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PLATINUM METALS REVIEW

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

VOL. 31 JULY 1987 NO. 3

Contents

Dr. Leslie Bernard Hunt 114

The Crevice Corrosion Resistance of Some Titanium Materials 115

New Air Pollution Control Unit 122

Platinum 1987 123

Noble Metals in Photography 124

Catalysed Reduction of Water by Ketyl Radicals 125

Coefficients of Thermal Expansion 132

New Platinum Analytical Standard 133

Palladium in a Modified Steel 136

The Use of Platinum Metal Complexes in Asymmetric Catalysis 137

A Fast Response Platinum-Iridium Thermocouple 144

Oxidation in Organic Synthesis 145

Abstracts 146

New Patents 155

Communications should be addressed to The Editor, Platinum Metals Review

Johnson Matthey Public Limited Company, Hatton Garden, London EClN 8EE

DR. LESLIE BERNARD HUNT 1906 - 1987

A TRIBUTE TO HIS MEMORY Leslie Hunt will be remembered not only with deep respect but also with great affection throughout the platinum-using industries of the world, to which he devoted the later part of his life. His single-minded commitment to the greater effective use of the platinum group metals has, perhaps, overshadowed his earlier contribution to the more general application of science to the needs of industry.

Born in Leicestershire, he graduated in chemistry from Imperial College, London, in 1927. In 1931 he was awarded the degree of M.Sc., and in 1934 he gained his doctorate for a thesis on “A Study of the Structure of Electrodeposited Metals”. While working for Vauxhall Motors Limited, Luton, Leslie Hunt gained wide metallurgical experience and published a number of scientific and technical papers.

He was editor of “The Metal Industry” for some years before joining Mallory Metallurgical Products in November 1937, where he was Technical Manager at the time that Johnson Matthey took a majority holding in that company. Relocated in Hatton Garden in 1939 his technical and commercial expertise were soon put to good use. After the war he was appointed manager of the newly created Industrial Division; with additional responsibility for salcs and technical publicity. In 1946 “Electrical Contacts”, his reference book for the electrical engineer was published.

During the mid-50s. in line with Johnson Matthey’s increasing desire to identify and exploit new opportunities for the use of platinum metals, Leslie Hunt proposed the publication of a specialist journal. Directed towards raising the level of awareness of the remarkable properties of the platinum metals, and demonstrating the industrial advantages of platinum tcchnology, the quarterly “Platinum Metals Review” was launched in January 1957, and Leslie Hunt continued as its editor until his tragic death earlier this year.

When he was appointed an Executive Director of Johnson Matthey in 1962, Leslie Hunt was given responsibility for all aspects of the Company’s research and development activities, a duty which he carried out with distinction until his retirement from the Executive Board in 1969.

His knowledge of the noble metals was put to further use when he was asked by thc Chamber of Mines of South Africa to found a journal similar to “Platinum Metals Review” to promote the industrial uses of gold. When “Gold Bulletin” was firmly established he was able to give more time to the history of science, an interest which had been growing for many years. Just one result of this was his complete revision of Donald McDonald’s “A History of Platinum and Its Allied Metals”, which is regarded as a modcl of scholarship in thc history of science and technology.

Thc grcat importance of the platinum metals to industry and to the well-being of the pcoplcs of the world is now an established fact. Leslie Hunt’s contribution to this achievement is immcasurablc. He was a man of high intellect combined with great personal charm. Without him the world is a poorer place.

Platinum Metals Rev., 1987, 31, (3), 114 114

The Crevice Corrosion Resistance of Some Titanium Materials A REVIEW OF THE BENEFICIAL EFFECTS OF PALLADIUM

By H. Satoh, K. Shimogori and F. Kamikubo Materials Research Laboratories, Kobe Steel Ltd., Chuo-ku, Kobe, Japan

The crevice corrosion that occurs on titanium in chloride solutions at elevated temperatures can constitute a serious problem. The resistance of three titanium materials to this form of corrosion has been evaluated by immersion and electrochemical tests. The results show that all three possess superior corrosion resistance to that of commercially pure titanium, and that the two which contain palladium are the best. On the basis of these tests, mechanical properties and in-service experience, guide lines for the advantageous use of these materials are proposed.

It is well known that one of the important properties of titanium is its immunity to both pit- ting corrosion and stress corrosion cracking in chloride solution, an environment which causes corrosion of stainless steels. Consequently titanium is used extensively for vessels in the chemical industries, and for heat transfer tubes in steam turbine condensers and multi-stage flashing type desalination plants. However titanium can suffer from crevice corrosion in hot chloride solution, and as titanium is com- monly used in such conditions this form of corrosion can constitute a practical problem.

For these reasons the effects of environmen- tal factors such as chloride ion concentration, temperature, and the pH of the solution on crevice corrosion have already been investigated ( I -4). Moreover, several methods of preventing crevice corrosion on titanium have been proposed, and some resistant materials have been developed. The most popular of these is titanium-0.15 per cent palladium (Ti-0. I 5Pd) (5). Currently titanium-0.3 per cent molybdenum-0.8 per cent nickel (Ti-o.3Mo-o.8Ni) is being investigated (6), because of its lower cost, while a mixture of palladium and titanium oxides (PdO/TiO , -Ti) is being applied to industrial equipment by a simple surface treatment. In this paper the

crevice corrosion resistance of these three materials is compared with that of commercially pure titanium (C.P. Ti).

Evaluation of Materials The test materials were in the form of sheet,

3 mm thick. Their chemical compositions are given in Table I. The procedure for coating titanium with palladium and titanium oxides has been reported previously (7). Methanol solution containing PdCl, and TiCl, was applied to the titanium, which had been prepared by sand blasting followed by pickling in hydrochloric acid. The surface was then oxidised to PdO and TiO, by heating in air for 10 minutes at a temperature of 6ooOC. The composition of the resulting coating was 70 molar per cent PdO and 30 molar per cent Ti0 , and the coating thickness 0.4 pm. Two types of specimen used for the immersion tests are shown in Figure I. The multi-creviced specimen (a) was prepared by bolting two PTFE (Teflon) spacers, each having 16 grooves on the contacting face, to the titanium sheet by means of titanium fasteners (8). A measure of the Occurrence of crevice corrosion in the metal/ Teflon crevices was obtained by comparing the number of crevices which suffered corrosion with the total number of crevices, namely 32.

Platinum Metals Rev., 1987, 31, (3), 115-121 115

ASTM Material grade

(8256)

Chemical composition, weight per cent

Fe 0, N, H, Mo Ni Pd Ti

Ti-0.1 5Pd G7 10.046 0.081 0.003 0 .003 - - 0 .16 Bal.

C.P. Ti G2

Ti-O.3Mo-O.8Ni G12

On the other hand, crevice corrosion in metal/metal crevices was determined using specimen (b), which consists of two titanium plates held together by titanium fasteners and Teflon spacers.

In addition, electrodes for electrochemical measurements were prepared by spot welding titanium lead wires onto specimen (b), or onto a piece of titanium sheet 15 mm x 20 mm. Apart from a I cm' test area, the surfaces were insulated with fluoric resin, and except for PdO/TiO,-Ti, the test areas were polished with abrasive paper before measurements were made.

After the specimens had been immersed in various boiling chloride solutions for several hours a visual check was made for crevice corrosion. To determine the initiation of crevice attack, the corrosion potentials (Ecor) of the test electrodes were measured continuously while they were in boiling chloride solutions, and the times for the potentials to shift sudden- ly to the less noble side were recorded.

The Occurrence of crevice attack on four different titanium materials/PTFE multi-creviced specimens, in boiling chloride solutions, is given in Table 11. From this it is clear that the resistance of the two alloys and the coated sample was much superior to that of commercially pure titanium. The surface appearance of the commercial titanium after crevice corrosion attack is illustrated in Figure 2. The effect of the pH value on the Occurrence of corrosion in a boiling 20 per cent sodium chloride solution is shown in Figure 3. The Occurrence on commercial titanium increased with decreasing pH and

- Bal. 0 .053 0.074 0.004 0 .002 - -

0.048 0.125 0.002 0 . 0 0 2 0.28 0 .87 - Bal.

reached 80 per cent at pH I. 5 . However in the pH range 6 to z the Occurrence was zero for the other three materials, but at pH I .5 the Occur- rence for the base metal alloy was 7 per cent. It is therefore suggested that the two palladium- containing materials were better than the other two in low pH solutions.

The variation in the corrosion potential of

I Multi-groovea)

Titanium t st piece A

Ti'tanium bolt P T F E spacer

Fig. 1 (a) The multi-creviced specimen consists of a titanium test piece, measuring 40 mm X 30 mm X 3 mm, to which two FTFE spacers 20 mm diameter and 8 mm thick are bolted. In each of the spacers, sixteen grooves are cut into the surface in contact with the test piece. (b) A titanium/titanium creviced corrosion specimen is made up of two 25 mm x 25 mm titanium pieces held together by titanium fasteners, separated from the test pieces by FTFE spacers

Platinum Metals Rev., 1987, 31, (3) 116

Table I

Chemical Compositions of Test Materials

commercial titanium and also of the Ti-o. 3Mo-o.8NiPTFE-creviced electrodes with time in a boiling solution of 42 per cent magnesium chloride is shown in Figure 4. The E,,, of the former showed a noble potential of about -0.4V at an early stage of immersion but the potential shifted abruptly to the less noble side after about I 5 hours, and steadied at about -0.6V. After 48 hours corrosion was visible, see Figure 5. Additional tests have shown that there is a correlation between the abrupt change in the E,,, and the onset of crevice corrosion; thus it was established that the time to initiation of crevice corrosion was 15 hours for commercial titanium/PFTE-creviced specimens. How- ever for the Ti-o.3Mo-o.8NiPTFE no abrupt change in the E,,, occurred, and no crevice corrosion was observed.

Using this technique, the time to initiation of the crevice attack on all four titanium materials was determined in boiling solutions of both sodium chloride and magnesium chloride; the results being given in Table 111. In magnesium chloride, Ti-o.jMo-o.8NiPTFE was subjected to attack after 168 hours, however no attack was observed on either of the palladium- containing materials, even after 240 hours. These results confirm the earlier findings of the immersion test.

The occurrence of crevice corrosion in titanium is attributable to C1- ion enrichment

C.P. Ti

Ti-O.3Mo-O.8Ni

Table II I Occurrence of Crevice Attack for

Titanium Materials in Boiling Chloride Solutions

(TiPTFE multi-creviced specimens)

I 20%NaCl(pH41 42%MgCI,

13 56

0 0

Material I 240 h 48 h

Occurrence of crevice attack, per cent

Ti-O.15Pd I 0 0 1

PdO/TiO.-Ti I 0 0 1

Fig. 2 After the immersion test for crevice corrosion, the surface of t h i s commercially pure titanium shows the intluence of the grooves cut into the contacting surface of the PTFE

and falling pH of the solution present in the crevice; this is followed by active dissolution of titanium in the crevice due to the breakdown of the passive film (9). As crevice corrosion resistance depends upon the maintenance of the passive state it is necessary to determine the critical hydrochloric acid concentration for depassivation. In th is study sodium chloride

L u

V

W

," 40- V

I!

w 20. 0 W

f O-

8 1 2 3 4 5 6 - .

pH OF SODIUM CHLORIDE SOLUTION

L

w 20. 0

8 1 2 3 4 5 6 - .

pH OF SODIUM CHLORIDE SOLUTION

Fig. 3 The occurrence of crevice attack is intluenced by the pH of the sodium chloride solution. These specimens were tested for 240 hours in 20 per cent sodium chloride solution at boiling point 0 C.P. titanium

Ti-0.3Mo-0.8Ni A Ti-0.15Pd A PdO/TiO,-Ti


Tabla 111

Time to Initiation of Crevice Attack for Titanium Materials in Boiling

Chloride Solutions (TilPTFE-creviced electrode)

Ti-O.BMo-O.8Ni

Ti-0.15Pd

I G%NaCI 20%NaCI

>720 >720 168

>720 >720 >240

(pH61 (pH41 42%MgCI, Material

Time to initiation of crevice attack, hours

C.P. Ti I 220 92 15

PdO/TiO,-Ti I >720 >720 >240

solution containing hydrochloric acid was used as the model solution.

Typical test results are given in Figure 6. Commercially pure titanium has a passive state potential up to o.06M hydrochloric acid concentration, but the Ecor shifts abruptly to the less noble side at o.o8M, and steadies at approximately -0.7V indicating the active state. This suggests that the critical hydrochloric acid concentration, for depassivation of commercial titanium is 0.07M. The results found for

I

0 10 20 30 40 50 TIME, hours

Fig. 4 The variation with time of the corrosion potential of two titanium materialPTFE-ereviced electrodes in 42 per cent boiling magnesium chloride solution is shown

Ti-o.3Mo-o.8NiY PdO/TiO,-Ti and Ti-o.15Pd were 0.8, 1.3 and I . ~ M , respectively.

The effect of solution temperature on the critical hydrochloric acid concentration is shown in Figure 7, where it is evident that the critical concentration for each of the materials decreases with increasing temperature. Thus:

Ti-o.IgPd = PdO/TiO,-Ti > Ti-o. 3Mo-o.8Ni% commercial Ti

Fig. 5 After 48 hours in a boiling solution of 42 per cent magnesium chloride this C.P. titaniumPTFE-creviced specimen (left) shows corrosion of the surface, while the surface of Ti-0.1 SPdPTFE-ereviced specimen after the test shows immunity from crevice corrosion (right)


The ability to maintain the passive state is highest for PdO/TiO,-Ti and Ti-o.15Pd, and this correlates with an excellent resistance to crevice corrosion.

In order to discuss the crevice corrosion resistance of the four test materials, anodic and

cathodic polarisation curves were measured in boiling IM sodium chloride + IM hydrochloric acid solutions. The test results are presented in Figure 8. The E,,, of commercial titanium was - 0.67V, and a high current peak corresponding to active dissolution was observed in the anodic

- U

F Q I 1

WO/Ti02-Ti

0 - g -0.8 0 1GZ lo" 100 a

U HYDROCHLORIC ACID ADDITION, M

Fig. 6 The corrosion potentials of four titanium materials in boiling 1 M sodium

T i - 0 . 3 M o -0.8Ni-

50 60 70 80 90 1 0 0 TEMPERATURE.'C

chloride solution are shown- to vary with hvdrochloric acid addition (free-surface Fig. 7 The influence of temperature

upon the critical hydrochloric acid con- electrode)

Fig. 8 Polarisation curves are ahown for four titanium materials in boiling 1 M sodium chloride with 1 M hydrochloric acid. The corrosion potentials of both Ti-0.15Pd and Pd01Ti02-Ti, where no anodic peaks occur, are more noble than those of C.P. titanium and Ti-0.3 Mo-O.8Ni

C.P. titanium . Ti-O.3Mo-O.8Ni A Ti-O.15Pd A PdO/TiOz-Ti

ckntration for the depassivation of four titanium materials in deaerated 1 M sodium chloride solution is shown. For each material the critical concentration decreases with increasing temperature

1

POTENT1AL.V ve~-5u5 Ag/AgCI


Tabla IV

Result of Crevice Corrosion Test for Creviced Specimens in Boiling 20 per

cent Sodium Chloride Solution of pH4 for 240 hours

Material

Ti-O.3Mo-O.8Ni

Crevice specimen assern bly

Situations where Maximum Advantage is Gained

Mechanical conditions Chemical Environment Remarks

Fixed or changing, can Only slightly High-temperature withstand abrasion aggressive strength

C.P. Ti with C.P. Ti

Application Material

Process Equipment

Ti-O.3Mo-O.8Ni Oil refinery Shell and tube heat exchanger

Ti-0.15Pd Salt purification Concentrator

Occurrence of crevice attack

Coupled Ti

C.P. Ti material

Service conditions Condition in the (possibility of crevice crevice corrosion in C.P. Ti)

Hydrocarbon+CI- Not fixed, scale 90- 1 7OoC is deposited (Critical)

CI- 220%. pH2 120- 13OOC deposited (Probable)

Not fixed, salt is

Severe Severe

PdO/TiO,-Ti

None None

Fertiliser Mono-tube heat CI-=30%, pH5 Fixed at the exchanger 130- 14OOC flange/gasket

(Possible) junction

polarisation curve. For Ti-o.3Mo-o.8Ni, E,, was -0.55V which was more noble than that of commercial titanium and the anodic current peak and cathodic polarisation were lower than that of commercial titanium. Consequently it can be considered that the corrosion resistance of this material is improved by suppressing anodic dissolution and decreasing cathodic polarisation. In contrast, the corrosion potential of Ti-0. I gPd and PdOiTiO, -Ti were more noble than those of the other two materials and no anodic peaks were observed. These phenomena were attributable to enrichment of the Ti-o.IgPd surface with metallic palladium (10) and to the low hydrogen overvoltage of the palladium and PdOiTiO films; which explains

Table V

Effective Application of Crevice-Corrosion-Resistant Titanium Materials I

Ti-0.1 5Pd Fixed or changing, can Aggressive Excellent service withstand abrasion performance

Pd01Ti0, -Ti Fixed, abrasion must Aggressive Coating is simple to I be avoided


Table VI

Typical Examples of Industrial Application of Crevice-Corrosion-Resistant Titanium Materials

C.P. Ti with Ti-O.3Mo-O.ENi

C.P. Ti with Ti-0.15Pd

C.P. Ti with PdO/TiO,-Ti

Slight None

None None

None None

why these two materials show such excellent resistance to crevice corrosion.

In chemical equipment, such as heat exchangers and reactors, crevices may occur between commercial titanium and dissimilar titanium materials. For example when commercial titanium and Ti-o.15Pd are used as tube and tube plate materials, respectively, in a heat exchanger crevices occur at the junctions of the tubes and the plates. In such situations the restraining effect of the Ti-o. 15Pd against the corrosion of the commercially pure titanium is of considerable practical importance. For this reason, immersion tests on creviced specimens of commercial titanium/dissimilar titanium material were carried out in boiling 20 per cent sodium chloride solution (of pH 4). For commercial titanium coupled with Ti-o. 15Pd or PdO/TiO,-Ti no crevice corrosion was observed, however commercial titanium coupled with Ti-o.3Mo-o.8Ni showed slight corrosion of the commercially pure titanium although the Ti-o.3Mo-o.8Ni was immune, as shown in Table IV. The results also show that the two palladium containing materials were superior to Ti-o.3Mo-o.8Ni for preventing crevice corrosion of the commercial titanium.

Differences exist amongst the titanium materials evaluated; the main features being summarised in Table V.

Although the corrosion resistance of Ti-o.3Mo-o.8Ni is better than that of commercially pure titanium, it is inferior to both Ti-o.15Pd and PdOiTi0,-Ti. It has good mechanical properties at elevated temperatures enabling it to be used in more highly stressed designs than commercial titanium (I I). In addition it is less expensive than Ti-o. I gPd.

Titanium-0.15 per cent palladium has the best resistance to corrosion and it has been used in actual equipment for periods of 20 to 25

years without any serious crevice corrosion problems. Therefore it is recommended for use in severely corrosive environments when high reliability against crevice corrosion is necessary.

The third material is not homogeneous, but a composite of commercial titanium protected against corrosion by a thin coating of oxides.

