PLATINUM METALS REVIEW a Quarterly Survey of Research on the Platinum Metals and of Developments in Their Application in Industry

E-ISSN 1471–0676

PLATINUM METALS REVIEW A Quarterly Survey of Research on the Platinum Metals and of Developments in their Application in Industry www.platinummetalsreview.com

VOL. 50 OCTOBER 2006 NO. 4 Contents

High-Temperature Mechanical Properties of the 158 Platinum Group Metals By R. Weiland, D. F. Lupton, B. Fischer, J. Merker, C. Scheckenbach and J. Witte

Rhodium and Iridium in Organometallic Catalysis 171 By Robert H. Crabtree

CAPoC7: The State of the Art in Automotive 177 Pollution Control Reviewed by Jillian Bailie, Peter Hinde and Valérie Houel

The Platinised Platinum Interface Under 180 Cathodic Polarisation By Jacques Simonet

SURCAT 2006 Conference 194 Reviewed by S. E. Golunski

Reliability of Platinum-Based Thermocouples 197 By Roy Rushforth

“Principles of Fuel Cells” 200 Reviewed by Tom R. Ralph

10th Ulm Electrochemical Talks 202 Reviewed by Sarah C. Ball

Susan V. Ashton 205 By M. C. F. Steel

Abstracts 207

New Patents 211

Indexes to Volume 50 213

Communications should be addressed to: The Editor, Barry W. Copping, Platinum Metals Review, [email protected]; Johnson Matthey Public Limited Company, Orchard Road, Royston, Hertfordshire SG8 5HE DOI: 10.1595/147106706X154198 High-Temperature Mechanical Properties of the Platinum Group Metals PROPERTIES OF PURE IRIDIUM AT HIGH TEMPERATURE

By R. Weiland and D. F. Lupton* Engineered Materials Division, W. C. Heraeus GmbH, Hanau, Germany; *E-mail: [email protected]

B. Fischer, J. Merker and C. Scheckenbach Department SciTec, Precision-Optics-Materials-Environment, University of Applied Sciences Jena, Germany and J. Witte Melting Technology, SCHOTT Glas, Mainz, Germany

In order to provide reliable data on the high-temperature deformation behaviour of iridium, the high-temperature material properties such as stress-rupture strength, high-temperature tensile strength and creep behaviour are determined for pure iridium in the temperature range 1650–2300ºC. Analyses of the stress-rupture curves and the creep behaviour of pure iridium samples at 1650ºC, 1800ºC and 2000ºC imply that the fracture behaviour is controlled by two different fracture mechanisms depending on test conditions, in particular applied load and test temperature. The existence of the different fracture modes is confirmed by SEM examination of the fracture surface of samples ruptured at high temperatures. Anomalies in the creep curves and the results of high-temperature tensile tests indicate that dynamic recrystallisation plays an important role in the high-temperature deformation behaviour of pure iridium.

Due to their excellent chemical stability, oxida- A knowledge of the high-temperature proper- tion resistance, and resistance to the action of ties of a material, for instance stress-rupture many molten oxides, the platinum group metals strength and creep behaviour, is crucially impor- (pgms): iridium, platinum and rhodium are widely tant for the design of components used at high used for high-temperature applications involving temperatures. The current investigation is part of simultaneous chemical attack and mechanical load- an extensive test programme focused on the deter- ing (1). Although iridium is more sensitive to mination of the high-temperature mechanical oxidation than platinum or rhodium, it is the most properties of the pgms, such as the stress-rupture chemically resistant of all metals. Its resistance to strength, creep behaviour (3) and elastic properties attack by stable oxide melts is maintained up to (4). In this work new investigations into the high- temperatures above 2000ºC. temperature properties of iridium are presented for The melting point of iridium (2454ºC) (2) and the temperature range between 1650ºC and its high strength even at temperatures above 2300ºC. The results are discussed in conjunction 2000ºC make it a particularly suitable material for with data determined from earlier studies (3). applications under extreme thermal and mechanical conditions which preclude the use of platinum Methodology for Stress-Rupture alloys or rhodium. Important applications of iridi- and High-Temperature Tensile Tests um and iridium alloys are as crucibles for pulling The stress-rupture strength and the creep single crystals (e.g. yttrium-aluminium garnet behaviour of pure iridium and iridium alloys were (YAG)) and components for manufacturing and determined with a testing facility developed at the processing high-melting special glasses. University of Applied Sciences Jena. The testing

Platinum Metals Rev., 2006, 50, (4), 158–170 158 Fig. 1 Schematic diagram of equipment for high-temperature creep measurements

device, for the measurement of high-temperature ing technique using a digital pyrometer material properties up to 3000ºC, is shown (INFRATHERM IS10). The infrared pyrometer schematically in Figure 1. It consists of a gas-tight has a small measurement spot (approximately 0.5 specimen chamber which permits investigations mm in diameter). Due to the ohmic heating the either in air or under a protective gas atmosphere. highest temperatures are found in the central part In the case of iridium and iridium alloys, a gas mix- of the sample. This region is therefore scanned ture of argon with 5 vol.% H2 was used to protect continuously by the pyrometer via a tilting mirror. the material from oxidation and thus avoid a By storing the maximum value of emitted radia- reduction in cross-section of the sample due to tion, the maximum temperature at the surface of evaporation of volatile oxides (5, 6). the sample may be determined. This value is used The load can be applied in two different ways. to adjust the heating current via a thyristor regula- For the constant-load stress-rupture experiments tor connected to the primary winding of a 100 the load is applied via a steel pull-rod by means of kVA transformer. The sample, short-circuited calibrated weights. For the high-temperature ten- across the secondary winding of the transformer, is sile tests the specimen chamber is mounted in a heated by alternating current at 50 Hz. Over a zone commercial servomotor-driven test machine and 30 mm in length around the centre of the sample the steel pull-rod is connected to the load cell at the temperature usually does not vary by more the crosshead of the test machine. This allows a than ± 5ºC. Once “necking” occurs in the sample, controlled variation of the applied load. Non-stan- the temperature outside the necking region dard specimens (with typical dimensions of 120 decreases, whereas the temperature within the mm × 4 mm × 1 mm) were used for all measure- necking region remains constant at the intended ments. The samples were laser cut from hot rolled value. The design of the equipment thus guaran- sheet material. The sample orientation was chosen tees uniformity of temperature throughout the parallel to the rolling direction. duration of the test, despite the sample deformation. Direct electrical heating achieves high heating The strain is measured with a non-contacting and cooling rates for the samples. The ohmic heat- video extensometer consisting of a 17 mm charge ing method allows easy access to the sample, and coupled device (CCD) camera with 1280 × 1024 generally straightforward operation. pixel resolution. A special arrangement of telecen- The temperature is measured by a non-contact- tric lenses allows only near-parallel rays to pass the

Platinum Metals Rev., 2006, 50, (4) 159 aperture, thus minimising perspective distortions material was then hot rolled at moderate tempera- caused by variations in the distance to the object. ture to 1 mm thick sheet. The iridium sheet was Both the CCD camera and frame grabber are con- finally subjected to a special annealing procedure trolled by “SuperCreep” software, developed at so as to recrystallise the deformed material without the University of Applied Sciences Jena, which significant grain growth. uses digital image analysis. As mentioned above, ohmic heating causes the Scanning Secondary Ion Mass highest temperature to be limited to the central Spectrometry (Scanning SIMS) part of the sample, to which creep deformation is The microanalytical investigations were per- normally also limited. Strain at this part of the formed with a Cameca IMS 4f-E6 scanning sample is determined by “SuperCreep” from con- secondary ion mass spectrometer. Secondary ion tinuous measurements of the distance between mass spectrometry (SIMS) allows the detection of two markers. Suitable markers for high-tempera- very small amounts of impurity elements in the ture tests on sheet materials are made by laser matrix. Since both the species of detectable sec- machining samples of the material with four small ondary ions and their detection limits differ as shoulders (Figure 2). The distance between the between the positive and negative secondary ion two corresponding markers on the same side of spectra, different primary ions were chosen for the the sample is 10 mm. Since the part of the sample excitation of the secondary ions. Oxygen primary between the markers experiences a uniform tem- ions were used for the investigation of the positive perature, the exactness of strain measurements can secondary ion spectrum emitted by the iridium be guaranteed, without their being influenced by samples. The emission of the negative spectrum the temperature gradients near the ends of the was induced by caesium primary ions. It could sample. thus be ensured that all possible impurity elements A detailed description of the testing facility and contained in the iridium samples were detected. the algorithm for strain measurement is given in Metallographically prepared samples were used (7) and (8). for the scanning SIMS investigations. So as to be able to investigate impurity levels both inside the Material Preparation grains and at the grain boundaries, areas of the The iridium raw material was melted inductive- samples containing grain boundaries were chosen. ly at 2550ºC in air in a zirconia crucible. After It should be mentioned that the intensity of the elemental analysis the ingot was forged at temper- emitted secondary ion spectrum is dependent on atures between 1400ºC and 1600ºC. The forged the crystallographic orientation of the grains. Thus, if several grains with different orientations are contained in the area under investigation, this will be indicated by differences in the brightness attributable to the respective grains due to differences in ionic emissivity. Thus grain boundaries may be identified in the secondary ion spectrum, even if they do not contain significant amounts of impurities.

Stress-Rupture Strength Results The stress-rupture strength of pure iridium was determined in the temperature range 1650–2300ºC. The results of these investigations Fig. 2 Image of a creep sample with markers for the are summarised in Figure 3. The present experi- video extensometer (7) ments showed an excellent degree of

Platinum Metals Rev., 2006, 50, (4) 160 Fig. 3 Stress- rupture strength of pure iridium in the temperature range between 1650ºC and 2300ºC

reproducibility; the results are in good agreement rupture strength values at testing times longer than with those of corresponding measurements for 300 h. It is not yet clear whether this steep decrease shorter testing times reported earlier (3). In con- in slope can be attributed solely to the change in trast to the conclusion in (3), additional data on fracture mechanism, or whether the effect of stress-rupture strength obtained recently, together weakening of the grain boundary coherence is with a detailed analysis of the rupture behaviour enhanced by very small amounts of impurities (see below under ‘Fracture Behaviour Results’), led accumulating at the grain boundaries after long to the conclusion that the stress-rupture data can testing times at high temperatures. As reported best be approximated by two intersecting lines. below, secondary ion mass spectrometric investi- The discontinuity in the slope of the stress-rupture gations showed that the impurity content in the curves correlates very well with a change in the iridium samples examined is very low. fracture behaviour of the samples examined. Nevertheless, it cannot be excluded that even very Under high loads pure iridium shows a ductile small amounts of impurity elements accumulating fracture mode, whereas under low loads and long at the grain boundaries can have a detrimental times to rupture, iridium tends towards brittle effect on grain boundary coherence, thus leading intercrystalline fracture. In fact, the discontinuity to significantly reduced times to rupture. does not usually occur as sharply as indicated in Measurements at 1650ºC and 1800ºC have been Figure 3. performed up to approximately 1000 h duration. Samples taken from near the discontinuity Extrapolations to testing times longer than 10,000 often show mixed fracture modes, partly intercrys- h may not be considered meaningful. Data on the talline and partly transcrystalline. Since insufficient stress-rupture behaviour of pure iridium at 2200ºC stress-rupture data in the range of the transition are and 2300ºC are available up to times to rupture of available, the stress-rupture curves for the temper- approximately 500 h and 150 h, respectively, and atures between 1650ºC and 2000ºC are not as yet for longer times to rupture. Within the approximated for the sake of simplicity in the man- available range the stress rupture curves do not ner shown in Figure 3. In particular, the show a visible discontinuity in slope. Because of stress-rupture curve at 2000ºC shows a very pro- the very distinct decrease in slope in the stress-rup- nounced change in the slope at loads between 4 ture curve at 2000ºC under low loads, no and 5 MPa. This leads to strongly reduced stress- extrapolations beyond the measured times to rup-

Platinum Metals Rev., 2006, 50, (4) 161 Table I Stress-Rupture Strength of Pure Iridium at Various Temperatures Time to Stress-rupture strength, MPa rupture, h 1650ºC 1800ºC 2000ºC 2200ºC 2300ºC

1 31.8 24.4 14.1 7.1 5.4 10 27.7 18.4 8.9 4.4 3.3 100 15.6 11.0 4.6 2.7 2.0 1000 8.8 7.0 1.5 – – 10,000 5.0 4.4 – – – ture have been performed for the data at 2200ºC Particularly at the lowest test temperature of and 2300ºC. 1650ºC, under moderate load, the creep behaviour The interpolated and extrapolated data on the is represented by typical creep curves such as those stress-rupture strength of pure iridium at different in Figures 4(a) and 4(b). These figures represent temperatures are given in Table I. the creep behaviour of pure iridium at 1650ºC under a constant load of 13 MPa exhibiting the Creep Behaviour Results three well known stages of creep – primary, sec- The investigation of the high-temperature ondary (or steady-state), and tertiary – frequently deformation behaviour of iridium revealed that, reported in the literature. depending on test temperature and load, its creep Under higher load, and particularly at higher behaviour can be described by two types of creep test temperatures, the creep curves of iridium curve which differ significantly in shape. show significant anomalies. In the range of steady- state creep the creep curve contains different plateaus, as shown in Figure 5. These plateaux are separated by an acceleration of the elongation. This acceleration of creep is clearly visible in Figures 5(b) and 5(d). The phenomenon may be caused by dynamic recrystallisation, as was reported in (9) and (10), whose authors obtained creep curves of similar shape when investigating the creep behaviour of lead and copper, respectively. It can be seen in Figures 5(c) and 5(d) that in some cases more than one discontinuity occurs in the secondary creep stage. This indicates that dynamic recrystallisation takes place successively several times during the secondary stage of creep. This is called periodic or cyclic creep (11). These accelerations of creep complicate the determination of a constant creep rate in the secondary creep range. The creep rate has therefore been calculated as an average for a time range from 10% to 90% of the period of measurement. Fig. 4 Creep curves: (a) of pure iridium at 1650ºC under Thus additional contributions to the average creep a constant load of 13 MPa in Ar/H2 atmosphere, and (b) corresponding creep rate as a function of time. The mean rate from the accelerated creep in the transient creep rate for the period 16.95–152.54 h is 1.3 × 10–7 s–1 creep stages are included in the values. This aver-

Platinum Metals Rev., 2006, 50, (4) 162 Fig. 5 Elongation and creep rate of pure iridium as a function of time in Ar/H2 atmosphere at 1800ºC for loads of: (a) and (b) 13 MPa. The mean creep rate at a constant load of 13 MPa for the period 5.68–51.12 h is 1.0 × 10–6 s–1. (c) and (d) 9.5 MPa. The mean creep rate at a constant load of 9.5 MPa for the period 22.5–225 h is 2.6 × 10–7 s–1 age creep rate has been used instead of the mini- the stress dependence of the average creep rate has mum creep rate for the calculation of the Norton been assumed to obey a power law (Equation (i)): plot (Figure 6). In the Norton plot, the average n dε/dt = f(S, T)σ (i) creep rate for pure iridium determined in this way for each test temperature is shown as a function of where ε is the elongation and f(S, T) is a function the initial applied stress on a double logarithmic of the structure of the material and of the temper- scale. ature. For the isothermal representation in the For the calculation of approximate trend lines, Norton diagram, f(S, T) has been assumed con-

Fig. 6 Average stationary creep rate of pure iridium as a function of the applied initial stress for temperatures between 1650ºC and 2300ºC (Norton plots)

Platinum Metals Rev., 2006, 50, (4) 163 Table II Coefficients for the Approximation of the Quasi-Stationary Creep Rate as a Function of Stress According to Equation (i)

Temperature, f(S,T) f1(S,T) f2(S,T) Norton exponents

ºC nn1 n2

1650 – 1.3 × 10–13 4.5 × 10–25 – 5.35 13.68 1800 – 1.2 × 10–11 4.4 × 10–16 – 4.40 8.28 2000 – 5.1 × 10–10 3.6 × 10–11 – 4.11 5.70 2200 2.5 × 10–9 – – 5.38 – – 2300 2.1 × 10–8 – – 4.99 – –

stant. The effects of structural changes, for considerably higher values (5.7 < n2 < 13.7), indi- instance, due to recrystallisation, have been cating that under these test conditions addressed to some extent by the use of the average diffusion-controlled dislocation climb is not the creep rate, determined as described above. The prevalent mechanism of deformation. The values

Norton exponent, n, contains information about for f(S,T), n1 and n2 determined by approximation the nature of the prevalent creep mechanism in the of the experimental data in the Norton plot using sample. For creep mechanisms that are based only Equation (i) are listed in Table II. on the diffusional transport of material due to The temperature dependence of the stationary vacancy gradients either inside the grains (12, 13) creep rate can be expressed by an Arrhenius term. or along the grain boundaries, a nearly linear stress Thus, Equation (i) can be rewritten in the form dependence of the creep rate will be obtained, and (Equation (ii)): n will be close to or equal to unity. For creep n dε/dt = ασ exp–(QC/RT) (ii) processes that are determined mainly by diffusion- controlled dislocation climb, n falls between 3 and where α is a factor dependent on structure, QC is 5 for many common pure metals. In rare cases, n the activation energy for creep, R is the gas con- values up to 11 have been found. stant and T is the temperature in K.

The distinction between the different creep The activation energy, QC, for the creep mech- mechanisms under low and high loads mentioned anism can be obtained by plotting ln(dε/dt) versus in the preceding section must also be taken into 1/RT. If QC is independent of temperature, account in the Norton plots. The data for each test ln(dε/dt) will show a linear dependence on 1/RT, temperature between 1650ºC and 2000ºC are with the slope of the straight line equal to the acti- therefore approximated by two intersecting vation energy QC. In the present investigations it straight lines. As already explained for the stress- was not possible to determine QC in the way strain diagram, the information available for described, as the creep tests were performed under 2200ºC and 2300ºC does not allow this distinction constant load, not under constant stress. In this to be made for these temperatures. case the true stress is a function of the elongation, For test temperatures between 1650ºC and thus invalidating this method for determining the 2000ºC, the values obtained for the Norton expo- activation energy. nent under low loads n1 fall in the range between 4 and 5.5, and are thus in good agreement with the Fracture Behaviour Results above-mentioned values of the Norton exponent The iridium samples showed excellent ductility for diffusion-controlled dislocation climb in many at the temperatures investigated. Particularly at other pure metals. For conditions under which high loads, rupture strain values up to 100% have iridium exhibited a ductile fracture mode, i.e. been measured. At lower loads, the values for the under high loads, the Norton exponent n2 took rupture strain proved to be considerably smaller.

Platinum Metals Rev., 2006, 50, (4) 164 Fig. 7 SEM images of the surface area near the fracture for pure iridium after stress-rupture test at 1800ºC under an initial load of 6.7 MPa: (a) and (c) ×20; (b) ×100; (d) ×50

This finding is in accordance with the observation make an additional contribution to the elongation that iridium exhibits two different fracture modes of the sample. This apparent ductility does not, in stress-rupture tests at high temperatures. however, influence the intrinsically brittle mode of According to the literature (9) this change in frac- fracture. Samples exposed to high stresses exhibit- ture mode should be accompanied by a ed only very few intercrystalline cracks. As a discontinuity in the slope of the log-log plot in the consequence the high apparent ductility of those stress-rupture diagram (Figure 3). samples can be assumed to be identical to the true Whereas intercrystalline fracture occurs without ductility of the material. necking at low loads (Figures 7(a) and 7(b)), On the surface of the samples exhibiting ductile together with the appearance of extensive inter- fracture behaviour, slip bands that have formed in crystalline crack formation across large parts of the the necked region are clearly visible. These are very sample (Figures 7(c) and 7(d)), the fracture at high distinct, and in some cases extend across grain stresses occurs by the transcrystalline mode, boundaries, sometimes covering several grains. accompanied by extensive necking as shown in Overlapping slip bands in different directions were Figures 8(a) to 8(c). This is in accordance with text- observed in some grains. This indicates that differ- book reports (11) of creep crack behaviour at high ent slip systems have been activated during the temperatures for many materials which are prone creep experiments. It is not yet clear whether the to brittle intercrystalline fracture under low loads, slip bands are formed only in the final stage of but tend to transcrystalline fracture under high creep deformation, when the load-carrying cross- loads. It should be mentioned that the numerous section of the sample is significantly reduced due cracks and fissures occurring along the grain to progressive strain and the true stress and creep boundaries during the creep tests under low loads rate increase rapidly, or whether the slip bands are

Platinum Metals Rev., 2006, 50, (4) 165 Fig. 8 SEM images of the surface area near the fracture for pure iridium after stress-rupture test at 1800ºC under an initial load of 18 MPa: (a) ×10; (b) ×50; (c) ×500; (d) ×200

formed throughout the creep experiment. summarises the results for the temperature range between 1600ºC and 2300ºC. The shapes of the High-Temperature Tensile Tests stress-strain curves, particularly those for temper- These tests were carried out in order to exam- atures between 1800ºC and 2100ºC, are typical for ine the behaviour of pure iridium at high materials that undergo dynamic recrystallisation. temperatures under dynamic loading. Figure 9 After a very steep rise in the stress-strain curve at

Fig. 9 Stress-strain diagram for pure iridium at different temperatures

Platinum Metals Rev., 2006, 50, (4) 166 the beginning of the tests, the slope of the curve decreases, probably due to both plastic deformation and softening of the material caused by dynamic recovery. When dynamic recrystallisation commences, the softening becomes more severe and the load decreases. This is followed by a period at a more or less constant load – in some cases this phase exhibits a slight oscillation – until the stress drops rapidly when the sample ruptures. This behaviour is typical for materials that are recrystallising dynamically during the high-temperature tensile tests. A comparison of the stress-strain curves with Fig. 10 SEM image (×200) of the surface morphology of the results of the SEM investigations reported in an iridium sample after creep test at 1800ºC under 23 the previous section shows that the slip bands, MPa load shown in Figures 8 and 10, are formed only in sam- made on at least three samples for each test tem- ples exposed to loads close to or greater than the perature. The values given for Rp0.2 and Rm are yield stress determined in the tensile test at the cor- averages over all three measurements. The stan- responding temperature. In the present dard deviation is indicated as an error bar for each investigation, the deformation mechanism under data point, revealing excellent reproducibility for high loads at high temperatures appears to be the measurements. The values for A, however, based on an interaction of plastic deformation due showed a greater scatter. Moreover, some of the to dislocation slip with common creep deforma- samples did not rupture between the markers, in tion. The plastic deformation in turn leads to an which cases it was not possible to determine the increase in the internal deformation energy, thus tensile elongation with the “SuperCreep” software. promoting the initiation of dynamic recrystallisa- No error bars are given for the relevant data points tion. in Figure 11.

Yield strength, Rp0.2, tensile strength, Rm, and tensile elongation, A, as determined in the high- Metallographic Investigations temperature tensile tests are plotted in Figure 11 as The microstructure of pure iridium exposed to a function of temperature. Measurements were the influence of high temperatures and different

Fig. 11 Yield strength, Rp0.2, tensile strength, Rm, and tensile elongation, A, of pure iridium as a function of temperature

Platinum Metals Rev., 2006, 50, (4) 167 Fig. 12 Longitudinal section of pure iridium in the initial recrystallised state

Fig. 13 Longitudinal sections of pure iridium after creep test at 1800ºC, 6.7 MPa, 1403.7 h loads during the creep tests was evaluated metallo- damage and cracked at a different position, sever- graphically. Comparative investigations were al hours later. Dynamic recrystallisation is carried out on longitudinal sections of samples apparent in areas of high stress concentration and before and after creep testing. The microstructure strong deformation, for instance at crack tips of a sample in the initial state (i.e. before creep (Figure 13(a)), and close to the fracture in the testing) is shown in Figure 12. The sample exhibits necking areas (Figure 15). Particularly in the area a uniform microstructure with an average grain around the crack tips, this may have led to a reduc- size of about 100 μm. tion in local stresses. As a consequence the crack Comparison with metallographic sections of propagation may have stopped in this area and samples that were exposed to high temperatures continued in another part of the sample. under different loads (Figures 13 and 14) shows The metallographic images show the existence that during creep tests specimens have undergone of individual voids along grain boundaries and the expected severe grain coarsening. Due to the their coalescence into large pores. These are typi- high temperatures and long test times, very coarse cally found in materials that have undergone creep grains with grain sizes up to 4 mm have formed. deformation. This phenomenon is most frequent- Furthermore, the samples exhibit strong intercrys- ly observed on grain boundaries that are oriented talline crack formation as mentioned above. perpendicular to the direction of applied stress. Figures 13 and 14 show that several – partly very This often leads to the formation of intercrys- deep – cracks have formed within the same sam- talline creep cracks during the final period of creep ple. Nevertheless, the material withstood this deformation.

Platinum Metals Rev., 2006, 50, (4) 168 Fig. 14 Longitudinal sections of pure iridium after creep test at 1800ºC, 13 MPa, 56.8 h

numerical simulation of its service performance, the stress-rupture strength, creep behaviour and tensile properties of iridium have been measured over the temperature range 1650–2300ºC. The investigations were performed on hot rolled iridium sheet. The results showed a very good degree of reproducibility. The iridium samples exhibit very high stress-rupture strength. A discontinuity in the slope of the stress-rupture curves indicates the existence of two different fracture modes, depending on the temperature and the initial load applied to the samples. The existence of Fig. 15 Longitudinal section through the fracture tip of different fracture mechanisms was confirmed by pure iridium after creep test at 1800ºC, 8.3 MPa, 385.9 h the examination of the fracture surfaces. The change in fracture mode is probably caused by dif- Microanalytical Investigations ferent deformation mechanisms prevalent under As has been demonstrated in previous investi- the various test conditions. gations (14–19), iridium generally tends to brittle A significant anomaly was observed in the creep intercrystalline fracture due to trace impurities at behaviour of pure iridium – the creep curves con- grain boundaries. Investigation by SIMS on the tained plateaus in the range of steady-state creep. present iridium samples has shown a very high Metallographic examination, investigations by purity for the material. Only very small traces of SEM, and high-temperature tensile tests indicated impurities in the ppm range were detected, show- that dynamic recrystallisation may be the cause of ing no enrichment at the grain boundaries. All the this phenomenon. A further influence may be the elements detected were distributed homogeneous- activation of various slip systems which can be ly in the matrix. deduced from the observed slip bands. Microanalytical investigations by means of Conclusions scanning SIMS showed a very high purity of the Due to its outstanding properties iridium is par- iridium heats investigated, without any enrichment ticularly suited to applications under extreme of trace impurities at the grain boundaries. thermal, chemical and mechanical conditions. In Initial results on the stress-rupture strength of order to obtain the materials data necessary for the an iridium-rhenium alloy doped with hafnium and design of high-temperature equipment and the molybdenum indicate that this alloy exhibits rup-

Platinum Metals Rev., 2006, 50, (4) 169 ture times three to four times longer than for pure Materials XIII, Singapore, 6th–8th December, 2004, iridium. Moreover, this alloy shows outstanding Stallion Press, Singapore, 2005, pp. 787–799 7 R. Voelkl, D. Freund and B. Fischer, J. Test. Eval., ductility, comparable to that of pure iridium. This 2003, 31, (1), 35 alloy is therefore of particular interest for high- 8 R. Voelkl and B. Fischer, Exp. Mech., 2004, 44, (2), temperature applications and is the subject of 121 ongoing research. 9 J. N. Greenwood and H. K. Worner, J. Inst. Met., 1939, 64, 135 10 M. J. Luton and C. M. Sellars, Acta Metall., 1969, 17, Acknowledgements (8), 1033 The authors would like to thank Margit 11 R. E. Reed-Hill and R. Abbaschian, “Physical Friedrich (SEM investigations), Erik Hartmann and Metallurgy Principles”, 3rd Edn., PWS Publishing Frank Lehner (creep tests) from the Department Company, Boston, 1994 12 C. Herring, J. Appl. Phys., 1950, 21, (5), 437 SciTec of the University of Applied Sciences Jena 13 F. R. N. Nabarro, Proceedings of the Bristol for their support for these investigations. Conference on Strength of Solids, Physical Society of London, 1948, p. 75 References 14 P. Panfilov, A. Yermakov, V. Dmitriev and N. Timofeev, Platinum Metals Rev., 1991, 35, (4), 196 1 “Edelmetall-Taschenbuch”, eds. G. Beck, H.-H. Beyer, W. Gerhartz, J. Hausselt and U. Zimmer, 15 P. Panfilov and A. Yermakov, Platinum Metals Rev., OMG AG & Co KG, Giesel Verlag GmbH, 2001, 45, (4), 179 Isernhagen, 2001 16 J. Merker, M. Schlaubitz, H.-J. Ullrich, S. Garbe, A. 2 C. R. Barber, Platinum Metals Rev., 1969, 13, (2), 65 Knoechel, M. Radtke, F. Lechtenberg, D. F. Lupton 3 B. Fischer, A. Behrends, D. Freund, D. F. Lupton and B. Fischer, DESY-HASYLAB Annual Report, and J. Merker, Platinum Metals Rev., 1999, 43, (1), 18 Hamburg, Germany, 1994, pp. 913–914 4 J. Merker, D. Lupton, M. Toepfer and H. Knake, 17 J. Merker, D. F. Lupton, B. Fischer, M. Schlaubitz, Platinum Metals Rev., 2001, 45, (2), 74 H.-J. Ulrich, A. Gebhardt and S. Garbe, Prakt. 5 D. F. Lupton and B. Fischer, Proceedings of the Metallogr., Sonderband 27, 1995, pp. 267–270 Second European Precious Metals Conference, 18 J. Merker, D. F. Lupton, H.-J. Ullrich, M. Schlaubitz Lisbon, 10th–12th May, 1995, Eurometeaux, and B. Fischer, Proceedings of the TMS Annual Brussels Meeting, 2000, TMS, Warrendale, Pennsylvania, pp. 6 J. Merker, B. Fischer, D. F. Lupton, C. 109–120 Scheckenbach, R. Weiland and J. Witte, Proceedings 19 R. Voelkl, A. Behrends, J. Merker, D. F. Lupton and of Processing and Fabrication of Advanced B. Fischer, Mater. Sci. Eng. A, 2004, 368, (1–2), 109

The Authors After studying Materials Jürgen Merker studied Prof. Dr.-Ing. habil. Bernd Science at the University materials science at the Fischer studied of Saarbrücken, Germany, Technical University, mechanical engineering Reinhold Weiland worked Dresden, where he also and materials science at as a research associate at earned his Ph.D. degree. the Technical University the Max-Planck-Institute Between 1995 and 2000, Chemnitz, Germany. After for Metals Research in Stuttgart, and he worked as a development project more than 25 years at the University of received his doctoral degree from the manager for W. C. Heraeus GmbH, Hanau. Jena, Bernd Fischer was appointed to the University of Stuttgart. Since 2002 he has After a short time in the R&D department Chair of Materials Science at the University been working at W.C. Heraeus GmbH in of KM Europa Metal AG, Osnabrück, he of Applied Sciences Jena in 1992. For Hanau as a development project manager. was appointed to a Professorship in many years, his research interests have His main interests are the processing and Materials Engineering and Applied Metals included the properties and applications of manufacture of precious metals products Science at the University of Applied noble and refractory metals. and composite materials. Sciences Giessen-Friedberg in 2002. In 2006 Dr Merker became Professor of Jörg Witte studied Carolin Scheckenbach Materials Technology and Materials Testing chemistry at the Technical studied materials at the University of Applied Sciences Jena. University of Darmstadt, technology at the Germany, from which he University of Applied Prof. Dr David Lupton is received his doctoral Sciences in Jena, Development Manager, degree in Materials Germany, where she Engineered Materials Science. Since 1999 he has worked at received her diploma degree. After one Division, W. C. Heraeus. Schott-AG, Mainz, where he is currently year as a research associate, she is now His main interests are the head of the Materials Competence working as a trainee in the Department of manufacture and applic- Department. His main interests are the Melting Technology and Hot Forming at ations of precious metal and refractory properties of refractory materials and Schott AG, Mainz. metal products. failure analysis.

