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Platinum Metals Rev., 2004, 48, (4), 190

doi:10.1595/147106704x13097

ABSTRACTS

of current literature on the platinum metals and their alloys

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PROPERTIES

Effect of Hydrogen-Sulfide on the Hydrogen Permeance of Palladium–Copper Alloys at Elevated Temperatures

B. D. MORREALE, M. V. CIOCCO, B. H. HOWARD, R. P. KILLMEYER, A. V. CUGINI and R. M. ENICK, J. Membrane Sci., 2004, 241, (2), 219–224 LINK doi:10.1016/j.memsci.2004.04.033 http://dx.doi.org/10.1016/j.memsci.2004.04.033

The H permeance of Pd-Cu foils (1) (0.1 mm thick) was evaluated using transient flux measurements over 603–1123 K and pressures ≤ 620 kPa, in the presence and absence of 1000 ppm H2S. S resistance (no significant change in permeance) was correlated with the temperatures associated with f.c.c. (1). The H permeance of b.c.c. (1) was up to two orders of magnitude lower on exposure to H2S. A smooth transition from S poisoning to S resistance with increasing temperature was correlated with the b.c.c. to f.c.c. transition.

Magnetism of CaRuO3 Crystal

A. KORIYAMA, M. ISHIZAKI, T. C. OZAWA, T. TANIGUCHI, Y. NAGATA, H. SAMATA, Y. KOBAYASHI and Y. NORO, J. Alloys Compd., 2004, 372, (1–2), 58–64 LINK doi:10.1016/j.jallcom.2003.10.026 http://dx.doi.org/10.1016/j.jallcom.2003.10.026

The magnetic properties of polycrystalline (1) and single-crystal (2) samples of CaRuO3 were studied. The M(T) curves of (1) showed irreversible behaviour and the M(H) curve showed weak ferromagnetic behaviour at < 60 K. The M(H) curve of (2) exhibited peculiar behaviour at 1.7 and 5 K, showing evidence of magnetic order at very low temperature.

CHEMICAL COMPOUNDS

Insertion of Phenylacetylene into [Pt(GeMe3)(SnMe3)(PMe2Ph)2]

T. SAGAWA, R. TANAKA and F. OZAWA, Bull. Chem. Soc. Jpn., 2004, 77, (7), 1287–1295 LINK doi:10.1246/bcsj.77.1287 http://dx.doi.org/10.1246/bcsj.77.1287

The reaction of Me3GeSnMe3 with a Pt(0) complex, in situ generated from [Pt(cod)2] and PhMe2Ph, gave a cis-trans mixture of [Pt(GeMe3)(SnMe3)(PMe2Ph)2] (1). Recrystallisation of crude (1) from CH2Cl2-pentane gave cis-(1). (1) underwent competitive insertion of phenylacetylene into the Pt–Sn and Pt–Ge bonds.

The Crystal Structure of [Pt(NH3)4][PtI4]: Comparison with Magnus' Green Salt

J. S. CASAS, Y. PARAJÓ, Y. ROMERO, A. SÁNCHEZ-GONZÁLEZ, J. SORDO and E. M. VÁZQUEZ-LÓPEZ, Z. Anorg. Allg. Chem., 2004, 630, (7), 980–982 LINK doi:10.1002/zaac.200400069 http://dx.doi.org/10.1002/zaac.200400069

The structure of [Pt(NH3)4][PtI4] (1) was found to be isotypic with Magnus' green salt and is unchanged at low temperature except for a slight contraction of the unit cell. (1) consisted of [Pt(NH3)4]2+ and [PtI4]2−; the Pt atoms are surrounded by 4 N or 4 I atoms in square-planar arrangements. At 173 K the intermolecular stacking interaction Pt–Pt was shortened.

N-Benzoylimido Complexes of Palladium. Synthesis, Structural Characterisation and Structure–Reactivity Relationship

G. BESENYEI, L. PÁRKÁNYI, G. SZALONTAI, S. HOLLY, I. PÁPAI, G. KERESZTURY and A. NAGY, Dalton Trans., 2004, (13), 2041–2050 LINK doi:10.1039/b403200d http://dx.doi.org/10.1039/b403200d

Benzoyl azides, ArC(O)N3 (Ar = phenyl or substituted phenyl), react with [Pd2Cl2(dppm)2] (1) (dppm = bis(diphenylphosphino)methane) to give novel benzoylnitrene complexes, [Pd2Cl2(μ-NC(O)Ar)(dppm)2]. The C2P4Pd2 rings are chiral. Crystallographic and solution IR studies of the reaction of a series of para-substituted benzoyl azides with (1) showed that the reaction obeys the Hammett equation.