Because this coating is simple to apply, fabricated components as well as plate, wire and tube can be treated. The corrosion resistance of coated material is the same as that of Ti-o.~gPd, but because the coating is thin degradation by mechanical erosion, which could be caused by flowing liquids, must be avoided. One application for this coating is for the flanges of reactors and for the joints of tubes and tube plates in heat exchangers.

Typical industrial applications of the titanium materials which are resistant to crevice corrosion are listed in Table VI.

Conclusion The crevice corrosion resistances of

titanium-0.3 per cent molybdenum-0.8 per cent nickel, titanium-o. I 5 per cent palladium and titanium coated with a mixture of palladium and titanium oxides have been evaluated and guide lines for the optimum use of these materials are proposed, on the basis of their resistance to corrosion, their mechanical properties and on in-service industrial experience. If these factors are taken into account then titanium materials can be used effectively, without crevice corrosion.

References I K. Shimose and A. Takamura, J . Jpn. Inst.

Met . , 1965, 29, 416 2 N. G. Feige and T. J. Murphy, Proc. NACE,

1969, Paper No. 7 3 K. Shimogori, H. Satoh and H. Tomari, J .

Jpn. Inst. Met., 1987, 42, 567 4 S. Tsujikawa and F. Iki, Proc. Annu. Conf.

Corros. Eng., (Jpn.), 1987, p.165 5 A. Takamura, Corrosion, 1967, 306 6 L. C. Covington and H. R. Palmar, “Corro-

sion and Biomedical Applications of Titanium”, Detroit, Michigan, 1974, Oct. 21 -24

7 T. Fukuzuka, K. Shimogori, H. Satoh and F. Kamakubo, “Titanium ’80 Science and Tech- nology’’, Proc. 4th Int. Conf. on Ti, ed. H. Kimura and 0. Izumi, Kyoto, 1980, p.2631

8 D. B. Anderson, ASTM STP 567, 1976, p.231 9 H. Satoh, F. Kamikubo, K. Shimogori and T.

Fukuzuka, Corns. Eng., urn.), 1983, 32, 69 10 M. Stern and H. Wissenberg, J. Electrochem.

SOC., 19599 106, 759 R. W. Schutz, J. A. Hall and T. L. Wardlaw, Proc. 30th Anniversary Symp. of Japan Titanium Society, Kobe, Japan, 1982, p.73

Platinum Metals R e v . , 1987, 31, (3) 121

New Air Pollution Control Unit PLATINUM CATALYST MAKES POSITIVE CONTRIBUTION TO THE EUROPEAN YEAR OF THE ENVIRONMENT

For over one hundred and fifty years the atmospheric pollution resulting from manufacturing processes has been recognised as a problem. However, all too frequently dilution of the offending substance with air has been considered to be a satisfactory solution which could be achieved relatively cheaply by ex- hausting the pollutants from a high stack, resulting in their dispersal over a wide area. Now an increasing scientific and public awareness of the short- and long-term effects of atmospheric pollution on all forms of life, and a greater appreciation of the fact that national boundaries do not provide a barrier to such pollution, has resulted at last in trans-national action to control industrial pollution more effectively.

One such initiative is the European Year of the Environment, and to coincide with this the Catalytic Systems Division of Johnson Matthey has launched its mobile Honeycat@ Pilot Trial unit. Based upon long established catalytic

principles, the unit incorporates technology that has been proven in a wide range of industrial processes which produce hydrocarbon emissions that are malodorous or noxious. These include ceramic and fibre manufacture, chemical processing, food processing, metal and paper coating and printing, and plastic, resin and rubber coating, extrusion and moulding.

Although the use of platinum oxidation catalysts for air pollution control was noted in the first volume of this journal, in 1957, and has been the subject of several articles since, none the less many organisations apparently do not appreciate that the technology does exist to remove offending contaminants from industrial waste gases in an effective manner. For this reason the Honeycat@ pilot trial is carried out on the premises of a potential customer where process conditions can be monitored accurate- ly. A representative sample withdrawn from the exhaust gas is passed over a Honeycat@ catalyst

The Honeycat@ mobile pilot unit is designed for a full site trial, and once located close to the process gas outlet it only requires connection to an electricity power supply


The platinum metals catalyst formulation is dispersed over the surfaces of the ceramic honeycomb support, providing the maximum reaction surface with the smallest possible volume. This configuration ensures high catalyst activity and minimum pressure drop within the Honeycat@ unit

where the organic components of the gas are destroyed by low temperature oxidation, yielding harmless carbon dioxide and water vapour. The catalyst unit consists of a frnely divided platinum metals formulation supported on a ceramic honeycomb, to ensure that the surface area of a given weight of catalyst is max- imised, and that there is little resistance to the flow of gas through the unit. While it is generally necessary to pre-heat the catalyst to the required operating temperature the fuel required

is significantly less than that required for thermal incineration of the pollutants.

By analysing the process exhaust gas composition and its temperature and flow characteristics a pollution control system incorporating a platinum metals catalyst can be designed which is optimised to meet the specific requirements of both the process and the plant. This is only one of the ways in which the platinum metals are contributing to an im- provement in the quality of life.

Platinum 1987 The third annual survey of commercial

aspects of the platinum group metals has just been published by Johnson Matthey. Well supported by statistical data, “Platinum 1987” concentrates on the events of 1986 that affected the six platinum group metals, and outlines the prospects for 1987, and beyond. Compiled from numerous sources, the 63 page review considers exploration and mining, prices, supply, major uses of the metals, demand for different purposes-and in the case of platinum and palladium demand by geographical region. While the emphasis is on these two metals, rhodium, ruthenium, iridium and osmium are also included.

In a year when the requirement for platinum for automobile emission control catalysts first exceeded I million troy ounces, and when the electronic industry in Japan consumed 750,000 troy ounces of palladium, record levels of demand for platinum, palladium and rhodium were closely matched by supplies of primary metals.

Readers of Platinum Metals Review who do not have ready access to a copy of “Platinum 1987”~ and who wish to receive one, should write to the compiler: Mr. G. G. Robson, Johnson Matthey P.L.C., New Garden House, 78 Hatton Garden, London ECIN 8JP.


Noble Metals in Photography

The history of the use of platinum in early photography has been described in this journal previously (I). In Great Britain the use of platinum metals in photography virtually ceas- ed at the time of the First World War; however, in the U.S.A. the tradition did not die out completely and it enjoyed a modest revival in the 1970s. The work of American photographers sparked an interest in other countries, including Great Britain. Among those drawn to the beauty and delicacy of platinum prints was Dr. Michael J. Ware, a lecturer in the Depart- ment of Chemistry at the University of Man- Chester. In recent articles he describes how he became attracted not only by the quality that could be obtained, but also by the chemical and practical principles behind the process (2 ) . He found that the techniques being used to produce the platino- and palladio-type prints were virtually identical to those employed in the late nineteenth century, so he set about bringing the technology up to date and understanding the chemistry governing image quality. (3).

The principle of platino- and palladio-type systems involves a first step in which a photosensitive material, normally an oxalato complex of Fe(III), for example ammonium trisoxalato ferrate(III), is photochemically reduced in the presence of ultraviolet light to yield the corresponding Fe(I1) species:

2 IFe (C,O,),l’- +

2 IFe (C,O,),I?- + C,O,’- + 2CO? (I)

The Fe(I1) complex thus formed is a powerful agent, readily reducing appropriate compounds of platinum, palladium and gold. In practice it is important to use the more labile complexes of the platinum metals to enable the metal image to develop in short times:

PtC1,’- + 2 [Fe (C?O,),l? ~ + 2C,04’- - Pt” + 2 IFe (C,O,),l’- + 4Cl- ( 2 )

Choice of paper (high alpha-cellulose) and its absorbency are important factors in producing successful prints. The sensitiser solution, con-

PLATINO-TYPE PRINTS OFFER PERMANENCE

Platinum Metals Rev., 1987, 31, (3), 124

taining the Fe(II1) complex and platinum, palladium or mixed palladium/platinum salts, is carefully applied to the paper which is then dried. However, water plays a significant part in the subsequent procedure. If the paper is equilibrated at 80 per cent relative humidity (RH) the image needs no wet development after exposure, while below 50 per cent RH considerable development is required. It is postulated that at 80 per cent RH the paper will contain typically 10 per cent by weight of water which is sufficient to confer limited mobility on the sensitiser ions; thus as the Fe(I1) ions are produced by exposure to ultraviolet light of an appropriate wavelength they are able to react with the platinum or palladium ions immediate- ly. However, below 50 per cent RH there is in- sufficient absorbed water to allow this, and therefore a separate development step is necessary. A particular advantage of the direct “printing out” process is that the print can be examined at intermediate stages of the exposure-particularly if specific effects of tone or texture are sought-then returned for further exposure if this is desirable.

In the second of his two part article in the British Journal of Photography, Ware describes the process for people wishing to try platinum- palladium printing for themselves (2 ) .

One advantage of platino-type prints is their permanence, platinum and palladium being more noble than silver. Furthermore, the prints do not contain organic materials such as gelatine which can nourish fungi and moulds. Therefore, use of the process for archival material could be important. D.E.W.

References I I. E. Gxtington, Platinum Metals Rev., 1984, 28,

2 M. J. Ware, Brit. 3. Phorogr., 1986, 133, (6583),

3 M. J. Ware, 3. Photogr. Sc i . , 1986, 34, (5/6), 13

( 4 , 178

1165; 133, (6584), 1190

124

Catalysed Reduction of Water by Ketyl Radicals By Anthony Harriman Davy Faraday Research Laboratory, The Royal Institution, London

Ultraviolet irradiation of a wide variety of ketones in aqueous solution containing a low concentration of an alcohol results in the formation of the two corresponding ketyl radicals, which are strong reducing agents. In the presence of colloidal platinum particles, these radicals will reduce water to hydrogen gas with high overall quantum efficiency. This is a general reaction, able to operate in sunlight, for which the mechanism is discussed in detail. The importance of the colloidal catalyst is stressed and, by changing the catalyst, different reaction products are obtainable.

Over the past decade or so, photochemists have become increasingly more aware of the interesting possibilities offered by the incor- poration of colloidal catalysts into their reaction mixtures. The nature of the reaction products can be changed markedly by using different types of colloidal catalyst and, indeed, useful products can be obtained from seemingly wasteful reactions. This situation is best exemplified by the photochemistry of benzophenone in aqueous alcohol solution. Under normal conditions, ultraviolet irradiation of benzophenone results in quantitative popu- lation of the lowest energy excited triplet state; which is of n,?r* character and which rapidly abstracts a hydrogen atom from the alcohol. The resultant ketyl radicals undergo addition andlor disproportionation reactions and benzpinacol is formed with high quantum yield.

2Ph,CO* + RCH,OH = Ph,C(OH)C(OH)Ph, + RCHO (i)

However, when the photolysis is carried out in the presence of small amounts of colloidal platinum, benzpinacol formation is inhibited and copious yields of hydrogen are obtained (I). This change arises because the intermediate ketyl radicals are powerful reducing agents and can reduce water to hydrogen on the surface of the platinum colloid (2 ) . Similar reactions are observed with other ketones having lowest energy n,?r* excited states, including acetone

(3), and with other metal colloids, including gold and iridium (4).

This type of reaction scheme is fairly general and, in principle, could be applied to the conversion and storage of solar energy. To do this successfully it is necessary to manufacture extremely effective colloidal catalysts since the colloid must be able to intercept the ketyl radicals before they combine together in the bulk solution. Also, it should be realised that the production of hydrogen, although attractive, might not be the most appropriate means of energy conversion under the circumstances. There is, therefore, a need to make the overall reaction more versatile and this can be achieved by changing the type of colloid used as the catalyst.

The Photosystem Water-soluble benzophenone derivatives are

readily available (9, a typical structure being shown below:

0 I1

This compound (I) and its close relatives absorb less than 5 per cent of the total energy available in sunlight and require ultraviolet excitation


>;-OH + \ * ,C-OH

’d ‘C=O + H + I

H2

H+ +>C=O

Fig. 1 The overall reaction scheme for the photochemical dehydrogenation of alcohol by benzophenone in dilute aqueous solution containing colloidal platinum is shown. This reaction operates at a sunlight conversion efficiency of about 1.7 per cent

(6) but the lowest energy triplet state, which is of n,r* character, is formed with unit quantum efficiency. Ultraviolet irradiation of I in water containing 4 per cent ethanol results in quantitative formation of the benzpinacol and acetaldehyde, and the intermediate formation of the benzophenone ketyl radical can be detected by flash photolysis techniques.

Ph,CO* + CH,CH,OH =

Ph,COH + CH,CHOH (ii) 2Ph,COH = Ph,C(OH)C(OH)Ph, (iii)

2CH,CHOH = CH,CHO + CH,CH,OH (iv) Addition of colloidal platinum (2 x IO+

mol/dm3) to the above solution causes evolution of hydrogen upon irradiation. The reaction mechanism for this is pictured in Figure I and, under optimised conditions, the quantum yield for formation of hydrogen was found

to be 0.34 (7). The initial reaction involves abstraction of a hydrogen atom from an ethanol molecule by the triplet excited state benzophenone derivative. This produces two ketyl radicals within a solvent cage. Geminate recombination can occur to reform the original reactants but some of the radicals escape from the cage into the solvent bulk. Radical recombination and addition reactions can occur in the solution but these bimolecular processes are in competition with electron transfer to a platinum particle. The particle functions as a microelectrode and accepts an electron from each ketyl radical. This oxidises the ketyl radical to the corresponding carbonyl compound, hence recycling the benzophenone, and stores electrons on the colloid. Discharge of the platinum colloid occurs via the reduction of surface-bound protons so that hydrogen gas is evolved and the overall reaction corresponds to the photochemical dehydrogenation of ethanol.

C,H,OH = CH,CHO + H? (V)

This overall reaction stores some 42 kJ/mol but, since the benzophenone derivative collects such a small fraction of the incident sunlight, it operates with only a low sunlight conversion efficiency (about 1.7 per cent). Of course, this is a problem as far as developing the system for practical purposes is concerned, but to some degree, it is offset by the simplicity and versa- tility of the system. This situation is exemplified by the experimental results collected in the Table. Here, the quantum yields for formation of hydrogen, @PH,, have been measured for a variety of different organic substrates (7). It is clear that almost any hydrogen containing organic material can be photodehydrogenated under such conditions. The turnover numbers refer to the ability of the benzophenone to be recycled before pinacol formation finally destroys it. The relatively high numbers obtained show that the platinum colloid used in these experiments is extremely efficient at intercepting the intermediate ketyl radicals and directing them towards water reduction. The limiting yields of hydrogen obtainable upon ex- haustive photolyses are impressive and compare favourably with all other photosystems

Plarinum Metals Rev., 1987, 31, (3) 126

reported to date. Also, it should be noted that the reaction employs only low concentrations of organic materials. With efficient donors, the required concentration of organic substrate is only about I per cent vlv in aqueous solution. This is the order of concentration that might be fcund in effluents from industrial processes and the photosystem could be used to p u r e water supplies.

Some other water-soluble benzophenone derivatives can be used in much the same manner as reported here for I ( 5 , 6). These compounds are cheap, easily prepared on a large scale, non-toxic and relatively stable. Opportunities do exist for improving their light harvesting properties without detracting from their high efficiencies. Indeed, we are actively engaged in modifying the structure of the benzophenone photosensitiser in order to collect a much higher fraction of the solar spectrum.

The Catalyst It is important that the catalyst is able to

intercept ketyl radicals generated in the bulk solution before they react with each other. This

kinetic problem can be solved by careful control of the light intensity and concentration of each reactant in such a way that the steady-state concentration of ketyl radicals is kept at a minimum. To ensure high rates of hydrogen formation, it is necessary to use high concentrations of catalyst and this is best achieved by employing ultrafinely dispersed particles. In- deed, for a given molar concentration of platinum the pseudo first order rate constant for trapping a ketyl radical (k , ) can be expressed in the following form:

k, = 0.027D (Pt)/R* (vi) Here, D is the diffusion coefficient of the ketyl radical (D = 8 x I O - ~ cm*/s) and R is the radius of the platinum particle (expressed in nm). It is seen clearly that k , increases with decreasing particle size. Thus, smaller particles give a definite advantage in this type of competitive reaction system.

Producing small particles is not the only means of ensuring that the catalyst can intercept self-annihilation of the reducing radicals. And, by the same reasoning, having small particles does not guarantee that trapping will be

Table

Efficiency of Hydrogen Generation upon Ultraviolet Irradiation of Compound I in Nitrogen-Saturated Aqueous Solution at pH9

Containing Colloidal Platinum (2 x lo4 molldm3) and a Donor (usually 4 per cent v/v)

Donor

Triethylamine Ethylamine Diethylamine Methanol Ethanol lsopropanol Tert-butanol Lactic acid Acetamide Glucose Acetonitrile Acetaldehyde Acetic acid

Quantum yield of hydrogen

W i *

1.03 0.53 0.09 0.24 0.34 0.32 0.23 0.13 0.12 0.10 0.075 0.014 0.0002

Turnover number

112 112

55 125 139 83

105 81 63 56 54 18

1

Hydrogen (0.01 rnol/dm3)

5.6 5.6 2.7 6.3 6.9 4.1 5.3 4.0 3.1 2.8 2.7 0.9 0.6


Platinum Metals Rev., 1987, 31, ( 3 )

Fig. 2(a) This electron micrograph shows freshly prepared colloidal platinum particles. The colloid is stable against flocculation for several months

Fig. 2(b) (below) A high resolution transmission electron micrograph of a colloidal platinum particle showing the arrangement of the platinum atoms within the lattice. Further details are given in (12)

128

effective. Consideration must be given to other factors, especially electrostatic forces and radical mobility. The colloidal particle will carry a surface charge due to ionisable groups. The sign and magnitude of this charge can be varied by pH and by adsorbing charged sur- factants to the metal surface. In this way, charged radicals in the bulk solution will be attracted to or repelled from the colloid surface. In general, it is not good policy to use strong electrostatic forces to attract radicals of the opposite charge to the colloid. This is because the catalyst surface becomes coated with highly reactive intermediates, such as hydrogen atoms, during the reaction. These species react with most organic and inorganic compounds, either to short-circuit the overall reaction or to reduce unsaturated bonds. The importance of these side-reactions is increased markedly in cases where the contact time between catalyst and reactant is increased by electrostatic binding (6).

Also, when considering the problems of kinetic control of the reaction balance, some thought should be given to the mobility and electron transferring properties of the reducing radical. For example, ketyl radicals generated by hydrogen atom abstraction are produced in very close proximity such that their interaction is favoured. Unless the radicals can freely migrate away from each other recombination will dominate. The ease of mobility is expressed by the diffusion coefficient D in Equation (vi) and it is related to the solvent viscosity and the molecular volume of the ketyl radical. Further- more, it is desirable that electron transfer to the colloidal particle occurs with high efficiency so that each encounter transfers an electron to the particle (8). If the electron transferring properties of the reducing radical are poor, due to a large reorganisation barrier or slow self- exchange rates, many encounters between a radical and a colloidal particle might be needed before electron transfer occurs. Competitive addition or dimerisation reactions might dominate over electron transfer in such cases, even if the reaction conditions favour encounter with a catalyst particle.

A further point to take into account concerns the actual structure of the colloidal particle. It is possible that much of the surface is inert due to adsorbed surfactant or unreactive groups. Electron transfer will occur only at clean metal surfaces and this introduces the concept of “active sites”. For such catalysts, a reducing radical might have to encounter many different particles before it finds an active site where it can disgorge its electron.