Platinum Metals Rev., 2006, 50, (4) 170 DOI: 10.1595/147106706X153117 Rhodium and Iridium in Organometallic Catalysis WORK IN THE LABORATORY OF OUR RHODIUM BICENTENARY COMPETITION WINNER

Robert H. Crabtree Department of Chemistry, Yale University, 225 Prospect St., New Haven, CT, 06520, U.S.A.; E-mail: [email protected]

Work to extend the catalytic chemistry of rhodium and iridium, with particular emphasis on the great versatility of the former, is outlined and summarised. Topics addressed include the design of chelating N-heterocyclic carbene ligands, and the cyclisation of alkynes using rhodium and iridium phosphine compounds as reagents or catalysts. The work was carried out by Ph.D. students sponsored through the prize awarded by Johnson Matthey to the winner of their Rhodium Bicentenary Competition.

In 2001, Johnson Matthey held a Rhodium Matthey Rhodium Bicentenary Fellowship with Bicentenary Competition to commemorate the this group was Anthony Chianese, who went on to publication of the discovery of rhodium in 1804 by postdoctoral work with Michel Gagné at the William Hyde Wollaston, the prize being the spon- University of North Carolina at Chapel Hill, and is sorship of a Ph.D. studentship (1–3). Then Mr, now a Faculty member at Colgate University, now Professor Xingwei Li was the first to benefit Hamilton, New York, one of the leading liberal from the Bicentenary Fellowship as a graduate stu- arts universities in the U.S.A. dent with the Crabtree group in the Yale University Chemistry Department (4). He went on Design of N-Heterocyclic Carbene to do postdoctoral work with John Bercaw at the Ligands California Institute of Technology (Caltech), and is Phosphines, particularly chelating phosphines, now working in Singapore, having joined the have been key to developing the catalytic chemistry Faculty in the Chemistry Department of Nanyang of the platinum metals, but in recent years N-hete- Technical University (NTU). Singapore is a rising rocyclic carbenes (NHCs), typically derived from power in science, and NTU was ranked 48th glob- deprotonation of imidazolium salts (Equation (i)), ally by the Times Higher Education Supplement in the have shown great value as spectator ligands in cat- 2005 ranking of the world’s best universities, and alytic chemistry (5, 6). Perhaps the most striking 26th among technology universities. It used to be example is the great improvement in Grubbs’ the case that Chinese graduate students almost metathesis catalyst obtained by introducing an always stayed in the U.S.A. on graduation. NHC ligand (7). For the present, monodentate However, in a healthy development, they are NHCs are mainly used, because of the lack of good increasingly deciding to return to the Asia-Pacific methods to make chelating examples. Attempts region as the opportunities there become much using well-established synthetic routes often lead more attractive. The second holder of the Johnson to the formation of 2:1 M:L complexes, each car-

(i)

Platinum Metals Rev., 2006, 50, (4), 171–176 171 (ii)

bene centre binding to a different metal centre. nitrogen was n-butyl (8), the outcome of the reac- The problem here is that, unlike phosphines, NHC tion depended on the linker length, n. For short binding is only rarely reversible (6), so the kinetic linkers (n = 1 or 2) the product was the 2:1 com- 2:1 M:L products do not usually rearrange to the plex, but for longer linkers (n = 3 or 4) the product desired 1:1 chelates (Equation (ii)). was the chelating 1:1 complex. A steric origin was Given the rising importance of NHCs, it is not suggested for the selectivity pattern. The NHC lig- surprising that the most highly cited result from ands have a bulky axis containing the linkers and the work of the two Johnson Matthey Fellows is a the wingtip n-Bu groups, and a slim axis normal to study (8) which provided an insight into how to the bulky axis. The preferred conformation of an design chelating NHCs to give the 1:1 or 2:1 com- NHC in square planar Rh(I) complexes has the plexes, as desired. In view of the origin of the NHC out-of-plane so that the bulky N-sub- award, the bicentenary of the discovery of rhodi- stituents occupy the empty sites above and below um, it is pleasing that rhodium produced optimal the square plane. For this to be achieved in a results in this study. chelate complex, the linker must be long (Figure Reaction of the bisimidazolium salt with strong 1). The preferred conformation can be achieved in base, as in the pathway of Equation (i), is problem- the case of a short linker only by the formation of atic because the linker C–H bonds can also be a 2:1 complex, where each NHC is conformation- deprotonated; so a selective procedure was necessary. The treatment of the imidazolium salt with silver(I) oxide (Ag2O) has proved (9) most useful for preparation of Rh(I) complexes suitable for subsequent catalytic testing. This involves intermediate formation of the Ag NHC complex, followed by transmetallation to Rh, as shown in Equation Fig. 1 The preferred conformation of the NHC (left) is (iii) for a nonchelating case. only achievable in a chelate with a long linker (right), In the event that the wingtip substituent at where n is 3 or 4

(iii)

Platinum Metals Rev., 2006, 50, (4) 172 (iv)

(v)

ally independent. Other factors governing the are less often encountered in prior reports. There reactivity have since emerged beyond the linker was a surprisingly strong dependence of the activ- length; this study is still in progress. ity on the nature of the wingtip substituent. Moving to a direct metallation procedure Neopentyl, lacking a β-hydrogen, proved to be the (Equation (iv)), a 1:1 Rh(III) chelate complex was best, perhaps because the presence of a β-hydro- formed for all values of linker length, showing that gen leads to Hofmann degradation of the chelation is in principle possible for the short link- substituent group. ers, and that the configuration adopted is a delicate function of the exact situation. The oxidation of Cyclisation of Alkynes the metal in Equation (iv) does not seem to Another piece of work, carried out by Xingwei depend on the presence of air; instead hydrogen is Li in collaboration with Anthony Chianese under probably evolved to maintain redox balance. Johnson Matthey and U.S. Department of Energy In later work (10, 11), these Rh(III) complexes sponsorship, involved reactions of alkynes using and their iridium analogues have been shown to be rhodium and iridium phosphine compounds as excellent catalysts (up to 6000 turnovers h–1) for reagents or catalysts. Ironically, since this was a hydrogen transfer reduction of ketones by iso- rhodium award, only iridium gave clean chemistry propanol (Equation (v)). By avoiding free with worthwhile results. The work involved metal- hydrogen, this is sometimes considered a ‘green’ mediated reactions of alkynes involving either or environmentally more benign reduction proce- insertion into M–H bonds or attack by N and O dure (12). These catalysts proved equally nucleophiles (Equation vi). applicable to aldehydes and imines, substrates that Acetophenone undergoes cyclometallation

(vi)

Platinum Metals Rev., 2006, 50, (4) 173 (vii)

(viii)

with the common Ir(III) precursor complex retention of a deuterium label on catalyst cycling. 1 [IrH2(Me2CO)2(PPh3)2]BF4 to give the air- and Direct observation of the catalytic solution by H moisture-stable catalyst, 1, which proves (13) to be NMR spectroscopy revealed that catalyst 1 was effective for the exclusive endo-dig cyclisation of a completely converted to the amine complex 3. variety of alkynylphenols and alkynylanilines Furthermore, the order in substrate was zero, con- (Equation (vi)). The reaction usually takes 2–3 h at sistent with amine dissociation from 3 and 0.5–4 mol% catalyst loading at 20–110ºC. A num- reassociation of the substrate via the C≡C triple ber of prior catalysts (14, 15) also bring about this bond to 4 being the key step. Once a π-bound reaction, but with exo-dig or poor selectivity. alkyne has been formed, nucleophilic attack Phenols, benzoic acids and anilines are also becomes possible. Since the fragment to which the effective substrates, but the alkyne must be inter- alkyne is bound has 16 valence electrons, the nal because terminal alkynes give a stable Fischer alkyne must bind as a 2 electron donor, not a 4 carbene complex instead, in which case there is no electron donor as is more usual (16). For the much turnover. If the alkyne bears a hydroxy substituent, less basic amine, 2b, the acetone complex 1 is the a spiroketal is formed (Equation (vii)). resting state of the catalyst and the reaction is now Transition metal catalysed hydroamination and first order in substrate, consistent with binding hydroalkoxylation are both rather rare, especially only via the C≡C triple bond without unproductive with iridium, so a mechanistic study was carried binding via N. In a competition between 2a and out for the case of substrate 2a (Equation (viii)) to 2b, the more strongly binding 2a inhibited reaction obtain some understanding of the key steps. The of the other substrate. Factoring out this inhibi- hydride ligand in 1 was unaffected, as shown by tion, substrate 2b was intrinsically more reactive,

(ix)

Platinum Metals Rev., 2006, 50, (4) 174 (x)

suggesting that proton transfer from the NH respect. Development of the work will include group to the newly formed Ir–C bond may be the appending molecular recognition functionality to key step that traps the product (Equation (ix)). the NHC ligand to bring about enhanced selectiv- Alkyne coupling proved possible for terminal ity via a biomimetic strategy (19). alkynes in a closely related system (Equation (x)) Funding is often provided with the research (17). Labelling studies showed that the reaction results as the main object in view. Less often con- goes via an alkyne-to-vinylidene rearrangement. sidered is the large multiplier effect which comes No catalytic version could be devised, however, from the development of a student’s career that because the butadienyl ligand proved too tightly the funding makes possible. Over time, a student’s bound. productivity – not to mention that of subsequent Oxidation is often difficult in organometallic generations – is likely to dwarf the output from the chemistry, but in this case it proved possible to initial funding. The future benefit does not often effect an oxidative intramolecular nucleophilic redound to the credit of the grantor, however, so attack on the coordinated alkyne by a nitro group. it should be considered a signal public good. In The heterocycle in the resulting complex was this case, both Johnson Matthey Fellows have extruded from the metal by treatment with CO to joined academic institutions and may well be influ- give the free heterocycle, anthranil (18) (Equation ential in determining the future course of the field. (xi)). References Remarks 1 Platinum Metals Rev., 2001, 45, (2), 59 This work extends the catalytic chemistry of 2 Platinum Metals Rev., 2001, 45, (3), 129 rhodium and emphasises its great versatility in this 3 S. V. Ashton, Platinum Metals Rev., 2002, 46, (1), 2

(xi)

Platinum Metals Rev., 2006, 50, (4) 175 4 R. H. Crabtree, Platinum Metals Rev., 2003, 47, (2), 73 12 J. S. M. Samec, J. E. Backvall, P. G. Andersson and 5 W. A. Herrmann, C.-P. Reisinger and M. Spiegler, J. P. Brandt, Chem. Soc. Rev., 2006, 35, 237 Organomet. Chem., 1998, 557, (1), 93 13 X. W. Li, A. R. Chianese, T. Vogel and R. H. 6 A. K. de K. Lewis, S. Caddick, F. G. N. Cloke, N. C. Crabtree, Org. Lett., 2005, 7, (24), 5437 Billingham, P. B. Hitchcock and J. Leonard, J. Am. 14 B. Gabriele, G. Salerno, A. Fazio and R. Pittelli, Chem. Soc., 2003, 125, (33), 10066 Tetrahedron, 2003, 59, (33), 6251 7 T. M. Trnka and R. H. Grubbs, Acc. Chem. Res., 15 K. Hiroya, R. Jouka, M. Kameda, A. Yasuhara and 2001, 34, (1), 18 T. Sakamoto, Tetrahedron, 2001, 57, (48), 9697 8 A. R. Chianese, X. W. Li, M. C. Janzen, J. W. Faller 16 R. H. Crabtree, “The Organometallic Chemistry of and R. H. Crabtree, Organometallics, 2003, 22, (8), 1663 the Transition Metals”, 4th Edn., Wiley, New York, 2005 9 H. M. J. Wang and I. J. B. Lin, Organometallics, 1998, 17, (5), 972 17 X. W. Li, C. D. Incarvito and R. H. Crabtree, J. Am. Chem. Soc., 2003, 125, (13), 3698 10 M. Albrecht, J. R. Miecznikowski, A. Samuel, J. W. Faller and R. H. Crabtree, Organometallics, 2002, 21, 18 X. W. Li, C. D. Incarvito, T. Vogel and R. H. (17), 3596 Crabtree, Organometallics, 2005, 24, (13), 3066 11 J. R. Miecznikowski and R. H. Crabtree, Polyhedron, 19 S. Das, C. D. Incarvito, R. H. Crabtree and G. W. 2004, 23, (17), 2857 Brudvig, Science, 2006, 312, (5782), 1941

The Author Bob Crabtree, educated at New College, Oxford, U.K. with Malcolm Green, did his Ph.D. research with Joseph Chatt at Sussex and then spent four years in Paris with Hugh Felkin at the Centre National de la Recherche Scientifique (CNRS). He has been at Yale University since 1977, where he is now Professor. He has received several awards: A. P. Sloan Fellow, Dreyfus Teacher-Scholar, American Chemical Society (ACS) and Royal Society of Chemistry organometallic chemistry prizes, H. C. Brown Lecturer, Mack Award, Baylor Medal and Sabatier Lecturer. He has chaired the Inorganic Division at the ACS. He is the author of a textbook in the organometallic field, and editor-in-chief of the “Encyclopedia of Inorganic Chemistry” and “Comprehensive Organometallic Chemistry”. Early research on catalytic alkane C–H activation and functionalisation chem-

istry was followed by work on C–F bond activation, H2 complexes, M–H...H–O hydrogen bonding, and halocarbon and HF complexation. His homogeneous hydrogenation catalyst is in wide use.

Platinum Metals Rev., 2006, 50, (4) 176 DOI: 10.1595/147106706X157744 CAPoC7: The State of the Art in Automotive Pollution Control PLATINUM, PALLADIUM AND RHODIUM CATALYSTS FEATURE IN DEVELOPING TECHNOLOGIES

Reviewed by Jillian Bailie, Peter Hinde and Valérie Houel* Johnson Matthey Technology Centre, Blounts Court, Sonning Common, Reading RG4 9NH, U.K.; *E-mail: [email protected]

The Seventh International Congress on regenerating trap (CRT®) and diesel oxidation cat- Catalysis and Automotive Pollution Control alysts (DOCs). The question of how catalysis can (CAPoC7) was held from 30th August to 1st help solve the problem was raised, and it was con- September 2006, in Brussels, Belgium. The cluded that the real challenges faced are not only Congress was attended by 300 participants from technological. It is also imperative to ensure that both academia and industry. Five half-day ses- suitable and timely legislation is in place, and that sions addressed the state of the art in catalysis and both the research community and industry have automotive pollution control, and discussed tech- comprehensive development plans with efficient nical perspectives and challenges in relation to information exchange operating in order to meet present and future legislative regulations. future emission control requirements. The introductory session on European emis- The second keynote lecture, entitled ‘Highly sions legislation for mobile sources by R. Schulte Active and Potential Soot Oxidation Materials for Braucks (European Commission, Brussels, Fuel Borne Catalysts and Catalysed Soot Filters’, Belgium) set the scene by reminding the audience was delivered by Professor Michiel Makkee (Delft that the regulations are becoming more stringent. University, The Netherlands). Makkee and M. Khair (Southwest Research Institute, San coworkers investigated fuel-borne platinum group

Antonio, U.S.A.) in his talk on developments in metal (pgm)-soot interactions with NO + O2. It diesel engine technology, highlighted the fact that was found that the Pt-soot showed the highest some of the requirements for emission reductions overall activity, followed by Pt-Ce-soot and then can be met by engine development. Ce-soot. The Pt-soot is most active for the oxida-

tion of NO to NO2; however, the Pt-Ce and Ce

Particulate Control showed the most efficient use of NO2 for soot The area of particulate control was the focus oxidation. Makkee’s group also studied rare earth for the first day’s talks. Jacques Lemaire of the (RE) modified CeO2 catalysts (CeREOx with RE Association Européenne d’Experts en = La, Pr, Sm and Y) on soot filters. The results

Dépollution (AEEDA, Brussels, Belgium) pre- showed that the addition of Pr to the CeO2 gave sented the initial keynote lecture outlining the the highest soot oxidation activity under both O2 current situation. Reducing emissions of particu- and NO + O2 conditions. It was concluded that late matter is the focus of much research, whereas the increased activity results from the easier trans- the amount and effect of NO2 emissions have port of oxygen to the surface of the soot, rather been underestimated in formulating current legis- than from any mechanistic change, and that the lation. The lecture, entitled ‘Diesel Exhaust bulk storage capacity was not an important factor Controls: a New Challenge for Diesel Oxidation affecting the soot oxidation over the catalysts test-

Catalysts and Catalytic Soot Filters: Zero ed. Makkee’s group showed that NO2 has a higher

Production of NO2’ described three case studies activity for the removal of soot than does O2. of air quality in urban areas throughout Europe. Therefore the oxidation of NO already present in

The increase in NO2 levels over recent years was the exhaust stream to NO2 is the preferred attributed to the introduction of continuously method of removing the soot present.

Platinum Metals Rev., 2006, 50, (4), 177–179 177 Another of the oral presentations, delivered by result has been attributed to the ether groups. The G. Koltsakis (Aristotle University of Thessaloniki, deNOx activity is also enhanced in the presence Greece) was closely linked to Makee’s comments. of hydrogen.

Koltsakis and coworkers studied soot oxidation The focus for NH3 SCR was mainly on mech- using Pt-based catalysts, and showed that there anistic studies and modelling. The transient are two main effects of the Pt/Al2O3 during the behaviour of Fe-exchanged zeolites was modelled oxidation of model soot under a flow of NO2 + for the sorption of ammonia, the reaction

O2, within the temperature range 300–450ºC. The between NH3 and NO, and the influence of the first effect of the Pt is to promote the formation NH3/NO ratio. This work was a collaboration of atomic oxygen that can then be transported to between Umicore, Germany, and Technische the soot surface. The second effect is to reform Universität Darmstadt, Germany. The mechanism the NO2 as it passes through the carbon-catalyst and modelling of a V-based commercial catalyst layer, which increases the overall oxidation of the were addressed by C. Ciardelli and coworkers carbon bed. It was also concluded that the use of (Politecnico di Milano, Italy).

NO, instead of NO2, was not detrimental to the A certain emphasis was placed on NOx storage soot oxidation, as the Pt was efficient at oxidising catalysts, with several presentations and posters

NO to NO2. dedicated to this subject. In the first keynote lecture on deNOx catalysts, J.-D. Grunwaldt and U. NOx Control Göbel (Umicore AG & Co KG, Germany) pre- The session on NOx control covered all three sented results on thermal ageing, and strategies deNOx approaches: hydrocarbon selective cat- towards reactivation of the Pt/Ba/CeO2 and alytic reduction (HC SCR), NH3 SCR and NOx Pt/Ba/Al2O3 NOx storage/reduction catalysts. storage. In a keynote lecture in the introductory After ageing of the catalyst, Pt sintering is believed session, Professor R. Burch (Queen’s University to be responsible for the loss of low-temperature Belfast, Northern Ireland, U.K.) compared HC activity, whereas composite formation (such as

SCR and NOx storage for low-temperature BaAl2O4 and BaCeO3) due to reactions between aftertreatment, focusing on the mechanism of the support and the storage component at high both reactions. He put a strong emphasis on the temperatures is generally believed to account for necessity of testing real catalysts in real condi- the loss in high-temperature activity. The aged tions. catalysts could be reactivated by decomposition of

Hydrogen is known to improve considerably BaCeO3 in the presence of H2O, NO2 and CO2. In the deNOx activity of the Ag/Al2O3 catalyst with the second keynote lecture on NOx control, X. a range of reductants. Several posters discussed Courtois (CNRS-Université de Poitiers, France) the SCR reaction mechanism on Ag/Al2O3 in the compared the NOx storage capacity, SO2 resis- presence of H2. A variety of explanations were tance and regeneration of CeZr-based NOx considered, such as formation of Ag clusters, storage catalysts. Pt/Ba/CeZr presented the best destabilisation of nitrate or cyanide species, or storage capacity at 400ºC, according to basicity creation of oxygenated species. There was also measurement by CO2 temperature programmed noticeable interest in the performance of lean desorption (TPD), and Pt/CeZr showed the best NOx catalysts with alternative fuels (biodiesel, performance at 200ºC, mainly due to its low sen- dimethyl ether (DME)). D. Yu. Murzin (Åbo sitivity to CO2 at this temperature. For all samples, Akademi University, Finland) presented results on sulfating induced a detrimental effect on the NOx the selective catalytic reduction of NOx over storage capacity, but regeneration at 550ºC under

Ag/Al2O3 using various biodiesel compounds rich conditions led to the total recovery of catalyt- (methyl laurate and ethyl laurate) as reducing ic performance. Several other presentations and agents. They showed improved light-off tempera- posters generated an animated debate on the roles ture as compared with the equivalent alkanes. This of the different components of the model

Platinum Metals Rev., 2006, 50, (4) 178 Pt/Ba/Al2O3 catalyst: Ba intermediates (carbon- as a possible surface species. ates, nitrates, oxides, etc.) and Pt/Ba proximity. Miscellaneous Topics: Ageing, Three-Way Catalysts, Mechanisms, Poisoning and Alternative Fuels Kinetics and Modelling The final session of the meeting focused on Martyn Twigg (Johnson Matthey, U.K.) deliv- ageing and poisoning. The range of topics covered a keynote lecture covering recent trends and ered included the regeneration of sulfur-poisoned future developments on three-way catalysts Pd and Pt-Pd catalysts for methane combustion (TWCs), reminding the audience that gasoline (in relation to natural gas fuelled vehicles), and spark-ignition engines still represent the major thermal ageing and sulfur oxide effects on Pt-Pd global market for passenger car applications, diesel oxidation catalysts. The latter was the sub- despite the growing diesel markets. The review ject of the first official presentation to be given by examined the drivers for catalyst development, the BASF Group in automotive catalysis follow- such as legislation, economic and technological ing its acquisition of Engelhard, now factors, and emphasised the huge environmental incorporated as BASF Catalysts LLC. benefits obtainable through the use of TWCs in terms of reduced tailpipe emissions. The impact Poster Sessions of pgm prices as an economic driver for catalyst Over 100 posters were presented by both aca- technology in terms of formulation development demic and industrial delegates during four and lowering metal loadings was discussed. viewing sessions. Additional time was allocated in Future challenges for TWCs were outlined: fur- the main programme for open discussions in ther reducing tailpipe emissions, demanding greater depth – many of which were very lively. OBD (on-board diagnostic) requirements, new Much of the discussion and debate during these engine types and the introduction of biofuels. sessions focused on NOx-trap catalysts. The

Only one other oral presentation was given on question ‘How does BaCO3 become nitrated?’ TWCs: that of H. J. Kwon (Pohang University of was raised. It was concluded that much work Science and Technology, Korea). This concerned remains to be done to understand the mechanism. the effects of ageing on activity and selectivity on a dual monolith system; that is, a small Pd catalyst Concluding Remarks followed by a larger Pt/Rh/Ce monolith. Ageing Overall, CAPoC7 proved to be an enjoyable resulted in a loss of CO oxidation activity for a Pd and informative congress. Many high-quality precatalyst, and for a Pt/Rh/Ce catalyst, the selectiv- sentations, both oral and written, generated an ity for the NO-CO reaction was decreased, advanced level of discussion. It is apparent that resulting in lower overall NOx reduction. pgms remain at the forefront of many aspects of On a different note to that of the preceding automotive catalysis. The congress also highlight- presentations on NOx storage, Professor Mike ed the need for good communication between Bowker (Cardiff University, U.K.) gave an industry and academia to ensure the efficient account of scanning tunnelling microscopy (STM) development of future technologies. studies on model catalysts with the aim of under- The Reviewers standing the structure of the BaO surface. In this Jillian Bailie is a Senior Scientist in the Gas Phase Catalysis Group case the ‘inverse’ catalyst method was employed. at the Johnson Matthey Technology Centre (JMTC), Sonning Common, U.K. Her main interests lie in developing NOx reduction Here the BaO was deposited onto a single crystal catalysts. Pt(111) surface. Bowker showed that it was possi- Valérie Houel is a Senior Scientist in the Gas Phase Catalysis ble to store NOx from a mix of NO and O2, and Group at the JMTC. Her main interests also lie in developing NOx reduction catalysts. concluded that it was not necessary to have NO2 in the gas phase in order to store NOx. A Ba-per- Peter Hinde is a Research Scientist in the Gas Phase Catalysis Group at the JMTC. His main interests lie in developing catalysts oxide species, metastable at 300°C, was discussed for diesel oxidation.

Platinum Metals Rev., 2006, 50, (4) 179 DOI: 10.1595/147106706X152703 The Platinised Platinum Interface Under Cathodic Polarisation MORPHOLOGY CHANGES UNDER THE INFLUENCE OF TETRALKYLAMMONIUM SALTS IN SUPER-DRY SOLUTION

By Jacques Simonet Equipe MaCSE, UMR 6226, Université de Rennes 1, Campus de Beaulieu, 35042 Rennes Cedex, France; E-mail: [email protected]

Under the use of super-dry dimethylformamide containing tetraalkylammonium salts (TAAX

with X = Cl, Br, I, ClO, BF4, etc.) platinised platinum layers may exhibit a reversible charging process that occurs at quite negative potentials (more negative than –2.2 V vs. saturated calomel electrode (SCE)). The mode of reactivity of the electrolyte and the reversibility of the platinum charging of platinised layers (whatever the type of conducting substrate – gold and glassy carbon can also be used successfully) are discussed in terms of the nature of the salt. After cathodic charge and oxidation by air of samples removed from the cell, a huge change of morphology of the original platinised layer was observed. During repeated reduction/oxidation stages, the original amorphous platinised layer was progressively transformed, with a noticeable swelling of the original layer. This transformation, based essentially on cathodic swelling due to the peculiar reactivity of platinum in the presence of bulky tetraalkylammonium salts, is the precondition for a new kind of platinum interface.

