Contents · Contents Chiral Complexes of ... Any discussion on such specialised topics as isomerism and chirality needs to be prefaced by ... such as C1-, etc. (2)

PLATINUM METALS REVIEW

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

VOL. 40 JULY 1996 NO. 3

Contents

Chiral Complexes of Platinum Metals

Palladium Facilitates Optical Switching

Emission Control Technology

Electronic and Nuclear Magnetism in Platinum-Iron at Ultralow Temperatures

Palladium Colloid Catalyst Used in Microcontact Printing

Platinum and Biological Systems

Hydrocarbonylation in Platinum Metals Metallurgy

Single Platinum-Rhodium Gauze for Partial Oxidation

Palladium Catalysts in Organic Synthesis

Platinum Complexes Used in DNA Binding Studies

Platinum 1996

Ruthenium: “A Dance to the Music of Time”

Abstracts

New Patents

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109

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143

Communications should be addressed to The Editor, Susan V. Ashton, Platinum Metals Review

Johnson Matthey Public Limited Company, Hatton Garden, London ECl N 8EE

Chiral Complexes of Platinum Metals A NEW CLASS OF COMPOUNDS WITH LIGANDS DERIVED FROM NATURALLY OCCURRING TERPENES HAVING PROMISING PROPERTIES

By Professor A. von Zelewsky Institute of Inorganic Chemistry, University of Fribourg, Switzerland

Molecular isomerism has been known about for well over 100 years and forms a very important part of organic chemistry It was one of the phenomena from which the Alsatian chemist, Aljred Werner, working, often with platinum group metals, at the University of Zurich, Switzerland (Nobel Prize for Chemistry 1918) derived his ‘theory of co-ordination’in 1893 ( 1 ) . However, more recently there has been a vast increase in the amount of work done on isomerism of co-ordination compounds, especially concerning chiral structures ( 2 ) . Thepre- sent paper describes some new developments on platinum metals complexes with chiral ligands derived from terpenes, where for thefirst time the chirality at metal centres can be controlled in a large number of compounds.

Any discussion on such specialised topics as isomerism and chirality needs to be prefaced by a description of some of the terms used. Co- ordination compounds have a central atom sur- rounded by other atoms or molecular entities called ligands, which are bound or co-ordinated to it. Some compounds are isomeric, which means that they exist as two or more structures with the same molecular composition but with a different spatial composition or constitution.

Background of Isomerism Isomerism can occur in several ways: the sim-

plest being constitutional isomerism, where the same atoms are connected in different ways. If, on the other hand two molecules contain identical atoms connected together in the same way, but with different spatial arrangement, one speaks of stereoisomers. Molecular stereoisomers can be divided unambiguously into two different classes: diastereoisomers and enantiomers.

Diastereoisomers are molecules that show the same connectivity, but differ in the spatial arrangement of the atoms. Internal co-ordinates (bond lengths and bond angles) will be in general different in different diastereoisomers, ren- dering them different chemical species in every

respect. A well-known example of diastereoisomers in platinum chemistry is cis- and trans- dichlorodiamino platinum(II), respectively. The former is the known anti-cancer agent cisplatin, whereas the latter has no therapeutic use (3).

The second class of stereoisomers are the so- called enantiomers (from the Greek word for opposite). The two molecular species of a pair of enantiomers differ from one another only in that they are non-superposable mirror images. From general symmetry considerations, it can be deduced that molecules which have neither planes of symmetry nor an inversion centre show enantiomerism (higher order so-called improper rotation axes must also be absent).

The Concept of Chirality Molecules that fulfil the conditions to show

enantiomerism are said to be chiral (from the Greek word of handedness, a concept introduced by Lord Kelvin in 1893). Molecules, where the mirror image is identical to the molecule itself are designated as achiral. The two enantiomers of a pair behave in a chemically identical way, unless the interacting partner is also chiral. For example, enantiomers rotate the plane of incident, linearly-polarised, light of a certain wavelength by the same angle, but in

Platinum Metals Rev., 1996, 40, (3), 102-109 102

opposite directions, since such polarised light can be considered as a pair of enantiomers: one right- and one left-handed circularly polarised component.

In general, enantiomers also behave very dif- ferently in real chemical reactions, if the reaction takes place between two chiral molecules. A substance composed of chiral molecules can occur either as an enantiomerically pure compound (EPC), or as a racemate, which is a 1 : 1 mixture of both enantiomers, or indeed as any- thing between these two limits. The enantiomeric purity is nowadays generally given as the so-called enantiomeric excess (ee), which is 1.0 (or 100 per cent) for an EPC and 0 (0 per cent) for a racemate.

Many molecules in living systems, such as amino acids or sugars, but also terpenes, are chiral and they occur as EPCs. Sometimes these naturally occurring enantiomerically pure compounds are referred to as the "chiral pool". It is unthinkable that biological systems could have developed without enantiomerically pure compounds, but it is still not completely explainable how nature achieved the single enantiomeric occurrence of most chiral compounds during early stages of evolution.

Racematea Syntheses of chiral molecules starting from

achiral precursors almost always yield racernates. A racemate can either crystallise as a macro- scopic conglomerate of two kinds of crystals that themselves are mirror images of each other, or as uniform crystals where in each unit cell an equal number of each enantiomer is present. The latter case occurs more frequently and these solid phases are called racemic compounds or racemic modifications. The former case (occurrence of a conglomerate) gave rise, almost 150 years ago, to the discovery of molecular optical activity by Louis Pasteur (4).

Chiral descriptors are needed in order to distinguish between the two enantiomers of a pair. In principle one pair of symbols would suffice. For practical reasons, however, several con- ventions have been established. For organic compounds, the WS convention (so named by Cahn,

.

n n

Fig. 1 The enantiomeric pair of a M(L"L), chiral complex; left is A, right is A

Ingold and Prelog) is mostly used (from the Latin rectus and sinister, respectively), whereas in co-ordination chemistry the N A designation is often applied to right- or left-handed helical chiral molecules.

Using symmetry considerations, Alfitd Werner had already predicted, in a paper published in 1899, that some types of octahedral co-ordination compounds should be chiral and hence, in principle, separable into enantiomeric compounds (5). In 191 1, the first report of such a successful separation was published (6).

Platinum Group Metal Co-ordination Sphere

The co-ordination sphere around many of the platinum group metal centres is octahedral, see Figure 1. In particular, the octahedral co-ordination spheres of ruthenium(II), osmium(II), rhodium(III), iridium(II1) and platinum(IV), yield a large number of chiral complexes of the classical Werner type, that is M(L"L)3 or M(L"L)& where L"L are bidentate ligands and X is a monodentate ligand, such as C1-, etc. (2). The number of such complexes is almost limitless, since there are a very large number of bidentate ligands.

Interesting examples of such Werner-type complexes are the purely "inorganic" ions [PtS,,12- and [PtSl7I2-, respectively (7). In these species, which should be written as [(Pt(S,),]'- and [Pt(S&S5]", the chelate rings around the central platinum atoms are formed by sulphur atoms (a chelate ligand is attached to the central atom through two or more co-ordinating atoms). For

Platinum Metals Rev., 1996, 40, (3) 103

Fw 2 c~mputer model repmaentation ofthe two isomers of a dinucIear eompIex, [(Ru(bpy)&Lqp~]'+ with identical (homoehird), and with opposite chiralitiea (heteroehiral), respectively, at the two ruthenium centres. To the left is A,A, to the right is A,A. Here, ruthenium is eoloured red, hydrogen pale blue, carbon grey and nitrogen dark blue

these species and for most other cases of chiral octahedral complexes, the chirality is a result of the helical arrangement of the chelate ligands. The symmetry group of these molecules (D1) does not contain any mirror plane or inversion centre, but only three-fold and two-fold rotation axes, see Figure 1.

Predetermined Helical Chirality As already mentioned, the synthesis from achi-

ral starting materials yields racemates, except for some very special cases (2). The two enantiomers are consequently formed in equal amounts, and applications for which EPCs are needed therefore require a separation procedure. Enantiomerically pure coordination compounds are relevant for several important applications: (i) The stereoselective step in enantioselective catalysis (a multi-billion pound sterling busi- ness) often takes place at the metal site. (ii) Multicentred supramolecular species of photochemically active coordination units often give rise to a large number of stereoisomers (which makes their detailed characterisation very difficult), unless enantiomerically pure building blocks are used. (iii) Enantiopure chiral metal complexes are potentially interesting species for solid state applications in non-linear optics (NLO), since such compounds must crystallise in non- centrosymmetric space groups.

(iv) EPCs are needed in therapeutic applications of chiral co-ordination compounds, since enantiomeric purity is nowadays required for pharmaceutical molecules.

Thus, for all four types of applications, the platinum group metals constitute co-ordination centres of prime interest.

Controlling the Chirality The control of chirality at the metal centre can

be achieved by various means. First, racemates can be separated into pure enantiomers which can then be used as chiral building blocks. This method has been applied for the synthesis of dinuclear ruthenium complexes with tris-diimine co-ordination spheres (8). Such complexes are the prototypes of species that can be functionalised to yield photochemical molecular devices (9). In Figure 2 two isomers of the ruthenium complex [(Ru(bpy)&bpym]'+, where bpy is 2,2'- bipyridine and bpym is 2,2'-bipyrimidine, are shown. The isomers have different stereochemistry; one is a homochiral complex (having the same chirality A,A at both metal centres), and the other is a heterochiral complex (different chiralities A,A at the metal centres), built from units which were obtained by classical resolution of a racemate (that is, separation of the two enantiomers).

However, there are two drawbacks to using enantiomerically pure building blocks obtained by resolution of a racemate. One drawback is

Platinum Me& Rev., 1996,40, (3) 104

Fig. 3 Bis-bidentate ligand, where the two I chelating units are linked by a chiral bridge

the inevitable loss of at least 50 per cent of the material, if one is only interested in a building block of a given chirality. The other, even more severe drawback is the possibility of racemisa- tion (back-transformation to the 5050 mixture of the two isomers) under certain reaction conditions. The latter effect is especially important for ruthenium complexes, which are known to racemise under the influence of light.

A second method, where complete control of chirality at the metal centre can be achieved using ligands that are themselves chiral, is therefore to be preferred. A chiral ligand is shown in Figure 3.

Here, two bidentate chelates are linked by a bridge that is anchored at the chiral centres (carbon atoms with four different substituents which were formerly called asymmemc carbon atoms, nowadays designated stereogenic carbon centres) A and B, respectively. The ligand mole-

cule is QOW a tetradentate chelate, where two bpy units are permanently connected. The chirality at the metal centre can be predetermined completely by this method as we have shown, by designating a ligand, which fulfils these requirements.

In Figure 3 the helical chirality is A. An inversion of the chiral centres, A and B, leads to A chirality at the metal centre, whereas the ligand is not capable of co-ordinating to one metallic centre with both bpy moieties if only one of the chirality centres, A or By is inverted. Since con- figurations at carbon centres are stable under most circumstances, inversion does not take place at all and the chirality at the metal centre is therefore completely fixed.

Chiral Ligands The first ligand of this type was CHIRA-

GEN[6], the ligand depicted in Figure 4; the number in square brackets, for instance [6] in this case, indicates the nature of the bridge, here six -CH2- groups. This type of ligand was called a CHIRAGEN

ligand [6], since it generates chirality at the metal centre. The original source of the chirality in CHIRAGEN ligands is in the saturated part of the molecule, which is derived from naturally occurring pinene, a “chiral pool” molecule. The ruthenium@) complex, [Ru(CHIRAGEN[6])- @Mbpy)l2’, shown in Figure 5, where DMbpy is 4,4’-dimethylbipyridine3 has been shown to

N \ 3 Fq. 4 Two chirally bridged bipyridine units are co-ordinated in a manner which predetermines the chirality at the metal centre

Plarinum Metals Rm., 1996,40, (3) 105

Fig. 5 A ruthenium complex where the chirality at the ruthenium centre is predetermined by the chirality centres in the ligand. The colour code is the same asinFigure2

possess the expected A-configuration, if the lig- and is derived from (-)-a-pinene. The latter is a low priced naturally occurring terpene, which is commercially available in either configuration ((-)-a- or (+)-a-) in enantiomeric purity of about 80 per cent.

Since only ligands that are homochiral (having the same configuration at both centres A and By respectively) can co-ordinate to one metallic centre, a considerable chiral amplifi- cation is obtained upon complexation, yielding

Fq. 6 A chird buildi i block with the CHI- RAGEN ligandr Ru(CHIRAGEN[6])Clr. The CI l i g ~ a S are green and ruthenium is red

a species of about 96 per cent enantiomeric excess. If more expensive pinene derivatives (for example myrtenal) with high enantiomeric purity are used, the ee-value (enantiomeric excess) of the product is very close to 100 per cent.

The methods used for the synthesis of CHI- RAGEN ligands are easy to vary (1 0), and consequently ligands for different purposes can be designed. For example, when osmium is the co-ordination centre, it prefers a longer bridge than ruthenium between the bpy units. Thus, Os(CHIRAGEN[7]), a ligand with a link of seven -CH2- groups between the two bpy moieties, is more stable than one with only six

Also the remaining ligands at the metal centre can be varied. For example, in Ru(CH1- RAGEN[6])C12 the fifth and sixth co-ordination sites are occupied by chloride ligands that can be easily substituted, see Figure 6.

In Figure 7 a survey is given of synthesised ligands derived from bipyridine and pinene as the chiral group. With all these ligands chiral octahedral complexes of the platinum metals, so far mainly of ruthenium(II), osmium(I1) and rhodium(III), have been synthesised.

-CHr POUPS.

Chiral “Planar” Complexes As discussed above, octahedral complexes

(OC-6 complexes according to W A C nomen- clature) with two or three bidentate ligands

Platinum Metah Rev., 1996,40, (3) 106

Fig. 7 A selection of chiral ligands derived from pinene and b i p y r i h Coqlexea of all these

metals have been prepared ligands with platinum group

are intrinsically chiral. The d” platinum group metals - rhodium(I), iridium(I), palladium(I1) and platinum(I1) - form complexes with square planar (SP-4) co-ordination geometry. A large number of such complexes has been investigated and they play an important role as catalysts, or at least as intermediates in many catalytic reactions. The SP-4 geometry is inherently achiral, but it can become chiral under special circumstances. This was observed for the first time in a ligand which has large substituents, as shown in Figure 8 (1 1). It is noteworthy that the strong trans-influence of the carbon-bonded ligand always directs these ligands into the cis- position.

Achiral ligands, such as those shown in Figure 8, again of course, yield racemates. The same type of synthesis that produced the pinene derivatives of bipyridine, shown in Figure 7, can be used to obtain cyclometallating ligands (with CAN co-ordination). In this case predetermi- nation of the chirality at the metal centre is achieved. For example, in the complex shown in Figure 9, where the ligand is chiral owing to the pinene substituents, chirality is predetermined at the metal centre (1 2). The chirality of the complex can again be described by the

descriptors used for octahedral complexes, because the two ligands form a two-bladed helix. In Figure 9, the A-form of the complex is depicted.

Oxidative Addition Reactions There are many possible reactions for these

types of complexes. Oxidative addition is one interesting type of reaction that square planar, SP-4, platinum(I1)-compounds undergo. Here the oxidation number of the metal is increased from +I1 to +IVY and simultaneously, the co- ordination number changes from four to six, yielding again an octahedral species. In the case of SP-4 complexes with predetermined chirality at the metal centre, an octahedral species is obtained which preserves the chirality in the resulting bis-bidentate OC-6 complex (12).

Conclusions A large number of chiral octahedral and a few

chiral “square planar” complexes of the platinum metals have been known for a long time. These complexes have hitherto always been prepared as racemic compounds. A newly developed synthesis of pyridine and bipyridine ligands with attached groups derived from

Platinum Me& Rev., 1996,40, (3) 107

Fig. 8 A two-bladed helix is formed by s ter idy demandq ligands in ‘‘quare planar” platinum complexea. Platinum ie pink here

naturally occurring terpenes, such as pinene or carene, leads to chiral ligands, and these direct the chirality at the metal centre into a predetermined configuration. Thus, in many instances, only one helical form of the complex is obtained.

Potential applications for such platinum group metal species lie in the field of enantioselective catalysis, the design of stereochemically well-defined large functionalised structures for

molecular devices, as materials with interesting non-linear optical properties and finally as chiral pharmaceuticals.

Acknowledgements This paper describes a small selection of results pro-

duced by teamwork. Thanks are due to Dr P. Hayoz, who introduced the synthesis of the terpene derivatives of pyidine ligands, and also to Profasor P. Belser, Dr N. Fletcher, Dr X. Hua, Dr S. Rupprecht, Dr E. Jandrasics, H. R Miirner, M. Gianini, M. Riwin, Ph. Collomb, M. Ziegler and B. Kolp.

Fig. 9 A “qmre-plannr” complex of platinum(II)r on the left in red, the pinene parte of the lig- an&, which are responsible for the chirality (A in the p-t awe) at the metal centre; on the right, platinum i E not visible, sdphnr atom are yellow with the lone pairs in pde pink

Platinum Met& Rev., 1996,40, (3) 108

References 1 A. Werner, Z. Anorg. Chem., 1893, 3, 267 2 A. von Zelewsky, “Stereochemistry of 34~ 5791

8 X. Hua and A. von Zelewsky, Inorg. Chem., 1995,

9 V. Balzani and F. Scandola, “Supramolecular Photochemistry”, Ellis Horwood, 199 1, New York

10 P. Hayoz, A. von Zelewsky and H. Stoeckli-Evans, 3 A m . Chem. SOC., 1993,115,5111;P.Hayozand A. von Zelewsky, Tetrahedron Len., 1992,33,5165

11 C. Deuschel-Cornioley, H. Stoeckli-Evans and A. von Zelewsky, J. Chem. SOC., Chem. Commun., 1990,121

12 M. Gianini, A. Forster, P. Haag, H. Stoeckli-Evans and A. von Zelewsky, h o r g Chem., 1996 to be

Coordination Compounds”, John Wiley and Sons Ltd., London, 1996

3 ‘‘Metal Compounds in Cancer Therapy”, ed. s. P. Fricker, Chapman and Hall, London, 1994

4 L. Pasteur, Ann. Chim., 1848,24,459 5 A. Werner and A. Vilmos, Z. Anorg. AIlg. Chem.,

6 A. Werner, Chem. Ber., 1911,44, 1887 7 P. Cartwright, R. D. Gillard, R. Sillanpaa and J.

1899,21, 145

Valkonen, Polyhedron, 1987,6, 1775 published

Palladium Facilitates Optical Switching HYDROGEN ADSORPTION ALTERS PROPERTIES OF RARE EARTH FILMS

Hydrogen gas can permeate palladium, diffuse through it and be stored in it. This prop- erty has been known for many years, and has been discussed in this journal on numerous occa- sions; see (1-3) and references therein. Similarly, the effects resulting from the alloying of palladium with rare earth metals have been reported here (4). Now, physicists at Vrije University in The Netherlands have combined these properties to produce thin yttrium and lanthanum films coated with palladium, which display an optical switching phenomenon as they adsorb hydrogen (J. N. Huiberts, R. Griessen, J. H. Rector, R. J. Wijngaarden, J. P. Dekker, D. G. de Groot and N. J. Koeman, “Yttrium and Lanthanum Hydride Films with Switchable Optical Properties”, Nature, 1996,380, (657 l),

Thin films of yttrium and lanthanum (500 nm) were evaporated under UHV and then coated with a thin layer of palladium (5 to 20 nm). The palladium film acts as a support for the films, forms an oxidation barrier, and allows hydrogen to permeate through and be adsorbed by the rare earths. It also enables various physical properties to be measured.

Films were examined by electrical resistivity and light transmission measurements. At the start of the experiment hydrogen, at room temperature and 0.9 x lo5 Pa pressure, was introduced into the apparatus and began to diffuse through the palladium overlayer. The yttrium film adsorbed hydrogen and changed to yttrium hydride, YH,, which remained metallic up to x - 2, but as more hydrogen was adsorbed, the YH, changed to a semiconductor, correspond-

The films also undergo optical changes as hydrogen is taken up. After 17 seconds of expo-

23 1-234).

ing to Y H Z . 8 6 .

sure to hydrogen, an initially perfectly reflecting yttrium film, begins to precipitate the dihy- dride phase, with resistivity - 5 times lower than that of pure yttrium. After 65 seconds the resistivity increases rapidly and for a few seconds there is increased optical transmission, shown by a partially reflecting film, close to the dihy- dride composition. As hydrogen adsorption increases, optical transmission drops to zero, but after 80 seconds there is an abrupt and dras- tic increase in the optical transmission inten- sity, shown by a non-reflecting, transparent yellow film. This corresponds to YH2.86 to the trihydride, YH,.

For a lanthanum-palladium film the pattern is similar, but without the transparency window which occurred around 67 seconds; optical switching in LaH. is more gradual than in YH,. Thus, there is a continuous, reversible metal-

insulator transition in thin yttrium films supported and protected by a palladium overlayer, which can be brought about at room temperature by changing the hydrogen pressure, between hydrogen : yttrium ratios of 1.8 and 2.9. As hydrogen pressures increase, the films change from a reflective, shiny, mirror-like state to a yellow transparent state.