Ultrafine Colloidal Particles It is now possible to produce ultrafine dis-

persions of many different metals by controlled hydrolysis and reduction of the corresponding metal salts. Extremely small particles (R<r.o nm) are afforded by gamma radiolysis of the metal salts in aqueous alcohol solution under an inert atmosphere (8-10). Slightly larger, but still very finely dispersed, colloids are obtained by reduction with citrate ions in water at elevated temperatures (I I). We have found that reduction of sodium hexachloroplatinate (8 x 10-‘ mol/dm’) in neutral water with sodium citrate (3 x 10-’ mol/dm’) at 7ooC occurs over 3 to 4 hours. After cooling over- night, the excess citrate ions can be removed by ion-exchange chromatography and the colloid protected by a low molecular weight poly- ethyleneglycol. The resultant colloid, which is stable against flocculation over many months standing, has an average particle radius of only 0.7 nm, as determined by high resolution electron microscopy. This is shown in Figure 2(a).

Recently, the structures of platinum and gold colloids were studied by transmission electron microscopy (12). It was shown that the platinum colloids are highly crystalline with the interplanar spacings, atomic environments and degree of translational symmetry as expected for crystalline bulk platinum electrodes. How- ever, the colloids show a high tendency for micro-twinning and there is considerable surface roughness. Such factors can be seen by close examination of the high resolution electron micrograph shown as Figure 2(b).

Colloids of other metals, such as gold, silver, thallium, iridium, ruthenium, palladium and


nickel, can be produced by similar methods. In general, the average particle sizes and distribu- tions depend upon the rate of reduction of the metal salt and upon the nature of the metal. For example, under the same experimental conditions, colloids of platinum and iridium tend to give very small particles with average radii of 0.7 to 1.0 nm, colloids of silver tend to be somewhat larger with average radii 3.0 to 4.0 nm and colloids of gold possess radii around 6.0 to 7.0 nm. The crystal structures of these colloids are being studied by high resolution electron microscopy and, very recently, bimetallic particles of gold and platinum have been prepared in colloidal form (I 3).

All the above colloids show catalytic properties and many are efficient catalysts for pro- moting the reduction of water to hydrogen. In particular, colloids of platinum or iridium favour hydrogen evolution when brought into contact with reducing species, such as ketyl radicals. Kinetic parameters associated with these reactions can be obtained from pulse radiolysis or flash photolysis studies and are useful for optimising experimental conditions.

Interfacial Electron Transfer Once the reducing radicals reach the surface

of the colloidal particle, an electron transfer reaction can occur. This reaction must take place across a liquidlsolid interface, as occurs in conventional electrochemistry. As such, it seems appropriate to consider the particle as a microelectrode and to describe the redox reaction in electrochemical terms. Two aspects of the overall reaction should be considered; namely, charging the particle with electrons and discharging the particle by transferring the electrons to protons or other reagents in the bulk solution. Kinetic parameters associated with the charging process are readily obtainable by pulse radiolysis methods and there have been many such studies. It is more difficult to follow the discharge process but some success has been obtained from time-resolved cpnduc- tivity studies.

Both the benzophenone ketyl radical and the r -hydroxyethyl radical produced in Reaction

(ii) are powerful reducing species that are thermodynamically able to reduce water to hydrogen. The two radicals donate electrons to colloidal platinum particles at the diffusion controlled rate limit, at least in neutral aqueous solution. The rate constants for these electron transfer reactions have been evaluated by pulse radiolysis studies (3, 6). Thus, the ketyl radical derived from I, which retains a single positive charge in neutral solution, can be monitored by optical absorption spectroscopy since it absorbs at 540 nm. Decay occurs by second order kinetics, due to rapid dimerisation (k, = 4.8 x xo8 dm’/mol/s), with a half-life of about I ms. The addition of colloidal platinum increases the rate of decay but the kinetics remain complex until the concentration of added platinum exceeds about 10-‘

mol/dm3. Using a platinum concentration of 2 x 10-‘ mol/dm3, the observed half-life of the ketyl radical is only 85 ps. This suggests that all the ketyl radicals are trapped by the platinum particles under such conditions. In contrast, a ketyl radical bearing a single negative charge under identical experimental conditions had a half-life of 1.25 ms and cor- responded to only 25 per cent trapping.

The platinum colloid used in these experiments had a particle radius of I .o nm, as determined by electron microscopy. This means that there is an average of 280 platinum atoms clustered into a single particle. Taking this factor into account, the bimolecular rate constant for interaction between the particle and a ketyl radical derived from I was 1.4 x I O I O

dm’ /mol/s. This interaction is assisted by electrostatic terms since the platinum colloid has a negative surface charge. Consequently, the bimolecular rate constant for the corresponding reaction with a negatively charged ketyl radical was found to be some twenty times lower.

This interfacial reaction involves transfer of an electron from a ketyl radical to the platinum particle. The added electron can migrate around the crystalline platinum particle or it may be trapped at the surface in the form of a hydrogen atom by reaction with an adsorbed


proton. Further electrons can be added to the same platinum particle, although the rate constant for the electron transfer step may depend upon the number of electrons already residing on that particle. These accumulated electrons may be discharged by reduction of adsorbed protons to hydrogen. Where many electrons are added to a single particle, the discharge process will be intraparticle but in cases where few electrons are stored on a single particle, that is when high concentrations of catalyst are used, discharge may involve an interparticle reaction.

It is important to bear in mind that the particles may be discharged in ways other than via the reduction of surface bound protons. Thus, easily reducible substrates present in the system are liable to be reduced in preference to hydrogen liberation. This becomes especially important as the hydrogen evolution reaction proceeds since the platinum particles retain a number of hydrogen atoms on the surface which can be added to unsaturated groups.

Reaction Products The above photosystem has been optimised

for the generation of hydrogen. Over the early part of the reaction at least, the benzophenone photosensitiser is recycled and it is not destroyed. During the later stages of the reaction, when the catalyst is charged with hydrogen atoms, the benzophenone is reduced to the corresponding alcohol. This stops further hydrogen evolution since the alcohol is not photoactive. As shown by Equation (v), the evolved hydrogen comes from the organic donor and, as such, the system is sacrificial. The advantage of the present system is that it is extremely simple and it will operate with a very wide range of donors, some of which are genuine waste products. It is not dependent upon any particular type of donor or pH, and

products. With an alcohol as donor, the reaction forms an aldehyde which can be treated with ammonia to give a primary amine. The aldehyde will also react with hydrogen cyanide and subsequent hydrolysis will give a hydroxy- acid. Further reaction with hydrogen cyanide and an amine permits formation of simple amino acids. Thus, a whole range of simple organic products are possible and the overall system has some interest as a model for the primordial synthesis of complex organic matter.

When platinum or iridium colloids are used to trap the intermediate ketyl radicals, the major reaction product is hydrogen, as described above. This is because these metals possess extremely low overpotentials for hydrogen evolution. Consequently, as soon as electrons are added to a particle they are discharged via hydrogen formation and, at any given time, there will be very few electrons stored on a particular particle. However, with other metal colloids this need not be the case. For example, gold colloids favour hydrogen liberation but silver colloids show a higher overpotential for hydrogen evolution and will exist for a finite time in aqueous solution with many tens of electrons stored on a single particle. Colloids of cadmium or thallium show even more resistance towards hydrogen liberation and many hundreds of electrons will reside on a particle. Upon addition of suitable substrates, these electrons can be discharged and used to drive multielectron reductions. Of particular importance are the reductions of carbon dioxide, on ruthenium colloids, and nitrate ions, on silver colloids. It is possible that future work will lead to the development of a system able to reduce nitrogen to ammonia, a reaction of tremendous significance.

it is not easily poisoned so that a mixture of waste organic materials could be fed into a

seems Dossible that a Dractical svstem could be

Acknow,edgemente I thank the S.E.R.C. for financial support of this

discussions. The electron micronraDhs were recorded reactor charged with the Photosensitiser. It work and Professor J. M. Thomas for many helpful

developed based on t6is type 0; photosystem. by Dr. G . R. Mil1ward Of the-Uhiversity Of Cam- bridge and the pulse radiolysis studies were made in Dehydrogenation Of the Organic donor collaboration with Dr. p. Nets of the National

in principle, give rise to some interesting Bureau of Standards, Washington DC.


References

I C. K. Gratzel, and M. Gratzel, 3. Am. Chem. SOL.,

2 L. Nadjo and J. M. Saveant, 3. Electroanal.

3 A. Henglein, B. Lindig and J. Westerhausen, 3. Phys. Chem., 1981, 85, 1627

4 A. Henglein in “Modern Trends of Colloid Science in Chemistry and Biology”, ed. H.-F. Eicke, Birkhauser Verlag, Stuttgart, 1985, p. 126

5 A. Bonarny, J. P. Fouassier, D. J. Lougnot and P. N. Green, 3. Polym. Sci., Polym. Lett. E d . , 1982, 20, 315

6 A. Harriman, 3. Chem. SOC., Faraday Trans. II,

1979, 101, 7741

C h e w 1971, 33,419

1986, 82, 2267

7 P. N. Green, W. A. Green, A. Harriman, M. C. Richoux and P. Neta, 3. Chem. SOL., Faraday Trans. I I , submitted for publication

8 A. Henglein, 3. Phys. Chem., 1979, 83, 2209 9 M. 0. Delcourt, N. Keghouche and J. Belloni,

10 J. Belloni, M. 0. Delcourt and C. Leclere, Nouv.

11 G. C. Bond, Trans. Faraday SOC., 1956, 52, 1235 12 D. A. Jefferson, J. M. Thomas, G. R. Millward,

K. Tsuno, A. Harriman and R. D. Brydson, Nature, 1986, 323, 428

13 G. R. Millward, P. A. Sermon, K. Keryiou and J. M. Thomas, in preparation

Nouv. J . Chim., 1983, 7 , 131

3. Chim., 1982, 6 , 507

Coefficients of Thermal Expansion NEW DATA ON PLATINUM AND PLATINUM-RHODIUM ALLOYS

The importance of an accurate knowledge of the properties of key reference materials such as platinum and its alloys has been emphasised here previously (I). For example, accurate values of thermal expansion are required in high temperature “constant volume” gas ther- mometry, where failure to take account of the unavoidable changes in the volume of the gas- containment bulb with temperature can lead to errors of several per cent in the measurement of the pressure ratios.

In support of its programme on gas ther- mometry, the National Bureau of Standards, Gaithersburg, U.S.A., has recently reported on the construction of apparatus for the measurement of thermal expansion, which allows changes in length to be measured to an accuracy of I part per million and temperature deter- minations to be made to within O . O I O C (2). In this paper, R. E. Edsinger, M. L. Reilly and J. F. Schooley also describe the use of the apparatus for measuring the thermal expansions of 99.95 per cent pure platinum and of two platinum-rhodium alloys, nominally containing 12 and 20 weight per cent rhodium, in the temperature range -27 to +570°C. The samples used were taken either from surplus materials used in the construction of bulbs for the Gas Thermometer or from pieces cut from used gas bulbs, all generally about ~ m m thick.

Optical interferometry was selected as the means of measuring the dimensional changes, using the Merritt-Saunders technique, and the samples were heated in a multi-chambered, sealed furnace, based on a design by H. F. Stimson. A quartz window, to allow interferometric measurement, and a platinum

resistance thermometer are incorporated into the furnace, which is capable of evacuation, so allowing variations in both the gas pressure and the type of gas employed. The platinum resistance thermometer was calibrated accor- ding to the IPTS-68 standard procedures.

The data obtained for the pure platinum and platinum-rhodium samples were analysed and fitted to 4th degree polynomial equations. From these equations, the values of the per cent linear expansion and hence the coefficient of linear expansion were calculated. These results show that substitution of rhodium into the platinum lattice reduces its thermal expansion in the range o to 35Ooc, then causes it to increase at higher temperatures.

A comparison of the results obtained in this study with previous work for pure platinum shows reasonable agreement, to within +2oppm; the current work generally showing larger values for the linear expansion. Similar comparisons for platinum-20 per cent rhodium show very close agreement with some earlier results; but there were differences of about 50 ppm with the data of Barter and Darling (3).

In summary, this work has provided improved, more accurate data on the thermal expansions of platinum and platinum-rhodium alloys.

C.W.C.

References I C. W. Corti, Platinum Metals Rev. , 1984, 28, (4), 164

2 R. E. Edsinger, M. L. Reilly and J. F. Schooley, 3. Res. Nail. Bur. Stand., 1986, 91, (6), 333-356

3 B. Barter and A. S . Darling, Platinum Metals Rev., 1960, 4, (413 138

Platinum Metals Rev. , 1987, 31, ( 3 ) 132

New Platinum Analytical Standard SYNTHETIC ROUTE TO A KNOWN IMPURITY COMPOSITION

By B. J. Reynolds and J. H. F. Notton Johnson Matthey Technology Centre

Relatively low levels of metallic and non- metallic impurities can cause severe degradation of platinum components used at high temperatures, for example in equipment for manufacturing specialised glass. Thus strict control of the impurity contents is required in order to ensure that the properties of the platinum are not impaired at these high temperatures.

To help to provide this control the Johnson Matthey Technology Centre has prepared a platinum standard containing fifteen impurity elements at concentrations of IOO ppm. The preparative route selected consisted of adding the elements as solutions to a high purity platinum sponge which, after drying, milling, blending and subsequent reduction under a hydrogen atmosphere, was spin-riffle sampled into 0.5 gram portions for analysis. Part of the sponge was compacted and forged down into wire, for use in spectrographic analysis of fabricated material.

Initially the doped sponge was analysed in two Johnson Matthey laboratories using Induc- tively Coupled Plasma Emission Spectrometry (ICPES) and also at the Institute of Geological Sciences, London, using Inductively Coupled Plasma/Mass Spectrometry (ICPMS) to estab- lish that the material had been homogenised correctly and to confirm that no major, unexpected losses had occurred.

As the contents of the impurities in the platinum standard had been established by means other than analysis, it was considered that a unique opportunity existed to involve other analysts outside the Johnson Matthey Group in a co-operative exercise designed to evaluate current analytical procedures. The authors are very grateful to the eight organisations that took part.

Results were received from sixteen laboratories. Six different techniques were employed, although the majority of laboratories used only one or two. Where sufficient results were available from the use of a particular technique, the means and standard deviations for that technique could be calculated separate- ly. Four groups of results could be treated in this way. These were Atomic Absorption spec- trophotometry (AA), Direct Reading Emission Spectrometry (DRES), Photographic Emission Spectrometry (PHES), and Plasma Emission Spectrometry which included results from both ICPES and Direct Current Plasma Emission Spectrometry (DCPES). Statistical analysis of the combined results was carried out using robust methods able to take account both of outliers and of the fact that some of the groups of results were non-normally distributed.

The mean values and standard deviations for each technique are presented in Table I, together with the overall mean values and 95 per cent confidence limits. The full results for two typical impurity elements, one a platinum group metal and the other a base metal, are shown in Figures x(a) and x(b), respectively. The data form typical “S” curves, from which it can be seen that the majority of the results cluster around the true content, although some outliers are obvious.

The elements which were deliberately added to the platinum standard were: antimony, arsenic, cobalt, copper, gold, iridium, iron, lead, magnesium, nickel, palladium, rhodium, ruthenium, silver, and zinc. Aluminium and calcium, which were also reported, may be expected as minor impurities in the starting sponge. The single outlier result of 138 ppm for calcium obtained by AA strongly influenced the overall mean for that element. Without it the


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alue

Platinum Metals Rev., 1987, 31, (3)

Fig. 1 Means and standard deviations of the analysis results for 100 ppm ad- ditions of (a) rhodium and (b) copper to the platinum standard are shown. The results have been plotted in ascending order of mean value, and produce the usual “S” shaped curve typical of the normal distribution. The captions to the results consist of a number referr- ing to the method used:

1-AA 2-ICPES 3-DRES 4-PHES

together with a letter indicating the laboratory. The overall mean value, ZH, calculated by a robust statistical method is included in the main distribution. A secondary group at the base of the figure presents the means of the different techniques used together with the arithmetic mean value:

ZD-DRES mean and standard

,ZS-PHES mean and standard

ZA-AA mean and standard

ZZ-Arithmetic mean and standard

ZI-ICPES mean and standard

deviation

deviation

deviation

deviation

deviation 8 1 - c 3 - F 3 - N 2 - M 4 - A 3 - € 2 - J 2 - H l - A 2 - Z H - D 2 - P 2 - K 4 - 5 4 - A 4 - K 2 -

N 4 A 1 M 2 M 4 5 4 F 3 A 2 N 3 A 3 L 2 H 1 G 1 P 2 0 2 Z H E 2 K 2 A 4 K 4

+ . -F + X *

3- + - X X X

X U ‘0 z59!00 I 81:W I 103.00 I 125.00 I 14: - c 70.00 92.00 114.00 136.00 CONCENTRATION. ppm

I 2 (a)

:: 1 G l M 2 c 1 G 2

+ I D ZI Z A

I S

0

+ + * X + - *

-K- + 1 + + * X X X X 9 * X

-x- * I

-x- 3-

* * -M- - -

X U I I

m u b I

b,O 7.00 I 4 5 0 0 1 83 00 1 121.00 1 1 5 9 0 0 * c 26.00 64.00 102.00 140.00

CONCENTRATION, p p rn


Table II

Mean Absolute Variations in Assay Values for Thirteen

of the Added Elements

Technique Average differences,

AA (1) ICPES (2) DRES (3) PHES (4)

7.5 13.7 21.7 16.6

overall mean was 3 ppm which is much more reasonable. As expected, silicon was picked up from the trays used for the sponge reduction stage.

The high palladium result is unlikely to be due to palladium in the starting sponge. A possible explanation may be that an error occurred during the preparation, resulting in a true content of 125 ppm. For most of the re- maining elements the results are in close agreement with the true content of 100 ppm. The exceptions are antimony and arsenic, where some volatilisation during the reduction stage was expected even though the temperature was kept as low as practicable.

Summary of the Results and Conclusions

On the evidence of the results, and providing that sufficient care is taken, AA should be preferred for standardisation assays on non- synthetic standard materials, since the values found agree well with the true contents and the variability is the lowest for the four methods. This may be visualised independently by sum- ming the absolute differences from the standard value for all the elements. For thirteen of the added elements, and with the value for palladium taken as 125 ppm, the average differences for the four techniques are given in Table 11. The advantages of ICPES are speed and, for some of the elements, sensitivity, but these may have been offset by the complex effects of the high platinum loadings which can

directly affect sensitivity and necessitate careful background correction.

The variability of the results both between laboratories and within laboratories when using different analysis methods has emphasised the need for standards of the type produced. The spread of results also means that analytical differences of less than 10 ppm (10 per cent relative) between samples may have no significance, unless large numbers of samples are analysed.

The successful method of preparation used for platinum is generally applicable, and is currently being used for some of the other platinum group metals.

Acknowledgement Grateful thanks are due to the following organisa-

tions whose co-operation ensured the success of this exercise: Degussa AG, Metalwerk Wolfgang; Engel- hard Ltd.; D.C. Griffiths Ltd.; Inco Europe Ltd.; Johannesburg Consolidated Investments Ltd. ; Ledoux & Company; Metallurgie Hoboken- Overpelt; and Alex Stewart (Assayers) Ltd.