Platinum is now considered one of the most To circumvent the inconvenience of the low practical materials for achieving electrochemical hydrogen evolution overpotential at platinum, the conversions (1, 2). In particular it can easily be use of solvents of low proton availability has been cleaned to a polished surface, and employed in developed. This may extend the cathodic domain most electrocatalytic transformations, especially by about 1 V. Given the desirability of reaching where adatoms deposited at the surface may extremely negative potentials (e.g. –3 V vs. SCE, induce a specific activity (3–13). Applications of known to be easily obtained in organic solvents in the perfectly defined interfaces obtainable with the presence of tetraalkylammonium salts if a con- platinum monocrystals are also noteworthy (14, ventional mercury cathode is used), the application 15). In the field of anodic processes, platinum is of “super-dry” media was developed (21, 22). known (16) to be electrochemically stable even at Significantly dry media have been obtained by very positive potentials. However, when platinum maintaining the solvent-electrolyte mixture over is employed as the cathode material, the situation is drying reagents such as strongly activated alumina. more complex (17): platinum indeed possesses a Extremely low moisture levels (often less than 50 very low overpotential towards proton reduction, ppm of water) have been attained. Unexpectedly, and this phenomenon seriously limits the accessi- however, the use of platinum cathodes in contact ble domain for achieving conversions of organic with a super-dry solvent-electrolyte mixture molecules when rather negative potentials are brought to light (23–27) a form of ion insertion of required. In general, beyond –1 V vs. SCE (saturat- (or reactivity with) the electrolyte (often an alkali ed calomel electrode), hydrogen is frequently metal or tetraalkylammonium salt) at the platinum- evolved (18–20). Thus even in organic solvents the solution interface. Thus, in the presence of an level of moisture strongly limits the cathodic electrolyte MX under conditions which effectively domain. prevent hydrogen evolution at the platinum sur-

Platinum Metals Rev., 2006, 50, (4), 180–193 180 face, the formation of a thin “ionometallic” layer electrolyte cations, and progressive swelling evi- – + of a general structure [Ptn , M , MX] could be dently associated with the stoichiometry of demonstrated. Here n depends on the saturation insertion into platinum. level of the platinum layer and therefore on its The present paper aims to describe in terms of maximum degree of reduction. In general, it was morphologic changes the cathodic behaviour of found that n = 2 for N,N-dimethylformamide platinised platinum, which has been found to be (DMF) containing dissolved alkali metal iodides or much more reactive towards electrolytes than + – bulky tetraalkylammonium halides (NR4 X ), smooth platinum. This study focuses especially on according to Equation (i): the effect of tetraalkylammonium salts (TAAX) on the electrochemical reduction of platinum. An – – + nPt + e + MX → [Ptn , M , MX] (i) explanation of the effect of the TAA+ cation size In some respects, such a cathodic reaction of plat- on structural changes to the layer is proposed. In inum with electrolytes – and the subsequent particular the behaviour of tetramethylammonium formation of an ionometallic layer – strongly salts (TMAX) appeared anomalous. This behav- resembles the formation of Zintl phases (28–30) iour provides information on the interfacial activity via the reaction of an electropositive alkali metal of the TMA+ ion, considered as the smallest non- with most of metalloids (such as Pb, Si or Ge). The acidic ammonium cation. Moreover, TMA+ cannot classical synthesis of Zintl phases generally form an ylide through the Hoffmann degradation involves heating a mixture of these reagents in a (38, 39). Also at non-reactive cathodes, the TMA+ closed tantalum or niobium vessel. Another ion has been reported as by far the most readily reported method is the reduction of a salt of a electroactive (39), meaning that the electrochemi- post-transition metal in the presence of sodium cal reactivity of TMA+ could occur at a potential + metal in liquid ammonia (28, 29). Electrochemical much less negative than those of other NR4 ions, methods may also be used (30–35): for example, especially within a potential range where there is cathodically polarised lead (or any other post-tran- no appreciable reduction of residual water (even sition metal) immersed in a solution of a when present in significant amounts (> 500 ppm)). non-electroactive cation (such as K+) may produce a reduced polyanionic form as shown in Equation Experimental Procedure (ii): Salts and Solvent

+ – 4– + In most of the experiments, the concentration 4K + 4e + 9Pb → [Pb9 , 4K ] (ii) of TAAX (X = I, Br, Cl, BF4, ClO4) was 0.1 M. All (Pb is the cathode material.) salts studied were obtained from Fluka; their puri- Similar phases have already been described (34, ty was at least 99%, and all were employed without 35) with polarised mercury in the presence of any additional purification after being thoroughly tetraalkylammonium ions. However, the implica- dried under vacuum at 60ºC (except for TAAClO4 tion of the choice of anion in the electrolyte was which, for reasons of safety, was used as received). never considered. Anhydrous DMF was obtained from SDS, France; Returning to platinum, the analogous electro- its water content was claimed to be 0.005%. chemical building of a complex layer owing to the Nevertheless, DMF was maintained continuously involvement of ions concomitantly with the asso- over alumina activated at 340ºC in vacuo for at least ciated electron motion raises a number of issues four hours before solutions were prepared. All (36, 37) about this new kind of interface: its stabil- experiments were performed under an argon ity, its conductivity, the reversibility of electron atmosphere, and the absence of dioxygen in the storage, the maximum attainable thickness as well solutions was carefully checked. The continuous as its reducing power. Additional factors to be use of alumina (acidic, Brockmann I, standard taken into account include progressive distortion grade from Aldrich) in solutions and in situ in the of the platinum lattice induced by the motion of electrochemical cell during the experiments kept

Platinum Metals Rev., 2006, 50, (4) 181 the moisture levels no higher than 50 ppm. possible at its interface chemical reactions catalysed by strongly basic media.) Electrochemistry All potentials are given with respect to the sat- Electrode Plating urated calomel electrode (SCE), although Coulometric experiments were carried out with measurements were obtained with a Ag⎪AgI⎪0.1 platinised platinum electrodes prepared by deposi- M TBAI system in DMF; this electrode, which is tion of the metal from an aqueous solution of 10 g –1 particularly suitable for scrupulously dry solutions, l H2PtCl6 (Aldrich) in 0.1 M HCl onto a metal has a potential of –0.52 V vs. SCE at 25ºC. For disk (effective area: 0.78 mm2). Gold was plated voltammetry, a three-electrode cell was used with- under the same conditions. Metal was deposited at out a separator. The counter electrode was a glassy a constant current density (30 mA cm–2). carbon or graphite rod. Platinum working elec- Morphology changes of the platinum layer during trodes had a diameter of 1 mm. The working charging/discharging cycles were followed by electrodes were polished with Norton polishing SEM analysis after rinsing each sample with alco- papers (grades 02 and 03) or DP Paste M made hol and acetone, and sonication to eliminate from monocrystalline diamonds (with particle size alumina particles. appropriate to the finest polishing). After polishing, the working electrode was sonicated for five Results minutes, rinsed twice with alcohol and acetone, Voltammetry for Tetramethylammonium and then dried at about 60ºC. Chronocoulometric Salts and ECQM (electrochemical quartz microbalance Figure 1 (curve (b)) summarises the voltammet- measurement) procedures have been fully ric response of smooth platinum under standard described in a recent paper (40). (Here the elec- aprotic conditions. In 0.1 M TMAClO4 (as with trode acts specifically as a base provider, making other TMA+ salts), a diffusion step (IC) with a

Fig. 1 Voltammetric responses of platinum electrodes in 0.1 M TMAClO4 in DMF. Super-dry conditions. Scan rate: 0.1 V s–1. Effective electrode area: 0.78 mm2. Potentials are referred to aqueous SCE: (a) Response of a platinised platinum electrode (two first scans) with a pause of 20 s at –2.8 V. Average thickness of the platinum deposit: 0.25 μm; (b) For comparison, the response of a smooth platinum electrode under the same conditions

Platinum Metals Rev., 2006, 50, (4) 182 half-peak potential of about –2.2 V vs. SCE is cases of TMAI, TMAClO4 and TMABF4 (Figures observed in the course of the first scan. At more 1 and 2). For example, platinised platinum in 0.1 M negative potentials (beyond about –2.5 V vs. SCE), TMAClO4 exhibits a pair of broad main steps (IIC the cathodic limit is reached. This limit is attribut- and IA) whose half-peak potentials are E0.5pc = able to electrolyte decomposition. Both the –2.0 V and E0.5pa = –1.7 V vs. SCE, respectively. At potential and the current for the main cathodic scan rates greater than 50 mV s–1, the relative areas step (IC) vary with the mode of polishing of the of these two steps are approximately equal. At platinum and the moisture level of the electrolyte potentials more negative than –2.3 V vs. SCE, solution. If the solution contains much more than another cathodic step may arise. Its presence 200 ppm water, step IC is progressively shifted apparently depends on the history of the electrode towards less negative potentials and becomes total- surface and on the amount of platinum galvanos- ly irreversible. Higher water content leads to a tatically deposited onto the substrate. Limiting

“cathodic wall” attributable to the water reduction. currents for step IIC (iII) do not depend directly, at However, the current at step IC depends on the a given sweep rate, on the amount of electrode- mode of polishing of the platinum electrode. posited platinum. The platinising procedure shifts Given particularly careful polishing (always under the main reduction step towards much less nega- super-dry conditions), the magnitude of step IC tive potentials, and the rate of the charging process may decrease, and it may even disappear. The (although not measured here) appears significantly nature of the surface, grain boundaries, as well as greater at a platinised platinum surface. The shapes the possible presence of fractals and activated sites of these steps and their current values would sug- would be expected to favour an interfacial charge- gest that only the external part of the deposit – discharge process. then in contact with the liquid phase – reacts with If the platinum interface described above is the components of the electrolyte. With longer now platinised galvanostatically so as to produce a electrolysis times, a sudden decay of the cathodic much larger active surface, the shape of the current is observed at very negative potentials voltammetric curves, as shown in Figure 1(a), (Figures 1 and 2). This may be induced by a self- changes dramatically. For a relatively thick film of inhibiting phenomenon. This inhibition is electrodeposited platinum (with, for example, an attributable to the weak electronic conductivity of average thickness significantly greater than 0.1 the ionometallic layer formed during the reduction μm), the use of a super-dry solvent-electrolyte process. Conceivably, compacting associated with enables a quasi-reversible step (IIC), at least in the a structural change in the platinised layer further

Fig. 2 Electrochemical behaviour of platinised platinum in 0.1 M TMABF4 in DMF. Super-dry conditions. Effective electrode area: 0.78 mm2. Average thickness of the galvanostatic platinum deposit: 0.3 μm. Scan rate: 0.1 V s–1. Two first scans. Reference electrode: aqueous SCE

Platinum Metals Rev., 2006, 50, (4) 183 restricts the motion of species participating in this associated with the thinness of the reduced film at charging phenomenon. the interface. Pauses were introduced into forward voltammetric scans on both smooth platinum surfaces Voltammetry for Other and substrates covered by very thin, strongly het- Tetraalkylammonium Salts erogeneous platings. In these cases, at very Voltammetric data obtained with bulky TAA+ negative potentials (as shown in Figure 1(a)), the salts (from tetra-n-butyl- to tetra-n-octylammoni- following scans towards negative potentials may um salts) indicated much less reversibility than that be significantly altered. The total cathodic current already described for TMAX salts. The cathodic is then strongly increased, and step IC completely step IIIC (Figure 4) attributable to the reduction disappears. Recurrent scanning and/or pauses in of platinum in the presence of the salt is shifted to scanning would be expected to contribute to more negative potentials. The corresponding changes in the nature of the platinum surface. anodic step IIIA is shifted in the anodic direction. Thus the presence of only the pair of steps IIC Half-peak potentials are –2.4 V and –1.5 V vs. SCE and IA would suggest that smooth platinum zones respectively. The current of the anodic step is rel- at the electrode surface have disappeared under atively small. At significantly more positive cathodic treatment. This could correlate with the potentials, two reversible steps H1 and H2 may observation that the presence of steps IC and IIC appear, even under super-dry conditions. These together depends on the conditions prevailing dur- are readily assigned to the reversible anodic oxida- ing the plating, and on the amount of electricity tion of hydrogen formed at very negative passed. Step IIC is observed alone in some cases; potentials at the polycrystalline platinum surface this could be attributable to changes in the plating during the forward scan. The steps could not be homogeneity. induced merely by residual water reduction For timescales much longer than those current- beyond –2.8 V. These steps were not observed ly used for voltammetric experiments, the charging with TMAX salts. Their presence tended to sup- processes remained reversible, but generally port the concept of a “probase” cathode (40) showed current efficiencies lower than 60%. previously proposed for tetramethylammonium Figure 3 shows the two distinct branches in the salts. On the other hand, it would be expected that chronocoulometric response of a platinised plat- large TAA+ ions under the conditions given here inum microelectrode in a 0.1 M solution of would produce hydrogen evolution, leading to

TMAClO4 in DMF. The very steep slope at the reductive degradation of the salt. This may be beginning of the discharge process is notable; it is regarded as a kind of cathodic Hoffmann reaction,

Fig. 3 Chronocoulometric curve for a platinised platinum electrode of area 0.78 mm2 in 0.1 M TMAClO4 in DMF. Superdry conditions. Plating thickness: 0.2 μm. Charge at –2.3 V vs. SCE for 10 s followed by discharge at –0.5 V until nil current

Platinum Metals Rev., 2006, 50, (4) 184 Fig. 4 Repeated voltammetric scans at a platinised platinum electrode of effective area 0.78 2 mm in 0.1 M TBAClO4 in DMF. Super-dry conditions. Average thickness of the platinum deposit: 0.4 μm. Scan rate: 0.5 V s–1. Potentials are with respect to aqueous SCE

in which the free electron plays the role of a base was taken into account. With tetra-n-butyl-, tetra- as shown in Equation (iii): n-hexyl- and tetra-n-octylammonium halides, the + – stoichiometry was found to correspond to one R3N CH2–CH2R′ + e electron per two atoms of platinum. This suggests → R3N + CH2=CHR′ + ½H2 (iii) a formula for the complex of the following form In a parallel process, the expected two-electron (Equation (iv)): + – cathodic cleavage of TAA (forming the anion R ) – + [Pt2 , TAA , TAAX] (iv) may trigger the classical Hoffmann degradation (protonation of the anion R– by the salt) – a partial A large series of TMAX salts was tested (with X – – – – – explanation for the poor reversibility of the charg- = ClO4 , BF4 , I , Br and Cl ), as well as the corre- ing process. In overall terms, this type of sponding sulfate salt (Figure 5). It was confirmed degradation leads to a broadly similar product dis- that bare platinum as such does not rapidly accu- tribution, with the formation of a tertiary amine mulate a high charge within the timescale necessary and an alkene. Only the hydrogen evolution (as for such processes (e.g. a few minutes). All coulo- proposed in Equation (iii)) appears specific to the metric experiments were conducted in very behaviour of TAA+ at the platinum interface. carefully dried DMF-electrolyte solutions. Complete dryness and neutrality of the platinised Microcoulometry platinum electrode were ensured by rinsing with Coulometric measurements were carried out at alcohol and/or DMF with the addition of platinised interfaces in super-dry DMF-TAAX Me4NOH, followed by double rinsing with ace- solutions. The conditions were close to those tone and drying. The gradient of the plot in Figure shown in Figure 3 (i.e. reduction beyond –2.4 V 5 reveals that four platinum atoms (abscissa) are and oxidation at about –0.8 V), having reached sat- correlated with the charge of one electron (ordi- uration of the deposited layer. Only the amount of nate), which supports the conclusion that the electricity recovered during the oxidation process stoichiometry of the phase, after saturation within

Platinum Metals Rev., 2006, 50, (4) 185 surface modifications and draw conclusions, the following parameters were considered: – the initial thickness of the platinum deposit; – the applied potential for the reduction; – the theoretical amount of electricity per unit area required to charge (partially or totally) the platinised layer. After cathodic polarisation of the platinised samples, two alternative modes of oxidation were used and compared. The sample was either simply exposed to air after the electrolysis, or the sample was kept in the cell at a potential generally between –0.5 and +0.3 V vs. SCE until the current decayed completely. The present study describes only morphology changes caused by contact with air at the completion of the reduction process. Surface Fig. 5 Microcoulometry of platinised platinum (area: modifications were generally controlled so as to 0.8 mm2) for different plating thicknesses. Charging at occur without any noticeable mass change. –2.2 V vs. SCE (reduction for 100 s, allowing full saturation of the deposit) and then oxidation at 0 V until nil However, when thick deposits are over-reduced current. Qd is the quantity of electricity recovered during for a long time, charging of the platinum layer discharge. Qf/4 is one quarter of the quantity of electrici- could possibly lead to a local collapse of the origi- ty required to convert PtIV to Pt0. Five TMAX salts were tested at 0.1 M concentration in DMF: + (X = Cl), • (X nal plating. Figure 6 shows the original appearance = ClO4), Δ (X = Br), { (X = BF4), (X = I) of a platinised platinum sample before any cathodic treatment in the presence of salts. the timescale of charging, can be written as follows A few results have been selected as being the (Equation (v)): most representative from a large number of exper-

– + iments demonstrating the huge modification of [Pt4 , TMA , (TMAX) ] (v) m platinum surfaces by TAA+ salts under cathodic Analysis of platinum microdeposits onto the gold polarisation. substrate (via the EQCM technique) confirmed that m = 1. Modification of Platinum Films In the absence of a visible degradation of the Morphology Changes to Large Electrodes film (which was easily checked with a magnifying on Macroelectrolysis glass and confirmed by the absence of mass A large number of potentiostatic electrolyses were performed in two-compartment cells on platinised sheets of commercial platinum in the presence of tetramethylammonium salts

(TMAClO4, TMABF4 and TMAI), tetra-n-butyl ammonium iodide (TBAI), tetra-n-hexylammon- ium bromide (ThexABr) and tetra-n-octylammonium bromide (ToctABr). Experimental conditions were as described for the voltammetric and coulometric studies. The main point of these experiments was to use super-dry solvent-elec- Fig. 6 SEM image of a platinised layer galvanostatically deposited onto smooth platinum from H2PtCl6 solution in trolyte; the addition of activated alumina to the cell 0.1 M HCl . Current density: 5 mA cm–2. Total quantity of appeared crucial to this. In order to compare the electricity: 1.6 C cm–2. Average thickness of plating: 0.4 μm

Platinum Metals Rev., 2006, 50, (4) 186 changes), the amount of electrodeposited platinum touching platinum spheroids, with average diame- could be related to the amount of electricity neces- ter depending on the thickness of the initial layer. sary to achieve the deposit. For example, by using The average diameter is estimated at about 0.5 μm the initial platinised layer shown in Figure 6, the for the structure shown in Figure 7(a). Apart from original deposit was made with a quantity of elec- the zones of spheroids, large flat zones were attrib- tricity of 1.6 C cm–2 (total reduction of PtIV), which uted to the original smooth platinum substrate. corresponds approximately to an average thickness Similar morphologies were observed with pla- of the deposit of δ = 0.4 μm. The reduction of the tinised films, in particular with TBAI (See Figures deposit at –2 V vs. SCE in the presence of 7(b) and 7(c)) and ToctABr (Figure 7(d)).

TMAClO4 was performed until an amount of elec- However, with thicker platinised films, and with tricity of 0.8 C cm–2 was passed. This theoretically large amounts of electricity involved in the reduc- corresponds to twice the amount of electricity tion process, the layer swells to different extents. required for total saturation of the layer, given that (The layer swells by transformation into spheres the charging yield would be about 50% platinum. during the cathodic reaction of platinum with The stoichiometry is given by Equation (v) with bulky salts, as indicated by the stoichiometry of the m = 1. Cathodic polarisation was followed by oxi- ionometallic complexes.) dation, simply by contact of the samples with air The case of some TMA+ salts is, however, more during rinsing. The samples were then thoroughly complex. These afford relatively limited swelling in sonicated. This electrochemical treatment resulted terms of the stoichiometry given by Equation (v). in a complex coverage consisting of more or less Primary spheres are covered by smaller spheroids,

Fig. 7 Reduction of thin platinised film in the presence of TAAX salts in DMF under super-dry conditions. After reduction, samples were rinsed and sonicated in contact with air: (a) Reduction in 0.1 M TMAClO4 of film of mean thickness 0.2 μm) at –2.5 V. Total amount of electricity: 0.8 C cm–2. Oxidation by air; (b) and (c) Reduction in 0.1 M TBAI of a platinum deposit of 0.22 mg cm–2 onto platinum substrate. Electrolysis at –2.5 V vs. SCE. Quantity of electricity: 1.7 C cm–2. No mass loss after oxidation by air, sonication and rinsing; (d) Reduction in 0.1 M tetra-n-octylammonium bromide. Deposit of platinum: 0.30 mg cm–2. Electrolysis at –2.5 V. Quantity of electricity passed: 1 C cm–2. No mass loss

Platinum Metals Rev., 2006, 50, (4) 187 giving the overall morphology the appearance of a platinum substrate (Figure 7(c)). The shrinkage of layer of blackberry-like structures. The uniform cathodically generated spheres under oxidation by volume of all the spheres is also striking. (See air, due to the expulsion of ions, is strongly expect- Figure 8 for the case of TMAI.) ed to yield almost empty structures. By contrast, The swelling may sometimes become chaotic, the anodic oxidation of spheroid layers leads to particularly where large amounts of electricity are profound changes, until a quasi-flattening of the involved. Large, regularly swollen cauliflower-like platinum surface occurs (43) through the bursting structures then arise (Figure 8). These are reminis- of the spheres. cent of the structures observed during the anodic polymerisation of pyrrole or thiophene (41, 42), in Discussion which the polymers are rendered electrically con- The use of tetraalkylammonium salts as elec- ductive by the progressive insertion of anions as trolytes in aprotic (super-dry) DMF can “dopants” inside the polymer matrix. In the pre- undoubtedly lead to the reversible charging of pla- sent work, cauliflower and macrospherical tinised layers electrochemically deposited onto structures were found, principally with thick pla- substrates such as platinum, glassy carbon or gold. tinised layers (Figures 9(a), 9(b) and 9(c)). During The finely divided structure of platinised deposits the oxidation of the platinised layer, movement of apparently enhances the cathodic reactivity of plat- the salt out of the platinum causes a shrinkage, as inum. Under these conditions, tetraalkyl- clearly evidenced by the formation of large cracks ammonium salts (R4NX with R bulkier than Me) (see Figure 9(d)) and large zones of uncovered react cathodically with the platinum surface, but at potentials significantly more negative than those observed with R = Me. At such potentials, significant reduction of residual water may occur, and the charging process observed in conjunction with hydrogen evolution is always poorly reversible in terms of charge recovery. By contrast, cyclic voltammetric experiments carried out at platinised layers in the presence of cathodically more reactive TMA+ salts provide evidence for a quasi-reversible charge process. Thus, under super-dry conditions and for rather thick platinum deposits, the quantity of electricity specifically involved in the charging process was found to be an increasing function of the scan rate. Electrochemical charging is definitely first associated with the external part of the platinised layer. However, with sufficiently high currents and long electrolysis times, the platinum layer may become saturated with the electrolyte salt. The charge recovered during the re-oxidation process reaches a limit, and becomes proportional to the amount of deposited platinum. Thus a simple calculation Fig. 8 Reduction (E = –2.5 V vs. SCE) of platinised performed for several TMA+ salts demonstrates platinum in 0.1 M TMAI. Thickness of platinum deposit: 0.2 μm. Moderate quantity of charge corresponding to that, at least with thin platinum films, the charging half that theoretically required to saturate the platinised process involves four atoms of platinum for each film. No mass loss. Two images of the layer at different magnifications; note the appearance of “cauliflower- transferred electron. like”structures All the ionometallic complexes obtained under

Platinum Metals Rev., 2006, 50, (4) 188 Fig. 9 Formation of more chaotic structures of cauliflower-like morphology. (a) Reduction of a platinised layer of thickness 0.2 μm in 0.1 TMAClO4 at –2.5 V under weak current density, with a moderate total quantity of electricity; (b) Reduction of a platinised layer (0.30 mg cm–2) in 0.1 M tetra-n-octylammonium bromide with a large over-reduction of the layer. Part of the deposit then collapses; (c) Reduction of a platinised film of thickness 2 μm in 0.1 M TBABF4. A large quantity of electricity passed. Evidence for strongly swollen structures; (d) Same conditions as image (c). During oxidation by air, the film shrinks strongly and forms deep cracks

+ similar conditions with bulky NR4 salts and alkali depending on such experimental parameters as the metal iodides exhibit reducing properties. They can thickness of the platinised layer and the amount of therefore produce anion-radicals from π-acceptors electricity involved in the reduction process. The such as fluorenone and 1,4-dinitrobenzene. appearance of spheres of uniform size, as well as Similarly, the reducing power of the layer was huge changes to the morphology of the original recently used to cleave diazonium cations, making platinum layer are highly intriguing. Does the for- possible the chemical functionalisation of the plat- mation of spheres or swollen structures occur inum surface (44). during the reduction process or later when the sur- With TMAX, as stated above, the structure of face is oxidised by contact with air? Recent in situ the platinum layer at the saturation stage is quite electrochemical scanning tunnelling microscopy different from those previously found (37) with (EC-STM) experiments in this laboratory (45) + bulky NR4 (such as tetra-n-butyl-, tetra-n-hexyl-, revealed, particularly in the case of tetra-n-buty- and tetra-n-octylammonium salts). This difference lammonium iodide, that the reversible swelling of seems to be due to the smaller size of the TMA+ platinum monocrystals can be followed using cation producing a change in the spatial structure cyclic voltammetry over relatively short durations. of the ionometallic complex. After cathodic polar- The swelling of platinum was found to be directly isation of platinum and air exposure of the related to the cathodic reaction of surface platinum + interface obtained in the presence of NR4 cations, atoms with the electrolyte. The complete restora- SEM images most frequently revealed either cauli- tion of the surface at the end of the reverse scan flower-like structures or layers of spheres, was highly effective, at least for short reaction

Platinum Metals Rev., 2006, 50, (4) 189 times and limited amounts of electricity. This find- The example of TMAI is then taken as representa- ing strongly supports the conclusion that the tive. On the basis of literature values of ionic radii platinum reactivity is fully reversible, at least in the for the phase constituents (43, 46), i.e., Pt = 0.80 case of tetra-n-butylammonium salts. Over- Å, I– = 2.2 Å, and TMA+ = 3.01 Å, it is possible to reduced ionometallic layers in the presence of assess the degree of swelling for closely-adjacent TMA+ (up to one TMA+ ion per platinum atom) ions. This calculation predicts a volume increase of could be reached in certain cases. Over-reduction approximately 30 times – which is huge. Similar – of platings could cause spectacular swelling and swelling factors can be estimated for X = ClO4 – deformation of platinum surfaces. and BF4 . By contrast, the swelling at platinum Returning to the quasi-uniform size of the without a specific insertion of the salt would be spheres (as shown in Figures 7 (a)–(d)), it may be limited to 14 times – again in the case of TMAI, on proposed that these structures grow under ther- attaining complete reduction of the platinum layer. modynamic conditions. (This assumption is Thus the deposition of a few platinum atoms onto supported by the quasi-reversibility of the electro- a conducting surface would lead to the progressive chemical process). The total conformational formation of a sphere-like volume, until attain- energy per sphere, Esp, may be split into two ment of the final stoichiometry based on the terms, relating to the bulk (ρV) and surface (ρS) availability of strongly reactive platinum atoms. energies respectively as shown in Equation (vi): Although the mode of swelling is unclear so far,

3 2 the rate of growth of such spheres would be deter- Esp = (4/3)πR ρV – 4πR ρS (vi) mined both by the number of starting points where R is the radius of the spheres. (perhaps randomly distributed on the surface) and At the equilibrium (Equation (vii)): the diffusion of ions. The mobility of the spheres

2 on the platinum substrate (under the condition (dE/dR)eq = 4πR ρV – 8πRρS (vii) that an electric contact promotes their growth)

The equilibrium radius, Req, of the spheres is given should probably also be taken into account. Since by Equation (viii): the volume of the spheres is not directly dependent on the amount of platinum deposited, one Req = 2ρS/ρV (viii) can foresee the existence of zones weakly covered Thus the radii of the spheres depend only on by a small number of spheres (see, for example, energy factors specific to the experimental condi- Figures 7(c) and 7(d)). tions (such as the nature of the salt used, its It would be expected that the huge swelling concentration, its level of dissociation, as well as described above starts from sites located at the the number of available platinum atoms). The for- interface between the platinised layer and the elec- mation of contiguous spheres of very similar trolyte solution, causing substantial volume volume suggests that the ionometallic layer turns changes and, in particular, the formation of out to be very mobile on the conducting substrate. spheres. A tentative approach is depicted in Therefore the model of growth of swollen struc- Scheme I. The charging process might involve a tures from randomly distributed activated centres front of charge moving progressively from the onto the substrate surface is probably incorrect. external interface until it reaches the much less A range of experiments were performed to reactive platinum substrate. The formation of visualise clearly the occurrence of the platinum spheres or more complex and bulky structures by swelling. The degree of swelling may be approxi- extrusion due to the swelling (cauliflower-like fea- mately estimated by adopting the following tures for thicker platinum deposits, Figure 9) may formula for the charged phase obtained with explain some of the alterations to the electrode TMAX salts (Equation (ix)): surfaces. If the ionometallic layer is oxidised simply by contact with air (presumably due to a slow – + [Pt4 , TMA , TMAX] (ix) electron transfer at the boundary of the spheres),

Platinum Metals Rev., 2006, 50, (4) 190 Scheme I

Schematic representation of the morphology change of a platinised platinum interface (shown in green) during the charging process by TMAX followed by air oxidation. The ionometallic layer (the fully reduced form of the platinised layer) is shown in red. The oxidation by dioxygen would lead to smaller spongy spheres, of which the shrinking factor illustrated here is arbitrary then the interface would be expected to keep Conclusions roughly its original structure. The oxidation first Under super-dry conditions, platinised plat- forms a platinum shell, and continues by the dif- inum layers exhibit a high cathodic reactivity fusion of dioxygen through this shell. The action towards the electrolyte. In particular, with TMA+ of dioxygen would tend to preserve the general salts, a fully reversible ion insertion has been features of the layer, including cracks and smaller demonstrated. A stoichiometry for this insertion spheres (often not immediately adjacent) owing to process has been proposed for the condition that shrinkage. Scheme II depicts swelling processes the platinised layer reaches is full reactivity. on a much larger scale, which would lead to cauli- Coulometric results for a large number of TAAX flower-like structures in the case of thicker salts strongly support the conclusion that two or platinum layers and/or over-reduction of four platinum atoms are associated with the trans- deposits. fer of one electron to produce thin modified

Scheme II

Schematic representation for the swelling of the platinised platinum surface. Note the possible transformation of (c) for a moderate swelling into (d), obtained with larger amounts of electricity injected into the platinum layer (termed “cauliflower-like” structures in the text). Arrows indicate the supposed direction of the swelling

Platinum Metals Rev., 2006, 50, (4) 191 (ionometallic) layers (up to 1 μm in thickness). In the presence of a source of electrons and pro- Under appropriate conditions, the salt-infused tons: ionometallic layer shows a huge swelling, which • CH3 → CH4 (xi) depends on the applied potential, the nature of the interface and the mode of the discharging process. Thus controlling the roughness of the platinum With the aid of SEM techniques, it has been found interface by the various treatments presented that charging and discharging of platinum layers are here might be used to impart particular proper- correlated with their swelling and shrinkage. ties to the resulting surface – for instance, by Dramatic structural changes of the platinised plat- achieving a clean platinum surface in the absence inum layer have been analysed and explained in of dioxygen, for catalytic and electrocatalytic terms of both the existence of a reversible charg- applications. ing-discharging process and the specific nature of the electrolytes employed. Finally, analysis of reduction processes revealed that side reactions may occur, such as the slow decomposition of the Acknowledgments ionometallic layer obtained at quite negative poten- The author is grateful to the Centre de tials. For example, methane may be evolved with Microscopie Electronique à Balayage et TMAX salts as shown in Equations (x) and (xi): MicroAnalyse (Dr Le Lannic, Université de Rennes) for its efficient help, and to Professor C. [Pt – , TMA+, TMAX] n Amatore (ENS, Université de Paris VI) for fruitful • → nPt + (CH3)3N + CH3 + TMAX (x) technical discussions.

