ABSTRACTS: January 1990
ABSTRACTS: January 1990
of current literature on the platinum netals and their alloys
Morphology, Structure and Stability of Oxides in Pt-Hf Alloys Subjected to Internal Oxidation
e. p. daneliya, m. i. doperchuk and g. i. kandyba, Izv. Akad. Nauk SSSR, Met., 1989, (4), 181-183
Studies of morphology and structure of oxidised phase formed by internal oxidation of low-alloy Pt-Hf alloys at 1000-1300°C were performed by X-ray diffraction techniques. Different stability of dispersed and coarse particles is explained by the growth of the oxides controlling diffusion of the components through the volume of the matrix, and by decomposition of dendrite controlling the diffusion on interphase oxide surfaces, respectively. Diffusion mobility of oxide elements in the grain volume is much lower than on the boundary and stability of dispersed particles is much higher.
Plasma Chemical Vapor Deposition of Thin Platinum Films
e. feurer, s. kraus and h. suhr, J. Vac. Sci. Technol. A, 1989, 7, (4), 2799-2802
Metal organic plasma-enhanced chemical vapour deposition of Pt films using cyclopentadienyl-trimethyl-Pt as starting material is reported. Three different reactors are compared and the influence of power, substrate temperature, and temperature of the reservoir with the organometallic has been studied. Films with ~100% Pt and a resistivity of 46μΩcm have been deposited.
A Thermodynamic Study of the Pd-Ti System
n. selhaoui, j. c. gachon and j. hertz, J. Less-Common Met., 1989, 154, (1), 137-147
A calorimetric determination of the enthalpies of formation of four compounds Pd0.75Ti0.25(Pd3Ti), Pd0.67Ti0.33(Pd2Ti), Pd0.625Ti0.375(Pd5Ti3) and Pd0 0.50Ti0.50(PdTi) were performed by direct reaction calorimetry.
Metastable Phases in Rapidly Solidified Pd-U-Si Alloys
c. antonione, l. battezzati, f. marino, r. marazza and d. mazzonejj. Less-Common Met., 1989, 154, (1), 169-175
Rapid solidification of Pd60U20Si20at various quenching rates yielded either an amorphous or a quasicrystalline phase. A new metastable f.c.c. phase was prepared by rapidly quenching Pd70U10Si20. The transformation behaviour of the amorphous and quasicrystalline phases is described.
Characterization Study of Ruthenium Dioxide Hydrate before and after Thermal Activation
r. mason, a. mills and d. milton, J. Less-Common Met., 1989, 155, (1), 89-109
Studies of RuO2.xH2O before and after thermal activation were performed by direct mass spectrometric thermal analysis and results were compared with differential thermal gravimetric analysis and differential scanning calorimetry data. The results for the corrodible, non-activated form of RuO2.xH2O show that two of the O atoms in RuO4 come from the solvent and indicate that any O evolved may also come from the solvent. The results for the non-corrodible, activated form of RuO2 .xH2 O confirmed that it was able to mediate the stoichiometric oxidation of H2O to O2 by Ce(IV) ions, without undergoing corrosion.
Some Effects of Zinc and Palladium Complexes in Photographic Silver Halide Systems
g. roewer, s. gahler, e. berndtand a. winzer, J. Photogr. Sci., 1989, 37, (2), 34-37
Pd, Zn and Au ions interact with gelatins as well as with thiocompounds (X) used in photographic Ag halide emulsions. These potential ligands X compete with the binder for the metal ions to give mixed complexes M(gel)nXm (M = Pd, Zn). It has been shown that Pd2+ and Zn2+ ions are able to stop the physical ripening process of Ag halide emulsions containing 1,8-dihydroxy-3,6-dithiaoctane. Pd2+ and Zn2+ displace Au ions from the gelatin complex. The utilisation of such reactions makes it possible to influence sensitometric parameters of emulsions. Pd2+ and Zn2+ exert a synergistic effect: Pd2+ decreases fogging and produces stabilisation, while Zn2+ compensates for loss in sensitivity. The synergistic effect is attributed to the favourable effect exerted on kinetics of clustering during chemical ripening.
The Kinetics of Rh(III) Complex Formation with Heterocyclic Azo Compounds in Organo-Aqueous Media
a. t. pilipenko, n. o. diyachenko and n. f. falendish, Dop. Akad. Nauk URSR, Ser. B, 1989, (6), 49-52
Studies of kinetics of Rh(III) complex formation with heterocyclic azo compounds in organo-aqueous media showed a great increase in the rate of complexing reaction in the presence of alcohols. This was due to the increased reaction ability of aqua-chloride Rh(III) complexes in the aqueous-alcohol medium.
Carbon Dioxide Chemistry of a Binuclear Iridium(O) Complex. Rapid and Reversible Oxygen Atom Transfer from Carbonate
m. k. reinking, j. ni, p. e. fanwick and c. p. kubiak, J. Am. Chem. Soc, 1989, 111, (16), 6459-6461
The activation of CO2 by a binuclear lr(0) complex is reported. The complex Ir2(CO)3(dmpm)2 was prepared and reacted with Co2 to form the μ- carbonate complex Ir2(μ-CO3XCO)2(dmpm)2 (dmpm is bis(dimethylphosphino)methane). The carbonate ligand of this complex showed unprecedented O atom transfer reactivity and has been found to undergo rapid and reversible O transfer to CO. The activation and reduction of CO2 are areas of potential importance for artificially recycling the products of combustion and respiration.
Microstructure of Pt Electrodes over Solid-Electrolyte and Its Effects on Inter-facial Impedance
k. sakurai, h. nagamoto and h. inoue, Solid State Ionics, 1989, 35, (3,4), 405-410
Two kinds of Pt electrode (paste and evaporated Pt), and two kinds of solid electrolyte (SE: Y2O3-stabilised ZrO2 and doped Bi oxide) have been used to determine the effects of microstructure of the electrode and material of the SE on the interfacial impedance of SE cells. A new method was used to analyse impedance spectra, and the effects of temperature (924-1125K) and O2 pressure (101 -105Pa) on various parameters are reported, giving information about the effects of electrode structure and the SE. Results showed that the magnitude of the electrode resistances was quite dependent on the electrode morphology, as well as on the SE. Reduction of electrode resistance is a route to increased electrode efficiency for application of SE in fuel cells, O2 pumps and O2 sensors.
The Cathodic Reduction of Carbon Dioxide in Acetonitrile. An Electrochemical and Infrared Spectroelectrochemical Study
j. desilvestro and s. pons, J. Electroanal. Chem. Interfacial Electrochem., 1989, 267, (1&2), 207-220
In situ FTIR reflectance spectra of the electrochemical reduction of CO: at a Pt electrode revealed quantitative formation of oxalate (C2O42-) in at least two different solvation states when the electrode potential was switched from 0.4V to increasingly negative values (vs.Ag/AgNO3 in CH3CN). Chemical reversibility of the CO2 reduction process was illustrated by the complete reversal of the spectral features on readjusting the potential to 0.4V. The majority of IR bands could be assigned to CO2, C2O42-, and to electrolyte ions and solvent migrating due to the electric field.
