ABSTRACTS: April 1989

Journal Archive

Platinum Metals Rev., 1989, 33, (2), 81

ABSTRACTS: April 1989

of current literature on the platinum metals and their alloys

PROPERTIES

Steady-State Kinetics of the Catalytic Reduction of Nitrogen Dioxide by Carbon Monoxide on Platinum

d. t. wickham and b. e. koel, J. Catal., 1988, 144, (2), 207–216

Steady-state kinetics of NO₂+CO reaction on polycrystalline Pt foil, producing CO₂+NO, have been studied at pressures of 1 × 10⁻⁷ −5 × 10⁻⁶ Torr and temperature of <400K. The CO₂ formation rate was at least one order of magnitude less than for CO+O₂ and CO+NO reactions under similar conditions. The rate was first-order in CO pressure when <0.25 and first-order in NO₂ pressure when activation energy was 7.2kcal/mol, consistent with CO+O₂ reaction. When activation energy was 4.3kcal/mol, 29kcal/mol less than that for CO+O₂ at low temperatures when the reaction was first-order in oxidant.

CO Adsorption on Pt(111) Modified with Sulfur

m. kishkinova, a. szabó and j. t. yates, J. Chem. Phys., 1988, 89, (12), 7599–7608

Adsorption of CO on clean and S-covered Pt(111) has been characterised by various techniques. Rate of CO adsorption on p (2 × 2)0.25S/Pt(111) decreased by a factor of 2 and only one CO adsorption state with maximum coverage, Θ_CO ≃ 0.25CO/Pt was detected. This was assigned to terminal-CO adsorbed on the next nearest Pt atom and separated from S by 3.72 Å. A lower CO binding energy compared to corresponding CO bonding on clean Pt(111), was observed. A reduction of the vibrational amplitude of CO bending modes indicated a S-induced stiffening of the CO surface motions.

Electron Microscope Study on Martensitic Transformations in Fe-Pt Alloys: General Features of Internal Structure

s. muto, r. oshima and f. e. fujita, Metall. Trans., 1988, 19A, (11), 2723–2731

Martensitic transformations of Fe-Pt alloys near the composition of Fe₃Pt with various degrees of order have been studied systematically by transmission electron microscopy. The two types of martensitic transformations, fcc-bct(bcc) and fcc-fct, were shown to be independent and competitive. As the degree of order of austenite (L1₂ superlattice) increased, the dislocation density of bct(bcc) martensite was remarkably reduced and the shape of internal twins changed, which was related to thermoelastic behaviour and reversibility of the transformation.

Nuclear Magnetic Resonance Study of Pt-Rh Bimetallic Clusters

z. wang, j. -p. ansermet, c. p. slichter and j. h. sinfelt, J. Chem. Soc., Faraday Trans. 1, 1988, 84, (11), 3785–3802

Pulsed NMR studies have been used to study the composition profile of Pt-Rh particles and the electronic properties of the adsorption sites. Results showed that each individual cluster contained both Pt and Rh. For lower dispersion samples energy-dispersive spectroscopy showed that the centre of the particles was pure Pt. Surface layer Pt concentration has also been measured for higher dispersion samples. ¹⁹⁵Pt-¹³C spin-echo double resonance (SEDOR) was used to measure the fraction of Pt atoms in the surface layer of clusters on which ¹³CO was adsorbed. Results showed that the resonance frequency of ¹³CO was independent of whether the CO was bonded to Pt or Rh, and thus the ¹³CO frequency shift was a non-local phenomenon, and corresponded to that of pure Rh particles.

Coevaporation and Ion Implantation of Pd₅₀Ti₅₀ and Pt₅₀Ti₅₀ on AISI Stainless Steels for Reducing Wear and Friction

l. r. zheng, l. s. hung and j. w. mayer, J. Appl. Phys., 1989, 65, (1), 300–304

Pin-on-disk type wear tests have been conducted on Pt₅₀ Ti₅₀ and Pd₅₀ Ti₅₀ alloy films deposited on stainless steel and irradiated with ion beams. The addition of Pt₅₀ Ti₅₀ and Pd₅₀ Ti₅₀ reduced wear and friction. Implantation of Xe slightly improved tribomechanical properties. Implantation of N dramatically reduced wear and friction, due, possibly, to nitride precipitation hardening and/or formation of lubricious oxides during sliding. The as-deposited films were amorphous and transformed to their corresponding intermetallic compounds on annealing. Sliding tests on amorphous and crystalline films did not show a significant difference in friction and wear behaviour.

Reaction of Thin Pd Films with Al(111) and Al(110) Surfaces

r. j. smith, a. w. denier van der gon and j. f. van der veen, Phys. Rev. B, 1988, 38, (17), 12712–12715

Results from high-resolution ion backscattering studies of Pd reaction with Al(111) and Al(110) have shown that alloy was formed on the surface for Pd coverages from 0 to 7×10¹⁵ atoms/cm². A reaction model is presented in which each Pd atom effectively displaced one Al substrate atom, with an additional two monolayers of disordered Al at the interface. A Pd film ultimately grew on the reacted layer.

Palladium-Cerium-Hydrogen Solid Solutions. I. Thermodynamic Properties. II. Kinetic Properties

m. yoshihara and r. b. mclellan, Acta Metall., 1988, 36, (12), 3217–3224; 3225–3229

Solubility isobars in the temperature range 625−1250K have been measured at H₂ pressure of 1.01×10⁵ Nm⁻² for solutions of H in Pd-Ce matrixes containing up to 12 at.% Ce. The partial enthalpies of the H atoms at any temperature showed a minima as a function of Ce concentration. H-diffusivity has been measured at 280−330K and obeyed an Arrhenius relation with reciprocal temperature and increased with increasing Ce content. The corresponding activation enthalpies progressively decreased. The kinetic and thermodynamic behaviour was interpreted in terms of a cell model in which the cells (interstitial sites) encompass two coordination shells of lattice atoms.

The Partitioning of Alloying Elements in Vacuum Arc Remelted, Pd-Modified PH 13–8 Mo alloys

m. j. cieslak, j. a. vandenavyle, m. j. carr, c. r. hills and r. e. semarge, Metall. Trans., 1988, 19A, (12), 3063–3069

Studies of the partitioning of alloying elements in as-vacuum arc remelted (VAR), Pd-modified PH 13–8 Mo stainless steels containing up to 1.02wt.% Pd have shown that the microstructure at room temperature was duplex martensitic-ferritic. Additions of Pd to PH 13–8 Mo caused a small reduction in the amount of retained ferrite and an apparent solubility limit of ∼0.15wt.% Pd in ferrite was observed. Pd partitioned strongly to the austenite (subsequent martensite) during solidification and cooling from solidus. The martensite start temperature, M_s, decreased with increasing Pd concentration by ∼ 26°C per wt.% Pd. Partition ratios of the other alloying elements were not affected by Pd and were consistent with those previously observed in duplex Fe-Cr-Ni stainless steel solidification structures.

On the Penetration and Solution of Hydrogen in Amorphous Pd₈₀Ge₂₀ and Pd₈₀Si₂₀ before and after Crystallization

g. jorge, r. durand, r. faure and r. yavari, J. Less-Common Met., 1988, 145, (1–2), 383–393

A low-amplitude potentiostatic step method and an impedance method have been used for the first time to accurately determine diffusion coefficients (D_H) and bulk H concentrations (C_H) in Pd₈₀Ge₂₀ and Pd₈₀Si₂₀ amorphous (a-) alloys and their corresponding crystallised alloys. For a-Pd₈₀Si₂₀, D_H values increased with C_H, from 0.3×10⁻⁸ to 1.7×10⁻⁸cm²s⁻¹, then decreased slowly. This behaviour has been attributed to the statistics of H-defect interactions, followed by the effects of internal stress. Similar behaviour was observed for a-Pd₈₀Ge₂₀ though c_H values were slightly higher at the same potential (the same equilibrium pressure).