It is suggested that this technique could be used to investigate other rare earth films which undergo similar changes, and that such a significant optical phenomenon might find wide technological applications.

References 1 F. A. Lewis, K. Kandasamy and B. Baranowski,

Platinum Metals Rev., 1988, 32, (l), 22 2 F. A. Lewis, op. cit., 1994, 38, (3), 112 3 J. E. Philpott, op. cic., 1985, 29, (l), 12 4 M. L. Doyle and I. R. Harris, op. cic., 1988, 32,

(31, 130

Platinum Metals Rev., 1996, 40, ( 3 ) 109

Emission Control Technology PROGRESS REPORTED AT THE SPRING SAE CONFERENCE

It was unusually warm during the traditional end-of-February Congress of the Society of Automotive Engineers (SAE), held this year flom 24th to 27th February - there was no snow on the downtown Detroit streets! This Spring conference is the major, general SAE conference covering all aspects of automotive engineering, with over 47,000 delegates attending this year. Fine weather and a broad range of interesting papers concerned with exhaust after-treatment made this a memorable event for those concerned with emissions control, and the continuing importance of developments in this area was reflected in the high attendance at the sessions.

Space prevents a review of all the relevant papers, so a selection has been made to illus- trate the direction catalyst technology is taking in response to increasingly stringent legis- lation on emissions. Reference numbers of the original papers are given in parentheses.

Autocatalyst formulations have become more complex over recent years and may, for example, involve separated platinum metals each with an optimal promoter package. A paper by Degussa (960802) gave some insight into the design of such formulations, and a comprehensive study by Volvo (960801) of reactions over a double-layer trimetal (platinum-palladium-rhodium) catalyst enabled a dynamic kinetic model to be developed, which included sulphur dioxide effects.

Solving the Cold Start Problem Starter Catalysts

Reduction of emissions during the “cold start” ‘period is the key objective for meeting future regulations, and the use of low temperature light- off catalysts mounted close to the exhaust manifold to decrease warm-up time is an attractive approach for achieving this. However, operation in this position demands particularly good thermal durability of the catalyst. Space constraints often preclude location of large volume close- coupled catalysts near the exhaust manifold, and

combinations of a small close-coupled starter catalyst with a larger underfloor unit can provide an effective system.

Toyota (960797) explored the effectiveness of such two-catalyst systems, and Johnson Matthey (960799) demonstrated that both the U.S.A. LEV/ULEV and European Stage 3 standards can be met with suitable high-activity catalysts of good thermal durability.

The attainment of low emission levels depends on rapid warm-up of the front catalyst and the presence of a sufficiently large total catalyst volume to maintain performance under normal operating conditions. Audi (960261) stressed the roles of engine management in rapid heating, and secondary air injection to enhance catalyst light-off. Starter catalyst performance depends on several parameters: a small volume heats up quickly, but a larger volume produces a greater exotherm (temperature rise), and this is reflected in the accumulated hydrocarbons emissions during a test cycle. Starter catalyst cell density also affects performance: there is a monotonic improvement as it increases. However, when a starter catalyst is combined with an underbody catalyst the system performance is less dependent on the characteristics of the starter, provided that it quickly gives a sufficient exotherm to light-off the main catalyst.

Metallic monoliths have typically been used in starter applications, and Corning (960262) reported a comparison of ceramic and metal foil-based starter catalysts. From their tests, they concluded that with the same outside diameter and back-pressure characteristics similar emission and durability performance can be obtained. Corning (960349) and NGK (960565) reported additional thermal durability results for ceramic monoliths in close-coupled locations. The latter proposed a design using a dual cone structure for both the converter inlet and outlet to minimise heat conduction, thus decreasing the temperature of the surrounding mat and

Platinum Metals Rev., 1996, 40, (3), 110-1 11 110

lowering the surface temperature of the converter to below 45OOC - when the catalyst itself is at a temperature of 1050°C.

Electrically Heated Catalysts An alternative approach for reducing cold start

emissions is to preheat electrically a small platinum group metal containing catalyst in front of the main catalyst. High electrical power requirements have tended to inhibit adoption of this concept, but the first electrically heated catalyst (EHC) application was described by Alpina/BMW and Emitec (960349), and it is interesting to note that, on the car which they describe, the power is switched between two EHCs on either side of the engine in order to minimise power consumption.

Emitec (960339) presented a separate paper on the general applicability of foil-based EHCs, and W. R. Grace (960341) also presented system performance with related EHCs. Honda (960342) compared foil-based and extruded EHCs in vibration, heat impact and distortion durability tests, and discussed the use of battery and alternator power supplies. They opted for a special alternator. In contrast, Hyundai (960350) investigated characteristics of both conventional lead/acid and nickeymetal hydride batteries for supplying EHC current, and concluded that the latter has significant attractions - as lead/acid batteries do not sustain the necessary heavy cur- renddepth of discharge over many cycles.

NGK (960340) gave details of the design concepts and durability data of extruded metal EHCs and Corning (960345) presented vehi- cle durability results for their latest EHC design. Clearly, EHC-based technology has been developed to a stage where it could be used in series production, but it appears that in practice pas- sive starter catalysts are more favoured, due to their not needing associated equipment.

Lean-Burn Technology Catalysts for lean-burn engines are likely to

become increasingly important; a concern here is NOx reduction in the presence of excess oxygen. Orbital (960361) highlighted the fact that extremely lean operation of a direct injection

stratified charge two-stroke engine results in inherently low NOx levels, while Degussa (960133) showed how zeolite can be used to store and activate hydrocarbons in diesel engine exhaust during the start-up phase. This improves NOx reduction. Corning (960343) described a by-pass system (two conventional ceramic platinum group metal catalysts and an adsorber) in which zeolite is used to absorb hydrocarbons during the cold start of a conventional gasoline engine. They also described (960348) an in-line adsorption system which uses a flow of air to prevent exhaust gas passing through a central by- pass in an adsorber monolith during start-up.

Developments in Sensors Sensors are important for the correct opera-

tion of emission control systems. Oxygen sensors are used to maintain accurate air/fuel ratios, and in the future it seems likely that other types of sensors will be needed. Several reports were concerned with other sensors: Matsushital Panasonic described (960336) a wide range ther- mistor for exhaust gas temperature measurement. NGK reported a new high performance platinum resistive temperature sensor (960333), and discussed its possible use in on-board diag- nostic applications in which the predicted temperature rise on a catalyst is compared with the corresponding measured increase.

Another NGK paper (960334) described a new NOx electrode; this multi-layer zirconia system, operating at 600 to 7OO0C, involves oxygen pumping with platinum electrodes and, in a separate zone, dissociation of nitric oxide takes place over porous rhodium. The oxygen formed is measured with an oxygen electrode, and the concentration is found to be proportional to the amount ofNOx originally present. Gold is used to inhibit nitric oxide dissociation on platinum electrodes, and to improve off-set current characteristics.

Thus, once again the SAE conference has highlighted the key role played by the platinum group metals in emission control technology, and has demonstrated the amount of worldwide effort and expertise committed to improving the performance of emission control systems. M.V.T.

Platinum Metals Rev., 1996,40, (3) 111

Electronic and Nuclear Magnetism in Platinum-Iron at Ultralow Temperatures LOW TEMPERATURE WORLD RECORD ESTABLISHED

By W. Wendler, T. Herrmannsdorfer,* S. Rehmann and E Pobell** Physikalisches Institut, Universitat Bayreuth, Germany

I n Februarx 1996, physicists at the University of Bayreuth claimed a world record for producing the lowest temperature yet achieved when they announced the results of their work with platinum. They cooled 31.4 grams of plat inum to 2 millionths of a degree Celsius above absolute zero temperature, -273.15"C. I n this paper they describe the theory and the practical work behind this accom- plishment. Research in low temperature physics involves the construction of detailed and precise knowledge of the atomic and nuclear structures and their interactions in atoms. Some effects due to atomic and nuclear structure, particularly magnetic effects, are only seen at very low temperatures; however their effects have consequences a t higher temperatures, although these are not usually observed. Thus , this and other low temperature work is contributing to a fundamental understanding of the magnetic behaviour of materials.

The study of magnetism is one of the most interesting fields in solid state physics. Electronic magnetism shows a wide spectrum of different ordering phenomena at temperatures from about lo3 K, where the ferromagnetic phase transition in iron occurs, to about 1 0.' K, where Ce3+ ions in the paramagnetic salt CMN order magnetically. (CMN is cerium magnesium nitrate. ?C.c''NO;) 3.3Mg(N03)2.24H20, which previously found application for electronic demagnetisation refrigeration before 'He-'He dilution refrigerators were used (1). Nowadays some research groups use it for thermometry at mK temperatures, but we used a PdFe thermometer in this temperature range).

Interacting magnetic moments of localised electronic shells or itinerant electrons are responsible for phenomena such as ferro-, ferri-, anti- ferro- and meta-magnetism or spin glass freezing. However, many elements and compounds do not contain such electronic magnetic moments, but very often their nuclei carry a

*Hahn-Meitner-Institut Berlin, Berlin, Germany Forschungszentrum Rossendorf, Dresden, Germany .*

magnetic moment due to the nuclear spin. Since nuclear magnetic moments are three orders of magnitude smaller than their electronic coun- terparts, and as the interaction energy is proportional to the square of the magnetic moment, ordering phenomena in the nuclear spin system are expected to occur only in the microkelvin temperature range or at even lower temperatures.

Apart from solid 'He with its strong quantum- mechanical direct exchange force, and the Van Vleck paramagnets with hyperfine enhanced magnetic moments, one has to distinguish between two groups of nuclear spin systems: . those in insulators and metals with a

coupling between the nuclei and the conduction electrons, and . those in metals with a strone: coupling between the nuclei and the conduction electrons.

The Korringa constant, K, is an important parameter to characterise the strength of this interaction. The Korringa constant is given by the conduction electron temperature, T.~rcr,o.,

Platinum Metals Rev., 1996, 40, (3), 112-1 16 112

multiplied by the spin lattice relaxation time, zI . For the first group of materials, the Korringa

constant is larger than 1 Ks. As the spin lattice relaxation time zI becomes very long at temperatures below 1 mK (zl > 1000 s), it is possible to cool only the nuclear spin system to nanokelvin or even picokelvin temperatures for a time long enough to perform nuclear magnetic investigations, while the conduction electrons stay at a much higher temperature (Tekmm > 100 pK). For systems such as these, nuclear magnetic ordering phenomena have been observed in silver (K = 12 Ks, T, = 0.6 nK) and copper (K = 1.3 Ks, T, = 60 nK) (2).

However, it is much more difficult to observe nuclear magnetic ordering phenomena in the second group, since in this case, the whole system has to be cooled because of the strong coupling between the electrons and the nuclei. On the other hand the indirect exchange interaction between nuclei in these systems is stronger than the dipole-dipole interaction, and therefore ordering phenomena are expected to occur at temperatures of up to tens of microkelvin.

Work with Platinum as a Strong Coupling System

Recently, we have been able to observe a nuclear ferromagnetic transition of this type with the 113”151n nuclei in AuInz (K = 0.1 1 Ks) at a temperature of 35 pK (3). Another very interesting material in this group is platinum, which has a very small Korringa constant, of size only K I 0.03 Ks. The nuclear magnetic moment of

Pt is a factor of 10 smaller than that of the indium nuclei and only 33.8 per cent of the platinum nuclei carry the rather small magnetic moment of 0.597 p“ (nuclear magneton p,, = 5.05 x 10.’’ Am’). Therefore, it is necessary to reach temperatures below 1 pK to observe ’

nuclear magnetic ordering in platinum (4). The additional interest in platinum comes from

the fact that electronic magnetic 3d impurities, such as iron, form so-called giant moments in this strongly enhanced electronic Pauli para- magnet. (Platinum and also palladium are both strongly exchange enhanced Pauli paramagnets.) The giant moments show spin glass freezing at

195

temperatures of a few mK at concentrations of ppm (5). This system of randomly distributed electronic magnetic moments may have a strong influence on the nuclear magnetic properties.

Searching for Nuclear Magnetic Ordering in Platinum

In order to search for a possible nuclear magnetic ordering of 195Pt and to study the above mentioned interaction between nuclear and electronic magnetism, we have investigated platinum samples containing magnetic impurities at concentrations of 1 1 and 4 1 ppm. The impurities were mainly iron, carrying an electronic magnetic “giant” moment of eight times the Bohr magneton pB (pB = 9.274 x Am’). The properties that we measured were: . heat capacity in magnetic fields, B;

(0 & 0.05) mT I B I 248 mT . AC susceptibility at B = (0 f 0.05) mT and . nuclear magnetic resonance a t fields 2.5 mT I B 122.8 mT.

Measurements were taken at temperatures T w t 0.3 pK and T,I,,~, 2 2 pK, the latter being the lowest temperature to which electrons and phonons of a material have ever been reftigerated.

Lowering the Platinum Temperature The ultralow temperatures that are neces-

sary for these experiments were obtained by using the adiabatic nuclear demagnetisation technique. First, 17 kg copper were precooled in the Bayreuth nuclear demagnetisation refrigerator (6) (6.5 kg in an external field of 8 T) by a commercial ’He-*He dilution refrigerator to a temperature of 11 mK.

Then, after a thermal decoupling of the copper nuclear refrigeration stage from the mixing chamber of the dilution refrigerator, the external magnetic field was slowly reduced. At the end of this process the copper stage reached temperatures of about 50 pK. The platinum sample (n = 161 mmole of weight 3 1.4 grams) was exposed to a magnetic field of 0.37 T and thermally connected to the copper stage via a superconducting aluminium heat switch. The platinum was then precooled, by the copper stage, to a temperature of approximately 100 pK.

Platinum Metals Rev., 1996,40, ( 3 ) 113

'O-5-4

Fig. 1 Heat capacity of BFe. samples, where z = 41 ppm and 11 ppm, in fields of: (a) 248 mT, (b) 22.8 mT, (c) 2.5 mT for z = 11 ppm and 0 mT for z = 41 ppm. The solid lines represent the behaviour of platinum in the nuclear paramagnetic state. The dashed liner are calculated assuming a spatially varying internal field, caused by the iron impurities

TEMPERATURE, mK

Subsequently, the platinum stage was thermally decoupled from the copper stage and the field was reduced. Eventually, in external fields of B 5 0.05 mT, the temperature of the nuclear spin system of platinum reached 0.3 pK. In these fields (B 5 0.05 mT) the temperature of the nuclei, Taw&,, was lower than the temperature of the conduction electrons, Tebcmn.

If the adiabatic demagnetisation was stopped at somewhat higher fields, for example 2.5 mT, nuclear temperatures of (0.8 f 0.2) pK could be measured directly after demagnetisation. Taking the measured heat leak of (1 2 f 2) pW into the platinum sample into account and the measured Korringa constant K = (7 f 3) mKs for platinum in these fields, the temperature of

Platinum Metah Rev., 1996, 40, (3)

the conduction electrons has to be below 2 pK. During the next three hours after finishing the

demagnetisation the conduction elecuons stayed below 3 pK. The small value of 7 mKs for the Korringa constant, in contrast to its literature value of 30 mKs, is caused by magnetic impurities.

Measurement of the Platinum Temperature The temperature of the platinum was deter-

mined from the magnetisation of its nuclear spin system, using pulsed nuclear magnetic resonance (NMR) in fields B 2 2.5 mT and the AC susceptibility technique in fields B = (0 f 0.05) mT. At temperatures of 2 20 pK the NMR signal was calibrated against an independent platinum-wire- NMR thermometer, which is itself calibrated

114

0 08

0 06

k >

%

i 0 0 4

I t U VI 3 VI

0 02

I

10-4 10- 10-2 10-1 1 0 0 101

TEMPERATURE, mK

Fig. 2 AC susceptibilities (f = 16 Hz) of the two RFe, samples. The solid lines at temperatures T > T,(T,are the spin glass freezing temperatures) show the Curie behaviour of the electronic magnetic impurities. The Curie constants are determined in a SQUID magnetometer at 1.6 K I T 5 40 K and are used to calibrate the data to obtain absolute values of susceptibility. The solid lines at T C 50 pK show the Curie behaviour of the '"Pt nuclei which is used to derive the temperature scale at T < 20 pK in zero field

against the paramagnetic susceptibility of a PdFex sample at temperatures T 2 10 mK (1).

For the temperature calibration we assume that the magnetisation, detected by the NMR signal and the measurement of nuclear AC susceptibility, follows a Curie law (x - llTnw~o,) at low polarisation. If it follows a Curie-Weiss law (x - l/(Tmuba,- On)), we would have to correct our temperature scale by 0. (see below).

The measured heat capacity data of the two PtFe, samples in different magnetic fields is shown in Figure 1. The solid lines show the nuclear paramagnetic behaviour. In a magnetic field of 248 mT, there is a good agreement at T I 1 mK. However, at higher temperatures the measured heat capacities are larger than expected and scale with the impurity concentration. At lower fields, such as 22.8 mT, this effect is much more pronounced, and at 2.5 mT or in zero field

we observe an enhanced heat capacity over almost the whole temperature range. This effect can be described by a spatially varying internal field caused by the electronic magnetic impurities, assuming that this field behaves in a similar way to the electronic polarisation cloud in the conduction electron system -which forms the giant electronic moment. The dashed lines in Figure 1 are calculated using only two fitting parameters. There is a good agreement with the measured data. Therefore, we are able to describe the internal field in platinum as being due to electronic magnetic impurities.

Does Platinum Have Nuclear Magnetic Ordering?

In order to search for a nuclear magnetic ordering transition in platinum, we have measured the nuclear and electronic AC susceptibilities


of the two platinum samples in an external field B 5 0.05 mT. The results are shown in Figure 2. The two maxima at millikelvin temperatures are caused by the “spin glass freezing” of the magnetic 3d impurities in platinum at freezing temperature, Tj. At temperatures T > Tj the AC susceptibility shows Curie behaviour with Curie constants CIlm = 122 pK and C41,m = 448 pK, determined at 1.6 I T I 40 K in a commercial SQUID magnetometer.

We used this known behaviour (5) to scale our measured data in units of differential volume susceptibility. At T < Tj the susceptibility decreases linearly with temperature and increases again at T < 0.1 mK. The latter increase is caused by the nuclear paramagnetic behaviour of the ’”Pt nuclei with a Curie constant of CR = 0.0 185 pK. No maximum in the susceptibility was found and therefore no evidence for

nuclear ordering in our samples could be detected down to the minimum nuclear temperature reached of 0.3 pK.

Conclusions The temperatures achieved in our platinum

samples, for the conduction electrons and phonons, which are below 2 pK, are the lowest temperatures ever reached in equilibrium. No evidence of nuclear magnetic ordering in platinum could be detected. This shows that the temperatures achieved were still measured in the nuclear paramagnetic state where the Curie (or Curie-Weiss) law is valid, and therefore our determination of temperature, assessed via this law is correct.

This work should aid in extending understanding of the interplay between electronic and nuclear magnetism at very low temperatures.

References 1 F. Pobell, “Matter and Methods at Low

Temperatures”, Springer Verlag, Berlin, Heidelberg, 1992

2 A. S. Oja and 0. V. Lounasmaa, to be published in Rev. Mod. Phys., 1996, July

3 T. Herrmannsdorfer, P. Smeibidl, B. Schroder- Smeibidl and F. Pobell, Phys. Rev. Len., 1995,74, 1665

4

5

P. Kumar, J. Kurkijarvi and A. S. Oja, Phys. Rev. B, 1986,33,444 T. Herrmannsdorfer, S. Rehmann, W. Wendler and F. Pobell, to be published in J. Low Temp. Phys., (1996) K. Gloos, P. Smeibidl, C. Kennedy, A. Singsaas, P. Sekowski, R. M. Mueller and F. Pobell, J. Lo4u Temp. Phys., 1988, 73, 101

6

J

There are several methods in current use for transferring very fine patterns onto substrates for printed electronic circuitry. These all involve the selective metallisation of the area to be treated and use various techniques, such as pho- tolithography or electroless plating. However, scientists at Harvard University have now announced a new method of electroless deposition, which they have demonstrated with copper but suggest could also be used for the deposition of other metals (P. C. Hidber, W. Helbig, E. Kim and G. M. Whitesides, “Microcontact Printing of Palladium Colloids: Micron-Scale Patterning by Electroless Deposition of Copper”, Langmuir, 1996, 12, (3, 1375-1380).

Their new strategy involves the manual transfer of a palladium colloid catalyst onto a substrate surface by microcontact printing (pCP); this uses a patterned elastomer stamp made from poly(dimethy1siloxane). The stamp is previously dipped into the palladium colloid, which has been stabilised with tetraalkylammonium

Palladium Colloid Catalvst Used in Microcontact Printing bromides. This is followed by the electroless deposition of copper which proceeds by immersion of the substrate in a copper plating bath, and occurs only at the regions coated with the palladium colloid, where a catalytic reaction occurs.