Fabrication and Characteristics of Vertically Separated Interdigitated Array Electrodes
o. niwa, m. moritaandh. tabei, J. Electroanal. Chem. Interfacial Electrochem., 1989, 267, (1&2), 291-297
A new type of electrode similar to an interdigitated array (IDA) electrode has been developed which incorporates a Pt anode and a Pt cathode formed by photolithography, Pt sputter-deposition and lift-off techniques. This IDA-like electrode is said to exhibit excellent electrochemical performance. The two arrays of microband electrodes are separated by a thin insulating step. A step height of 0.5μm can be realised easily; compared with 5μm for ordinary planar IDA electrodes.
Influence of Iron Impurities on the Time Dependence of the Hydrogen Evolution Reaction on Platinum Cathodes during Electrolysis of 30 w/o KOH
l. brossard and j.-y. huot, J. Appl. Electrochem., 1989, 19, (6), 882-888
The H evolution reaction (HER) on polished pure Pt cathodes in 30 w/o KOH at 70°C in the absence or presence of dissolved metallic impurities was studied at 100mA/cm2. The loss of efficiency for the HER which occurred during the fust thousand seconds and took the form of an increase in the cathodic over-potential with time is attributed to the penetration of atomic H into the Pt lattice.
Behaviour of a Platinum Electrode in Solid Electrolytes Based on Silver Iodide
e. a. ykshe, a. m. mikhailova and n. g. bukun, Elektrokhimiya, 1989, 25, (6), 739-742
Impedance method was used to study the behaviour of Pt in contact with some solid electrolytes based on Ag iodide. Existence of two slow processes during contamination on the Pt-solid electrolyte boundary was discovered. These processes proceed in parallel but are practically independent of each other, and are connected with the presence of I adsorption centres on the surface of Pt and their penetration in the surface of the electrode layer.
Studies of the Corrosion Behaviour of Platinised Titanium Electrodes during Electrodialysis of Sea Water
l. a. mikhailova, s. d. khodkevich, l. m. yakimenxo, e. k. spasskaya and e. r. shaposhnikova, Elektrokhimiya, 1989, 25, (10), 1352-1356
Radiometric studies of the corrosion rates of Pt surface of platinised Ti electrodes with Pt layer thickness of 6-8 μm were performed during electrodialysis of imitation sea water containing 3.5wt.% of salts in anodic and cathodic periods of the electrolyte. The results showed that with current density of the electrodialysis of 150-500A/m2, one reverse cycle in 8-24h and Pt layer thickness of 8μm, the lifetime of these platinised electrodes could be 10-20 years.
Bonded Solid Protonic Conductor/Platinum Electrochemical Cells
j. d. canaday, a. k. kuriakose, t. a. wheat, a. ahmad, j. gulens and b. w. hildebrandt, Solid State Ionics, 1989, 35, (1,2), 165-175
Hydrogen-conducting β”-Al2O3 and NASICON have been prepared by a new method which overcomes the problem of disintegration of the polycrystalline ceramics during ion exchange. Pt was found to be the most suitable electrode material for use with these electrolytes in hydronium cells at 25-200°C. The composition and morphology of the Pt porous electrodes are described.
Peculiar Corrosion and Electrochemical Behaviour of Oxidised Surface Layers of Titanium with Ionic Implanted Palladium
n. d. tomashov, o. a. zhil’tsova, g. p. chernova, r. kh. zalavutdinov, d. b. bogomolov, m. i. guseva, b. g. vladimirov and n. p. aparina, Zashch. Met., 1989, 25, (3), 502-506
Studies of the corrosion of anodicalfy oxidised Ti electrodes containing Pd+ and of ionic implanted Pd on Ti samples showed that implantation of Pd+ in the surface of the oxidised Ti layer improves their protective properties in 20% H2SO4 at 100°C. The implantation results in the formation of cathodically active Pd centres on the surface of the samples and also increases electroconducuvity of passivating oxides. The screening effect of Pd results in corrosion inhibition of the Ti metallic base in pores.
Voltammetric Reduction and Determination of Hydrogen Peroxide at an Electrode Modified with a Film Containing Palladium and Iridium
j. a. cox and r. k. jaworski, Anal. Chem., 1989, 61, (19), 2176-2178
A stable film on a glassy C electrode was produced by cyclic voltammetry of a mixture containing o.2mM Na2IrCl6, 0.1mM PdCl2, K2SO4 and HCl between 1.2 and -0.3V vs. Ag/AgCl for five cycles. This electrode can measure H2O2 reduction with an amperometric flow cell at only -0.2 V vs. SCE, has long term stability and can be used at ambient temperature. Two limitations to its use are discussed, one being the overlap of reductions of O 2 and H2O2, the other being the necessity of using a basic supporting electrolyte instead of neutral KC1.
New Chlor-Alkali Activated Cathodes
m. jaccaud, f. leroux and j. c. millet, Mater. Chem. Phys., 1989, 22,(1-2), 105-119
A new activated composite cathode for chlor-alkali electrolysis consists of a RuO2 thermal layer, on a Ni support, modified by a second layer of electroless Ni. This is a highly efficient catalyst for H2 evolution in strong causdc solution and shows a 250mV saving in H overpotential compared to smooth Ni. The cathode is stable for long-time operation in membrane cell conditions and is not affected by Fe impurities.
Silicon Electrodes Coated with Extremely Small Platinum Islands for Efficient Solar Energy Conversion
k. ueda, y. nakato, n. suzuki and h. tsubomura, J. Electrochem. Soc, 1989, 136, (8), 2280-2285
Platinum islands of 5-5011m were deposited on n-type single-crystal Si (n -Si) wafers by reduction of H2PtCl6 with H2. Photoelectrochemical cells made from such an n -Si electrode coated with minute Pt islands generated open-circuit photovoltages of 0.63V, which is about 8% higher than those for normal p-n junction Si solid solar cells (~0.58V). The results show the importance of control of the size and density of the metal islands on scales of several run in order to improve the cell performance. This method of discontinuous metal coating is very promising as a novel approach to efficient and stable photoelectrochemical solar cells.
A Study of the Method of Loading Platinum on Ti02 Photocatalyst
n.-c. cai, c.-y. jian and q.-h. dong, J. Catal. (Dalian, China), 1989, 10, (2), 137-142
A combined method involving photo-infusion and reduction with H2 has been used to load Pt on TiO2, and the activity of the resulting catalysts for decomposition of organic carboxylic acids studied. Pt/TiO2 catalysts thus prepared showed higher activity than those prepared by a photoelectrochemical method. The mechanism of loading Pt on TiO2 involved partial reduction of PtCl62- ions to metallic Pt in the presence of TiO2 powder, and partial reduction to some lower valence state ions which photo-adsorb uniformly on the surface of TiO2 particles under illumination. This partial reduction to lower valence state ions produced a Pt/TiO2 catalyst with a highly dispersed and higher loading of Pt.