Surface Modification of Pd-Plated Ti Alloys by Ion Beam Mixing

y. chen, j. jin, p. wang, j. chen and y. wang, Nucl. Instrum. Methods Phys. Res., 1988, B34, (1), 47–52

Studies on Ti-Pd surface alloys, prepared by bombarding a Pd-plated Ti alloy with Xe ions, have shown that Pd distribution was homogeneous through the thickness of the surface layer, a TiC hardening phase was formed in the surface layer and a TiO₂ passive film was present on the exposed surface. The corrosion rate of the Ti-Pd surface alloy in boiling H₂SO₄ was ∼ 1/60 that of the Ti alloy substrate and in the outer-surface region it made a 3 orders of magnitude improvement in corrosion rate. Many differences in micromorphology between Ti-Pd surface alloy and the Ti alloy substrate were observed after corrosion testing. Microhardness of the surface alloy increased 43% and the dry friction coefficient decreased 40% compared to the Ti alloy substrate.

Hydrogen Solubility in Palladium-Yttrium Alloys

y. sakamoto, k. kajihara, y. fukusaki and t. b. flanagan, Z. Phys. Chem. Neue Folge, 1988, 159, (1), 61–74

Pressure-composition isotherms have been determined for the absorption of H by disordered Pd-Y alloys (2−10at.% Y) at up to 100atm H₂ and at 273−534K. The relative partial molar enthalpy, of solution of H at infinite dilution became more exothermic with increased Y content, showing analogous trends to “expanded” Pd alloys. The partial molar entropy of decreased with Y content. The apparent H-H attractive interaction decreased with Y content and the activity coefficient of H increased. The standard enthalpy change for β -hydride formation became more exothermic with Y content, and the entropy change decreased slightly.

The Kinetics and Mechanisms of Alkali Metal-Promoted Dissociation: A Time Resolved Study of NO Adsorption and Reaction on Potassium-Precovered Rh(100)

l. j. whitman and w. ho, J. Chem. Phys., 1988, 89, (12), 7621–7645

A comprehensive characterisation of the co-adsorption of NO and K on Rh(100) at 100K has been determined using LEED, AES, work function change measurements, TPRS and TREELS. It has been shown that the effects of alkali metals on all the different steps along the reaction pathway leading to dissociation (adsorption, interconversion among adsorption sites, desorption) play an important role in the promotion of catalytic reactions. Adsorption of K on Rh(100) and K coverage calibration are described. The determination of absolute NO coverages is explained. The NO sticking coefficient and maximum coverage were determined as a function of K precoverage. Individual NO adsorption sites were determined, as well as the kinetics of the NO dissociation reaction.

CHEMICAL COMPOUNDS

Synthesis and Characterization of a New Class of Organo-Polynuclear Complexes Containing Cationic Palladium Atoms

k. onitsuka, h. ogawa, t. joh and s. takahashi, Chem. Lett. Jpn., 1988, (11), 1855–1856

Cationic organopalladium complexes having an extended structure are described as a new class of organo-polynuclear complexes containing cationic Pd atoms. The synthesis and properties of these complexes containing unique backbones of cationic Pd atoms with regular arrangement and alternate linkages of acetylene and bipyridyl, are reported.

Iridium Liquid Crystal Complexes by Coordination of Non-Mesogenic Organic Ligands

m. a. esteruelas, l. a. oro, e. sola, m. b. ros and j. l. serrano, J. Chem. Soc., Chem. Commun., 1989, (1), 55–56

The first family of Ir liquid crystal complexes [IrCl(CO)₂L], where L is NC₅H₄-CH=N-C₆H₄R, formed by the complexation of a non-mesogenic organic ligand directly to the metal is reported. The mesogenic complexes melted at similar or even lower temperatures than their corresponding ligand and showed a clear thermochromism to a red colour at their melting points.

Synthetic Routes to New Polypyridyl Complexes of Osmium(II)

e. m. kober, j. v. caspar, b. p. sullivan and t. j. meyer, Inorg. Chem., 1988, 27, (25), 4587–4598

The complexes [Os^II(N-N)₂(L)(L′)]ⁿ⁺, where N-N is 2,2′-bipyridine or 1,10-phenanthroline as chromophoric acceptor, and L and L′ are π -acid ligands, and the complexes [Os^II(N-N)(L)₄]ⁿ⁺, where ligands L are not necessarily equivalent, have been prepared by established and new methods. This extended series of new photochemically and thermally stable photosensitisers have tunable redox properties and metal to ligand charge transfer excited-state properties that can be varied systematically by changing the nonchromophoric ligands. The spectral, electrochemical and chemical properties of the Os(II) complexes were compared to those of Ru complexes.

ELECTROCHEMISTRY

SNIFTIRS with a Flow Cell: the Identification of the Reaction Intermediates in Methanol Oxidation at Pt Anodes

r. j. nichols and a. bewick, Electrochim. Acta, 1988, 33, (11), 1691–1694

Adsorbed COH and CH_xOH have been identified as the intermediates in CH₃OH oxidation at Pt electrodes in acid solution using a spectrochemical flow cell and SNIFTIRS, an external specular reflectance method. The flow of solution prevented depletion of the reactant in the thin electrolyte layer.

In Situ Scanning Tunneling Microscopy for Platinum Surfaces in Aqueous Solutions

k. itaya, s. sugawara and k. higaki, J. Phys. Chem., 1988, 92, (17), 6714–6718

Detailed in situ scanning tunnelling microscope (STM) studies of fine structures of hemispherical Pt particles electrodeposited on highly ordered pyrolytic graphite revealed many irregular dislocations such as steps and boundaries, and the presence of Pt whiskers. The first in situ STM studies of Pt electrode surfaces activated by electrochemical potential cycles in sulphuric acid are also reported. Very regular parallel-terraces appeared after activation.

Peculiarities of Sorption of Platinum(II) Complexes on Hydrated Zirconium Dioxides from Aqueous Solutions

s. a. simanova, g. s. krylova, e. s. boichinova and l. v. nikolskaya, Zh. Prikl. Khim., 1988, 61, (10), 2220–2223

Studies of sorption properties of ZrO₂ in aqueous solution of K₂[PtCl₄] in the presence of various background electrolytes showed that during sorption of Pt(II) on ZrO₂ from alkali metal salts (Na⁺,K⁺) elecrolytes, the extraction of Pt(II) decreased in order of anions NO₃⁻> SO₄²⁻> Cl⁻. The effect of the nature of background salt anions on the extraction of Pt(II) was determined by three factors which were the relationship with regards to ZrO₂, structural behaviour and activation capacity of the initial chlorocomplex.

Intermediates and Products of Ethanol Oxidation on Platinum in Acid Solution

b. bittins-cattaneo, s. wilhelm, e. cattaneo, h. w. buschmann and w. vielstich, Ber. Bunsenges. Phys. Chem., 1988, 92, (11), 1210–1218

Adsorption and anodic oxidation of EtOH on Pt electrodes in acidic solutions has been studied by three independent methods. Fourier transform i.r. reflection-absorption spectroscopy identified CO_ad adsorbate at Pt electrodes, and thermal desorption mass spectroscopy identified, in addition, COH_ad. On-line mass spectroscopy showed CH₄ formation occurred during the cathodic sweep of the voltammogram. The main products of EtOH oxidation from the bulk were CO₂ and acetaldehyde.

Electro-Catalytic Activity on Supported Platinum Crystallites for Oxygen Reduction in Sulphuric Acid

m. watanabe, s. saegusa and p. stonehart, Chem. Lett. Jpn., 1988, (9), 1487–1490

Studies have shown that the “lost activity” of highly dispersed Pt catalysts caused by the so-called crystallite size effect can be recovered completely by using a series of high surface area C-black supports, that is even at Pt crystallite size of 1.4nm. The apparent specific activity for all dispersions was obtained when the intercrystallite distance was <20nm.

Electrodeposition of Platinum Microparticles into Polyaniline Films with Electrocatalytic Applications

k. m. kost, d. e. bartak, b. kazee and t. kuwana, Anal. Chem., 1988, 60, (21), 2379–2384

Microparticles of Pt have been electrodeposited as a 3-dimensional array in fibril-type polyaniline (PA) films on glassy C electrodes. These Pt/PA/C electrodes showed high activity for H₂ evolution and CH₃OH oxidation, and remarkable catalytic and mechanical stability in acidic media. The PA films contributed a substantial amount of charge during CH₃OH oxidation at potential 0.6V vs. Ag/AgCl, and also protected the Pt microparticles against particle loss and contamination from the bulk solution.