Iridium(III) and Rhodium(III) Cyclometalated Complexes Containing Sulfur and Selenium Donor Ligands

M.-K. LAU, K.-M. CHEUNG, Q.-F. ZHANG, Y. SONG, W.-T. WONG, I. D. WILLIAMS and W.-H. LEUNG, J. Organomet. Chem., 2004, 689, (14), 2401–2410 LINK doi:10.1016/j.jorganchem.2004.04.033 http://dx.doi.org/10.1016/j.jorganchem.2004.04.033

Reaction of [M(Buppy)2Cl]2 (M = Ir (1), Rh (2); BuppyH = 2-(4′-tert-butylphenyl)pyridine) with Na(Et2NCS2), K[S2P(OMe)2] and K[N(Ph2PS)2]2 gave monomeric [M(Buppy)2S^S] (S^S = Et2NCS2, S2P(OMe)2, N(PPh2S)2). Treatment of (1) with Na[N(PPh2Se)2] gave [Ir(Buppy)2{N(PPh2Se)2}]. Reaction of (1) and (2) with AgOTf followed by treatment with KSCN gave [{M(Buppy)2}2(μ-SCN)2].

Mixed Iridium(III) and Ruthenium(II) Polypyridyl Complexes Containing Poly(ε-caprolactone)-bipyridine Macroligands

V. MARIN, E. HOLDER, R. HOOGENBOOM and U. S. SCHUBERT, J. Polym. Sci. A: Polym. Chem., 2004, 42, (17), 4153–4160 LINK doi:10.1002/pola.20185 http://dx.doi.org/10.1002/pola.20185

Coordination of a poly(ε-caprolactone)-bipyridine macroligand to Ir(III) and Ru(II) precursor complexes yielded the title complexes. Both photophysical and electrochemical properties of the metal-containing polymers confirmed the formation of the tris-Ir(III) and tris-Ru(II) polypyridyl species.

ELECTROCHEMISTRY

The Electrochemistry of Gold–Platinum Alloys

H. MÖLLER and P. C. PISTORIUS, J. Electroanal. Chem., 2004, 570, (2), 243–255 LINK doi:10.1016/j.jelechem.2004.04.003 http://dx.doi.org/10.1016/j.jelechem.2004.04.003

Au–Pt electrodes are more active for ethylene glycol electrooxidation than either Pt or Au electrodes. The Au–Pt electrodes in the solid solution condition are more active than two-phase electrodes. More severe poisoning occurs during the first few cycles at the Au–Pt electrodes than at both the Pt or Au electrodes. Longer potential pulsing cleaning cycles are needed to remove the poisons at the Au–Pt electrodes.

PHOTOCONVERSION

Micelle-Mediated UV-Photoactivation Route for the Evolution of Pdcore–Aushell and Pdcore–Agshell Bimetallics from Photogenerated Pd Nanoparticles

M. MANDAL, S. KUNDU, S. K. GHOSH and T. PAL, J. Photochem. Photobiol. A: Chem., 2004, 167, (1), 17–22 LINK doi:10.1016/j.jphotochem.2004.04.002 http://dx.doi.org/10.1016/j.jphotochem.2004.04.002

UV-photoactivation of aqueous PdCl2 gave Pd nanoparticles (1) with narrow size distribution (∼ 5 nm) in poly(oxyethylene)isooctyl phenyl ether micelles, TX-100, as reducing agent. The TX-100 also acted as a stabiliser. The bimetallic colloids (10–30 nm) with varying metal ratios were prepared by successive ion loading using a seed-mediated method where (1) act as seeds.