References 1 A. J. Bard and L. R. Faukner, “Electrochemical 13 K. B. Kokoh, J.-M. Léger, B. Beden, H. Huser and Methods: Fundamentals and Applications”, J. Wiley C. Lamy, Electrochim. Acta, 1992, 37, (11), 1909 and Sons, New York, 1980 14 Y.-Y. Yang and S.-G. Sun, J. Phys. Chem. B., 2002, 2 H. Lund, in “Organic Electrochemistry”, 4th Edn., 106, (48), 12499 eds. H. Lund and O. Hammerich, Marcel Dekker, 15 J. Clavilier, A. Fernandez-Vega, J. M. Feliu and A. New York, 2001, p. 243 Aldaz, J. Electroanal. Chem., 1989, 261, (1), 113 3 R. Albalat, J. Claret, E. Gómez, C. Muller, M. Sarret 16 H. J. Schäfer, ‘Organic Electrochemistry’, in and J. M. Feliu, J. Chem. Soc., Faraday Trans., 1990, 86, “Encyclopedia of Electrochemistry”, Volume 8, eds. (10), 1845 A. J. Bard and M. Stratmann, Wiley-VCH, 4 L. D Burke and K. J. O’Dwyer, Electrochim. Acta, Weinheim, 2004 1990, 35, (11–12), 1821 17 G. W. Morrow, in “Organic Electrochemistry”, 4th 5 M. Shibata and S. Motoo, Hyomen Gijutsu, 1989, 40, Edn., eds. H. Lund and O. Hammerich, Marcel (10), 78 Dekker, New York, 2001, p. 589 6 V. N. Korshunov, V. A. Safonov and L. N. 18 G. P. Klein, K. J. Vetter and J. W. Schultze, Z. Phys. Vykhodtseva, Russ. J. Electrochem., 2005, 41, (9), 911 Chem., 1976, 99, (1–3), 1 7 P. Ocon and J. Gonzalez Valesco, J. Appl. 19 B. E. Conway and G. Jerkiewicz, Electrochim. Acta, Electrochem., 1988, 18, (1), 43 2000, 45, (25–26), 4075 8 Lj. V. Minevski and R. R Adzic, J. Appl. Electrochem., 20 J. Fournier, L. Brossard, J. Y. Tilquin, R. Côté, J.-P. 1988, 18, (2), 240 Dodelet, D. Guay and H. J. Ménard, J. Electrochem. 9 R. R. Adzic, W. E. O’Grady and S. Srinivasan, J. Soc., 1996, 143, (3), 919 Electrochem. Soc., 1981, 128, (9), 1913 21 O. Hammerich and V. D. Parker, Electrochim. Acta, 10 B. F. Gianetti, C. M. V. B. Almeida, S. H. Bonilla, M. 1973, 18, (8), 537 O. A. Mengod and R. Raboczkay, Phys. Chem., 2003, 22 J. Heinze, Angew. Chem., 1984, 96, (11), 823 217, (10), 35 23 J. Simonet, E. Labaume and J. Rault-Berthelot, 11 H. A. Lyazidi, M. Moukhedena, M. Mestre and J. F. Electrochem. Commun., 1999, 1, (6), 252 Fauvarque, Bull. Soc. Chim. Fr., 1995, 132, (10), 1039 24 C. Cougnon and J. Tanguy, unpublished observa- 12 J. M. Felui, E. Herrero and M. J. Llorca, Book of tions Abstracts, 210th ACS National Meeting, Chicago, 25 C. Cougnon and J. Simonet, J. Electroanal. Chem., IL, 20th–24th August, 1995 2002, 531, (2), 179

Platinum Metals Rev., 2006, 50, (4) 192 26 C. Cougnon and J. Simonet, Electrochem. Commun., 37 C. Cougnon, Ph.D. Thesis, Université de Rennes 1, 2001, 3, (5), 209 2002 27 C. Dano, Ph.D. Thesis, Université de Rennes 1, 38 A. Merz and G. Thumm, Justus Liebigs Ann. Chem., 1998 1978, 1526 28 E. Zintl and G. Woltersdaf, Z. Electrochem., 1935, 41, 39 C. E. Dalm and D. G. Peters, J. Electroanal. Chem., 876 1996, 402, (1–2), 91 29 E. Zintl and W. Dullenkopf, Z. Phys. Chem., 1932, 40 J. Simonet, Electrochem. Commun., 2003, 5, (6), 439 B16, 183 30 E. Zintl, J. Goubeau and W. Dullenkopf, Z. Phys. 41 A. F. Diaz, K. K. Kanazawa and G. P. Gardini, J. Chem., 1931, 154, (Abt. A), 1 Chem. Soc., Chem. Commun., 1979, (14), 635 31 J. B. Chlistunoff and J. J. Lagowski, J. Phys. Chem. B, 42 G. Tourillon and F. Garnier, J. Electroanal. Chem., 1997, 101, (15), 2867 1982, 135, (1), 173 32 J. B. Chlistunoff and J. J Lagowski, J. Phys. Chem. B, 43 “Handbook of Chemistry and Physics”, 46th Edn., 1998, 102, (30), 5800 CRC Press, Cleveland, OH, 1965–1966, F 117 33 V. Svetlicic, P. B. Lawin and E. Kariv-Miller, J. 44 J. Ghilane, M. Delamar, M. Guilloux-Viry, C. Electroanal. Chem., 1990, 284, (1), 185 Lagrost, C. Mangeney and P. Hapiot, Langmuir, 34 E. Kariv-Miller, P. D. Christian and V. Svetlicic, 2005, 21, (14), 6422 Langmuir, 1995, 11, (5), 1817 45 J. Ghilane, M. Guilloux-Viry, C. Lagrost, P. Hapiot 35 E. Kariv-Miller and P. B. Lawin, J. Electroanal. Chem., and J. Simonet, J. Phys. Chem. B, 2005, 109, (31), 1988, 247, (1–2), 345 14925 36 C. Cougnon and J. Simonet, Platinum Metals Rev., 46 Y. H. Zhao, M. H. Abraham and A. M. Zissimos, J. 2002, 46, (3), 94 Chem. Inf. Comput. Sci., 2003, 43, (6), 1848

The Author Emeritus Professor Jacques Simonet is Directeur de Recherche, Electrochemistry Group, Université de Rennes, France. His principal interests are organic electrochemistry, the activation of organic reactions by electron transfer, electro-polymerisation and the formation of redox polymers. He also researches on the reversible cathodic charging of precious metals (platinum and palladium) in super-dry conditions, in contact with polar organic solvents containing electrolytes, mimick- ing Zintl phases for transition metals.

Platinum Metals Rev., 2006, 50, (4) 193 DOI: 10.1595/147106706X150543 SURCAT 2006 Conference THE ANNUAL CONFERENCE OF THE ROYAL SOCIETY OF CHEMISTRY SURFACE REACTIVITY AND CATALYSIS GROUP

Reviewed by S. E. Golunski Johnson Matthey Technology Centre, Blounts Court, Sonning Common, Reading RG4 9NH, U.K.; E-mail: [email protected]

SURCAT 2006 was held at the University of tion with the surface concentration of cationic Cardiff from 25th to 27th July 2006. Thirty-three gold. However, Ton Janssens (Haldor Topsøe, years after Professor Wyn Roberts organised the Denmark) showed that conventional supported- first Surface Reactivity and Catalysis Group meet- gold catalysts conform to the model in which ing, this annual event is still going strong. In spite maximum CO-oxidation activity coincides with an of global competition from conferences with iden- optimum Au0 particle size. In fact, the particle size tical or closely related themes, SURCAT 2006 per se is not as critical as the associated particle attracted over a hundred delegates, mostly from geometry. In Au/TiO2 and Au/MgAl2O4, the the U.K. home countries (England, Northern activity seems to relate directly to the number of Ireland, Scotland and Wales) – with the U.K. aca- corner atoms on the metallic gold particles. demic centres of excellence in catalysis being particularly well represented. For an international Selective Oxidation conference, SURCAT 2006 must have left an Though CO oxidation has become established impressively small carbon footprint! A strong cast as a benchmark reaction for screening gold cata- of speakers from laboratories around the world lysts, their ability to catalyse selective oxidations is provided the international dimension and gave the now seen as a more exploitable quality. Taking the conference an outward-looking feeling. The range conversion of glucose to gluconic acid as his model of catalytic materials discussed was relatively wide reaction, Professor Michele Rossi (University of ranging, but the precious metals, particularly gold Milan, Italy) has been studying liquid phase oxida- and the three key platinum group metals (platinum, tions using colloidal gold as the catalyst. He sees a palladium, rhodium) were undeniably the centre of linear correlation between rate and the total num- attention. ber of exposed gold atoms. The particles have intrinsically high selectivity and turnover frequen- Supported Catalysts cy, comparable to those of enzymes, and cannot be Opening the first session, Professor Bruce promoted by adding typical catalyst support mate- Gates (University of California, U.S.A.) described rials to the colloid. Professor Graham Hutchings an integrated approach to the study of the active (Cardiff University, Wales) broadened the range of phase, support material and reactive intermediates selective oxidation reactions by discussing the in heterogeneous catalysis. He uses synthetic meth- preferential oxidation of CO in the presence of ods to deposit metal species on real support excess H2, and the direct synthesis of H2O2 from materials, avoiding standard impregnation routes H2 and O2. By fine tuning the calcination tempera- that can leave the surface contaminated with trace ture of supported gold, highly selective catalysts impurities. These methods allow Gates to control can be produced that can convert 99.95% of the the oxidation state of the active metal and, in some CO in reformate in a single step. In peroxide syn- cases, to deposit complexes in which the ligand is thesis, the challenge is to design high performance designed to be an intermediate in the catalytic reac- catalysts that will operate in a dilute gas-feed, out- tion. He has made a range of supported gold side the explosive limit. The Cardiff group has complexes that catalyse the oxidation of CO at low developed highly active and selective Au-Pd for- temperature, with the activity showing a correla- mulations, which are stable, reusable and do not

Platinum Metals Rev., 2006, 50, (4), 194–196 194 require the usual bromide or phosphate promot- based on a simple redox cycle, but involves a com- ers. Hutchings showed some beautiful TEM mon intermediate formed from CO and H2O. images (produced by Lehigh University, U.S.A.) revealing a core-shell particle structure, with the Epoxidation of Ethylene palladium completely encasing the gold. A similarly rigorous study has allowed Professor Ken Waugh (University of Manchester) Alkyne Hydrogenation to identify the key intermediate in the epoxidation The delicate balance between complete and par- of ethylene on silver catalysts. Best described as a tial hydrogenation of alkynes over relatively simple surface oxametallacycle, it consists of an palladium catalysts (for instance, 1% Pd on car- H2CO–CH2 species bridging two silver atoms. bon) reflects different steady states during their Ethylene adsorption on a series of pretreated operation. David Lennon (University of Glasgow) Ag/Al2O3 samples reveals that the presence of sur- showed that there is a step change in both activity face chlorine promotes the reaction by weakening and selectivity during propyne hydrogenation as the Ag–O bond in the oxametallacycle, so freeing the H2:hydrocarbon ratio is increased. He the terminal oxygen to form the epoxy group of explained this in terms of two different active sites the product molecule. formed on the palladium surface during exposure to the reactants. At low H2:hydrocarbon ratios, a Catalyst Coking high surface coverage of hydrocarbon-like species In some parts of the world, such as China and results in exposed sites that can only be accessed Singapore, methane dehydroaromatisation is being by propyne and H2; at high ratios, more of the sur- considered as a means of converting natural gas to face is exposed and complete hydrogenation can higher value chemicals. Taking a different view of occur. In the case of acetylene, Shamil the same reaction, Justin Hargreaves (University of Shaikhutdinov (Fritz-Haber Institute, Germany) Glasgow) sees it as a potential route to CO-free attributed changes in selectivity to the nature of the hydrogen. Using Mo-impregnated ZSM5 zeolite as adsorbed hydrogen species. Partial hydrogenation the catalyst, the product stream has a much higher to ethylene occurs by reaction with surface species, H2:benzene ratio than expected. The carbon bal- but the consecutive step to ethane requires subsur- ance is completed by taking into account the coke face hydrogen. The formation of the subsurface deposited on the catalyst. Whereas the group at species can be suppressed by adding silver to the Glasgow is just beginning to probe the nature of palladium. this coke, Geomar Arteaga (Aberdeen University) described a well advanced study of similar effects

Water Gas Shift on platinum catalysts. When Pt/Al2O3 is exposed Water gas shift is a deceptively simple reaction, to pyrolysis gasoline, very rapid coking takes place, for which each new catalyst seems to pose a fresh leading to the formation of two different deposits. challenge when it comes to unravelling the surface ‘Soft’ coke has a relatively high hydrogen content mechanism. Sergiy Shekhtman (Queen’s and is removed by oxidation at moderate tempera- University Belfast) has used temporal analysis of ture, whereas ‘hard’ coke is more carbon-like and products to study Pt/CeO2, which is notable for requires a much higher oxidation temperature. matching the activity of conventional Cu-Zn-Al Although blocking active sites, the coke modifies catalysts, but has the advantages of being non- the platinum surface, leading to the suppression of pyrophoric and not being deactivated by exposure hydrogenolysis reactions and the promotion of to air. Following pretreatment of Pt/CeO2 with aromatisation.

H2O, CO-pulsing experiments show a deficit in the amount of CO2 formed compared with the Vanadium Catalysts amount of CO consumed. This implies that the Vanadium-based catalysts are very topical, predominant mechanism for water gas shift is not cropping up in a seemingly diverse range of appli-

Platinum Metals Rev., 2006, 50, (4) 195 cations. Sreekala Rugmini (University of Glasgow) of things to come in electron microscopy, where it showed that, for the direct dehydrogenation of is becoming possible to determine composition butane, the best performance of V/Al2O3 coin- and morphology on a particle-by-particle basis. At cides with a high surface concentration of the same time, the long-standing ‘material gap’ two-dimensional polyvanadate domains. This opti- between surface science and catalysis is being mum surface state is achieved at a vanadium bridged by the design of industrially realistic model loading of 3.5%. At lower loadings, monomeric catalysts. Using real precursors, Professor Hans vanadia species promote the formation of coke; at Niemantsverdriet (Eindhoven University, The higher loadings, the activity declines as V2O5 crys- Netherlands) has produced flat model chromium tallites are formed. In the case of butane oxidation catalysts on silica wafers, which are ideal for study to maleic anhydride, Taufiq Yap (Universiti Putra by surface science techniques. His dream is to be Malaysia) has improved the preparation of V-P-O able to observe a single active site in action! catalysts with a mechanochemical step: ball-milling Undoubtedly, though, the most futuristic ideas on the hydrated VOHPO4 precursor in solvent so as catalyst design and catalyst applications came from to alter the microstructure of the finished catalyst. Professor Richard Lambert (Cambridge University). By using a bifunctional ligand as an Fresh Approaches in Well-Trodden axle for a porphyrin molecule, he has been able to Fields produce a nanoscopic rotor – the first component Two presentations provided fresh approaches in a catalytic nanomachine? in some well-trodden fields. As Professor Rob Brown (University of Huddersfield) pointed out, Conclusion temperature programmed desorption of ammonia It was highly appropriate that the closing is routinely, but often uncritically, used to measure remarks were made by Professor Roberts, who the acidity of catalysts. Brown has developed an asked the question ‘What has changed since the ammonia-pulsing technique, which allows the con- first SURCAT conference?’. Well, the catalytic centration and strength of acid sites to be building blocks are still very similar – the platinum determined calorimetrically. The technique is sub- group metals, reducible metal oxides and gold tle enough to exclude the contribution from were all on the agenda in 1973. Perhaps the most ammonia adsorbed on non-acidic sites. The striking difference is in the array of tools now Huddersfield group has used it to study some of available for the study of catalysis. A major theme the ‘designer’ catalysts and support materials, of the first conference was the use of surface including polystyrene sulfonic acid resins and reflectance infrared spectroscopy, which heralded Nafion. In the field of chiral catalysis, the ultimate the development of the techniques that we now aim is to achieve an enantiopure product. Paul describe as in situ and operando. Perhaps, in terms of Kilday (University of Aberdeen) has used the impact, the modern equivalent is high-resolution novel approach of adding ionic liquids to the reac- electron microscopy, which is taking us ever clos- tion medium, during the Pt-catalysed hydrogen- er to understanding the relationship between the ation of alkyl pyruvates in the presence of cin- active site and its surface environment. The story chonidine. In some instances, the enantioselective will no doubt be continued at SURCAT 2007, excess is improved by almost 20%. which will be held at The University of Manchester. Future Prospects The Reviewer As with all the best conferences, SURCAT Dr Stan Golunski is Technology Manager 2006 highlighted the hot topics, the recurrent of Gas Phase Catalysis at the Johnson Matthey Technology Centre. Since join- issues, and the likely future trends. With the aid of ing the company in 1989, he has worked some spectacular images, Professor Chris Kiely on fuel reforming, process catalysis, and catalytic aftertreatment for internal com- (Lehigh University, U.S.A.) showed us the shape bustion engines.

Platinum Metals Rev., 2006, 50, (4) 196 DOI: 10.1595/147106706X154882 Reliability of Platinum-Based Thermocouples INFLUENCES OF CONTAMINANTS AND OPERATING ATMOSPHERE

By Roy Rushforth Charles Booth Ltd, 49–63 Spencer Street, Birmingham B18 6DE, U.K.; E-mail: [email protected]

A series of articles in this Journal by Wilkinson on platinum-based thermocouples and their use (1–4) addressed most of the potential problems and performance-limiting factors. The author referred to the possibility of deterioration of thermocouple performance through contamination. This article expands on this, demonstrating that the prevailing atmosphere in which the thermocouple is operating can have a profound effect on its life and accuracy.

In his article on minimising thermocouple drift tory insulation material. At high temperatures, par- (2), Wilkinson referred to the possible effects of ticularly above about 1300ºC, the potential for contaminants, and recommended cleaning each such processes to occur, under specific conditions, limb of the thermocouple thoroughly prior to use. can increase. Serious platinum limb contamination This is excellent advice, and will help to reduce the and even catastrophic failure of the unit can result. potential for subsequent performance deterioration. However, despite the best efforts to keep the Platinum–Refractory Reactions system clean, it is still possible for performance- So what are these specific conditions? The affecting contaminants to be introduced into the nature of any potential reactions between the plat- thermocouple. inum and the refractory must first be understood. Alumina is generally considered a very stable oxide Refractory Insulators – after all, as bauxite, it is one of the most preva- In practice, thermocouples are fitted with lent natural sources of aluminium. It dissociates as refractory insulation between the two limbs (5). follows: Either the limbs are threaded through insulators, 2Al2O3 ' 4Al + 3O2 (i) or they are surrounded by compacted refractory (as in a metal sheathed unit). In either, alumina has In air, as the temperature is increased the equi- been the most frequently used refractory. The librium shifts from right to left, i.e. the stability of premise here is that platinum and its alloys can be alumina increases. This remains true even when heated in contact with the more refractory oxides, oxygen levels are reduced, for instance, by the use including alumina, without deleterious effect. of a vacuum or argon/nitrogen/hydrogen/cracked Indeed platinum thermocouples have shown great ammonia atmospheres. However, if platinum is stability in contact with alumina at temperatures up introduced into the system, with an alumina- to 1600ºC for 1000 hours, in a variety of atmo- sheathed platinum versus rhodium-platinum spheres, including high grade argon with an oxygen thermocouple, the renowned stability of alumina content of only 50 ppm. can be undermined. The phase diagram for the This long-established view of the stability of platinum-aluminium system (6) confirms that at platinum in contact with refractory oxides must the platinum-rich end, intermetallic compounds however be tempered by the knowledge that this are formed – generally readily; the process is apparent inertness is not invincible. The mecha- exothermic and typical of those where intermetal- nisms by which some contaminants can be lic compounds are formed. The resultant product, introduced into the platinum thermocouple, subse- probably Pt3Al in the first instance, is very stable. quently to affect its performance, can be complex. Thus at high temperatures, if the partial pres- They involve the active participation of the refrac- sure of oxygen in the working atmosphere is

Platinum Metals Rev., 2006, 50, (4), 197–199 197 reduced, and is maintained so, the potential nificant detrimental effects will occur before at increases significantly for two reactions to occur to least 100 hours usage at temperatures in excess of the detriment of thermocouple performance: 1300ºC. In extreme instances, where strong reducing conditions prevail, ensuring very low oxygen 2Al2O3 → 4Al + 3O2 (ii) levels, such reactions will occur quickly, within a (Oxygen is removed by the ambient atmosphere.) few hours. Even then, compositional changes in the platinum limb would only adversely affect ther- 3Pt + Al → Pt3Al (iii) mocouple accuracy if they occurred in that part of (A stable intermetallic compound is formed and the unit located in the thermal gradient. Any cont- heat is evolved.) amination occurring in that part of the Darling et al. studied these reactions in some thermocouple held in the stable hottest zone of the detail in the early 1970s, (7–10) with respect to a furnace would not affect accuracy. Catastrophic number of refractory materials such as alumina, failure through incipient melting of the intermetal- thoria, boron nitride, hafnia, zirconia and magne- lic products could occur where the furnace running sia. (Boron nitride and hafnia are not referred to in temperature exceeds the melting point of the com- References (7–10) but were included in the original pound. Such failures have been observed in a investigation.) Thorium, boron, hafnium and zir- platinum thermocouple limb after reaction with conium will, similarly to aluminium, form alumina at 1450ºC (10). intermetallic compounds with platinum given There is one exception to vulnerability to appropriate conditions. Darling et al. demonstrated reduction and intermetallic reactions among the that intermetallic reactions are possible with these commonly available refractories, namely magne- refractories, in fact extremely probable, at temper- sium oxide (magnesia). Given the absence of ‘the atures above about 1300ºC, once the oxygen usual suspects’ such as silicon, it is extremely diffi- potential of the ambient atmosphere is maintained cult to promote significant dissociation of at a reduced level. Such levels were shown to be magnesia and the formation of platinum-magne- achievable by evacuation using a conventional sium compounds, even in the most aggressive roughing/diffusion vacuum pump system down to oxygen removal environments at temperatures up 10–3 Pa pressure or by the use of hydrogen-con- to 1700ºC. The affinity between platinum and taining atmospheres where oxygen removal was magnesium is very low, and there is therefore no ‘continuous’, as found in many high-temperature thermodynamic driver for them to react to form melting or heat treatment furnaces. If silica, or a stable compounds. silicon-containing compound, is present, for It is important to remember that these reactions instance a silicate-containing alumina, the reaction can only continue in environments where the oxy- potential is further increased through the very gen is continuously removed; once the partial strong affinity between platinum and silicon (10). pressure of oxygen increases, the reaction will slow The resultant Pt/Si compound has a very low down and eventually cease as the equilibrium par- melting point – less than 1000ºC; therefore once tial pressure is attained. Therefore one would not the compound has formed in the limb of the ther- expect deleterious breakdown of a dispersed oxide mocouple, catastrophic failure through incipient phase such as zirconia in, for instance, a disper- fusion will occur once this temperature has been sion-strengthened platinum product, since exceeded. dissociated oxygen cannot normally be continuously removed. However, it has also been shown Preconditions for Adverse Reactions that silica can be reduced simply by the presence of The timescale for such reactions depends oil, via, for example, an oil-soaked refractory parti- strongly on the efficiency of oxygen removal. In a cle being rolled or drawn onto the surface of the continuously maintained vacuum, the reaction will platinum (10). At high temperatures a very local progress quite slowly, and it is unlikely that any sig- reducing environment is created by the oxidation

Platinum Metals Rev., 2006, 50, (4) 198 of the oil, promoting the dissociation of the silica, ensure that these reactions do not occur to the and the exothermic reaction of the silicon with the detriment of its performance. Clearly, where the platinum to form a platinum silicide. prevailing environment might either very locally or generally tend towards low oxygen/reducing con- Specification and Maintenance of ditions, and if a conventional unit is to be Thermocouples employed, then the user must consider carefully The selection of the appropriate refractory the thermocouple/refractory combination, the insulation material is clearly very important. For quality of the refractory and the prevailing operat- instance, a range of ‘grades’ of alumina insulator ing atmosphere. In such instances, the use of a are available, some containing quite high levels of metal sheathed thermocouple, although these have silicates, while others consist of virtually pure alu- their own drift problems (2), would at least pre- mina. At low operating temperatures, say below vent thermocouple/refractory reactions from 1000ºC, the potential for contamination between occurring. thermocouple and insulator will be small, and alu- References mina insulators of lower specification can be used. 1 R. Wilkinson, Platinum Metals Rev., 2004, 48, (2), 88 At higher temperatures, particularly above about 2 R. Wilkinson, Platinum Metals Rev., 2004, 48, (3), 145 1300ºC, the presence of silicates and other impuri- 3 R. Wilkinson, Platinum Metals Rev., 2005, 49, (1), 60 ties can increase the potential for contamination 4 R. Wilkinson, Platinum Metals Rev., 2005, 49, (2), 108 and subsequent catastrophic failure of the unit, 5 L. Michalski, K. Eckersdorf, J. Kucharski and J. McGhee, “Temperature Measurement”, 2nd Edn., depending on operating conditions. John Wiley & Sons Ltd, New York, 2001 It is possible that thermocouples fail or lose 6 “Binary Alloy Phase Diagrams”, 2nd Edn., eds. T. accuracy in service, particularly during long-term, B. Massalski, H. Okamoto, P. R. Subramanian and high-temperature usage, more often than is L. Kacprzak, ASM International, Ohio, U.S.A., 1990 7 A. S. Darling, G. L. Selman and R. Rushforth, realised through the reactions described here. Platinum Metals Rev., 1970, 14, (2), 54 Paraphrasing Wilkinson’s point, ‘cleanliness is next 8 A. S. Darling, G. L. Selman and R. Rushforth, to godliness’ if optimal performance is to be Platinum Metals Rev., 1970, 14, (3), 95 obtained from the thermocouple. However, the 9 A. S. Darling, G. L. Selman and R. Rushforth, Platinum Metals Rev., 1970, 14, (4), 124 user must also be fully aware of the conditions 10 A. S. Darling, G. L. Selman and R. Rushforth, under which the thermocouple is to be used, to Platinum Metals Rev., 1971, 15, (1), 13

The Author

Roy Rushforth is Managing Director of Charles Booth Ltd (part of the Stephen Betts Group), a U.K. dental alloy manufacturer supplying precious and non-precious materials for crown and bridge restorations. His 40 years experience in platinum group metals and gold has been first at Johnson Matthey, where he completed a major project for the Atomic Energy Authority at Harwell investigating platinum-refractory stability. He later developed new alloys and processes for the Johnson Matthey jewellery and dental businesses. He then worked at the Birmingham Assay Office, U.K., as Development Director, before joining Charles Booth in 2000.

Platinum Metals Rev., 2006, 50, (4) 199 DOI: 10.1595/147106706X158789 “Principles of Fuel Cells” BY XIANGUO LI, Taylor & Francis, New York, 2005, 572 pages, ISBN 978-1-59169-022-1, £50.00, U.S.$125.00

Reviewed by Tom R. Ralph Johnson Matthey Fuel Cells, Lydiard Fields, Great Western Way, Swindon SN5 8AT, U.K.; E-mail: [email protected]

This new book by Xianguo Li attempts to Major Fuel Cell Types cover both the fundamental aspects associated At twenty pages, the treatment of the alkaline fuel with the thermodynamics and the electrochemical cell (AFC) in Chapter 5 is perhaps a little excessive, processes in the fuel cell, with a review of the given that this technology is limited to space applica- development of the six major fuel cell types. tions. This is because the lack of CO2 rejection by Chapter 1 provides a sound introduction to fuel the electrolyte, even at the level of ca. 300 ppm found cells, covering the main points in terms of the in air, produces a significant performance loss. The operating principles and the typical classification discussion of the impact of operating conditions on of the different types of fuel cells, by electrolyte or the performance of the AFC is nevertheless educa- operating temperature, as a prelude to tackling tional, and the general approach is applicable to all first the fundamentals and then the technology of fuel cell types. In contrast to the AFC, the phosphor- fuel cells. ic acid fuel cell (PAFC) dealt with in Chapter 6 has met the 40,000 h operational lifetime criterion, if not Target Audience and Fundamentals the cost targets, required for the 200 to The author identifies the main audience as 300 kW stationary cogeneration market. The PAFC undergraduate senior-level and first-year graduate is the most commercially developed fuel cell type. students in the engineering disciplines. It is perhaps Most of the important areas of the technology are no surprise that a key strength of the book is the touched upon in Chapter 6, including the durability thorough treatment of the thermodynamics of the issues, although more detail on the construction and fuel cell in Chapter 2. The worked examples are performance of the cell materials could have been especially helpful in understanding a subject area added, along with a more detailed discussion of nat- that many students struggle to comprehend. The ural gas reforming. treatment of the electrochemical losses in Chapters In Chapter 7 the proton exchange membrane fuel 3 and 4 reflects the current level of understanding cell (PEMFC) receives by far the largest attention of of this difficult area. The electrochemical kinetic all the fuel cell types, reflecting the focus placed on losses are perhaps more clearly dealt with in other the PEMFC over the last two decades. There is a electrochemistry books (1), but the coverage of the decent review of the different flow field designs concentration overpotential in terms of both a sim- employed by stack developers and academic plistic and a more rigorous engineering approach to researchers, and a fairly expansive discussion of the mass transport losses near the limiting current, with membrane electrolyte based on the Nafion® materi- worked examples, is particularly well done. These al developed by DuPont de Nemours. The chapters on fundamentals do provide the engineer- membrane structure, water sorption properties, pro- ing student with a solid basis for tackling fuel cell tonic conductivity and the water movement technology at a higher level. mechanisms are highlighted. The development of The remaining chapters deal with the different the membrane electrode assembly (MEA) is fuel cell types. While pitched at the correct level for broached in several sections of the chapter. The dif- students, practising engineers or other profession- ferent fabrication routes and the importance of als would also benefit from a more comprehensive carbon supported catalysts, with impregnation of the treatment of the current state of the art of fuel cell platinum catalyst layer with proton conducting elec- technology (see for instance, (2)). trolyte to improve catalyst utilisation, are clarified.