Palladium in a Modified Steel The degradation induced by the presence of

hydrogen in some steels may be reduced or eliminated by the addition of palladium, but the mechanism for this effect is not fully understood. Little is known about the distribution of the palladium in such modified steels so a recently published study by M. K. Miller, of the Oak Ridge National Laboratory, and S. S. Brenner and M. G. Burke, of the University of Pittsburg, used high resolution atom probe field-ion microscopy and conventional transmission electron microscopy to examine the microstructure and microchemistry of laboratory melted low carbon alloy steels containing 0.31 and 0.65 atomic per cent palladium (Metall. Trans.A, 1987, 18A, (4), 519-523).

The authors concluded that the solubility of palladium in the tempered steel was between 0.25 and 0.5 atomic per cent, considerably less than indicated by the iron-palladium phase diagram. Although most of the palladium re- mained in solution in the ferrite, some had segregated to the ferrite-ferrite lath boundaries where it formed a mono-atomically thick adsorbate layer. Palladium-manganese precipitates were detected both at lath boundaries and in the ferrite matrix.


The Use of Platinum Metal Complexes in Asymmetric Catalysis CONTINUING DEVELOPMENTS WILL INCREASE POTENTIAL

By John M. Brown Dyson Perrins Laboratory, University of Oxford

Since the original demonstrations of homogeneous organometallic catalysis under mild conditions in the 1960s there has been much progress. A central focus for development has been asymmetric synthesis, through the use of optically active ligands. Chiral chelating biphosphines have played a key role in these advances, which have led to: asymmetric hydrogenation as a route to amino-acids and Vitamin E precursors, kinetic resolution in directed hydrogenation, asymmetric isomerisation of olefins in a route to citronellol, and asymmetric catalytic C-C bond formation. This review highlights recent developments.

The organic chemistry of the noble metals is literally unique, since it has no counterpart in biology. This means investigations have to start without the guidelines provided by enzymo- logy, which have contributed so much to the development of synthesis. It makes asymmetric catalysis a very signifcant feature of noble metal chemistry, since it affords competition with natural sources for optically active materials by an approach which is completely different in concept. The current level of interest in asymmetric synthesis in both the pharmaceutical and chemical industries, for the production of optically pure drugs, agro- chemicals, chiral smectic C liquid crystals and polymers of controlled helicity , gives the topic a vigorous present and a secure future.

At the moment, the most substantial contri- butions lie in the formation of C-H and C-C bonds. It is a curious fact that all the examples of highly effective asymmetric catalysis involve low-valent complexes of ruthenium, rhodium and palladium; the lower block platinum metals are much less important in this area of catalysis. To some extent this is because they tend to form more stable complexes, and stability is counter productive in catalysis. However, when the correct procedures are learned iridium and

platinum complexes can be highly effective, as is demonstrated by platinum hydroformylation and iridium hydrogenation, the latter pi ineered by R. H. Crabtree (I). But the application of these complexes in asymmetric catalysis is not advanced.

In the remainder of th is article, the various methods for asymmetric synthesis of C-C and then C-H bonds are described. Due emphasis is given to methods providing an enantiomer excess of 2 95 per cent.

Asymmetric Catalysis in C-C Bond Formation

Palladium chemistry is pre-eminent in catalytic C-C bond formation, as a result of its early applictions in both cross-coupling reactions and allylic alkylation. The development of asymmetric synthesis in this area is much newer, with recent breakthroughs from the research group of Hayashi in Japan being pre-eminent.

Almost single-handedly, Trost made catalytic allylic alkylation part of the essential repertoire of synthetic organic chemistry (2). His reaction sequence is illustrated in Figure I , and it should be noted that the key step involves reaction between a cationic palladium ally1 and a soft nucleophile such as malonate ion. With an


Fig. 1 between the starting material and the product

Catalytic allylic alkylation; note the configurational relationship

NaCH(CO,Me),

a) ~ h + ~ : ~

OAc Ph\ ,Ph (Me02C),01 Ph

BOSNlCH J;;pd+L) I \ R (-), 85% E.e.

ph Ph '"4

(catalytic)

NaCH(C02Me), c PhPPh

(Me02C)2CH Ph Ph OAc

RN. CH(CH,OH),

(catalytic)

Fig. 2 High enantiomer excess in catalytic allylic alkylation

optically active biphosphine such as CHIRA- PHOS, asymmetric synthesis can occur. Be- cause the new bond is formed some distance from the metal and its chiral ligand, optical yields were modest in most early studies. Bosnich and co-workers found that diphenyl- ally1 derivatives were better (Figure 2(a)) because their bulkiness elicited a stronger interaction with the ligand, so that one of the two possible intermediates was strongly favoured

(3). The best examples to date are due to Hayashi's group (4). They use a rather unusual ferrocenyl-phosphine, with a polar side-arm. This acts so as to bias the reaction towards one end of a symmetrical or near-symmetrical intermediate. Although the details are not properly understood the effect is dramatic, leading to allylic products with high optical purity, as shown in Figure 2(b).

Cross-coupling is the enigma of asymmetric


catalysis. This straightforward reaction, whereby a carbon-carbon bond is assembled within the co-ordination sphere, seems a perfect arrangement for stereochemical control (s), see Figure 3. The intrinsic limitations of existing procedures, particularly incompati- bility towards polar substituents, have yet to be overcome and few good examples of asymmetric synthesis with high enantiomer excess are available. Again the best work comes from Hayashi’s group, and makes optically active allylsilanes available (6) , as illustrated below in

Figure 4. A feature of their approach is the clever use of ferrocene as a template for design- ing asymmetric ligands. The allylsilanes have a well-developed organic chemistry and can be converted into many other chiral products.

Asymmetric Catalysis in C-H Bond Formation

Wilkinson’s classic work on rhodium catalysed homogeneous hydrogenation encouraged many other groups to make optically active phosphines; hydrogenation is widely utilised in

R*R

xl p , , , ,

R*X 7 p/Pd- R T

p;p*i

R

“a p , , , ,

p/Pd-

R M L p , , , , P N P d > , R .-i Mx

R

Fig. 3 The basic catalytic cycle for cross-coupling

H

11 THF I O°C - I H

95% E.e.

P h Ph

”\

Fig. 4 Asymmetric cross-coupling via a racemic Grignard reagent

Platinum Metals Rev., 1987, 31, ( 3 ) 139

I

\o

m

U

"Z

h

v

w

-I

Fig.

5 Th

e bi

phos

phin

e m

etal

por

tion

of

an o

ptic

ally

act

ive

ligan

d-m

etal

com

plex

sho

wn

in

(a)

elev

atio

n and

in (b) p

lan

proj

ecti

on. T

he C,

sym

met

ry i

s de

mon

stra

ted

by highlighting P

-ary

l pai

rs

140 Plaritlurn Metals Rev., 1987, 31, (3)

MeOzC Kc OH

R

OH S

H, I THF

99% Anti. threo

Fig. 6 Stereoselection by directed hydrogenation with an achiral catalyst. With (RR-DIPAMP)Rh+ as catalyst, the R-enantiomer of the starting material is consumed seven times faster, leading to kinetic resolution of the S-enantiomer

synthesis, and the potential for introducing optical activity seemed highly attractive. Pro- gress only became rapid when Kagan showed that the important step was to employ biphosphines, and now there are upwards of fifty ligands which give good results in asymmetric hydrogenation (7). Application tends to be limited to dehydroamino acids and related compounds where a substituent on the olefin provided the necessary “bite” by occupying a co-ordination site throughout the catalytic cycle. The source of chiral recognition is still not fully understood, despite much effort (8), but the role of the biphosphine has been clarified by X-ray studies on a rigid biphosphine rhodium complex, see Figure 5. The asymmetric centres enforce a chiral conformation on aryl groups bound to phosphorus. This permits a discrimination between the reaction channels leading to “left-hand” and “right-hand” products because of the way that the catalytic reactant is bound to rhodium during the catalytic cycle. For dehydroamino acids, it appears that the interactions involving the - CO H group are the most critical. By analogy with en- zymology, asymmetric hydrogenation works because this substituent operates as a key on the arylphosphine lock, but only when one pro- chiral face of the olefin is bound to rhodium. For the other face, there is a mismatch which

makes the addition of hydrogen energetically unfavourable.

One recent development widens the scope of asymmetric hydrogenation (9). When the olefin being reduced includes a neighbouring chiral centre there can be two possible isomeric products, depending on which face accepts hydrogen. For example, the /3-hydroxyacrylate of Figure 6 can give rise to syn- and ant& hydrogenation products, and it turns out that the latter is strongly predominant. With a simple chelate rhodium catalyst both enantiomers of racemic starting material are reduced with equal facility; the most interesting experi- ment involves an optically active catalyst such as DIPAMP-Rh+. Here the reactivity of the two enantiomeric forms of starting material is quite different, and one is efficiently drained off in a fast hydrogenation. This leads to kinetic resolution of the slow reacting enantiomer. It may be recovered in cp to 95 per cent optical purity at 265 per cent reaction. In similar manner, /3-carboxyacrylates and acylamino- acrylates can be subjected to kinetic resolution. The sequence of two hydrogenation steps, one with an optically active catalyst and the second with a simple chelate rhodium catalyst leads to 0-hydroxyesters and /3-aminoesters or to 2,3-dialkylsuccinic acid derivatives in a state of high optical purity. This represents the first

Platinum Metals Rev., 1987, 31, ( 3 ) 141

Enriched

slow

Fig. 7 Kinetic resolution of rseemic itaconates

H ‘ BF4 99%

Fig. 8 Face eelectinty in directed hydrogenation

case of a catalytic kinetic resolution which does not require enzymes or micro organisms, as is shown in Figure 7.

The secret of success is to find reactants possessing a functional group in proximity to the olefin which can bind to the metal and control the stereochemical course of hydrogenation. In a cyclic compound, this can lead to face-selectivity, where the functionality directs hydrogen to the double bond in a constrained way. Some of the best examples involve iridium catalysts, which work well for cyclic systems. It is of interest that the alcohol or amide group which controls reaction stereochemistry can be quite remote from the double bond undergoing hydrogenation, see Figure 8. The stereo- selectivity can exceed the limits of conventional measurement by g.c. or h.p.1.c. techniques, and product discrimination of >IOOO:I has been reported (9).

Over a period of twenty years, rhodium catalysts have dominated homogeneous hydrogenation, so it was natural for asymmetric catalysts to be closely related. Their dominance has been challenged in recent Japanese work, particularly that emanating from Noyori’s laboratory. He developed the binaphthyl- derived ligand, BINAP, which made a useful but not outstanding contribution to the asymmetric hydrogenation of dehydroamino acids (Ioa). When the corresponding ruthenium complexes were prepared, they were also found to be active in hydrogenation, but in the opposite stereochemical sense to their rhodium counterparts. More recent applications to the production of enantiomerically pure isoquino- line alkaloids are impressive (lob). Even more so is the hydrogenation of trisubstituted allylic alcohols, for it solves a long-standing problem in organic chemistry and provides a route to


Catalyst is Bu'

98% E.e.

Fig. 9 BINAP-ruthenium complexes in asymmetric hydrogenation

enantiomerically pure compounds in the Vitamin E series ( IOC) shown in Figure 9. This takes the field of asymmetric hydrogenation one stage further, and closer to being a completely general method for the asymmetric synthesis of tertiary centres.

The final example again comes from Noyori's group and involves catalytic isomerisation in the generation of a new asymmetric centre (I I). This brings the discussion full circle, since the reactive intermediate in the catalytic cycle is presumably an allylrhodium hydride, quite

closely related to the allylpalladium intermediates in allylic alkylation. The rhodium complex is prepared from BINAP and is an efficient catalyst for olefin isomerisation in the absence of hydrogen around 40OC; olefin isomerisation has long been known as a com- peting side-reaction in some homogeneous hydrogenations. The most successful case (Figure 10) is with dimethylgeranylamine and dimethylnerylamine, which were converted in- to opposite enantiomers of the same enamine, with high optical purity. The product can be

THF I 4OoC

c

THF I 40°C

NEt,

Fig. 10 Catalytic olefin isomerisation as a route to optically active citronellol precursors

Platinum Metals Rev . , 1987, 31, ( 3 ) 143

hydrolysed in acid to citronellol, providing an the asymmetric induction have not been satis- elegant and commercially viable route to this factorily solved. Optical yields in rhodium important perfumery intermediate. hydroformylation have been uniformly low;

platinum-tin complexes give better results, but Summary and Future Trends under rather forcing conditions (12). Clearly

These examples demonstrate that asymmetric much work remains to be done but the future catalysis has become a significant contributor to of platinum metal complexes as asymmetric the “chiral economy” over the last ten years catalysts looks most encouraging, for both and promises to provide further developments. industrial and academic applications. There is a conspicuous gap in our knowledge at the Dresent time. Most industrial chemists think first of hydroformylation or hydro- carboxylation in the Context of homogeneous

The author’s own work referred to herein was supported by the Science and Engineering Research Council. usine noble metal salts kindlv loaned bv

I . .

catalysis, but here the problems associated with Johnson Matthey.

Refe I R.H.Crabtree, Acc.Chem.Res.,1979, 12, (9), 331 2 B. M. Trost and T. R. Verhoeven, “Comprehen-

sive Organometallic Chemistry”, ed. G. Wilkin- son, F. G. A. Stone and E. W. Abel, Pergamon, Oxford, 1982, 8, p. 799

3 P. R. Auburn, P. B. Mackenzie and B. Bosnich, J. Am. Chem. Soc., 1985, 107, (7), 2033; P. B. Mackenzie, J. Whelan and B. Bosnich, ibid.,

4 T. Hayashi, A. Yamamoto, T. Hagihara and Y. Ito, Tetrahedron Lett., 1986, 27, (2), 191; T. Hayashi, A. Yamamoto and Y. Ito, 3. Chem. Soc., Chem. Commun., 1986, (14), 109; T. Hayashi, A. Yamamoto and Y. Ito, Chem. Lett.,

5 For a general discussion see T. Hayashi and M. Kumada, in “Asymmetric Synthesis”, ed. J. D. Morrison, Academic Press, 1985, 5, p. 147 ff.

6 T. Hayashi, M. Konishi, Y. Okamoto, K. Kabeta and M.Kumada, 3.Org.Chem., 1986,51,(20),3772

7 H. B. Kagan and T. P. Dang, J . Am. Chem. Soc.,

8 C. R. Landis and J. Halpern, J. Am. Chem. Soc., 1987,109, (6), 1746; J. M. Brown and P. J. Mad- dox, J. Chem. Soc., Chem. Commun., 1987, in

198.59 107, (71, 2046

1987, (11, 177

1972, 94, (181, 6429

!re lnces press; J. M. Brown and P. A. Chaloner, “Homo- geneous Catalysis with Metal Phosphine Com- plexes”, ed. L. H. Pignolet, Plenum Press, New

9 J. M. Brown, Angew. Chem. Int. Ed. Engl., 1987, 26, (3), 19, and references therein

10 (a) A. Miyashita, A. Yasuda, H. Takaya, K. Toriumi, T. Ito, T. Souchi and R. Noyori, J. Am. Chem. Soc., 1980, 102, (27), 7932; (b) T. Ikariya, Y. Ishii, H. Kawano, T. Awai, M. Saburi, S. Yoshikawa and S. Akutagawa, J. Chem. Soc., Chem. Commun., 1985, (ID, 922; R. Noyori, M. Ohta, Y. Hsiao, M. Kitamura, T. Ohta and H. Takaya, J . Am. Chem. Soc., 1986, 10% (221, 7117; (c) H. Takaya, T. Ohta, N. Sayo, H. Kumo- bayashi, S. Akutagawa, S. Inoue, I. Kasahara and R. Noyori, 3.Am. Chem. Soc., 1987,109,(5),1596

I I K. Tani, T. Yamagata, S. Akutagawa, H. Kumo- bayashi, T. Taketomi, H. Takaya, A. Miyashita, R. Noyori and S. Otsuka, J . Am. Chem. Soc., 1984, 106, (IS), 5208

12 G. Consiglio, P. Pino, L. I. Flowers and C. U. Pittman, 3. Chem. Soc., Chem. Commun., 1983, (II), 612; C. U. Pittman, Y. Kawabata and L. I. Flowers, ibid., 1982, (9), 473

York, 1983, P. I37

A Fast Response Platinum-Iridium Thermocouple The use of thermocouples made from

platinum group metals and their alloys for the measurement of high temperatures is long established and widespread, and is based upon their reproducible thermoelectric properties, their accuracy over a wide temperature range and their resistance to corrosion. Now it is possible to fabricate thin-film thermocouples using integrated circuit technology and a recent paper from the IBM Thomas J. Watson Research Center describes a process for producing thin-film platinum-iridium thermocouples

with the same thermoelectric behaviour as bulk couples (H. M. Tong, G. Arjavalingam, R. D. Haynes, G. N. Hyer and J. J. Ritsko, Rev.Sci.Znstrum., 1987, 58, (9, 875-877).

The thicknesses of the platinum and iridium films were 0.51 and 0.29 lm , respectively, which ensured continuity on the alumina substrate. The thermocouple has been calibrated up to 79oOC. With a fast response time and low thermal capacity the thermocouple is very suitable for monitoring instan- taneous temperatures during device processing.

Platinum Meials Rev., 1987, 31, ( 3 ) 144

Acknowledgement

Oxidation in Organic Synthesis Organic Syntheses by Oxidation with Metal Compounds EDITED BY W. J. MIJS AND C. R. H . I . DE JONGE, Plenum Press, New York, 908 pages, $138

This book is concerned with the synthetic aspects of oxidation reactions involving metal compounds which are either readily available or easy to prepare. It considers reagents which are both stoichiometric and catalytic. There are a total of 16 chapters, together with a helpful ap- pendix in tabular form which contains a list of substrate and product classes, and gives references to experimental procedures in the preceding chapters. At the end of each chapter representative synthetic procedures are given, including experimental details. The majority of chapters are concerned with transition metal complex reagents, including vanadium, chromium, cobalt, copper, manganese, nickel, silver, thallium, bismuth and cerium. There are, however, three chapters devoted to complexes of ruthenium, palladium and osmium.

Ruthenium tetroxide oxidation is discussed by J. L. Courtney, and the major sections within this chapter deal with mechanism, scope and limitations of reactions, and experimental considerations and procedures. The advantages that ruthenium tetroxide has as a reagent over osmium tetroxide in terms of rigour and ver- satility are emphasised. In addition to discuss- ing the formation of aldehydes and ketones, acids, imides, sulphoxides and sulphones from various substrates, attention is focused on some more novel organic transformations. These include the formation of esters and lactones from ethers, also oxygen insertion reactions, the oxidation of cycloalkanes, and the formation of quinones and diacids, the latter via the destruc- tion of the aromatic nucleus. Throughout this section comparisons are made with more established oxidants; this should prove useful to practising synthetic organic chemists.

The use of palladium compounds in oxidation transformations is well documented, and S. F. Davison and P. M. Maitlis summarise this in a 31 page review. The oxidation of alkenes, in particular ethylene, is discussed objectively

and problems relating to the formation of acetaldehyde (the Wacker process), vinyl acetate and ethers are discussed. Vinylic substitution reactions and in particular the arylation of olefins and variants of this based around the Heck reaction are described and it is demonstrated that this can result in mild regio- and stereoselective reactions which can be utilised for a wide range of functionalities on the substrate. Other sections deal with aromatic substitution reactions, oxidative aryl coupling, oxidative carbonylations and the oxidation of alcohols. In this chapter it is noted whether the reagent may be used stoichiometrically or catalytically, and limitations to the utility of synthetic routes are discussed.