Effect of Platinum Loading on the Photocatalytic Activity and Luminescence of Cadmium Sulfide Powder
t. uchihara, m. matsumura, a. yamamoto and h. tsubomura, J. Phys. Chem., 1989, 93, (15), 5870-5874
The effect of Pt loading on the efficiency of CdS-photocatalysed H2 evolution from an aqueous solution of Na2SO3 and on the intensity of the green emission (510nm) of CdS suspended in the same solution has been studied. When the amount of Pt deposited on CdS was increased, the Fermi level of CdS at the working stage moved down toward a more positive potential, leading to a stronger band bending, and stimulation of the photocatalytic reaction occurred. Too much Pt loading, however, lowered the photocatalytic activity because of the enhanced rate of electron-hole recombination as well as light absorption by Pt. The temperature effect on the reactivity and the reason for the presence of a reaction induction period are also elucidated in relation to the band bending of the photocatalyst.
Optimization of p -Silicon Surface by Etching and Electrodeposition of Pt and Ni for Photosplitting of Water
s. u. m. khan and s. a. majumder, Int. J. Hydrogen Energy, 1989, 14,> (9), 653-660
Platinisation for 3s and nickelisation for is on bare p- Si semiconductor electrodes at a current pulse of 250μA/cm2 and light intensity of ioomW/cm2 was found to produce the most efficient surface conditions of this semiconductor. Pt showed a better photoelectrocatalytic effect on the p -Si surface than Ni in terms of the limiting photocurrent and potential shift, ΔV. Optimisation of surface condition for best photoresponse in terms of etching time showed that etching of bare p -Si with aqua regia-HF for 4 min and subsequent treatment with HF for 3 min gives rise to better active sites towards photoelectrochemical splitting of H2O. The electrocatalytic effect dominates over the Schottky junction effect for improved photoeffect at metal deposited p -Si photoelectrodes.
Alkene and Dihydrogen Formation by Catalytic Dehydrogenation of Alkane with RhCl(PR3)2 Photogenerated from RhCl(CO)(PR3)2
k. nomura and y. saito, J. Mol. Catal, 1989, 54, (1), 57-64
It has been shown unequivocally for the first time that dehydrogenation of alkanes to alkenes and dihydrogen is catalysed by metal-to-ligand charge transfer (MLCT)-photogenerated species from RhCl(CO)(PR3)2 without further photoassistance at high turnover frequencies (1404 h-1 for nonane at 132°C and PR3=PMe3). This one-photon dehydrogenation process takes place with light (360nm, 79kcal/einstein) that is not much higher in energy than some of the C-H bonds that are broken. The activity increased in the order for PR3 = PPh3 <PEtPh2 <PEt2 Ph<PEt3 <PMe3.
Electrochemical Behaviour of Transparent Heavily Doped Sn02 Electrodes. Effect of Radiolytic Grafting of Iridium Nanoaggregates
j. bruneaux, h. cachet, m. froment, j. amblard and m. mostafavi, J. Electroanal. Chem. Interfacial Electrochem, 1989, 269, (2), 375-387
Efficient transparent counter-electrodes (TCEs) for use in sandwich-type photoelectrochemical cells which operate in aqueous media have been prepared by grafting of Ir aggregates onto highly-doped SnO2 sprayed films. These modified electrodes proved to be stable for a long time, compatible with the working conditions in photoelectrochemical cells. Grafting of Ir aggregates influences charge transfer in 3 ways: (a) by an increase in the degeneracy for highly-doped SnO2 short-circuiting the tunnelling process inside the film; (b) by freezing of band bending in the oxide, resulting in an overpotential fully applied at the electrode/solution interface; and (c) by replacing often poor kinetics at bare SnO2 by a faster transfer rate at the metal-covered surface.
Electrochemical Continuous Emission of Ru(2,2'-bipyridine)32+in Polymer Matrix
r. igarashi, y. nosaka, n. fujii, h. miyama and m. yokoyama, Denki Kagaku, 1989, 57, (4), 302-306
Electrochemiluminescence (ECL) has been observed from a quasi-solid state DC ECL cell consisting of a Pt or Al cathode, a polymer layer of Nafion containing Ru(bpy)32+, a H20-soluble polymer layer of AQ-NYLON containing two supporting electrolytes, and an In-Sn oxide anode, by applying a DC voltage. The threshold voltages for DC ECL at the Pt and Al cathodes were 1.3V and 2.4V, respectively; lower than voltages previously reported for liquid cells.
Radiolytically Prepared Ni-Pd Sols as Catalysts for Water Photoreduction
e. amouyal, m. georgopoulos and m.-o. delcourt, New J. Chem., 1989, 13, (7), 501-502
Radiolytically prepared Ni-10% Pd sols were found to be more active than pure Ni sols toward the catalytic photoreduction of H2O to H2. The test system was Ru(bpy)32+/methylviologen/N-phenylglycine: a favourable pH effect was shown at pH 2.5. The H2 evolution rate was not far from the optimum values obtained with Pt sols in acidic medium. These Ni-Pd aggregates are the first example of an aqueous colloid metal catalyst being improved by an alloying effect.
Nafion Modified TiO2 Electrodes: Photoresponse and Sensitization by Ru(II)-Bipyridyl Complexes
l. kavan and m. grätzel, Electrockim. Acta, 1989, 34, (9). 1327-1334
A TiO2/Nafion/Ru(bpy)32+ system showed relatively weak sensitised photocurrents with a maximum at 45onm. ARuL3 (L = 2,2'-bipyridyl-4,4'-dicarboxylic acid) complex can be incorporated into the Nafion. At lower pH values, when RuL3 is protonated to the cation form, the Nafion film shows enhanced electrochemical response. At pH > 4.2 the film is non-permeable to RuL3 and electrochemical activity is zero. This effect was used for protecting the adsorbed layer of RuL3 on TiO2 against desorption.
Ground- and Excited-State Properties of a Photostable Hemicage Ruthenium(II) Polypyridine Complex
r. f. beeston, s. l. larson and m. c. fitzgerald, Inorg. Chem., 1989, 28, (23), 4187-4189
A preparation of a novel ligand, (Mebpy)3Bz, which co-ordinates to Ru in a singly capped, hemicaged structure [Ru((Mebpy)jBz)]n+, and consists of three 5,5'-dimethyl-2,2'-bipyridine (5,5'-dmb) groups linked to a central benzene ring via only methylene groups is reported. The redox and absorption properties, as well as the emission energies in acetonitrile are similar for [Ru((Mebpy)3Bz)](PF6)2 and the parent compound [Ru(5,5'-dmb)3](PF6)2, but the room-temperature lifetime and emission quantum yield of the hemicage complex are increased 10 times in comparison to that of the parent complex.
