals of K,Pt(CN)IBr,.,.3H20. This

(K,[P~(cN) ,IC~, . , .~H,~)

1974, 33, (I6), g63-$5


observation results directly from the existence of large dielectric constants; values for the longtitudinal and transverse dielectric constants at 4 K are q l ~ 3 0 0 0 and ~ 1 ~ 4 .

On Fluoropalladates(I1) KPdF,, RbPdF,, TlPdF, and K,PdF, E. ALTER and R. HOPPE, 2. Anorg. Allgem. Chem., 1974,408, (21, I I ~ - J Z O RbPdF,, TlPdF, and KI’dF, were obtained by heating the binary fluorides in a closed system; lattice parameters and the colour of the compound in each case are given.

Composition and Stability of Osmium(1V)- Amino Acids Complexes 0. FAROOQ and N. AHMAD, J . Electroanal. Chem. Interfac. Electrochem., 1974, 53, (9, 461-464 The interaction of Os(1V) with some amino acids using sodium chlaroosmate in an aqueous medium was studied. p H measurement and potentiometric titrations were used to calculate the successive equilibrium constants, the overall stability constants, and the compositions.

ELECTROCHEMISTRY Effect nf Chemisorbed Carbon Monoxide on Hydrogen Adsorption at Platinum Electrodes M. W. BREITER, Extended Abstr., 14gk Mtg., Electrochem. SOC., 1974, 74-1, (May), 730-731, abstr. 303 Studies of the effect of chemisorbcd CO on H adsorption on Pt electrodes at room temperature showed that the potential-H coverage plots did not change their shape much on the three electrodes at CO coverages below 0.4. Theoretical predictions require a larger effect than that observed at 8,,<0.4.

Clad Metal Anodes R. BABOIAN, Extended Abstr. 145th Mtg., Electro- ckenz. SOC., 1974, 74-1, (May), 601-602, abstr. 256 Studies of the anodic polarisation behaviour and the stability of the clad metal electrodes (consisting mainly of Pt coatings on Ta, Nb and Ti) using Pt group metals and some of their alloys were conducted in HC1.

Chemisorptive and Catalytic Properties of Platinum-Rhodium Alloys D. A. J. RAND and R. WOODS, Extended Abstr., 145th Mtg., Electrochem. SOC. 1974, 74-1, (May), 734-735 Studies of the electrocatalytic activity of Pt-Rh electrodes during methanol oxidation showed that at 0.58V the activity versus composition curve passes through a maximum at 347”Rh-R. The catalytic behaviour is interpreted as a mechanism involving reaction between organic intermediates and hydroxyl radicals adsorbed on the alloy surface.

ELECTRODEPOSITION AND SURFACE COATINGS Refractory Intermetallic Compound Coatings P. J. FICAI.ORA, v. SRIKRISHNAN and L. PECORA, U.S. Rept. AD $$4893/zGA, 1974,zopp Crystal structure, electronic configuration and thermodynamics of HfPt, and ZrPt, were studied. Films of HfPt, and ZrPt, are suitable for coatings for components subjected to high temperature oxidising atmospheres.

Electron Microscope Investigation of Mixed Stannous Chloride/Palladium Chloride Cata- lysts for Plating Dielectric Substrates N. FELDSTEIN, M. SCHLESINGER, N. E. HEDGECOCK and S. L. CHOW, 3. Electrochem. Soc., 1974, 121,

Electron microscopy and electron diffraction studies of surfaces treated by the catalysing system (SnCl,/PdCl,/HCl) in conjunction with various accelerating solutions show that the best plating results are obtained when Pd,Sn is present on the treated surface prior to the metallisation step.

Kinetics of the Electrodeposition of Palladium

J . Electroanal. Chem. Interfacial Electrochem.,

Surface area changes which occur when Pd is deposited on to Pd from chloro-complexes were studied electrochemically. A three-dimensional nucleation and growth model is used to evaluate the kinetics of the process.

738-744

J. A. HARRISON, H. B. S . ALCAZAR and J. THOMPSON,

1974, 53, (I), 145-150

HETEROGENEOUS CATALYSIS Effect of Addition of Iridium on the Activity of Platinum/Alumina Catalysts in the Dehydrogenation of Cyclohexane N. s. KOZLOV, L. YA. MOSTOVAYA and G. A. ZHIZHENKO, Neftekhimiya, 1974, 14, (4), 591-594 Studies of the effects of Ir additions to Pt/Al,O, on catalyst activity, thermal stability and resistance to S poisoning during cyclohexane dehydrogenation showed that Pt-Ir/Al,O, possesses greater thermal stability and resistance to the action of S compounds than does Pt/Al,O,.

Activity of Platinum Catalysts, Prepared on Supports of Type L Dealuminised Zeolites, in the Reactions of Isomerisation and Dehydroisomerisation

M. F. RUSAK and N. S. KOZLOV, Neftekhimiya, 1974,

Isomerisation activity of Pt!type L dealuminised zeolites rises with increases in the amount of

L. P. SHIRINSKAYA, V. S. KOMAROV, I. I. URANOVICH,

14, (411 568-571


dealuminisation and reaches its maximum when Si0,:A1,0a=7.3. Increased dealuminisation of these zeolites leads to a decrease in the dehydrogenation activity of the Pt catalysts.