Copper lines of micron and submicron widths, having edge resolution of 100 nm, were produced on a variety of substrates, including glass, silicon with a silicon dioxide layer, and poly- mers. Both flat and curved surfaces can be plated without loss of resolution. In addition, free- standing, flexible structures can be produced by dissolving the substrate when the metal film reaches the required thickness or by allowing the internal stress in the electroless copper layer to exceed the adhesion strength, when delam- ination occurs.

While films of approximately uniform thickness can be produced by this method, ways of obtaining structures which have different layer thicknesses have also been developed.

Platinum Metals Rev., 1996, 40, ( 3 ) 116

Platinum and Biological Systems Metal Ions in Biological Systems, Volume 32: Interactions of Metal Ions with Nucleotides. Nucleic Acid, and Their Constituents EDITED BY ASTRID SIGEL AND HELMUT SIGEL, Marcel Dekker, New York, 1996, 848 pages, ISBN 0-8247-9549-0, U.S.8225.00

Nucleotide- and nucleic acid-metal ion interactions have been a major focus of research for over forty years. Many of the enzymes involved in RNA and DNA biochemistry utilise metal ions. Metal ions affect the stability of the three dimensional structures of nucleic acids and nucleic acid-protein complexes, and indeed, the platinum-based anticancer drugs exert their effect by interaction with DNA. This volume and Volume 33 (to be reviewed in a future issue) bring together international experts who review the present status of research in this field.

The book can be subdivided into four sections, with the first ten chapters covering the interaction of metal ions with the low molecular weight nucleotides. Chapters 11 to 15 review interactions with high molecular weight ligands, such as nucleic acids and nucleic acid-protein complexes. These chapters provide the background for two chapters on the role of metals in gene regulation. The final chapters exam- ine the interaction of the platinum anticancer drugs with nucleic acids.

Interactions of naturally occurring metals (with biological systems) are a key feature of this volume, and though not of direct relevance to this journal, their significance should not be over- looked. The chapters on gene regulation are at the leading edge of an important area in modern inorganic biochemistry.

The platinum group metals feature strongly throughout the book. The interactions of metal ions and nucleic acids can be studied in the solid state using X-ray diffraction, or in solution using techniques such as NMR or UV-Visible spectroscopy. The use of platinum complexes as probes for these techniques forms sections in Chapters 4,6 and 1 1. In Chapter 3, R B. Martin describes the use of palladium complexes to provide the empirical basis for a discussion of metal ion binding to purines. In Chapter 9, T. Rau

and R. van Eldik, and in Chapter 10, J. Arpalahti, describe the kinetics of palladium(I1)- and platinum(I1)-nucleobase interactions.

An important reason for studying metal-DNA interactions is to understand the mechanism of the platinum anticancer drugs. A review of the current status of structure-activity relationships of platinum anticancer drugs, is presented by N. Farrell in Chapter 18, focusing on recent work on the biological activity and unique DNA interactions of truns-platinum complexes, previously thought not to have activity as anticancer drugs. In Chapter 19, M. J. Bloemink and J. Reedijk review the mechanism of cisplatin binding to DNA from both a structural and a kinetic perspective, and discuss the significance of this for new platinum complexes.

The still unanswered question of how cisplatin- DNA binding leads to tumour cell death is addressed by J. P. Whitehead and S. J. Lippard in Chapter 20, who describe the current understanding of the repair of platinum lesions on DNA. They discuss the binding of a DNA damage-recognition protein, leading to the formation of a platinum-DNA-protein ternary complex, and its involvement in platinum-induced cell death. Since the discovery of cisplatin many laboratories have attempted to identify other metal-based anticancer drugs, and in Chapter 2 1 , M. J. Clarke and M. Stubbs discuss the interaction of experimental ruthenium and rhodium metallopharmaceuticals with DNA.

Metal ions play an important role in many biological processes - the rationale for this long run- ning series. This is an excellent book and maintains the high standards set by this series. There are occasional overlaps between chapters, perhaps only to be expected in such a long book; however, this is offset by the quality and topical nature of the conmbutions, making this a valuable addition to bioinorganic literature. S.P.F.

Platinum Metals Rev., 1996,40, (3), 117 117

Hydrocarbonylation in Platinum Metals Metallurgy By Professor I. Y Fedoseyev Kaluga Branch of the Moscow State Technical University, Kaluga, Russia

For manyyears we have been studying the reactions of carbon monoxide with chlorocomplexes of the platinum metals in various solutions, such as hydrochloric acid. These hydrocarbonylation reactions result in the formation of various plat inum metals carbonyl complexes. Hydrocarbonylation has been used to extract the plat inum group metals from the anode muds which remain after the production of copper and nickel. The processes involved, which are described below, produce no waste and therefore do not require special reagents or apparatus. This makes their use very effective for the metallurgy of the platinum group metals. In this paper we discuss the general results of these investigations and some of their applications, such as in the production ofpowders and catalysts, for which the hydrocarbonylation process is suitable.

We have been studying the extraction of platinum group metals from the anode mud residues which remain after copper and nickel have been extracted from mineral mined in the nickel-copper sulphide deposits at Noril'sk in the Arctic Circle in North Russia ( 1).

Carbon monoxide is known to react in solution with platinum metal chlorocomplexes. The redox reactions which take place are:

CO + HzO = CO2 + 2H' + 2e- M"' + xe- = M"-"

(0 (ii)

where M is a platinum group metal. This results in the production of lower valency

carbonyl chlorides, carbonyls or metals. The combination of reactions (i) and (ii) is a hydrocarbonylation process of which the kinetics and reaction mechanism are already well known.

The rate of the reaction of carbon monoxide with solutions of chlorocomplexes of the platinum group metals takes place in the following order:

However, there is only limited information available about various technological aspects of the process (2-6). The utilisation of the hydrocarbonylation reaction (for extraction of the plat-

inum group metals) depends on characteristic properties of carbonyl complexes and involves: . a redox decomposition with formation of the corresponding metal

extraction of carbonyl complexes in the organic phase

formation of insoluble substances a sorption process

Selective Concentration of Platinum Group Metals from Anode Muds

The main metals produced in the Noril'sk- Talnakh region within the Arctic Circle in Russia are copper, nickel and the platinum group metals. Noril'sk lies on the northwestern edge of the Siberian platform and is the main source of the platinum group metals in Russia, the other production area being at Pechenga near the Finnish border, and the city of Murmansk in the Kolskiy Peninsula.

After copper and nickel have been extracted the anode muds still contain non-ferrous metals and noble metals. The technology for processing copper-nickel muds has many stages including burning, smelting and electrolysis, and as a result, the platinum metals are distributed among three concentrates, which also contain many non-ferrous metals. One of the

Platinum M e & Rev., 1996,40, (3), 118-125 118

Pdn > Pt' > Pt" > Rh"' > Ru" > = 0s" >> Irw

Initial solutton Carbon monoxide

concentrate-1 Pt , Pd. Au. Ag. Se, Te Rh, Ru, Ir and non-ferrous metals

1 Water phase Extraction

I I

water phase

* Obtaining non-ferrous metals

Re-extraction

* I Organic phase

I I Metal distribution, in per cent, from the initial amount

99.97 98.32

103.90 none

100.40 98.25

, none

~

e3-J Organic phase

0.04 none none none none none 1.15

,

100.46 100.04 105.05 80.63

11 5.20 100.40 99.40

Obtaining concentrate -TI' Rh. R u , I r

The principles of the hydrocarbonylation process for obtaining concentrates of the noble metals

concentrates has, for example, the following composition, in per cent: palladium 35 to 45, platinum 15 to 20, rhodium 0.4 to 0.6, ruthenium 0.08 to 0.15, iridium 0.04 to 0.06, silver 8 to 10, copper 0.7 to 2.5, nickel 0.6 to 2.5, iron 1.5 to 4.0, sulphur 3 to 5, selenium 1 to 1.7 and tellurium 1.5 to 2.5.

Hydrocarbonylation is the principle technology which is then used for obtaining concentrates of the platinum group metals from solutions of anode muds. Such solutions can be

prepared, for example, from the copper and nickel anode muds by the action of chlorine gas, or by addition of hydrochloric acid.

The principles of the hydrocarbonylation process are shown in the Scheme, and the processes were used in our laboratory with copper and nickel anode mud solutions produced by the Noril'sk Nickel Combine, which is the only mining and metallurgical works in that area. The hydrocarbonylation process, used for such complex anode mud solutions, conforms to the

Table I

Distribution of Noble Metals Produced from the Copper Anode Mud Solution Using the Hydrocarbonylation Process

Metal

Pd Pt Rh Ru Ir Au Ag

Washings I Concentrate-I

0.42 1.69 none 7.63 none none none

Organic phase

Total I Water I phase

0.03 0.03 1.15

73.00 1 15.20

none none


LI 0

.I 8

!3 Y .I

s s

N C D c D r n c n

0 0 0 0 0

c n o r - m e 9 9 9 9 9 O N ( ? . - N

0 0 0 0 0

o q m ~ c n h l 9 9 9 9 0 0 0 0 0

- * * N

2

z 0

- N N

8

8

- ?

0, cn 0, P

k

I

I

-

I

-

I

m cn A

2 cn A

-0- s i P C x i

o c 4-

L L I C

usual rules that are obeyed by other binary systems, for example: palladium(I1)-copper (11) , palladium(I1)-iron(III), platin-

platinum(IV) and other similar binary aqueous systems: (a) before palladium and platinum are precipitated, copper(I1) and iron(II1) are catalytically reduced to copper(1) and iron(I1) (b) before platinum is precipitated, platinum(IV) is reduced (also catalytically) to platinum(I1) (c) rhodium(III), ruthenium(1V) and iridium(IV) are reduced to the lower carbonylchloride complexes: [Rh(CO)2C12]-, [Ru(CO)~CL]'- and [Ir(C0)2C12] ., respectively, which are easily extracted by various organic reagents, for example, butyl phosphate.

The metals which are extracted from processing the copper anode mud solution are listed in Table I. Carbon monoxide was added at atmospheric pressure to the initial solution which was held at a temperature of about 100°C for four hours.

The precipitation of rhodium from its various chlorocomplex solutions depends mainly on the temperature and the concentration of the hydrochloric acid. However, the presence of other platinum metals in the solution considerably affects the precipitation of the rhodium. Therefore, we can arrive at a sit- uation where rhodium practi- cally does not precipitate in the first concentrate, concentrate- I, if the hydrocarbonylation

~rn-COPPerrn , palla&=rn-


1

Tota

l S

e pe

rimen

t 1 Pd

num

ber

67.0

0 66

.17

67.3

5 66

.20

5 66

.75

Te

Ni

Fe

Tabl

e II

The

Com

posi

tion

of N

oble

Met

als C

once

ntra

tes O

btai

ned

from

Cop

per-

Nic

kel A

node

Mud

Sol

utio

ns

by t

he H

ydro

carb

onyl

atio

n Pr

oces

s, p

er c

ent,

per

cen

t

cu

0.12

0.

16

0.26

0.

23

0.19

0.19

A

vera

ge

I 66.6

9

Tota

l no

n-fe

rrou

s m

etal

s

0.15

0.

18

0.32

0.

26

0.22

0.22

””

Ext

ract

ed,

>99.

9 pe

r ce

nt

I

Pt

14.6

3 16

.12

14.7

2 14

.70

17.1

9

15.4

7

98.0

none

0.02

I 0.5

4

loo

I2O.

O

Rh

0.00

7 0.

009

0.01

0

0.01

2 0.

008

0.00

9

0.4”

- pr

ecio

us

met

als

82.4

8 82

.84

02.7

3 84

.71

84.1

3

9.61

9.

90

10.1

0 9.

73

8.95

0.01

9

0.00

9 0.

020

0.03

7 0.

018

0.02

4

~ 83

.37

-

l-

*

Ru

and

lr ar

e no

t ext

ract

ed in

the

conc

entr

ate

** th

e co

ncen

trat

e ad

ditio

nallv

con

tain

s -

1% S

O:

process is carried out at a temperature of 60°C or less, and the concentration of the hydrochloric acid is greater than 1 molllitre.

Besides platinum, palladium, gold and silver, the metals selenium and tellurium are also precipitated out in concentrate-I. However, Table I shows the composition of concentrate- I after it has been heated to 9OO"C, which is why the selenium and tellurium are missing.

In order to obtain concentrate-I, from which the metals rhodium, ruthenium and iridium can be extracted, and to study the behaviour of selenium and tellurium during this process, we carried out a series of experiments using the hydrocarbonylation process on a solution of nickel anode muds.

The composition of the nickel anode muds, in gramdlitre, was as follows: copper 15.52; nickel 10.47; iron 3.03; sulphate, SO:., 16.4; chloride, C1-, 21 2.3; and in milligramsllitre the following: selenium 170.6; tellurium 101.8; palladium 1134.0; platinum 321.4; rhodium 41.4; ruthenium 8.67; iridium 3.58; gold 0.17 and silver 86.7. Carbon monoxide was passed through the initial solution, which was held at a temperature below 60°C, and thoroughly mixed for 3 to 4 hours. A black powder (concentrate-I) was obtained. It precipitated easily and was simple to filter. The composition of the obtained concentrates and the proportions of the extracted metals are shown in Table 11.

The results of the experiments confirm that by the reaction of carbon monoxide with solutions of copper and nickel anode muds, a high quality platinum-palladium concentrate can be obtained with:

a high selectivity to the platinum group metals and only small admixture of non-ferrous metals (0.2 to 0.3 per cent) . a high noble metal concentration (82 to 84 per cent)

Besides the high quality of concentrate-I, it is also possible to achieve a high yield of platinum, palladium, gold, selenium and tellurium in the concentrate.

The process of hydrocarbonylation can be used for selective precipitation of metals from more concentrated solutions. For example, we have

used a solution with the following composition, in gramshtre: platinum 18.4; palladium 5 1 .O; rhodium 6.5; iridium 2.9; gold 1.02; copper 16.2; nickel 3.8; iron 1.90; selenium 2.6; tellurium 3.2 and hydrochloric acid 110. Because of the carbon dioxide, selenium, tellurium, gold and palladium are precipitated; platinum is precipitated at 96 to 98 per cent, but the total amount of rhodium and iridium precipitated is less than 5 per cent. These results therefore confirm the practicality of obtaining platinum group metals concentrates from complex solutions, using the hydrocarbonylation process.

Regeneration of the Platinum Metals from their Alloys

A considerable quantity of the platinum group metals are in circulation at any one time, and recycling them from their various alloys presents an important technological problem. It has been reported that carbon monoxide can be used to separate rhodium or iridium from the other platinum group metals (3). However, the processes which achieved this were performed in dilute acids, but dissolving the alloys in the hydrochloric acid + chlorine gas system produces solutions containing highly concentrated hydrochloric acid. These must be neutralised by the addition of sodium hydroxide, thus this process produces waste.

We have been investigating the possibility of recovering the platinum metals from solutions containing a high concentration of hydrochloric acid, for systems of the chlorocomplexes of palladium(I1)-platinum(IV), platinum(1V)- rhodium(II1) and platinum(1V)-iridium(1V). Palladium, platinum and rhodium can be obtained as metallic powders by the action of carbon monoxide on solutions of the single chlorocomplexes in hydrochloric acid. The rate of the reductions is:

palladium(I1) > platinum(IV) > rhodium(II1).

This process has an induction period, Tkd, the duration of which is a function of the type of metal, the temperature and the concentrations of chlorine and hydrogen ions.

Therefore, there is every reason to think that


Table 111

Composition of the solutions I I

I Experimental Precipitation of conditions metals, per cent

I Results of the Hydrocarbonylation Process in the H2PtC16-H&hC16-HCI System I

Pt'", gll

40.5 29.2 30.2 30.2

Rh"', gll HC1, M Temperature, O C Time, h Pt Rh

30.8 6 75 4 77.5 3.3 12.3 3 50 4 99.2 2.3 4.4 4 50 5 99.5 0.9 4.4 4 25 6 99.7 0.1

Composition of the solutions Experimental conditions

Pt'", gll I?. gll HCI, M Temperature, O C Time, h

28.0 23.2 6 75 2.5 41 .O* 8.5 0.6 75 2.5

Precipitation of metals, per cent

Pt Ir

99.90 0.08 99.99 0.24

41 .O"

* the mixture (NH&PtCI, t (NH4)212CIt was used here

8.5 1 .o 75 2.5 99.99 0.10

Table V

Effects of the Hydrocarbonylation Process in the H2PtCl6-H~dCl4-HCI System I Pd", g/l

30.8 30.8 15.8 15.8 15.8 15.8 7.5

15.8 2.0

Composition of the solutions

HCI, M

6 6 6 8 6 6 4 6 3

Pt'", g/l

33.2 53.2 45.0 45.0 45.0 45.0 7.2 45.0 2.0

Precipitation of metals, per cent I Experimental

conditions _ _ _ _ _ _ _ _ _ _ _ ~

Temperature, O C

25 25 40 40 50 50 60 70 75

~

Time, h

1 .o 1.5 1.5 2.0 4.0 2.0 0.5 2.5 1 .o

Pd

83.20 99.98 96.70 99.40 93.70 99.99 79.90 99.70 99.8

Pt

3.2 6.3 2.1 3.4 2.0 3.7 7.6 8.4

10.1

these metals can be separated by modifying the composition of the solution and by adjusting the temperature. Thus, carbon monoxide was bubbled through the initial solutions at atmospheric pressure, while undergoing a thorough

mixing at a temperature of 25 to 75°C. The composition of the solutions and the

experimental data are shown in Tables I11 to V. Our assumption was confirmed for the systems platinum(1V)-rhodium(II1) and platinum(IV)-


Table IV

Results of the Hydrocarbonylation Process in the Platinum(1V)-Iridium(1V)-HCI System

Table VI

The Effects of the Preparation Conditions on the Characteristics of the Palladium Powders

Sample I Experimental conditions

iridium(1V): in both cases platinum can be almost completely precipitated with only a little admixture of the other platinum metal.

However, a different reaction occurred in the platinum(W)-palladium(II) system where up to about 10 weight per cent of platinum, together with palladium, is precipitated over a wide range of temperatures and hydrochloric acid concentrations, see Table V. This is probably due to the formation of rather stable heteronuclear car- bony1 complexes of palladium-platinum.

Preparation of Palladium and Platinum Powders

Metallic powders of palladium, platinum and their alloys find wide application in the electronics industry. They are obtained by the reduction of corresponding solutions using, for example, hydrazine.

We have studied the possibility of utilising the hydrocarbonylation process for obtaining platinum metals powders with the required physicochemical properties for these uses, such as specific surface area, volume density, dispersion and resistance to oxidation.

For palladium, the rate of reduction in the Pd(II)-H'-CT-H20-C0 system can be expressed in the following way (7):

dCpd/dT = K . C d . C-'H+ . C-'cr. C'H,O . Cco

where C represents the concentration of each component in the system and K is the reaction constant for this particular reduction, z is time.

By using the concentrations of palladium and hydrochloric acid, and the temperature as the variables, we have obtained the equation of the regression, which correlates these parameters with the value of the volume density of the palladium powders. Experimental results are shown in Table VI.

Analysis of the experimental data has enabled us to produce palladium powders with the necessary physicochemical properties for use in electronics, according to the following rules: . for powders with low volume density and small particle size, the hydrocarbonylation process should be performed at room temperature in low concentrations of hydrochloric acid;

to obtain powders with greater volume density and larger particle size, the hydrocarbonylation should be carried out at about 80°C in high concentrations of hydrochloric acid.

For electronic applications palladium powders must be thermally stable. To test for this, samples of palladium powders were investigated by thermography. The samples were distributed into two groups: (i) thermally stable powders having oxidation temperatures higher than 500°C with the proportion of oxidised palladium being around 20 to 30 per cent (ii) thermally unstable powders having oxidation temperatures of 200 to 280°C with the proportion of oxidised palladium being above 70 per cent.

From all the experimental data, we have


Sample

PdW. gll

44.0 50.0 55.0 76.0 46.0

HCI, M Temperature, OC

2 35 1 80 1 80 1 80 6 80

Specific surface,

m2/g

9.1 4.2 3.1 1.7 0.74

Volume density,

g/cm3

0.91 1.34 1.89 2.1 1 2.60

1 2 3 4 5

Sample a, MPa 0, per cent

2OoC llOO°C 2OoC llOO°C

I * 350 60 8 8 2"" 293 60 14 4

concluded that palladium powders, suitable for use in electronic applications, can be produced by the hydrocarbonylation process.

Temperature, 11 OOOC

Loading, Timeto E. 0 0 2

MPa gap, min percent

50 --3 45 7 17 58.5 40 32 7.5 56

Alloy Powders Using the hydrocarbonylation process for the

production of platinum and palladium alloy powders has also been examined. A solution of H2PtCI, and H2PdC14 was reacted with carbon monoxide under atmospheric pressure at a temperature of around 80°C for three to five hours. Phase analysis showed that the alloy powders obtained were solid solutions with a concentration of chlorine ions less than 0.005 weight per cent (8).