Photoelectrochemical Oxidation of Water at CdS and CdSe Anodes Coated with Composites of Conducting Polymer Containing RuO2
d. gningue, g. horowitz, j. roncali and f. garnier, J. Electroanal. Chem. Interfacial Electrochem., 1989, 269, (2), 337-349
A stabilisation of 85% for CdS and CdSe single-crystal semiconductor photoelectrodes used for visible light induced oxidation of H2O to O2, has been obtained by coating with protecting composites of electrically conducting poly(bithiophene)-poly(pyr-role) copolymer and hydrophobic poly(vinyl chloride) in combination with catalytic dispersion of RuO2. The power efficiency of the self-driven CdS-based photoelectrolysis cell under 5omV/cm2 W-halogen light is 0.42%. CdSe-based cells require the help of an external power source in order to achieve H2O cleavage. The photoanode efficiency is 0.98%.
ELECTRODEPOSITION AND SURFACE COATINGS
Pulse Plating of Silver-Palladium Alloys
s. -j. dong, y. fukumoto and t. hayashi, Plat. Surf. Finish., 1989, 76, (7), 56-61
The optimum pulsing conditions for depositing bright, smooth Ag alloy containing ~25% Pd have been determined as 200-400mA/cm2 current pulses with an on-time of 0.1ms and an average current density of 4 mA/cm2. Deposit composition appeared to be controlled by diffusion polarisation.
APPARATUS AND TECHNIQUE
Activated Platinum Electrodes as pH Indicator Electrodes. Analytical Applications to Acid-Base Titrations
]. m. fernández alvarez, a. costa garcia and p. tunon blanco, An. Quim., 1989, 85, (1), 32-37
The pH response of activated Pt indicator electrodes subjected to both anodic and cathodic currents has been studied. The response is based on background currents displacements with pH. A zero current indicator electrode was similarly studied. Electrochemical pretreatment for the electrodes enables wide linear ranges of response vs. pH to be achieved.
Platinum-Dispersed Nafion Film Modified Glassy Carbon as an Elec-trocatalytic Surface for an Amperometric Glucose Enzyme Electrode
h. gunasingham and c. b. tan, Analyst, 1989, 114, (6), 695-698
A Nafion film dispersed with Pt particles formed on a glassy C electrode has been found to combine the electrocatalyuc activity of Pt with the background stability of glassy C. It serves as a selective and sensitive electrode surface for an amperometric glucose enzyme electrode.
Determination of Chloride in Platinum-Rhenium Alumina-Based Reforming Catalyst by Ion Chromatography
r. p. singh, k. alam, d. s. redwan and n. m. abbas, Anal. Chem., 1989, 61, (17), 1924-1927
A method to detect Cl- ions in Pt-Re/Al2O3) reforming catalysts, free from sulphide, bromide or iodide ion interference, and faster than present means is presented. Extraction of chloride is carried out with NaOH solution in a Teflon Parr bomb at 150°C. After filtration, ion chromatographic analyses show that the minimum chloride in the sample is 0.1% by weight, with a relative standard deviation of 3%.
Catalytic and Gas Sensing Characteristics in Pd-Doped Sno2
j. g. duh, j. w. jou and b. s. chiou, J. Electrochem. Soc, 1989, 136, (9), 2740-2747
A SnO2 based ceramic doped with ThO2, MgO and PdCl2 has been developed as a CO gas detector. The sensitivity of gas sensing was measured with respect to the relative resistance change in the ceramic matrix on the introduction of the CO gas. Intermediate operating temperature was required for the gas sensing and higher sensitivity and fast response rate were observed at 300°C. Metallic Pd was observed in the sensing matrix after mixing in ethyl alcohol, while PdO appeared after sintering at 800°C and its presence improved the CO gas sensitivity.
Sensor for Detecting the Stoichiometric Composition in a Combustion Flame
s. sekido, h. tachibana and y. yamamura, Sens. Actuators, 1989, 19, (4), 393-400
Addition of 0.4-0.8wt.% Pd and 60-70 mol% SrTiO3 to Sr0.65La0.35Co0.7Fe0.3O3-δ was found to improve the sensitivity, response time and lifetime of this sensor for detecting stoichiometric composition of combustion gas. The sensor also showed superior catalytic activity for conversion of noxious gas to harmless gas. The sensor can also be used as a temperature sensor (or flame detector) as its temperature dependence of resistivity with >40mol% SrTiO3 at <400°C is semiconductor like and does not rely on the gas atmosphere. Gas sensitivity begins at >400°C. The working temperature is lowered by ~100°C by the addition of Pd.
Applications of Small Iridium-Based Mercury Electrodes to High Concentrations of Depolarizers
j. golaś and z. kowalski, Anal. Chim. Acta, 1989, 221, (2), 305-318
Voltammetric and microscopic data on the analytical properties of small Ir-based (127μm diameter) Hg film electrodes have shown that, with thin Hg deposits these electrodes offer interesting applications as they combine features of thin-film electrodes and micro-electrodes. A possible application is in the determination of high concentrations of depolarisers; voltammetric data for the determination of Pb in the range 10-120mM are given.
The Selectivity of the Platinum Group Metals in Catalytic Hydrogenation
s.nishimura, Nippon Kagaku Kaishi, 1989, (7), 1055-1066
The selectivities of Pt, Pd, Rh, Ir, Os and Ru have been studied in the hydrogenation of cycloolefins, cyclic enol ethers and aromatic compounds. Hydrogenation and deuteration of cycloolefins and hydrogenation of enol ethers derived from cyclohex-anones over Pd showed opposite trends in stereoselectivity. The observed trend in hydrogenolysis of enol ethers in EtOH is explained by consideration of the activity of adsorbed ionised H and the olefin isomerisation activity of the metal. Studies of selectivities in hydrogenation of aromatic compounds showed that Pd is highly selective for formation of ketone, enol ether and imine intermediates in the hydrogenation of phenols, aryl ethers and methoxyanilines, respectively.
Adsorption of Surfactant-Stabilized Colloidal Noble Metals by Ion-Exchange Resins and Their Catalytic Activity for Hydrogenation
y. nakao and k. kaeriyama, J. Colloid Interface Sci., 1989, 131, (0, 186-191
Hydrosols of Pt, Pd, Rh, Ru, Au and Ag have been prepared in the presence of surfactants stearyltrimethylanunonium chloride (SC), Na dodecylbenzenesulphonate (SD), or polyethylene glycol mono-p -nonylphenyl ether (PN). All positive colloids with SC were successfully adsorbed by cation-exchange resins (CER), and all negative colloids with SD or PN were adsorbed by anion-exchange resins (AER). The negative colloids Rh-PN, Ru-SD and Ru-PN were adsorbed by H-form CER as well as AER. Catalytic activity of resin-supported catalysts for hydrogenation of cyclohexene at 30°C and under 1atm H2, decreased in the order: Rh>Pt>Pd>Ru.