Osmium tetroxide is one of the oldest metal compounds to be used in the oxidation of organic compounds and its uses, particularly in the hydroxylation of alkenes-where it finds widespread application-are described by H. S. Singh, who also reviews the use of alkene, diene, quinone, pyran and steroidal substrates. In the past, these reactions have been carried out stoichiometrically, but the use of co- oxidants for alkene oxidation is described; this renders the reaction catalytic in osmium. More recent work which improves the scope of osmium reagents and can improve the effec- tiveness of osmium tetroxide in alkene oxida- tions is exemplified by the use of alkylimidoosmiurn reagents and chloramine-T for the formation of aminoalcohols. The use of ferricyanide with catalytic amounts of osmium tetroxide in the synthesis of acids, diacids and hydroxyacids is discussed; a section is devoted to the use of osmium in more complex transformations relevant to biorganic synthesis.

This book should prove a useful addition to departmental libraries, providing an overview of oxidation transformations using metal compounds and demonstrating, in part, the ver- satility of the platinum metals. M.J.H.R.

Platinum Metals Rev., 1987, 31, (3), 145 145

ABSTRACTS of current literature on the platinum metals and their alloys PROPERTIES Positive Ion Emission from a Platinum Hot Wire Gas Sensor

F R I N D T ~ ~ ~ s. R. MORRISON, Sens. Actuators, 1987, 11, (3), 209-220

A clean Pt wire when heated to gw0C produces a steady positive ionic current in the presence of organic vapours. Higher responses were obtained for vapours with more C atoms per molecule and greater ease of oxidation by the wire. Oxidisable gases with little or no C produced little or no ionic response. Ionisation potentials of - 6 eV were calculated. Wires at ~ W - I O O O ~ C in contact with organic vapours or contaminated by surface C also emitted positive ions in air. Both clean and C-contaminated wire responses can be used to design selective gas sensors.

Electrical Resistivity of Ordered Fe,-,Pt,-, Alloys between 4 and 1200K s. u. ]EN and Y. D. YAO, Phys. status Solidi, 1987,

The electrical resistivity of ordered Fe -,Pt, -, alloys containing 20, 22, 24, 26, 28 and 3oat.%Pt was investigated from 4 to ~ z o o K . A new phase was found at low temperatures (T<24oK) for alloys with 26, 28 and 3oat.%Pt. Both the a - y transition and the transition to the new phase exhibit hysteresis in the electrical resistivity curves.

Formation of PtSi in the Presence of A1 c.-A. CHANG, 3. Appl. Phys., 1987, 61, ( 5 ) , I 864-1868 The formation of Pt silicides in the presence of Al using Al/pt/Si structures with different Al thicknesses was studied. The Pt-Si and Pt-A1 reactions occur simultaneously at - zw0C and PtSi and PtAl formation is completed by 4w°C. With three equal layer thicknesses the two alloys formed stay in contact and are stable up to -5co°C. With twice or more Al thickness to Pt and Si, the PtSi layer is completely converted to PtAl, at 45oOC.

Superconductivity and Antiferromagnetic Order in the U(Pt, Pd), System

SPRANG and A. DE VISSER, 3. Appl. Phys., 1987, 61, (8), Part IIA, 3380-3382 A phase diagram for the superconducting and antiferromagnetic states in U(Pt, J'd,) XQO. 10 is presented. Superconductivity is depressed for x>o.w5, whereas antiferromagnetism is observed for O.OI<X<O.I. Specific heat experiments show a sharp transition at the Nee1 temperature of 6.1K for x=o.o5, in contrast to x=o.oz and 0 . 0 7 where rather broad anomalies are observed at -3.6 and 5.5K.

W. M . SEARS, V. A. MOEN, B. K. MIREMADI, R. F.

100, (11, 269-275

J. J . M. FRANSE, K. KAWWAKI, A. MENOVSKY, M. VAN

Synthesis and Electrocatalytic Properties of Rare Earth Platinum and Palladium Bronzes K.-I . MACHIDA, M. ENYO, G.-Y. ADACHI and J. SHIOKAWA, Bull. Chem. soc. Jpn., 1987, 60, ( I ) , 411-413 DyPt and DyPd bronzes DyM,X, (M=Pt, I'd; X=O, S, Se or Te) were synthesised by a solid state technique, except for DyPt,S,. They all had high electrical conductivity, with e =0.3-2.6x Io-Qm, and the oxide bronzes crystallised with a Na,Pt,O, type structure. The Pt oxide bronzes in particular had high activity for the methanol electro-oxidation, as compared to ordinary Pt electrodes.

The High-Temperature Elastic Proper- ties of Palladium Single Crystals M. YOSHIHARA, R . B. MCLELLAN and F. R. BROTZEN, Acta Metall., 1987, 35, (3), 775-780 A thin-line acoustic method was used to measure the single crystal elastic moduli of Pd between 30-12ooK. The single crystal constants behave, at high temperatures, in a classical manner, in contrast to a large modulus defect observed in polycrystalline Pd. The latter effect may be due to grain boundary relaxation.

Magnetic Interface Anisotropy in PdKo and PdlFe Multilayers

BROEDER, 3. Ma@. & ' M a @ . Muter., 1987, 66, (3), 351-355 I'd/& and I'd e multilayer thin films containing

vapour deposition in UHV. Their magnetisations were measured at room temperature in fields parallel and perpendicular to the film plane. The Pd/Co multilayers show a transition of the preferred direc- tion from lying in the film plane towards lying along the film normal whe the thickness of the Co layer is decreased below 8 1 . The Pd/Fe multilayers are preferably magnetised in the film plane, although the anisotropy decreases with lower Fe layer thickness.

Structural and Electronic Properties of Implanted Metal Hydrides A. TRAVERSE and H. BERNAS, 3. Less-Common Met., 1987, 129, 1-11

A review of I'd and Ni low temperature H implanted hydrides is presented, and comparisons between the properties of both are discussed and related to various methods of preparation. Similarities include superconducting transition temperatures and photon energies, while differences include the phase diagrams. Metastable hydrides can thus be prepared with properties very similar to those of classically charged hydrides. (33 Refs.)

H. J . G. DRAAISMA, W . J. M. DE ]ONCE and F. J. A. DEN

ultrathin, 2 - 1 2 f Co and Fe layers were prepared by


Preparation of Amorphous Ni-Pd-P Par- ticles by Melt Ejection into Stirred Water and Their Hardness and Thermal Stability

T. MASUMOTO and N. MIYAKE, Metall. Trans. A , 1987,

The preparation of amorphous spherical particles with diameters 0.5-1.- by melt ejecting Ni-rich Ni-Pd-P alloys into stirred cold water with I vol.% surfactive agent is described. The sphericity of the particles was better than 98%. Particles with diameters < I .omm have hardness, crystallisation temperatures and heat of crystallisation similar to those of amorphous ribbon of the same composition and - 40pm in thickness, but the onset temperature and heat of relaxation are different. Thus the particles have the same thermal stability as that of the amorphous ribbon but their structure is in a more disordered state than the ribbon.

Effect of Ambient Gases on Emission Pro- perties of Pd-Ni-Si-Be-B LM Ion Source

Appl. Phys., Pt . 2. Lett., 1987, 26, (z), L103-Lroq The effects of ambient gases on the emission properties of a Pd,, Ni ,, Si, Be, B, liquid metal ion source were studied. 0, and water vapour had a significant effect on the ion emission stability. A very stable and reliable ion emission with a lifetime > r o o hours was obtained by operating the source at 8 x I O - ~ torr.

Absorption of Hydrogen in Pd-Co and

A. INOUE, T. EKIMOTO, H. M. KIMURA, Y. MASUMOTO,

(31, 377-383

H. ARIMOTO, E. MIYAUCHI and H. HASHIMOTO, 3pn. 3.

Pd-U Alloys R. FEENSTRA, D. G. DE GROOT, R. GRIESSEN, J. P.

1987, 130, 375-386 BURGER and A. MEMOVSKI, 3. Less-Common Met.,

The absorption of H, in structurally disordered Pd,,Co,, Pd,Co,,, Pd,U, and Pd,U was studied experimentally between 300--600K and up to 50bar H? pressure. Pure U readily absorbs H,, while Co does not; however absorution of H , is reduced more

Electrical Resistance Anomalies and Hydrogen Solubilities in the Disorder- Order System Pd,Mn

P. CRAFT, Scr. Metall., 1987, 21, (3), 299-303 Pd Mn was prepared and rolled into foils 100- 140opm thick. The foils were then rolled in Ti foil and disordered by heating under vacuo in a SiO, tube. As temperature increased the order increased and thus HI solubility increased, for temperatures below critical T,. The maximum in the electrical resistance is caused by scattering of electrons from the boundaries between the partially ordered domains, and the disordered matrix increases the resistance, while growth and ordering of the domains decreases the resistance. There are no anomalous resistance changes.

Superconductivity and Magnetism in

N. ALI and w. R. DATARS, 3. Less-Common Met., 1987, 1273 49-54 The electrical resistivity, magnetoresistance and up- per critical field of single crystal LuRh ,,, Sn,,, were studied. A superconducting transition temperature of 4.rK was observed and the critical field slope near T, was r7kOe/K. There was a logarithmic decrease in the resistivity with increasing temperature, with a minimum at ZIOK. The low temperature "esistivity and magnetoresistance suggest a weak itinerant antiferromagnetic ordering below 5.zK.

Direct Observation of Reconstructed Sur- faces in the Field Ion Microscope J. W I ~ and K. MULLER, Appl. Phys. A, 1986, &I, (I), 103-106 Field ion microscopy was used at 2 x 16," mbar base pressure at ZOK to observe Ir surfaces. Ir(1ro)r x2 and Ir(roo)~ x 5 reconstructed surfaces were imaged. The observations agree with results obtained on macroscopic single crystal surfaces. Evidence for a I x z reconstruction of the Ir(Ir3) surface is shown.

K. BABA, Y. SAKAMOTO, T. B. FLANAGAN, T. KUJI and A.

LuRh 1 . 2 Sn, . o

in the Pd-U alloys than h the Pd-& alloys. In Pd,U no appreciable absorption could be detected.

Electrical Resistance and Hydrogen Iridium-Carbon Composite Films

Solid Solution Alloy

Electrochromism in Iridium Oxide Films Prepared by Thermal Oxidation of

Y. SATO, K. ONO, T. KOBAYASHI, H. WAKABAYASHI and H. YAMANAKA, 3. Electrochem. SOC., 1987, 134, (3),

in a PdSat*%Y

M. DOYLE, R. C. J. WILEMAN and I. R. HARRIS, 3. Less- Common Met., 1987, 130, 79-87 The H, (protium and deuterium) solubility and electrical resistance measurements have been made on a Pd-8at.OhY solid solution alloy over a range of temperatures and pressures. A solubility enhance- ment effect occurs for the Pd-lat.%Y-H, system, and enhanced resistance values at low temperatures occur for Pd-8at.%Y-H, and Pd-lat.%Y-D,. Both effects disappear at a critical value of H:metal atom ratio of 0.32, which may correspond to a diamagnetic to paramagnetic transition. The effects disappear on sample cooling but can be recreated by removing the H and reannealing the sample.

5 70- 57 5 Electrochromic Ir oxide fdms have been prepared by thermal oxidation of Ir-C composite fdms, which were obtained by evaporation of Ir from a graphite crucible with an electron gun. The change in transmittance of the Ir-C fdms begins after heating to 225OC or higher. The thermally oxidised Ir oxides (TOIROFS) are amorphous when heated up to 3o0°C, and polycrystalline when heated at 35O0C. The degree of electrochromism is closely related to these structures. The coloration efficiency of the TOIROFS lies in the range 13.5 to 15.4cm'/C at a X of 633nm. Colour-bleach cycles of 4x 10' were recorded without degradation.

Platinum Metals Rev. , 1987, 31, (3) 147

Crystal Structure and Superconductivity of New Ternary MTGe Germanides (M=Ti, Zr, Hf and T=Ru, Os, Rh, Ir)

HAGENMULLER, Mater. Res. Bull., 1987, 22, (3), 331-336 ZrIrGe and HfIrGe crystallise with a TiNiSi-type structure and exhibit a superconducting transition at 2.75 and 4.98K, respectively. TiIrGe and HfRhGe have two allotropic varieties and their superconducting properties are strongly influenced by their crystal structure. No superconducting transition above I .6K was observed for TiTGe (where T=Ru, Os, Rh), ZrTGe(T=Ru, 0s) or HffGe(T=Ru, 0s). The TiNiSi-type structure thus favours the occurrence of superconductivity in ternary germanides.

W. X. ZHONG, B. CHEVALIER, J. ETOURNEAU and P.

Some Reactions of Ruthenium Cluster Carbonyls under Mild Conditions M. I. BRUCE, Coord. Chem. Rev.,1987, 76, 1-43 Substitution reactions of Ru cluster carbonyls with t-butyl isocyanide, and of Ru,(CO) ,, with a range of isocyanides, tertiary phosphines, phosphites, arsines and SbPh, resulted in a range of easily made new complexes which were then characterised and the facile reaction routes described. (174 Refs.)

A Double Cluster of Ruthenium and Boron; [1-772-{(776-CgMe6)2Ru2 H,}-isocl- OSO-~-RUB,~H,-~,~-(OE~)~I M. BOWN, X. L. R. FONTAINE, N . N. GREENWOOD, P. MACKINNON, J. D. KENNEDY and M. THORNTON-PETT, J. Chem. SOC., Chem. Commun., 1987, (6), 442-443

~ ~ u ~ i ~ ~ ~ ~ ~ ~ i ~ ~ i ~ ~ for the system The novel double cluster title compound, obtained in BaO-RuO -Fe 0 with Less than 31 YO yield as an unexpected product from the reaction

between the mononuclear Ru complex arachno-[(q * - 55m01'%Ba0 at 13000c in 'latinurn C,Me,)CIRuB,H,I and closo-[B,,H,,l'- in ethanol, Capsu1es; A and has a unique non-carbonyl containing triangular Leaching Study {Ru,] cluster and a closo-type eleven-vertex {RUB I u] D. VERWES, H. w. ZANDBERGEN and D. J. w . IJDO, cluster joined at a common Ru atom. Mater. Res. Bull., 1987, 22, (I), 1-10

The system Ba0-Ru01-Fe20, with <55mol.% BaO, was investigated after heating at 130o0C in Pt cap- sules. The Ru valence was not constant and was therefore considered as an extra variable. Thus the system is considered as a description of the equilibria and not as a ternary phase system. Three quaternary compounds were determined and a new ternary compound was found.

CHEMICAL COMPOUNDS Cobalt, Rhodium and Iridium. Annual Survey Covering the Year 1985 1. T. MAGUE, J. Organomet. Chem., 1987, 324, (I-3), 57-282 A review covering continuing studies in Rh, Ir and Co organometallics covering literature, including dissertations, published in 1985 is presented. The range of complexes covered include metal-C u- bonded, metal carbenes, metal isocyanides, metal carbonyls and related compounds, nitrosyls and aryldiazos, alkenes, alkynes, n-allyls, carbocyclics, metallaboranes and -carbaboranes and other miscellaneous complexes. (822 Refs.)

Reactivity of Pentaammineosmium(I1) with Benzene W. D. HARMAN and H. TAUBE, 3. Am. Chem. SOC., 1987, 109, (6), 1883-1885 The reduction of Os(NH,),(CF,SO,), with Mg in the presence of excess benzene gives a deep orange coloured solution containing [Os(NH ,) (7 - benzene)](TFMS),(x). NMR and i.r. spectroscopies were performed, and compound ( I ) in acetone liberates benzene and forms complex [Os(NH,),(7!- acetone)]' +. Compound (I) will react with a variety of ligands, and especially amides and esters.

ELECTROCHEMISTRY Electrochemical and Surface Science In- vestigations of PtCr Alloy Electrodes

CAMPBELL, J. Electroanal. Chem. Interfacial Elec- trochem., 1987, 220, (2), 269-285 Electrodes of supported Pt, modified with Cr, have an increase in electrochemical activity for 0, reduction in phosphoric acid fuel cells, compared to Pt supported electrodes. A series of Pt,Cr(,.,) bulk alloys (x = 0.9,0.65,0.5,0.2) were tested to clarify the role of the Cr. Surface characterisation of the electrode surfaces were performed by various techniques, and the H I SO, electrolyte was also analysed. The surface Cr was oxidised to Cr' + oxide for various potentials, and to soluble Cr6+ for potentials >+1.3V. Alloys with Cr content >p.~ produce very porous Pt-rich surfaces. Loss of Cr was also observed for Cr content a.5. Ptu.2Cr,., gave Pt'+ and Cr6 + species.

"Transparent" Metallic Electrocatalysts

T. T. SHENG, Extended Abstracts, Spring Meeting of the Electrochem. Soc., Philadelphia, May 10-1 5 ,

Highly transparent films of thickness 30-60 nm, of Pd, Rh, Pb, Re on InP have been prepared. The films contain 30-60% metal, yet transmit most of the light of wavelengths between 2x0 and 750 nm. The Nms contain three microstructural levels, and because the particles and their aggregates are smaller than the U.V. wavelength, and because they are not well con- nected, the film appears specular and transparent. The films are prepared by photoelectrodeposition on- to p-InP-photocathodes and exhibit normal catalytic bahaviour and have normal crystal structures.

M. T. PAFFE'IT, K. A. DAUBE, S. GOTTESFELD and C. T.

A. HELLER, D. E. ASPNES, Y. DEGANI, J. D. PORTER and

1987, 87-1, 727


Iridium-Based Small Mercury Electrodes J. GOLAS, Z. GALUS and J . OSTERYOUNG, Anal. Chem., 1987, 59, (3, 389-392 The preparation of Ir-based small Hg electrodes, for use in electroanalytical chemistry is described. Ir was used as a base because of its very low solubility in Hg, and because Hg can be electroplated onto Ir so that it wets the surface. The prepared electrodes were hemispherical and had the chemical properties of a hanging Hg drop electrode. The amount of Hg used was -50% of that needed to form a regular hemisphere with the radius of the Ir base. The most stable electrode was prepared by electrolysis of Hg in O.IM HCIO, at -0.4V for 11-13 minutes using a 127 pm diameter Ir disk as substrate.

Electrooxidation of Methanol on Iridium in Acidic Solutions: Electrocatalysis and Surface Characterization by Infrared Spectroscopy A. ARAMATA, T. YAMAZAKI, K . KUNIMATSU and M. ENYO, J. Phys. Chem., 1987, 91, (9), 2309-2314 Theelectro-oxidationof methanol was studied on Ir in H, SO, and HCIO, to examine the catalytic activities of the electrode in various oxidation states, and of the adsorbed CO, examined by i.r. spectroscopy. Ir had a higher catalytic activity than Pt at low positive potential regions, but its catalytic activity decreased with time at a constant-potential polarisation, and was inhibited by CO gas. Adding CO shifted the max- ima in the i.r. spectra to higher wave numbers.