Sample

1 2 3

4 5

Dispersion Strengthened Material The hydrocarbonylation process may also be

used for obtaining dispersion strengthened materials, such as platinum-zirconium oxide. A pow-

support Catalyst composition*, Relative Selectivity, mol activity per cent

Pd : Pt = 7.8 : 1 96 75 Ti02 Pd : Pt = 6.5 : 1 116 80

Pd : Pt = 6.0 : 1 128 85

charcoal Pd : Pt = 6.0 : 1 66 78 Pd : Pt = 7.5 : 1 74 76

der of platinum and 0.25 weight per cent zirconium oxide was obtained by hydrocarbonylation from initial solutions containing platinum(IV) and zirconium oxide. From this powder, a resulting compact metal was produced, having a hardness of 137.2 to 142.6 W. The results of thermomechanical tests are given in Table VII.

Preparation of Supported Catalysts Redox decomposition of the carbonylchloride

complexes of palladium(I), platinum(1) and rhodium(1) was used for the preparation of supported catalysts. A catalyst containing 3 weight per cent palladium supported on alumina was prepared by the decomposition of water-organic solutions of the palladium(1) carbonylchloride complex on alumina. This palladiudalumina material was then tested as a hydrogenation

*A l l samples contained 3 weight per cent of the metals Relative activity is the catalyst activity with regard to some standard sample


'The wire was first annealed in hydrogen at 95OoC for 30 minutes ** I& strength (limit) E relative strain 0 0 2 conventional tensile yield limit "Time to gap" is the time needed for the destruction of the sample

The wire was first annealed in vacuum at 1 100°C for 20 minutes a the stretch of the sample at the moment of destruction (in per cent)

Table VII

Thermomechanical Data of Platinum Wire 1 mm in Diameter Containing + 0.25 weight per cent Zirconia

Table Vlll Test Results of Palladium and Platinum Catalysts for the Reduction of

Propylene into Glycols

catalyst for phenylacetylene. It had high activity and produced more than 10 litres of HJmidg Pd with 94.5 per cent selectivity (9). This is better than results from the same catalyst which has been produced by other methods.

Catalysts with supports such as titania and charcoal, were obtained using the same method from binary solutions of the carbonylchloride complexes of the platinum metals (platinum and palladium). Results of tests using them are shown in Table VIII. These catalysts have the same activity and selectivity as catalysts prepared by standard methods, however, their method of production is simpler.

Conclusions Thus, the results of our investigations show

that the hydrocarbonylation process and car- bony1 complexes of the platinum matals can

be used for the concentration, extraction and refining of the platinum group metals. The use of these processes for the production of composite materials and processing by powder metallurgical methods offers a potentially successful alternative to current means of production. However, as yet, these methods have not been put to industrial use.

References 1 2 French Patent 2,305,398; 1976 3 British Patent 1,472,176; 1977 4 British Patent 1,507,792; 1978 5 US. Patenr4,163,664; 1979 6 Russian Patent 1,637,352; 1990 7

8 Russian Patent 1,541,894; 1989 9 Russian Patent 1,593,008; 1990

Platinum Metals Rev., 1991, 35, (2), 96

V. I. Spi-, I. V. Fedoseyev and I. V. Znamensky, J. Inorg. Chem., 1980, 25, (lo), 2754

Single Platinum-Rhodium Gauze for Partial Oxidation TheFossibility of using a small reactor for con-

verting the light alkanes found in remote natural gases into more useful liquid fuels and commercial products, by an efficient and fast process, has been suggested in work performed by scientists at the University of Minnesota (D. A. Goetsch and L. D. Schmidt, “Microsecond Catalytic Partial Oxidation of Alkanes”, Science,

Using a single layer of woven platinum-1 0 percent rhodium gauze, they were able to perform catalytic reactions of microsecond duration at atmospheric pressures with very high reaction rates. This allowed selective partial oxidation of the reactants to take place. Reacting gases were heated from room temperature to > 800 “C, on entering the single layer of gauze, for a contact time of 8 to 500 ps. After reaction the products were rapidly quenched from 800°C to - 400°C within 200 ps, as they mixed with the cold unreacted gases that had passed between the gauze wires of the catalyst. This allows selective production and survival of oxygenates.

A single Pt gauze catalyst layer produces high oxygen conversions and very different selectivities from coated monoliths or multiple gauzes, with parent olefin, formaldehyde and acetaldehyde being the most partially oxidated products. For ethane, propane, n-butane and isobu- tane different reactivities and selectivities were observed selectivity to olehs strongly decreased, while selectivity to oxygenates increased with

1996, 271, (5255), 1560-1562).

alkyl chain length. At least 40% of reacted butane was converted, mostly to formaldehyde and acetaldehyde.

Steady conversions and selectivities were reached after several hours, with temperatures at > 800°C. The near-adiabatic conditions prevent carbon formation.

Besides being used as a single gauze, the gauze may also be used to preheat gases for partial oxidation by oxide catalysts, such as VzOs. These catalysts produce partially oxidised products with high selectivity and require very high igni- tion temperatures, so preheating is necessary for high conversions and adiabatic operation. A single platinum gauze, placed in front of the oxide catalyst, could preheat the gases to the required temperature. Rapid quenching would keep the conversion low so alkanes and oxygen would remain for reaction on the catalyst.

The reactor has also been operated at 70 d s , which suggests that sonic flow could be obtained, with supersonic quenching. This increased speed of reaction might further stabilise useful chemical species.

At present, the reactors are producing - 20 kg/day of aldehydes and butylene from butane. A reactor of 0.3 m diameter could produce - 1000 metric tondday at 70 d s under these conditions. With higher pressures and velocities, and ifproducts are removed and reactants added between catalyst layers, even higher yields and greater selectivities may result.

Platinum Metals Rm. , 1996, 40, (3 ) 125

Palladium Catalysts in Organic Synthesis Palladium Reagents and Catalysts - Innovations in Organic Synthesis

BY JIRO TSW, John Wiley & Sons, Chichester, 1995, 574 pages, ISBN 0471-95483-7, E125.00

The main catalysts which are traditionally used for the hydrogenation of organic compounds are supported platinum group metals, and while these heterogeneous catalysts are generally not effective in carbon-carbon bond forming reactions, there has been a growing interest in recent years in soluble complexes of the platinum group metals for use as catalysts in organic synthesis. Rhodium catalysed alkene hydroformylation and carbonylation of methanol to acetic acid are two particularly notable industrial successes in this area, and there have also been many dramatic advances in laboratory-scale carbon- carbon bond forming reactions.

A tremendous amount of research has shown that palladium is one of the most versatile centres in this context, and many otherwise difficult-to-achieve organic transformations can be accomplished in convenient practical procedures, when mediated by soluble palladium species. This is illustrated by two important reaction types: coupling processes - of the kinds developed by R. F. Heck and reviewed in his book “Palladium Reagents in Organic Synthesis”, Academic Press, 1985; and direct incorporation of carbon monoxide into certain organic compounds to give a variety of car- bony1 derivatives (aldehydes, carboxylic acids, amides, esters, etc.) - often under conditions as mild as room temperature and atmospheric pressure, which palladium compounds have the abil- ity to promote. A book on these reactions by the present reviewer and his colleagues appeared more recently (“Carbonylation - Direct Synthesis of Carbonyl Compounds”, by H. M. Colquhoun, D. J. Thompson and M. V. Twigg, Plenum Press, 199 1 (1)).

The present book is to be welcomed, since it not only gives an update of progress in the two areas mentioned, but also embraces the entire field of palladium reagents and catalysts in organic synthesis. In his authoritative book Professor Tsuji provides more than 2400 orig-

inal literature references, as well as information about relevant monographs and other texts. It comprises three short and two long chapters. The first chapter, of only ten pages, describes characteristic features of palladium catalysed reactions, and fundamental concepts in palladium organometallic chemistry. The second, even shorter, chapter (six pages) describes how reactions are classified in the book, while the third chapter, of over one hundred pages, deals with oxidation reactions involving palladium(II), such as Wacker chemistry (alkenes to aldehydes, etc.). The fourth chapter is very long, some four hundred pages, and is concerned with carbon-carbon bond forming reactions. The fifth and final chapter, of twenty pages, brings together various catalysed reactions, which have unclear mechanisms, or which, for other reasons, do not fit into any of the categories of the two main chapters.

The index is useful, although not exhaustive. References are collected at the end of chapters and also at the end of some main sections in the largest chapter; this could cause confusion for readers wishing to pursue the original papers. The two other previously mentioned books give practical details for those wanting to make use of palladium-based procedures in their own work. In contrast, the present book does not provide such information, but as the discussion is detailed, and there are copious references, there should be no major problems translating theory into practical applications.

As suggested by the layout of the chapters, material is organised according to the involvement of the metal, while in the two main chapters it is organised according to the organic transformations. This could make it rather difficult for a reader who wants to establish how palladium catalysis might help with a particular transformation. However, by using the contents list and the index, specific information can be tracked down. Due to the wealth of informa-

Platinum Metals Rev., 1996, 40, (3), 126-127 126

tion it contains, browsing through this book will always be a rewarding experience. It is nicely

about modern applications of palladium chemistry to organic synthesis. It is comprehensive in the literature coverage to early 1994, and it

is recommended for purchase by research libraries associated with palladium chemistry or

produced, and is an important addition to books synthetic organic chemistry. M.V.T.

Reference 1 Plurinum Metals Rev., 1992,36, (l) , 39

Platinum Complexes Used in DNA Binding Studies DNA binding studies need unsaturated com-

plexes with emissions sensitive to environmental changes to bind to DNA. Some ruthenium and platinum complexes have photoluminescence changes upon intercalation into calf-thymus (ct) DNA. Scientists at the University of Hong Kong, (H.-Q. Liu, T.-C. Cheung and C.-M. Che, Chem. Cummun., 1996, (9), 1039-1040) have now found two platinum complexes with dramatically en-

hanced photoluminescence on binding. [ptn(dpp- C,N,N)(MeCN)]’ had a 271-fold increase in emission and [Pt”2(pby-C,N,N)2(p-dppm)]2+ had a 1 17-fold increase; dpp-C,N,iV = C-deprotonated 2,9-diphenyl-l,lO-phenanthroline; pby- C,N,N = C-deprotonated 6-phenyl-2,2‘-bipyridine and dppm = diphenylphosphinomethane. This is attributed to intercalation into ct DNA, and may be used as luminescent switches for DNA.

Platinum 1996 For more than a decade Johnson Matthey

has conducted an annual survey of commercial aspects of the platinum metals, and presented the findings in a comprehensive yet readable fifty-two page review.

The recently launched “Platinum 1996” records that during 1995 a recovery in South African production and increased Russian shipments lifted platinum supplies by 10 per cent to 4.98 million oz, while platinum demand improved by 5 per cent to a new peak of 4.79 million oz. Despite a fall of 20,000 oz, at 1.85 million oz autocatalyst manufacture still formed the major requirement for platinum, followed by jewellery with an increased demand of 1.81 million oz.

It is interesting to note that usage by the automotive industry is not confined to emission control catalyst manufacture. Platinum-tipped spark plugs continue to replace base metal plugs on new vehicles, the oxygen sensors used in engine management systems employ platinum, and the lightweight plastics increasingly used in body parts and engine components are rein- forced with glass fibre formed using platinum bushings. In addition, the petroleum industry uses platinum catalysts in the production of gasoline and cleaner-burning diesel fuels, while for the future, pro- ton exchange membrane fuel cells could

be used to power zero emission vehicles. During 1995 industrial demand for plat-

inum increased by 2 1 per cent to 990,000 02, the highest level for sixteen years. At the same time sales of palladium for electronics applications rose by 19 per cent to 2.65 million oz, while high demand from the chemical and glass industries boosted industrial off-take for rhodium by 12 per cent to 48,000 oz. Despite a 12 per cent increase in demand for ruthenium from the electronics industry, a decline in purchases by electrochemical companies contributed to an overall fall in demand of almost 5 per cent, compared with 1994. Iridium demand increased from 42,000 oz in 1994 to 52,000 oz in 1995; although the electrochemical sector accounts for about half of the demand for iridium, smaller applications including crucibles, biomedical and spark plug tips for aerospace applications all increased.

Readers of Platinum Metals Review who wish to have access to this authoratitive source of information on the many fac- tors that influence the supply and demand of the platinum metals are invited to direct their request for a free copy of “Platinum 1996” to the author: Alison Cowley, Johnson Matthey PLC, 78 Hatton Garden, London EClN8JP, England; Fax: +44- 171-269-8389.

Platinum Metals Rev., 1996, 40, (3 ) 127

Ruthenium: “A Dance to the Music of Time” By Professor K. R. Seddon School of Chemistry, The Queen’s University of Belfast

This short review was written to celebrate simultaneously the one hundred andfijlieth anniversary of the discovery of ruthenium by K . K . Klaus, and the bicentenary of his birth. A personal and (necessarily) selective overview o j the highlights of the past decade of ruthenium chemistry is presented, and an attempt is made to place these in an historical perspective.

The year 1994 marked the one hundred and fiftieth anniversary of the isolation of ruthenium by Karl Karlovitch Klaus (1796-1864). K. K. Klaus (Carl Ernst Claus is the Germanic form of his name) was born and died in Dorpat (now Tartu, in Estonia), and 1996 is the bicentenary of his birth. A number of excellent accounts of his life and scientific work already exist (1, 2), and an article, soon to be published here, will carry a new perspective of his work (3). The purpose of this review, therefore, is to mark these anniversaries by selecting some of the advances in ruthenium chemistry over the last ten years, and placing them in an historical perspective.

They are waiting on the shingle ‘They are waiting on the shingle - will you come and join the dance? Will you, wo’n’t you, will you, wo’n’t you, will you join the dance? Will you, wo’n’t you, will you, wo’n’t you, wo’n’t you join the dance?’

Lewis Carroll, “Alice’s Adventures in Wonderland”

Between 195 1 and 1975, Anthony Powell published a sequence of twelve related novels under the title “A Dance to the Music of Time”(4), fkom the Poussin painting, Figure 1. These novels, which can only be read as a whole, represent a unique view of British twentieth century life. The characters pursue an intricate temporal Terpsichorean path, with characters of initial colossal importance disappearing, while others, some of whom dominate the sequence, appear initially insignificant. The novels rep-

resent the personal impressions of a narrator of selective events and their complex temporal interrelation. In his view the characters perform a dance to the music of time, reminiscent of

‘Poussin’s scene, in which the Seasons, hand in hand, facing outward, tread in rhythm to the notes of the lyre that the winged and naked greybeard plays’.

The chemistry of ruthenium also seems to be dominated by this mythical being; some compounds reported in the original accounts of the discovery of ruthenium ( 5 ) still are of prime importance today, others attract only passing interest. Some of the developments reported in the following pages were unimaginable in 1844, others are a natural consequence of the observations made by Klaus. Some complexes, such as [R~(bipy),]~’ (bipy = 2,2’-bipyridine), appear as mildly interesting upon their discovery in 1936 (6), but blossom into supreme importance much later, in 1976 (7).

Where shall I begin? ‘Where shall I begin, please your Majesty?’ he asked. ‘Begin at the beginning,’ the King said, very gravely, ‘and go on till you come to the end: then stop.’

Lewis Carroll, “Alice’s Adventures in Wonderland”

Georges Franju: ‘Movies should have a beginning, a middle and an end.’ Jean-Luc Goddard: ‘Certainly. But not necessarily in that order’

Time, 14th September, 198 1

So, whose advice to follow? 1’11 opt for Powell

Platinum Metals Rev., 1996,40, (3), 128-134 128

Fig. 1 LL Dance to the Music of Time”, by N. Poussin, 1594-1665; (reproduced with per- mission from the Wallace Collection)

and Goddard, ignore Carroll, and begin in 1984, when I co-authored a monograph entitled “The Chemistry of Ruthenium” (8). This was sup- plemented by a series of annual reviews in Coordination Chemistry Reviews (9-1 6). Later, the text was complemented by the appearance of articles in “Comprehensive Coordination Chemistry” (1 7), “Comprehensive Organo- metallic Chemistry” (18-26), and entries in the “Dictionary of Inorganic Compounds” (27-29).

If this wealth of published review material is combined with the now routine and cheap on- line access to Chemical Abstracts and Science Citation Index, it will be appreciated that a short review of the chemistry of ruthenium, even restricted to the past decade, will add little of value to the literature, as it cannot hope to be either comprehensive or even cover all the major highlights.

The magnitude of the problem will be seen by examining the trend in published papers concerning the chemistry of ruthenium, see Figure 2. In 1967, Griffith published an essentially comprehensive review of the chemistry of ruthenium, from its discovery up to 1966 (30): the coverage included 408 citations. In 1984, my book appeared, giving comprehensive coverage of the ruthenium literature from 1804 to 1978

(8): it cited 3254 references. Between 1981 and 1995, Science Citation Index (via the Bath Information and Data Services) lists 1 1,100 references citing ruthenium: there were 1407 papers in 1995 alone (more than three times the total number published from 1844 to 1966). The annual review of only the co-ordination chemistry of ruthenium (no organometallic compounds included) for 1993 lists 405 references (1 6). The literature concerning, and interest in, ruthenium is burgeoning. If this rate of publication continues (and with increasing pressures to publish in academia, it will), we should antic- ipate over 25,000 papers by the year 2005. It

16000 ul U

L 12000 k h. 8000

3 4000

2 0

U

f 1966 1 978 1995

YEAR

Fig. 2 The trend in the integrated appearance of papers about ruthenium chemistry up to 1995


- - CI

CI CI CI

- -

should be remembered, however, that there is no established link between quantity and quality; it is also evident that ruthenium is no longer considered to be an expensive metal! (The average Johnson Matthey base price for ruthenium for May 1996 was $1.77/g). It would not be a daring prediction to suggest that the percent- age of handle-turning pot-boilers will be increasing at a rate proportional to the publication rate.

So, where do I begin? Let us this time listen to Lewis Carroll.

4 - Fig. 3 The dodecachloro- trirutheuate (4 -) ion: a clue to the structure of ruthenium blue

The beginning 'The characters of this metal [ruthenium] are so distinct, that no doubt can be entertained as to its being Werent fkom all previously b o r n . Its highest chloride has a fine orange colour; and when ammonia is added to its aqueous solution, a black oxide is precipitated, whereas the solutions of the other platina metals are not precipitated at all by ammonia at common temperatures. The solution of the chloride is not altered by hydrosulphuric acid (H'S) till the action has been long continued, and then a brown precipitate is at first obtained, which afterwards becomes a black sul- phuret, and the solution assumes a magnificent azure-blue colour. These changes depend upon the precipitation of a small portion of metallic sul- phuret and the conversion of the chloride into a higher one, which has a blue colour, and which is not decomposed by the hydrosulphuric acid. If a plate of zinc be put into the solution of the

orange chloride, acidified by a little hydrochloric acid, a black metallic powder is precipitated after some time, and the solution becomes of a deep indigo-blue colour; eventually the whole of the metal is precipitated, and the solution becomes colourless.'

C. Claus, 1845 ( 5 )

One of the abiding mysteries of ruthenium chemistry is the nature of ruthenium blue (ascribed to ruthenium for the first time, in English, in the above quote). Forty years before Klaus discovered ruthenium, Fourcroy and Vauquelin noted that the action of zinc upon certain solutions of the platinum metals generated an azure-blue solution (31-33). Ten years later, Vauquelin attributed this blue colour to iridium (34,35). In 1846, Claus demonstrated that this blue colour was characteristic of ruthenium chemistry, suggesting that it was due to the presence of RuCL in solution (36).

In 1996, we are little further forward in iden- tifying the complex responsible for this colour, despite the extensive use of ruthenium blue as a synthetic reagent (8). The closest clue to the identity of ruthenium blue is a mixed-valence salt isolated by Bin0 and Cotton (37), containing the [Ru3CllrI4- anion, see Figure 3.

Recently, see Figure 4, mixed-valence phosphine derivatives of this anion, [ R U ~ C ~ ~ ( P R ~ ) ~ ] +

Fig. 4 Mixed-valence phosphine derivatives of the ion shown in Figure 3, [RusCI.(PR3)r]', R = Et or Bu


(where R = Et or Bu) have also been isolated, and characterised (3840).

The past ten years have also seen many simple halide complexes redefined, or observed in a pure form for the first time.

The anion [RU~OB~,~]’, analogous to the well established [RuzOCllo]‘~ (1 l), has been shown not to exist (41); salts of this anion which have been reported in the literature (42, 43) were demonstrated to be salts of [RuzBr9Is, an anion with an almost idealised confacial bioctahedral structure, see Figure 5, but containing a significant metal-metal interaction { r(Ru-Ru) = 0.2880 nm}.

The hexachlororuthenate(II1) anion has been generated in solution in ambient-temperature chloroaluminate(II1) ionic liquids by electrochemical reduction of hexachlororuthenate(IV) (44), and the electrochemistry of the [ R U C ~ ~ ] ” ~ couple has also been recently investigated in conventional molecular solvents (45).

Twelve years ago, an important paper appeared (46) describing the formation of the novel salts A[RuO,CL] (A = [PPh,] or [AsPh,]), which now have a widespread utility as organic oxidants (converting alcohols to aldehydes and ketones, without attacking C=C double bonds) (47-50). The green anion in these salts was tentatively described as a dimeric species, [Ru,O,Clr]”, in the solid state, but as a monomer, [Ru02Cls]-, in solution (46). It is now known to be five- co-ordinate in both solution and the solid-state, although its precise geometry is cation depen- dant (51).