Oxidation-Reduction Treatment on Supported Metals and Their Catalytic Activities and Microstructure—Alkane Hydrogenolysis over Ru, Rh, Ir, Ni, Pt and Pd on Silica
s.-q. gao and l. d. schmidt, J. Catal. (Dalian, China), 1989, 10, (3), 221-228
Studies of SiO2 supported platinum group metals catalysts reduced at low temperature showed their high activities for alkane hydrogenolysis. The highest activities were obtained on Rh and Ru catalysts which were five orders of magnitude higher than those of Pt and Pd catalysts. Annealing at high temperature reduces the activities by a factor of 1000 on Rh and Ru but only by 2 on Ni catalysts. Studies showed a formation of large regular polyhedral particles in the annealed state which split to form clusters of small irregular particles upon complete oxidation and low-temperature reduction.
The Ignition of Methane/Ethane Boundary Layer Flows by Heated Catalytic Surfaces
t. a. griffin, l. d. pfefferle, m. j. dyer and d. r. crosley, Combust. Sci. Technol, 1989, 65, (1-3), 19-37
Studies of the influence of activity of Pt catalysts on the boundary layer ignition of ethane/methane fuel mixtures showed that catalytic surface reactions reduce the sensitivity of ignition behaviour to the ethane content of the fuel mixture. This suggests that a catalytically stabilised thermal (CST) burner would be less sensitive to the ethane content of natural gas than a non-catalytic counterpart. Using laser-induced fluorescence, spatially resolved measurements of O and OH radical concentration were made in boundary layers formed over Pt and quartz surfaces. The data suggest the production of O atoms and OH radicals prior to gas phase ignition for the catalytic surface reactions.
New Data on the State and Catalytic Activity of Platinum in the Reforming Catalysts
v. k. duply akin, a. s. belyi, n. m. ostrovskii, m. d. smolikov, e. m. chalganov and a. i. nizovskii, Dokl. Akad. Nauk SSSR, 1989, 305,(3), 648-652
A method for quantitative measurement of Pt surface atom numbers which are in various electronic states, is presented. The results show that in the catalytic system Pt/Al2O3, surface Pt atoms are present in two states. The first being Pt0 which is highly dispersed metallic form, and the second Ptσ which is stabilised by support of Pt(II) complexes containing chloride ligands which are able to form stable co-ordination bonds with σ-donor ligands. Catalysts used in dehydrogenation of cyclohexane hydrocarbons should contain Pt predominantly in Pt° state while catalyst containing maximum amount of Ptσ are effective for aromatisation of paraffin.
Effect of High Temperature Oxidative Treatment on the State and Catalytic Activity of Platinum-Aluminium Catalysts in the Reactions of Complete Oxidation of Alkanes
v. a. drozdov, d. i. kochubei, p. g. tsyrul’nikov and v. v. popovskii, Kinet. Katal., 1989, 30, (4), 879-884
Studies of calcination of Pt-Al catalysts at 773-1273 K showed a decrease in activity of ig of Pt due to coking of Pt, changes in the phase state and the texture characteristics of the support. Samples heat treated up to 1080K practically did not change the specific catalytic activity, while on heating at 1020-1080K the activity increased by 5-15 times. The increase in specific catalytic activity was connected with stability changes in Pt-Oabs bond during increase of the average size of Pt crystallites. The observed effect is explained by changes in chemical composition of calcinated catalysts and by the increase in the ratio Pt0:Ptn+ on the catalyst surface.
Acid Properties of Surface of (Pt+Re + Cr)/γ-Al2O3 Catalysts during Dehydrocyclisation of n -Heptane
e. a. skrigan, f. m. sen’kov, l. a. kupcha, m. f. gorbatsevich and n. s. kozlov, Vest. Akad. Navuk BSSR, Ser. Khim. Navuk, 1989, (3), 15-20
Studies of donor-acceptor properties of the γ-Al2O3 surface with Pt, Re and Cr being plated onto it separately and simultaneously were performed by reflective spectroscopy using n -dimethylaminoazobenzol as an acidity indicator. The results show strengthening or attenuation of acceptor sites of a carrier in bi- and three-component systems relative to mono-component catalysts in dependence on the order of plating the components and the means of their activation.
Highly Selective Decomposition of Methanol to Syngas on Nickel-Based Composite Catalysts Using an Artificial Intelligence Control Reactor System
y. nakazaki and t. inui, Ind. Eng. Chem. Res., 1989, 28, (9), 1285-1289
A flow reactor system controlled by a personal computer has been developed and used to life-test an 8.2%Ni-4.2%CeO2-0.41%Pt/SiO2 composite catalyst for MeOH decomposition. Deactivation-regeneration processes were repeated on the composite catalyst and were controlled by the computer. The catalyst had a very high activity with a space-time yield of H, in the initial stage of each cycle of 700 mol 1-1 h-1. CH4 was formed as a by-product in the first few hours on stream but after ~ 60 h H2 and CO were qualitatively produced in a stoichiometric ratio. Deactivation with time was caused by suppression by adsorbed H, which was removable by N2 flow. Catalytic MeOH decomposition has potential applications in internal combustion engines with expected clean combustion.
Non-Faradaic Electrochemical Modification of Catalytic Activity. 1. The Case of Ethylene Oxidation on Pt
s. bebelis and c. g. vayenas, J. Catal., 1989, 118, (1), 125-146
Studies have shown that electrochemical pumping of O2 “ anions onto the surface of polycrystalline Pt increases the catalytic activity for the oxidation of C2H4 to CO2 and H2O by up to a factor of 50. The induced non-Faradaic electrochemical modification of catalytic activity leads to rate enhancement of up to 5000%. The change in catalytic rate is up to 105 times higher than the rate of O2- supply. The main parameter for the interpretation of the observations is the catalyst-solid electrolyte (ZrO2-8 mol% Y2O3) overpotential η. Over a wide range of conditions the reaction rate was found to increase exponentially with ηwhich is proportional to the change in catalyst work function. Reaction activation energy decreased with increasing η. The phenomena are reversible and show that the catalyst work function and activity can be varied by adjusting the catalyst potential.
Reforming-Type Catalysis with Zeolite-Supported PtRe
c. dossi, c. m. tsang, w. m. h. sachtler, r. psaro and r. ugo, Energy & Fuels, 1989, 3,(4), 468-474
It is shown that the addition of Re markedly changes the activity, selectivity, and stability of Pt/NaY and Pt/NaHY catalysts for n -heptane conversion at 500°C and 0.5 MPa. The effect of Re was found to depend strongly on the method of catalyst preparation. Sublimation of volatile Re2(CO)10 onto NaY is very effective for preferential deposition of Re in the supercages of the zeolite. In the presence of prereduc-ed Pt clusters that act as nucleation sites, bimetallic PtRe clusters are predominantly formed. Their catalytic signature is a very high activity and selectivity for deep hydrogenolysis of S-free n -heptane to CH4. Addition of Re to Pt also lowers the rate of catalyst deactivation even in the absence of S. Catalysts prepared by solvent impregnation of PtRe2(CO)12 showed no formation of bimetallic particles and a product pattern similar to Pt/Al2O3 catalysts.