Dissolution of Platinum Anodes in Sulphuric Acid Solution

k. -i. ota, s. nishigori and n. kamiya, J. Electroanal. Chem. Interfacial Electrochem., 1988, 257, (1–2), 205–215

Studies of the Pt corrosion on H₂SO₄ aqueous solution made by measuring the weight loss showed that rate of weight loss of the Pt anode in H₂SO₄ increased with increasing current density, temperature and concentration of H₂SO₄ up to 1M (M = mol/dm³). At 40°C, the corrosion rate was proportional to the first order of the current density and its value was ∼ 5μ g A⁻¹h⁻¹. The corrosion of Pt was retarded by the formation of an oxide layer.

Electrochemical Formation of Platinum/Aluminium Surface Alloys

i. bahatt, l. nacamulli-piran and e. gileadi, Denki Kagaku, 1988, 56, (5), 339–346

Cyclic voltammetry studies of Pt electrodes in solutions of Al₂Br₆ (1.0M) and KBr (0.8M) in ethylbenzene have shown that two cathodic processes can take place: reduction of the solvent and formation of Pt-Al surface alloy. The Pt-Al alloy formation was shown by an anodic peak when the cathodic limit of the potential sweep was more negative than +0.2V vs. a reversible Al electrode (RAlE) in the same solution. The height of this peak was a measure of the amount of alloy formed and increased as the cathodic limit of the cyclic voltagram was made more negative. The surface alloy maintained an open-circuit potential of +(20−35)mV vs. RAlE.

Study of the Methanol Adsorbates on Pt(100) and Pt(111) Single Crystal Surfaces

b. bittins-cattaneo, e. santos, w. veilstich and u. linke, Electrochim. Acta, 1988, 33, (11), 1499–1506

The formation of CH₃ OH adsorbate as a structure sensitive process has been studied on reproducibly prepared, clean and either well ordered (undisturbed) or cycled (disturbed) Pt(100) and Pt(111) single crystal electrodes. Essential differences were found. The data is interpreted in terms of parallel pathways to both COH and CO adsorbed intermediates.

Voltammetric Stabilization of Electrofaceted (100)-Type Platinum Electrodes in Acidic Solutions

s. a. d. aldabe de bilmes, m. c. giordano and a. j. arvia, Can. J. Chem., 1988, 66, (9), 2259–2267

The voltammetric stabilisation of electrofaceted (100)-type Pt electrodes has been followed by conventional voltammetry in the H-electroadsorption/electrodesorption potential range in 1M H₂SO₄ (0−35°C) or 0.5M HClO₄ (−2−35°C). The influence of CO adsorption was studied. Two well-defined stabilisation profiles at 0.1V/s corresponding to H-and O-adsorption stabilised electrofaceted (100)-type Pt, were observed. The changes in conventional voltammetric profiles were associated with adsorption or electroadsorption processes. The influence of competitive adsorption between anions in the electrolyte and H-adatoms is reported. The influence of temperature was less than that of solution structure at the electrode/solution interface.

Catalytic Behaviour of the Palladium Electrode in Oxidation Processes of Methanol and Formic Acid. 1. Activity of the Palladium Electrode. 2. Activity of the Palladium Electrode, Modified on its Surface by Traces of Other Metals

a. mayor, p. regull and l. victori, Afindad, 1988, 45, (417), 411–416; 417–421

Cyclic voltammetry has been used to study the catalytic activity of a Pd electrode in acid (0.5M H₂SO₄) and alkali (1M KOH) media, and a Pd electrode modified with diverse metals, for the oxidation of CH₃OH and HCO₂H. Oxidation of CH₃OH was not catalysed by Pd in acidic medium. Formation of strongly adsorbed organic intermediates which blocked the electrode surface is also reported and depended on the limiting anodic potential. Electrodes modified with Cd and Tl showed increased activity due to inhibition of formation of poisoning organic species.

The Generalized Lewis Acid-Base Titration of Palladium and Niobium

m. cima and l. brewer, Metall. Trans., 1988, 19B, (6), 893–917

An electronic interaction model analogous to the Lewis acid-base concept for non-transition elements has been used to explain the high thermodynamic stability of Nb-Rh, Ti-Pd and Ti-Rh alloys. The analogy was demonstrated by titration of Pd by addition of Nb. The activity of Nb in solid Pd was measured as a function of concentration using solid state galvanic cells, Pt/NbO₂, Nb₂O_4.8/Y-doped ThO₂/NbO_y,Nb_(Pd)/Pt, and study of ternary phase diagrams for Pd-Nb-O and Rh-Nb-O. Thermochemical data for the alloys studied is reported. Results showed that both the nuclear charge of the atom and the crystal field splitting of the valence orbitals significantly affected the basicity of the platinum group metals. The results were consistent with a generalised Lewis acid-base concept.

PHOTOCONVERSION

Suspensions of Semiconductors with Microheterojunctions—A New Type of Highly Efficient Photocatalyst for Dihydrogen Production from Solution of Hydrogen Sulphide and Sulphide Ions

e. n. savinov, yu. a. gruzdkov and v. n. parmon, Int. J. Hydrogen Energy, 1989, 14, (1), 1–9

Active photocatalysts have been prepared with ease by developing suspensions of semiconductors with heterojunctions. Additions of colloidal Pt to a suspension of Zn_0.17Cd_0.83S/Cu_xS increased the rate of photocatalytic H₂ production from a solution of S²⁻ and SO₃²⁻, and a record quantum yield of φ(H)=0.5±0.05 is reported. The system Pt-Zn_0.17Cd_0.83S/Cu_xS provided a wide spectrum of action and a much higher efficiency of solar energy conversion in comparison to a CdS photocatalyst used for H₂ formation from S²⁻ and SO₃²⁻ solution.

Pt-TiO₂ Thin Films on Glass Substrates as Efficient Photocatalysts

m. takahashi, k. mita, h. toyuki and m. kume, J. Mater. Sci., 1989, 24, (1), 243–246

The photocatalytic activity of Pt-TiO₂ thin films (20−100nm thickness) prepared on Vycor glass substrates by spray-coating has been studied through the CH₃OH dehydrogenation reaction. X-ray diffraction observations revealed a dramatic increase in activity for film thickness of > ∼ 50nm, on the formation of anatase. Below 50nm amorphous TiO₂ was formed. Compared with Pt-TiO₂ powders the thin films showed a remarkable improvement in photocatalytic activity due to the high dispersion of the catalyst.

Polymerized Micelle-Protected Platinum Clusters. Preparation and Application to Catalyst for Visible Light-Induced Hydrogen Generation

n. toshima, t. takahashi and h. hirai, J. Macromol. Sci.-Chem., 1988, A25, (5–7), 669–686

Micelle-protected Pt clusters have been successfully prepared by photoreduction of H₂PtCl₆ in H₂O in the presence of unsaturated surfactants, which facilitated radical polymerisation of the micelle. The Pt clusters proved to be highly active catalysts for visible light-induced H₂ generation in the system EDTA/Ru(bpy)₃²⁺/MV²⁺ (where MV²⁺ is methyl viologen; bpy is 2,2’-bipyridine; EDTA is ethylenediaminetetraacetic acid). These Pt clusters showed higher activity than linear polymer protected clusters. Non-ionic polymer systems enhanced catalytic activity compared to those which had hydrophilic ionic groups. The non-ionic polymerised micelle formed rigid hydrophobic cores which helped charge separation and formation of a sequential potential field: excited Ru(bpy)₃²⁺ in aqueous phase >MV²⁺ near the micelle surface > Pt cluster near the centre of the micelle.