Conversion of Cyclic Hydrocarbons on Platinum/Alumina Catalyst R. A. BAKULIN, M. E. LEVINTER and F. G. UNGER, Neftekhimiya, 1974, 14, (9, 707713 Diene condensation products tend to form on Pt/Al,O, for diene, cyclo-olefin, indene, acenaphthalene, phenanthrene, and anthracene hydrocarbons. Indane, indene, acenaphthalene, phenanthrene, anthracene, and more condensed structures appear to form by C,- and C,- dehydrocyclisation of paraffins, aIkylaromatic hydrocarbons and diene condensates of intermediate dienes and cyclo-olefins. Coke formation on Pt/A1,0, tends to occur in the order: cyclo- pentadiene > indene > indane > methylcyclo- pentane > bis- butylbenzene > hexene > decalin > hexane > d-methylnaphthalene > styrene > tetralin.

Effect of Pore Diameter of Aluminium Oxide on the Activity, Stability and Selectivity of Platinum/Alurnina Catalysts v. G. DYRIN, M. E. LEVINTER, A. N. LOGINOVA and L. I. VLASOVA, Neftekhimiya, 1974, 14, (s), 7i4-719 Fine-pore catalysts have greater activity and stability for aromatisation, hydrocracking and coke formation of petroleum fractions but less selectivity because of increased Pt dispersion and filling of the pores by molecules of the reactants. Fine-pore catalysts have less selectivity than wide- port catalysts because of secondary aromatisation, transposition of H,, hydrocracking, and destructive polycondensation with coke formation.

On a New Platinum on Alumina Catalyst. I. Preparation and Composition of the Catalyst C. HOANG-VAN, P. A. COMPAGNON and s. J. TEICHNER, Bull. SOC. Chim. Fr., 1974, (7-8 pt.I), 1225-1228 Finely divided Pt was deposited on N,O, without any change in the amorphous state of the support. The amounts of Pt and C1 contained in the samples were determined, as was their specific surface area by the adsorption of N,.

On the Activity of the Platinurn Group Metals in the Demethylation of Toluene with Water Vapour

MASLYANSKII and M. I. DEMENT’EVA, Kinet. Kataliz, 1974, 159 (41, 949-953 Pt metals on y-Al,O, catalyse demethylation of toluene with H,O vapour. Catalyst activity decreases in the order Rh>Pt>Pd>Ir, Ru, Os, as for demethylation in He. The catalysts are considered to be bifunctional, the metal possessing destructive activity and the support possessing hydrophilic properties.

G. L. RABINOVICH, G. V. DYDYKINA, G. N.

Determination of the Surface of Dispersed Platinum Catalysts on Electrically Condnct- ing Supports

z. I. KUDRYAVTSEVA, I. I. ASTAKHOV and v. s. BAGOTSKII, Kinet. Kataliz, 1974, 15, (4), 1009 1014 The specific surface u in m2/g for Pt supported on active C, graphite and C black was determined by four independent methods. Supported Pt has 2-4 times the surface of Pt black; a tends to increase as the Pt concentration decreases.

Adsorption of Hydrogen on Pt/Zeolite Catalysts T. G. MARTYNYUK, v. I. SHEKHOBALOVA and V. s. BORONIN, Vest. Maskov. Univ., Ser. I I , Khim., 19741 (41, 450-454 Studies of the mechanism of H, chemisorption on various Pt/zeolite catalysts with respect to Pt content, zeolite type and method of application of Pi to the zeolites showed complexity of adsorption isotherms.

Crystallite Size Effects in the Low-temperature Oxidation of Ammonia over Supported Platinum

J . Catalysis, 1974, 33, (3), 457-473

N. A. URISSON, L. N. MOKROUSOV, G. V. SHTEINBERG,

J. J. OSTEFXAIER, J. R. KATZER and W. H . MANOGUE,

The effect of crystallite size on the specific catalytic activity of supported Pt catalysts in NH, oxidation with 0, was determined. Rates of NH, oxidation were measured in a differential, fixed bed, flow reactor at 393-473 K and catalysts with crystallite size of 20, 27 and 155 A were used. The initial specific catalytic activity of the 155 A catalyst was higher than those of the 20 and 27 A catalysts by factors of 5.7 and 3.7, respectively.

Deactivation of a Platinum Monolithic Carbon Monoxide/Hydrocarbon Oxidation Catalyst D. LIEDERMAN, s. E. VOLTZ and P. w. SNYDER, Ind. Engng. Chem., Prod. Res. Dev., 1974, 13, (3), 166-172 The effects of ageing on the CO/hydrocarbon oxidation activity and important physical properties of a Pt monolithic catalyst were determined. Catalyst samples were aged to 25,000 equivalent miles at a maximum temperature of 1450'F with unleaded fuel on an engine dynamometer. The activity for the oxidation of CO, C,H,, and engine exhaust gas hydrocarbons decreased rapidly during the first 1000-5000 miles with very little additional deactivation during further ageing. A large decrease in C,H, oxidation activity continued through the 25,000 miles of ageing. The growth of very large Pt crystallites appeared to be a primary cause of catalyst deactivation. No significant changes in surface area or solid-state phase composition were noted. Small amounts of Pb were detected on aged catalyst samples.

Heats of Adsorption of Hydrogen on Skeleton Platinum, Rhodium and Platinum -Rhodium Catalysts in Hydrochloric Acid Solutions

and G. D. VOVCHENKO, Zh. FizKhim., 1974, 48, (8),2093--2096 The heats of adsorption of Hz on skeleton Pt, Rh and Rh-Pt catalysts in IN HCI solutions were determined and the bonding energies between the adsorbed H, and the surfaces were calculated.