The Nature of the Surface Site for Iso-cyanate Produced in the Reaction of Ammonia and Carbon Monoxide over Supported Catalysts
d. k. paul, s. d. worley, n. w. hoffman, d. h. ash and j. gautney, Chem. Phys. Lett., 1989, 160, (5, 6), 559-563
Reaction of CO and NH3 over M/X (M = Pd, Rh, Ru; X=A12O3, SiO2, TiO2) films is of potential importance to the fertiliser industry. IR spectroscopy has been used to monitor the formation of isocyanate (NCO) on the metals and on the supports. NCO was detected for all the metals when the support was Al2O3 or SiO2, but not for TiO2. NCO resided on the A12O3 support for all M/A12O3 catalysts, but on the metal for M/SiO2. It is concluded that the formation and location of the NCO was dependent upon the extent of the NH4+ formation on the various supports.
Characterization of Supported Palladium Catalysts. III. Pd/Al2O3
w. juszczyk, z. karpinski, i. ratajczykowa, z. stanasiuk, j. zielinski, l.-l. sheu and w. m. h. sachtler, J. Catal, 1989, 120, (l), 68-77
Earlier studies of the supported Pd/Al2O3 catalysts using the catalytic conversion of neopentane as a non-coking probe showed that after reduction at 573-773K the catalyst was about two orders of magnitude more active than Pd/SiO2. It is now reported that after reducing Pd/Al2O3 and extensively purging it in He at 873 K, much higher, though transient, catalytic activity is observed. The IR spectra of adsorbed CO showed the presence of Pdn+ ions in superactive Pd/Al2O3 and their concentration positively correlated with catalytic activity. It is proposed that Pdn+ ions are sites of high catalytic activity. A possible mechanism of their formation and a model of neopentane hydrogenolysis are discussed.
Effect of High-Temperature Reduction on Carburization of Alumina-Supported Palladium: Evidence for Palladium-Aluminium Alloy Formation
l. kepinski, m. wolcyrz and j. m. jablonski, Appl. Catal., 1989, 54, (2), 267-276
XRD studies of the effect of high temperature treatment in H2 on carburisation of Pd in a commercial 10%Pd/Al2O3 catalyst showed that reduction in H2 at 970 and 1070 K for 40h resulted in contraction of the Pd lattice by 0.22% and 0.38%, respectively, due probably to Pd1-xAlx alloy formation (x = 0.06 at 970 K and 0.10 at 1070 K). Due to alloying, Pd/Al2O3 loses its ability to constitute a supersaturated Pd-C solid solution on carburisation in C2H2 at 550 K. The initial activity of Pd can be restored by a two-step process consisting of oxidation at 770 K followed by reduction in H2 at 720 K.
Synergism in Bimetallic Pd-Tc Catalysts in Dehydration of Hydrocarbons
g. n. pirogova, n. n. popova and g. e. kalinina, Izv. Akad. Nauk SSSR, Ser. Khim, 1989, (7), 1482-1485
Studies of the catalytic properties of supported Pd-Tc catalyst during dehydrogenation of cyclic hydrocarbons and n -hexane showed synergism activity of the Pd-Tc catalyst. The most active were catalysts with ratio Pd:Tc = 1:1 to 2:3. Activity during cyclohexane dehydrogenation was: Pd-Tc/γ-Al2O3 > Pd-Tc/MgO > Pd-Tc/TiO2 > Pd-Tc/Y2O3 > Pd-Tc/SiO2.
Formation of Acetals from Carbonyl Compounds and Alcohols in the Presence of Giant Palladium Clusters and Palladium Black
v. p. zagarodnikov, m. n. vargaftik, a. p. lyudimov and 1.1. moiseev, Izv. Akad. Nauk SSSR, Ser. Khim., 1989, (7), 1495-1499
Studies of the giant Pd clusters and Pd black showed them to be very effective for the formation of acetals from carbonyl compounds and alcohols. Comparison of acid properties of the Pd clusters, Pd black and mononuclear Pd(II) complexes showed the presence of aprotonic acidic catalytic centres in the reaction.
Effect of Pd/C Dispersion on Its Catalytic Properties in Acetylene and Vinylacetylene Hydrogenation
yu. a. ryndin, m. v. stenin, a. i. boronin, v. i. bukhtiyarov and v. i. zaikovskii, Appl. Catal., 1989, 54, (3), 277-288
The effect of Pd particle size supported over active C on its electronic and catalytic properties was studied in selective hydrogenation reactions of acetylenic hydrocarbons. The specific catalytic activity (turnover number, TON) and selectivity of Pd were obtained via reduction of C3H5PdC5H5 anchored on active C, within a particle-size range of 30-110Å, and was roughly constant and close to the TON of Pd over oxide supports (SiO2, Al2O3).
Mode of Migration of Isocyanate from Palladium to Silica
d. k. paul, s. d. worley, n. w. hoffman, d. h. ash and j. gautney, J. Catal., 1989, 120, (1), 272-277
he reaction of CO and NHj over preoxidised Pd/SiO2 was studied by IR spectroscopy. An isocyanate (NCO) surface intermediate on Pd providing an IR band at 2168cm-1 was detected after heating to 500K and subsequent cooling to ambient temperature. No migration of NCO from Pd to the SiO2 was observed but the decomposition of for-mamide over preoxidised Pd/SiO2 at ambient temperature produced an NCO species which migrated to the SiO2 via the formation of HNCO gas.
Hydrogenation of Carbon Monoxide on Supported Palladium Catalysts
yu. i. pyatnitskii, g. v. filonenko, t. m. shaprin-skaya, v. p. stasevich, v. i. gritsenko, v. l. struzhko and g. g. girushtin, Neftekhimiya, 1989, 24, (3). 374-383
Studies of the activity and selectivity of Pd supported catalysts during methanol synthesis from CO and H2 showed them to depend on the nature of the support, on Pd dispersion and on Cl- presence. The addition of small amounts of O2 (up to 0.5vol.%) in the synthesis gas increased the activity and selectivity of the Pd catalysts supported on MgO, ZrO2, SiO2-ZrO2 and SiO2 supports (no Cl-), during methanol synthesis while supressing methane formation. In the similar reaction of methanol formation from CO and H2 over Pd/SiO2 catalyst, formation of aromatic hydrocarbons was observed in addition to the yields of dimethyl ester and aliphatic C1-Cg hydrocarbons.
Catalytic Oxygenation of Benzene. Catalyst Design and Its Performance
a. kunai, t. wani, y. uehara, f. iwasaki, y. kuroda, s. ito and k. sasaki, Bull. Chem. Soc. Jpn., 1989, 62, (8), 2613-2617
A catalyst system for oxygenation of benzene is composed of PdCl2 and CuSO4 species supported on SiO2 and operates in neat benzene under ambient conditions by feeding H2 and O2 to the system. By selecting the reaction conditions properly, either phenol or benzoquinone can be obtained as the major product. No other product was detected in the reaction mixture. The catalyst preparation is simple and catalysts of the same activity were always obtained.