‘The metal [ruthenium] thus obtained, and all its combinations, when mixed with a large quantity of nitre and heated strongly to redness, give a blackish-green mass, which, when dissolved in water, yields a solution of a fine orange-red colour. This solution of the potash salt of the metaUic acid blackens organic bodies, and is decomposed by the addition of organic substances, such as alcohol, and also by the action of acids, &c.; and there is precipitated a velvet-black compound of the oxide and potash; this is soluble in boiling hydrochloric acid, and yields an orange-coloured solution of the chloride.’

C. Claus, 1845 (5)

Continuing on our intricate temporal Terpsi- chorean path, the above quote returns us again

1 3 -

Br Br 1 0r

Fig. 5 The anion [Ru,Brr]’- has an almost idealised confacial bioctahedral structure, containing a metal-metal interaction

to Klaus, in the first report of the discovery of ruthenium. Connoisseurs of ruthenium chemistry will recognise the blackish-green mass described above as potassium ruthenate(V1) , Kz[Ru04].Hz0 (52), which dissolves in water to give an orange solution.

The barium analogue of this salt was reported in 1888 (53), however, it was almost one hundred years before it was recognised that the barium salt contained not the expected tetrahedral (Td) tetraoxoruthenate(VI) anion, but the five- co-ordinate trigonal bipyramidal (D3h) dihy- droxytrioxoruthenate(V1) species, see Figure 6 (54).

Klaus noted that potassium ruthenate(VI)

‘blackens organic bodies, and is decomposed by the addition of organic substances, such as alcohol, and also by the action of acids, &c.’ (5).

This astute observation predates by nearly 150 years the use of rutheniumw) as an important oxidising agent in organic chemistry, chemistry

r

L

Fig. 6 The five-co-ordinate bipyramidal dihydroxytriororuthenate(V1) species


that has been dominated by the excellent work of Griffith (46,47,49, 55, 56), although other scientists have been active too (57, 58).

Will you come and join the dance? Of course, some of the most interesting chem-

istry which has appeared in the last decade was not even suspected in the nineteenth century. Some (but by no means all) of the most notable examples of exciting new chemistry have included:

The reaction between [Ru(CO)~] and buck- minsterfullerene, C,,, in toluene produces the complex [RU(CO)~(~’-C~O)] (59).

Molecular wires with directional photoin- duced electron transfer, based on alkyne- substituted terpyridine ligands, such as (terpy- Ca-terpy, see Figure 7), have been developed (60-63): complexes include such species as [ (terpy)Ru(pterpy-Ca-terpy)M(p-terpy-Ca- terpy) Ru(terpy)],’. (M = Fe, Co or Zn; terpy = 2,2’:6’,2”-terpyridine).

A perfluorinated ruthenium(I1) phthalocyanine complex, [Ru(F,,Pc)] has been encap- sulated in zeolite NaX, and used (in the presence of tert-butyl hydroperoxide) to oxidise cyclohexane at room temperature (64-66), whereas a simple water-soluble ruthenium(I1) phthalocyanine complex, K[Ru(Pc)L2] (LH = diphenylbhenyl-3-sulfonic acid)phosphine , see Figure 8) is an exceptionally active agent for photodynamic cancer therapy (67).

[Ru(CO),]*’ has been prepared for the first

Fig. 7 The ligand terpy-C*-terpy, which has been used in the development of molecular wires, based on ruthenium complexes

Fig. 8 The water-soluble ruthenium complex K[Ru(Pc)L2] is an exceptionally active agent for photodynamic cancer therapy, where LH represents diphenyl(pheny1-3-sulfonic acid) phosphiue

time, as a thermally-stable [Sb2FII]- salt, by the reductive carbonylation of Ru(SO,F), under one atmosphere of carbon monoxide at 60 to 90°C (68).

Sr2Ru0, has been shown to be a copper-free superconductor (69, 70).

Gratzel has developed an efficient nanocrystalline photovoltaic device, using cis-di(thio- cyanato)bis(2,2’-bipyridine-4,4’-dicarboxylato) ruthenate(I1) as the sensitiser (71). . In perhaps one of the most elegant synthetic studies in ruthenium chemistry of this century, Newkome and his co-workers have prepared ruthenium-containing dendrimers, as illustrated in Figure 9, containing twelve ruthenium atoms (72-74). The isolated salts are red, crystalline materials.

Come to the end: then stop As is evident from the flavour of the papers

discussed above, ruthenium continues to deliver some of the most exciting chemistry to be found today. Perhaps this is not surprising in the element which exhibits the most oxidation states in the Periodic Table. The number of papers published is growing at a phenomenal rate, as is the amount of tedious trivia, but the quality of the best work is quite outstanding. No chemist could read the highlights of the past few years, presented here, without feeling a thrill of excite- ment, a debt of gratitude to Klaus, and without wanting to join the dance. And so:

‘On with the dance! let joy be unconfin’d’ Lord Byron, “Childe Harold”, 1812-1817.


Fig. 9 A metallomicallauol (R = CH2CHs), containing twelve ruthenium atoms

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ABSTRACTS of current literature on the platinum metals and their alloys

PROPERTIES High Coercivity in ColPt Multilayers J.-H. KIM and s.-c. SHIN, Jpn. 3 Appl. Phys., 1996, 35, (lB), 342-345 The coercivity in a CoPt multilayer on a Si& underlayer increased more than tw-fold when using a rotating substrate. The increase was due to the enhance- ment of domain wall pinning effects caused by an increase of surface roughness in the Si,N, underlayer. The Si,Na underlayer surface prepared on a rotating substrate was rougher than that on a stationary substrate, which may be due to the oblique incidence of sputtered materials onto the rotating substrate.

Long-Range Order and Magnetic Properties of MnxPt1, Thin Films K W . WIERMANandR D. K I R B Y , ~ Magn. Magn. Muter.,

Thin films of Mn,Ptl., (x = 0.18, 0.22, 0.25, 0.30, 0.34) prepared by magnetron sputtering onto quartz substrates were annealed in vacuum for 1 h at 850°C. After annealing, XRD showed the 6lms to have the CuAu cubic structure and be highly textured with the (1 11) axis along the 6lm normal. The films dis- played a high degree of long-range order, shown by the ratio of the intensities of the superlattice (1 00) and fundamental (200) XRD reflections.

Growth of Ultrathin Pd Films on Al(001) Surfaces

1996,154, (l), 12-16

V. SHUTIWANANDAN, A. A. SALEH, N. R. SHIVAPARAN and R.J.SMITH, s U t $ SCi., 1996,350, (1-3), 11-20 The growth mode and the interface structure of ultrathin Pd films deposited on Al(OO1) surfaces were determined at loom temperature. Pd atoms intermixed with and displaced Al substrate atoms. The mixing continued for Pd coverages from 0-5 monolayers, when a Pd metal film began to grow on the alloy surface. X P S indicated that AlPd formed during mixing, followed by the formation of Pd metal.

Effects of Y2BaCu05 and Platinum Additions on the Unidirectional Solidification of YBa2Cu307d L. DURAND, D. DIERICKX, P. F&GNIER, 0. VAN DER BEST and S. POISSOtiNET, Supercond Sci. Technol., 1996, 9, (4), 296296 The effects of 21 1 and/or Pt additions on the solidification ofYBaCu0 was studied. Mjxing the pure 123 powder with 20 wt.% very fine (1 pn) and regular sized Pt 2 1 1 particles strongly increased the viscosity of the peritectic liquid and resulted in a dramatic refine- ment in the dismbution of the 21 1 particles trapped in the 123 ma& of the samples. Extra addition of 0.5 wt.% Pt further refined this dismbution.

Magnetic Excitations and the Search for Crystal-Field Transitions in the Heavy- Fermion Superconductor Wd2Al, A. KRIMMEL, A. LOIDL, R ECCLESTON, c. GEIBEL and F. STEGLICH, 3 Phys..: Condens. Mutter, 1996, 8, (1 l),

Crystalline-electric field (CEF) excitations in the antiferromagnetic heavy-fermion superconductor UPd,Al, were studied by inelastic neutron scattering. UPd& is an example of 5f-electron systems with a residual line width which corresponds to the macroscopi- cally estimated Kondo lattice temperature. However, significant deviations from this suggest additional inelastic conmbutions that persist up to T = 150 K. This additional scattering could be due to CEF excitations or intersite magnetic correlations.

Superconductivity in Heavy-Fermion GF&Si, R MOVSHOVICH, T. GRAF, D. MANDRUS, J. D. THOMPSON, J. L. S M I T H and z. HSK, Phys. Rea B, 1996, 53, (13), 8241-8244 A superconducting transition in the heavy-fermion compound CeRhSi, was discovered under hydrostatic pressure of > - 9 kbar, near the critical pressure needed to suppress antiferromagnetic order (T, (P = 0) = 36 K) . Superconductivity occurred at - 350 mK. Magnetic AC susceptibility showed a diamagnetic response corresponding to - 1 % of perfect diamagnetism.

The Effect of Si/Ir Codeposition Ratio on the Ir SiliciddSi(100) Interface Roughness C. K. CHUNG andj. HWANG, Muter. C h m . Phys., 1996,

The effect of the Si/Ir codeposition ratio on Ir sili- cide/Si( 100) interface roughness was studied on Ir silicides grown on Si(100) by codeposition at Si/Ir atomic ratios of 0, 1 and 2 at 450°C under UHV. Epitaxial I r S , grew on Si(100) as pure Ir was deposited at all deposition ratios. The Ir,Sb/Si(lOO) interface remained smooth, although intermixing occurred during deposition, but at higher deposition ratios the Ir3SidSi( 100) interface became rougher.

Electrical Conductivity and Superconductivity of Metal Phosphides with Skutterudite-Type Structure Prepared at High Pressure

1677-1685

43, (2), 191-194

I. SHIROTANI, T. ADACHI, K. TACHI, S. TODO, K. NOZAWA, T. YAGI and M. KINOSHlTA, 3 PhyS. chem. sol&, 1996, 57, (2), 211-216 Nip,, LaR~c,0s,P,~ ( x = 0, 1,2, 3,4) and CeRwP,, phosphides with skutterudite (CoAs,)-type structure were prepared at around 1100°C and 4 GPa using a wedge-type cubic-anvil high pressure apparatus. Superconductivity was observed in LaRu,P,,, LaRu,OsP,, and I.~RLI~OS,P,~ at - 7 K. The upper critical field of LaRaP,, was 3.65 T at 0 K.

Platinum Metals Rev., 1996,40, (3), 135-142 135

Quantum Oscillations in the Layered Perovskite Superconductor Sr2Ru0,

M. P. RAY, G. G. LONZARICH, Y. MAENO, s. NISHIZAKI and

A comprehensive study is presented of observed mag- neto-oscillatory phenomena in the normal state of Sr,RuO,, which is the first layered perovskite superconductor (Tc i 1 K) not based on Cu. All sheets of the Fermi surface, including the large ones, have been observed, thus permitting consistent correlation of a number of physical properties. The observations are compatible with a Fermi liquid, which may be liked with coherent interplane transport at low temperatures.

A. P. MACKFNZIE, S . R JULIAN, A. J. DIVER, G. 1. MCMULIAN,

T. FWJITA, Phys. Rev. k t r . , 1996,76, (20), 3786-3789

CHEMICAL COMPOUNDS Size-Evolution Towards Metallic Behavior in Nano-Sized Gold and Platinum Clusters as Revealed by 19'Au Mossbauer Spectroscopy F. M. MULDER, R. c. THIEL, L. J. DE JONGH and P. c. M. GUBBENS, NanoStructured Muter., 1996, 7 , (3),

Au Mossbauer spectroscopic studies were made on the large Pt, cluster and four types of molecular Au,, clusters, with different types of ligands, using Ip7Au produced by neutron activation. The ligands had a large effect on the charge densities at the surface atoms of the cluster cores. For the Ptm9 compound, the inner core atoms had the same charge density at the nucleus as in the bulk metal. The inner core of the Ptlw cluster is metallic, but the Au,, cluster is not.

269-292 1'17

Spectroscopic and Electrochemical Investigation of Mixed-Valence Rh'-Rh"' Complexes with Cyanide Bridge T. V. MAGDESIEVA, S . I. GOREL'SKY, K. P. BUTIN, A. A. BEZRUKOVA, V. S. KHANDKAROVA and YA. S . WGODSKII, Izv. Akad. Nauk, Ser. Khim., 1996, (3), 726-731 New mixed valence Rh'-R"'' complexes with cyanide bridges were studied using electronic spectra and redox potentials. Interaction between Rh atoms in the complexes is small (the ''tixed valences" case). Intervalence transition from Rh' to Rh'" were not observed in the 7000-50,000/cm region. Some of the complexes in the solid state have additional absorption bands in diffise reflectance spectra due to the interaction of the Rh(1) group orbitals of appropriate symmetry.

Synthesis and Characterization of Superstructured Rhodium Porphyrins H. R. JIM&NEZ and M. MOMENTEAU, Inorg. Chim. Acta,

Three Rh "two-face'' hindered porphyrins were synthesised by the metallation of "basket-handle" porphyrins in dimethylformamide, for example, [e- BHP(C,,),Rh"'Q(H,O)]Cl, etc., where e-BHP(CI,), = a5,15:p 10,20-bis [2,2'-(dodecamethy1eneoxy)- diphenyllporphyrinato dianion and L = dimethylamine. In these new neutral or cationic Rh porphyrins, the two faces of the porphyrin are protected by two chains linked at the opposite phenyl rings. Studies of the derivatives of these porphyrins show different reducing tendencies, which follow in general the order for the axial ligand NH(CH,), > H,O or C1-.

1996,244, (2), 171-177

on a N~~ Oxoiridate(V) of the SrSt06-~ype: NaSrrIrOn Fission The Activation of C-H Bonds via Ru-Ru Bond

. .

s. m z m and H, M--BUSCHBAUM, z. Namtforsch. A. J. BLAKE, P. J. DYSON, P. E. GAEDE and B. F. G. JOHNSON,

B. 1996. 51. f2). 225-228 Inorg. Chim. Acta, 1996, 241, (2), 11-12 , , . , I

X-ray studies were performed of single crystals of NaSrlIrOs prepared by heating mixtures of NanOz, SrO and Ir in closed Ag tubes. NaSr,IrO, crystallises with trigonal (rhombohedral) symmetry in the space group D,,"- R3c with a = 9.636(2), c = 11.556(3) A, Z = 6, and is isotypic to compounds of the Sr,PtOa type. The substitution of SrZ+ by Na' in NaSrJrO, resulted in an ordered metal distribution and in an increase of the oxidation state from 11'" to Ir".

Synthesis and Spectral Studies of 1,3- Diketonate Derivatives of ortho-Palladated a- Arylalkylamines

ZAGOREVSK~ and YU. S . NEKRASOV, Izv. Akad. Nauk, Ser. Khim., 1996, (3), 733-740 Acetylacetonato derivatives of a series of orzho-palladated secondary and tertiary a-arylalkylamines were prepared and characterised. An unusual rearrange- ment involving migration of an H atom from the alkyl aminoalkyl group to the Pd atom leading to a hydride intermediate and followed by PdH elimination was observed. This may be due to isomerisation of qz-O',O- coordinated w e t o n a t e ligand into the ql-C-bonded diketonyl form, to give the unsaturated metal centre.

V. V. DUNINA, 0. A. ZALEVSKAYA, S. P. PALII, D. V.

New metallacyclic cluster, Ru,(CO),(CUHs) (1) is produced in low yield by heating the RU,(CO)~(C~H,,) cluster in heptane under reflux. In (l), the fission of a Ru-Ru bond induced the cleavage of two C-H bonds with the concomitant formation of two Ru-C (J bonds. 'H NMR spectra show the two H atoms lost in the reaction are the most activated of those present on the ligand, giving resonances at 0.88 and 1.56 ppm, which are low compared with - 7 ppm for the free ligand.

A Chain Complex of Ruthenium(II,III) Cation Dimer Linked by a Nitroxide Radical, [Ruz(OzCCMe,),(NITPh)] n(BF,)n (NITPh = 2-Phenyl-4,4,5,5-tetramethyl-4,5-dihydro- 1H-imidazolyl-1-oxy-3-oxide)

(3), 201-202 The above Ru chain complex was characterised by the X-ray analysis, showing a structure with the alter- nated alignment of S = 3/2 (Ru(II,IQ core) and S= 1/2 (NITPh). The magnetic moment decreased mono- tonically with decreasing temperature. This chain complex has a paramagnetic dimetal centre with a metal-metal bond linked by the nitroxide radical.

M. HANDA, Y. SAYAMA, M. MIKURIYA, R. NUKADA, 1. HIROMITSU and K. KASUGA, Chem. Lett. &n., 1996,


ELECTROCHEMISTRY Electro-oxidation of C1 Molecules at Pt-Based Catalysts Highly Dispersed into a Polymer Matrix: Effect of the Method of Preparation w. T. NAPPORN, H. LABORDE, J.-M. ~ G E R and c. LAMY, J. Electroanal. Chem., 1996,404, (l), 153-159 Highly dispersed Pt-based electrodes modified with Ru andor Sn inserted in a conducting polymer matrix exhibited weak poisoning effects compared with pure Pt particles. The Pt-Ru alloy was the most promising catalyst for the electro-oxidation of MeOH, while Pt- Sn electrodes gave a very significant negative shift to the oxidation potentials during electro-oxidation of formaldehyde and formic acid. An important decrease in poisoning was found mainly with Pt-Sn electrodes, but also with Pt-Ru and Pt-Ru-Sn electrodes.

The Electrooxidation of Formaldehyde on Pt(100) and Pt(ll0) Electrodes in Perchloric Acid Solutions

and C. IAMY, Elecnochim. Acta, 1996,41, (6), 927-932 Studies of the electro-oxidation of formaldehyde on Pt( 100) and (1 10) electrodes in a perchloric acid medium showed both undergo two oxidation processes involving either methylene-glycol oxidation or adsorbed CO formation. The Pt(100) electrode is more active for the methylene-glycol oxidation. The CO species were adsorbed linearly on both electrode surfaces, but multibonded and bridge bonded CO forms were only present on the Pt( 100). The adsorbed CO species block the surfaces during methylene-glycol oxidation, with Pt(ll0) being more blocked than Pt(100).

Hydrogen Evolution Reaction in Alkaline Solution. Catalytic Influence of Pt Supported on Graphite vs. Pt Inclusions in Graphite

DODELET, D. GUAY and H. M&NARD, J. E l e c m c h . Sac.,

Electrocheinical behaviour of Pt having graphite powders bonded by polymerised LaPO, was studied for the HER in 1 M KOH solution. Pt-supported electrodes, Pt(s)/C/LaPO, (1) were more active than those containing Pt inclusions in graphite, Pt(i)/C/LaPO, (2). In high-current-density conditions of 0.25 Nanz, (2) was stable while (1) disintegrated after 24 h.

Fabrication of Ptl(Ta,O,+Pt) Coated Titanium Electrodes Using Combination of Partial Thermal Decomposition and Electrolytic Reduction of Pt and Ta complex Y. KAMEGAYA, J. SAITO, H. KOBAYASHI, M. OKWAMA and T. MITAMURA, DenkiKagaku, 1996,64, (2), 138-142 A three-layered Pt/(Taz05+Pt)/Ti electrode was fabricated, to protect the Ti substrate from corrosion, by partial thermal decomposition (1) and electrolytic reduction of Pt(NOz),(NH3),, and (1) of Ta(OC2Hr)s. The interlayer is amorphous Ta20, and Pt, with a Pt top layer. It has excellent stability during anodic O2 evolution in HzSO,, high conductivity and durability.

P. OLIVI, L. 0. S. BULHdES,J.-M. L k G W F. HAHN, B. BEDEN

J. FOURNIER, L. BROSSARD, J.-Y. TILQUIN, R. C6T& J.-P.

1996, 143, (3), 919-926

A New Successive System for Hydrogenation of Styrene Using a Two-Compartment Cell Separated by a Pd Sheet Electrode c. IWAKURA, T. ABE and N. mom, 3: Elecmchem. Sac. ,

A new successive system for the hydrogenation of styrene using a Pd sheet electrode is reported. The activated H atoms are electrochemically produced at the front side of the Pd sheet electrode and supplied through it to be used for hydrogenation at the back surface of the Pd sheet electrode. Only ethylbenzene was produced, and the production rate depended on the applied current. The current efficiency of > 93% occurred at an applied current of 10 mA.

Voltammetric Study of the Immobilization of Palladium at the Surface of Carbon Paste Electrodes K.-H. LUBERT, M. GUITMANN and L. BEYER, Electroandysis, 1996,8, (4), 32&325 Cyclic voltammetric studies were performed of Pd immobilisation at the surface of unmodified C paste electrodes. During pretreatment at 0 V, Pd was bound at the surface of the C paste, and the amount of immo- bilised Pd depended on the composition of the solution, polarisation time, electrode potential and stirring. During an anodic scan, the surface-bound Pd was oxidised at - + 0.6 V and the well-shaped peaks could be utilised for the determination of the immo- bilised Pd. The detection limit was - 5 x 10-6M Pd2' after 5 min polarisation at 0 V with stirring. Pd and H can be "deposited" simultaneously at the C paste surface through cathodic polarisation.