Effect of Temperature on the Adsorption of Hydrogen by Skeleton Platinum-Rhodium Catalysts in Hydrochloric Acid Solutions

and G. D. VOVCHENKO, Zh. €%z. Khim., 1974, 48, (9192330-2332 Galvanostatic and potentiodynamic studies of H, adsorption on Pt, Rh and Rh-Pt skeleton catalysts in rNHCl at 10-70°C showed that the adsorption capacity for H, on heating is significantly dimi- nished on Rh and Rh-rich alloys.

Effect of the Composition and Conditions of Heat Treatment of Palladium-Rhodium Alloys on Their Catalytic Activity in the Dehydrogenation of Cyclobexane

N. R. ROSHAN and B. DZHUNTINI, Izv. Akad. Nauk S.S.S.R., Sw.I<him., 1974, (IO), 2182-2188 Catalytic activity for cyclohexane dehydrogenation of 7-209/~Rh-Pd alloys decreases as H, is removed from them and is completely reduced after treatment by H,. The activity increases with the temperature for treatment in air from 350 to 750°C. Activity increased after tests at 450- 470°C in a stream of Ar, prcsumably due to the removal of firmly adsorbed H,.

The Catalytic Chemistry of Nitric Oxide. 11. Reduction of Nitric Oxide over Noble Metal Catalysts T. P. KOBYLINSKI and B. w. T A Y L O R , ~ . Catalysis, 1974, 33> (3h 376-384 The reduction studies of NO with H2, CO, and equimolar mixture of H,/CO over supported Pt, Pd, Rh, and Ru catalysts showed that when H, was used the activity of the catalyst was Pd>Pt,Rh>Ru. When CO or CO/H, mixtures were used, this activity sequence was re- versed. The results show that CO inhibits NO reduction strongly over Pt and Pd, the presence of CO over Ru catalyst accelerates the reaction and the reduction of NO in the presence of Pt and Pd gives NH, as major product.

Hydrogenation of Ally1 Alcohol on Rhodium A. M. SOKOL'SKAYA, K. KH. NURGOZHAEV and T. O&IARKULOV, zh. Fix. Khim., 1974, 48, (i), 1740- 1742 The rate of hydrogenation of ally1 alcohol on Rh

T. M. CRISHINA, L. I. LOGACHEVA, T. V. SHESTAKOVA

T. M. GRISHINA, L. I. LOGACHEVA, T. V. SHESTAKOVA

E. V. KHRAFOVA, V. M. GRYAZNOV, R. 0. MZEE,


black is high because of weakly adsorbed H, on the Rh surface. Greatest yield (93%) of propanol occurred at 20°C, 20 atm HP; greatest yield of propanol occurred at 20°C and 80°C, 60 atm.

Hydrogenation of Aliphatic Ketones under Pressure of Hydrogen A. M. SOKOL'SKAYA, A. I. LYASHENKO and A. K. ZHARMALAMBETOVA, zh. Fiz-Khirn., 1974, 48, (8), 2 I 16-2 I 18 I wt.% Ru/y-Al,O, in H,O at 20-100 a m H, supports a high rate of conversion of acetone and methylethylketone to saturated secondary alcohols. T o increase the rate of ketone hydrogenation the H, is stabilised by Ru using an alkaline solvent. Hydrogenation takes place by the formation of free radicals not exposed to condensation.

Hydrogenation of Epoxycyclododecadiene over Group W I Metals

LEBEDEVA and v. v. SEMENOVA, Neftekhimiya, 1974,

Hydrogenation of epoxycyclododecadiene (trans- epoxy-cis,tram-cyclododecadiene) on Group VIII metals takes place at the double bonds in two stages; first to the cis and tram forms of epoxycyclododecene, which is then reduced to epoxycyclododecane. Yield of the latter is 87- 9696 on Pd, Ru, Rh, or Pt. Oxirane rings are not reduced on these catalysts. Hydrogenation of the cis and tram double bonds of epoxyclodo- decadiene and epoxycyclodecene on Pd and Rh proceeds at similar rates.

Catalytic Transfer Hydrogenation

F. A. CHERNYSHKOVA, D. V. MUSHENKO, E. G.

141 (51, 677-681

G. BRIEGER and T. J. NESTRICK, Chem. Rev., 1974, 74, t5)l 567-5x0 Studies of the catalytic transfer hydrogenation with an organic molecule as H donor, using Pd but occasionally also Raney Ni showed that this reaction permits the reduction of olefins, nitriles and nitro compounds, as well as hydrogenolysis of benzylic and allylic functional groups and the replacement of aromatic halogen. The reaction is more selective than regular hydrogenation and in special cases, such as the reduction of polyun- saturated steroids, has proved superior.

HOMOGENEOUS CATALYSIS Investigation of the Catalytic Action of Pt-Sn(I1) Complexes in Hydrogenations of Acetylene Hydrocarbons

MUKHTAROV and N. I. MALOPEEV, Nefzekhirniya, 1974, 14, (4), 572-57s Pt-Sn complexes catalyse a higher rate of hydrogenation for mono-substituted C =C bonds than for disubstituted, irrespective of the length of the substitutcd alkyl chain. The amount of hydrogenation of pentyne-1 and phenylacetylene

N. V. BORUNOVA, L. KH. FREIDLIN, YA. G.

is closely connected with catalyst concentration and with the pressure of Ha. Monoalkylacetylenes and phenylacetylene are hydrogenated in stages, and diphenylacetylene adds two moles of Hz via the intermediate stage of diphenylethylene.