Palladium Carbonyl Clusters Entrapped in NaY Zeolite Cages: Ligand Dissociation and Cluster-Wall Interactions
l.-l. sheu, h. knozinger and w. m. h. sachtler, J. Am. Chem. Soc, 1989, m, (21), 8125-8131
Highly structured FTIR spectra, which indicate presence of Pd carbonyl clusters, were obtained after adsorption of CO on Pd/NaY which was reduced at 200°C, but broad IR bands were observed with samples reduced at higher temperature. As the clusters lose some of their CO ligands, old IR bands erode and new bands with isosbestic points appear.
AES Studies on a Pd-Modified Silver Catalyst
m. szustakowski, j. baron and j. jarmakowicz, React. Kinet. Catal. Lett., 1989, 39, (2), 351-356
The difference in Pd concentration on the surface and in the bulk of Pd-modified Ag catalysts may have importance for the technology of production of these catalysts and their application in commercial formaldehyde production. AES studies of Ag crystals electrodeposited from AgNO3 (8%) and Pd2+ (250mg/dm3) electrolyte before and after exposure to conditions of MeOH to HCHO oxidation showed surface Pd concentration ~100 times bulk Pd concentration. The amount of Pd on the surface decreased with temperature increase. C, S, and O were also observed on the surface.
Investigation of the Wacker Process in Formamide Microemulsions: Oxidation of Various Olefins Catalysed by Palladium Chloride
n. alandis, i. rico and a. lattes, Bull. Soc. Chim. Fr., 1989, (2), 252-255
Formamide microemulsions have been used as reaction media for the PdCl2 catalysed Wacker process, giving much faster oxidation rates of various internal and terminal olefins and giving better yields in product ketones than using classical media. Detailed analysis of the reaction mechanisms is given.
Effect of Sulphur on the Coking of Rhodium in the Steam Reforming of 1 -Methylnaphthalene
g. delahay and d. duprez, Appl. Catal., 1989, 53, (1), 95-105
The effect of S on the coking of Rh/Al203 in the steam reforming of 1-methylnaphthalene has been studied at 440-500°C, 1 atm, and a steam-to-1-methylnaphthalene molar ratio of 14, with S content 690, 80 and <5 ppm. In all cases the coking rate was increased considerably by the presence of S. Coke progressively invades the whole of the catalyst bed and the interior of the catalyst grains but, in every instance, the coke deposit was located near the S-adsorption sites. Profiles of coke and S were very similar in the catalyst bed and inside the pellets.
Effects of Drying on the Preparation of HF Co-impregnated Rhodium/Al2O3 Catalysts
j. s. hepburn, h. g. stenger and c. e. lyman, Appl. Catal., 1989, 55, (2), 287-299
Quantitative electron probe microanalysis of the effects of drying rate on the internal distribution of Rh within HF co-impregnated Rh/Al2O3 catalysts showed catalysts with uniform Rh distribution, inner bands (egg-white) of Rh and inner cores (egg-yolks) of Rh. During drying at <500°C, evaporation appeared to proceed mainly at the external surface of the support. At 500°C, however, evaporation occurred only from a receding front within the support.
Effects of High-Temperature Oxidation and Reduction on the Structure and Activity of Rh/Al2O3 and Rh/SiO2 Catalysts
c. wong and r. w. mccabe, J. Catal, 1989, 119, (1), 47-64
Rh/Al2O3 catalysts have been compared to Rh/Si02 catalysts after exposure to high-temperature oxidising (HTO) and reducing (HTR) environments in order to elucidate the mechanism of deactivation of Rh-containing automotive catalysts. The fresh Rh/Al3O3 catalyst contained Rh as isolated atoms and particles above the surface of the A12O3, with CO oxidation mainly on the particles. Most of the Rh in HTO Rh/Al2O3 was dissolved in the bulk of the Al2O3 and so CO oxidation rate was 5-10 times lower than that of the fresh catalyst. In HTR Rh/Al2O3 virtually all of the Rh existed as particles on the A12O3 surface and so had greater CO oxidation activity (but similar activadon energy). In HTO-HTR and HTO-HTR-reoxidised (RO) Rh/Al2O3 most of the Rh was near or on the surface and probably exists as small Rh clusters and larger particles. CO oxidised at higher rates on HTO-HTR-RO Rh/Al2O3 and with lower activadon energy than the fresh catalyst. The Rh clusters are thought to be active here.
Determination of Ce Valence in Rh-Ce/Al2O3 Catalysts by X-Ray Absorption
d. d. beck, t. w. capehart and r. w. hoffman, Chem. Phys. Lett., 1989, 159, (2, 3), 207-213
Measurements of the Ce LIII absorption edges of model Rh-Ce/Al2O3 automotive catalysts have been made to determine changes in the Ce valence produced by high temperature treatments in O2 or H2. From studies it is concluded that on Rh-Ce/Al2O3 treated in H2 at 900°C, Ce exists as a mixture of Ce2O3 and CeAlO3. Air exposure at 25°C converts the Ce2O3 portion to CeO2. The measured oxidation states and deduced stoichiometrics provide some insight about the behaviour of Ce in reducing and oxidising environments, and in particular about the involvement of Ce in the storing and releasing of O during cycles of high temperature oxidation and reduction.
Reactive Chemisorption and Methanation of Carbon Dioxide on Rhodium Particles Approaching Atomic Dispersion
s. ichikawa, J. Mol Catal, 1989, 53, (1), 53-65
The turnover frequency for the CO2 methanation reaction on highly dispersed Rh/SiO2, prepared by cation exchange and characterised by chemisorption, was found to be ~50 times that on a low dispersion Rh/SiO2 catalyst and comparable to a high dispersion Rh/TiO2 catalyst. The high adsorption stoichiometry and the high catalytic activity for small Rh clusters are discussed in terms of the intrinsic particle size effect due to changes in the cluster work function derived from classical electrostatic concepts and Mulliken’s definition of electronegativity. The effects due to the thermodynamic driving force and metal-support electronic interaction are also discussed.
Synthesis, Characterization and Activity of Ru/SiO, Catalysts Prepared by the Sol-Gel Method
t. lópez, a. lópez-gaona and r. gómez, J. Non-Cryst. Solids, 1989, 110, (2, 3), 170-174
The preparation of Ru catalysts by the sol-gel method is described. The preparation consists of adding the active metal to a sol which by hydrolysis and condensation reactions, turns into a gel. The catalytic activity for benzene hydrogenation shown by these catalysts was higher than that of catalysts prepared by impregnation of a commercial silica. Catalysts prepared by this method showed superior resistance.
Effects of Alumina Dissolution and Metal Ion Buffering on the Dispersion of Alumina Supported Nickel and Ruthenium Catalysts
j. a. mieth and j. a. schwarz, Appl. Catal., 1989, 55, (1), I37-H9
Studies of the effects of A12O3dissolution and metal ion buffering on the dispersion of Ru/Al2O3 and Ni/Al2O3catalysts showed that Ru salts are stronger buffers of the impregnating solution. Thus, at low initial pH values of each impregnant, more free Al is released to the aqueous phase in Ru electrolytes than in Ni electrolytes. The Ru/Al2O3catalysts showed comparable dispersions for more than a factor of five increase in weight loading.