Rapid Oxidation of Ru(NH,),J' by Os(bpy)? within Nafion Coatings on Electrodes M. SHI and F. c. ANSON, Langmuir, 1996, 12, (8),

When Ru(NH,)S)' (1) and Os(bpy)? (2) reactants are incorporated in Nafion coatings on electrodes, the oxidation of (1) by (2), which is normally a very slow process, can proceed much more rapidly, especially with Nafion coatings that are not fully hydrated. The Ru(NH,)? is oxidised to R u m at a rate that is first order in Ru(NH,)S)' and Os(bpy)?, and inverse first order in H'. The higher reaction rate obtained upon incorporation of the reactants into Naiion results ftom their higher concentrations rather than &om enhance- ment in the intrinsic redox reactivity of either cation.

Electrochemical Behavior of the RuODiO, Anodes during the Electrolysis of Sea Water c. LIANG and Q. GU, Corm. Sci. h t . Technol. (China),

Studies of the electrochemical behaviour of the anode RuOJTiO, during the electrolysis of sea water showed that use of the anode could improve current effi- ciencies and decrease energy consumption. The best results were obtained at current density of 100 &anz and electrode gap of 5 mm. The cathode was electrochemically protected at potentials from - 820 to - -1450 mV (SCE).

1996,143, (4), L71-L72

2068-2075

1996, 8, (2), 125-129


Investigation of the Formation of RuO,-Based Mixed Oxide Coatings by Secondary Ion Mass Spectrometry

DE BATTISTI, J. Murer. Chem., 1996,6, (4), 567-57 1 The evolution of a Ru0,-TiO, film electrode with temperature was studied using a coating mixture prepared on a Ti support from an isopropyl alcohol solution of hydrated Ru chloride and Ti diisopropoxide bispentane-2,4-dionate precursors. Concentration depth profiles monitored film evolution and identi- fied surface segregation phenomena resulting from the increased metal dispersity.

S. DAOLIO, J. KRIST6F, C. PICCIRILLO, C. PAGURA and A.

PHOTOCONVERSION The Role of Acidity in the Photoreaction of Carboplatin w. LIU, Y. YANG, H. XIONG and z. QUE, Precious Met. (China), 1996, 17, (l), 19-22 Photochemical studies of acidic solutions of carboplatin on irradiation at 313nm showed that the pho- tolytical product is C~~-[P~(NH,),.(H~O)~]’+ and the quantum yield is 0.89. Acidity is a major factor in the photoreaction of carboplatin and the mechanism is discussed.

Vibrational Sidelines in the Localized 3MLCT Emission of [Ru(bpy),(bpz)12’ in

= 2,2 -Bipyrazine) H. =EN, L. WALLACE and E. KRAUSZ, J. phys. Chem., 1996,100, (1 l), 4390-4394 The luminescence spectrum of [R~(bpy)~(bpz)]” (1) and [Ru(bpy-d&(bpz)lZ+ complexes in the host [Zn(bpy),] (ClO,), (2) was studied and sidelines associated with the spectator bpylbpy-4 ligands were iden- tified over the entire vibrational frequency range. Although the lowest excited ’MLCT states in Ru diimine systems are localised, the coupling in the ‘MLCT excitations is 3 4 orders of magnitude larger. Dominant sidelines reported earlier for (1) in (2) are caused by contamination by [O~(bpy)~(bpy-&>]”.

Photosensitization of Nanocrystalline Semiconductor Films. Modulation of Electron Transfer between Excited Ruthenium Complex and SnOI Nanocrystallites with an Externally Applied Bias P. v. KAMAT, I. BEDJA, s. HOTCHANDANI and L. K. PATTERSON, 3. Phys. Chem., 1996, 100, (12), 49004908 The charge injection from excited Ru(bpy),(dcbpy)”, Ru(II), into SnOZ nanocrystallites was studied by in situ specnoelectrochemical measurements. Laser flash photolysis of Ru(II)-modified SnO, nanocrystalline film was used to record the transient absorption spectra at different applied potentials. The yield of elec- mn transfer product, R u m , decreased as the applied bias was switched to negative potentials. At a bias of -0.7 V, Ru(II)* was the only observed transient.

[Zn(~py)3](cI04)2 (bpy = 2 4 -Bipyi&e, bpz

ELECTRODEPOSITION AND SURFACE COATINGS Characterization of a Colloidal Pd(II)-Based Catalyst Dispersion for Electroless Metal Deposition W. J. DRESSICK, L. M. KONDRACKI, M:S. CHEN, S. L. BRANDOW, E. MATlJEWd andJ. M. WVERT, colloid surf: A:Physicochem. Eng. Aspects, 1996,108, (l), 101-1 11 An aqueous Pd(I1) dispersion for the selective electroless deposition of Ni at ligand-bearing surfaces, was prepared by hydrolysis of PdCL, at pH 5 in NaCl solution. The dispersion comprised anionic and uncharged Pd(I1) species, from monomeric to colloidal, with colloidal species starting the electroless metal deposition. The colloidal catalysts have a diameter - 4-53 nm, with an average size of 30 f 12 nm.

Electroplated Palladium Coating as a Nickel Migration (Thermal) Barrier J. K. m, J. s. RUSSO and E. ANTONIER, Pkzt. surf: Finish., 1996, 83, (3), 64-67 Ni-Co plated chip carriers were coated with an acid Pd strike and electrolytic Pd deposits, using three different plating combinations: Ni-Co/Au (Pd strike), Ni-Co/Pd and Ni-Co/Pd/Au. Ni-Co/Au plated carriers were the standard. The tested samples showed equivalent or better Ni migration and solderability than the standard, that is, less than 10 at.% Ni migration and nearly 100% solder flow.

APPARATUS AND TECHNIQUE Flow Injection Amperometric Detection of Ammonia Using a Polypyrrole-Modified Electrode and Its Application in Urea and Creatinine Biosensors

KRAWCZYK, I. LAHDESMAKI and w . SZCZEPEK, Electroanalysis, 1996,8, (3), 233-243 Amperometric NH, detection, using an anodically polarised Pt electrode, modified with PPy, was used in biosensors. NH, detection in a flow injection system with 5 100 ph4 of analyte at a detection limit of 0.6 pM was used to detect urea and creatinine by immobiling urease and creatinine iminohydrolase, respectively, at the PPy surface. A biosensor of very low sensitivity was obtained by urease entrapment in the PPy layer during electropolymerisation.

Effect of Electrode Materials on the Sensitive Properties of the Thick-Film Ceramic Humidity Sensor w . QU, Solid Scare Ionics, 1996, 83, (3, 4), 257-262 A thick-film humidity sensor with excellent stability was produced by depositing a humidity sensitive layer between two metal electrodes on an AlzO, substrate. The sensor response depended on the sensing layer and the properties of the electrode material. Pt electrodes gave higher sensitivity over the whole humidity range, and faster response than AgPd electrodes.

M. TROJANOWICZ, A. LEWENSTAM, T. KRAWCZYtkKI, V.


Composite PdlTa Metal Membranes for Hydrogen Separation N. M. PEACHEY, R C. SNOW and R C. DYE, J. Membrane Sci., 1996, 111, (l), 123-133 A composite metal membrane was fabricated by vapour deposition using 13 p Ta foils cleaned by ion milling, then coated with 1 p of Pd metal on each side. The membrane of area - 2 an', gave exceptionally high H gas fluxes from 18.7 standard cm3/min (sccm) at 300°C to 27.4 sccm at 365°C with a H differential pressure of - 355 torr. The deposited Pd films were oriented along the (1 1 1) crystal axis.

HETEROGENOUS CATALYSIS Deep Hydrodesdfurization of DBT and Diesel Fuel on Supported Pt and Ir Catalysts

J. F. CAMBRA and P. L ARIAS, Appl. C a d . A: Gen., 1996,

Deep hydrodesulphurisation (HDS) of dibenzothio- phene (DBT) and diesel fuel (with 0.08 wt.% S) was performed using Ptl- and Wamorphous SiO,-Al,O, (ASA) and on a stabilised HY zeolite. The normalised activities of PtlASA and PdHY catalysts were better than those of the Ir catalysts, with the HDS being dominant over hydrogenation. In HDS of diesel fuel (at 623 K), both Pt catalysts were a little more active than a commercial Co-Mo/Alz03 catalyst. The normalised activity for HDS of DBT (593 K) increased as: PdHY > WASA >> Ir/HY >Ir/ASA, and the HDS of diesel fuel (623 K) increased as: Pt/HY >> Pt/ASA >> WHY > IrlASA.

Regioselective Hydrogenation of Alkenes over Pt-Loaded Zeolite BEA

and H. VAN BEKKUM, J. Chem. Soc., Faraday Trans.,

The hydrogenation of dec-1-ene (1) and (E)-dec-5- ene (2) was studied over Pt/Na-BEA and non-zeolitic Pt catalysts. Under specific conditions using m a - BEA, (1) is hydrogenated 18 times faster than (2), whereas the ratio is only - 2 for Pt on non-micro- porous supports. Compared with Pt/Na-BEA, Ptl amorphous mesolmacroporous support shows a higher activity in the catalytic hydrogenation of (1) and (2) but a much lower regioselectivity. The hydrogenation over Pt/Na-BEA deviates from zero-order kinetics.

Kinetic Modeling of CO Oxidation on PtlCeO, in a Gradientless Reactor M. A. SHALAFJI, B. H. HARJI and c. N. KENNEY, 3 Chem. Tech. Biotechnol., 1996, 65, (4), 317-324 Pt/CeOz was studied in order to understand the pro- moting effects of CeO, in the CO oxidation reaction, at 100-170°C. At low concentrations of reactants, Pt/CeOz exhibited multiple steady states, similar to the multiplicity behaviour of F't/Alz03. CeO, low- ers the activation energy for CO oxidation, increases the activity of the reaction by being a good 0, store and suppresses the usual CO inhibition effect.

R NAVARRO, B. PAWELEC, J. L G. FIERRO, P. T. VASULEVAN,

137, (2), 269-286

E. J. CREYGHTON, R A. W. GROTJNBREG, R. S. DOWNING

1996,92, (5), 871-877

Synthesis and Characterization of Sol-Gel PtlTiO, Catalyst E. S h C H E Z , T. L6PEZ, R &MEZ, BOKHIMI, A. M O W S and 0. NOVARO, J. Solid State Chem., 1996, 122, (2), 309-3 14 PvTiO, catalysts with 1 .O wt.% Pt were prepared in a one-step operation by the sol-gel technique with Ti(OBut)r and Pt acetylacetonate, without any reduction of the sample in H,. The fresh samples had three nanophases: rutile (the majority), anatase and Pt. Pt promoted the formation of rutile, either due to the presence of an intermediate PtO, phase, having the rutile structure, or to the Pt-catalysed dehydroxyla- tion of anatase. Pt atoms do not enter into the crystalline structure of rutile, despite both PtO, and rutile having the same crystalline structure.

Crotonaldehyde Hydrogenation over Bimetallic Pt-Sn Catalysts Supported on Pregraphitized Carbon Black. Effect of the SdPt Atomic Ratio F. c o m a A. SEW~L.~~?DA--ESCIUBANO, J. L G. FJERRO and F. RODR~GUEZREINOSO, Appl. Catal. A: Gen., 1996,

Three bimetallic Pt-SdC catalysts, prepared by successive impregnation of pregraphitised C black with an aqueous solution of hexachloroplatinic acid and Sn(I1) chloride, were studied during crotonaldehyde hydrogenation. When Sn was added to the samples, the amount of surface Pt was greatly reduced. Both Pt' and Pt" were detected by X P S in the fresh bimetallic catalysts. After reduction in flowing Hz at 623 K, Pt was completely reduced to metal, and some Sn was reduced to Sno, possibly allowing Pt-Sn alloy formation. Catalytic activity for gas phase hydrogenation of crotonaldehyde was greatly improved by Sn.

A Pt-Rh Synergism in PtlRh Three-Way

Z.HU, Chem. Commun., 1996, (7), 879-880 Performances of Pt, Rh and Pt/Rh catalysts were assessed after ageing in exhaust to mimic in-use catalyst operation. The activity of the Pt/Rh catalyst was about one order of magnitude higher than either a Pt or an Rh catalyst for HCICOINO three-way conversions. This high activity of the PtRh three-way catalyst is attributed to a R-Rh synergism. The W A l catalyst also gives HC/CO conversions of 50% at temperatures 70 K lower than the WAI catalyst and lower than the WAl catalyst by 100 K.

Structure and Catalysis of a SiOl-Supported Gold-Platinum Cluster [(PP~)Pt(PPhAu),] -

136, (2), 231-248

catalysts

(NO,), Y. YUAN, K ASAKURA, H. WAN, K TSAI and Y. IWASAWA, Chm. ZAZ. Jpn., 1996, (2), 129-130 A Pt catalyst [(PPh3)Pt(AuPPh3)6](N0,)z (l)/SiOz was very active for H,-D, equilibration with a TOF of 29.8/s, but had low activity for ethene hydrogenation and CO oxidation at 303 K. Pt atoms bonded to Au atoms in the cluster. The cluster fixmework of (l)/SiOz was stable during the reactions at 303 K. The number of Au-Pt bonds fell after heat treatment.

Platinum Metals Rw. , 1996,40, (3) 139

The Shape-Selectivity of Activated Carbon Fibers as a Palladium Catalyst Support H.JIN, S.-E. PARK, J. M. LEE and S. K. RYU, Carbon, 1996, 34, (3), 429-431 Activated C fibre (ACF) was used as a shape-selective catalyst support for Pd. Pd was deposited on pitch- based ACF and was used as the catalyst in the liquid- phase heterogeneous hydrogenation of olefinic C, hydrocarbons. As the adsorption capacity increased, the pore size distribution became wider, and meso- pores and wider micropores increased. HNO, treatment and Pd loadings did not greatly affect the types of adsorption isotherm. For 1-hexene, the hydrogenation rate was a function of mean pore radius: the reaction does not occur at a mean pore radius of < 0.9, but for > 0.9 the reaction rate increased considerably. Shape-selectivity occurs inside the pores.

Liquid Phase Hydroformylation of Ring Substituted Styrenes Catalyzed by Rh-B and Rh-Zn-B Systems Supported on Silica

and R. ZANONI, J. Mol. Catul. A: Chem., 1996, 105,

Rh based catalysts/Si02 were prepared by low temperature reduction of the preadsorbed salts with NaBI-h and Zn(BH,),. A remarkable B and Zn surface enrichment was observed from ESCA data in both catalysts. Both catalysts were active in the hydroformylation of liquid phase ring-substituted styrenes. The resulting reaction was really heterogeneous as no catalyst leaching occurred. The chemoselectivity was always close to loo%, and regioselectivity appeared to be controlled by the nature of the ring substituents.

Synthesis of Cyclopentanone Derivativea with Polystyrene-Supported Cyclopentadienyl Rhodium Catalysts D. P. DYGUTSCH and P. EILBRACHT, Tetrahedron, 1996,

A polystyrene-supported q5-cyclopentadienyl Rh catalyst was applied to two different methods of cyclopentanone synthesis. The synthesis of substitued cyclopen- tanones was performed either by hydrocarbonylative cyclisation, starting from 1,4-dienes or from ally1 vinyl ethers via tandem Claisen reanzmgement, and intramolecular hydroacylation of the 4-pentenal intermediates. The polymer-attached CpRh(cod) complex was a very efficient and reusable hydroformylation catalyst.

Ruthenium Catalyst Supported on CeO, for Ammonia Synthesis Y.NIWAandK-I.m, Chem. Lett. Jpn., 1996, (l), 3-4 Lanthanide oxides, Sm,O,, La,O,, especially CeO,, were more effective, when supporting Ru catalysts, rather than being a dopant during NH, synthesis. The activity of Ru/La,O, catalyst was superior to other metal oxide-supported Ru catalysts, such as RdMgO. The activity, Ru dispersion, BET surface area and the amount of H consumption by Ru/CeOz depended on H2 treatment, thus suggesting a SMSI phenomenon. Partially reduced CeOz donated electrons to Ru atoms, which then formed the active sites.

M. LENARDA, R. GANZERLA, S. PAGANELLI, L. STORARO

(3), 117-123

52, (15), 5461-5468

A Novel Basic Alkaline-Earth Zeolite- Supported Ruthenium Catalyst for Ammonia Synthesis c. T. FISHEL, R. J. DAVIS and J. M. GARCES, Chem. Commun., 1996, (3, 649-650 Studies of the promotional effect of alkaline-earth cations on the catalytic activity of Rdzeolites during NH, synthesis showed an increase in the reaction rates that exceeds those for analogue catalysts containing only alkali-metal cations. The Ru clusters were supported on basic zeolite using as a starting material KX, CsX, CaX, BaX and MgO. Ru/BaX and RdCaX catalysts were three times more active than RdCsX; this is the highest value for zeolites in NH, synthesis.

Carbon Monoxide Hydrogenation on Supported Manganese-Ruthenium Catalysts T. TERCIOGLU andJ. F. AKYURTLU, &l. C d . A: Gm., 1996,136, (2), 105-111 CO hydrogenation over 6.3% Mn-2.5% RdA120, catalyst was studied in a flow system with a dserential fixed-bed reactor operating under atmospheric pressure at 553-613 K, H,:CO = 1:3 and space velocity 5 100-27,600 cm’/gh. Modification with Mn resulted in a shift of the product distribution to lower olefins. The activity and selectivity of the catalyst changed atbelow and above 573 K. It is suggested that atmelow 573 K, monolayer C deposits and > 573 Kmultilayer C deposits affect the performance of the catalyst.

Hydrogenation of Citral and Ciamaldehyde over Bimetallic Ru-Me/Al,O, Catalysts

and S . GALVAGNO, Mol. catal. A: Chem., 1996,108,

Hydrogenations of citral and cinnamaldehyde were studied over Ru-Me/Al,O, catalysts, where Me = Ge, Sn or Pb. Two series of catalysts were prepared by using the controlled surface reaction (CSR) technique (RuEC series) and the more conventional co-impregnation method (RuNI series). Addition of Ge increased the catalytic activity of the RuEC series, but had no effect on RuNI series. Addition of Sn universally increased both activity and selectivity. The Pb present did not modlfy the selectivity and slightly decreased the catalytic activity on RuNI series samples.

G. NERI, L. MERCADANTE, C. MILONE, R. PIETROPAOLO

(l), 41-50

HOMOGENEOUS CATALYSIS Intramolecular Heck-Type Reactions in Aqueous Medium. Dramatic Change in Regioselectivity S. LEMAIRE-AUDOIRE, M. SAVIGNAC, C. DUPUIS and J:P. GE-T, Tetrahedron Lett., 1996,31, (12), 2003-2006 Intramolecular Heck-type cyclisations promoted by P d ( 0 A c ) m M S and PdClJrpPTS catalytic systems, in CH,CN/H,O medium, are reported. The cyclisations were efficiently performed in aqueous medium. Unexpected endo selectivity was observed rather than the usual ex0 process, the reaction reversing in favour of the endo cyclised compounds. Either endo or exo- ring closure can be obtained from the same substrate.


Mild hide-Mediated Palladium-Catalysed Cleavage of Allyloxycarbonyl Protected Alcohols in Aqueous Media S. SIGISMONDI and D. SINOu, J. Chem. Res. (s), 1996, (113 4 6 4 7 The deprotection of allyloxycarbonyl-protected alcohols was efficiently performed under neutral conditions using Pd(OAc),-tppts catalyst in MeCN-H,O, in the presence of NaN, as ally1 scavenger. The deprotection reaction proceeded smoothly with alloc-pri- mary and alloc-secondary alcohols, giving quite good yields. The H,O-soluble catalyst can be easily reused without the addition of more nucleophile.

An Improved Procedure for the Synthesis of Substituted Acetylenes from the Reaction of Acetylene Gas with Aryl Iodides under Palladium-Copper Catalysis M. PAL and N. G. KUNDu, J. Chem. soc., perkin Trans. I, 1996, (59,449-451 The use of dimethylformamide @MF) as a solvent promoted the Pd-Cu catalysed reaction of acetylene gas with aryl iodides in a closed system to give disubstituted acetylenes in fair to excellent yields. The reaction was carried out in the presence of [Pd(PPh,),] Ch, E t a and CuI in Dh4F in acetylene gas. When chlo- roform was used as the solvent, mixtures of mono- and disubstituted acetylenes were produced; some of these have biological interest.