Tetrakis( triphenylphosphine)palladium(O) -Homogeneous Catalyst for the Hydro- genation of Acetylene and Ethylene G. K. SHESTAKOV, A. M. VASIL'EV, L. M. TISHCHENKO, 0. N. TEMKIN and R. M. FLID, Kinet. Kataliz, 1974, 15, (41, 1070--I072 Tetrakis(triphenylphosphine)palladium(O) in o- xylene effectively catalyses hydrogenation of C,H, and C,H, at IOO'C, I atm. Butene in the product is formed by hydrodimerisation of C,H, and C,H,. The reducing agent may be toluene sulphate and formamide.

Polymerisation of Some Cycloolefins with Palladiuni-5;-complexes F. HOJABRI, Abstr. Papers, 168th Nat. Mtg., Am. Chem. SOC., 1974, (Scpt.), INDE 44 Studies of the Pd z-allylic complexes prepared by the reaction of PdC1, with pinenes at high temperature showed them to be very active catalysts for the polymerisation of bicyclohepta- (2,5)-diene at 130-2oo0C. The polymerisation pattern revealed that only one double bond of the diene was opened by this reaction.

Catalysis by Supported Transition Metal Complexes. 11. Hydrogenation of Ally1 Alcohol on a Palladium Resin R. L. LAZCANO, M. P. PEDROSA, J. SABADIE and J.-E. GERMAN, Bull. soc. Chim. Fr., 1974, (5-6 pt.II), 1129-1132 The liquid phase hydrogenation of ally1 alcohol in the presence of a catalyst obtained by ion exchange with a basic resin having a PdCla2- anion gives a mixturc of propanol and the corresponding aldehyde. The activity and selectivity of the catalyst was studied as a function of solvent, temperature (25--28OC), H, pressure (1-100 bar), and was compared with those of the usual Pd catalysts. Differences in results indicate the presence on the resin of active centres, with markedly different properties to highly dispersed Pd.

The Selectivity of Palladium(I1) in Sub- stitution Reactions of Their Chloro-complexes with Diamines R. ERNST and R. ROULET, Chirnia, 197428, (7), 347- 349 The rate constants of the substitution reactions of C1- and HzO by various diamines in Pd(I1) chloro-complexes were determined spectrophoto- metrically. The substitution mechanism is associative, and comparison with the corresponding Pt (11) complexes shows the selectivity of Pd(I1) to be smaller than that of Pt(I1).


Rhodium Carbonyl Chloride Anion, [Rh (CO)2C12]-: a True Catalyst in the Reduction of NO by CO

Papers, 168th Nat. Mtg., Am. Chem. SOL, 1974, (Sept.), INOR 116 Studies of the RhCl,/EtOH catalyst during reduction of NO by CO showed that addition of HCl to the catalyst system shortens an induction period, during which Rh(CO),Cl,- is formed, and acid accelerates the reaction between NO and CO. The interaction of Rh(CO),Cl,- with NO has been examined and i.r. spectroscopy reveals the presence of several nitrosyl species.

C. D. MEYEK, J. REED and R. EISENBERG, Abstr.

Preparation of Hydridometallocarboranes and Their Use as Homogeneous Catalysts T. E. PAXSON and M. F. HAWTHORNE,J. Ant. Chetn.

Methanol solution of the tris(tripheny1phoshine) rhodium(1) cation was reacted at 60°C with a methanolic solution of either (CH,),NHT[7,8- C,B ,HI 2]- or (CH,),NH+[7,9-CPB,H,,]- and high yields of 3,3-[(C6H,),P],-3-H-3,~,2-RhC,BJI, and 2.2-[(CsHs),P] ,-2-H-z,r,7-RhC,B sH1l, respectively, were obtained. These compounds catalyse the deuterium exchange of terminal {BH) groups in boranes, carboranes and metalloboranes, and the hydrosilation of ketones.

Transition Metal Catalysed Exchange of Deuterium Gas with Terminal Boron- Hydrogen Bonds in Carboranes, Metallo- carboranes, and Other Boron Compounds E. L. HOEL and M. F. HAWTHORNE, Zbid., 4676-4677 In the presence of catalytic amounts of (PPh,),, RuHCl which is an effective catalyst for the specific ortho deuteration of triphenylphosphine, carboranylphosphine was found to exchange H atoms for deuterium gas at B atoms but not at Ca atoms. The nucleophilic character of transition metal complexes in ortho metallation and other oxidative additions was discussed.

SOL., 19749 96, (I4)i 4674-4676

Homogeneous Catalysis of Hydrogen Isotope Exchange between D, and Ethanol by Chlorotris(triphenylphosphine)rhoclium(I).I. In Benzene-Ethanol G. STRATIIDEE and R. GIVEN, Can. J. Chem., 1974, 52, (IZ), 2216-2225 The kinetics and mechanism of D,-C,H,OH exchange catalysed by RhCI(Ph,P), was studied in 50 vol.%C,H,-C,H,50H. The exchange rate was low and was limited by the D, transfer rate from dideuteridochlorotris(tripheny1phosphine) rhodium(II1) to the solvent, and not by the rate of activation of D,. The activation energy for the overall process=3gkJ/mol. New data is given for the catalysis of H2-D, exchange in C,H, by RhCl(Ph,P),. Analysis of the apparent HD:D, isotope effect observed during D ,-C,H,OH