Platinum Metals Rev., 2006, 50, (4), 200–201 200 The design of the anode for improved reformate number of companies. The key challenges of

(CO and CO2) tolerance is discussed in detail, with improved methanol oxidation kinetics and reduced the importance of platinum-ruthenium (PtRu) alloys methanol crossover are identified. It would have highlighted, although the application of platinum- been appropriate, however, to discuss the large body molybdenum (PtMo) alloys for improved CO of work on developing improved membranes and tolerance is discussed without drawing attention to MEA designs for DMFCs, to reduce methanol the problems with CO2 tolerance (3); these negate crossover and MEA Pt loadings. Some comment on any benefit. Durability, however, is not discussed the expanding research on alternative fuels, such as and this is an important gap. The mechanisms of direct ethanol and formic acid, might usefully have membrane failure that have limited adoption of the been added. technology are not considered. Mechanical failure due to the stresses induced by dimensional change in Conclusion the membrane, as it is hydrated then dehydrated dur- While there are a few important areas that are not ing operation, and failure due to chemical attack covered, and the text could have been smoothed to from peroxide decomposition, are currently key improve its comprehensibility, the book does suc- areas of research and development (4). Nor has the ceed in the main aim of educating students important area of cell reversal due to fuel starvation, (particularly in mechanical engineering) in the chal- which can destroy a stack in minutes, been consid- lenges presented by fuel cell technology. As the ered. The addition of water oxidation catalysts to the author advises in the preface, for fuel cell technolo- anode to mitigate against cell reversal is favoured by gy to succeed, a multidisciplinary approach from Johnson Matthey (3). electrochemists, engineers and materials scientists is Development of the much higher-temperature required. There is a growing need to educate and molten carbonate fuel cell (MCFC) and solid oxide motivate the fuel cell engineers of the future. fuel cell (SOFC) for large-scale MW grid applications is discussed in Chapters 8 and 9, respectively. The References important technical disadvantages that have prevent- 1 D. Pletcher and F. C. Walsh, “Industrial ed adoption of the technologies are explained. For Electrochemistry”, 2nd Edn., Chapman and Hall, London, 1990 the MCFC the problems brought by the highly cor- 2 “Handbook of Fuel Cells: Fundamentals, rosive Li-K carbonate electrolyte in terms of Technology, Applications”, eds. W. Vielstich, A. electrode stability, electrolyte containment in the cell Lamm and H. A. Gasteiger, J. Wiley & Sons, Chichester, U.K., 2003, Vols. 1–4 matrix and gas sealing of the stack are fully discussed. 3 T. R. Ralph and M. Hogarth, Platinum Metals Rev., In the SOFC, the thermal mismatch between the 2002, 46, (3), 117 ceramic cell and stack components that induces 4 A. B. LaConti, M. Hamdan and R. C. McDonald, in “Handbook of Fuel Cells: Fundamentals, material cracking is highlighted, as is the desire to Technology, Applications”, eds. W. Vielstich, A. lower the operating temperature to minimise the Lamm and H. A. Gasteiger, J. Wiley & Sons, problem and to reduce the cost of the balance of Chichester, U.K., 2003, Vol. 3, Chapter 49, pp. 647–663 plant. The engineering student will find it illuminat- ing to consider the ability of these fuel cells to use The Reviewer Professor Tom R. Ralph is Head of natural gas as a direct or indirect fuel, without the Electrochemical Engineering with Johnson need to remove CO or CO2, and to consider the Matthey Fuel Cells, Swindon, U.K. At Johnson Matthey he has been involved in impact of the stack operating conditions on the per- the development of unit cells for PAFCs and formance through worked examples. MEAs for PEMFCs since 1989. During this time he has published widely, has Finally in Chapter 10 there is a very brief discus- generated over 20 patents, has run fuel cell sion of the direct methanol fuel cell (DMFC) courses at Strathclyde and Reading Universities, and has presented at a number of international operating in a PEMFC design, which is out of step conferences on the science and technology of fuel cells. He is with the increasing development of this technology presently visiting professor at the School of Engineering Sciences, University of Southampton and his main interests are in the for mobile telephone and leisure applications by a engineering of materials for fuel cells, redox batteries and solar cells.

Platinum Metals Rev., 2006, 50, (4) 201 DOI: 10.1595/147106706X158374 10th Ulm Electrochemical Talks PGMS FEATURE IN RELIABILITY AND DURABILITY GAINS AND COST REDUCTION FOR ELECTROCHEMICAL ENERGY STORAGE AND CONVERSION

Reviewed by Sarah C. Ball Johnson Matthey Technology Centre, Blounts Court, Sonning Common, Reading RG4 9NH, U.K.; E-mail: [email protected]

The 10th Ulm Electrochemical Talks (UECT) cathode where voltages up to 1.7 V RHE were held from 27th to 28th June 2006 in Neu- (reversible hydrogen electrode) may be encoun- Ulm, Germany. The Talks were organised by a tered. UTC recommended a solution at the system number of Ulm-based organisations: the Zentrum level to mitigate this problem, as a materials solu- für Sonnenergie- und Wasserstoff-Forschung tion requires an improvement of two to four orders (ZSW), DaimlerChrysler R&D Center, the of magnitude in corrosion resistance. This is not University of Ulm and the University of Applied considered feasible using carbon support materials. Sciences. Trends in the development of batteries, UTC platinum-cobalt (PtCo) and platinum-iridium- supercapacitors and fuel cells were discussed. cobalt (PtIrCo) alloy materials showed high stability Increasing consumer independence, requirements in voltage cycling tests up to 1.15 V, with no leach- for emergency power and environmental concerns ing of Co observed. Peroxide attack is the critical were cited as overall drivers for the development cause of membrane decay. The hydrocarbon mem- and commercialisation of these technologies. brane biphenyl sulfone (BPSH) survived during

Batteries and supercapacitors are already commer- open-circuit hold tests due to a low level of O2 per- cially available for a wide range of applications, meation, although this material failed Fenton’s test, from hybrid vehicles to laptop computer and generally used for assessing membrane stability. mobile telephone batteries. By contrast, fuel cell Freeze-start capability and the importance of the systems, on which this review primarily focuses, robustness of seal materials, as well as of the MEA are still under development. However, advances in components, were also discussed. performance, lifetime and robustness were key C. Stone (Ballard Power Systems, Canada) cited themes, recurring throughout the meeting for all cost, durability, power density and freeze start the various technologies discussed. Higher power capability as significant parameters for the com- densities and no need for recharging represent the mercialisation of proton exchange membrane fuel significant advantages of fuel cell systems over bat- cell (PEMFC) stack technology, and outlined ‘road teries and supercapacitors, but wide-scale map’ objectives in terms of all these parameters to introduction of fuel cell technologies is currently be achieved by 2010. Ballard Power Systems’ strat- limited by considerations of cost and durability, egy aims to stimulate commercialisation by and the requirement for a hydrogen infrastructure accelerating the development of emerging tech- or on-board hydrogen storage. nologies such as higher-activity catalysts (enabling metal loading and hence cost to be reduced), Proton Exchange Membrane Fuel Cells hydrocarbon composite membranes, and low-cost Mechanisms of component decay and accelerat- gas diffusion layer materials. An ultimate cost tar- ed tests were key features of the fuel cell sessions, get of U.S.$30 kW–1 was quoted, compared to the as they were of the battery and supercapacitor ses- current U.S.$73 kW–1. However the attainment of sions. T. Jarvi (UTC Power, U.S.A.) discussed the this would also require improvement in balance of failure modes of the different fuel cell components plant (BOP) and the removal of any requirement within the membrane electrode assembly (MEA). for external humidification. Achieving high perfor- Transient phenomena during start-up and shut- mance using continuously coated MEA down accelerate degradation of the fuel cell components and low-cost metal flow field plates is

Platinum Metals Rev., 2006, 50, (4), 202–204 202 also essential for future scale-up plans. A. Khokhlov (Moscow State University and R. Ströbel presented results from DANA Russian Academy of Sciences, Russia) presented Corporation (Germany) and Zentrum für recent results on polybenzimidazole (PBI) mem- Sonnenergie- und Wasserstoff-Forschung (ZSW; branes for operation from 150–200ºC. Centre for Solar Energy and Hydrogen Research, 4,4′-Diphenylphthalidecarbonic acid and 3,3′,4,4′- Germany) on stamped metal bipolar plates for use tetraminodiphenyl ether derived PBI polymers are in PEMFC applications. Use of metal plates doped with 85% phosphoric acid, producing films improves the power density of PEMFC systems by holding 12–18 molecules of phosphoric acid per reducing weight and volume. Costs are also monomer unit. Protonic conductivity is retained reduced, and mass production is ultimately up to 160ºC. Fuel cell testing at 175ºC showed enabled. However, the sensitive nature of the around 5% performance loss using reformate con- MEA components requires that a highly corro- taining 1.5% CO as the anode fuel. This is a sion-resistant, low-cost coating be found for the significant enhancement in anode CO tolerance metal bipolar plates. The coating must also be compared with that of MEAs operating at less than compatible with and chemically resistant to the 100ºC. sealing materials used within the PEMFC stack. T. Schmidt (PEMEAs GmbH, Germany) also B. Bauer (FuMA-Tech, Germany) described the discussed PBI-based high-temperature MEAs, various membrane products available, including describing the enhanced tolerance of the Celtec®-P ® the ‘fumapem ’ series of membranes which MEA to the CO, H2S and methanol in reformate include the fully fluorinated F-series, partially fluo- mixtures, which is made possible by MEA opera- rinated P-series and other membranes with no tion at higher temperatures of 120–180ºC. The fluorination. Strategies to reduce the overall cost of advantages of the system are simplification of the membrane materials were described, including fuel processor, made possible by greater tolerance low-cost ionomers, reinforcement to reduce thick- to impurities, no need for external humidification, ness and retain strength, and the use of fillers or and no membrane stability issues caused by perox- additives. However, cost reduction via the use of ide. Major disadvantages of higher-temperature excessively thin membranes will compromise dura- operation are the accelerated degradation of Pt/C bility, and high performance rather than low cost catalysts, and redistribution of the H3PO4 elec- was cited as the key requirement for membrane trolyte doped into the electrodes during operation, materials. The addition of inorganic films of silica, reducing catalyst utilisation and peformance. zirconium phosphide and carbon nanotubes in G. Scherer (Paul Sherrer Institute, Switzerland) small concentrations have been used to reinforce reported how neutron radiography could be used the polymer reducing swelling and gas crossover to visualise the liquid water distribution in different and improving mechanical stability without affect- components of a PEMFC in a segmented cell. By ing conductivity or flexibility of the membrane. coupling the technique with in situ electrochemical Annealing of membranes doped within inorganic impedance spectroscopy, changes in mass flow films enhanced their mechanical stability. and current density may be correlated with humid- S. Ball (Johnson Matthey, U.K.) described ification conditions. C. Hartnig (ZSW, Germany) PtCo/C alloy materials with improved kinetic also described the use of neutron radiography to activity for the PEMFC cathode, and high stability image the liquid water within the serpentine flow during voltage cycling tests. Electronic and struc- field of a working fuel cell. The test can be per- tural effects present in alloy particles enhance formed without modifying or disturbing the fuel activity over that of Pt-only catalyst materials. cell stack, producing a three-dimensional image of Catalysts prepared on corrosion-resistant carbon an operating cell. This can be correlated with cur- supports of lower surface area showed improved rent mapping and performance data to improve resistance to corrosion at 1.2 V, as compared with understanding of water transport processes within that of commercially available carbon supports. the PEMFC.

Platinum Metals Rev., 2006, 50, (4) 203 Direct Alcohol Fuel Cells carbonate fuel cell. This has the advantage of flex- The challenges associated with direct alcohol ibility in fuel type: natural or biogas, methanol, fuel cells (DAFCs) were discussed by U. Stimming coal gas or sewage/landfill gas are all possible

(Technische Universität München, Germany and fuels. High levels of CO2 – from 40–60% in some Bayerischen Zentrum für Angewandte of these fuel types – were initially thought prob- Energieforschung eV, Germany). Liquid fuels are lematic; however, fuel cell voltage actually rose as particularly attractive for portable power applica- CO2 was observed to migrate to the cathode side tions due to their greater energy density than that of the molten carbonate fuel cell (MCFC). of hydrogen. Much recent progress has been made using liquid-fed direct methanol fuel cells Poster Session (DMFCs). An ultimate aim is to extend usage to Information presented within the poster ses- other fuels such as ethanol, which can be pro- sion reflected the main themes of the Talks, duced by fermentation, or glycerol, which is covering high-temperature membranes, novel cat- available as a byproduct of fatty acid production. alysts for oxygen reduction and alcohol oxidation, Oxidation of higher alcohols within low-tempera- new Li-ion battery materials and the investigation ture PEMFCs requires improved catalyst materials of corrosion processes. The application of such as platinum-tin (PtSn), as the platinum-ruthe- microscopy and spectroscopy techniques to nium (PtRu) materials currently used for methanol PEMFC components and system modelling was systems cannot fully oxidise ethanol, and become also presented. poisoned by organic fragments. DAFCs can operate using either acid or alkaline membranes, with Conclusion the advantages of faster oxygen reduction kinetics New pgm-based alloy catalysts described at the and the capacity to use non-noble metal catalysts conference showed enhancements in activity and under alkaline conditions. Better electrolyte mate- stability over current Pt-only materials, and rials are required to reduce alcohol crossover, or remain significantly more active than non-pgm highly selective catalysts are needed if cells are to catalysts. PtCo and PtIrCo alloys showed good be operated using a mixed alcohol/air feed. A activity and stability in voltage cycling tests repre- PtRu black catalyst at the anode and a ruthenium- sentative of long term operation in automotive selenium (RuSe) catalyst at the cathode were applications. PtSn and PtRu are key materials found to perform well in a mixed feed system. required for the operation of direct alcohol fuel G. S. Park (Samsung Advanced Institute of cells (DAFCs), while RuSe catalysts have the ben- Technology, Korea) reported on the long-term efit of alcohol tolerance and can be used as stability of DMFC systems where agglomeration cathodes in DAFCs. and migration of Pt and Ru from the anode was The 10th UECT concluded with a farewell observed during fuel cell testing. Accumulation of party at the Center for Solar Energy and Ru at the cathode was observed to increase linear- Hydrogen at ZSW in Neu-Ulm. Historic Ulm was ly with the MEA performance drop. However, the birthplace of Albert Einstein, and the site of a both Pt and Ru migrated from the PtRu anode, so tailor’s failed hang-glider launch across the the Pt:Ru ratio observed at the anode did not Danube in 1811. The Minster has Europe’s tallest change. Pt particles, up to 10 nm in size, were also church tower, and according to legend, a famous observed within the membrane, along with evi- sparrow helped with the logistics of construction. dence for membrane degradation from attack by radicals and peroxide. The Reviewer Sarah Ball is a Research Scientist in the Electrotechnology/Catalyst Preparation Group Molten Carbonate Fuel Cells at the Johnson Matthey Technology Centre in the U.K. She is interested in anode catalysis for S. Rolf (MTU CFC Solutions GmbH, reformate-tolerant applications, and novel Germany) described the ‘HotModule’ stationary cathode materials and alloys for PEMFCs.

Platinum Metals Rev., 2006, 50, (4) 204 DOI: 10.1595/147106706X158103

SUSAN V. ASHTON A TRIBUTE ON HER RETIREMENT AS EDITOR

Platinum Metals to maintain and Review (PMR) has develop the high been fortunate over standard of contribu- the fifty years of its tions from the existence in having a various research and very stable staff development estab- establishment. In lishments throughout particular, the pre- the world of plat- sent Editor of PMR inum group metals is only the fourth to (pgms). This she did hold that title. The admirably. Susan was founding Editor, Dr well known for her Leslie Hunt, held the desire to maintain the position from 1956 highest possible qual- until his death in ity for all the papers 1987. Dr Hunt’s successor, Ian Cottington, was published in PMR, and if this meant a long and Editor for seven years until his retirement in detailed exchange of correspondence with her 1994. The third Editor was Susan Ashton, who contributors to get things right to mutual satis- held the position from June 1994 until May faction, then that was what was done. Many 2006. authors, especially perhaps those whose first Susan joined Johnson Matthey as language was not English, will have greatly Patents/Information Assistant on PMR in appreciated the advice that Susan gave to help August 1977. She had them finalise their papers for publication. obtained a B.A. In addition to (Hons) in Physics content, Susan was from the University also most determined of Lancaster and an to make PMR appear M.Sc. in Information as attractive as possi- Science from City ble, without compro- University, London. mising its long-estab- Prior to joining lished reputation and Johnson Matthey she traditions. For 43 taught physics and years PMR was worked as Editorial issued with a charac- Assistant on Metals teristic plain cover. Abstracts for the Then, in 1999, Susan Metals Society. arranged for a com- What were plete redesign of the Susan’s achievements (Left) The cover design used for Platinum Metals cover, giving the Review from its inception until 1999. (Right) The as Editor of PMR? redesigned cover introduced by Susan Ashton, and used journal a bright, Primarily they were until PMR became solely an E-journal modern scientific

Platinum Metals Rev., 2006, 50, (4), 205–206 205 appearance that was in context with develop- of the journal. The PMR website has achieved ments in the world of pgms. The appearance of high ranking on internet search engines. the internal content was also enhanced with www.platinummetalsreview.com provides a improved design, including new layout and treasure trove of information: the journal itself, fonts. In 2003, it was decided to publish PMR now augmented by the facility to search articles solely as an electronic journal. Susan herself online; files in PDF format of past issues of the would admit to having reservations about this journal; a Question and Answer section; directo- move, feeling that it risked cutting off readers ries of people and organisations working with without access to a computer and the internet. pgms; recommended reading lists; an events cal- But once these initial fears were resolved, she endar; and links to a wide variety of relevant realised that a journal with its own internet site scientific and commercial information. would provide many more opportunities for Susan successfully brought PMR into the 21st interaction with users, and instant access to any century and can be proud of her legacy. We potential reader with an internet connection, thank her for that, and wish her a long and happy thereby greatly extending the global readership retirement. M. C. F. STEEL

Pavla White Susan Ashton was ably supported during her Editorship by another long- serving member of the PMR team, Pavla White. Born in Ostrava, Czech Republic, Pavla obtained a degree (Dipl.-Ing.) in Chemical Engineering from Vysoká Škola Bánská (Technical University) in Ostrava. She retired as the Senior Editorial Assistant on PMR in December 2005.

The Author Dr Mike Steel was Market Research & Planning Director of Johnson Matthey’s Precious Metal Products Division until his retirement in May 2006. He was in charge of the company’s precious-metals market research and publications, including Platinum Metals Review, the biannual market reviews Platinum and the internet portal Fuel Cell Today (www.fuelcelltoday.com). In addition, Dr Steel was responsible for Johnson Matthey’s Moscow office.

Platinum Metals Rev., 2006, 50, (4) 206 DOI: 10.1595/147106706X157753 ABSTRACTS of current literature on the platinum metals and their alloys PROPERTIES CHEMICAL COMPOUNDS Size Effects on the Thermal Conductivity of Growth and Characterization of Partially Oxidized Polycrystalline Platinum Nanofilms Platinum Polymers in Nanoscale Templates Q. G. ZHANG, B. Y. CAO, X. ZHANG, M. FUJII and K. TAKAHASHI, B. M. ANDERSON, S. K. HURST, L. SPANGLER, E. H. ABBOTT, P. J. Phys.: Condens. Matter, 2006, 18, (34), 7937–7950 MARTELLARO, P. J. PINHERO and E. S. PETERSON, J. Mater. Sci., The thicknesses of the studied polycrystalline Pt 2006, 41, (13), 4251–4258 nanofilms (1) ranged from 15.0–63.0 nm and the The partially oxidised (PO) salts of the bis(oxala- mean grain sizes varied from 9.5–26.4 nm. The ther- to)platinate(II) (1) and tetra(cyano)platinate(II) mal conductivities of (1) measured by a direct complexes were electrochemically prepared in glass electrical heating method are greatly reduced from the capillary templates (900 nm in length), as well as bulk values, due mainly to grain-boundary scattering. through porous anodic Al oxide templates with pore diameters of 200 nm and 20 nm. The PO (1) poly- Demixing of Solid-Soluted Co-Pd Binary Alloy mers have significant flexibility on the nanoscale. The Induced by Microwave Plasma Hydrogen formation of the PO polymers could be directed by varying the positions and the number of electrodes. Irradiation Technique T. TOKUNAGA, Y. HAYASHI, T. FUJITA, S. R. P. SILVA and G. A. Multiple Additions of Palladium to C J. AMARATUNGA, Jpn. J. Appl. Phys., Part 2, 2006, 45, (32), 60 L860–L863 O. LOBODA, V. R. JENSEN and K. J. BØRVE, Fullerenes, Nanotubes, Demixing in a solid-soluted Co-40 at.% Pd alloy Carbon Nanostruct., 2006, 14, (2–3), 365–371 was induced by microwave plasma H irradiation on a DFT calculations on exohedral PdnC60 show that the Pd–fullerene bond energy remains essentially con- mixture of Pd-Co island grains on a Si substrate. 2 Microstructure observation and X-ray microanalysis stant for n = 1–6. A Pd2(η -C60) structure with the by TEM before and after the irradiation provided evi- two metal atoms bridging over a six-membered ring is dence of demixing in the metallic Co-Pd alloys. The the most stable arrangement of two Pd atoms on the possibility of the decomposition into Pd hydride and surface of C60. Entropy considerations suggest that Co under irradiation at high temperatures is indicated. isolated atoms and weakly bonded metal aggregates may exist in equilibrium. Binding of Pd atoms to the Surface Segregation and Homogenization of fullerene is preferred over Pd dimerisation. Pd70Ag30 Alloy Nanoparticles Fluorous Nanodroplets Structurally Confined in an K.-W. WANG, S.-R. CHUNG and T.-P. PERNG, J. Alloys Compd., 2006, 422, (1–2), 223–226 Organopalladium Sphere S. SATO, J. IIDA, K. SUZUKI, M. KAWANO, T. OZEKI and M. In this study Pd70Ag30 nanoparticles (1) with the smallest size and the highest homogeneity were pre- FUJITA, Science, 2006, 313, (5791), 1273–1276 Arrow-shaped N-donor ligands with perfluoroalkyl pared using the strong reducing agent NaBH4. After heating (1), the surface segregation of Ag was small tails self-assembled with Pd ions in DMSO to form a and the sintering was retarded by the high surface Pd shell in which the fluorinated chains (1) are directed concentration or by the residual B. There was signifi- inward toward the centre. Crystallographic analysis cant surface segregation of Ag and sintering for (1) confirmed the rigid shell framework and amorphous prepared by HCHO, where a higher concentration interior. By varying the lengths of (1), the shell size gradient existed inside (1). The behaviour of (1) pre- could be tuned to encapsulate a liquid-like, disordered phase of ~ 2–6 perfluorooctane molecules. pared by N2H4 was intermediate between those of the other two samples. Crystal Structure and Infrared Spectroscopy of Crystal Growth, Structure, Magnetic, and Bis(2-hydrazinopyridine)palladium(II) Chloride

Transport Properties of TbRhIn5 and its Isotopomers W. M. WILLIAMS, L. PHAM, S. MaQUILON, M. MOLDOVAN, Z. FISK, P. DROZDZEWSKI, M. MUSIALA and M. KUBIAK, Aust. J. Chem., D. P. YOUNG and J. Y. CHAN, Inorg. Chem., 2006, 45, (12), 2006, 59, (5), 329–335 4637–4641 Reaction of PdCl2 with 2-hydrazinopyridine (hypy) Single crystals of TbRhIn5 (1) were synthesised in DMF gave [Pd(hypy)2]Cl2, whereas it recrystallised using the flux growth method. (1) is isostructural to from MeOH to give [Pd(hypy)2]Cl2·2MeOH (1). CeRhIn5. The easy axis of magnetisation in (1) (TN = Single crystal X-ray analysis of (1) revealed the planar 47 K) is along the c axis. TN is enhanced by ~ 24% structure of the metal vicinity and trans-orientation of compared to that in TbIn3 (TN = 36 K). Although (1) the ligands, chelating the Pd through amine and pyri- is not a heavy fermion superconductor, it does have dine N atoms. IR spectroscopy and DFT modelling 2+ strong antiferromagnetic correlations. were used to study the vibrations of [Pd(hypy)2] .

Platinum Metals Rev., 2006, 50, (4), 207–210 207 Preparation of Five- and Six-Coordinate Electrochemical Capacitors Based on Aryl(hydrido) Iridium(III) Complexes from Benzene Electrodeposited Ruthenium Oxide on Nanofibre and Functionalized Arenes by C–H Activation Substrates H. WERNER, A. HÖHN, M. DZIALLAS and T. DIRNBERGER, Y. R. AHN, M. Y. SONG, S. M. JO, C. R. PARK and D. Y. KIM, Dalton Trans., 2006, (21), 2597–2606 Nanotechnology, 2006, 17, (12), 2865–2869 Reaction of the in situ generated cyclooctene Ir(I) Electrodeposition of RuO2 on electrospun TiO2 derivative trans-[IrCl(C8H14)(PiPr3)2] with benzene at nanorods using CV increased the capacitance of 80ºC gave a mixture of [IrH2(Cl)(PiPr3)2] and RuO2. This is attributed to the large surface areas of [IrH(C6H5)(Cl)(PiPr3)2] in the ratio of ~ 1:2. C6H5X the nanorods. The electrode deposited from 0.25– (X = Cl, F), C6H4F2 and C6H4F(CH3) also reacted by 1.45 V (with respect to Ag/AgCl) exhibited a specific –1 C–H activation to afford [IrH(C6H4X)(Cl)(PiPr3)2], capacitance of 534 F g after deposition for 10 cycles –1 [IrH(C6H3F2)(Cl)(PiPr3)2] and [IrH{C6H3F(CH3)}(Cl)(PiPr3)2], with a scan rate of 50 mV s . The structural H2O respectively. The formation of isomeric mixtures was content in RuO2 varied depending on the deposition 1 13 19 31 detected by H, C, F and P NMR spectroscopy. potential range. Higher amounts of structural H2O in RuO2 increased the charge storage capability. Oligo(U-terpyridines) and Their Ruthenium(II) Complexes: Synthesis and Structural Properties ELECTRODEPOSITION AND SURFACE A. WINTER, J. HUMMEL and N. RISCH, J. Org. Chem., 2006, 71, (13), 4862–4871 COATINGS The domino reaction of tetrahydroquinolinone with Catalyst-Enhanced Chemical Vapor Deposition of bisiminium salts gave rigid U-shaped substituted ter- Palladium-Platinum Bilayer Films on Polyimide pyridines, bis(U-terpyridines) (L). Treatment of L J. ZHENG, J. ZHOU, K. YU, X. GE and S. YU, Chin. J. Catal., 2006, 4+ with [(tpy)RuCl3] afforded [(tpy)Ru(L)Ru(tpy)] . A 27, (6), 465–467 star-shaped tris(U-terpyridine) and [{(tpy)Ru}3(tris(U- Catalyst-enhanced CVD of Pt, Pd and Pd-Pt bilayer 6+ terpyridine))] were also obtained. The Ru complexes films on polyimide using N2 and O2 as the carrier were light-emitting upon excitation at 340 nm, with gases was studied at 220–300ºC under reduced or broad emission maxima between 400–500 nm. normal pressure. The films were deposited at a rate of 70–80 nm h–1. When a mixture of Pt complex and Pd ELECTROCHEMISTRY complex was used as precursors in the same chamber, only Pt was deposited. Sequential deposition of Pd Electrochemical Polymerization of Acetylene on and Pt metals formed a Pd-Pt bilayer. Rh Electrodes Probed by Surface-Enhanced Raman Spectroscopy Tarnishing Resistance of Silver–Palladium Thin G.-K. LIU, B. REN, D.-Y. WU, J.-M. LIN, R.-A. GU and Z.-Q. TIAN, Films J. Electroanal. Chem., 2006, 594, (2), 73–79 M. DORIOT-WERLÉ, O. BANAKH, P.-A. GAY, J. MATTHEY and P.- The electrochemical behaviours of C2H2 (1) on a A. STEINMANN, Surf. Coat. Technol., 2006, 200, (24), roughened Rh electrode in 0.1 M HClO4 were studied 6696–6701 by a combination of CV and SERS. On both rough- Thin Ag–Pd films (1) were deposited by magnetron ened and smooth Rh surfaces, a clear loop in the cosputtering from Pd and Ag targets. Increasing Ar cyclic voltammogram was present in the negative gas pressure and substrate temperature caused a dras- potential region. However, a surface species Raman tic decrease of the specular reflectivity of (1). At signal was only observed for the roughened Rh sur- constant deposition conditions the reflectivity of (1) face. The resemblance of the detected signal to that of decreased with increasing Pd content. Sulfidation test polyacetylene indicates the occurrence of polymerisa- results indicated an improvement of tarnishing resis- tion of (1) at potentials more negative than –0.3 V. tance of (1) with increasing Pd content. Preparation and Characterization of

RuO2–IrO2–SnO2 Ternary Mixtures for Advanced APPARATUS AND TECHNIQUE Electrochemical Technology Hydrogen Isotope Separation by Permeation L. VAZQUEZ-GOMEZ, S. FERRO and A. DE BATTISTI, Appl. through Palladium Membranes Catal. B: Environ., 2006, 67, (1–2 ), 34–40 M. GLUGLA, I. R. CRISTESCU, I. CRISTESCU and D. DEMANGE, The title coatings (1) were prepared by a thermal J. Nucl. Mater., 2006, 355, (1–3), 47–53 decomposition method, requiring an oxidative pyrol- Based on an experimentally verified mathematical ysis step of precursor salt deposits at 480ºC. The model, a computational study was performed to show coating compositions were: IrxRu0.34–xSn0.66O2 (x the net isotope effects in permeate and bleed flows nominal values = 1.7, 3.7, 7.3, 11.6, 17.9, 23.3, 28.4, when feeding a Pd permeator with H isotope mix- 31.6 and 33.5%). (1) were deposited on Ti supports. tures under different feed and permeate pressures. A compromise between catalytic properties and wear The feasibility of H isotope permeation as a method resistance was found with coatings containing ~ 20% for separation is discussed with regard to the process of Ir (hence ~ 15% of Ru). control for a single permeator or a cascade.