Synthesis and Characterization of Poly(ethynyltrimethyIsi1ane) Containing Pd(II) Coordination Sites M. v. RUSSO, A. FURZANI, M. cuccu and G. POLZoNEm,

Polymerisation reaction of ethynyltrimethylsilane (HC=C-Si(CH;),) are reported in the presence of the bis(acetiy1ide) complex {Pd [C=C-Si(CH3)3],(PPh,)z} in 1:lOO; 1 5 0 and 1:25 catalyst : monomer ratios. The catalyst plays different roles, such as activation by Pd of the mple CIC bond of the monomer and insertion into the Pd-C a-bond with growth of the polymer chain; oxidation of PPh, to OPPh, which can be released leaving free co-ordination sites on Pd followed by crosslinking with the C=C bonds of neigh- bouring polymer chains; and in the presence of NH(C,H5),, the C-Si bond is activated followed by substitution of some Si(CH,), groups with N(C,H,),.

Hydroformylation of Unsaturated Alcohols Catalyzed by Rh(acac)(CO), Modified with Different Phosphorus Ligands A. M. TRZECIAK, E. WOLSZCZAK and J. J. ZI~LKOWSKI,

The activity of Rh(acac)(CO), catalysts modified with mono- and diphosphorus ligands of different electronic and steric properties was studied during hydroformylation of unsaturated alcohols at 6040°C under 10 atm HJCO = 1. The reaction of the 3-buten-2- 01 and 1-octen-3-01 yielded the cyclic 2-hydroxy-5- methyltetrahydrofuran and 2-hydroxy-5-pentyl- tetrahydrofuran, respectively. Ph2P(CH2),PPh2 and P(O-m-MeCsH,), gave the highest catalytic activity.

Pol’et, 1996,37, (9), 1715-1722

N m J . Chm., 1996, 20, (3), 365-370

Direct Formation of Alcohols by Hydrocarbonylation of Alkenes under Mild conditions Using Rhodium Triaikylphosphine catalysts J. K. M A C D O U G U M. C. SIMPSON, M. J. GREEN and D. J.

(6)y 1161-1172 COLE&AMILTON,J. Chem. SOC., Dalton Trans., 1996,

The hydroformylation of hex-1-ene to heptanal and 2-methylhexanal in toluene was catalysed by the complex m ( P E t , ) , ] , while in tetrahydrofuran significant amounts of heptanol and 2-methylhexanol were formed, especially over long reaction times. In pro- tic solvents only alcohols were produced even after short reaction times. The reactions were very rapid and occurred readily with alkenes. The highest rates were observed for ethene (54,000 turnoversh) and the products were always alcohols. A new mechanism for this direct hydrocarbonylation is proposed.

Catalytic Alkane Dehydrogenation by 1rClH2(PPri&: Evidence for an Alkane Associative Mechanism J. BELLI and c. M. JENSEN, OrganometaUics, 1996, 15,

The dehydrogenation of alkanes to alkenes was catalysed by IrClH,(PW,), in the presence of the H accep- tor, tert-butylethylene, at 15OOC. Mechanistic studies, including labelllng experiments with IrClD2(PW3)z, showed that reversible co-ordination and hydride migration to ten-butylethylene is facile and that the slower, subsequent elimination of ten-butylethane required prior co-ordination of alkane.

Ru-Catalyzed Hydrogenolysie of Chiral AUylic and Propargylic Cyclic Carbonates: Synthesis of Optically Active (Q-Allylic and Allenic Alcohols s.-K KANG,D.-Y. KIM,H.-S.RHO,S.-H.YOON~~~P.-S. no, Spth. Commun., 1996,26, (8), 1485-1492 Optically active (E)-allylic, (EYE)-dienylic and allenic alcohols were synthesised with excellent regioselectivity by RuH2(PPh3), (1) catalysed reductive cleavage of chiral allylic cyclic carbonates with NH, for- mate. Also, hydrogenolysis of propargylic cyclic carbonates by (1) afforded only allenic alcohols.

(6), 1532-1534

FUEL CELLS The Chemical State of Sulfur in Carbon- Supported Fuel-Cell Electrodes K. E. SWIDER and D. R ROLISON, 3 Electrochem. Soc. , 1996,143, (3), 813-819 The chemical state of S in W C elecwcatalysts, using vulcan C, was studied by measuring its oxidation state by XPS during the preparation of a “mock” fuel- cell electrode to find if the S from the C affects the electrocatalyst. Pt catalytically oxidised some of the covalent S in the vulcan C to sulphate when H,O, heat and strong physical contact between Pt and C were all present. However, most of the zero-valent S remained in the C after treatment, without any initial contact with Pt, so may be a source of Pt poisoning.

Platinum Metals Rm., 1996,40, (3) 141

Analysis of Reaction Kinetics for Carbon Monoxide and Carbon Dioxide on ENGINEERING Polvcrvstalline Platinum Relative to Fuel Cell

ELECTRICAL AND ELECTRONIC

OGraiion R. J. BELLOWS, E. P. MARUCCHI-SOOS and D. T. BUCKLEY, Ind. Eng. Chem. Res., 1996,35, (4), 1235-1242 Hydrogen can be produced in a polymer electrolyte fuel cell by reforming hydrocarbons or alcohols. Such H, contains CO and CO, (COX) impurities which adsorb onto the Pt anode electrocatalyst, reducing the efficiency for H, electro-oxidation. Studies showed that the rate of CO electro-oxidation is an important factor in determining the CO tolerance of Pt anodes. It is suggested that for CO tolerance, all CO in the feed must be effectively consumed during electro-oxidation at low potentials; CO adsorption fluxes will be much faster than CO, electroreduction on Pt.

Work Function Variations and Oxygen Conduction in a Pt I ZrO,(Y,O,) I Pt Solid Electrolyte Cell N. G. TORKELSEN and S. RAAEN, A@l. s U l $ sci., 1996, 93, (3), 199-203 The working electrode in a Pt I ZrO,(Y,O,) I Pt solid electrolyte cell was studied by photoelectron spectroscopy in UHV, and changes in the electrode work function were correlated with the 0 ion transport through the cell. The change in work function was independent of the cell temperature, when the cell operated as an 0 conductor. Negative 0 species at the working electrode during 0 pumping were indicated.

CHEMICAL TECHNOLOGY Preparation of PdlCeramic Composite Membrane. 1. Improvement of the Conventional Preparation Technique A. LI, G. XIONG, J. GU and L. ZHENG, Membrane sci.,

An improved method of making Pd/ceramic composite membranes has been developed. Thin Pd films were deposited on the surface of a porous ceramic substrate by the conventional and the improved electroless plating technique. The improved method pre- seeds Pd nuclei in a new way: Pd” modified by y- AlOOH sol is deposited on the surface of the porous A120, disk support by a slip-casting process, calcined in air, then the Pd ion in the top layer is reduced to metallic Pd in H2 for 2 h at 400°C. The Al,O, membrane + Pd nuclei is then elearolessly plated in a Pd bath.

Sonochemical Preparation of Ultrafine Palladium Particles K. OKITSU, H. BANDOW and Y . MAEDA, Chem. Muter.,

Ultrafine Pd particles were prepared by using ultra- sound to reduce tetrachloropalladate ions in aqueous solutions. Stable fine particles of Pd were readily produced in the presence of a protective agent, such as a surfactant or a H,O-soluble polymer. The Pd particles obtained were very fine and their sizes had only a nar- row dismbution in the range of several nanometres.

1996, 110, (2), 257-260

1996, 8, (2), 315-317

PtmZTln-SrTiO, Ferroelectric Memory Diode K. GOTOH, H. TAMIJRA, H. TAKAUCHI and A. YOSHIDA, Jpn. J. Appl. Phys., 1996, 35, (lA), 39-43 A non-volatile ferroelectric memory was fabricated from vertical metal-ferroelecaic-semiconductor diodes with simpler structure than a ferroelecmc random access memory (FRAA4) cell. It operates at a lower voltage than metal ferroelectric semiconductor field effect transistors or flash memories. The correct non- volatile and non-destructive memory read-outs were shown with the Pt/PZT/n-SrTi0,diode. The write voltages were - 5 V to write a logic “0” and > 2.5 V to write a logic “1”. The read voltage was 0.8 V.

Material and Electrical Characteristics of Iron Doped Pt-InAIAs Schottky Diodes Grown by

K. HONG, D. PAVLIDIS and F. S&JALON, J. Elecmm. M u m ,

The effect of Fe doping on elecmcal properties and on noise characteristics of devices was studied using Pt-Schottky diodes fabricated on undoped and Fe- doped InAlAs. Fe-doped InAlAs showed a Lorentzian component in the noise spectra not found in undoped materials. An activation energy of - 0.77 eV was found for traps due to Fe incorporation, using temperature dependent low frequency noise measurements.

Barrier Characteristics of PtSilp-Si Schottky Diodes as Determined from I-V-T Measurements

Solid-state Electron., 1996, 39, (4), 583-592 The current-voltage-temperature characteristics of PtSVp-Si Schottky barrier diodes were measured at 60-1 15 K. Deviation of the ideality factor from unity below 80 K was modelled using the so-called To parameter with To = 18 K as an inhomogeneous Schottky contact. A mean barrier height at T = 0 K, = 223 mV, with an assumed Gaussian dismbution of standard deviation, 0, = 12.5 mV was determined.

LP-MOCVD

1996, 25, (4), 627-632

P. G. MCCAFFERTY, A. SELLAI, P. DAWSON and H. EIABD,

TEMPERATURE MEASUREMENT Progress on Fabrication of Iridium-Gold Proximity-Effect Thermometers J. HOHNE, G. FORSTER, C. ABSMAIER, P. COLLING, S. COOPER, F. V. FEILITZSCH, P. FERGER, J. IGALSON, E. KELLNER, M. KOCH, M. LOIDL U. NAGEL, F. PROBST, A.

A, 1996,370, (l), 160-161 RULOFS and w. SEIDEL, Nwl. Insm Methods, Phys. Res.

Ir-Au proximity-effect bilayers with critical temperatures 20-1 00 mK were made as superconducting phase transition thermometers for low temperature calorimeters. Film thickness for the Ir and Au films is controlled during evaporation to f 3% and varies < 15 A at different positions on the film. The measured residual resistivity ratio of the Ir films is - 2 for substrate temperatures of 300°C and- 8 for 630°C.


NEW PATENTS METAL AND ALLOYS Retention of Drinking Water Quality

High Purity Hard Platinum Material ISHIFUKU KINZOKU KOGYO K.K.

Japanese Appl. 713 10,132 High purity hard Pt material with at least 99.9% purity is obtained by adding 0.014.1 wt.% of Nb, Eu and Er, and one or more of Be, Ca, B and Si, to Pt of high purity. This Pt material is used for making jewellery, such as Mgs, necklaces and tie-pins.

CHEMICAL COMPOUNDS Tris(acety1aeetonate)iridium (III) TANAKA KMINZOKU KOGYO K.K.

Japanese Appl. 71316,176 In the preparation of ms(acety1acetonate)iridium (l), Ir(II1) chloride is dissolved in H,O and reacted with acetylacetone to give a reactant solution. The solution is controlled so as to be alkaline, and reacted, extracted by benzene, condensed, washed and dried. The preparation takes place in one step, under stable conditions at 100°C and with high yield.

ELECTROCHEMISTRY Electrolytic Reduction of Disulphide PERMELEC ELECTRODE LTD.

British Appl. 2,291,887A The electrolytic reduction of disuiphide in the cathode chamber of a bath partitioned by a diaphragm uses a metallic cathode composed of Ti, Ta or Zr as an electrode-active surface or an alloy of two or more of Pd, Ti, Ta, Nb, Zr, Ag, etc., and a corrosion-resistant anode composed of Ti, Ta, Nb or Zr or their alloy, coated with Ir oxide as the active material. In an example, the Ti or Zr anode is coated with _> 20 wt.% Ir oxide. Cystine can be reduced to cysteine with high efficiency over long periods.

Electrode Manufacture TOY0 KOHAN CO. LTD. Japanese Appl. 71268,695 An electrode is made by repeating a series of the following processes at least once: applying a catalyst coating solution containing SiOz sol and Pt group metal compounds on a corrosion resistant valve metal matrix, drying and tiring the dried coating. The electrode is used for electrolysis, as an insoluble electrode.

Platinum-Tantalum Electrodes TDK COW. Japanese Appl. 7/31 3,980 An electrode comprises a conductive substrate coated with 85-97 mole % Pt and 3-15 mole % Ta and is used both as an anode and a cathode. After coating the substrate with Pt and Ta components, it is heated in an acidic atmosphere. The electrode, which is used to ionise HzO, has a longer life, even when the polarity of the electrodes is frequently changed.

TDK COW. Japanese Appl. 7/313,985 The quality of drinking HzO is retained by electrolysis using insoluble electrodes coated with Pt, Ir oxide and Ta oxide containing 1-50 mole% of Pt, 40-80 mole% of Ir and 10-50 mole% of Ta. The polarity of the electrodes is changed to prevent scale adsorption on the equipment. The electrodes have longer life, even with the changing polarity.

Electrode for Oxygen Generation FURUKAWA ELECTRIC CO. LTD.

Japanese Appl. 7/33 1,494 The structure of an electrode for 0, generation has a base of Ti or a Ti alloy, upon which is a Ti single layer and an intermediate mixed oxide layer, comprising non-Pt metal oxides, and a mixed oxide catalytic layer mainly of a Pt group metal oxide. The electrode is used in electroplating, electrolytic refining, electrolytic organic synthesis and cathodic protection.

ELECTRODEPOSITION AND SURFACE COATINGS Aqueous Ammoniacal Bath w. C. HERAEUsG.m.b.H. European Appl. 693,579A An aqueous ammoniacal bath for the electrolytic deposition of Pd-Ag alloys contains: 5-50 gll Pd as a Pd ammine complex, 2 4 0 g/l Ag as an Ag compound, 30-150 gll conductive salt, 5-100 gll aliphatic polyamines with 2-10 amino groups and 2-50 pfl mer- captoalkane carboxylic and/or sulphonic acid and/or salts thereof, adjusted to pH 7.0-10.0 withNH40H. The bath is used for electroplating small components, smps and wires with Pd-Ag alloys in the form of shiny, ductile, non-porous and crack-free coatings.

Noble Metal Coated Metal Powder Substrates M. J. OSTOLSKI US. Patent 5,476,688 Noble metal is coated onto a substrate of Cu, Ni, Al, Ti, Zr, etc., or a mixture of one of these seeded with a second, by using a starter plating solution of ionic Pt, Pd, Rh, Ir, Os, Ru, Au or Ag to obtain a coating weight of 2-60 wt.% of the wholly coated product. The substrate is immersed into one bath at 20-100°C until the bath is depleted of noble metal ion before transferring to another bath. The coatings are uniform, with good corrosion resistance and electrical conductivity.

Electromagnetic Wave Shield Coating KOREA MACHINERY RES. INST. Korean Appl. 9414,054 An electromagnetic wave shield coating for a plastic surface is made by mixing a solution of 0.5-100 gll Pd chloride and 0.5400 gA Sn chloride with acetone, tetrahydrofuran, methylethyl ketone, etc., as the solvent. The solution is coated onto the resin surface and then dipped into an electroless plating liquid.

Platinum Me& Rev., 1996, 40, (3), 143-148 143

APPARATUS AND TECHNIQUE Platinum Container TANAKA KIKINZOKU KOGYO K.K.

Japanese Appl. 81 1 ,O 1 7 A Pt container, for scientific use and manufacturing processes, has good mechanical strength, softens less under heating, and can prevent crystals growing. The container is composed of a deposited layer produced by electroforming. The Pt containers have good heat resistance and a long service life.

Water-Tight Plug Seal Composition SHINETSU CHEM. CO. LTD. German Appl. 1195128,232 A water-tight plug seal composition, with short moulding time, contains organopolysiloxane, organohydro- genpolysiloxane, finely-divided SiO, filler, a catalytic amount of a Pt catalyst, and sulphide and triazine peroxide compounds. The composition is easily fixed to the plug housing to reduce the resistance to plug- ging in and maintains HzO tightness. The seal has excellent resistance to heat, cold and oil.

HETEROGENEOUS CATALYSIS Palladium and Silver Containing Catalyst PHILUPS PETROLEUM c o . European Appl. 689,872A The preparation of a Pd and Ag-containing catalyst involves contacting a solid composition of Pd, Ag and an inorganic support material with a liquid composition comprising at least one reducing agent at I 6OOC. The contacting conditions are effective at enhanc- ing the selectivity of the solid composition to C,H,, when it is used as a catalyst for hydrogenating C,H, to produce C,H,, which is also claimed. The catalyst has good activity.

Dehydrocyclisation in Naphtha Reforming EXXON RES. & ENG. CO. European Appl. 690,119A A catalyst composition comprises a halogen and catalytically active amounts of Zn, and non-alloyed Pt, Pd, Ir, Os, Rh, Re and/or Ru, preferably Pt, on an A1203 support. No Co or Ni is present. The catalyst is used during naphtha reforming, giving enhanced 5+C selectivity and dehydrocyclisation of at least part of the naphtha feed stream on contact with the above catalyst. The catalyst is stable and suppresses undesirable hydrogenolysis reactions, thus increasing the product yield and minimising undesirable light gas. Hz yields are increased.

Purification of Engine Exhaust Gas CATALER IND. CO. LTD European Appl. 692,302A The purification of CO, hydrocarbons and NOx at the stoichiometric point or in exhaust gases in 0,-rich atmospheres involves contacting with a catalyst comprising: a porous support on which is a Pt group metal selected from Pt, Pd and/or Rh, and one NOx adsor- bent loaded on the support and selected from alkali metals, alkaline earth metals, etc., and of average particle diameter 0.1-20 pn. The catalyst provides good performance and high temperature durability.

Diesel Engines Exhaust Gas Catalyst

A catalyst for treating exhaust gas from diesel engines comprises a Pt group metal on a ceramic support which is a mixture of TiO,, SO,, AlzO, and ZrO,. The catalyst is prepared by impregnating the support with a solution of the compounds of the Pt group metal, followed by calcination. The catalyst has enhanced CO oxidation, NOx reduction and reduced SOz oxidation and is more resistant to high temperatures.

Exhaust Gas Purification Catalyst MITSUBISHI JUKOGYO K.K. European Appl. 696,470A A catalyst for cleaning exhaust gases comprises a first catalyst layer of Pt, Rh and/or Pd on a support and a layer of Ir catalyst overlaying the first layer. The carrier for carrying the Ir in the second layer is a crystalline silicate, containing preferably Al,O,, SO,, ZrO,, TiO,, or a zeolite. The catalyst operates at high temperatures, is durable and stable. Deterioration of the catalyst by heat, H,O and excess 0, is alleviated.

Attrition-Resistant Catalyst ENGELHARD COW. World Appl. 961612A An attrition-resistant catalyst as CO promoter, used especially in fluid catalytic cracking, comprises Pt supported on transition AlzO, particles which have been impregnated with 3-8 wt.% CeO, and 2 wt.% La,O,, followed by calcination at 2 1 OOO"C, prior to Pt addition. Also claimed are: microspheres of the above bodies; and CO catalysts for use in a fluid catalytic cracking process. The attrition-resistant catalyst has high catalytic activity, long durability and better retention in a cracking unit.

Dehydrogenation of Hydrocarbons AMOCO cow. World Appl. 9611,239A The dehydrogenation of a hydrocarbon feedstock and production of an olefinic product involves contacting the feedstock under dehydrogenation conditions with 0.01-5 wt.% of a Pt group metal and 0.02-10 wt.% Zn catalyst supported on a borosilicate molecular sieve and an alkali metal. The catalyst provides higher performance without the need for regeneration. It has an extended operating cycle life with or without the addition of H, and increases paraffin conversion, olefin selectivity and olefin yield. The olefinic products are used especially as oxygenates for gasoline blend- ing and for chemical industry feedstocks.

Catalyst for Production of p-Xylene CHEVRON CHEM. CO. World Appl. 9613,209A A catalyst for the production of p-xylene from paraflins or olefins by reforming or aromatisation comprises an intermediate pore size molecular sieve support, Pt and one of Ga, Zn, In, Fe, Sn or B. T h e catalyst has an activity sufficient to produce a yield of 2 30% of benzene-toluene-xylene-ethyl benzene from a 5-9C paraffinic or olefinic feedstock. 8C aromatics are obtained, which are enriched to above equilibrium levels in pxylene. The shape selective catalyst produces high yields of xylenes rich in pxylene from feed, which does not contain aromatics.

JOHNSON MATTHEY P.L.C. European 694,332A


Appl.

2~-Dichl0~hexatlu0mprope Hydrogenolysis

U S . Patent 5,481,051 Monohydrogenolysis of 2,2-dichlorohexafluoro- propane (1) to 2-chloro-2-hydrohexafluoropropane (2) is effected by reacting with N, at 5 150°C in the presence of PdCr,O, catalyst, and HCl or H F acid or mixtures of these, to give (2) with a selectivity of > 70% based on the amount of (1) converted. (2) is a valuable intermediate for the synthesis of other F- containing materials, such as CF3CHFCF,, which is useful as a fire extinguishing agent.

Catalytic Reforming Process EXXON RES. & ENG. CO. U S . Patent 5,482,615 A catalytic reforming process with enhanced 5C+ selectivity, including dehydrocyclisation of at least a portion of a naphtha feedstream comprises: contacting the feedswam with the catalpt composition which consists of a halogen and a catalytically active amount of non-alloyed Pt and Zn on an A 2 0 3 support in the absence of Co and Ni. The catalyst suppresses undesirable hydrogenolysis reactions, and therefore decreases the yield of undesirable light gas made during dehydrocyclisation of the feedstream.