exchange suggests that this effect originates from the relative stabilities of the D,, H D and H, adducts with RhCl(Ph,P),, or by control of the H D and H, product distribution by the H2-Dn equilibrium reaction. Homogeneous Catalysis of Hydrogen Isotope Exchange between D, and Ethanol by Chlorotris( triphenylphosphine)rhodium(I), 11. In Chloroform-Ethanol Ibid., 2226-2235 The kinetics and mechanism of D, exchange catalysed by RhCl(Ph,P), was studied in CHCI, -C,H,OH solutions. The DP exchange reaction rate is strongly dependent on solvent composition and decreased 30 times between 6-$)6mol.0/, C,H,OH. The activation energy for D2 exchange =101fgkJ/mol at 58 mol.:/o C,H,OH, and 86 8kJ/rnol at 6 mol.O/,C,H,OH. Results thus indicate solvent-catalyst bonding interactions to be important in this respect. Homogeneous Catalysis of Olefin Isomerisa- tion. Part IV. The Isomerisation of Pent-l- ene Catalysed by Solutions of IrH(CO) (PPh,) ,, IrHCI,(PEt,Ph) 3, IrCI(CO)(PPh,) IrCI(O,)(CO)(PPh,),, and of PtH(SnC1,)

D. BINGHAM, D. E. WEBSTER and P. B. WELLS, J . Chem. SOC., Dalton Trans., 1974, (14), 1514- 1518 The isomerisation of pent-1-ene to pent-a-ene at 80°C is catalysed by solutions of (I) IrH(C0) (PPh,),, (2) IrHCl,(PEt,Ph),, (3) IrCl(C0j (PPh,), or IrCl(O,)(CO)(PPh,), each in the presence of 0 source, and (4) PtH(SnCl,)(PPh,), in benzene. System (I), (2) and (4) catalyse the preferential formation of cis-pent-2-ene where as (3) provides preferential formation of trans- pent-2-ene. Bart V. Pent-1-ene Isomerisation Catalysed by Solutions of RuHCl(PPh,), and of RuHCI(CO)(PPh,),; Variation of the Iso- meric Composition of Pent-2-ene and Its Attribution to Steric Factors Zbid., 1519-1521 Isomerisation of pent-I-ene to pent-2-ene at 3540°C is catalysed by solutions of RuHCl (PPh,), and RuHCl(CO)(PPh,), in benzene. Preferential formation of cis-olefin occurs at higher catalyst concentrations but a change to preferential trans-olefin formation is observed as catalyst concentration is reduced. Part VI. Pent-1-ene Isomeration Catalysed by Solutions of Dodecacarbonyltri-iron(0) and of Bis(benzonitrile)dichloropalladium (11) in Benzene D. BINGHAM, B. HUDSON, D. E. WEBSTER and P. B. WELLS, Ibid., 1521-1524 Isomerisation of pent-1-ene to cis- and trans- pent-a-ene is catalysed at 50’C and above by solutions in benzene of Fe,(C0)12 and of PdC1,

(PPh,) 2


(C,H,CN),. In both cases, preferential formation of trans-pent-2-ene occurs. The reaction mechan- isms involve z-allylic intermediates; for the Pd- catalysed reaction bis-n-ally1 complexes may also participate.

Homogeneous Hydrogenation of Buta-1,3- diene and Ethylene Catalysed by Carbonyl- hydridotris(triphenylphosphine)iridium(I) and by Carbonyltrihydridobis(triphenylphosphine)iridium(III) M. G. BURNETT, R. J. MORRISON and c. J. STRUGNELL, J. Chem. Sac., Dalton Trans., 1974,(16), 1663-1671 Spectrophotometric and kinetic studies of the individual steps in the catalytic cycle of buta-1,3- diene hydrogenated to a mixture of butenes and butane by IrH(CO)(PPh,), and IrH,(CO)(PPh,), at 50°C in dimethylformamide, were quantitatively interpreted in terms of a mechanism based on the reductive elimination of butenes by Ir(a-C,H,)Hz(CO)(PPh,)2. The intermediate Ir(T;-C,H,)(CO)(PPh,), was also isolated and characterised.

Complex Metal-Polymer Catalysts for Ben- zene Hydrogenation E. N. RASADKINA, T. V. KUZNETSOVA, A. T. TELESHEV, I. D. ROZHDESTVENSKAYA and I. V. KALECHITS, Kinet. Kataliz, 1974, 15, (4), 969-973 Studies of Rh, Ir and Pd catalysts complexed with nylon showed how conditions of their preparation affect their properties in C,H, hydrogenation. Cyclohexene is formed as well as cyclohexane. The order of activity of these complexes is Ir>Pt>Rh>Pd.

NEW PATENTS METALS AND ALLOYS Palladium Alloy for Hydrogen Membranes URALSKY ORDENA TRUDORAGA KRASNOGO ZNAMEI POLITEKHNICHESKY INSTITUT Britzsh Patent i,365,271 Alloys for H diffusion contain 1-26?" Ag, I - 2 6 O 0 Au, o.r-o.go/, Ru, 0.1-2;; A1 and 0.1-2.5O1, Pt, remainder Pd. In one example an alloy contains 75% Pd, 2076 Ag, 2.57" Au, 0 . 5 ~ 6 Ru, I"/, A1 and 1% Pt.

CHEMICAL COMPOUNDS Synthesis of Silyl Metal Complexes DOW CORNING CQRP. British Patent 1,363,158 Silyl Pt and Pd complexes are formed by reacting disilanes or hydrosilanes with Pt or Pd phosphine complexes. Thus Si,Cl, with Pd(PPhzMe),C1, gives Pd(PPh,Me) ,(SiCl,)Cl.