Platinum Metals Rev., 2006, 50, (4) 208 Improved Photocatalytic Deposition of Palladium Effect of Carbon Nanotubes on Activity of Rh-Ce-

Membranes Mn/SiO2 Catalyst for CO Hydrogenation to X. LI, Y. FAN, W. JIN, Y. HUANG and N. XU, J. Membrane Sci., Oxygenates 2006, 282, (1–2), 1–6 L. HUANG, W. CHU, J. HONG and S. LUO, Chin. J. Catal., 2006, A TiO2 support was immersed into a photocatalytic 27, (7), 596–600 deposition bath (PdCl2, HCl, EDTA, deionised H2O). The catalytic performance of C nanotubes (CNTs)- Then the TiO2 membrane was lifted out, and subse- promoted Rh-Ce-Mn/SiO2 (1) for CO hydrogenation quently a thin liquid film was formed on the TiO2 to oxygenates was studied. The CNTs improved the surface. The liquid film-coating was directly irradiated dispersion of Rh and increased the active compo- at room temperature. A tubular Pd membrane (0.4 nents on the surface of (1). The amount of strongly μm thickness) was synthesised, which exhibited high –6 –2 –1 –1 adsorbed H2 or CO on the surface of (1) was H2 permeance of 4.8 × 10 mol m s Pa and increased. The results of CO hydrogenation showed H2/N2 selectivity of 120 at 704 K. that the CNTs enhanced the activity of (1). HETEROGENEOUS CATALYSIS Ruthenium Hydroxide on Magnetite as a Naphthalene Oxidation over Vanadium-Modified Magnetically Separable Heterogeneous Catalyst for Liquid-Phase Oxidation and Reduction Pt Catalysts Supported on γ-Al2O3 E. N. NDIFOR, T. GARCIA and S. H. TAYLOR, Catal. Lett., 2006, M. KOTANI, T. KOIKE, K. YAMAGUCHI and N. MIZUNO, Green 110, (1–2), 125–128 Chem., 2006, 8, (8), 735–741 Ru(OH) /Fe3O4 (1) can be used as the catalyst for: Pt/γ-Al2O3 catalysts (1) modified by V were pre- x pared and then tested for the complete oxidation of (a) aerobic oxidation of alcohols; (b) aerobic oxida- naphthalene. Only 0.5% V promoted the activity of tion of amines; and (c) reduction of carbonyl compounds to alcohols using 2-propanol as a H 0.5% Pt/γ-Al2O3. The enhancement is related to the presence of a more easily reducible V species coupled donor. Separation of (1) from the product(s) was eas- with the enhanced number of surface Pt sites. The ily achieved with a permanent magnet, and > 99% of reduced activity of (1) with higher V content (1–12%) (1) could be recovered for each reaction. (1) recov- is attributed to the presence of crystalline V2O5. ered after these reactions could be reused.

Pd and Pt Catalysts Supported on Carbon-Coated HOMOGENEOUS CATALYSIS Monoliths for Low-Temperature Combustion of A User-Friendly, All-Purpose Pd-NHC (NHC = N- Xylenes Heterocyclic Carbene) Precatalyst for the Negishi A. F. PÉREZ-CADENAS, F. KAPTEIJN, J. A. MOULIJN, F. J. MALDONADO-HÓDAR, F. CARRASCO-MARÍN and C. MORENO- Reaction: A Step Towards a Universal Cross- CASTILLA, Carbon, 2006, 44, (12), 2463–2468 Coupling Catalyst C-coated monoliths (1) were prepared from poly- M. G. ORGAN, S. AVOLA, I. DUBOVYK, N. HADEI, E. A. B. furfuryl alcohol coated cordierite structures. Pd and KANTCHEV, C. J. O’BRIEN and C. VALENTE, Chem. Eur. J., 2006, Pt catalysts were obtained by equilibrium impregna- 12, (18), 4749–4755 tion of (1). The catalysts were pretreated in H2 at The air stable, highly active, precatalyst PEPPSI-IPr 300ºC. The Pt catalysts were more active in xylene (PEPPSI = pyridine-enhanced precatalyst prepara- combustion. Complete combustion was reached at tion, stabilisation and initiation; IPr = 150–180ºC with a total selectivity to CO2 and H2O. diisopropylphenylimidazolium derivative) can be used Combustion of m-xylene was easier than p-xylene. with PdCl2 for the Negishi reaction. Organohalides and routinely used pseudohalides were excellent cou- A Selective Synthesis of Acetic Acid from Syngas pling partners. General laboratory techniques are employed for all of the reactions. over a Novel Rh Nanoparticles/Nanosized SiO2 Catalysts Open-Vessel Microwave-Promoted Suzuki W.-M. CHEN, Y.-J. DING, D.-H. JIANG, T. WANG and H.-Y. LUO, Catal. Commun., 2006, 7, (8), 559–562 Reactions Using Low Levels of Palladium Microemulsions of polyethyleneglycol-p-nonylphenyl Catalyst: Optimization and Scale-Up ether in cyclohexane were prepared by injecting aque- N. E. LEADBEATER, V. A. WILLIAMS, T. M. BARNARD and M. J. ous RhCl3 solutions. Rh–N2H4 nanoparticles (1) were COLLINS, Org. Process Res. Dev., 2006, 10, (4), 833–837 formed by addition of hydrazine hydrate. (1) were Suzuki couplings using low Pd catalyst concentra- separated from the oil phase. After the supernatant tions (1–5 ppm Pd) with microwave heating have was decanted, (1) were washed, dried and calcined. Rh been transferred from sealed-vessel to open-vessel nanoparticles/nanosized SiO2 (2) was prepared by reaction conditions. The procedure is scalable from grinding the resultant Rh nanoparticles with nano- the mmol to the 1 mol scale. The reactions can be sized SiO2. The total selectivity of acetic acid and performed in air and are run using H2O/EtOH as the ethyl acetate in the oxygenate products of CO hydro- solvent system. The couplings are complete within 20 genation on (2) reached 74.8%. min of heating at reflux.

Platinum Metals Rev., 2006, 50, (4) 209 Highly Enantioselective Fluorination Reactions of FUEL CELLS β-Ketoesters and β-Ketophosphonates Catalyzed Preparation of High Catalyst Utilization Electrodes by Chiral Palladium Complexes for Polymer Electrolyte Fuel Cells Y. HAMASHIMA, T. SUZUKI, H. TAKANO, Y. SHIMURA, Y. J. M. SONG, S. SUZUKI, H. UCHIDA and M. WATANABE, Langmuir, TSUCHIYA, K. MORIYA, T. GOTO and M. SODEOKA, Tetrahedron, 2006, 22, (14), 6422–6428 2006, 62, (30), 7168–7179 Pt/C black (high surface area) and Nafion ionomer Using chiral Pd enolates as key intermediates, high- solution were heated in an autoclave at 200ºC, fol- ly enantioselective fluorination reactions (≤ 98% ee) lowed by quenching to form an ink (1). A cathode of β-ketoesters and β-ketophosphonates have been prepared with (1) exhibited high catalyst utilisation carried out. These reactions were carried out in alco- and improved gas diffusivity. The autoclave treatment holic solvents without any need to exclude air and promoted an effective introduction of Nafion H2O. Transformation of the fluorinated products was ionomer into primary pores of the Pt/C black successfully achieved. agglomerates.

Nitrogen Ligand-Containing Rh Catalysts for the Characteristics of a Platinum Black Catalyst Layer Polymerization of Substituted Acetylenes with Regard to Platinum Dissolution Phenomena I. SAEED, M. SHIOTSUKI and T. MASUDA, J. Mol. Catal. A: Chem., 2006, 254, (1–2), 124–130 in a Membrane Electrode Assembly Rh complexes having a phenoxy-imine ligand, a β- K. YASUDA, A. TANIGUCHI, T. AKITA, T. IOROI and Z. SIROMA, J. Electrochem. Soc., 2006, 153, (8), A1599–A1603 diiminate ligand, and NH3 ligands were used in the polymerisation of substituted acetylenes. Polymers in Pt dissolution and precipitation in a PEM of a MEA moderate to high yields with high molecular weights was studied using a potential holding experiment at were afforded. A cocatalyst was not required in these 1.0 V vs. a reversible H electrode and HRTEM. The electrochemically active surface area decreased systems in contrast to [Rh(nbd)Cl]2 and [Rh(cod)Cl]2. In the case of the phenoxy-imine catalysts, the nbd- depending on the holding time, and Pt deposition was bearing one was more active than the cod-bearing observed in the PEM near a cathode catalyst layer. counterpart, while the opposite trend was observed However, Pt dissolution and deposition out of the for the β-diiminate catalysts. catalyst layer were greatly reduced when a Pt black electrode was employed. Using a double-layered cata- The Hydrogenation of Cinnamaldehyde by lyst layer, Pt redeposited on the Pt black surface. Supported Aqueous Phase (SAP) Catalyst of Characterization of Membrane Electrode RhCl(TPPTS) : Selectivity, Kinetic and Mass 3 Assembly for Fuel Cells Prepared by Electrostatic Transfer Aspects Spray Deposition K. NUITHITIKUL and J. M. WINTERBOTTOM, Chem. Eng. Sci., 2006, 61, (18), 5944–5953 M. UMEDA, S. KAWAGUCHI and I. UCHIDA, Jpn. J. Appl. Phys., The hydrogenation of trans-cinnamaldehyde was Part 1, 2006, 45, (7), 6049–6054 A Pt/C MEA prepared by electrostatic spray depo- catalysed by RhCl(TPPTS)3/SiO2 (1) (TPPTS = trisodium salt of tris(m-sulfophenyl)phosphine). The sition was installed in a fuel cell and demonstrated as hydrogenation is selective at the C=C bonds in cin- high a performance as that of a MEA prepared by air- namaldehyde giving hydrocinnamaldehyde as the spraying. The cross-sectional morphology of the main product. High selectivity (99.9%) was achieved catalyst layer explained the coupling strength in a by employing a low initial concentration of cin- peel-off test and the dependence of current-voltage characteristics on catalyst layer thickness. namaldehyde. Optimum H2O content of (1) giving maximum activity occurred when the pore volume of the supports was completely filled with H2O. Synthesis, Characterization, and Electrocatalytic Activity of PtBi and PtPb Nanoparticles Prepared Isomerizing-Hydroboration of the by Borohydride Reduction in Methanol Monounsaturated Fatty Acid Ester Methyl Oleate C. ROYCHOWDHURY, F. MATSUMOTO, V. B. ZELDOVICH, S. C. K. Y. GHEBREYESSUS and R. J. ANGELICI, Organometallics, 2006, WARREN, P. F. MUTOLO, M. BALLESTEROS, U. WIESNER, H. D. 25, (12), 3040–3044 ABRUÑA and F. J. DiSALVO, Chem. Mater., 2006, 18, (14), [Ir(cyclooctene)2Cl]2/dppe catalysed the hydrobora- 3365–3372 tion of methyl oleate (18:1) with pinacolborane to give PtPb and PtBi nanoparticles displayed enhanced a product (1) in which the boronate ester group is in electrochemical activity toward formic acid and the terminal (C18) position. The formation of (1) MeOH oxidation as compared with those of Pt and shows that the catalyst promotes both the isomerisa- PtRu nanoparticles. The electrocatalytic activity of the tion of the double bond from the 9,10-position of PtPb nanoparticles was studied as a function of soni- 18:1 to the terminal position and the selective hydro- cation time of the catalyst ink, and morphology boration of this isomer to give (1) in 45% yield. This changes were followed by SEM. The activity of the tandem reaction is claimed to have the potential to be PtPb catalyst initially increased with sonication time, capable of converting all isomers of 18:1 into (1). peaked at 6 h, and then decreased.

Platinum Metals Rev., 2006, 50, (4) 210 DOI: 10.1595/147106706X154602 NEW PATENTS METALS AND ALLOYS Rhodium-Containing Catalysts CELANESE INT. CORP European Appl. 1,694,435 Palladium-Containing Silver Alloy A method of producing a catalyst or precatalyst for KYOCERA CORP Japanese Appl. 2006-037,183 making alkenyl alkanoates includes four aspects A Pd-containing Ag alloy (1), having a blackish which may be applied separately or in combination. colour and a metallic lustre, with good resistance to The first aspect includes a Pd/Au catalyst or precata- sulfur is claimed. (1) contains (in wt.%): 10–40 Sn, lyst with Rh on a support material (1), which may 1–10 Pd and 50 Ag. Further, if necessary, either one ≥ optionally be calcined. The second aspect is that (1) or both of (in wt.%): 1–5 Co and 1–5 In, may be may be layered, with one layer free of catalytic com- added. (1) may be used for ornamental objects. ponents; the third aspect is that (1) may contain zirconia; the fourth aspect is that the catalytic compo- ELECTRODEPOSITION AND SURFACE nents may be substantially Cl-free. COATINGS 1,2-Diamino-3-methylcyclohexane Production Fabrication of a Rocket Engine Chamber BASF AG World Appl. 2006/066,762 AEROJET-GEN. CORP U.S. Appl. 2006/0,124,469 A method for producing 1,2-diamino-3-methylcy- A method for manufacturing a rocket engine com- clohexane and/or 1,2-diamino-4-methylcyclohexane bustion chamber uses electrodeposition to form a is disclosed. 2,3- and/or 3,4-diaminotoluene is react- uniform layer of Ir on a mandrel. A controlled atmos- ed with H2 under high pressure (100–300 bar) and phere plasma spray (CAPS) process is then used to high temperature (130–220ºC), in the presence of a deposit a structural refractory layer such as metals or Rh/γ-alumina catalyst containing 1–25 wt.% Rh rela- alloys of Re, Mo, W, Ta, or a mixture, onto the Ir tive to substrate. A dialkyl ether and/or an alicyclic layer. A second CAPS process applies a transition ether is used as the solvent, with 5–500 mol% NH3 refractory layer containing Nb or Ta. added relative to substrate. APPARATUS AND TECHNIQUE Preparation of Palladium Biocatalysts Neutron Detector Assembly with Rhodium Emitters CNRS World Appl. 2006/087,334 A. Y. C. CHENG U.S. Appl. 2006/0,165,209 A bacterium strain (1) having a gene coding for a A system to measure neutron flux in a nuclear fuel membrane-bound [NiFe] hydrogenase (2), or mem- assembly includes at least two detectors of differing brane extracts (3) containing (2) are used for the length, made from Rh. Each detector has an outer preparation of metallic biocatalysts containing Pd, Pt, sheath forming an inner volume into which an inner Ru, Rh or Ir. For example, a solution of Pd(II) is emitter is placed, which is structured to accept neu- brought into contact with (1) or (3) to allow initial trons and provide an electrical signal. The signal is sorption of Pd(II), then H2 gas is bubbled through to transmitted to an exterior lead by at least one lead precipitate Pd in reduced form. The resulting Pd(0) connected to each emitter. particles are cheaper to produce, have smaller particle size and higher catalytic activity than other methods. Material for Air Bag Inflator Primer TANAKA KIKINZOKU KOGYO KK Electrochemical Palladium Catalysed Reaction Japanese Appl. 2006-046,797 COMBIMATRIX CORP U.S. Appl. 2006/0,151,335 A Pd alloy (1) for an air bag inflator primer having An isolated Pd(0) catalysed reaction, preferably a high specific resistance value, good workability, and Heck reaction, is performed on an electrode array excellent corrosion resistance is claimed. (1) contains device. The electrodes are immersed in a solution of 5–30 wt.% Mo and the balance Pd. (1) is used as a a transition metal catalyst system containing Pt or Pd, fuse for an air bag inflator and can be manufactured plus a confining agent such as an oxidant to convert at low cost, compared with alternative materials. Pd(0) to Pd(II), to limit diffusion of catalyst. Catalyst is regenerated by biasing one or more electrodes.

HETEROGENEOUS CATALYSIS Spongy Platinum Nanoparticles Water Gas Shift Reactor UNIV. MIYAZAKI Japanese Appl. 2006-045,582 JOHNSON MATTHEY PLC British Appl. 2,423,489 Spongy nanoparticles (1) containing Pt are fabricat- A water gas shift reactor is claimed which includes ed by reducing a chloroplatinic acid salt with a two different catalyst zones arranged in close proxim- borohydride salt, in the presence of two ionic or non- ity. The temperature of the gases leaving the first ionic surfactants. (1) have a porous single crystal zone is the same as that of the gases entering the sec- structure with outer diameter 20–100 nm, with rod- ond. The first zone catalyst has positive-order kinetics like frames of diameter 1.5–4 nm interconnected in 3 and consists of Au dispersed on ceria or zirconia, and dimensions, to give fine pores of size 0.3–2 nm. (1) the second zone catalyst has negative-order kinetics can be used as catalysts for fuel cells or exhaust gas and consists of Pt dispersed on ceria or zirconia. treatment, and in electrodes or sensors.

Platinum Metals Rev., 2006, 50, (4), 211–212 211 HOMOGENEOUS CATALYSIS Superconducting Oxide Material NIPPON STEEL CORP Japanese Appl. 2006-062,896 2-Substituted Propionic Acids and Amides A bulk oxide superconductor, high in critical cur- PHOENIX CHEM. British Appl. 2,422,603 rent density, consists of particles of BaCeO3 or A process for preparation of 2-substituted propi- Ba(Ce1– M )O3– (0 < a < 0.5 and 0 b 0.5, M is a onic acids and amides includes converting a substrate a a b ≤ ≤ metal such as Zr, Hf, Sn) dispersed as pinning centres by enantioselective hydrogenation. Preferred hydro- in a crystal of RE1+ Ba2- Cu3O (0 x 0.1 and 6.5 genation catalysts include a ligand containing a x x y ≤ ≤ ≤ y 7.2, RE is at least one element selected from the metallocene group with a chiral P or As substituent, a ≤ group consisting of Y, La, Nd, Sm, Eu, Gd, Dy, Ho, linker group such as a ferrocene or a diphenyl ether, Er, Tm, and Yb). One or both of Pt and Rh are and a metal chelating group. A metal such as Rh, Ru, added, between 0.1–5 wt.% of the material. Ir, Pd, Pt or Ni is coordinated to the ligand.

FUEL CELLS MEDICAL USES Antitumour Compositions with Platinum Derivatives Palladium-Cobalt Particles as Electrocatalysts SCHERING CORP World Appl. 2006/057,998 BROOKHAVEN SCI. ASSOC. World Appl. 2006/086,457 Combination compositions including a Pt-based Pd/Co particles (1) are used in O2-reducing cath- compound, such as satraplatin, along with another odes for fuel cells. (1) may be in the form of chemotherapeutic agent such as temozolomide or nanoparticles of diameter between ~ 3–10 nm and lonafarnib are claimed. The combinations can be used may be supported on C black, graphitised C, graphite for the prevention or treatment of various cancers in or activated C. (1) may have a binary alloy composi- human patients. The pharmaceutical composition can tion represented by the formula Pd1–xCox, where x is be formulated into a single oral dosage form with a between ~ 0.1–0.9. pharmaceutically acceptable carrier or administered as separate components. Anode Electrode NITTO DENKO CORP Japanese Appl. 2006-019,133 Noble Metal Dental Alloy An anode and a membrane-electrode junction are P. J. CASCONE U.S. Appl. 2006/0,147,334 claimed which can reduce the cost of a solid polymer A dental alloy containing Ru which can be cast or fuel cell, by improving the output of a Pt catalyst used machined into a dental prosthesis consists of > for the anode. The catalyst layer includes Pt and a 25% metal selected from Ru, Pt, Pd, Ir, Os and Au, proton conductive polymer carried on a porous base. with > 15% or the greater portion being Ru, plus Particles of diameter < 100 nm, selected from Si 15–30% Cr. The balance consists of a metal cho- oxide, Ti oxide or Al oxide are also included. sen from Fe, Ni and Co. Optionally, other elements can be added (in %): ≤ 15 Ga, ≤ 5 Si, ≤ 1 ELECTRICAL AND ELECTRONIC B; and/or ≤ 5 Nb, Ta or Re. ENGINEERING New Gene Expression Inhibitor Platinum(II) Complexes in OLEDs SCI. UNIV. TOKYO Japanese Appl. 2006-045,131 BASF AG European Appl. 1,692,244 A new Pt-containing compound (1) capable of Pt(II) complexes (1) are used as emitter molecules inhibiting gene expression based on a specific in OLEDs. (1) may include phosphine, bathophen or sequence is described. The structure of (1) includes bipyridyl ligands, which may contain CN, acetylide, two 5- or 6-membered rings each containing at least thiocyanate or isocyanate groups plus aryl, alkyl, het- one N atom, with one N atom in each ring binding to eroaryl or alkenyl groups. The OLEDs can be used in Pt. The rings may be pyridine, pyrazine, pyrimidine, various devices including static screens for computers triazine, thiazole or imidazole rings. (1) is combined and televisions, or in screens for mobile devices such with a nucleic acid sequence related to a specific gene as mobile phones, laptops and vehicles. to achieve gene expression inhibition.

Recording Medium and Reproducing Method High Frequency Treatment Tool for Endoscope KYOTO UNIV. Japanese Appl. 2006-039,225 PENTAX CORP Japanese Appl. 2006-068,407 A high density recording medium (1) for digital A high-frequency treatment tool consists of a stain- holograms contains a recording layer consisting of a less steel or W alloy electrode (1), partly or completely thin film of nanoparticles (2) containing Pt, Pd or Ni, coated with Pt or Au metal or their alloys, by plating, with average particle size and film thickness of 3–20 vacuum evaporation or ion plating. (1) is arranged at nm. (1) uses laser light from near-UV to visible wave- the distal end of an electrically insulated sheath insert- lengths to give instant recording and good stability. ed into the treatment tool insertion channel of an Information is recorded as a pattern of interference endoscope. (1) can be used to cauterise living tissue, fringes between aggregated and non-aggregated without causing viable tissue to stick to it even under regions of (2), induced by two beams of laser light: an conditions of high-frequency treatment, and can be information beam and a reference beam. used continuously and repeatedly at high frequency.

Platinum Metals Rev., 2006, 50, (4) 212 NAME INDEX TO VOLUME 50 Page Page Page Page Abbott, E. H. 207 Bercaw, J. 171 Chen, R. 48 Drozdzewski, P. 207 Abruña, H. D. 210 Bernhard, S. 47 Chen, W.-M. 209 Du, Y. W. 46 Adams, R. D. 152 Betancourt, P. 48 Chen, Y.-W. 105 Du, Z. 104 Ager, D. J. 54 Bhagwat, S. V. 152 Chianese, A. 171 Duan, C.-G. 153 Ahn, Y. R. 208 Birss, V. I. 153 Chisholm, J. D. 106 Dubovyk, I. 209 Akita, T. 210 Boardman, A. 67 Chiuzbaian, S. G. 150 Dunleavy, Alapieti, T. 13 Boelhouwer, C. 36 Choudhury, B. 151 J. K. 52, 110, 156 Alexeev, O. S. 152 Bogart, K. H. A. 153 Chu, W. 209 Dupont, J. 153 Amaratunga, Bolton, C. 42 Chung, S.-R. 207 Dziallas, M. 208 G. A. J. 207 Børve, K. J. 207 Ciardelli, C. 178 Amiridis, M. D. 152 Bottini, S. 152 Cimino, S. 64 Echegoyen, L. 150 Anandan, S. 47 Bowker, M. J. 24, 179 Cipriano, G. 42 Eleuterio, H. S. 36 Anderson, B. M. 207 Boyko, V. 104 Cohen-Karni, I. 46 Emrick, T. 49 Anderson, J. A. 20 Braucks, R. S. 177 Coldea, M. 150 Ernst, W. 39 Angelici, R. J. 210 Britovsek, G. J. P. 150 Collins, M. J. 209 Evans, C. L. 104 Apanel, G. 40 Bronstein, L. 25 Compton, R. G. 105 Arblaster, J. W. 97, 118 Brown, R. 196 Cottington, I. 205 Fagalde, F. 151 Arm, K. J. 104 Browning, D. 43 Courtois, X. 178 Fan, Y. 209 Arteaga, G. 195 Bruneau, C. 95 Crabtree, R. H. 171 Feast, J. M. 36 Ashfield, L. 95 Bruno, C. 105 Cristescu, I. 208 Fernández, M. B. 152 Ashton, S. V. 205 Bruss, A. J. 153 Cristescu, I. R. 208 Fernandez-Ruiz, P. 44 Athawale, A. A. 152 Buchmeister, M. R. 36 Cristiani, C. 106 Ferreira, F. C. 153 Aubuchon, S. R. 153 Buchwald, S. L. 106 Crofton, J. 153 Ferreira, J. L. 104 Avola, S. 209 Burch, R. 24, 178 Crowhurst, J. C. 104 Ferreira, P. J. 49 Azambuja, V. M. 150 Crowson, P. 42 Ferro, S. 208 Cabeza, G. F. 151 Fierro, J. L. G. 152 Baboo, R. 106 Cagran, C. 144 Damiani, D. E. 152 Finkel’stein, E. 36 Bahnemann, D. 24 Cai, P. 48 Danheiser, R. L. 48 Fischer, B. 158 Bailey, G. C. 36 Calderon, N. 36 Danylyuk, O. 104 Fischer, N. O. 49 Bailie, J. 177 Cameron, D. S. 38 De Battisti, A. 208 Fischmeister, C. 95 Balaban, A. T. 36 Cao, B. Y. 207 de Vries, A. H. M. 54 Fisk, Z. 207 Baldwin, E. 105 Cao, Y. 47 de Vries, J. G. 54 Fontana, J. 134 Ball, S. C. 202, 203 Captain, B. 152 De, G. S. 2 Fontana, M. 112 Ballarin, B. 105 Carano, M. 105 Delmas, M. 47 Frey, G. D. 104, 150 Ballesteros, M. 210 Carrasco-Marín, F. 209 Demange, D. 208 Fruchart, D. 150 Banakh, O. 208 Casci, J. L. 23 Demonceau, A. 36 Fu, Q. J. 21 Banks, C. E. 105 Caseri, W. 112 Demoulin, O. 65, 66 Fübi, M. 39 Banks, R. L. 36 Castellani, N. J. 151 Deubel, D. V. 107 Fujii, M. 207 Bard, A. J. 105 Cawthorn, R. G. 13, 130 Devi, R. N. 24 Fujita, M. 207 Barnard, T. M. 209 Centi, G. 22 Diels, G. 49 Fujita, T. 48, 207 Basini, L. 64 Chan, J. Y. 207 Ding, Y.-J. 209 Fürstner, A. 36 Basset, J. M. 36 Chaplin, B. P. 152 Dirnberger, T. 208 Furukawa, K. 49 Batchelor-McAuley, Chatani, N. 95 DiSalvo, F. J. 210 Furuta, H. 150 C. 105 Chatterjee, D. 2 Dixneuf, P. H. 36, 95 Baturina, O. A. 153 Chatterjee, U. K. 47, 104 Dolgoplosk, B. A. 36 Gagné, M. 171 Bauer, B. 203 Chauvin, Y. 35 Doriot-Werlé, M. 208 Galanski, M. 49 Beamson, G. 46 Chen, C.-C. 105 Dos Santos, D. S. 150 Gale, P. A. 47 Bellussi, G. 23 Chen, C. Y. 107 Dragutan, I. 36, 81 Garcia, T. 209 Bencze, L. 36 Chen, J. 48 Dragutan, V. 36, 81 García, M. F. 20