Controlled Decomposition Process o m cow. US. Patent 5,485,722 A controlled decomposition process for a liquid mono- propellant composition, containing hydroxylammonium nitrate, involves contacting the liquid with a solid catalyst of Pt andor transition metal groups, thus producing a gaseous propellant of steam, CO, and N,. The decomposition process is used for wastes, which contain hydroxylammonium nitrate, and provides a method for the continuous production of gaseous propellant. The waste treatment and decomposition processes produce innocuous and environ- mentally acceptable gaseous products.

Catalyst Composition PHILWS PETROLEUM co. U S . Patent 5,489,565 A catalyst composition, for the selective hydrogenation of 4-1OC diolefins to their corresponding monoolehs, contains 0.01-2 wt.% Pd andor its oxide; 0.02-10 wt.% Ag andor its oxide; 0.05-10 wt.% alkali metal fluoride; and an inorganic support comprising Alz03, SiO,, TiO,, ZrO,, etc. It is prepared by contacting a starting material containing Pd, Ag and support material with an alkali metal fluoride solution, then drying and calcining at 300-600°C for 0.2-20 h. The catalyst is stable and can be regenerated.

Catalyst for Exhaust Gas Cleaning BABCOCK-HITACHI K.K. Japanese Appl. 71256,105 A catalyst is supported on a composite oxide carrier comprising SO,, TiO, and CeO,. At least 1 wt.% of Pd or P a t is dispersed and carried in the carrier. The catalyst has improved resistance to steam and S. It is used for cleaning exhaust gas which contains a combustible malodorous or poisonous component, for example, hydrocarbon and CO from engines and industrial facilities.

E.I. DU PONT DE NEMOURS & CO.

Production of 2-Phenylbenzotriazolee KYODO YAK= K.K. Japanese Appl. 71258,229 2-Phenylbenzotriazoles (1) are produced by the catalytic hydrogenation of azo compounds in the presence of a 0.1-10 wt.% Pt catalyst, preferably supported on active C, and inorganic bases in amounts of 2 0.3 times mole per azo compounds in organic solvents. Azo compounds are prepared by diazodsing o-nitroanilines with nitrous acid and HCl and coupling the diazonium salts formed with phenols. (1) are used as UV absorbers for polymeric coatings, etc.

Exhaust Gas Purification Catalyst MATSUDA K.K. Japanese Appl. 71265,706 Silicate slurry containing metal, such as Pt, is coated repeatedly onto a monolith support by a wash coat method to form a purification catalyst for NOx, where the slurry viscosity is controlled by adding H,O. The apparatus used is also claimed. The purification catalyst has uniform loading of the active component.

Promotion of Oil Combustion K. SAT0 Japanese Appl. 71277,812 Ceramics used to promote combustion of oil and to reduce combustion exhaust are produced by mixing natural zeolite powder, Pt, Au, Cu, Ca and ALO, powder and moulding the mixture into a spherical shape, followed by firing at 750°C for 6 h, and further heating at 880°C for 12 h. The ceramics reduce CO,, NOx and unburnt HC in the exhaust. The amount of 0, needed for combustion can be reduced by 20%.

NOx Purification Catalyst TOYOTA CHUO KENKYUSHO K.K.

Japanese Appl. 71289,895 A catalyst for purlfylng NOx consists of at least one alkali metal and Pt on a porous support with the mole ratio of the supported alkali meta1:Pt of 20-100: 1. With t h i s catalyst, NOx emissions from automotive internal combustion engines can be reduced over a wide range of temperatures in excess 0, atmospheres.

Catalysts for NH, Decomposition NPPON SHOKUBAI co. LTD. Japanese Appl. 71289,897 A catalyst for decomposing NH, comprises at least one binary or ternary compound oxide@) selected ffom Ti and Si, binary compound oxides containing Ti and Zr, and ternary compound oxides of Ti, Si and Zr; a catalytic component of an oxide of V, W and Mo, and at least one of Pt, Pd, Rh, Ru and Ir. The catalyst is used for oxidising and decomposing NH, emit- ted fkom coke ovens, etc., to N, and H20.

Catalysts for Purifying Exhaust Gases NISSAN MOTOR co. LTD. Japanese Appl. 71289,904 Catalysts for punfying exhaust gases are multi-component compound oxides of form*. PdJvioJWYdO, where a = 0.01-5 wt.%; b, c and d = atomic ratio of each element; and when b = 10, c = 0.1-1 1 and d = 30-200, and g = number of 0 atoms required. The catalysts are effective over a wide temperature range and are durable. They can efficiently remove NOx from atmospheres containing excess 0,.

Platinum Met& Rev., 1996,40, (3) 145

Exhaust Gas Purification MATSUDA K.K. Japanese Appl. 71299,365 A catalyst for purifvlng exhaust gases contains Pt and at least one metal selected from Ir and Groups IIB and IVB elements supported on base materials. Exhaust gas can be purified in an atmosphere with excess 0, at low temperatures. It is used for the effective removal of CO, HC and NO, from exhaust gases.

Purification Catalyst for NOx TOKYO GAS CO. LTD. Japanese Appl. 71303,838 A Pd salt solution, such as Pd nitrate and Pd acetate is supported on mordenite by immersion or ion exchange with the coexistence of NH, ions and acetic acid, to form a NOx purification catalyst. Pd supported on mordenite (SiO,:Al,O, ratio of 10:30) is denatured with acidic Fe salt solution or Mg. The catalyst removes NOx efficiently and is used in the presence of a hydrocarbon reducing agent, such as CH,.

Catalyst for Purification of Exhaust Gases

A catalyst for exhaust gas purification, especially of NOx, comprises a perovskite type double oxide powder, Lao,Ceo,NiO, which carries 0.04 wt.% of Rh, and is obtained by mixing and drying a mixture of La, &eo ,NiO, and Rh. With this catalyst, NOx can be removed at lean range conditions.

Polymetal Multi-Gradient Reforming Catalyst UOP Japanese Appl. 71308,582 A hydrocarbon conversion catalyst comprises: a Group VIII Pt group metal, preferably made of homoge- neously dispersed Pt and a surface metal other than Pt (preferably Pd), in a catalytically effective amount; and a non-acidic macro hole molecular sieve, such as Lzeolite, containing an inorganic oxide binding agent. The surface density of the metal is preferably twice that of the centre of the catalyst. The catalyst is useful for reforming hydrocarbons for producing gasoline of high octane value. The catalyst has high catalytic activity and good stability.

Hydrogenation of Edible Fat and Oil CHIYODA COW. Japanese Appl. 713 16,585 A Pt catalyst is used for the hydrogenation of edible fat and oil to obtain a product with a low content of trans acids. Preferably, the catalyst consists of a support of specific surface area of 2 10 m’lg with a poros- ity o f t 0.1 d g , supporting 0.1-10 wt.% of Pt catalyst(s). The method controls the formation of trans acids and allows less severe hydrogenating conditions.

Purification of Contaminated Soil EBARA COW. Japanese Appl. 71328,595 A purification process for contaminated soil involves heating the soil to 300-500°C and evaporating any aromatic halogens it contains by contacting with a catalyst at 250400°C in the presence of > 5% 0,. The catalyst contains more than one of Pt, Pd, Cu, Co, Mn, V or their oxides supported on A1,0, or SiO,:Al,O,. The process can purify soil contaminated by aromatic halogen without addition of any reagents.

DAIHATSU MOTOR CO. LTD. Japanese & i d . 71308,578

Catalyst for Ozone Decomposition NE CHEMCAT K.K. Japanese Appl. 81 1 0,6 1 9 An ozone decomposition catalyst contains amorphous Mn oxide and Pd oxide, carried on SiOz-BzO,-Al,O, composite oxide, and also contains at least one of Ir, Ag, La, Ce, Fe, Ni, Y and Sm. The catalyst can decompose ozone efficiently from gases containing S compounds and/or H,O.

Purifying Diesel Engine Exhaust Gas

A sorption-oxidation catalyst for combined sorptive and oxidative purification of diesel engine exhaust gas comprises a solid acid system doped with Pt metal oxide(s) to increase barrier activity, especially after cold start, and reduce odour emission. The catalyst also has satisfactory CO oxidation activity, avoids partial oxidation to odorous substances and increases the highly volatile organic components’ sorption activity under load, especially after cold start.

Hydrogen Peroxide Production Catalyst BASF A.G. German Appl. 4,425,672 An oxidation catalyst (1) used in the preparation of epoxide or H2OZ is based on Ti or V silicates with zeolite structure and contains 0.01-20 wt.% Ru, Rh, Pd, Os, Ir and/or Pt. The novelty is that each Pt metal is present in t 2 different energy states. (1) is used as a heterogeneous catalyst in the production of propylene oxide, from olefins, H, and 0, and of H,Oz fkom H, and 0,. It can be regenerated by controlled combustion of C deposits and reactivated, preferably with H, or simply by washing.

CH, Steam Reforming or Oxidation Catalyst SUED-CHEMIE A.G. German Appl. 4,427,665 A catalyst for auto-thermal steam reforming andor oxidising CH, reactions which proceed in parallel, comprises Pt/Al,O, where the carrier contains 2-12 wt.% Ni and 1-10 wt.% Ce, both calculated as metal and based on the whole catalyst. The catalyst has high activity in both oxidation and steam reforming, and is highly stable mechanically and catalytically at > 850°C. It is used in the production of synthesis gases or Hz fkom CI-h, for the production of MeOH, Fischer- Tropsch hydrocarbons, 0x0 alcohols and NH,.

MAN NUTZFAHRZEUGE A.G. German Appl. 4,424,235

HOMOGENEOUS CATALYSIS Preparation of Optically Active Cyclohex-2- ene-1-one Derivatives F. H O F F M A ” LA ROCHE & CO. A.G.

European Appl. 691,325A Optically active cyclohex-2-ene-1-one derivatives (1) are prepared by asymmetric hydrogenation of enol derivatives of keto-isophorone using a Rh complex of an optically active diphosphine ligand as catalyst. The Rh complex comprises lower alkyl or lower alkoxy, phosphine, benzyl, etc. (1) are valuable intermediates in the preparation of 3-hydroxy carotenoid derivatives, especially in the preparation of zeaxanthin. The process gives high optical yields.

Platinum MetaLF Rev., 1996,40, (3) 146

Hydrosilation Process DOW CORNING CORP. US. Patent 5,481,016 A hydrosilation process using an alcohol or silylated alcohol accelerator comprises reacting SiH and the unsaturated reactant in the presence of a Pt catalyst, selected from Pt compounds and Pt complexes. The process is carried out with 0.1-10% stoichiometric excess of SiH with respect to the unsaturated C-C linkages in the unsaturated reactant. The concentration of Pt catalyst provides 1-1000 moles of Pt per 1 X 1 O6 moles of unsaturated C-C bonds. The reaction is carried out at 15-1 7OOC. The accelerators are effective in the presence or absence of 0 , and are used in hydrosilation of unsaturated reactants.

Preparation of 2-Aryl Aliphatic Ester ALBEMARLE CORP. US. Patent 5,482,596 2-Aryl aliphatic ester is prepared from styrene derivatives and CO at 1 am and 25-200°C in the absence of 0, and in the presence of a catalyst composed of a mixture of Pd(0) or Pd salts, or a mixture of Pd(O), Pd salts and Cu salts; and phosphine or phosphine oxide and a mixture of ligands. The reaction is used particularly for preparation of the drug ibuprofen, and the process does not require a solvent.

4-Methylidene Cinnamic Acid Derivatives MERCK PATENT G.m.b.H. German Appi. 4,424,489 The preparation of substituted 4-methylidene cinnamic acid derivatives (l), with benzylidene camphor substituents, comprises reacting an aryl halide and an acrylic acid derivative in the presence of a Pd catalyst. The derivatives are obtained in fewer stages, with good spaceltime yield and with little use of addi- tives. They are UV absorbers in cosmetics.

Vinyl Carbamates BASF A. G. German Appl. 4,425,677 Vinyl carbamates are prepared in high yield and selectivity by reacting secondary amines and CO, with acetylenic compounds added during reaction in the presence of a Pt group metal compound, especially a Ru compound. The reaction is carried out in the presence of a tertiary amine. The process gives high yields and/or selectivity and avoids the use of COCl, and highly toxic organo-Hg compounds.

FUEL CELLS Supported Platinum Alloy Catalyst DEGUSSA A.G. European Appl. 694,982A A Pt alloy catalyst on a conductive C support contains a ternary alloy of Pt, Co and Cr as the catalytically active component. The catalyst is obtained by co-precipitation from an aqueous solution of nitrates of the alloy components onto the suspended support, as their hydroxides; reducing the hydroxides; washing, drying and calcinating at > 800°C to form an ordered alloy. The catalyst is used for making fuel cell electrodes. It has higher activity and stability than other available catalysts and can be produced quickly at lower manufacturing cost.

Anode Catalyst for Fuel Cells STONEHART ASSOC. INC. Japanese Appl. 71299,359 An anode catalyst for fuel cells contains an alloy of 1-70 at.% Ge and/or Mo and at least one of Pt, Pd and Ru. Poisoning of the catalytic metals by CO contained in fuels is inhibited and the fuel cells can be operated for a longer period. There is no need to purify the fuels to remove CO.

Phosphoric Acid Fuel Cell FUJI ELECTRIC co. LTD. Japanese Appl. 71307,156 A phosphoric acid fuel cell has an electrode catalyst layer in which Ru powder-retained C grains are bound together with fluororesin and laminated on a porous C electrode base. The cell prevents a drop in cell voltage and corrosion in the C electrode base, respectively, due to the presence of CO. The cell can be cheaply manufactured.

Hydrogen Containing Gases for Fuel Cells IDEMITSU KOSAN c0. LTD. Japanese Appl. 812,902 H,-containing gases for fuel cells are prepared using a selective oxidation catalyst of Pt/L-type zeolite. The H,-containing gas is produced by reforming a fuel to a fuel gas, then mixing with an O,-containing gas, and also with 1 7 4 0 vol.% CO, and CO. On contact with the PtL zeolite catalyst, CO is changed to COz. The gases obtained can be used as fuels for fuel cells operated at low temperatures, in for example, phosphoric acid, KOH and polymeric solid electrolyte type fuel cells. The lifetimes of the fuel cells are extended, due to CO being prevented from poisoning the Pt in the fuel cell electrodes.

CHEMICAL TECHNOLOGY Preparation of 1,2-Butylene Oxide BASF A.G. German Appl. 4,422,046 1,2-Butylene oxide (1) is prepared by the catalytic hydrogenation of vinyl-oxirane, using a Pd catalyst supported on BaS04, ZrO, or TiOz, or a supported Pd catalyst optionally containing Re. (1) is a fuel addi- tive or a stabiliser for chlorohydrocarbons. Improved conversion, yield and selectivity are obtained.

ELECTRICAL AND ELECTRONIC ENGINEERING Manufacture of PCB LEARONAL MC. European Appl. 697,805A The manufacture of printed circuit boards (PCB) involves contacting the board with an electroless Pd solution after covering the circuit pattern with a solder mask, thereby protecting Cu from oxidation. The contact time is sufficient to provide a finish layer of Pd (alloy) at the required thickness, to protect the Cu deposits in the holes and on the circuit board from oxide formation. The finish layer is smooth and flat, and gives good solderability. Also claimed is the method which provides the finish layer with good wire bonding capabilities.


High Density Magnetic Recording Medium A.G. TECHNOLOGY co. LTD. US. Patent 5,478,661 A magnetic recording medium has a magnetic thin film of composition Co,~o-,-b-.-y-~Ni.CrbPt.MyOl (where a = 0-15, b = 0-15, x = 0-20, y = 0-20, z = 0110 (x, y, z # 0) and a+b+x+y+z I 60, a and b cannot both be zero; M = Si, B, Zr, Al, P, Ti, Sn andor In. M may be an oxide, MO,, where c = 0-5 (not zero). The Nm is deposited by sputtering a target of MO, incorporated into a base material of CoNiPt, CoCrPt or CoNiCrPt alloy. The film has a coercive squareness of 2 0.7, a coercivity of 2 2000 Oe at a remanence of 3.0 x lo-’ emdcm’ and low noise. The medium is used in high density recording.

Opto-Magnetic Recording Medium TDK COW. Japanese Appl. 71272,334 The recording medium has a multilayered structure of layers of PtSb and MnSbPt thin films formed alter- nately, until the specified thickness is obtained. The layers have NiAs-type crystalline structure. The total thickness of the artificial lattice film is 50-2000 A. The medium records and reproduces information, and simplifies magnetisation in the vertical direction.

Spherical Bump Electrode NIPPON STEEL cow. Japanese Appl. 7,283,227 A spherical bump electrode for a semiconductor chip, is made of Au alloy with 0.001-0.05 wt.% Pt and 0.0014.05 wt.% In, and constitute O.OOlA3.05 wt.% of the total composition. Components such as 0.0005-0.01 w t % Pd, 0.00050.005 wt.% Cu and one or more types of 0.001A3.005 wt.% Ag are also added, and also constitute O.OOl-O.O5wt.% of the total composition. Anisotropic deformation of the electrode is prevented and damage to the elemode during mounting is min- imised. Enhanced manufacturing yield with high reliability is achieved.

Ceramic PWB Resistor MATSUSlUTA ELECTRIC WORKS LTD.

Japanese Appl. 1/297,5 13 A ceramic PWB has a thick Nm resistor layer (A) and a conduction circuit layer (B) on a ceramic substrate. A connection terminal layer (C) is between (A) and (B), and a protection layer of 0.5-2 pm in thickness is formed on (C) and is produced by baking a paste made from Pd or Pt at 800-900°C. A glass layer hides the resistor layer. The resistor reduces the occurrence of faults.

Semieonductor Memory for DRAM NIPPON STEEL COW. Japanese Appl. 7/32 1,232 A semiconductor memory for DRAM has a multilayered structure. The memory has capacitors formed on the inner wall of contact holes. Both of the electrodes of the capacitor are formed with RuO,. The lower electrode is made of dielectric film. There is increased wiring connection reliability and the wiring can be formed by a sputtering method. The value of the capacitance and the integration density are increased. The memory area is reduced and the manufacturing process is simplified.

Manufacture of Polyimide Board wmcn K.K. Japanese Appl. 71321,457 The surface of a polyimide film is treated with HNO, and alkali, and optionally with polyamide acid solution treated with PdC1, to produce polyimide board, which has good adhesiveness to metal and good electrical characteristics. The board is heated to > 200°C and a metal layer is formed by a wet plating process. Reduction of PdCl, is achieved after further treatment. Laminated polyimide board is obtained.

Single Crystal Fe-Si-A1 Based Alloy MITSUMI ELECTRIC CO. LTD.

Japanese Appl. 71330,495 A single crystal of an Fe-Si-Al based alloy, used for a magnetic head, consists of: 9.35-9.55 wt.% Si, 10-6.25 wt.% Al, 0.30-0.35 wt.% Ru; and the bal- ance Fe. The plane orientation is the (100) plane. Adding Ru to the alloy reduces rust and enhances corrosion resistance. Ru also enhances magnetic permeability; starting from 47,100, a maximum magnetic permeability of 277,900 was obtained at 5 MHz.

Iridium Thick Film Conductor SUMlTOMO KMZOKU CERAMICS K.K.

Japanese Appl. 71335,782 A ceramic substrate, with a bump for mounting a chip carrier in an external mother board, has a number of wiring layers in and on its surface. The ceramic substrate has a thick film electric conductor made from W andor Mo (40-90 wt.%) and Ir (60-10 wt.%) which connects the internal wiring layer and a Cu ball. The construction provides reliable junctions which can withstand the effect of the mounting conditions.

MEDICAL USES Silicone-Based Dental Impression G.C.CORP. British Appl. 2,292,153A Silicone-based dental impression compositions for the production of crowns, inlays or dentures, comprise 100 parts by weight of organopolysiloxane (1) with 2 2 aliphatic unsaturated groupslmolecule; 0.1-30 parts of organohydrogen polysiloxane (2) with 2 3 H atoms directly bonded to a Si atom; 10-500 ppm, with respect to (1) and (2) of silicone-soluble Pt compound; 5-500 parts of inorganic filler and 1-200 parts of polyvinyl ether of 1000-50,000 degree of tpolymeri- sation. Compositions have good elastic properties.

Dental Impression Material

A dental impression material which allows visual core monitoring is claimed. It comprises a curable silicone polymer containing a crosslinker with at least two S M groups, a hydrosilation catalyst comprising a complex of Pt and an unsaturated organo-Si material, and core- indicating dyes showing a colour change within - 10 min at 25°C to indicate gel point or set time.

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

MINNESOTA MINING & MFG. CO. Woru Appl. 961560A


Documents

Contents · Contents Chiral Complexes of ... Any discussion on such specialised topics as isomerism and chirality needs to be prefaced by ... such as C1-, etc. (2)