CHEMICAL TECHIYOLQGY Morphology of Dimensionally Stable Anodes K. J. O'LEARY and T. J. NAVIN, Extended Abstr., 145th Mtg., Electmchem. SOC., r974, 74-1, (May), 603-608, abstr. 257 X-ray studies of 2:1 molar ratio solutions of Ti and Ru painted on a clean T i substrate and fired at 10oyoo"C showed that below 300°C they are amorphous and above 700°C they are fully crystalline with extremely small crystals of roo-5008. Electrical conductivity of fully crystalline solid solutions falls between the insulator T i 0 and metallic conductor RuO 2.

ELECTRICAL AND ELECTRONIC ENGINEERING Reliability Studies of the PtSi-Ta-Au Metal- lisation System for Microwave Power Tran- sistors H. M. DAY, A. CHRISTOU, w. WEISENBERGER and J. K. HIRVONEN, Extended Abstr., Iqjth Mtg., Electrochem. SOC., 1974, 74-1, (May), 188-189, abstr. 75 X-ray and electron diffractometry studies of the Si-Ta-Pt-Au and Si-Pt layers showed formation of TaAu, TaBSi and Ta,Pt compounds at > 450"cJ while PtSi formed at the Si-Pt interface at 200°C in 20 min. The ion backscattering data indicate that no further reaction takes place at the Si-Pt interface when annealed in vacuum at 700°C. Auger electron data on the Si-Ta-Pt-Au system are also obtained and discussed.

Platinum Metals Rev., 1975, 19, (l), 3 7 4 0 37

ELECTRODEPOSITION AND SURFACE COATINGS Ruthenium Dioxide Electrode Coating ELECTRONOR CORP. British Patent 1,370,529 Finely-divided RuO, having a particulate size of 0.1 p or less dispersed in an organic polymer, resistant to degradation in an electrolytic process exhibits a low oxygen overvoltage for a surpris- ingly long period of time. Also a combination of finely-divided RuO, and organic polymer on an electrically-conductive substrate provides an efficient electrode for many electrochemical reactions.

HETEROGENEOUS CATALYSIS Aromatic Hydrogenation

British Patent 1,363,179 The hydrogenation of aromatic hydrocarbons in

TEXACO DEVELOPMENT CORP.

the presence of S may be achieved by adding CO to the feedstock before it passes over a fiuorided Pt/AI,O,.

Deuterium from Hydrogen-containing Com- pounds

British Patent 1,364,714 A vapour of a deuterium-containing hydrocarbon undergoes deuterium transfer to another hydrocarbon at high temperature in the presence of a hydrogenation-dehydrogenation catalyst, especially Pt.

Reforming Catalyst

British Patent r,364,744 Hydrocarbon reforming is catalysed by an A1,03 support carrying o.oo5-r0/, Pt, O.OOS-I~,, I r and 0.05-3'b T1 and,'or In.

Combination Reforming Process

British Patent 1,364,875 The naphthene content of a paraffininaptha feedstock is increased in contact with a Pt group metal and then the product stream is mixed with H and contacted with a support mixture of Pt with either Ir, Rh or Ru. Suitably, 0.01-2q:, of both metals are present on an A1,0, support.

Trimethyl Hydroquinone Production KURARAY CO. LTD. British Patent 1,365,035 2,3,6-Trimethyl-p-benzoquinone is reduced to the corresponding hydroquinone using H in the presence of a Pd catalyst and an aliphatic ketone solvent, e.g. Pd/C plus MIBK.

Isopropylaniline Production

British Patent 1,365,106 N-Isopropylaniline is obtained when aniline and acetone are reacted in a hydrogen atmosphere at elevated temperatures and pressures using a Pt catalyst, for example, 126 Pt/A1,0,.

Hydrocarbon Conversion Catalyst UNIVERSAL OIL PRODUCTS CO. British Patent 1,366,334 A reforming catalyst is obtained by impregnating a support (Al,Os) with a complex Sn-Pt group metal anionic species and calcining in the usual way. An acidic SnCl solution mixed with a H,PtCI, solution supplies a suitable impregnating solution.

Saturated Hydrocarbon Isomerisation NIPPON OIL co. LTD. Brirish Patea 1,366,784 The isomerisation of hydrocarbons, e.g. straight chain paraffins, is catalysed by a mixture of 0.013% Pt or Pd and 0.01-150/~ halogen on a mordenite support where the halogen is intro-

GULF RESEARCIi & DEVELOPMENT CO.

STE. FRANCAIS DES PRODUITS POUR CATALYSE

ESSO RESEARCH & ENGINEERING CO.

ESZAKMAGYARORSZAGI VEGYIONUK

duced by contact with a fluorohalohydrocarbon, e.g. CHC1,F.

Epoxy Spirolactones S. D. SEARLE & CO. British Patent 1,368,731 Spirolactones are produced in a process where an epoxy androstene furandione is hydrogenated over Pd jC to give the corresponding androstane derivative.

Platinum-Cobalt Catalyst Bed for Flameless Catalytic Heater BRUEST INDUSTRIES INC. U S . Patent 3,802,856 A catalyst bed unit employing a measured amount of cobalt in conjunction with Pt forms the fuel- reactive catalyst of the unit to render the heater capable of operation at low CO emission levels. The catalyst is applied to its support by dissolving chloroplatinic acid and cobalt nitrate in a solution of methanol and water, spraying the mixture on to the support and heating the unit to reduce the H,PtCl, and Co nitrite to Pt and Co metals.