Electronic and Photophysical Properties of a Novel Phenol Bound Dinuclear Ruthenium Complex: Evidence for a Luminescent Mixed Valence State

T. E. KEYES, B. EVRARD, J. G. VOS, C. BRADY, J. J. MCGARVEY and P. JAYAWEERA, Dalton Trans., 2004, (15), 2341–2346 LINK doi:10.1039/b405114a http://dx.doi.org/10.1039/b405114a

A dinuclear Ru(II) complex (1), bridged by 3-(2-phenol)-5-(pyridin-2-yl)-1,2-4-triazole, was prepared electrochemically. A weak intervalence charge transfer transition was observed. Upon oxidation of the O,N moiety luminescence from (1) is reversibly switched on at 0.3 V and reversibly switched off by the application of 1.3 or 0 V.

ELECTRODEPOSITION AND SURFACE COATINGS

Microstructure and Mechanical Properties of Ir–Ta Coatings on Nickel-Base Single-Crystal Superalloy TMS-75

P. KUPPUSAMI, H. MURAKAMI and T. OHMURA, J. Vac. Sci. Technol. A, 2004, 22, (4), 1208–1217 LINK doi:10.1116/1.1763913 http://dx.doi.org/10.1116/1.1763913

Ir–Ta coatings (1) with 16.2, 23.9, 40.7 and 65.1 at.% Ta were deposited at 573 K on the Ni-base single crystal superalloy, TMS-75, by DC magnetron sputtering by selecting the ratio of the surface areas of the Ir and Ta targets. (1) had a nanocrystalline structure where crystallite size and rms roughness decreased with increase in Ta content. Young's modulus and hardness of the coatings generally decreased with the increase in Ta content. However, the hardness peaked in the 16.2–23.9 at.% Ta range, possibly due to Ir3Ta formation.

Cathodic Electrodeposition of RuO2 Thin Films from Ru(III)Cl3 Solution

B.-O. PARK, C. D. LOKHANDE, H.-S. PARK, K.-D. JUNG and O.-S. JOO, Mater. Chem. Phys., 2004, 87, (1), 59–66 LINK doi:10.1016/j.matchemphys.2004.04.023 http://dx.doi.org/10.1016/j.matchemphys.2004.04.023

RuO2 films (1) of different thicknesses were cathodically deposited on Ti substrates under galvanostatic conditions from aqueous acidic Ru(III)Cl3 solution. XRD and TEM established that (1) are nanocrystalline. SEM showed that (1) are porous and that surface morphology changes with film thickness.

HETEROGENEOUS CATALYSIS

Hydroisomerization of n-Heptane and n-Tetradecane over Pt/SAPO-11

F. ZHANG, C.-H. GENG, Z.-X. GAO and J.-L. ZHOU, J. Fuel Chem. Technol. (Chin.), 2004, 32, (3), 340–345

Hydroisomerisation of n-heptane and n-tetradecane over Pt/SAPO-11 was carried out in a fixed-bed, down-flow reactor at 200°C ∼ 420°C, 0.5 MPa and WHSV of 2.0 h−1. High n-alkane conversion with 90% selectivity to isomers was achieved. Paraffin isomerisation may occur inside the SAP0-11 channels.

Pd-Catalyzed Heck Arylation of Cycloalkenes–Studies on Selectivity Comparing Homogeneous and Heterogeneous Catalysts

L. DJAKOVITCH, M. WAGNER, C. G. HARTUNG, M. BELLER and K. KOEHLER, J. Mol. Catal. A: Chem., 2004, 219, (1), 121–130 LINK doi:10.1016/j.molcata.2004.04.035 http://dx.doi.org/10.1016/j.molcata.2004.04.035

Heck reactions of aryl bromides with cyclohexene and cyclopentene were catalysed by: Pd/C, Pd/SiO2, Pd/MgO, Pd/Al2O3, Pd(0)/Z, Pd(II)/Z and [Pd(NH3)4]2+/Z (Z = NaY, HY or ZSM-5 zeolites); and Pd(OAc)2/PPh3, Pd2(dba)3·dba/PCy3 and the {Pd[P(o-C6H4CH3)2-(o-C6H4CH2)(CH3CO2)]}2 “palladacycle”. Dissolved molecular Pd species are involved in the Heck coupling for all of the catalysts. The dehalogenation mechanism involves the surface of solid Pd metal particles and radical processes.