Mechanism of Oxygen Reactions at Porous Oxide Electrodes. Part 1. Oxygen Evolution at RuO, and Ru,Sn, -x02 Electrodes in Alkaline Solution under Vigorous Electrolysis Conditions M. E. G. LYONS and L. D. BURKE, J. Chem. soc., Fara- day Trans. I , 1987, 83, (2), 299-321 The electrocatalytic performance and long-term stability of thermally prepared RuO, and Ru,Sn,-,O, coated Ti anodes with respect to 0, evolution in strongly alkaline solution at elevated temperatures under vigorous electrolysis conditions has been studied. Adding a controlled amount of an inactive oxide improves the long-term stability and electrocatalytic activity of RuO, electrodes. RuO, electrodes could possibly be used in large-scale water electrolysis cells.

Cathodic Metal Oxide Electrocatalysts vs. Metals in Chlor-Alkali Membrane Cell Technology A. NIDOLA and R. SCHIRA, Extended Abstracts, Spring Meeting of the Electrochem. Soc., Philadelphia, May

A cathode for use in chlor-alkali membrane cells is described. It consists of a Ni substrate with a roughened surface, coated with RuO, for the H evolution reaction, ZrO, as an electrochemical stabilising agent and La sesquioxide as a mechanical stabilising agent.

10-15, 19879 87-19 552-553

Electrochemical Properties and Corro- sion Behaviour of Ruthenium-Titanium Oxide Anodes w. w . LOSSEW, Z . Phys. Chem. (Leipzig), 1987, 268,

Kinetic reactions of by-processes on RuO, based anodes in chlor-alkali electrolytes have been studied. The investigation of parallel electrode processes allows the kinetics of the by-process to be established by studying the dependence of its partial rate on the overall current density. With the increase of the overall current density, the rates of 0, evolution and Ru dissolution increase much more slowly than the rate for the anodic CI, evolution process, and thus the specific Ru consumption and the current efficiency for 0, evolution are decreased.

(I) , 129-141

PHOTOCONVERSION A New Photosynthesis-Like System for the Light-Induced Reduction of Water to Molecular Hydrogen

Chem., Int. Ed. Engl., 1987, 26, (3), 241-243 Two Zn porphyrinate-modified Pt electrodes, one ac- ting as a n-type semiconductor, the other as a p-type semiconductor (cathode) were used in a photosynthesis-like system for solar energy conversion to H, upon visible light irradiation. The cathode compartment contains the ZnTPyP electrode sur- rounded by aqueous electrolyte of KCl, N,N- dimethylbipyridinium dichloride and highly dispersed platinised TiO, . Photo-Oxidation of Water Sensitised by Cadmium Sulphide Dispersions A. MILLS and G. WILLIAMS, J. Chem. soc., Chem. Commun., 1987, (ti), 606-608 A dispersion of CdS in alkali, of ~ H > I z , was used to sensitise the photo-oxidation of water to 0, by a sacrificial electron acceptor, PtCl: -. Heat treatment and platinisation of the C d S particles prior to irradiation markedly improved (20-40 times) their sensitis- ing power. Below pH 12 no 0, evolution was observed. After prolonged use at pH 13 the Pt/CdS loses the capacity for water photo-oxidation.

Photocatalytic Hydrogenation of Ethylene on the Bimetal-Deposited Semiconductor Powders R. BABA, s. NAKABAYASHI, A. FUJISHIMA and K. HONDA, 3. Am. Chem. SOC., 1987, 109, (8), 2273-2277 The photocatalytic hydrogenation of ethylene was studied on bimetal loaded/TiO, powders and on monometal loaded samples, using Pt, Pd, Cu and Ni. Pt and Cu co-catalysts produced ethane selectively. When the selectivity of C,H, production over CH, was optimised by the Pt/Cu catalyst, the volume of H , concurrently evolved diminished. This suggested that the Pt surface was suitable for the photohydrogenation of C,H,.

W. SCHUHMANN, H.-P. JOSEL and H. PARLAR, Angezu.


Photoelectrochemical Properties of

s. PIAZZA and H. TRIBUTSH, 3. Appl. Electrochem.,

RuS, crystals were grown and doped to produce p-type conductivity. An impedance study of the p-RuS, /aqueous electrolyte interface confirmed the existence of a Fermi level pinning of the semiconductor. The photocurrent is limited by the moderate quality of the barrier which allows forward currents flowing through the interface.

P-RuS 2

1987, 173 (3), 613-624

Gas Sensors Based on Catalytic Metal- Gate Field-Effect Devices

QUIST, Sens. Actuators, 1986, 10, (3&4), 399-421 A review of the properties of gas-sensitive semiconductor devices with catalytic metal gates (Pt, Ir, Pd), mostly of structure metal-SO,-Si, is presented. Em- phasis is on field effect structures sensitive to H- containing molecules, such as H, , NH,, HIS, alcohols, ethylene, etc. The principles of H sensors with Pd gates are described and NH, sensitive field effect devices with thin catalytic metal gates are

I . LUNDSTReM, M. ARMGARTH, A. SPETZ and F . WIN-

discussed. (66 Refs.)

Interferometric Fibre-Optic Hydrogen Sensor

LABORATORY APPARATUS AND TECHNIQUE Optimization of Ammonia-Sensitive Metal-Oxide-Semiconductor Structures with Platinum Gates A. SPETZ, M. ARMGARTH and I . LUNSTRBM, sens. Ac- tuaton, 1987, 11, (4), 349-365 NH, gas sensitive MOS capacitors with Pt as a thin active metal gate were studied. Pt thicknesses of 10-3onm were favourable for a large response to a small NH , concentration.

Optical-Fibre Flammable Gas Sensor F. FARAHI, P. AKHAVAN LEILABADY, J. D. c. JONES and

The sensing element of a flammable gas sensor is a Immm monomode fibre coated with Pt. The rate of the exothermic reaction of the hydrocarbon gases with 0, is increased in the presence of Pt, and the resultant heat is transduced to a phase retardance by a fibre-guided light beam, which is recovered interferometrically . A Solid-state Proton Conductor Sensor with an Ammonia Sensitivity at Room Temperature N . MIURA and w. L. WORRELL, Chem. Lett. Jpn., 1987, (2), 319-322 A new type of solid-state gas sensor using an an- timonic acid proton conductor has been used to detect small amounts of NH, in air at room temperature. The sensor has a four-probe type structure with two outer Pt electrodes and two inner Ag probes. The sensor response varied with NH, concentration from 50 ppm to 5030 ppm in air.

Ion Beam Mixing of Pt with Rent5 N4 Alloy v. SRINIVASAN and R. s. BHATTACHARYA, Surf. Inter- .face Anal., 1987, 10, (2 & 3), 131-134 Ion mixing was studied in the Pt-Rent! N4 alloy system. The substrate, Rent! N4, is a Ni-base superalloy with about 66% of ordered y' precipitates by volume. The average precipitate size is - 0.42pm. Mixing was performed by IMeV Pt + ions at two different doses and followed by Rutherford back scattering and Auger sputter profiling.

D. A. JACKSON, 3. PhyS. E , 1987, 20, (4,435-436

F. FARAHI, P. AKHAVAN LEILABADY, J. D. c. JONES and

A H, sensor has been developed, where the sensing element is a Pd wire mechanically attached to a monomode optical fibre. In the presence of H, the Pd is converted to Pd hydride with resulting changes in the physical dimensions of the wire. These dimensional changes produce a longitudinal strain in the optical fibre, which is transduced to a phase retardance in a light beam guided by the fibre, and which is recovered interferometrically.

The Effect of 0 s Addition on Sputtered Iron Oxide Films

Phys., 1987, 61, (8), Part IIB, 3825-3827 The average grain size of sputter deposited y-Fe, 0 , films is markedly decreased by 0 s addition. The grains grow during the reduction process from a- Fe * 0 , to Fe , 0, and maintain the same size in subsequent oxidation from Fe ,O, to y-Fe,O,. The reduction temperature decreases by I W ~ C at >o.88at.%Os addition. Thus the grain size of r-Fe,O, films decreases from 84 to 35nm as the 0 s content increases from o to over 0.88at.Yo. An accelerating effect on the reducing reaction increases the saturation magnetis- tion and the squareness ratio of y-Fe,O, films. Thus an 0s-added y-Fe,O, thin-film disk has higher output voltage and signal-to-noise ratio than other disks.

D. A. JACKSON, J. Phys. E , 1987, 20, (4), 432-434

0. ISHII, F. YOSHIMURA and A. TERADA, 3. Appl.

JOINING Enhanced Dry Solder Wetting Using AuIPt Coating Layer Res. D i d , 1987, (z75), 158 A thin Pt film can be incorporated between an anti- oxidant layer and a conducting layer to achieve dry solder wetting, which overcomes the problems of outdiffusion through the overcoating layer to the surface where they are oxidised and thus prevent subsequent wetting and joining by solder. A Au/Pt/Cu interface can be formed with only interdiffusion between the Cu and Pt and no outdiffusion of Cu to the Au surface. The Au/Pt/Cu layers can be deposited by any technique and the layers are 1000-20cd thick.


HETEROGENEOUS CATALYSIS Is There a Single Mechanism of Catalytic Rate Oscillations on Pt? S. B. SCHWARTZ and L. D. SCHMIDT, surf. sci . , 1987, 183, (1/2), L269-L278 Experiments are summarised which show that the NO+CO reaction on clean pt(100) or on clean polycrystalline Pt can exhibit oscillations at all pressures between 10-' and I torr and that this is caused by the hexagonal - I x I surface phase transition. Many of the rate oscillations on Pt surfaces may arise from the adsorbate induced I x I - hexagonal surface phase transition of Pt(10o).

Development of a Wetproofed Catalyst Recombiner for Removal of Airborne Tritium

L. 1. PUISSANT, Appl. Catal., 1987, 30, (z), 115--224 A catalyst system capable of removing airborne tritium from nuclear fusion experiments, converting it in a recombiner to water vapour, which is then adsorbed, has been developed for use at ambient temperatures. Wetproofed Pt/C and Pt/SiO, catalysts were prepared and their activities measured with H, . Pt/C was comparable to conventional Pt/AI , 0, under similar conditions. The Pt/SiO, was similar to the Pt/C but its activity could be increased by a factor of

K . T . CHUANG, R. J . QUAIATTI, D. R. P. THATCHER and

5 by exposure to air at 150°C containing 50-200 ppm

quid water or air at 100% humidity were maintained. Chemical Reduction of Chloroplatinic The weturoofer catalvst recombiner enables the

Synthesis and Characterization Of H,. The activities ofthe catalysts when exposed to li- Formed the

Acid operation to be performed at room temperatures. P . R. VAN RHEENEN, M. J. McKELW and W . S. GLAUNS- INGER, J . sold state Chem., 1987, 67, (I), 151-169

Pt s heres of diameter -20-30& Pt strands of -601 diameter and Pt composites of - 100-2001 size could be synthesised from the chemical reduction of chloroplatinic acid, where careful control of the nature of the reducing agent, the presence and type of protective agent and the reduction conditions were undertaken. The optimum protective agent was polyvinylpyrrolidone. The distribution of particle diameters for the spherical Pt can be described by a log-normal distribution function. It may be possible to incorporate unprotected Pt or other metal alloy particles in the hydrosol state into biological systems, such as vesicles, to give high catalytic activity.

Catalytic Dehydration of Acetic Acid on a Graphitized Platinum Surface

Chem., 1987, 91, (9, 1153-1158 A continuous flow microreactor was used for the steady-state catalytic dehydration of acetic acid to ketene and water at 8 x 1 0 - ' and 7 x 1 0 - ' torr pressure and 500-800K. A polycrystalline Pt wire with a monolayer of graphite acted as catalyst.

Selective Aromatization of Light Paraf- fins on Platinum-Ion-Exchanged Gallium- Silicate Bifunctional Catalysts T. INUI, Y. MAKINO, F. OKAZUMI, s. NAGANO and A. MIYAMOTO, Id. Eng. Chem. Res. , 1987, 26, (4), 647-652 The direct conversion of propane to aromatics was investigated on Ga-ion exchanged H-ZSM-5, Pt-ion- exchanged H-ZSM-5, Ga silicate and Pt-ion- exchanged Ga silicate. Pt/Ga silicate had the best performance; the conversion of propane and selectivity to aromatics was 92.3% and 60.7%, respectively at 6ooOC. Pt/H-ZSM-s was much more active than Ga silicate, but was not selective for aromatisation. Pt/Ga silicate was also effective for the aromatisation of light paraffins. The Pt in Pt/Ga silicate reduces catalyst decay and regenerates the decayed catalyst with air.

J . J. VAJO, Y. K. SUN and W. H. WEINBERG, J. Phys.

Silica-Supported Alloy Catalysts for Triglyceride Hydrogenation: The Preparation and Properties of Pd-Ag and Pd-Ni Systems

Technol. Bwtechnol., 1987, 37, (4), 257-270 The binary metal systems Pd-Ag and Pd-Ni were prepared on a Si support with a total metal loading of 2.5%. Twelve catalysts of each were prepared covering the range o-rooat.%Pd. The catalysts were characterised by various techniques, and their activity and selectivity were measured for the hydrogenation of soya bean oil in stirred and shaken batch reactors at Iatm H, pressure and ICCJ-I~O~C. The Pd-Ag system had an activity maximum in the go-Iooat.%Pd range, while the Pd-Ni system had constant activity for alloys containing o-60at.YoNi.

Effect of Hydrogenation Catalyst Activity on Adsorption and Surface Reaction Rates S.-Y. CHEN, J. M. SMITH and B. J. McCoy, Chem. Eng. Sci., 1987, 42, (21, 293-306 Dynamic studies of the hydrogenation of cr-methyl styrene over a Pd/A120, catalyst prepared from PdCl , in a three phase slurry reaction were performed. Measurements were taken at 22,38 and 5o°C. In- creasing the reduction temperature of PdC12 to Pd in H, from 250-@0-51o~C decreased Pd dispersion and reduced the equilibrium adsorption, etc.

A. I. THOMSON and 1. M. WINTERBOTTOM, 3. Chem.

Hydrogenation Activity and Acidity of Bifunctional Catalysts J. WEIWMP and H. DAUNS, Erdoel Kohle Erdgas Petrochem., 1987, 40, (3), 1 1 1 - 1 1 4 The hydrogenating and acidity characteristics of two Pd/LaY zeolite catalysts containing 0.27 and 1.3owt.YoPd were investigated by a simple method for ethylbenzene conversion. Ethylbenzene acted as a probe molecule in H, and in an inert gas atmosphere, where it was hydrogenated to ethylcyclohexane and disproportionated to benzene/diethylbenzenes.


Sulfur Poisoning of Supported Palladium Methanol Synthesis Catalysts M. N. BERUBE, B. SUNG and M. A. VANNICE, Appl. Caial., 1987, 31, (11, 133-157 The deactivation of Pd dispersed on SiO,, q-AI,O,, SiO,-Al,O,, TiO, and Nd,O, was studied in the presence of ippm H, S during CO hydrogenation at 5 q K , I.5MPa and a H,:CO ratio of 3. Activities and selectivities without S were first established. Pd/SiO, and Pd/Nd,O, were most selective to methanol, while Pd/TiO, was the most active CO hydrogenation catalyst, giving CH,OH, CH, and CH , OCH , . Addition of H , S reduced methanation activity by - 50%, but all oxygenate activity was lost, giving a marked selectivity shift to CH, . Pd/SiO, was more S tolerant and stabilised at - 40% of its initial methanol activity. The Pd catalysts are more active than other metals when H, S is present. There may be at least two different types of active sites for CO hydrogenation.

Dehydrogenation of Cyclohexane on Alumina-Supported Rhodium Catalysts. Effect of Oxidation-Reduction Treatment on the Catalytic Activity A. MAEDA, K . KUNIMORI and T. UCHIJIMA, Chem. Lett. Jpn., 1987, ( I ) , 165-166 The cyclohexane dehydrogenation and H , chemisorption on Rh/Al , 0 , catalysts was studied as a function of reduction temperature (373-773K) preceded by 0, treatment at 673K. The catalytic activity increased by a factor of 5 after reduction at 773K, while there was almost no change in the H, chemisorption on varying the reduction temperature.

Preparation of Highly Active Hydrogena- tion Catalysts by Immobilization of Polymer-Protector Colloidal Rhodium Particles H. HIRAI, M. OHTAKI and M. KOMIYAMA, Chem. Lett.

Colloidal Rh particles were firmly immobilised onto a polyacrylamide gel having amino groups at pH 4-9. The resultant catalysts had high activities for olefin hydrogenation, 2-22 fold larger than a Ru/C catalyst at 3ooC under Iatm, and could be used repeatedly without measurable decrease in the activity.

Hydrogenation of Carbon Dioxide into Light Hydrocarbons at Atmospheric Pressure over Rh/Nb205 or CulSi02-Rh/Nb20, Catalyst

Catal., 1987, 104, (21, 339-346

JP~., 1987, (I) , 149-152

F. NOZAKI, T. SODFSAWA, S. SATOH and K. KIMURA, 3.

The two title catalysts give C, + hydrocarbons, mainly C,H, and C,H, with 30-50% selectivity at 2so-350°C and atmospheric pressure. The activity and selectivity of the Cu/SiO , containing catalyst are significantly greater than of the Rh/Nb,O, alone. The Cu/SiO,-Rh/Nb,O, catalyst is composed of two layers and the Cu/SiO, is at the inlet of the catalyst when it converts CO, into CO.

Evidence for the Role of a “Hydridic” Hydrogen on the Selective Hydrogena- tion of Ethyl Acetate to Ethanol with the Bimetallic System Rh-Sn Supported on Silica

NONVILLE and J. M. BASSET, 3. Less-Common Met., 1987, 131, 426-427 Catalyst Rh-Sn/SiO, resulting from the interaction of Sn(n-C,H,), and Rh/SiO,, is more active and selective than Rh/SiO, for the hydrogenation of ethyl acetate to ethanol. Conversions of IW% and 98% selectivities are attainable, depending upon conditions. There is an inverse relationship between the amount of Sn fixed and the amount of H “weakly” adsorbed on Rh, and a linear relationship between the amount of Sn fixed and the amount of “strongly” adsorbed H. The selectivity for ester hydrogenation to alcohol may be due to the “strongly” adsorbed H resulting from the presence of Sn.

Selective Synthesis of Acetic Acid in High Pressure Carbon Monoxide Hydrogena- tion over a Rh-Mn-Ir-LilSiO Catalyst T. NAKAJO, K.-I. SANO, s. MATSUHIRA and n. ARAFAWA, 3. Chem. SOC., Chem. Commun., 1987, (9), 647-649 A highly efficient Rh-Mn-Ir-Li/SiO, catalyst for the direct synthesis of acetic acid from syngas has been developed. Acetic acid was produced with a >65% selectivity in C efficiency and with high space time yield, a typical value being 13og/dm’cat/h at 28ooC and Icokg/cmI pressure, a space velocity of I O ‘ ~ and a H,:CO ratio of 1:9. The Mn, Ir and Li act synergistically towards the Rh/SiO, . Electronic Effects on CO Hydrogenation over Ru-Metal Oxide Catalysts Y. M I , H. MIYAKE and K. SOGA, 3. Chem. soc., Chem. Commun., 1987, (9, 347-348 The electronic structure of supported Ru catalysts is shown to be markedly affected by the nature of the metal oxide support, and the specific activity of CO hydrogenation increases as the electron density of the Ru particles decreases. Seven supports were investigated, including TiO, , MgO, SiO, , etc.