Absorption Spectra, Luminescence Properties and Electrochemical Behaviour of Two New Cyclometallated Palladium(II) Complexes

d. sandrini, m. maestri, m. ciano, v. balzani, r. lueoend, c. deuschel-cornioley, l. chassot and a. von zelewsky, Gazz. Chim. Ital., 1988, 118, (9), 661–665

Results from studies of cyclometallated Pt(phpz)₂ and Pt(phpz)(thpy), where phpz⁻ and thpy⁻ are the ortho-C-deprotonated forms of 1–phenylpyrazole and 2–2’ (thienyl)pyridine, have been compared with those for free protonated ligands and the previously studied Pt(thpy)₂ complex. The complex Pt(phpz)(thpy) showed a very high luminescence quantum yield (φ_em=0.4; 10 times that of [Ru(bpy)₃]²⁺) and long lived (τ =15μς ) luminescence even in fluid solution at room temperature. Luminescence originated from the lowest metal-to-ligand charge transfer (MLCT) state and involved the more easily reduced thpy⁻. Correlations between spectroscopic and electrochemical data are discussed.

Direct Current Electrochemiluminescence of Ru(bpy)₃²⁺

r. igarashi, y. nosaka, h. miyama, m. kaneko and m. yokoyama, J. Electrochem. Soc., 1988, 135, (12), 2987–2990

Direct current (dc) electrochemiluminescence (ECL) of Ru(bpy)₃²⁺ (bpy is 2,2’-bipyridine) has been observed in acetonitrile solution by using an Al-sheet working electrode at negative potential. The dc ECL originated from the excited state of Ru(bpy)₃²⁺. Continuous emission of ECL was observed over all of the sheet cathode, and response time of the luminescence was faster than that of alternating current ECL.

The Dependence of the Redox Potentials in the System Ru[(C_nH_2n+1)₂bpy]₃^2+/3+/Methylviologen^2+/+ on the Hydrocarbon Chain Length and on the Ratio of Water and Acetonitrile in the Solvent

g. greiner, m. wörner and h. rau, Ber. Bunsenges. Phys. Chem., 1988, 92, (11), 1380–1383

Cyclic voltammetry in acetonitrile has shown that there was a marked decrease of the redox potential of Ru[(C_nH_2n+1)₂bpy]₃ (bpy is 2,2’-bipyridine; n=0,1,5,7) on hydrocarbon substitution but the chain length had no strong effect. The free enthalpy of electron transfer reaction between oxidised complexes and reduced methylviologen was obtained for different H₂O/acetonitrile compositions. The electron transfer was less exergonic for the substituted complexes and the ∆G° vs. solvent composition plot showed a minimum for the unsubstituted and methyl-substituted complex. The effect of the supporting electrolyte on ∆G° is reported for the methyl-substituted complex. The relevance of these results for photo-induced electron transfer is given.

Photocurrent Measurements at the Interface between Two Immiscible Electrolyte Solutions

f. l. thomson, l. j. yellowlees and h. h. girault, J. Chem. Soc., Chem. Commun., 1988, (23), 1547–1549

The electrochemical measurement of a photocurrent has been successfully achieved using the [Ru(bpy)₃]²⁺/C₇V²⁺ system (bpy is 2,2’-bipyridine; C₇ V is heptyl-4,4’-bipyridinium) across a liquid/liquid interface, with the organic phase containing the quencher C₇ V²⁺ and the aqueous phase containing the sensitiser [Ru(bpy)₃]²⁺.

ELECTRODEPOSITION AND SURFACE COATINGS

A New Pure Palladium Electrodeposit for Electronic Applications

a. blair, g. karustis and j. wilcox, Trans. Inst. Met. Finish., 1989, 67, (1), 10–12

A new Pd electroplating bath has been developed which operates at high deposition speeds (4.5μ m/min was achieved comfortably) and over wide pH and temperature ranges, without excessive maintenance or operator discomfort. The bath consisted of a combination of a stable Pd complex, a simple conducting salt which did not hydrolyse and a salt buffer which was especially effective at inert anode surfaces where local pH tends to fall dramatically due to destruction of OH⁻ ions. The cathode efficiency was ∼85%.

Initiation of Electroless Copper Plating Using Pd⁺²/Poly(acrylic acid) Films

r. l. jackson, J. Electrochem. Soc., 1988, 135, (12), 3172–3173

A new method for the initiation of electroless deposition of Cu onto dielectric substances using Pd²⁺/poly(acrylic acid) films is reported. A printed circuit board substrate was coated with a thin film of poly(acrylic acid) by dip-coating. The carboxyl groups of the poly(acrylic acid) film were then complexed with Pd²⁺ upon immersion in aqueous PdSO₄. On subsequent immersion in the electroless Cu plating bath the Pd²⁺ was reduced to Pd⁰, forming the active catalyst for initiation of Cu plating.

Electrodeposition of Palladium-Nickel Coatings from Sulphamate Electrolytes

l. i. kadaner, t. v. slyusarskaya and z. v. ivanova, Ukr. Khim. Zh. (Russ. Ed.), 1988, 54, (12), 1284–1286

The 90−20%Pd-Ni alloys were prepared by electrodeposition from sulphamate electrolyte containing Pd and Ni chlorides in the metal ratio of 8–10 and 25–30, respectively, NH₄-sulphamate 60–130, NH₄Cl 50–100, in 25% NH₃, pH 8.3–8.5, at 25−35°C and cathodic current density of 2–3A/dm². The microhardness of the Pd–Ni coatings was 1.7–2.0 times higher than that of Pd coatings.

Laser-Induced Selective Copper Deposition on Polyimide

h. s. cole, y. s. liu, j. w. rose and r. guida, Appl. Phys. Lett., 1988, 53, (21), 2111–2113

The selective deposition of catalytic amounts of Pd on polyimide by laser irradiation of organometallic Pd compounds with an Ar ion laser at 351nm is reported. Subsequent electroless Cu deposition was catalysed by a few monolayers of the deposited Pd, producing smooth Cu lines. Fast scanning rates of a few cm/s were achieved. The process constitutes a fast direct writing technique useful in packaging applications for high-density discretionary interconnects.

APPARATUS AND TECHNIQUE

High Performance Micro-Enzyme Sensor Using Platinized Microelectrode

y. ikariyama, s. yamauchi, m. aizawa, t. yukiashi and h. ushioda, Bull. Chem. Soc. Jpn., 1988, 61, (10), 3525–3530

A unique micro-enzyme sensor for the determination of glucose has been fabricated by incorporating glucose oxidase into the micropores of a platinised microelectrode of diameter (d) from 10 to 200μ m. Electrodes with d>50μ m had a detection limit of 5×10⁻⁷ mol/l for glucose and showed excellent linearity in the concentration range 5 × 10⁻⁷ to 10⁻² mol/l. For d= 10μ m, the detection limit was 10⁻⁵ mol/l and linearity range 10⁻⁵ to 5×10⁻⁵ mol/l. Sensor response time was <3s for all samples, and the coefficient of variation for glucose (1mM) determination was within 2%. Sensor output was stable over four weeks.

Catalytic-Adsorptive Stripping Voltammetric Measurements of Hydrazines

j. wang and z. taha, Talanta, 1988, 35, (12), 965–968

Voltammetric determinations of hydrazines based on their H₂ catalytic wave in formaldehyde-Pt-sulphuric acid media, is reported. Compared to conventional (anodic) measurements this method showed enhanced sensitivity due to adsorption of Pt-formazone complex on the hanging Hg drop electrode, (μ M concentrations of simple hydrazines were determined), and showed better selectivity as oxidisable compounds do not interfere.

Catalytic Removal of Hydrogen

a. k. chakraborty, Kerntechnik, 1988, 53, (1), 53–54

A passive device based on the catalytic transformation of H₂ to H₂O has been designed for reducing the potential danger of H₂ burning in the containment of a reactor during a severe accident. The device was based on a sandwich foil of Pt,Ru(20nm) on Pd(100nm) on V(30μ m) on Pd(100nm) on Al(20μ m). Alloys of Pd, Ni and Cu have been developed as fast acting catalytic surfaces and as highly active protection against catalyst poisons.