Catalyst of Zinc Lanthanide Exchanged Zeolite MOBIL OIL CORP. U S . Patent 3,804,780 Pt and Pd catalysts may be supported on a crystalline zeolite having 6-13 yo lanthanide cations and less than 2.5"/0 Zn cations.

NO, Abatement

U.S. Patent 3,806,582 A process is described for the purification of gases containing NO, formed in the manufacture of HNO ,. A gas containing the oxides and including 0 and a gaseous reducing fuel, is passed at a temperature above the ignition temperature of the gas and the fuel through a catalyst comprising an inert ceramic material impregnated or coated with a mixture or alloy of Pt and Rh metals in which Rh ranges from 20-507'0 by weight but is preferably present to the extent of 35?/0 by weight of the catalytic metal content of the catalyst.

Preparing Amino-substituted Phosphonates

The preparation of amino-substituted phosphonates from their corresponding cyano- substituted phophonate precursors, consists of hydrogenating the cyano-substituted phosphonates in the presence of NH, and Rh catalyst.

Ruthenium NO, Removal Catalyst FORD 'MOTOR CO. U.S. Patent 3,819,536 A fixing compound, selected from an alkaline earth material or a rare earth material which decomposes to an oxide of the material, is deposited on a catalytic support. A hydrated, halogenated Ru compound which reduces to Ru is also deposited on the catalytic support. The materials on the support are heated in a reducing

JOHNSON MATTHEY & CO. LTD.

THE GATES RUBBER CO. U.S. Patent 3,813,456


atmosphere to form the Ru metal. After the reducing step the materials are fixed by heating them to a ruthenate-forming temperature.

Platinum Reforming Catalyst

French Appl. 2,196,192 The catalyst, for use in hydrocarbon reforming, has an A1,0, support, O.OOS-I.O~( Pt, o.ooS-I.o% Ir and O.OOS-~.O?~ Nb.

Acetic Acid Production BASF A.G. German Offen. 2,303,271 Acetic acid, optionally with methyl acetate, is obtained by the reaction of methanol with CO in the presence of Co catalysts promoted with Br and/or I and Pd, Pt, Ru, I r or Cu.

STE. FRANCAIS DE PRODUITS POUR CATALYSE

HOMOGENEOUS CATALYSIS Carbon Monoxide Copolymerisation Catalyst

British Patent 1,362,908 High molecular weight polymers are produced from CO and other monomers, e.g. C,H,, in the presence of an aryl phosphine-palladium halide complex, e.g. (PPh,),PdCl, or Pd(PR,),.

Cationic Platinum Catalysts BP CHEMICALS INTERNATIONAL LTD. British Patent 1,362,997 New catalysts for alcohol carbonylation and other reactions are complexes of univalent or trivalent Rh or Ir with acetonitrile, benzonitrile, butyl isocyanate, benzene, toluene, phosphite or phosphine; the anion must be a phosphate, sulphate, perchlorate, borate, iodate or bromate. A typical catalyst is Rh(P(OPh),),BPh,.

Silane Production DOW CORNING CORP. British Patent 1,363,157 Pt, Pd and Ni phosphine complexes are used to catalyse the rcaction of a Si,Cl, and a halide to form mixed substituted silanes. For example, PhSiC1, is prepared by the reaction of Si,CI, and PhCl in the presence of Pd(PPhMe,),Cl,.

Unsaturated Organosilicon Compounds

British Patent 1,363,317 Silane addition to a diene is catalysed by an inorganic Pd compound or organic complex. For example, the addition of triethoxysilane to butadiene is catalysed by bis(ally1)Pd chloride.

Cyanobenzoic Acid Hydrogenation ASAHI KASEI K.K.K. British Patent 1,368,415 p-Aminomethyl benzoic acid is produced in one step by the reaction of an alkyl ester of p-cyanobenzoic acid in aqueous alkaline medium containing a catalyst, e.g. Rh, Ru, RuO,, Rho,, etc.

SHELL INTERNATIONALE RESEARCH MIJ. B.V.

CESKOSLOVENSKA AKADEMIE VED


New Rhodium Complex

British Patent 1,368,431 New complexes of Rh(1) for use in catalysing hydrogenation, oxidation, decarbonylation, isomerisation, hydroformylation and other reactions are obtained by adding excess of an arsine, phosphine, stibine, sulphide or amine stabilising ligand (susceptible to oxidation) to a Rh(I1) carboxylate solution protonated by an acid. The complexes are of the type Rh(CO)(PPh:,),BF,, e.g. prepared from a rhodium acetate (HBF,) phosphine solution by bubbling through carbon monoxide.

Palladium Complex in Oligomer Production

British Patent 1,369,128 A chain oligomer is produced from a vinyl or vinylidene aromatic compound in the presence of a Pd compound, a compound containing a fluoro complex or perchlorate anion and a trivalent organic P compound, e.g. methallyl Pd chloride, tributyl phosphine and Ag chlorate or boro- fluoride.

Producing Oligomers of Unsaturated Com- pounds

U.S. Patent 3,803,254 Pd phosphine, arsine and stibine complexes, e.g. [PdL,(PPh,)][BF,] ,, where L is benzonitrile, are used to oligomerise styrene and other unsaturated compounds.

Ruthenium Complexes

U.S. Patents 3,804,868 & 3,804,869 New Ru complexes of the formula Ru(diket),L, in which (diket) represents a bidentate ligand derived from a P-diketone and L is a tertiary phosphine ligand, are useful as catalysts in, for example, isomerisations (such as the REPPE synthesis), hydrogenations and dimerisations (such as the hydrodimerisation of acrylonitrile to adiponitrile).