The Catalytic Hydrogenation of Benzene over Supported Metal Catalysts. 111. Gas- Phase Hydrogenation of Benzene over Silica-Supported Ru-Cu Catalysts M. c . SCHOENMAKER-STOLK, J . w. VERWIJS and J. 1. F.

The gas phase hydrogenation of benzene over Ru- Cu/SiO, was studied from 3w-qwK and total pressure 13okPa. Two catalysts, one with - 10% RU surface covered by Cu, the other with -70% CU coverage were prepared. With I I % Cu coverage the lifetimes of the catalysts are considerably increased without seriously affecting the activity/Ru surface atom. A shift in the Cu electron binding energy is observed, indicating a small electron transfer from Ru to Cu; at 68YoCu coverage this shift disappears.

J. P. CANDY, 0. FERRETTI, G. MABILLON, J . P. BOUR-

SCHOLTEN, Appl. Catal., 1987, 30, (2), 339-352

Platinum Metals Rev . , 1987, 31, (3) 152

Chemisorption and Catalysis by Metal Clusters. Hydrogenation of Carbon Monoxide and Carbon Dioxide Catalysed by Supported Ruthenium Clusters Deriv- ed from Ru,(CO),~ and H , R U ~ ( C O ) , ~ S. D. JACKSON, R. B. MOYES, P. B. WELLS and R. WHYMAN, 3. Chem. Soc., Faraday Trans. I, 1987,83, (31, 905-911 The properties of catalysts containing active clusters derived from Ru, (CO) ,z and H, Ru , (CO) ,, supported on SO,, Al,O, and TiO, are described. The clusters, with ligand-COY ligand-C and support- cluster interaction, are thus protected from sintering and are stable under a range of reaction conditions, giving highly reproducible activity for CO and CO, hydrogenations. After preparation the catalysts have an initial none-steady state when C is progressively retained and activity rises to a maximum, then declines to a steady-state value.

HOMOGENEOUS CATALYSIS Reduction of Nitroaromatics with Poly-(vinylpyridine). Complexes of Palladium@) and Platinum(I1) C. R. SAHA and s. BHATTACHARYA, 3. Chem. Technol.

Pd(I1) and Pt(I1) anchored to 2- and 4-vinylpyridine polymers of different molecular weights were used for the H, reduction of various nitroaromatics and benzaldehyde in ethanol at 50%. Pd(I1) complexes were far more effective than their Pt(I1) analogues and the activity decreased with increasing polymer molecular weight. The nitroaromatics were selectively and almost completely reduced to anilines.

Aldehydes via Palladium Catalysed Reductive Carbonylation of Esters 1. L. GRAFP and M. G. ROMANELLI, J. Chem. soc., Chem. Commun., 1987, (9, 337-338 A route to produce acetaldehyde from synthesis gas at low pressures is presented. The aldehydes and acetic acid are obtained in high selectivity from the Pd(OAc), catalysed reaction of esters and syngas. The acetic acid can be esterified with methanol and recycled as methyl acetate. The Pd catalyst gives acetaldehyde selectivities of 70-80%.

S tereospecifc Palladium-Catalyzed Coupling Reactions of Vinyl Iodides with Acetylenic Tin Reagents J. K. STILLE and J. H. SIMPSON, 3. Am. Chem. soc.,

The Pd-catalysed coupling of alkenyl iodides with alkynylstannanes takes place under mild conditions, stereospeciflcally and chemoselectively to give high yields of conjugated enynes. The reaction of (E)- or (Z)-vinyl iodides with alkynyltrimethylstannanes in the presence of catalytic amounts of bis(acetonitrile)(dichloro)Pd(II) is completed in a few minutes at 22OC, giving geometrically pure products.

Bwtechnol., 1987, 37, (4), 233-245

1987, 109, (71, 2138-2152

EMiciently Catalytic C-H Activation. Direct and Mild Carbonylation of Benzene and Cyclohexane by RhCI(CO)(PMe ,) under Irradiation T. SAKAKURAandM. TANAKA, Chem. Lett. Jpn., 1987, (2), 249-252 A high turnover number was achieved in the photo- assisted carbonylation of C-H bonds of benzene catalysed by RhCI(CO)(PMe,), under mild conditions (Iatm, 37OC) to give mainly benzaldehyde. Cyclohexane could also be carbonylated under the same conditions.

A New Homogeneous Rhodium Catalyst for Formation of Ethylene Glycol from Synthesis Gas: Novel Effect of Imidazole Promoters

Organomet. Chem., 1987, 322, (3), C32-C36 A homogeneous Rh catalyst, when treated with a large excess of a imidazole compound shows high activity for the formation of ethylene glycol from synthesis gas. Results suggest that HRh(CO), (imidazole) plays an important role in ethylene glycol formation.

Asymmetric Hydrogenation Catalyzed by Aminophosphine-Phosphinite Rhodium Complexes Derived from Natural Amino Alcohols

Gaze. Chim. Ital., 1987, 117, (2), 129-133 The asymmetric catalytic reduction with Rh aminophosphine-phosphinite complexes was studied to find the best conditions for complete conversion with the highest enantiomeric excess. A new aminophosphine-phosphinite ligand was synthesised, and the Rh complex, Rh [(SS)-biprolophosl (I) was prepared. The stereodifferentiating ability of (I) in asymmetric hydrogenation was dramatically affected by the solvent. CU(I) complexes of aminophosphine- phosphinite were used as a source of chiral ligands in asymmetric hydrogenation with Rh complexes.

Alcohol Electrooxidation Catalysts from Degraded Polyanionic Chelating Ligand Complexes. The Uncertainty for Catalyst Identification that Accompanies a Decom- posing Catalytic System

Y. KISO, M. TANAKA, T. HAYASHI and K. SAEKI, 3.

E. CESAROTTI, A. CHIESA, L. PRATI and L. COLOMBO,

F. C. ANSON, T. J. COLLINS, S. L. GIPSON and T. E. KRAFFT, I n o ~ . Chem.9 1987, 26, (513 731-736 The electro-oxidation of trans-Os(q' -CHBA-Et)- ( p ~ ) ~ , where H,CHBA-Et = 1,2-bis(3,5-dichloro- 2-hydroxybenzamido)ethane, in the presence of alcohols produced several catalytic systems for the electro-oxidation of alcohols. The 0s complex under- went a multistep ligand oxidationhydrolysis sequence. The degradation sequence and catalytic reactions were studied. primary alcohols were con- densed to aldehydes at high alcohol concentrations. Cyclohexanol was oxidised to cyclohexanone.


Synthesis of Ketones and Esters from Olefms, Carbon Monoxide and Alcohols by Using Ruthenium-Iodide Catalysts M. HIDAI, Y. KOYASU, K. CHIKANARI and Y. UCHIDA, J. Mol. Caral., 1987, 40, (2), 243-254 Ru-iodide systems catalyse the reaction of olefins, CO and alcohols to give esters and ketones. Using PhI and CH,I for the carbonylation of ethylene with methanol gives a mixture of methyl propionate and diethyl ketone, the ratio of which depends upon I:Ru ratio. Using ionic iodides, such as NaI, gives methyl propionate selectively, and the catalytic activities increase with increasing iodide concentration.

Ruthenium Catalyzed Oxidation of Alkanes P. H. J. CARLSEN, Synrh. Commun., 1987, 17, (I), 19-23 A Ru catalysed oxidation of alkanes in CC1,-CH, CN- water is described. The products are a mixture of tertiary alcohols and ketones. Norbornane and bicyclo- 12.2.2.loctane are oxidised to the corresponding ketones, while adamantane is transformed to I-adamantanol.

FUEL CELLS Carbon-Based Electrodes Carrying Platinum-Group Bimetal Catalysts for Oxygen Reduction in Fuel Cells with Acidic or Alkaline Electrolytes K. V. RAMESH and A. K. SHUKLA, J. Power Sources,

The electrochemical activity for 0 reduction in acid and alkali electrolytes at C electrodes with Pt-Ru and Pt-Pd bimetal catalysts was measured as a function of electrode composition. Electrodes containing 4Wf.%Pt +6wt.%Pd exhibit the maximum catalytic acuvity, which is also higher than that of the in- dividual metal catalysts.

1987, 19, (4, 279-285

ELECTRICAL AND ELECTRONIC ENGlNEERING Platinum-Tungsten Electrodes for the Alkali Metal Thermoelectric Converter R. M. WILLIAMS, B. JEFFRIES-NAKAMURA, B. L. WHEELER, M. E. LOVELAND, C. P. BANKSTON and T. COLE, Extended Abstracts, Spring Meeting of the Electrochem. Soc., Philadelphia, May 10-15, 1987, 87-19 795 High power, co-sputtered W-Pt electrodes for the alkali metal thermoelectric converter (AMTEC) are reported. The electrodes provide stable power den- sities of o.gW/crn’ over goh. The electrodes have trilayer construction, consisting of an inner layer 0.1-0.2pm thick of W, an intermediate co-sputtered Pt-W layer 1-Wm thick and an outer Pt layer 0. I -0.2pm thick. Pt-Na interactions were studied.

Stable Silicon Solar Cells with High Temperature Survivability J. L. TANDON and K. D. DOUGLAS, Solar cells, 1987, 20, (9, 177-186 By incorporating a thin layer of reactively sputtered TiN in the cell structure, stable solar cells could be produced which had no degradation in their electrical performance after heat treatments up to 6m0C for 15 mins. The TiN is initially sputtered on the entire wafer area. The Ti, Pd and Ag were then applied, and cells were fabricated onto IW Si. A junction -0.3pm deep was formed on p-Si w fer by P diffusion. back metallisation was 12001 Ti, 350A Pd and 35k Ag. The Pd acts as a barrier to 0, to prevent TiN oxidation.

Long-Life High-Reliability Iridium- Coated M-Type Dispenser Cathode Y OUCHI, s. KIMURA, T. HICUCHI and K . KOBAYASHI, Toshiba Rev . , 1987, ( ~ s g ) , 25-29 A long-life Ir-coated M-type cathode has been developed for use in various electron tubes such as space travelling wave tubes. The Ir coating is 0.1-o.5pm thick and is produced by sputtering. The cathode, operating at a current density of o.8A/cm2 and 10ooOC or below has a I5o ,mh life before the emission decreases by 4%, which far surpasses that of conventional 0s-Ru-coated M-type cathodes. The long-life of this type of cathode is attributable to the Ir-W alloy layer (the 6 I , phase) formed by alloying the Ir coating with the W substrate.

Reactively Sputtered RuOl Diffusion Barriers

NICOLET, Appl. Phys. Lett., 1987, 50, (r3), 854-855 The thermal stability of reactively sputtered RuO, films was investigated as diffusion barriers in Si contact metallisations with an Al overlayer. Backscatter- ing spectra of Si/RuO,/Al samples and electrical measurements on shallow junction diodes with <Si>/TiSi,,,/RuO,/Al contacts show that RuO, films are effective diffusion barriers between Al and Si for 30 minutes annealing at 6ooOC. Thus RuO, is interesting for application as diffusion barriers in VLSI technology.

2

E. KOLAWA, F. C. T. SO, E. T.4. PAN and M.-A.

TEMPERATURE MEASUREMENT Stability of Industrial Grade Platinum Resistance Thermometers in the Range

1. VEPREK, Ctyogenics, 1987, 27, (4), 202-204 A comparison is made between the stabilities of five two-lead industrial grade IWQ Pt resistance thermometers used from 13-273K. The static stability was tested by storage over 3 months, and the dynamic stability was tested by cycling the thermometers over 5 and 50 cycles in the range between room temperature and liquid He temperatures.

13-273K

Platinum Metals Rev. , 1987, 31, ( 3 ) 154

NEW PATENTS METALS AND ALLOYS Nickel Base Superalloy UNITED TECHNOLOGIES CORP.

European Appl. 208,645A A high strength Ni base superalloy contains Ru, Rh, Pd, Os, Ir, Pt, Re, plus many other metals. The superalloy is useful for cast single crystal articles such as gas turbine engine blades and vanes.

New Rhodium Alloys STANDARD OIL CO. (OHIO) European Appl. 209,264A Novel amorphous Rh alloys may contain B, P, As or mixtures; or Ir, Pd, Ru, Ti, Zr, Nb, Ta, Y, Hf or mixtures. The alloys are useful as highly corrosion resistant halogen-evolution anodes, with high selectivity to CI,, or can be used as H, permeable mem- branes.

Nickel-Palladium-Beryllium Alloy I.B.M. CORP. U. S. Patent 4,636,25 I An alloy consisting of Ni, Pd and Be is useful as a base material for electrical contacts, especially electrodes and lead frames for packaging electronic components. No barrier layer is required to prevent diffusion, and the alloy is less expensive than conventional materials.

Thin Film Membrane UOP INC. U.S. Patent 4,636,314 A thin fdm membrane consists of electrically conductive particles, typically Pt, Pd or a PtlNi alloy, deposited on a support, and dispersed in a single phase blend of a heteropoly acid or salt and a compatible polymer. The membrane is strong, transparent, and useful for the separation of gases, especially H, in sensors and solid state thin fdm electrolytes.

Thick Film Conductor Composition

A thick fdm conductor composition comprises a fine particle mixture of a noble metal alloy, a binder, and a glass bleed-out inhibitor which may contain Ru, Ir, Rh or Pt. The composition has good solderability and adhesion, and has a short fuing time.

Photographic Material Containing Rhodium

DU PONT DE NEMOURS CO. U.S. Patent 4,636,332

FUJI PHOTO FILM K.K. Japanese Publ. Appl. 611238,049

A Ag halide photographic material contains Rh in the halide particles in the emulsion layer, and a hydrazine derivative in the emulsion layer or hydrophilic colloid layer. The product can be treated under a bright safe light without inhibiting curing, and provides superhard photographic characteristics.

Light Transmitting Conductive Film SUMITOMO ELEC. IND. K.K.

Japanese Publ. Appl. 611253,722 A light transmitting conductive fdm having superior light transmittance and conductivity is produced by forming a fdm of Pt, Pd, Ir, Au, Ag on a metallic backed transparent substrate, and irradiating with ionising radiation.

Photomagnetic Recording Media MITSUBISHI CHEM. IND. K.K.

Japanese Publ. Appl. 611258,387 A photomagnetic recording medium consists of a Pt- Mn-Sn thin film which is crystallographically stable on temperature rise and has good stability to oxidation and chemical reaction.

Platinum or Palladium Colloid SEIKEN KAGAKU K.K.

Japanese Publ. Appl. 611272,026 A high purity Pt or Pd colloid is produced by mixing H, and a sprayed aqua regia solution of Pt or Pd, bur- ning in a flame, and blowing into a liquid medium. The colloids are useful as oxidation or reduction catalysts, or as a drug for detoxificationlcell activation.

Metallising Composition MATSUSHITA ELEC. IND. K.K.

Japanese Publ. Appls. 6 I 1289,69 I 1292,394 A metallising composition contains an inorganic com- ponent with at least one of Pt, Pd and Ni powders, Cu oxide powder, optionally Mn oxide powder, vehicles and a solvent composition. The metallising composition is used as high density packaging boards for mutual wiring of mounted ICs, LSIs, etc.

CHEMICAL COMPOUNDS Noble Metal-Surfactant Adducts AGENCY OF IND. SCI. TECH.

Japanese Publ. Appl. 611243,091 An anionic noble metal complex of at least one metal of Pt, Ru, Rh, Pd, Ir, Au and Ag is reacted with a water-soluble cationic surfactant to form a precipitated noble metal-surfactant adduct. Such adducts are stable, can be stored for a long time and are useful for preparing supported noble metal catalysts.

New Palladium or Platinum Containing Complexes BASF A.C. German Offen. 3,~05,750 New camphor dithiolene complexes of Pt, Pd and Ni are claimed for use as stabilisers, antioxidants, corrosion inhibitors, catalysts or in optical recording media. They are readily available and readily soluble.


Complex Ruthenium Salts HETEROORG. CPDS. Russian Patent 999,523 Salts of bis-arene Ru cations of formula (C,H,RuR), +, where R is the arene group, are produced by reacting the arene with benzene Ru dichloride dimer. The products are used as starting materials for the preparation of catalysts.

ELECTROCHEMISTRY Electrochlorinator R. GREAVES & SONS LTD. British Appl. 2,176,497A An electrochlorinator has an inner tubular anode of Ti coated with Pt and Ir, which is concentrically sur- rounded by a tubular cathode. The electmchlorinator sterilises sea water by forming Na hypochlorite.

Cathode for Electrolysis Cell ATOCHEM European Appl. 209,427A A cathode consists of an electrically conducting substrate coated with an oxide of a platinum group metal, and optionally other metal oxides. For example, it may consist of layers of RuO, associated with one or more layers of TiO, andlor ZrO,. The cathode is used for electrolysis of water or halides.

Gas Diffusion Electrode ASAHI GLASS K.K. Japanese Publ. Appl. 611266 ,591

A gas diffusion electrode has a catalyst of Pt, Pd, Ag, h e y Ag or a spinel series oxide, and is produced by removing C powder from one side of a porous electrode sheet consisting of the catalyst, C powder and a F-containing polymer. The electrode can be used in a H , - 0 , fuel cell or gas sensor.

Electrode Material Production TOY0 SODA MFG. K.K.

Japanese Publ. Appl. 61/281,889 An amorphous alloy containing Ta, one or more of Ru, Rh, Pd, Ir and Pt, Ni and optionally other metals is used to produce highly corrosion resistant and active electrodes for electrolysis of acidic solutions.

Platinum Anode for Plating SUMITOMO M T A L IND. K.K.

Japanese Publ. Appl. 61/288,093 An anode for electrolytic plating consists of Pt coils placed next to an opening in a masking plate in such a way that the anode coils do not interfere with the plating liquid stream.

Platinum Alloy Electrode V.E.B. MANSFELD-KOMB. PIECK

East German Patent 238,706 The electrode consists of Pt or a Pt-Rh alloy on a Ti, Ta, Nb or Zr substrate. It is especially useful as an anode in aqueous solution at which C1, and 0, are evolved; it is stable, has high electrical conductivity and is simple and inexpensive to manufacture.

ELECTRODEPOSITION AND SURFACE COATINGS Palladium Alloy Electrodeposition LEARONAL INC. U.S. Patent 4,628,165 A Pd alloy is coated upon a substrate by dual phase electrodeposition of Pd and Ni or Co, followed by a thicker layer of Pd-Ag, to produce an electrical contact claimed to have increased ductility, reduced porosity and reduced tendency for cracking of the dual layer.

High Adherence Metal Conductor Films

Japanese Pu bl. Appl. 61 / I 79,875 Metal conductor films and metal conductor circuits of printed circuit boards are formed by heating a Pd containing polymer fdm to deposit Pd on a substrate, followed by electroless plating. The metal conductor fdms so formed are highly adherent.

Platinum Group Metal Alloy Coating

NISSAN CHEM. IND. K.K.

MATSUSHITA ELEC. IND. K.K. Japanese Publ. Appls. 61/281,028/29

A surface coating of a platinum group metal alloy containing additional metals such as Zr, Ti, Hf, or their oxides, is used in press-shaping moulds for the production of optical glass elements. The thin film exhibits improved wear resistance, and the element does not need polishing after press-shaping.

Platinum Alloy Plating Bath YASUKAWA ELECTRIC MFG. K.K.

Japanese Publ. Appl. 611288,ogo A Ag-Zn-Pt alloy plating bath contains cyanide and chloride compounds and produces a plating layer with excellent resistance to sulphiding, and which is suitable for the production of electrical contacts, etc.