Platinum Metals Rev., 2006, 50, (4), 213–216 213 Page Page Page Page

Gasteiger, H. A. 49 Hester, H. R. 151 Janssens, T. 194 King, D. 38 Gates, B. 194 Heymann, G. 46 Jarvi, T. 202 Kinyanjui, J. M. 151 Gay, P.-A. 208 Hinde, P. 177 Jaswal, S. S. 153 Kitamura, M. 95 Gayatri 106 Hine, P. J. 46 Jaworska, M. 47 Kitano, M. 24 Ge, X. 208 Hirano, M. 96 Jazzar, R. F. R. 95 Klak, J. 47 Gelesky, M. A. 153 Hocker, H. 36 Jensen, V. R. 207 Klotsman, S. M. 29 Gelin, P. 65 Hoffmann, R.-D. 46 Jia, L. 105 Ko, F.-H. 105 Ghaleb, R. A. 65 Höhn, A. 208 Jiang, D.-H. 209 Kocha, S. 49 Ghebreyessus, K. Y. 210 Holmes, A. B. 48 Jiang, N. 106 Koike, T. 209 Giani, L. 106 Holmes, K.-A. 153 Jiang, S. P. 49 Koltsakis, G. 178 Girishkumar, G. 107 Hong, J. 209 Jin, W. 209 Komiya, N. 95 Glugla, M. 208 Hong, R. 49 Jin, Z.-L. 153 Konagawa, J. 150 Göbel, U. 178 Hostyn, S. 49 Jo, S. M. 208 Kondo, K. 152 Goldsmith, J. I. 47 Hotanen, U. 106 Johnson, A. 42 Kondo, T. 95 Golunski, S. E. 194 Hou, Q. 47 Johnston, P. 20 Kongkanand, A. 107 Goncharov, A. F. 104 Houel, V. 177 Johrendt, D. 46 Kopperud, T. 103 Goto, T. 210 Hrapovic, S. 47 Joliot-Curie, F. 98 Korotcov, A. 151 Gottesfeld, S. 41 Huang, L. 209 Joliot-Curie, I. 98 Kosarev, V. F. 22 Gray, P. 41 Huang, Y. 209 Jones, T. 67 Kotani, M. 209 Greig, D. 46 Huang, Y.-S. 151 Jones, T. G. J. 105 Kotobuki, M. 48 Grela, K. 106 Hugh, M. 119 Jurczakowski, R. 104 Koyima, S. 96 Griffith, W. P. 77 Hummel, J. 208 Krummrich, S. 42 Groppi, G. 106 Hummel, K. 36 Kadish, K. M. 150 Kruszynski, R. 47 Groszek, A. J. 46 Hungria, A. B. 152 Kajihara, M. 46 Kubiak, M. 207 Grubbs, R. H. 35, 95 Hunt, L. 205 Kakiuchi, F. 95 Kündig, E. P. 95 Grunwaldt, J.-D. 178 Huppertz, H. 46 Kalantari, D. J. 105 Kurokawa, N. 46 Gu, R.-A. 208 Hurst, S. K. 207 Kalchenko, V. 104 Kuwabata, S. 107 Gulajski, L. 106 Hutchings, G. 22, 194 Kamat, P. 107 Kuwai, T. 150 Guldi, D. M. 150 Kamiya, N. 107 Kwok, T. J. 48 Gummert, G. 44 Igarashi, A. 152 Kantchev, E. A. B. 209 Kwon, H. J. 179 Guo, C. 104 Iida, H. 152 Kapteijn, F. 209 Kwon, Y. H. 49 Guo, F. 151 Iida, J. 207 Katre, P. P. 152 Guy, K. A. 152 Ikariya, T. 107 Katz, N. E. 151 la O’, G. J. 49 Gwak, J. 152 Ikehara, T. 152 Katz, T. J. 36 La Parola, V. 152 Ikeno, T. 150 Kawaguchi, S. 210 Lalik, E. 46 Haber, J. 46 Iljana, M. 13 Kawaguchi, Y. 39 Lambert, R. 26, 196 Hadei, N. 209 Ilkenhans, T. 22 Kawamara, M. 44 Lampeka, Y. 104 Hamashima, Y. 210 Imamoglu, Y. 36 Kawano, M. 207 Lang, C. 15 Hanks, J. 151 Inoue, A. 46 Keppler, B. K. 49 Lasia, A. 104 Hargreaves, J. 195 Ioroi, T. 210 Khair, M. 177 Latha, S. 47 Hartinger, C. G. 49 Ishihara, A. 107 Khinast, J. G. 48 Law, D. J. 150 Hartnig, C. 203 Isikawa, Y. 150 Khokhlov, A. 203 Leadbeater, N. E. 209 Hatchett, D. W. 151 Isnard, O. 150 Khosravi, E. 36 Lebedeva, N. P. 49 Hayashi, Y. 207 Itoh, K. 95 Kiely, C. 196 Lee, J. W. 105 Heinen, J. 43 Ivin, K. J. 36 Kihn, Y. 47 Lee, K. 107 Helminen, J. 106 Iwasawa, Y. 48 Kilcoyne, S. H. 46 Légaré, P. 151 Henry, C. R. 24, 26 Kilday, P. 196 Lemaire, J. 177 Herdtweck, E. 150 Jackson, K. M. 15 Kim, D. Y. 208 Lennon, D. 195 Hérisson, J.-L. 35 Jackson, S. D. 24 Kim, H.-I. 49 Leslie, W. 104 Herrmann, Jacobs, P. 23 Kim, Y.-G. 151 Li, F. 47 W. A. 36, 104, 150 Janssen, G. J. M. 49 King, A. E. 153 Li, Q. 46

Platinum Metals Rev., 2006, 50, (4) 214 Page Page Page Page

Li, W. 152 Mauger, C. 106 Noels, A. F. 36 Ralph, T. R. 200 Li, X. 171, 200, 209 Meelich, K. 49 Nolan, S. P. 36 Rehren, Th. 120 Liao, S. 153 Mei, W.-N. 153 Noyori, R. 95, 107 Ren, B. 208 Light, M. E. 47 Melada, S. 22 Nuithitikul, K. 210 Rendina, L. M. 104 Lightner, V. 44 Mellace, M. G. 151 Nuyken, O. 48 Reynolds, J. R. 151 Lin, H.-Y. 105 Melo, L. 48 Riecken, J. F. 46 Lin, J.-M. 208 Merker, J. 158 O’Brien, C. J. 209 Risch, N. 208 Lin, M. 105 Michrowska, A. 106 Ohkubo, K. 69 Roberts, W. 194 Lipkowski, J. 104 Midgley, P. A. 152 Okajima, K. 49 Rodik, R. 104 Liu, C. 107 Mignani, G. 106 Organ, M. G. 209 Rodriguez, K. J. 107 Liu, G.-K. 208 Mino, T. 48 Ota, K.-I. 107 Rodríguez, R. 48 Liu, T.-F. 105 Mitra, A. 2 Ou, Z. 150 Rohl, R. 47 Liu, Y. 47 Mitsudo, T. 95 Ozeki, T. 207 Rolf, S. 204 Liu, Z. 49 Mitsushima, S. 107 Rombouts, G. 49 Livingston, A. G. 153 Miura, S. 69 Paatero, E. 106 Rooney, J. J. 36 Lloyd, A. 38 Mizuno, N. 209 Pacurariu, R. 150 Rossi, M. 194 Loboda, O. 207 Mizushima, T. 150 Palazzi, A. 105 Rotello, V. M. 49 Loones, K. T. J. 49 Mohri, T. 69 Pan, M. 49 Roundy, E. 152 Louzguine-Luzgin, Mol, J. C. 36 Panarello, A. P. 48 Roy, A. G. 107 D. V. 46 Moldovan, M. 207 Paolucci, F. 105 Roychowdhury, C. 210 Lowry, M. S. 47 Monari, M. 105 Park, C. R. 208 Rudenko, V. K. 29 Lu, M. 46 Mondal, K. 47, 104 Park, G. S. 204 Rugmini, S. 196 Lu, Q. 150 Morales, M. 150 Parmon, V. N. 22 Rushforth, R. 197 Luo, H.-Y. 209 More, K. 105 Pascal, R. A. 47 Luo, S. 209 Moreno-Castilla, C. 209 Pascut, L. G. 150 Sabirianov, R. F. 153 Luo, Z. 49 Morgan, D. 49 Pawelec, B. 152 Sadigh, B. 104 Luong, J. H. T. 47 Moriya, K. 210 Peng, J. 47 Sadykov, V. A. 64 Lupton, D. F. 158 Morrall, P. G. 104 Pérez-Cadenas, A. F. 209 Saeed, I. 210 Lux, K. W. 107 Mortreux, A. 36 Perng, T.-P. 207 Saito, A. 48 Moulijn, J. A. 209 Persson, K. 66 Sakamoto, K. 46 Machado, G. 153 Muneer, M. 24 Petch, M. I. 21 Sakamoto, M. 48 Madhavan, J. 47 Murahashi, S.-I. 95 Peterson, E. S. 207 Salehi, A. 105 Maeda, R. 152 Murakoshi, Y. 152 Pettersson, L. J. 25 Salomons, S. 66 Maes, B. U. W. 49 Murata, K. 107 Pfaff, C. 48 Sao Joao, S. 26 Makharia, R. 49 Murty, B. S. 47, 104 Pham, L. 207 Saotome, H. 48 Makino, K. 49 Murugesan, S. 47 Piccolo, L. 26 Sarova, G. H. 150 Makkee, M. 177 Murzin, D. Yu. 178 Pinhero, P. J. 207 Sato, S. 207 Maldonado-Hódar, Musiala, M. 207 Pink, C. J. 153 Sato, Y. 48 F. J. 209 Muthuraaman, B. 47 Piqueras, C. M. 152 Savadogo, O. 107 Malecki, J. G. 47 Mutolo, P. F. 210 Podyacheva, O. Yu. 22 Schanze, K. S. 151 Malliaras, G. G. 47 Pontonnier, L. 150 Scheckenbach, C. 158 MaQuilon, S. 207 Nagashima, H. 96 Pop, V. 150 Scherer, G. 203 Marcaccio, M. 105 Naldrett, A. J. 13 Poquillon, D. 47 Schlogl, R. 23 Marcinec, B. 36 Natta, G. 36 Pöttgen, R. 46, 150 Schluga, P. 49 Markus, H. 25 Ndifor, E. N. 209 Pottlacher, G. 144 Schmehl, R. 151 Martellaro, P. 207 Nelson, A. J. 104 Poulston, S. 22 Schmidt, L. D. 106 Maruthamuthu, P. 47 Neumann, M. 150 Prins, R. 25 Schmidt, T. 203 Masuda, T. 36, 210 Neurock, M. 23 Scholz, U. 106 Matsumoto, F. 210 Niemantsverdriet, H.196 Quesada, R. 47 Schönfelder, D. 48 Matthew, J. A. D. 46 Nikfarjam, A. 105 Schrock, R. R. 35 Matthey, J. 208 Nishimura, C. 152 Rabiei, A. 105 Schuster, D. I. 150 Matveev, S. A. 29 Nishiyama, H. 95 Ragauskas, A. J. 106 Schütz, J. 150

Platinum Metals Rev., 2006, 50, (4) 215 Page Page Page Page

Seol, H.-J. 49 Sugimura, Y. 46 Tsang, M. W. S. 48 Williams, W. M. 207 Seymour, R. 27 Sulman, E. 25 Tsang, S. C. 21 Wilson, S. R. 150 Sha, J. B. 46 Sun, P. 150 Tsao, C. S. 107 Winter, A. 208 Shaikhutdinov, S. 195 Sunley, G. J. 150 Tsaprailis, H. 153 Winterbottom, J. M. 210 Shao-Horn, Y. 49 Surareungchai, W. 47 Tsuchiya, Y. 210 Witte, J. 158 Shapley, J. R. 152 Susanti, D. 151 Tsymbal, E. Y. 153 Wiyaratn, W. 47 Shekhtman, S. 195 Suwinska, K. 104 Tsymbal, L. 104 Wollaston, W. H. 77 Shen, M. 105 Suzuki, H. 96 Turner, P. 104 Wong, H. 153 Shi, J.-C. 153 Suzuki, K. 207 Twigg, M. V. 65, 179 Wu, C.-J. 105 Shi, Z. 151 Suzuki, S. 210 Wu, D.-Y. 208 Shido, T. 48 Suzuki, T. 210 Uchida, H. 48, 210 Wu, S. 151 Shimura, Y. 210 Szpunar, J. A. 151 Uchida, I. 210 Wynne, K. J. 153 Shinar, J. 151 Umeda, M. 210 Shinar, R. 151 Tada, M. 48 Xia, D. 107 Shiotsuki, M. 210 Takács, A. F. 150 Vahlas, C. 47 Xie, B. 48 Shukla, N. 107 Takahashi, K. 207 Valente, C. 209 Xiong, Y. 48 Siani, A. 152 Takano, H. 210 Valetsky, P. 25 Xu, H. 152 Silva, S. R. P. 207 Takao, T. 96 Valldor, M. 150 Xu, N. 209 Simm, A. O. 105 Takenaka, T. 46 Vassylyev, O. 48 Simonet, J. 180 Tanaka, Y. 48 Vayenas, C. 26 Yamabe-Mitarai, Y. 46 Simplicio, L. M. 66 Tandon, P. K. 106 Vazquez-Gomez, L. 208 Yamaguchi, K. 209 Singh, A. K. 106 Tang, H. 49 Venturi, M. 40 Yamamoto, Y. 95 Siroma, Z. 210 Tang, N. J. 46 Verpoort, F. 36 Yamashita, H. 48 Sjunnesson, L. 38 Tang, S. L. 46 Vigier, F. 104 Yang, P.-Y. 153 Slinker, J. D. 47 Taniguchi, A. 210 Virgilio, J. A. 48 Yap, T. 196 Smith, A. 22 Tat, F. T. 150 Vlassak, J. J. 46 Yasuda, K. 210 Smith, C. J. 48 Tatarinova, G. N. 29 Yeh, W.-C. 151 Smith, P. 112 Taylor, R. A. 150 Wagener, K. 36 Yeh, Z.-H. 105 Sodeoka, M. 210 Taylor, S. H. 209 Wang, G. 151 Yermakov, A. V. 29 Solonenko, O. P. 22 Tennant, S. 77 Wang, J. 105 Yeung, C. M. Y. 21 Soltner, T. 46 Terada, Y. 69 Wang, K.-W. 207 Yin, J. 106 Son, K.-H. 49 Tester, J. W. 48 Wang, R. L. 46 Young, D. P. 207 Song, J. M. 210 Thomas, B. 105 Wang, T. 209 Yu, C.-H. 49 Song, M. Y. 208 Thomas, J. M. 152 Wang, X.-P. 153 Yu, H.-W. 153 Spangler, L. 207 Thomas, S. 152 Ware, M. 78 Yu, K. 208 Spitsberg, I. 105 Thompsett, D. 21 Warren, S. C. 210 Yu, K. M. K. 21 Stafyla, E. 152 Thorn-Csanyi, E. 36 Watanabe, M. 48, 210 Yu, S. 208 Stagni, S. 105 Tian, Z.-Q. 208 Waugh, K. 195 Stahl, S. S. 153 Tillmetz, W. 38 Weberskirch, R. 48 Zacchini, S. 105 Steel, M. C. F. 205 Timerbaev, A. R. 49 Weiland, R. 158 Zeldovich, V. B. 210 Steichen, E. 78 Timofeev, A. N. 29 Weiss, K. 36 Zhang, H. 153 Steinhoff, B. A. 153 Toganoh, M. 150 Wells, R. 20 Zhang, J. 105, 152 Steinmann, P.-A. 208 Tokunaga, T. 207 Werner, H. 208 Zhang, L. 107 Stelzer, F. 36 Tonetto, G. M. 152 Werth, C. J. 152 Zhang, Q. G. 207 Stieglitz, A. 78 Torbati, R. 64 White, A. J. P. 150 Zhang, S. 150 Stimming, U. 204 Trasatti, S. 151 White, M. 43 Zhang, W. 46 Stone, C. 202 Trasatti, S. P. 151 White, P. 206 Zhang, X. 207 Streck, R. 36 Trnka, T. M. 95 Wiesner, U. 210 Zhang, Y. 47, 152 Strobel, R. 22 Tronconi, E. 106 Wijeratne, N. R. 151 Zheng, J. 208 Ströbel, R. 203 Trueba, M. 151 Williams, J. A. G. 104 Zhou, J. 208 Su, H. L. 46 Truett, W. E. 36 Williams, K. A. 106 Zhou, Z. 150, 151 Sudoh, M. 49 Tsai, D.-S. 151 Williams, V. A. 209 Ziolkowski, E. J. 104

Platinum Metals Rev., 2006, 50, (4) 216 SUBJECT INDEX TO VOLUME 50 Page Page a = abstract Catalysts, (cont.) Acetic Acid, from syngas, a 209 deactivation, in catalyst design 22 Acetylenes, hydrogenation, selective 156 electrochemical promotion 22 polymerisation, a 210 improving service life 52 ADMET, production of specialty polymers 81 N2O greenhouse gas abatement 103 Alcohols, aryl, coupling, of amines, a 106 poisons, Hg, removal 156 benzyl, oxidation, a 106 S species 110 cyclohexanol, oxidation, a 106 recycling, a 48, 106, 153, 209 EtOH, from Fischer-Tropsch reaction 22 S additions, activity control 110 MeOH, electrooxidation, a 107, 153 supported, application, characterisation, preparation 20 fuel, for fuel cells 38 three-way, see Three-Way Catalysts oxidation, a 210 Catalysts, Iridium, Co/alumina, + Ir, Fischer-Tropsch 22 reforming 22 electrocatalysts, PtIrCo, for PEMFCs 202 sensor, a 152 Catalysts, Iridium Complexes, Ir phosphine, oxidation, aerobic, a 153, 209 cyclisation of alkynes 171 Aldehydes, aromatic, oxidation, a 106 [Ir(COE)2Cl]2/dppe, methyl oleate hydroboration, a 210 Alkanes, oxidation, partial, a 106 Ir(III) N-heterocyclic carbene, H transfer reduction 171 propane, dehydrogenation 22 Catalysts, Palladium, Au-Pd, oxidation of CO, + H2 194 Alkenes, metathesis 35 synthesis of H2O2 194 Alkylation, asymmetric allylic, a 48 AuPtPd/SiO2-Al2O3, naphthalene hydrogenation, a 152 Alkynes, addition, to cyclopropenes, a 106 coupling of aryl alcohols, aryl halides, + amines, a 106 cyclisation 171 electrocatalysts, Pd-Co, Pd-Cr, Pd-Ni, for DMFCs, a 107 hydrogenation 22, 194 Pd, addition, TiO2, degradation of organics 22 Amination, aryl, in sc-CO2, a 48 + Ag, hydrogenation of acetylene 194 Buchwald-Hartwig, a 49 CH4 combustion 64 Amines, coupling, of aryl alcohols, aryl halides, a 106 foil, pentyne hydrogenation 22 oxidation, aerobic, a 209 for motorcycles, a 105 2– Aniline, oxidation, by PtCl6 , a 151 oxidative reactions, diesel, gasoline 64 Aromatisation, pyrolysis gasoline 194 S-poisoned, regeneration, for CH4 combustion 177 Aryl Halides, in reactions, a 48, 106, 153 surfaces, pentyne hydrogenation 22 N-Arylation, N-silyl derivatives, a 48 Pd + Au/alumina (from Ni3Al (111) single crystal) 22 Arylboronic Acids, Suzuki-Miyaura couplings, a 153 Pd monolith + Pt/Rh/Ce monolith TWC 177 Pd nanoparticles-polymer, fine chemicals synthesis 22 Biaryls, by Suzuki coupling, a 106 Pd shell-Ni core/MgO, butadiene hydrogenation 22 Biomolecules, sensor, a 105 CO oxidation 22 Book Reviews, “Electrodeposition of the Precious Metals” 67 Pd(111), single crystal, pentyne hydrogenation 22 “Principles of Fuel Cells” 200 Pd/Al2O3, CH4 combustion 64 “Ruthenium in Organic Synthesis” 95 Pd/γ-Al2O3, hydrogenation of sunflower oil, a 152 “Supported Metals in Catalysis” 20 Pd/γ-Al2O3 on metallic foams, washcoating method, a 106 Brazil, PGEs, geology 13, 134 Pd/Al2O3/metal foil, CH4 combustion 22 Buchwald-Hartwig Couplings, microwave-assisted, a 49 Pd/Al18B4O33, CH4 combustion 64 Bushveld Complex 130, 134 Pd/alumina, Hg posioning 156 hydrogenation of acetylenes 156 Cancer, anti-, Pt complexes, a 49 hydrogenation of dibenzothiophenes 22 Ru-pac complexes 2 pentyne hydrogenation 22 Capacitors, RuO2/TiO2 nanorods, a 208 Pd/C, hydrogenation of alkynes 194 Carbenes 35, 48, 104, 150, 153, 171, 209 Pd/C/asymmetric α-Al2O3 membrane, H2O2 synthesis 22 Carbocycles, synthesis, through metathesis 81 Pd/C-coated monoliths, combustion of xylenes, a 209 Carbon Oxides, CO, hydrogenation, a 209 Pd/polymer fibres, hydrogenation of sterols, a 106 oxidation 22, 106, 152, 177 Pd/TiO2, nitrate hydrogenation 22 selective 22, 48, 152, 194 Pd/TiO2 (P25), reforming MeOH, using UV 22 as probe for Pt 21 Pd-TiO2 film, oxidation of formic acid, a 48 tolerance, of PEMFC anodes 200 Pd/zeolite, matairesinol production 22 – CO2, reduction, Ru catalysis 95 Pd-Cu/γ-Al2O3, NO3 reduction, a 152 supercritical, solvent, a 48 Pd-Mn/Al2O3/metal foil, CH4 combustion 22 tolerance, of PEMFC anodes 200 Pd-Pt, CH4 combustion 64 Carbonylation, Ru catalysis 95 diesel oxidation 177 Carbonyls, reduction, to alcohols, a 209 S-poisoned, regeneration, for CH4 combustion 177 Carboxylic Acids, formic, oxidation, a 48 Pd-Pt/alumina, hydrogenation of dibenzothiophenes 22 Catalysis, asymmetric 54, 107 Pd-Pt/Ce-ZrO2, CH4 combustion 64 book reviews 20, 95 PdPt nanoparticles-, PdZn nanoparticles-polymer 22 conferences 22, 64, 177, 194 PdO/Al2O3, CH4 combustion 64 François Gault Lectureship, Johnson Matthey Award 22 Pt-Pd/Al2O3, CH4 combustion 64 fundamental studies; theoretical methods 22 PtPd/C MWNTs, naphthalene hydrogenation, a 152 heterogeneous, a 48, 105–106, 152, 209 PtPd/SiO2-Al2O3, naphthalene hydrogenation, a 152 homogeneous, a 48–49, 106–107, 153, 209–210 Catalysts, Palladium Complexes, Pd, Suzuki couplings, metathesis reactions, 2005 Nobel Prize for Chemistry 35 microwave-promoted, a 209 by supported metals 20 Pd carbenes + poly(2-oxazoline)s, couplings, in H2O, a 48 Catalysts, activity, test: microreactor; pilot plant 52 Pd enolates, chiral, enantioselective fluorination, a 210 book reviews 20, 95 Pd(II) + N ligands/SiO2, Suzuki couplings, a 48 conferences 22, 64, 177, 194 Pd2dba3 + X-Phos, amination reactions, in sc-CO2, a 48 contaminant levels 52 Pd2(dba)3-CHCl3, Suzuki couplings, a 153

Platinum Metals Rev., 2006, 50, (4), 217–222 217 Page Page Catalysts, Palladium Complexes, (cont.) Catalysts, Platinum, (cont.) 3 [Pd(η -C3H5)Cl]2 + chiral fluorous aminophosphine, Pt/Ba/CeO2, NOx storage/reduction 177 asymmetric allylic alkylation, a 48 Pt/Ba/CeZr, NOx storage 177 PdCl2 + PEPPSI-IPr, Negishi reaction, a 209 Pt/C-coated monoliths, combustion of xylenes, a 209 Pd(DPPF)Cl2, Suzuki coupling, aryl bromides, a 106 Pt/CeO2, WGSR 21, 22, 194 Pd(OAc)2 + 2-(di-t-butylphosphanyl)biphenyl, a 49 Pt/ceria-zirconia oxide, + Gd, La, Sm, CH4 oxidation 64 Pd(OAc)2 + 2-(dicyclohexylphosphanyl)biphenyl, a 49 Pt/CeZr, NOx storage 177 Pd(OAc)2 + imidazolium salt, SM couplings, a 153 Pt/mordenite, oxidation of CO, in H2, a 48 Pd(OAc)2/DMSO + MS3A, alcohol oxidation, a 153 Pt/SiO2, CO oxidation, a 152 Pd(OAc)2/[(Me)3PH]BF4/Et3N, addition of alkynes, a 106 Pt/TiO2 (rutile), preparation, effect of Pt precursor, a 152 Pd(OAc)2/P(OCH3)3, Heck coupling, a 48 WGSR, at low-temperature, a 152 Pd(OAc)2/pyridine + MS3A, alcohol oxidation, a 153 Pt/TiO2 thin film, visible light-responsive 22 Pd–phosphine, addition of alkynes, a 106 Pt/YSZ, monolith-type reactor 22 Catalysts, Platinum, AuPtPd/SiO2-Al2O3, Pt-Ce, soot + NO + O2 177 naphthalene hydrogenation, a 152 Pt-Fe, + Na-A zeolite, oxidation of CO, in n-butane 22 BaO/Pt(111), NOx storage 177 Pt-Fe/mordenite, oxidation of CO, in H2, a 48 CeO2-encapsulated Pt, -encapsulated Pt/Au, WGSR 21 PtFe/SiO2, CO oxidation, a 152 Co/alumina, + Pt, Fischer-Tropsch reaction 22 PtFe2/SiO2 cluster-derived, CO oxidation, + H2, a 152 electrocatalysts, Au/Pt, anodes, for AFCs 38 Pt5Fe2/SiO2, cluster-derived, CO oxidation, + H2, a 152 Pt, for fuel cells 38, 107, 200 Pt-Pd/Al2O3, CH4 combustion 64 polycrystalline, electrode, MeOH oxidation, a 107 PtPd/C MWNTs, naphthalene hydrogenation, a 152 porous, electrode, for nano fuel cells, a 107 PtPd/SiO2-Al2O3, naphthalene hydrogenation, a 152 Pt black layer, MEA, for PEMFCs, a 210 Pt-Re, catalytic reforming units 52 Pt nanoparticles, MeOH oxidation, a 210 Pt-Rh gauze pack 103 Pt nanoparticles/Nafion, for PEMFCs, a 49 Pt-Sn/HZSM-5 zeolite, denitration of drinking H2O, a 48 Pt/C, cathodes, for AFCs 38 Catalysts, Rhodium, Pt-Rh gauze pack 103 MEA, for fuel cells, a 210 Pt/Rh/Ce monolith TWC 177 for PEMFCs 49, 202 Rh, oxidative reactions, diesel, gasoline 64 Pt/C black, cathodes, for PEFCs, a 210 Rh coated K-β''-alumina, Fischer-Tropsch reaction 22 Pt/C cloths, cathodes, for DMFCs, a 49 Rh-coated foams, alkane oxidation, a 106 Pt/SWCNTs, cathodes, for DMFCs, PEMFCs, a 107 Rh nanoparticles, hydroformylation of olefins, a 153 Pt/Vulcan XC 72, thermal stability, a 153 Rh nanoparticles/nanosized SiO2, CO hydrogenation, a 209 Pt/Vulcan XC 72/Nafion layer, thermal stability, a 153 Rh/C, hydroformylation of olefins, a 153 PtBi nanoparticles, MeOH oxidation, a 210 Rh/LaMnO3, CH4 combustion 64 PtCo, for PEMFCs 202 Rh/YSZ, monolith-type reactor 22 PtCo/C, cathodes, for PEMFCs 202 Rh-Ce-Mn/SiO2 + CNTs, CO hydrogenation, a 209 PtIrCo, for PEMFCs 202 Catalysts, Rhodium Complexes, Rh, + β-diiminate, PtMo, anodes, for PEMFCs 200 + NH3 ligands, + phenoxy-imine, PtMo/C, anodes, for PEMFCs, a 49 polymerisation of acetylenes, a 210 PtPb nanoparticles, MeOH oxidation, a 210 Rh/BINOL, asymmetric hydrogenation 54 PtRu, anodes, for AFCs 38 Rh/MonoPhos ligands, asymmetric hydrogenation 54 anodes, for PEMFCs 200 Rh phosphine, cyclisation of alkynes 171 for DMFCs 38, 202 Rh/phosphoramidites, asymmetric hydrogenation 54 Pt/Ru/C, electrodes, for DMFCs 38 RhCl(TPPTS)3/SiO2, cinnamaldehyde hydrogenation, a 210 PtRu black, anodes, for DAFCs 202 Rh(COD)2BF4 + phosphoramidites 54 PtRu nanoparticles, MeOH oxidation, a 210 [Rh(cod)Cl]2, a 210 PtRuIr/C MWNTs, anodic oxidation of MeOH, a 153 Rh(III) N-heterocyclic carbene, H transfer reduction 171 PtSb, MeOH electrooxidation, a 107 [Rh(nbd)Cl]2, a 210 PtSn, for DAFCs 202 Rhodium Bicentenary Competition, research 171 Pd monolith + Pt/Rh/Ce monolith TWC 177 Catalysts, Ruthenium, carbonylations 95 Pd-Pt, CH4 combustion 64 Co/alumina, + Ru, Fischer-Tropsch reaction 22 diesel oxidation 177 CO2 reductions 95 S-poisoned, regeneration, for CH4 combustion 177 electrocatalysts, PtRu, anodes, for AFCs 38 Pd-Pt/alumina, hydrogenation of dibenzothiphenes 22 anodes, for PEMFCs 200 Pd-Pt/Ce-ZrO2, CH4 combustion 64 for DMFCs 38, 202 PdPt nanoparticles-polymer, fine chemicals synthesis 22 Pt/Ru/C, electrodes, for DMFCs 38 Pt, addition, TiO2, degradation of organics 22 PtRu black, anodes, for DAFCs 202 catalytic reforming units 52 PtRu nanoparticles, MeOH oxidation, a 210 hydrogenation of alkyl pyruvates, + ionic liquids 194 RuSe, cathodes, for DAFCs 202 for motorcycles, a 105 Fischer-Tropsch reactions 95 Olefex process (propane to propylene) 22 oxidations 95 oxidative reactions, diesel, gasoline 64 RuCl3, with H2O2, oxidation of organics, a 106 propane dehydrogenation 22 Ru(OH)x/Fe3O4, aerobic oxidations; reductions , a 209 for reforming 110 separation, with a permanent magnet, a 209 soot + NO + O2 177 Catalysts, Ruthenium Complexes, π-allyl-Ru 95 Pt coated Na-β''-alumina, NOx storage device 22 chiral, in asymmetric synthesis, a 107 Pt/Al2O3, + AE oxide, NOx storage-reduction, a 105 Grubbs’ catalysts, first, second generation 35 pyrolysis gasoline, aromatisation, hydrogenolysis 194 in organic synthesis 95 + RE oxide, NOx storage-reduction, a 105 Ru alkylidenes bearing N-heterocyclic carbenes 35 soot + NO2 + O2 177 Ru allenylidenes, cationic, neutral 81 Pt/γ-Al2O3 + V, naphthalene oxidation, a 209 metathesis, ADMET, enyne, RCM, ROMP 81 Pt/alumina, hydrogenation of dibenzothiophenes 22 Ru carbene, asarone-derived, olefin metathesis, a 106 Pt/Ba/Al2O3, by one-step flame synthesis 22 ruthenacycle intermediates, in C–C bond formation 95 NOx storage 22 Cinnamaldehyde, hydrogenation, a 210 NOx storage/reduction 177 Cisplatin, dinuclear analogues, DFT/CDM study, a 107