Ruthenium(I1) Complexes as Selective Hydrogenation Catalysts PHILLIPS PETROLEUM CO. U.S. Patent 3,804,914 Cyclic polyenes are selectively hydrogenated to cyclic monoenes in the presence of a Ru(I1) catalyst complex having the general formula LnRUXm where L is a ligand, X is a halogen or hydrogen, n is 2,3 or 4, m is 2 or 3 and the sum of n f m is 4, 5 or 6, e.g. (Ph,),(CO),RuCl,.

Platinum Catalyst for Siloxane Curing WACKER-CHEMIE A.G. U.S. Patent 3,814,731 Polyorganosiloxanes in non-stick coatings are cured with a reaction product of H,PtCl, and a ketone.

JQHNSQN MATTHEY & CO. LTD.

MITSUBISHI CHEMICAL INDUSTRIES LTD.

MITSUBISHI CHEMICAL INDUSTRIES LTD.

RHONE-POULENC S.A.

Production of Carboxylic Acids

U.S. Patents 3,816,488 & 3,816,489 An improved process for the production of carboxylic acids by the reaction of ethylenically unsaturated compounds with CO and water uses catalyst compositions consisting of Rh compounds and complexes together with an iodide promoter in critical proportions, e.g. RhCl, promoted with HI, and I r compounds and complexes together with an iodide promoter in critical proportions, e.g. IrCl, and HI.

Preparing Linear Fatty Acids TEXACO INC. U.S. Patent 3,819,669 A process for preparing linear fatty acids and esters from alpha olefins and CO uses homogeneous Pt complexes, e.g. a Pt(AsPh,),-SnC12 system.

MONSANTO CO.

CHEMICAL TECHNOLOGY Electrolysis Electrodes HOOKER CHEMICAL CORP. British Patent ~,366,429 A new design of electrode has a sandwich structure in which the outer layers consist of slotted plates of a valve metal, e.g. Ti, coated with a Pt group metal or metal oxide (except 0 s ) .

GLASS TECHNOLOGY Ceramic Inductor W. L. MUCKELROY U.S. Patent 3,812,442 An inductor consists of a tape of ceramic material carrying a helical path of metal film, e.g. a Pt-Au- glass paste film.

ELECTRICAL AND ELECTRONIC ENGINEERING Electrodes for Acid Electrolytes

British Patent 1,360,255 Two electrically conducting bodies, e.g. Pt foil and a metal electrode base, are cemented together by an ethylene-unsaturated acid copolymer filled with an electrically conducting medium, e.g. Au, Pt, silvered Ti, gilded Ti, platinised Ti, etc.

Electron Discharge Heater G.T.E. SYLVANIA INC. British Patent i,366,007 A dark heater coating consists of Al, Zr or Be oxide coated with 2-2.546 W which is protected from oxidation by Pt or Ir.

Lead-based Alloys for Electrode

British Patent 1,369,707 Pb-based alloys used for solid or grid electrodes are further improved in their efficiency and life

BADISCHE ANJLIN- & SODA-FABRIK A.G.

BADISCHE ANILIN- & SODA-FABRIK A.G.

when they contain Pd as a component. A pre- ferred Pb alloy contains 0.05 to o.i5O/O of CU, 0.05 to 0.15~6 of Sn and 0.05 to 0.276 of Pd. In one example 0.i "/o of each of these was used.

Bilevel Thin Film Integrated Circuit

U. S. Patent 3,s i i,973 Bilevel thin film circuits having Au metallised through holes require protection from attack by Au conductor etchants. A new procedure for this involves plating an etch stop such as Rh or Pt on the walls of the through holes and around the entrance and exit ports. Since Rh plating is normally required in the fabrication of such circuits for solderable components, the through hole protection and Rh plating may be performed simultaneously.

Gold Alloy Metallisation for Capacitor Electrodes E. I. DU PONT DE NEMOURS & GO. US. Patent 3,817,758 Powder compositions useful in making ceramic capacitors electrodes and capacitors contain specific alloys of 5-15U/o Pt, 15-3oyh Pd and 60-807; Au.

BELL TELEPHONE LABORATORIES INC.


TEMPERATURE MEASUREMENT Implantable Thermopiles

British Patents 1,370,382-1,370,386 Thermopiles for use in human bodies contain a semiconductor thermoelectric wired up using a wire made of Au, Ag, Pt or their alloys.

Temperature Measurement BRITISH IRON & STEEL RESEARCH ASSOCIATION British Patent 1,370,465 Temperatures in steelmaking furnaces, for example, are measured by a couple formed by dissimilar metal conductors placed side-by-side in a refractory insulating matrix with a conducting path between their ends in the furnace. In one example, Pt and Pt-Rh conductors are embedded in magnesia.

High Temperature Thermocouple Alloy Systems t

U.S. Patent 3,817,793 A thermocouple system capable of delivering a substantially linear EMF response as a function of temperature up to 1800°C in a thermal neutron environment has a positive leg and a negative leg consisting of a Cr-base binary alloy having sufficient ductility to be drawn into wire form; the alloy contains 15-25 at.?; Ru, 15-20 at.% 0 s and the balance Cr.

NUCLEAR BATTERY CORP.

U.S. ATOMIC ENERGY COMMISSION

Documents

VOL. 19 JANUARY 1975 NO. 1 - Platinum Metals Review · A Honeycat Diesel Exhaust Purijier unit forming part of the exhaust train of a Ford- Stamford 40 kVA diesel alternator set assembled