Palladium-Nickel Plating Bath KOJIMA KAGAKU YAKUH

Japanese Publ. Appl. 61 /288 ,091

A Pd-Ni alloy plating bath with excellent stability is prepared by blowing gaseous sulphurous acid into Pd sulphate solution, then adding NH, and a Ni salt. The Pd-Ni alloy plating layer obtained has excellent white brightness and corrosion resistance.

LABORATORY APPARATUS AND TECHNIQUE

Air Flow Measurement POTTERTON INT. LTD. British Appl. 2,176,292A A heated filament of Pt-Ni or nichrome wire, having approximately linear change of resistance with temperature, is used in an air flow measurement apparatus for an anemometer. This type of filament avoids the need for a second non-heated temperature- dependent resistance.


Surface Ion Sensor UKR TOWNS SERVICING

World Patent Appl. 871276A An improved surface ionisation sensor for a halogen leak detector consists of a Pt anode wound spirally around a central cathode wire, inside a tubular holder of white sapphire. The sensor has a longer life, less thermal inertia, and improved sensitivity.

Electrokinetic Measurements of Fibrous Material FORSCHUNGSANWENDUNG

World Patent Appl. 87f285A Perforated Pd electrodes are included in a unit for simply and exactly measuring the electrokinetic potential of fibrous materials. Information about washability and contamination resistance of the material is also provided.

Palladium Alloy Hydrogen Purifier ULVAC CORP. Japanese Publ. Appls. 61/157,323/26/27 A stable, high purity H , purifier consists of a Pd alloy tubular membrane welded to a stainless steel body, etc., which allows only H, to pass through when heated.

Hydrogen Detecting Element NOMMI BOSAI KOGYO K.K.

Japanese Publ. Appl. 6 I 1223,642 A stannic oxide based gas detecting element containing Pt and Sb is treated in a silane atmosphere to produce a H, gas detecting element, which can be used selectively, at relatively low temperature, and which has an improved response time of 100-150s.

Platinum Alloy Gas Sensor SANE1 SEIKO K.K.

Japanese Publ. Appls. 611246,659160 A catalytic combustion type gas sensor has Pt alloy coils, for example Pt-Ni or Pt-Rh, which may be coated by Pd oxide or Cu oxide layers, depending on the application. It can be used to detect CH, or CO with high sensitivity, and has high durability (CH,) and low cost (CO).

Flame Ionisation Detector HORIBA LTD. Japanese Publ. Appl. 611265,562 A heated combustion catalyst such as Pt is present in the gas blowing nozzle andlor passage leading to the combustion chamber of a flame ionisation detector. The Pt can be linear, mesh, or fibrous-shaped.

Dewing Inhibitor Sensor NIPPON MINING K.K.

Japanese Publ. Appl. 611269,054 A dewing inhibitor sensor includes a humidity sensing element with a parallel external short circuit, preferably made up of a RuO,, CuO, and NiO, paste. The sensor has definite switching characteristics and is stable.

Ruthenium (Oxide) Powder Production SHINCIJUTSU KAIHATSU

Japanese Publ. Appl. 611270,222 Ru oxide powder andlor Ru metal powder are produced by reacting a Ru compound-preferably a halide-with an alkali metal alkoxide, and hydrolys- ing the resulting product. Using this method fine powders of ipm diameter can be produced for hybrid integrated circuits, without high energy grinding.

JOINING Activating Layer for Welding

A thin activating layer of maximum thickness 0.1-1pm comprises at least one carbide andlor silicide forming element, which may consist of Pd, Pt, Ag, Au and other metals. The layer is used to coat fitting surface(s) of Sic parts to be bonded together by welding. Stable, gas-tight welding seams are obtained, which are resistant to corrosion, oxidation and temperature changes.

Brazing Metallising Composition KYOCERA CORP. Japanese Publ. Appl. 611251,590 A metallising composition comprises W, Mo andlor Mn and at least one of Ru, Rh and Ir, or an alloy of Ru, Rh or Ir. It is useful for the formation of a metallised metal layer for brazing an external lead ter- minal or integrated circuit element onto a ceramic body. High bonding strength is realised.

Brazing Filler Material for Ceramics

KERNFORSCHUNGS JULICH European Appl. 209,672A

TANAKA KIKINZOKU KOGYO Japanese Publ. Appls.

6 1 / ~ ~ ~ , ~ ~ ~ / ~ 8 ~ , ~ ~ 1 1 ~ ~ / ~ 8 6 , o 8 8 A brazing fder material consists of a Ag andlor Cu alloy containing Pd, Ti andlor Zr, and possibly Ga. The filer is suitable for directly joining ceramics to ceramics, or to metals. The brazing time is decreased, and good brazed joints can be obtained.

Brazing Filler Material NIPPON DENS0 K.K.

Japanese Publ. Appl. 611291,939 A metal composition containing at least one of Pt, Pd, Rh, Ir, Ru and Os, and at least one of Cr, Mn, Fe, Co, Ni and Cu, is effective as a brazing fdler for joining non-oxide ceramics and metal, or as a metallising metal, in joining ceramic turbo-rotors and shafts.

HETEROGENEOUS CATALYSIS Ruthenium Hydrogenation Catalyst RHONE-POULENC CHIMI European Appl. 192,587A A catalyst consisting of a Ru compoundISi0, gives good selectivity for the vapour phase hydrogenation of acetic acid to produce ethanol andlor ethyl acetate.

Platinum Metals Rev . , 1987, 31, (3) 157

Waste Gas Catalyst HITACHI K.K. European Appl. 208,434A A catalyst containing at least one of Pt, Pd or Rh, Ti oxide, and at least one other metal oxide, is used to remove NOx and CO from exhaust gas in the presence of steam and NH , . The exhaust gas may be from power plant boilers, gas turbines, nitric acid plants.

Acetal Preparation NATIONAL DISTILLERS CORP.

European Appl. 210,453A A noble metal selected from Rh, Pd or Pt, or preferably Ru, or a metal halide, pFeferably RuCl ,, is used to accelerate acetal preparation from an allylic ether and an organic hydroxy compound under anhydrous conditions.

Palladium Oxidation Catalyst STAMICARBON (DSM SUBS.) European Appl. 210,705A An improved catalyst for the gas phase oxidation of alkene(s) and cycloalkene(s) to ketones or aldehydes, in the presence of H, 0 and 0 , , consists of a Pd compound and a monolayer dispersion of V supported on y-A120J. The catalyst does not lose its activity by clogging with V,O,.

Platinum Re-ignition Coating WILLIAMS RES. CORP. U.S. Patent 4,603,547 Improved construction of a gas turbine combustion chamber includes a catalytic surface coating containing a noble metal, such as Pt, covering about 90% of the area. This facilitates relighting of the air:fuel mixture reliably and economically, minimising failure.

Palladium Hydrogenation Catalyst

Selective hydrogenation of acetylenic compound with up to 30C, to a cis-olefinic compound uses a catalyst of Pd supported on CaCO,, Pb acetate, and an aromatic amine oxide. High selectivities are obtained, without costly low-temperature operation.

Platinum Zeolite Reforming Catalyst CHEVRON RESEARCH CO. U.S. Patent 4,627,909 A Ptlzeolite catalyst is used during the second stage of an improved low pressure hydrocarbon reforming process in a dual recycle pressure-step reformer which uses a bifunctional catalyst containing one or more platinum group metals/Al , 0, in the first stage. The catalyst is protected by a desulphurisation stage in the process.

Sulphur Oxide Removal

A catalyst containing Zn,TiO, and promoters which can be Ru, Pt, Pd, Rh, or Re or their compounds or mixtures, is used for the removal of S oxide from a gaseous stream, especially tail gas from S manufacture, in the presence of a H donor. S oxide is converted to H, S and absorbed.

PHILLIPS PETROLEUM CO. U.S. Patent 4,605,797

PHILLIPS PETROLEUM CO. U.S. Patent 4,636,371

Catalytic Combustion Apparatus BABCOCK-HITACHI K.K.

Japanese Publ. Appl. 611168,725

A catalytic combustion apparatus contains a Pd honeycomb catalyst and has a peep-window of sapphire glass to monitor temperature.

Fixed Biocatalyst Preparation MATSUSHITA ELEC. WORKS

Japanese Pu bl. Appl. 6 I /I 87,792 The Pt support on which a crosslinked albumin film is formed is treated with aldehyde, to form aldehyde groups, which are used to fur the catalyst. A high activity biocatalyst can be prepared reliably.

Waste Gas Purification Catalyst NIPPON SHOKUBAI KAGAKU

Japanese Pu bl. Appl. 61 1222 ,541

A catalyst containing Pd, Rh or Pt together with a V compound and a double oxide of P and Al, supported on a refractory structure, shows improved durability for purification of waste gas containing C.

Aldehyde Hydrogenation Catalyst AGENCY OF IND. X I . TECH.

Japanese Publ. Appls. 611230,7381741 Catalysts containing Pd, Fe andlor Mo, or compris- ing Ir, Fe and optionally Rh, show high conversion activity for aldehyde hydrogenation to alcohols.

Gamma-Ray Shield TORAY SILICONE K.K.

Japanese Publ. Appls. 6 11240, I 971241,699 A Pt catalyst with an organopolysiloxane, an organohydrogen polysiloxane fluid, a metal fine powder and organopolysiloxane raw rubber andlor silica powder, or C fine powder, are the components of a composition having excellent ?-ray shielding performance. The product can be used effectively in atomic power stations and flame retardancy.

Catalytic Combustion System KIKAI SYST. SHINKO K.

Japanese Publ. Appls. 611252,40819 A catalytic combustion system has an active catalyst layer containing Pd and Pt, or Pd, Pt and Ni dispersed on a monolithic support coated with a stabilised oxide layer. Methane-based fuels can be completely burned to give high temperature combustion gases, without NOx, CO or unburned HC.

Catalyst Indicating Deterioration during Combustion DODENSEI MUKIKAGO

Japanese Publ. Appl. 61 1274,748 A catalyst consisting of a complex oxide, a Sr containing oxide such as SrTiO,, andlor Pd or Rh, is sprayed on an insulating refractory substrate, and is used to indicate deterioration during combustion by an abrupt increase in its resistance.


Hydrocarbon Isomerisation Catalyst KEISHITSU RYUBUN SH.

Japanese Publ. Appl. 61/280,440 The catalyst is obtained by calcining a mixture of a S and halogen containing reagent, one of Pt, Ru, Rh, Pd, Os, Ir and Ni, etc., and a carrier of a Group IV metal hydroxide or oxide andlor a Group 111 metal hydroxide or oxide. The catalyst has a long life and gives a high isomerisation rate for linear paraffins and some cyclic hydrocarbons.

Olefm Hydrogenation Catalyst INST. FRANCAIS DU PETROLE

German Offen. 3,623,777 An active catalyst consisting of supported noble metals contains first metal(s) from Pd, Rh, Ir and Pt, and different second metal(s) selected from Au and Pt. It is useful for hydrogenating olefins in ethers for chemical and pharmaceutical use, it is active in the presence of S, and is used to increase the octane number of unleaded motor fuel.

Palladium Oxidation Catalyst NIKKI UNIV. K.K. Japanese Publ. Appl. 611287,425 HOMOGENEOUS CATALYSIS The catalytic oxidation of waste gas containing organic solvents and 0, is achieved by using supported Pd catalysts operating at high temperature. Pd catalysts have higher resistance to heat and catalyst poisons than Pt catalysts; so the waste gas, such as toluene, can be treated at high temperature without air dilution.

Exhaust Catalyst NGK INSULATORS K.K.

Japanese Publ. Appl. 62 /4 ,441

Catalytic components such as Pt, Pd, Rh, rare earth metals or others, are deposited on a cordierite honeycomb structure which has been treated with acid and heated. The catalyst is used as an oxidation or three-way catalyst for the purification of automobile exhaust, or as an industrial deodorising catalyst. It has improved resistance to thermal shock.

Carbon Monoxide Oxidation Catalyst NIKKI UNIVERSAL K.K.

Japanese Publ. Appl. 62114 ,944

A catalyst which can oxidise CO at room temperature under atmospheric pressure consists of Pd, and one or more of Fe, Mn and Ce, supported on AI,O,. It is used for ventilation of combustion heaters, highway tunnels, chemical plants, etc., and also in gas masks.

Organosiloxane Preparation

A metallic Pd, Ru or Rh catalyst or one of these metals as a complex or comopound, is used to catalyse the preparation of organosiloxane compounds containing a halogen bonded to Si, by the reaction of a siloxane and ally1 halide. Products are obtained rapidly with high yields using relatively small amounts of catalyst.

Exhaust Gas Purifier R. EIGLMEIER German Offen. 3,528,107

Perforated steel discs on an axial support are coated with a noble metal and glass catalyst; a first and second set of discs having a coating of Rh-glass and Pt- glass, respectively. The discs have a working temperature of 2 0 o O C . The purifier is used to react with CO, NOx and hydrocarbons in exhaust gas from a vehicle using lead-free petrol.

WACKER CHEMIE G.rn.b.H. German Offen. 3 ,518 ,605

Rhodium Hydroformylation Catalyst EXXON CHEM. PATENTS European Appl. 195,656A The hydroformylation of an internal olefin to the corresponding aldehyde uses a liquid Rh tri- organophosphine catalyst system, CO, H,, and a sterically hindered tri-cycloalkylphosphine. Rapid reaction rates are achieved compared with conventional Rh systems; also high selectivity, catalyst stability, and negligible degradation are obtained.

Carboxylic Acid Preparation HOECHST A.G. European Appl. 206,054 Carboxylic acids are prepared by Pt catalysed oxidation of primary alcohols in a mixture of water and glycol ether as solubiliser. The method enables almost insoluble primary alcohols to be oxidised easily and economically.

Platinum Catalyst for Silicone Foams DOW CORNING CORP. U.S. Patent 4,613,630 Water blown, low density, open cell silicone foams are produced by mixing a hydroxy or vinyl end block- ed polydiorganosiloxane, a Si hydride compound, water, a Pt catalyst and optionally a profoamer. The low cost elastomeric foam produced is useful for cushioning and sealing applications.

Palladium-Phosphine or -Arsine Catalyst TEXACO INC. U.S. Patent 4,629,807 Pd-phosphine or Pd-mine catalysts are used for the preparation of aliphatic dicarboxylic acids and ester(s) from alpha, omega-diene(s) and CO. The catalysts afford improved yields of these acids, especially the desired linear di-acids, which are corrosion inhibitors for antifreeze. Improved Pd catalyst recovery is possible, and temperature staging allowed.

Vinyl Phosphonic Acid Preparation DAIHACHI KAGAKU KOCYO K.K.

Japanese Publ. Appl, 611275,288 A catalyst containing a Pd halide andlor Pd acetate and at least one tertiary phosphine compound is used in the preparation of vinyl phosphonic acid from a P diester and an olefinic halide. The catalyst can be used repeatedly without treatment, is inexpensive, and gives a high purity product in high yield.


Rhodium Carbonylation Catalyst

A catalyst system of enhanced stability for the carbonylation of methanol to acetic acid includes Rh triiodo-tris(dimethy1-sulphide), HI, CH, I, water, acetic acid and methanol.

A.S. U.S.S.R. CHEM. PHYS. Russian Patent 1,204,251

FUEL CELLS Electrocatalyst for Fuel Cells HITACHI K.K. Japanese Publ. Appl. 611274,747 Catalysts consisting of noble metal particles, preferably Pt, highly dispersed on the surface of conductive particles, preferably C, are prepared by the reduction of complexes of noble metal ions in aqueous solution. When used for air electrodes in fuel cells they give higher initial output and long life.

ELECTRICAL AND ELECTRONIC ENGINEERING Platinum Cathode for Laser RAYTHEON CO. British Appl. 2,175,438A The electrode assembly for a CO, waveguide laser comprises an anode, and a cathode with a portion preferably Pt with a smal l addition of Rh for emitting the electrical discharge towards the anode. Electrical discharge is constrained directly between electrodes.

Conductive Cable for Underwater and Space Application MATERIAL CONCEPTS U.S. Patent 4,634,805 A conductive cable consists of polyaramid rows of parallel, untwisted fdaments coated preferably with Pd, Ni, Au, Cu or Co. A second metal coating of Pt, Rh, Ru, Ag, In or other metals may be present. The cable has good strength and conductivity, and is used in underwater and space tether applications.

MEDICAL USES Antimicrobial Noble Metal Layer BECTON DICKINSON CO. European Appl. 206,024A Wcroorganism growth on the surface of a medical device, such as a catheter, is inhibited by layers of Pt, Au or Ag, and Ag or Al in contact on its surface. The device is preferably used as part of a urinary catheter, and reduces the incidence of infection.

Biochemical Sensor UNIV. OF CALIFORNIA Eumpean Appl. 206,531A An electrochemical cell sensor capable of being implanted into an animal body has an electrode in a housing coated with biocompatible material. The housing is a hollow needle of Pt or stainless steel. The

Microorganism-Propagation Inhibiting Sheet UNITIKA K.K. Japanese Publ. Appl. 611182,943 A metallic thin fdm of Pd, Pt, Au or Ag is formed in vacuo, on a sheet-form material, by vapour deposition. This article may be in the form of paper, fabric, film, etc., and is used as a microorganism- propagation inhibiting sheet on clothes, food packaging, filters, health and sanitary materials, etc.

Platinum Anti-Tumour Agent TANABE SEIYAKU K.K.

Japanese Publ. Appl. 611249,993 N-substituted aspartato-trans-levo-diamino cyclohex- yl Pt complexes are useful as anti-tumour agents effective in the treatment of ovarian, prostate and mammary cancers and leukemia.

Palladium Alloy for Dental Use DEGUSSA A.G. German Offen. 3,522,523 Ag-free Pd alloys containing Pd, Pt, Ru, Au andlor Re, Cu, Sn, In, one of W, Mo, Nb or Ta, and Co, are cheap, extra hard and compatible with dental ceramics.

Diagnostic Agents Containing Ruthenium M. WENZEL German Offen. 3,523,262 Metallocene derivatives preferably containing ruthenocene and labelled with a radioactive metal isotope, such as Ru ’’ or Ru 9 5 , are useful as diagnostic agents for scintigraphic imaging of brain and lungs.

Lower Toxicity Platinum Anti-Tumour Agents

New Pt crown ether complex compounds are useful as anti-tumour agents with comparable activity to cisplatin, lower toxicity, and higher water solubility.

New Platinum Anti-Tumour Complexes ASTA WERKE A.G. German Offen. 3,605,191 New 3-aryl-I ,~-propylenediamine Pt(I1) complexes are prepared by reaction of, for example, 3-phenyl- propylene-I ,z-diamine with tetrahaloplatinic acid. The new compounds are well tolerated and show good anti-tumour activity.

Platinum Complex for Rubber Com- position CABLE IND. DES. BUR. Russian Patent 1,219,621 A Pt and ferrocene complex is included in a vinyl- siloxane-based rubber composition used in the manufacture of medical items. The Pt complex improves resistance to overcuring, while preserving physico-mechanical properties and hygiene.

MEDAC GES. KLINISCHE German offen. 3,524,841

sensor is used to determine the concentration of cer- tain biochemicals-glucose, alcohol or uric acid.

The New Patents abstracts have been prepared from material published by Dement Publications Limited.


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