Drastic Increase of Selectivity for H2O2 Formation in Direct Oxidation of H2 to H2O2 over Supported Pd Catalysts Due to Their Bromination

V. R. CHOUDHARY, C. SAMANTA and A. G. GAIKWAD, Chem. Commun., 2004, (18), 2054–2055 LINK doi:10.1039/b405415f http://dx.doi.org/10.1039/b405415f

Pd catalysts have high activity for H2O2 decomposition which limits their use for formation of H2O2 from H2. The incorporation of bromide anions (1.0 wt.%) into Pd supported on Al2O3, ZrO2, SiO2, H-β zeolite or Ga2O3 overcomes this. These catalysts were used for the direct oxidation of H2 to H2O2 by O2 (at room temperature) in 0.03 M H3PO4. A large increase in selectivity for H2O2 formation was accompanied by a large decrease in the H2O2 decomposition activity. The bromide anions change the electronic properties of the Pd.

Rietveld Refinement and Activity of CO Oxidation over Pd/Ce0.8Zr0.2O2 Catalyst Prepared via a Surfactant-Assisted Route

J. A. WANG, L. F. CHEN, M. A. VALENZUELA, A. MONTOYA, J. SALMONES and P. DEL ANGEL, Appl. Surf. Sci., 2004, 230, (1–4), 34–43 doi:10.1016/j.apsusc.2003.08.111 http://dx.doi.org/10.1016/j.apsusc.2003.08.111

Ce0.8Zr0.2O2 nanophases (1) were synthesised using a surfactant-assisted method. Structural refinement by the Rietveld method confirmed that many cationic lattice defects were formed in the crystals of (1). Pd/Ce0.8Zr0.2O2 calcined at 873–1173 K exhibited a more stable catalytic activity for CO oxidation, and also performed a lower light-off temperature at cool start < 373 K, in comparison with Pd/CeO2.

Drastic Enhancement of SCR of NO over Ir Catalyst through Formation of Metallic Iridium on Na-Zeolite

J. SHIBATA, H. YOSHIDA, A. SATSUMA and T. HATTORI, Chem. Lett., 2004, 33, (7), 800–801 LINK doi:10.1246/cl.2004.800 http://dx.doi.org/10.1246/cl.2004.800

Ir/Na-zeolite catalysts (1) have excellent activity at 500 K for the SCR of NO in a He atmosphere also containing CO/H2. Low loaded (1) (0.5 wt.% Ir) could be used. Ir LIII-edge XANES and CO2–H2 titration were carried out. The Ir forms a highly active metallic species with low oxidation; this Ir species is highly dispersed. Ir/Na–MOR mordenite zeolite has the highest activity.

Local Barrier Height of Ir/TiO2 Model Catalysts

Y. MAEDA, T. AKITA, M. OKUMURA and M. KOHYAMA, Jpn. J. Appl. Phys., 2004, 43, (7B), 4595–4598 LINK doi:10.1143/JJAP.43.4595 http://dx.doi.org/10.1143/JJAP.43.4595

Ir was deposited on TiO2 (110)-(1×2) surfaces by vacuum evaporation to form Ir/TiO2 model catalysts (1). The local barrier height (LBH) of (1) was measured using scanning tunnelling microscopy and compared with that of Au/TiO2 catalyst. The Ir was oxidised to IrO2 by annealing at 1073 K. The LBH of IrO2 particles was almost the same as that of the TiO2 support, while the LBH of Au particles was 0.3 eV larger. The charge transfer between IrO2 and TiO2 is small. Electrons are transferred from TiO2 to Au.

HOMOGENEOUS CATALYSIS

Synthetic Applications of Oxime-Derived Palladacycles as Versatile Catalysts in Cross-Coupling Reactions

D. A. ALONSO, L. BOTELLA, C. NÁJERA and M. C. PACHECO, Synthesis, 2004, (10), 1713–1718 LINK doi:10.1055/s-2004-815992 http://dx.doi.org/10.1055/s-2004-815992

Palladacycles derived from 4,4′-dichlorobenzophenone and 4-hydroxyacetophenone oximes are efficient and versatile pre-catalysts for C–C bond coupling reactions. These coupling reactions include Mizoroki-Heck, Suzuki-Miyaura, Stille, Ullmann-type, Sonogashira, sila-Sonogashira, Glaser and acylation of alkynes under very low loading conditions. The high yielding reactions can be carried out in air using either organic or aqueous solvents.