Adjustable Selective Profiles Using Cermet Absorbing Films

c. sella and j. lafait, Thin Solid Films, 1988, 164, 387–390

Optical simulations of some specially adjusted spectral profiles and their experimental realisation using a 3-layer coating of a Pt-Al₂O₃ cermet (metal-dielectric composite) absorbing film, an Al₂O₃ anti-reflecting film, and an Al₂O₃ underlayer, deposited on a metallic substrate, are reported. The cermet films were spectrally selective showing total absorption in the visible range and high reflection in the i.r., with an adjustable cut-off wavelength. These coatings were stable at high temperatures and showed high mechanical resistance. These profiles can be used as selective absorbers for many specific applications as a result of their cut-off wavelength.

Effects of Hydrogen Gas on Palladium/LB Film/Silicon MIS Devices

n. j. evans, g. g. roberts and m. c. petty, Sens. Actuators, 1989, 16, (3), 255–261

The electrical properties of metal-insulator-semiconductor (MIS) devices incorporating Langmuir-Blodgett (LB) films of ω -tricosenoic acid (ω TA) deposited onto freshly-etched Si to prevent the formation of the natural passivating oxide layer, have been studied. Results from C-V and G-V studies of Pd-gate devices formed on the LB film/Si structure showed that the number of impurity states at the Si surface was increased by this treatment. The sensitivity to H₂ of these states was greatly improved.

Microionic Insertion Sensors

r. d. rauh, Solid State Ionics, 1988, 20–30, (II), 1479–1485

A new class of solid state chemical sensor with a configuration described as catalytic metal/insertion compound/insulator/semiconductor is reported. Studies on Si/SiO₂ MOS (metal-oxide-semiconductor) structures incorporating WO₃, an H-insertion compound, and Pd as the gate layers showed that the insertion layer accepts H atoms produced at the catalysts, and is reduced, leading to an increase in capacitance. The thermodynamic driving force for the reaction of H with WO₃ was sufficient to give rapid response to H₂ at room temperature.

Low-Energy Proton Detection by Pd Metal-Insulator-Semiconductor Diodes

r. c. hughes and r. bastasz, J. Appl. Phys., 1988, 64, (12), 6839–6844

Studies have shown that Pd-gated metal-insulator-silicon Schottky barrier diodes are very sensitive to fluxes of energetic protons in high vacuum. Data for the dosimetric response of the diodes to energetic protons and the subsequent decay in the induced signal is reported. The sensitivity at 300K was ∼ 10⁹ protons (10¹¹cm⁻²). The inventory of H⁺ stored in the bulk Pd, the surface and at the interface indicated that the arial site density for the surface and interface was ∼10¹⁵cm⁻².

Hydrogen Sensitivity of Pd/SiO₂/Si Structure: A Correlation with the Hydrogen-Induced Modifications on Optical and Transport Properties of α -Phase Pd Films

g. fortunato, a. bearzotti, c. caliendo and a. d’amico, Sens. Actuators, 1988, 16, (1&2), 43–54

The effects of H₂ absorption and desorption in Pd films have been studied by reflectivity and conductivity measurements. Bulk effects were induced in the film at room temperature even for low partial pressures of H₂ that do not induce the α-β phase transition. Reflectivity variations were associated with a rise in the Fermi level, while the conductance decrease in a H₂ atmosphere was related to the behaviour of scattering centers of the absorbed H atoms. These effects were correlated to the flat-band voltage shift measured in Pd-gate MOS capacitors, and the temporal correlation of the processes gave an explanation based on two different H₂ absorption sites.

A Palladium/Porous-Glass Composite Membrane for Hydrogen Separation

s. uemiya, y. kude, k. sugino, n. sato, t. matsuda and e. kikuchi, Chem. Lett. Jpn., 1988, (10), 1687–1690

Electroless plating has been used to deposit Pd on a porous glass tube, with Pd thickness of ∼13μ m. This composite membrane showed a remarkable permeability to H₂. Permeation of H₂ linearly increased with increasing temperature. At 673K and 773K the rates of H₂ permeation were 19.8 and 25.4cm³/cm²/min, respectively, under pressure difference of 2kg/cm², showing a 10-fold enhancement of efficiency compared to Pd-metal membranes. Selective separation of H₂ from H₂-N₂ and H₂-CO gas mixtures through the composite membrane was also observed.

HETEROGENEOUS CATALYSIS

On Non-Additive Effects on Activity of the Mixed Systems Platinum Black-Oxides in the Complete Oxidation of Butane

v. s. sal’nikov and p. g. tsyrul’nikov, Kinet. Katal., 1988, 29, (5), 1117–1122

Studies of activity of the mixed systems Pt black-MOx where MOx is Fe₂O₃, ZnO, V₂O₅, SiO₂ or Al₂O₃, performed during complete oxidation of butane showed an appearance of non-additive increase in activity in all cases except over V₂O₅ and ZnO, in comparison with Pt black. The dependence of reaction rate on hydrocarbon concentration was observed in the initial reactions. The observed effect was explained by development of radical-chain reactions on the surface of the oxides, initiating active particles to enter Pt black. During studied conditions, it was possible to transfer oxidation process from heterogeneous to heterogeneous-homogeneous.

Catalyst Deactivation Due to Transient Behavior in Nitric Acid Production

h. c. lee and r. j. farrauto, Ind. Eng. Chem. Res., 1989, 28, (1), 1–5

During start-up of a fixed bed HNO₃ acid reactor, unusually high surface temperatures or “hot spots” which cause loss of platinum group metals from catalyst gauzes, can be generated due to ignition of transient species. A laboratory study of the unique conditions leading to catalyst surface temperatures far in excess of the gas phase and steady state adiabatic temperature, causing considerable damage to a pure Pd recovery gauze (which is located immediately below a Pt alloy oxidation gauze), is reported. Models are presented. The effect of NH₃:air fuel ratio is discussed.

The Passivating Oxidation of Platinum

r. w. mccabe, c. wong and h. s. woo, J. Catal., 1988, 114, (2), 354–367

Studies of Pt oxidation by O₂ for a series of Pt powder, Pt/SiO₂ and Pt/Al₂O₃ catalysts of widely varying particle size have shown that Pt oxidation is highly passivating, that is, essentially limited to the surface layer of Pt atoms. With higher dispersion of supported Pt samples a greater fraction of Pt oxidation was observed. The passivating nature of oxidation was independent of both particle size and type of support. Evidence for a PtO₂ phase formed in particles with radii <0.75nm is reported.

Deactivation of the Pt-Re/Al₂O₃ Catalytic Functions during a Commercial Cycle

j. m. parera, c. a. querini and n. s. figoli, Appl. Catal., 1988, 44, (1–2), L1–L8

The distribution of coke over acid and metallic catalytic functions and the changes in selectivity have been studied for samples of a coked sulphided Pt-Re/Al₂O₃ catalyst taken from a commercial reactor during a 7 month cycle. It is concluded that long-term deactivation was due to the acid function, from the observation that catalytic activity for dehydrocyclisation of n-heptane decreased in the same way as activity for acid-controlled isomerisation of n-pentane. Furthermore, dehydrogenation of cyclohexane decreased with time at the beginning of the cycle but remained constant toward the end.

Catalytic Properties in n-Heptane Dehydrocyclisation on the (Pt+ Re + Cr)/γ -Al₂O₃ Systems

e. a. skrigan, g. m. sen’kov, m. f. gorbatsevich and n. s. kozlov, Vest. Akad. Navuk BSSR, Ser. Khim. Navuk, 1988, (6), 18–24

Studies of the effect of Cr addition on catalytic properties of (Pt+Re+Cr)/γ -Al₂O₃ catalysts during n-heptane dehydrocyclisation showed that modification of Pt-Re/Al₂O₃ catalysts by 0.2−3wt.% of Cr resulted in an increase of degree of conversion of n-heptane, and in an increase of aromatisation activity, selectivity and stability of the catalysts. It also decreased cracking and coke production.