Platinum Metals Rev., 2006, 50, (4) 218 Page Page Coatings, Al-Pt, on Ti6242, a 47 Films, FePt nanocubes, a 107 thermal barrier, with PtNiAl diffusion bond coats, a 105 Pd, Pd-Pt bilayer, Pt, on polyimide, a 208 Combustion, catalytic, VOC emissions 64 platinised Pt, reduction 180 CH4 22, 64, 177 polypyrrole, + Ir, Pt, Ru particles, H evolution, a 151 xylenes, a 209 ‘Final Analysis’ 52, 110, 156 Composites, Pt-polyaniline, synthesis, a 151 Fine Chemicals, synthesis 20 Conferences, 9th Grove Fuel Cell Symp., London, 2005 38 Fischer-Tropsch Reactions, Rh coated K-β''-alumina 22 10th International Platinum Symposium, Finland, 2005 13 Ru catalysis 95 2+ 10th Ulm Electrochemical Talks, Germany, 2006 202 Fluorescence, [Ru(bpy)(bpy-C60)] , a 150 CAPoC7, Brussels, 2006 177 Fluorination, enantioselective, a 210 EUROPACAT-VII, Bulgaria, 2005 22 Fracture, Ir 158 IWCC6, Isle of Ischia, Italy, 2005 64 Fuel Cells, a 49, 107, 153, 210 SURCAT 2006, Cardiff, 2006 194 AFC 38, 200 Coupling Reactions, industrial-scale, a 106 book review 200 Creep, Ir, high temperature 158 conferences 38, 202 CRT®, for diesel emission control 177 DAFC, electrocatalysts 202 Crucibles, Ir 29, 158 DMFC, electrocatalysts 107, 200, 202 Crystallographic Properties, Pt 118 electrodes 38, 49, 107, 202 CVD, Pd, Pd-Pt bilayer, Pt, films, on polyimide, a 208 electrooxidation, MeOH, a 107 Cyclisation, alkynes 171 ORR, a 49 Cycloolefins, ROMP 81 electrocatalysts 38, 153, 210 Cyclopropanation, Ru catalysis 95 electrochemical losses 200 Cyclopropenes, addition of alkynes, a 106 fuels 22, 38, 152, 200, 202 Fuel Cell Knowledge Transfer Network 119 Dehydrogenation, propane 22 MCFC 200, 202 Denitration, drinking H2O, a 48 membrane electrode assemblies 38, 49, 107, 200, 202, 210 Dental, Au-Ag-Pd-In alloy, precipitation hardening, a 49 nano, a 107 Deposition, Ag–Pd films, a 208 PAFC 200 electroless, Pd nanowires, a 151 PEFC, Pt/C black + Nafion ink, a 210 electrostatic spray, Pt/C MEA, a 210 PEMFC, anodes 49, 202 photocatalytic, Pd membranes, a 209 CO tolerance, CO2 tolerance 200 TiPdNi thin films, a 105 cathodes 107, 202 Dibenzothiophenes, hydrogenation 22 electrocatalysts 38, 49, 200, 202 Dienes, butadiene, hydrogenation 20, 22 Pt/Vulcan XC 72/Nafion layer, thermal stability, a 153 Diesel, oxidation catalysts 64, 177 power, auxiliary supplies 22, 38 Diffusion, volume, Au, into single crystal Ir 29 consumer electronics 38 Diffusion Couples, Sn/Pd/Sn, a 46 Pt, availability, recovery, recycling 38 SOFC 200 Electrical Conductivity, Magnus’ salt derivatives, fibres112 transport, road vehicles: buses, cars, motorbikes 38 Electrical Contacts, ohmic, Ni/Pd, oxidised; Pd, a 153 Fuels, H2 22, 38, 48, 152, 202 Schottky, Pd/GaAs, Pd/porous-GaAs, H sensing, a 105 MeOH 38 Electrical and Electronic Engineering, a 107, 153 for motorcycles, a 105 Electrical Resistivity, Pd 144 Electrochemical Promotion, catalysts 22 Gasoline, emissions, catalytic oxidation 64 Electrochemistry, a 47, 151, 208 Gauzes, Pt-Rh 103 cathode reactivity, of platinised Pt, in super-dry DMF 180 Geology, Pt 13, 130, 134 polymerisation, C2H2, a 208 2+ 2+ [Ru(bpy)(bpy-C60)] , [Ru(tpy)(tpy-C60)] , a 150 Hardening, Ir-Hf-Nb, a 46 synthesis, Pt-polyaniline composite, a 151 precipitation, Au-Ag-Pd-In, a 49 Zr-Pd, Zr-Pt, in different solutions, a 47 Heat Capacity, isobaric, Pd 144 Electrodeposition, Ir, Os, Rh, Ru 67 Heck Reactions, a 48 Pt-Cu nanowires, a 107 Heterocycles, synthesis, through metathesis 81 RuO2, on electrospun TiO2, a 208 High Pressure, synthesis, CePtSn, a 46 Electrodeposition & Surface Coatings, a 47, 105, 151, 208 High Temperature, mechanical properties, Ir 158 Electrodes, in fuel cells, see Fuel Cells synthesis, CePtSn, a 46 micro-, array, Pd plated B-doped diamond, a 105 ultra-, Rh3X, thermophysical properties 69 Pd nanoparticles/B-doped diamond, a 105 High Throuhput Screening, ligands, used in catalysis 54 platinised Pt, cathode, reactivity, in super-dry DMF 180 History, Frédéric Joliot-Curie, Iréne Joliot-Curie 97 polypyrrole films, + Ir, Pt, Ru particles, H evolution, a 151 Hans Merensky 130 Pt, with ferroelectric films, a 153 Ir discovery, Smithson Tennant, commemorative plaque 77 Pt-Zn porphyrin nanocomposite/Nafion/glassy C, a 47 metathesis, alkenes 35 Rh, roughened, polymerisation of C2H2, a 208 Os discovery, commemorative plaque 77 RuO2–IrO2–SnO2/Ti, preparation, characterisation, a 208 Pd isotopes, discoverers 97 RuO2/TiO2 nanorods, a 208 Pd print, Alfred Steiglitz; platinotype, Edward Steichen 78 SrRuO3, with ferroelectric films, a 153 Pt, discovery, in the Bushveld Complex 130 Electroless Plating, Ir, Os, Pd, Pt, Rh, Ru, Pt-Rh 67 Pt, roubles, production, refining 120 Pd nanowires, a 151 Hydrazine, sensor, a 105 Electrospinning, Magnus’ salt derivatives, to fibres 112 Hydroboration, methyl oleate, a 210 Elongation, by tensile tests, Pt-Cu, Pt-Ru 15 Hydrocarbons, oxidation 64, 106 Emission Control, motor vehicles 64, 177 processing applications 110 VOCs, catalytic combustion 64 Hydrodearomatisation, pgm/alumina 22 Enthalpy of Fusion, Pd 144 Hydrodesulfurisation, pgm/alumina 22 Enyne Metathesis, in synthesis 81 Hydroformylation, solventless, olefins, a 153 Hydrogen, absorption, into Pd81Pt19 foil, a 104 Fibres, Magnus’ green salt derivatives 112 displacement, from Pd, by noble gases, a 46

Platinum Metals Rev., 2006, 50, (4) 219 Page Page Hydrogen, (cont.) Kharasch Addition Reactions, Ru catalysis 95 evolution, from polypyrrole, + Ir, Pt, Ru particles, a 151 fuel 22, 38, 48, 152, 202 Lignans, matairesinol production 22 isotope separation, a 208 Luminescence, bis-terpyridyl Ir(III), + pyridyl groups, a 104 microwave plasma irradiation, Co-Pd, a 207 electro-, [Ir(dF(CF3)ppy)2(dtbbpy)](PF6), a 47 permeation, of Pd membranes, a 152, 208, 209 Ru(II) polypyridyls, containing 5-aryltetrazolates, a 105 presence, CO oxidation 48, 152, 194 production 20, 22, 47 Magnetism, Ce(Pd1–xAgx)2Al3, a 150 sensor, a 105 CePtSn, a 46 Hydrogen Peroxide, + RuCl3, oxidation of organics, a 106 FePt nanoparticles, a 49 synthesis 22, 194 FePt/Fe composite nanotubes, a 46 Hydrogenation, alkyl pyruvates 194 MnxPd1–x, a 150 alkynes 194 [Ru(C9H6NO)3]·MeOH, a 47 asymmetric 54 in separation of Ru(OH)x/Fe3O4, a 209 asymmetric transfer, a 107 TbRhIn5, a 207 butadiene 20, 22 MEAs 38, 49, 107, 200, 202, 210 cinnamaldehyde, a 210 Mechanical Properties, high temperature, Ir, a 158 CO, a 209 Pt-5 wt.% Cu, Pt-5 wt.% Ru 15 dibenzothiophenes 22 Medical Uses 2, 49, 107 naphthalene, a 152 Membranes, Pd, H2 permeation, a 152 nitrates, in H2O22microfabrication, a 152 in organic synthesis 95 permeation, for H isotope separation, a 208 pentyne 22 Pd/C coated asymmetric α-Al2O3, H2O2, synthesis 22 selective, acetylenes 156 Pd/TiO2, by photocatalytic deposition, a 209 sterols, a 106 reactor; series; Pd, in H2 generation, a 152 sunflower oil, a 152 Metallopharmaceuticals, Ru polyaminocarboxylates 2 transfer, in organic synthesis 95 Metathesis 35, 81, 95, 106 α,β-unsaturated carbonyl compounds 20 Methane, combustion 22, 64, 177 Hydrogenolysis, hydroxymatairesinol 22 emissions, oxidation 64 pyrolysis gasoline 194 Methyl Oleate, hydroboration, isomerisation, a 210 Microwaves, in organic synthesis, a 49, 209 Imines, transfer hydrogenation, asymmetric, a 107 plasma H irradiation, Co-Pd, a 207 Ionic Liquids 153, 194 MOCVD, Al-Pt coatings, on Ti6242, a 47 Iridium, creep, high temperature 158 IrO2 nanorods, a 151 crucibles 29, 158 discovery, commemorative plaque 77 Nanocomposites, Pd-polyaniline, synthesis, a 152 electrodeposition, electroless deposition 67 Pt-Zn porphyrin, in detection of organohalides, a 47 high-temperature mechanical properties 158 Nanodroplets, fluorous, in organopalladium sphere, a 207 impurities, mass transfer 29 Nanofilms, polycrystalline Pt, thermal conductivity, a 207 particles, in polypyrrole films, H evolution, a 151 Nanofiltration, solvents, a 153 single-Ir, volume diffusion of Au 29 Nanoparticles, FePt, a 49, 107 stress-rupture strength, high temperature 158 Pd, a 105, 151, 152 tensile strength, high temperature 158 Pd70Ag30, a 207 vacancy-impurity complexes, growth 29 Pt, a 47, 49, 210 Iridium Alloys, Ir-Hf-Nb, hardening behaviour, a 46 PtBi, PtPb, PtRu, a 210 superalloys, refractory, a 46 Rh, a 153, 209 Iridium Complexes, Ir N-heterocyclic carbenes 171 Nanorods, IrO2, by MOCVD, a 151 trans-[IrCl(C8H14)(PiPr3)2] + benzene, a 208 Nanotubes, composite, FePt/Fe, a 46 IrCl(CO)2(p-toluidine) + tetraphenylporphyrin, a 150 Nanowires, Pt silicide, a 105 [Ir(dF(CF3)ppy)2(dtbbpy)](PF6), electroluminescene, a 47 Pt-Cu, a 107 photoinduced H2 production, a 47 self-assembled, Pd, by electroless deposition, a 151 [IrH2(Cl)(PiPr3)2], preparation, a 208 Naphthalenes, hydrogenation, a 152 [IrH(C6H3F2)(Cl)(PiPr3)2], preparation, a 208 oxidation, a 209 [IrH(C6H4X)(Cl)(PiPr3)2], preparation, a 208 Naptha, reforming 20 [IrH(C6H5)(Cl)(PiPr3)2], preparation, a 208 Negishi Couplings, PdCl2 + PEPPSI-IPr, a 209 [IrH{(C6H3F(CH3)}(Cl)(PiPr3)2], preparation, a 208 Nitrates, in H2O 22, 48, 152 Ir(I), inverted N-confused porphyrin, a 150 Nitric Acid, plants, N2O abatement catalyst 103 Ir(III), bis-terpyridyl/pyridyl groups, luminescence, a 104 Nitrogen, from nitrate hydrogenation, in H2O22 (MeCp)Ir(COD), precursor for MOCVD, a 151 Nitrogen Oxides, N2O, abatement catalyst 103 Iridium Compounds, Ir nitride, synthesis, a 104 NO, + O2, soot oxidation 177 IrO2 nanorods, by MOCVD, a 151 scavengers, Ru-pac complexes 2 RuO2–IrO2–SnO2/Ti electrodes, a 208 NO2, + O2, soot oxidation 177 Isomerisation, methyl oleate, a 210 NOx, HC SCR, NH3 SCR 177 organic substrates, Ru catalysis 95 lean, catalysis 22 Isomerism, [Pt(SC(NH2)2)4][C5O5]·4DMSO crystals, a 47 storage 22, 177 Isotopes, Pd, discoveries 97 storage-reduction 105, 177 trap, regeneration, by H2 22 Johnson Matthey, Award for Innovation in Catalysis 22 Nobel Prize, Chemistry, metathesis reaction 35 marketing, N2O abatement catalyst 103 Noble Gases, displacement of H, from Pd, a 46 “Platinum 2006” 143 Rhodium Bicentenary Competition 171 Oil, sunflower, hydrogenation, a 152 Susan V. Ashton, retirement as Editor, a tribute 205 OLEDs, in O2 sensor, a 151 Olefex Process, propane, to propylene 22 Ketones, H transfer reduction 171 Olefins, hydroformylation, solventless, a 153 transfer hydrogenation, asymmetric, a 107 metathesis 81, 95, 106

Platinum Metals Rev., 2006, 50, (4) 220 Page Page Optical Properties, Magnus’ salt derivatives, fibres 112 Palladium Complexes, (cont.) Organohalides, Negishi couplings, a 209 [Pd(hypy)2]Cl2·2MeOH, crystal structure, a 207 sensor, a 47 Pd(II), with tetrazolecalix[4]arenes, a 104 Osmium, discovery, commemorative plaque 77 phospha-palladacycle, with an acyclic carbene, a 104 electrodeposition, electroless deposition 67 Palladium Compounds, NbPdSi, structure, synthesis, a 150 Hf–Os system, thermodynamic assessment, a 104 Particulates, control 177 patents 27 Patents 50–51, 108–109, 154–155, 211–212 Oxidation, aerobic, alcohols, a 153, 209 Os 27 amines, a 209 Phoscorite-Carbonatite Pipe Complexes, PGEs 134 Al-Pt coatings, on Ti6242, a 47 Phosphoramidites, synthesis 54 aldehydes, aromatic, a 106 Phosphorescence, electro-, PFO-PtTPP, a 47 alkanes, a 106 Photocatalysis 22, 209 aniline, a 151 Photoconversion, a 47, 104–105, 151 benzyl alcohol, a 106 Photoproperties, Magnus’ salt derivatives, fibres 112 CH4 64 Pt-acetylide polymer, a 151 2+ CO 22, 106, 152, 177 [Ru(bpy)2(5-CNphen)] , a 151 in n-butane 22 Ru(II) fullerene polypyridines, a 150 4+ in presence of H2 48, 152, 194 [(tpy)Ru(bis(U-terpyridine))Ru(tpy)] , a 208 6+ cyclohexanol, a 106 [{(tpy)Ru}3(tris(U-terpyridine))] , a 208 electro-, MeOH, a 107, 153 Photoreactions, H2PtCl6/Zn porphyrin, + ascorbic acid, a 47 enzymatic 2 Photosensitisers, [Ir(dF(CF3)ppy)2(dtbbpy)](PF6), a 47 2+ formic acid, a 48 [Ru(bpy)2(5-CNphen)] , a 151 hydrocarbons 64, 106 Plating Baths, Ir, Os, Pd, Pt, Pt-Rh, Rh, Ru 67 MeOH, a 210 Platinotype, photograph, record price 78 naphthalenes, a 209 Platinum, Al-Pt coatings, on Ti6242, a 47 Pd0.97Ce0.03, a 150 availability, for fuel cells 38 Ru catalysis 95 “blackberry-like”, “cauliflower-like” structures 180 soot 177 crystallographic properties 118 Zr-Pd, Zr-Pt, a 104 discovery, in the Bushveld Complex 130 Oxygen, reduction, in fuel cells, a 49, 107 electrodes, a 153 sensors, a 151 electroless deposition 67 film, on polyimide, a 208 Palladium, Ag–Pd films, tarnish resistance, a 208 geology 13, 130, 134 electrical resistivity 144 nanoparticles, a 47, 49, 210 electroless deposition 67 particles, in polypyrrole films, H evolution, a 151 enthalpy of fusion 144 Pd-Pt bilayer film, on polyimide, a 208 film, on polyimide, a 208 platinised Pt films, reduction 180 H displacement, by noble gases, a 46 polycrystalline, nanofilms, thermal conductivity, a 207 isobaric heat capacity 144 print, Edward Steichen, record price 78 isotopes, history of the discoveries 97 production, history 120 membranes 22, 152, 208, 209 Pt-polyaniline composite, synthesis, a 151 nanoparticles, a 105, 151, 152 Pt/Co overlayers, adhesion, bonding, a 151 nanowires, self-assembled, by electroless deposition, a 151 Pt/Ni overlayers, adhesion, bonding, a 151 ohmic contacts, oxidised Ni/Pd, Pd, a 153 reactions, with refractories 197 Pd hydride, from Co-Pd, by microwave H plasma, a 207 recovery, recycling, from fuel cells 38 Pd nanoparticles/B-doped diamond electrode, a 105 refining, history 120 Pd plated B-doped diamond microdisc array, a 105 roubles 120 Pd-polyaniline nanocomposite, synthesis, a 152 thermal expansion 118 Pd-Pt bilayer film, on polyimide, a 208 thermal vacancy 118 Pd/GaAs, /porous-GaAs, Schottky contact, a 105 thermocouples, maintenance, reliability, specification 197 print, Alfred Steiglitz 78 Platinum Alloys, (Fe0.75P0.25)75B25, phase tranformations, a 46 Sn/Pd/Sn diffusion couples, a 46 FePt nanoparticles, self-assembly, a 107 specific enthalpy 144 surface PEGylation, a 49 thermal conductivity 144 FePt/Fe composite nanotubes, synthesis, a 46 thermal diffusivity 144 Pd81Pt19 foil, H absorption, a 104 thermophyical properties 144 PtBi nanoparticles, a 210 Palladium Alloys, Ce(Pd1–xAgx)2Al3, magnetism, a 150 Pt-5 wt.% Cu, mechanical properties 15 Co-Pd, demixing, a 207 Pt-Cu nanowires, electrodeposition, a 107 dental, Au-Ag-Pd-In, precipitation hardening, a 49 PtNiAl, diffusion bond coats, a 105 Fe-Pd shape-memory thin films, stress evolution, a 46 PtPb nanoparticles, a 210 MnxPd1–x, preparation, magnetism, a 150 Pt-Rh, electroless deposition 67 Pd0.97Ce0.03, oxidisation, a 150 Pt-5 wt.% Ru, mechanical properties 15 Pd70Ag30 nanoparticles, preparation, a 207 PtRu nanoparticles, a 210 Pd40Ni40B10P10, preparation, properties; Pd40Ni40P20, a 46 Rh-Pt thermocouples 197 Pd81Pt19 foil, H absorption, a 104 Zr-Pt, electrochemical behaviour, in solution, a 47 PdSn2, PdSn3, PdSn4, a 46 oxidation, a 104 TiPdNi thin films, shape memory effect, a 105 Platinum Complexes, bis(oxalato)platinate(II), PO, a 207 Zr-Pd, electrochemical behaviour, in solution, a 47 Me3(MeCp)Pt, for MOCVD, a 47 oxidation, a 104 PFO-PtTPP, phosphorescence, a 47 – + – + Palladium Complexes, arrow shaped N-donor ligands, a 207 [Pt2 , TAA , TAAX], [Pt4 , TMA , TMAX] 180 Pd-octaethylporphyrin, OLED-based O2 sensor, a 151 Pt-acetylide polymer, in solar cells, a 151 2 Pd2(η -C60) structure, a 207 Pt-octaethylporphyrin, OLED-based O2 sensor, a 151 PdnC60, DFT calculations, a 207 Pt(II), containing N-bonded acetamide, a 104 + [Pd(hypy)2] , DFT modelling, IR spectroscopy, a 207 containing O-bonded acetamide, a 104 [Pd(hypy)2]Cl2, a 207 Pt(II) + aminoalcohol ligands, antitumour agents, a 49

Platinum Metals Rev., 2006, 50, (4) 221 Page Page Platinum Complexes, (cont.) Russia, Pt 13, 130, 134 [Pt(L)Me2], protonation, a 150 Ruthenium, electrodeposition, electroless deposition 67 + [Pt(L)Me(CH3CN)] , by protonation, a 150 particles, in polypyrrole films, H evolution, a 151 tetra(cyano)platinate(II), PO, a 207 Ruthenium Alloys, Pt-5 wt.% Ru, mechanical properties 15 Platinum Compounds, CePtSn, magnetism, a 46 Ruthenium Complexes, [(C6H6)RuCl2]2 + quinolines, a 47 cisplatin, dinuclear analogues, DFT/CDM study, a 107 Ru polyaminocarboxylates, as antitumour drugs 2 Magnus’ salt derivatives, fibres, by electrospinning 112 as metallopharmaceuticals 2 Pt nitride, synthesis, a 104 as NO scavengers 2 Pt-silicide nanowires, biomolecule sensing, a 105 as protease inhibitors 2 2+ Pt-Zn porphyrin nanocomposites, synthesis, a 47 Ru(bpy)2(5-CNphen)] , photoproperties, a 151 2– 2+ PtCl6 , oxidation of aniline, a 151 [Ru(bpy)(bpy-C60)] , electrochemistry, fluorescence, a 150 reduction, a 151 [Ru(C9H6NO)3]·MeOH, magnetism, a 47 2+ [cis-{Pt(NH3)2}(μ-OH)]2 , a 107 Ru(II) polypyridyls + aryltetrazolates, luminescence, a 105 2+ [Pt(NH2dmoc)4][PtCl4], [Pt(NH2eh)4][PtCl4], fibres 112 [Ru(tpy)(tpy-C60)] , electrochemical study, a 150 [Pt(SC(NH2)2)4][C5O5]·4DMSO crystals, isomerism, a 47 solar cells, a 47 Platinum Group Elements, geology 13, 130, 134 [(tpy)Ru(bis(U-terpyridine))Ru(tpy)]4+, photo, a 208 6+ Pollution Control, flame combustion, fossil fuels 20 [{(tpy)Ru}3(tris(U-terpyridine))] , photo, a 208 motor vehicles 177 Ruthenium Compounds, RuO2, electrodeposition, a 208 photocatalysed degradation, organic pollutants 22 electrodes, a 153, 208 Polyaminocarboxylates, Ru complexes 2 Polymerisation, acetylenes, a 210 Selective Catalytic Reduction, HC, NH3 177 by metathesis 35, 81 Sensors, biomolecules, a 105 electrochemical, of C2H2, a 208 H2, a 105 Polymers, bis(oxalato)platinate(II), partial oxidised, a 207 hydrazine, a 105 Pd-polyaniline nanocomposite, synthesis, a 152 MeOH, a 152 PFO-PtTPP, phosphorescence, a 47 O2, a 151 polypyrrole films, + Ir, Pt, Ru particles, H evolution, a 151 organohalides, a 47 Pt-acetylide polymer, in solar cells, a 151 Shape Memory Effect, Fe-Pd thin films, a 46 Pt-polyaniline composite, synthesis, a 151 TiPdNi thin films, a 105 specialty, by ADMET, ROMP 81 Single Crystals, Ir, volume diffusion of Au 29 synthesis, Ru catalysis 95 Solar Cells, a 47, 151 tetra(cyano)platinate(II), partial oxidised, a 207 Soot, oxidation 177 Protonation, [Pt(L)Me2], a 150 South Africa, Pt 13, 130, 134 Pyruvates, alkyl, hydrogenation, + ionic liquids 194 Specific Enthalpy, Pd 144 Sputtering, co-, magnetron, of Ag–Pd films, a 208 RCM, in synthesis 81 Fe-Pd shape-memory thin films, a 46 Reactors, industrial, hydrogenation of sterols, a 106 Pt, on C cloths, a 49 membrane, Pd, in H2 generation, a 152 Sterols, hydrogenation, a 106 micro-, catalyst activity tests 52 Stress, by tensile tests, Pt-Cu, Pt-Ru 15 monolith-type, YSZ, coated with Pt, Rh 22 Stress-Rupture, strength, Ir, high temperature 158 pilot-plant, hydrogenation of sterols, a 106 Sulfur, catalyst poison 110 Reduction, asymmetric, carbamates, enamides, Superalloys, Ir-Hf-Nb, hardening behaviour, a 46 enol acetates 54 Supercritical Solvents, propane, in catalysis, a 152 to α-alkyl succinic acid derivatives 54 Suzuki Couplings, a 48, 106, 153, 209 to α-amino acid, β-amino acid, derivatives 54 Suzuki-Miyaura Couplings, a 153 α,β-unsaturated acids 54 Syngas, in synthesis of acetic acid, a 209 carbonyl compounds, a 209 CO2 95 Tensile, strength, high temperature, Ir 158 H transfer, ketones 171 Tetraalkylammonium Salts, influences on platinised – – NO2 , NO3 , a 152 Pt layers 180 O, in fuel cells, a 49, 107 Thermal Conductivity, Pd 144 platinised Pt films 180 polycrystalline Pt nanofilms, a 207 2– PtCl6 , a 151 Rh3X (X = Hf, Nb, Ta, Ti, V, Zr) 69 Refining, Pt, history 120 Thermal Diffusivity, Pd 144 Reforming, catalysts 52, 110 Thermal Expansion, Pt 118 dimethyl ether 22 Rh3X (X = Hf, Nb, Ta, Ti, V, Zr) 69 MeOH 22 Thermal Vacancy, Pt 118 naptha 20 Thermocouples, Pt, reliability 197 Refractories, insulation, for Pt-based thermocouples 197 Thermophysical Properties, Pd 144 reactions, with Pt 197 Rh3X69 Rhodium, electrodeposition, electroless deposition 67 Thin Films, Ag–Pd, deposition, tarnish resistance, a 208 electrodes, roughened, polymerisation of C2H2, a 208 Fe-Pd, shape memory, a 46 nanoparticles, a 153, 209 TiPdNi, shape memory, a 105 Rhodium Bicentenary Competition, research 171 Three-Way Catalysts, ageing 177 Rhodium Alloys, Pt-Rh, electroless deposition 67 developments 177 Rh-Pt thermocouples 197 Rhodium Complexes, Rh N-heterocyclic carbenes 171 Vacancy-Impurity Complexes, growth, in Ir 29 Rh(CO)2I(NHC), structure, a 150 Vitamins, intermediates, synthesis 22 Rh(COD)X(NHC), synthesis, structures, a 150 VOCs, emissions, catalytic combustion 64 Rhodium Compounds, CeRhIn5, a 207 intermetallic, Rh3X (X = Hf, Nb,Ta, Ti, V, Zr), Water, -soluble, FePt nanoparticles, a 49 thermal conductivity, thermal expansion 69 drinking, denitration 22, 48 TbRhIn5, crystal growth, magnetic properties, a 207 Water Gas Shift Reaction 21, 22, 152, 194 ROMP, cycloolefins; production of specialty polymers 81 Roubles, Pt 120 Xylenes, combustion, a 209

Platinum Metals Rev., 2006, 50, (4) 222