Dioxygen-Promoted Regioselective Oxidative Heck Arylations of Electron-Rich Olefins with Arylboronic Acids

M. M. S. ANDAPPAN, P. NILSSON, H. VON SCHENCK and M. LARHED, J. Org. Chem., 2004, 69, (16), 5212–5218 LINK doi:10.1021/jo049434t http://dx.doi.org/10.1021/jo049434t

Heck arylations of electron-rich heteroatom-substituted olefins with arylboronic acids to give acyclic enamides were carried out using Pd(OAc)2 with 2,9-dimethyl-1,10-phenanthroline (dmphen) as the catalyst system. The reactions were carried out under O2. The dmphen ligand controls the internal regioselectivity and mediates a reoxidation of Pd(0) with O2, thus allowing a low catalyst loading. Controlled microwave heating and increased O pressure were used to reduce the reaction time to 1 h.

Microwave Promoted Heck Reactions Using an Oligo(ethylene glycol)-Bound SCS Palladacycle under Thermomorphic Conditions

D. E. BERGBREITER and S. FURYK, Green Chem., 2004, 6, (6), 280–285 LINK doi:10.1039/b316342c http://dx.doi.org/10.1039/b316342c

Pd catalysed Heck couplings using an air-stable, H2O-soluble oligo(ethylene glycol)-bound SCS palladacycle catalyst (1) and microwave irradiation gave cinnamic acid derivatives in < 1 h. Recycling of (1) was achieved using a 10% aqueous dimethylacetamide-heptane thermomorphic system that was biphasic during the catalyst recovery step.

The RuO4-Catalysed Dihydroxylation, Ketohydroxylation and Mono Oxidation–Novel Oxidation Reactions for the Synthesis of Diols and α-Hydroxy Ketones

B. PLIETKER and M. NIGGEMANN, Org. Biomol. Chem., 2004, 2, (17), 2403–2407 LINK doi:10.1039/b407937j http://dx.doi.org/10.1039/b407937j

A study of RuO4-catalysed oxidations of alkenes resulted in the development of the first RuO4-catalysed ketohydroxylation of olefins. Mechanistic studies of both dihydroxylation and ketohydroxylation gave rise to the first regioselective catalytic monooxidation of vic-diols. When applied in a two-step sequence of asymmetric dihydroxylation and regioselective monooxidation, enantiopure α-hydroxy ketones were obtained.

FUEL CELLS

CO Tolerance of Commercial Pt and PtRu Gas Diffusion Electrodes in Polymer Electrolyte Fuel Cells

F. HAJBOLOURI, B. ANDREAUS, G. G. SCHERER and A. WOKAUN, Fuel Cells, 2004, 4, (3), 160–168 LINK doi:10.1002/fuce.200400021 http://dx.doi.org/10.1002/fuce.200400021

The CO tolerance of Pt and PtRu anodes from E-Tek and Tanaka were examined in PEFCs using AC impedance spectroscopy along steady-state current-voltage curves. The Tanaka PtRu (40:60) anode is reported to have better CO tolerance under the selected operating conditions. The impedance spectra of the Tanaka PtRu anode did not show any inductive behaviour and its CO surface coverage was low.

Synthesis and Characterization of Methanol Tolerant Pt/TiOx/C Nanocomposites for Oxygen Reduction in Direct Methanol Fuel Cells

L. XIONG and A. MANTHIRAM, Electrochim. Acta, 2004, 49, (24), 4163–4170 LINK doi:10.1016/j.electacta.2004.04.011 http://dx.doi.org/10.1016/j.electacta.2004.04.011

The title nanocomposites (1) were prepared by: depositing hydrated TiO2 on Pt/C; reducing H2PtCl6 with Na formate on C-supported hydrated TiO2 (TiO2/C); and simultaneously depositing hydrated TiO2 and reducing H2PtCl6 with Na formate on C support. (1) underwent heat treatment at 500 and 900°C in 90% Ar/10% H2. Some of (1) had higher catalytic activity than Pt/C. (1) also exhibited better MeOH tolerance than Pt/C.

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