Platinum-Tin/Alumina Catalysts: Modification of the Metallic Phase after Successive Oxidation-Reduction Cycles

s. r. de miguel, g. t. baronetti, a. a. castro and o. a. scelza, Appl. Catal., 1988, 45, (1), 61–69

Test reactions and TPR have been used to characterise Pt-Sn/Al₂O₃ catalysts prepared by different deposition techniques and submitted to successive oxidation-reduction cycles, and comparison made with fresh samples. Catalysts prepared by co-impregnation and successive impregnation, and submitted to oxidation-reduction cycles, showed a higher quantity of Pt-Sn alloys than corresponding fresh catalysts. In catalysts prepared by impregnating the support with [PtCl₃(SnCl₃)₂]²⁻ the cycles produced either a modification of surface alloy phase composition or surface enrichment of Sn in the alloy particles. Higher quantities of [PtCl₃(SnCl₃)₂]²⁻ deposited during impregnation produced a higher % of Sn reduced to the metallic state and a higher Pt-Sn alloy concentration.

Exhaust-Catalyst Development for Methanol-Fueled Vehicles. III. Formaldehyde Oxidation

r. w. mccabe and p. j. mitchell, Appl. Catal., 1988, 44, (1–2), 73–93

Formaldehyde oxidation over Al₂O₃ supported Pt, Pd, Rh, Ag, Pd-Ag, and Cu-Cr catalysts has been studied by laboratory experiments simulating lean-exhaust from CH₃OH-fuelled vehicles. High Pt activity was observed for CO-free feedstocks, but strong inhibition by added CO. The Pd-Ag showed enhanced activity compared to Pd and Ag alone for CO+H₂CO feed stock. Poor activity was shown by Rh. Unusual H₂CO conversion against temperature profiles were observed for Pd. The difference in activity and selectivity between Pt, Pd and Rh catalysts is attributed to differences in oxidation state. Pt remained in reduced form, Ru remained oxidised, while the unusual behaviour of Pd was due to the oxidation state changing with temperature and feed composition.

Catalytic Activity of Platinum/Carbon Fibers Catalysts in Hydrogenation of Carbon Monoxide

a. l. lapidus, o. a. malykh, a. yu. krylova and g. i. emel’yanova, Izv.Akad.Nauk SSSR, Ser.Khim., 1988, (11), 2478–2481

Studies of catalytic activity of Pt/C fiber catalysts in CO hydrogenation were performed using catalysts prepared by impregnation of C fibers with H₂PtCl₆ or (NH₄)₂PtCl₆ solutions for 10–12 hours at 100−110°C, followed by reduction in H₂ for 5 hours. The activity depended on Pt content and temperature. The greatest specific activity was obtained on 8%Pt/C fiber catalysts. When the Pt content increased from 0.8−12%, the activity increased accordingly. The highest activity was obtained at 550−600°C. Temperature stability of Pt/C fiber catalyst was higher than of Pt/Al₂O₃ or Pt/SiO₂.

Preparation and Characterization of Pt/Silicalite Catalysts with High Pt Loadings

h. a. rangwala, j. a. szymura, s. e. wanke and f. d. otto, Can. J. Chem. Eng., 1988, 66, (5), 843–848

The preparation of the first Pt/silicalite catalysts to have Pt loadings >7wt.% and Pt dispersion >0.8, is reported. Equilibrium of silicalite, a pentasil zeolite, in aqueous solutions of Pt(NH₃)₄Cl₂ containing excess NH₃ resulted in catalyst formation. X-ray diffraction, H₂ chemisorption and transmission electron microscopy studies of the catalysts showed that the majority of the Pt was located in the silicalite pores. These heavy-loaded Pt/silicalite catalysts are described as precursors for potential wet-proofed catalysts for use in heavy water production by H-D exchange between water and H₂ gas.

Diacetoxylation of 1,3-Butadiene on Modified Platinoid Catalysts

a. v. devekki, m. i. yakushkin and t. yu. kul’chitskaya, Kinet. Katal., 1988, 29, (6), 1355–1361

Diacetoxylation of 1,3-butadiene on heterogeneous Pt, Pd and Rh catalysts yielded cis- and trans-1,4-diacetoxybutene-2 in 70−84% selectivity and 3,4-diacetoxybutene-1. The ternary Pd or Rh catalytic systems containing p-elements of Groups III-VI were more active and selective than analogue binary systems. Modification of the catalysts by d-elements of Periods 4–6 resulted in inhibition of the catalytic properties. The consecutive-parallel mechanism of isomer formation observed for the studied conditions is discussed.

Selective Hydrogenation by a Novel Palladium(II) Complex

j. m. kerr, c. j. suckling and p. bamfield, Tetrahedron Lett., 1988, 29, (43), 5545–5548

A novel insoluble green complex of Pd(II) and salicylidene ethylene diamine (salen) has been prepared. This was found to be an active and selective heterogeneous hydrogenation catalyst especially for the preferential reduction of alkynes in the presence of alkenes, and for the preferential reduction of alkenes in the presence of other functional groups such as nitro or cyclopropyl.

Properties of Pd/Al₂O₃ Film Catalysts during Deep Oxidation of Methane

e. v. sidash, v. n. belyatskii, s. n. mal’chenko, g. a. branitskii, s. v. baran and v. v. ponaryadov, Vest. Akad. Navuk BSSR, Ser. Khim. Navuk, 1988, (6), 31–35

Studies of catalytic properties and chemical composition of Pd/Al₂O₃ catalysts containing 0.1, 0.5 and 5wt.% of Pd, prepared by air pyrolysis of γ -Al₂O₃ supported Al resinate films containing PdCl₂, were performed during deep oxidation of CH₄. The studied catalysts showed high stability and activity as compared to the Pd/Al₂O₃ catalysts prepared by impregnation from aqueous PdCl₂ solutions.

Study of Conversion of Ethylene and Acetylene in Chemisorbed Layer of Hydrogen on Pd/Al₂O₃

l. v. babenkova, i. g. kokh and n. m. popova, Kinet. Katal., 1988, 29, (6), 1400–1406

Studies of the interaction of C₂H₂ and C₂H₄ in chemisorbed H layer on 5%Pd/Al₂O₃ catalyst prepared by saturation of γ -Al₂O₃ by PdCl₂ solution in HCl followed by treatment in Ar at 623K, were made by thermosorption and spectroscopic techniques. A molecular H was found to be reactive during C₂H₄ hydrogenation whereas an atomic H was reactive during C₂H₄ hydrogenation. The diffused H obstructed the formation of stable C₂H₂ and C₂H₄ complexes with Pd but the adsorbed H allowed their bonding with Pd/Al₂O₃ surfaces. Hydrogenation of C₂H₂ and C₂H₄ occurred through two types of adsorbed hydrocarbon complexes depending on their bonding stability with the surface.

The Preparation of Palladium Metal Catalysts Supported on Carbon. Part I: Selection and Treatment of the Carbons. Part II: Deposition of Palladium and Metal Area Measurements

g. r. heal and l. l. mkayula, Carbon, 1988, 26, (6), 803–813; 815–823

Adsorption of N₂ has been used to examine surface properties of a number of commercial C supports used in Pd/C catalysts. A large proportion of undesirable microporosity remained after C burnoff, although mesopore volume was increased. Four techniques for Pd deposition were compared. Increasing burnoff produced higher area of support and higher Pd area initially, but increased gasification lead to a decrease in Pd area. Although C area was not increased by HNO₃ treatment, there were significant increases in catalyst area for some deposition techniques. A favourable technique is described as 15−20% burnoff followed by HNO₃ washing, and the impregnation adsorption desorption method.

Double Promotion of Palladium/Silica Catalysts by Iron and Magnesium Oxide in the Synthesis of Methanol from Carbon Monoxide and Hydrogen

g. lietz, m. nimz, j. völter, k. lázár and l. guczi, Appl. Catal., 1988, 45, (1), 71–83

Mössbauer spectroscopy, H₂ chemisorption and temperture programmed reduction have been used to characterise 2wt.% Pd/SiO₂ catalysts promoted with 2wt.% MgO and 0.2-5wt.% Fe. Studies of catalytic activity for CH₃OH formation showed a sharp maximum of activity for 16at.% Fe modified catalysts. Simultaneous independent promoting effects due to bimetallic PdFe alloy formation modifying H₂ and CO bond to the Pd rich metallic component, and due to MgO favourably increasing the dispersion of metallic components as well as moderating the acidity of the SiO₂ support containing Fe²⁺ ions in a favourable way, are described.

Ruthenium-Palladium Catalysts: The Effect of Palladium on the Catalytic Behaviour of Ruthenium

m. viniegra, v. arroyo and r. gómez, Appl. Catal., 1988, 44, (1–2), 1–9

Catalytic activity for the hydrogenation of benzene over Ru-Pd/SiO₂ at 1 atm pressure has been studied in order to determine the nature of the synergistic effect shown by these bimetallic catalysts with respect to monometallic Ru. This enhancement of catalytic activity is explained by a self deactivation process with the bimetallic catalyst showing more resistance to deposition of carbonaceous residues than pure Ru. Catalytic self-poisoning by carbonaceous residues was further reduced by the presence of thiophene during the hydrogenation.

Model Study of Supported Bimetallic Catalysts

z. knor and j. šotola, Collect. Czech. Chem. Commun., 1988, 53, (10), 2399–2411

Field electron microscopy has been used to study the interaction of N₂ with the sandwich systems Pd,Mo/WO_x/W, prepared by vacuum deposition. For the system Pd,Mo/WO_x it has been proved that at room temperature Mo represents the trapping region for N₂ molecules which were dissociatively chemisorbed there and afterwards, when the gap between Mo and Pt islands was <1nm, a N₂ spillover effect was observed.

Effect of Rh Dispersion on Vapour Phase and Pressurized Hydroformylation of Ethylene over Rh/SiO₂ Catalyst

h. arakawa, n. takahashi, t. hanaoka, k. takeuchi, t. matsuzaki and y. sugi, Chem. Lett. Jpn., 1988, (11), 1917–1918

Variation of surface Rh atom composition and electronic state of Rh particles resulted in a significant dispersion effect on vapour phase and pressurised hydroformylation of C₂H₄ over Rh/SiO₂ catalysts. Favourable catalysts had high Rh dispersion and Rh particle sizes <30Å. A striking structure sensitivity was also observed for the hydrogenation of C₂H₄ to C₂H₆, as a by-product.

Study on the Selectivity for the Synthesis of C₂-Oxygen Compounds from Syngas over Rh/V₂O₃ Catalysts

h.-y. luo, a.g.t.m. bastein and v. ponec, J. Catal. (Dalian, China), 1988, 9, (3), 248–253

Study of the selectivity of Rh/V₂O₃ catalysts prepared by impregnation of V₂O₃ with H₂RhCl₅.H₂O or HRhCl₄.2H₂O, used during synthesis of C₂-O compounds showed that their selectivity is much higher than those prepared from RhCl₃.3H₂O. When VOCl₂.5H₂O was deposited jointly with Rh precursor onto the surface of the catalyst, an improvement of the selectivity for C₂-O compounds occurred. The addition of VOCl₂.5H₂O as a promoter to Rh/SiO₂ greatly increased the activity and C₂-O compounds selectivity of the catalyst.

Aminated Polystyrene-Bound Rhodium Carbonyl Clusters as a Catalyst for Deoxygenation of Various N-O Bonds

k. kaneda, t. takemoto and t. imanaka, Chem. Lett. Jpn., 1988, (10), 1759–1762

Aminated polystyrene-bound Rh carbonyl clusters have been prepared by treatment of Rh₆(CO)₁₆ with various aminated polystyrenes, to provide re-usable catalysts which facilitate easy separation of products from reaction mixtures. The polymeric catalysts showed activity for deoxygenation of nitro compounds, oximes, hydroxylamines, and N-oxides under conditions using CO and H₂O.

HOMOGENEOUS CATALYSIS

New Aspects of Carbonylations Catalyzed by Transition-Metal Complexes

i. ojima, Chem. Rev., 1988, 88, (7), 1011–1030

Of various Pt, Rh, Ru and Co catalysts investigated Rh₆(CO)₁₆ was found to be extremely active and regioselective for the hydroformylation of fluoro olefins. The nature of the central metal atom played a key role in the regioselectivities. Phosphine-Pd complexes were shown to be superior for hydroesterification and hydrocarboxylation of fluoro olefins. These processes were applied to synthesis of fluoro amino acids, which have a wide variety of biological applications. The use of Co-Rh systems such as the novel CoRh(CO)₇ catalyst for hydroformylation-amidocarbonylation of fluoro olefins is reported and the potential for multi-step synthesis in one-pot is described.

To Activate Irradiate!

m. tanaka, Chemtech, 1989, 19, (1), 59–64

High regioselectivities, like those of enzymatic reactions, unusual regioselectivities compared with classical reactions, and high catalytic performance have been observed for C-H bond activation reactions via RhCl(CO)(PR₃)₂ catalysts under irradiation. Various carbonylations with CO were studied including those of benzene, toluene, benzonitrile, chlorobenzene, and other aromatics, and paraffins for which the reaction showed high terminal selectivity. Dehydrogenation of paraffins to give olefins was observed in the absence of other reactants capable of insertion into the C-H bond.

Hydroformylation of Allyl Alcohol Catalyzed by Ru(III)-EDTA Complex Using Carbon Monoxide and Water as a Source of Hydrogen

m. m. taqui khan, s. b. halligudi and s. h. r. abdi, J. Mol. Catal., 1988, 48, (1), 7–9

Indirect generation of H₂ using CO and H₂O in a water-gas shift reaction was catalysed by the complex K[Ru^III(EDTA-H)Cl].2H₂O (EDTA is ethylene-diaminetetraacetic acid) which created hydroformylation conditions in situ for conversion of allyl alcohol to γ -hydroxy-butyraldehyde, is reported.

An Efficient Water-Soluble Ruthenium Hydroformylation Catalyst for the Exclusive Formation of 1-Heptaldehyde from 1-Hexene

m. m. taqui khan, s. b. halligudi and s. h. r. abdi, J. Mol. Catal., 1988, 48, (2–3), 313–317

Hydroformylation of 1-hexene has been carried out in a high pressure reactor using H₂O soluble catalyst [Ru(III)-EDTA] catalyst (where EDTA compound is ethylenediaminetetraacetic acid), synthesis gas (1:1) CO+H₂ at 50atm, in 80:20 EtOH-H₂O mixture at 130°C. The reaction proceeded with a turnover rate of 11.83 mol product per mol catalyst per hour. The specificity to linear aldehyde was 100%. This is the first report of total specificity for this type of reaction.

FUEL CELLS

A New Approach to the Problem of Carbon Monoxide Poisoning in Fuel Cells Operating at Low Temperatures

s. gottesfeld and j. pafford, J. Electrochem. Soc., 1988, 135, (10), 2651–2652

The study of CO poisoning of Pt catalysts in proton exchange membrane (PEM) fuel cells operating at 80°C has shown that injection of low amounts of O₂ into the H₂ anode feed stream, contaminated by 100ppm CO, completely eliminates the deleterious effects of the CO.

Bimetalliç Carbon Supported Anodes for the Direct Methanol-Air Fuel Cell

a. hamnett and b. j. kennedy, Electrochim. Acta, 1988, 23, (11), 1613–1618

Studies of the electro-oxidation of CH₃OH on porous C electrodes impregnated with bimetallic platinum group catalysts, Pt/M (M is Pd, Ir, Os, Ru and Au) in a H₂SO₄ electrolyte have shown that Ir, Os, and Ru promoted the reaction while Pd and Au acted as inhibitors. X-ray photoelectron spectroscopy was used to study metal oxides. The role of the second metal in promoting or inhibiting the CH₃OH oxidation reaction was found to be a result of the ease of formation of “active oxygen” groups.

A Rechargeable Redox Battery Utilizing Ruthenium Complexes with Non-Aqueous Organic Electrolyte

y. matsuda, k. tanaka, m. okada, y. takasu, m. morita and t. matsumura-inoue, J. Appl. Electrochem., 1988, 18, (6), 909–914

The development of a new type of redox battery is reported with the single cell system [Ru(bpy)₃](BF₄)₂/CH₃CN which had an open circuit voltage of 2.6V and a discharge current of 5mAcm⁻² (at a smooth C electrode). The charge-discharge efficiency at the positive electrode was ∼70% while efficiency at the negative electrode was 20−40%. Cell efficiencies were enhanced using diaphragms with selective permeability.

CHEMICAL TECHNOLOGY

Palladium in Spent Power Station Fuel Solvent-Extraction Reprocessing

v. s. shmidt and n. a. shorokhov, Sov. At. Energy-Eng. Tr., 1988, 64, (2), 119–126

A survey of Pd extraction from nitrate solutions by various types of agent containing P, N and S, is presented. Effective agents for Pd extraction from refinement products were phosphine oxides, quaternary ammonium salts, and particularly sulphides and sulphoxides. Complete extraction of Pd from spent fast-reactor fuel and purification from fission products, by means of several extraction cycles can be achieved. The inherent activity of Pd due to ¹⁰⁷Pd (1/2-life 6.5×10⁶ years) was low and corresponded to ∼30% content in the stable-isotope mixture. Calculated β -particle flux from Pd was ∼2000cm⁻²s⁻¹ (E_max=33keV; E_av≍10keV). The results indicate the utility of Pd recovered from spent power station fuel if γ -active nucleides can be removed completely.

ELECTRICAL AND ELECTRONIC ENGINEERING

Electrical Characteristics of PtSi Formed by Incoherent Light Annealing

a. s. pedersen, j. chevallier and a. nylandsted larsen, Thin Solid Films, 1988, 164, 487–492

Thin films of PtSi have been formed by short duration incoherent light annealing of evaporated Pt on {100}- or {111}-oriented single Si crystals. After annealing for 15s between 500 and 900°C the silicide was characterised with reference to its application in integrated circuits. It was found to have resistivity independent of Si orientation and formation temperature, and similar to long duration furnace-processed PtSi. Specific contact resistivity of Al/PtSi/n⁺-Si contacts was significantly lower than for reference samples without PtSi. Characteristics of PtSi/n-Si Schottky diodes were temperature and orientation dependent. Diodes on Si{111} degraded with temperature at 500−900°C while diodes on Si{100} only degraded above 700°C.

Enhancement of T_c of Heavy-Fermion Superconductor UPt₃ by Alloying with B

t. vorenkamp, k. kadowaki, a. de visser, p. haen, v. j. m. meulenbroek, m. van sprang and j. j. m. franse, J. Magn. & Magn. Mater., 1988, 76&77, 531–532

The influence of B on the superconductivity of the heavy-fermion superconductor UPt₃ has been studied by resistivity measurements. A shift of the superconducting transition temperature, T_c, value from 530mK in pure UPt₃ up to 600mK in annealed UPt₃B_x with x0.3 was observed. This is reported as the first experimental evidence that the T_c of UPt₃ can be increased by adding impurities.

High-Temperature Behaviour of Pd-n-GaAs Contacts

c. y. nee, c. y. chang, t. f. cheng and t. s. huang, J. Mater. Sci., Lett., 1988, 7, (11), 1187–1189

Studies of the electrical and structural behaviour of Pd-n-GaAs contacts over a wide range of annealing temperatures, 300−850°C, have revealed a crucial temperature at 550°C. A correlation was found to exist between variation of electrical properties and variation of structural properties over the temperature range. Below 550°C electrical properties were dominated by some Pt-As compounds. Above 550°C the contact area became smaller and the contact resistance increased.

Pd Overlayer Growth on InP(110), GaAs(110), and InSb(110): Comparisons of Anion Surface Segregation

i. m. vitomirov, c. m. aldao, z. lin, y. gao, b. m. trafas and j. h. weaver, Phys. Rev. B., 1988, 38, (15), 10776–10786

Studies of the reaction, atomic redistributions and Schottky-barrier formation for Pd/InP(110), Pd/GaAs(110) and Pd/InSb(110) interfaces have shown adatom-induced substrate disruption of ∼6Å for InP and GaAs and ∼5Å for InSb, and release of anions and cations. Distribution of the released semiconductor atoms changed with Pd deposition, and showed a characteristic profile after ∼10Å corresponding to preferential anion segregation. Anion segregation was most pronounced for Pd/InSb(110) and smallest for Pd/InP(110).

Superconducting Properties of the Pd-Se System

t. takabatake, m. ishikawa and a. junod, J. Phys. Soc. Jpn., 1988, 57, (8), 2763–2767

Studies of the transport and superconducting properties of the series of Pd-rich selenides, Pd₉Se₂, Pd₄Se, Pd₇Se₂, Pd₃₄Se₁₁, Pd₇Se₄ and amorphous Pd_0.7Se_0.3 have shown that they are superconductive above 0.38K, except Pd₄Se and Pd₇Se₄ which like the rest of the compounds in the whole Pd-Se system are not. Specific heat measurements have shown that a relatively strong electron-phonon coupling exists in Pd₃₄Se₁₁, which is responsible for both enhanced T_c(2.66K) and anomalous temperature dependence of resistivity. The solid solutions of Pd(Se) and Pd(Te) did not show superconductivity above 0.38K.

Thermal Stability of Amorphous Ta-Ir between Y-Ba-Cu-O and Silicon

r. de reus, f. w. saris and t. s. baller, J. Less-Common Met., 1988, 145, (1–2), 217–222

Studies have shown that amorphous buffer layers of Ta-Ir sandwiched between Y-Ba-Cu-O thin films and Si(100) substrates prevent interface reactions during annealing in O₂ ambient up to 800°C. Above 650°C, amorphous Ta-Ir-O which was formed during annealing, crystallised into Ta₂O₅ and IrO₂, and pinholes in the Y-Ba-Cu-O film and buffer were observed. Si did not react after annealing up to 900°C.

Critical Relationships between Particle Size, Composition, and Microstructure in Thick-Film Resistors

s. m. chitale and r. w. vest, IEEE Trans. Components, Hybrids, Manuf. Technol., 1988, 11, (4), 604–610

Studies have shown that the microstructure of RuO₂-based thick-film resistors depends on volume fraction of RuO₂, particle size of RuO₂, and particle size of glass. These variables were related by a coverage factor which described the extent of coverage of glass particles by RuO₂ particles in the unfired resistors. Two critical values of the coverage factor were identified which separated regions of constant microstructure, changing microstructure, and unstable microstructure.

MEDICAL USES

Cis- and Trans- Dihalotetrakis(dimethyl sulfoxide)ruthenium(II) Complexes (RuX₂(DMSO)₄; X=Cl,Br): Synthesis, Structure, and Antitumor Activity

e. alessio, g. nestroni, g. nardin, w. m. attia, m. calligaris, g. sava and s. zorzet, Inorg. Chem., 1988, 27, (23), 4099–4106

The structural characteristics of a new crystal of cis-RuCl₂(DMSO)₄ together with the synthesis and structure of previously unknown trans-RuCl₂(DMSO)₄ and cis-RuBr₂(DMSO)₄ are reported. Photochemical isomerisation of the more stable cis species to trans species in DMSO solution was observed. Kinetic parameters for trans-cis thermal isomerisations for trans-RuCl₂(DMSO)₄ and trans-RuBr₂(DMSO)₄, are also reported. Substitution kinetics in aqueous solution directly reflected anti-tumour activity. The trans-RuCl₂(DMSO)₄ isomer showed higher activity than the cis against Lewis lung carcinoma, a metastasising murine tumour.

219.Bathophenanthroline-Ruthenium(II) Complexes as Non-Radioactive Labels for Oligonucleotides which Can Be Measured by Time-Resolved Fluorescence Techniques

w. bannwarth, d. schmidt, r. l. stallard, c. hornung, r. knorr and f. müller, Helv. Chim. Acta, 1988, 71, (8), 2085–2099

The specific attachment of bathophenanthroline-Ru(II) complexes as non-radioactive label molecules to synthetically 5’-NH₂-modified oligonucleotides is described. After excitation by light pulses, the fluorescence of these labels was measured by a time-resolved mode with high sensitivity. No quenching took place due to coupling of the Ru complexes to the DNA. Oligonucleotides labelled in this way still hybridised specifically to complementary DNA sequences, and no quenching was observed during the hybridisation process.