Ammonia Synthesis over Ruthenium Supported Catalysts Derived from Ru3 (CO) u
p. moggi, g. predieri, g. albanesi, s. papadopulos and e. sappa, Appl. Catal., 1989, 53, (1), L1-L4
The activity for NH3 synthesis of Ru/Al2O3-K catalysts derived from Ru3(CO)12 has been compared with corresponding catalysts derived from RuCl3. The maximum activity of a 2wt.% Ru catalyst prepared from the carbonyl cluster was 4.39 mg/h of NH3 produced per gram of catalyst at 400°C; about twice the maximum activity of a corresponding 2wt.% Ru catalyst derived from RuCl3. Comparison of 5wt.% Ru catalysts derived from carbonyl clusters with data previously reported for a corresponding 5wt.% Ru catalyst derived from RuCl3 showed a 20- fold increase in activity at 300-350°C for theRu3(CO)12-derived catalyst, and a 10-fold at 400°C.
Calorimetric Study of the Coadsorption of Hydrogen and Carbon Monoxide over Ruthenium Graphitized Carbon Black Catalysts
a. guerrero-ruiz, Appl. Catal., 1989, 55, (1), 21- 31
A calorimetric study of the H2 and CO adsorption and coadsorption over Ru graphitised C black catalyst was carried out in order to explain the differing catalytic behaviour of C supported Ru particles with different metal crystallite sizes, in CO hydrogenation. Preadsorbed H did not inhibit CO adsorption while preadsorbed CO greatly prevented H adsorption.
A Polyethylene-Bound Ruthenium(II) Catalyst for Inter- and Intramolecular Kharasch Reactions
j. c. phelps, d. e. bergbreiter, g. m. lee, r. villani and s. m. wienreb, Tetrahedron Lett., 1989, 30, (30), 3915-3918
The preparation of a soluble, recoverable polyethylene-bound Ru(II) catalyst, RuCl2[PE-PPh2]3, and its application to inter- and intramolecular Kharasch additions of chlorocarbons to alkenes is described. The catalyst is also as efficacious as RuCl2(PPh3)3 in promoting intramolecular Kharasch cyclisation of various halo olefin substrates.
Electrochemical Synthesis of Dimeric Platinum Hydride Species Responsible for Highly Regioselective Alkene Hydroformylation
e. paumard, a. mortreux and f. petit, J. Chem. Soc, Chem. Commun., 1989, (18), 1380-1383
The complexes PtL2Cl2 where L2 is diop, 2,3-O-isopropylidene-2,3-dihydroxy-1,4-bis(diphenylph-osphino)butane, have been used as catalyst precursors for alkene hydroformylation after electroreduc-tion using a soluble Sn or Fe anode, followed by treatment with CO-H2. The remarkable regioselec-tivities for linear aldehyde formation (~98% from hex-1-ene and 90% from styrene) are explained by the production of chelated, bridged Pt hydride cationic species [L2Pt(H)μ-L2)Pt(H)L2]2+.
Polymerization of Methyl Methacrylate Initiated by Various Hydridoplatinum(II) Complex-Carbon Tetrachloride Systems
n. kameda, Nippon Kagaku Kaishi, 1989, (7), 1172-1174
Polymerisation of methyl methacrylate initiated by fraro-PtHX(PEt3)2-CCl4, where X is Cl, Br, I, NO3 NO2, or CN, has been studied at 50°C. The ligand effect of the hydrido-Pt(II) complex on polymerisation activity was found to decrease in the order: NO3>Cl>Br>I> NO2>CN. These results agree with the direction, forward decrease, of the value of Pt-H stretching vibration in the IR spectra of the hydrido-Pt(II) complex.
Oxidation of Carbon Monoxide by Pd(II) in Aqueous Solutions
v. a. golodov and l. v. kashnikova, Kinet. Ratal, 1989, 30 (3), 739-742
Kinetics of CO oxidation by Pd(II) catalyst was studied in aqueous solutions at 293 K in presence of O; and with CO content in gaseous phase of <1%, in order to determine the suitability of this reaction for cleaning of gases containing small amounts of CO. It is concluded that aqueous solutions of Pd(II) salts with sufficient Pd content of >0.005M and not containing HCl or LiCl, are suitable for CO oxidation in gases containing small amounts of CO.
Palladium Catalyzed Double Heck Aryla-tion of Cyclopentene
m. prashad, j. c. tomesch, j. r. wareing, h. c. smith and s. h. cheon, Tetrahedron Lett., 1989, 30, (22), 2877-2880
A convenient synthesis of 1,3-diarylcyclopentenes is described via a Pd(OAc)2 catalysed double Heck arylation of cyclopentene with aromatic halides. If the reaction is performed under phase transfer conditions there is increased selectivity favouring the formation of one olefin regioisomer, which contrasts with results obtained under classical Heck conditions.
Chelate-Assisted, Pd-Catalyzed Efficient Carbonylation of Aryl Chlorides
y. ben-david, m. portn0y and d. milstein, J. Am. Chem. Soc, 1989, in, (23), 8742-8744
Direct catalytic carbonylation of aryl chloride under mild pressure is reported using the new complex (dippp)2Pd (or its precursors) as catalysts [dippp = bis(diisopropylphosphino)propane], resulting in high-yield synthesis of carboxylic acids, esters and amides. No catalyst deactivation or decomposition was observed. The reactions studied were highly ligand dependent, pointing to the uniqueness of dippp.
Rhodium Catalyzed Hydrogenation of Quinolines and Isoquinonnes under Water-Gas Shift Conditions
s. -i. murahashi, y. imada and y. hirai, Bull. Chem. Soc Jpn., 1989, 62, (9), 2968-2976
A wide variety of quinolines and isoquinolines which occur naturally in coal, oil shale and tar sand, can be hydrogenated selectively in the N-containing ring by means of CO and H, 0 in the presence of catalytic amount of Rh carbonyl cluster, Rh6(CO)l6. These reactions provide a useful method for the preparation of compounds 1,2,3,4-tetrahydroquinolines and 1,2,3,4-tetrahydroisoquinolines which are key intermediates for the synthesis of isoquinoline alkaloids and other biologically active N compounds.
Phospholes as Ligands for Rhodium Systems in Homogeneously-Catalysed Hydroformylation Reactions. Part 1. Stereoelectronic Properties of the Ligands and Hydroformylation of 1-Hexene
d. neibecker and r. réau, J. Mol. Catal, 1989, 53, (2), 219-227
The Rh-phosphole catalysed hydroformylation of i-hexene has been studied with reference to stereoelectronic properties of the phosphole ligands. The phosphole catalysts were compared to triphenylphosphine catalysts under typical hydroformylation conditions (80°C, 20 bar syngas). 1,2,5-triphenylphosphole (TPP) has been found to be by far superior to triphenylphosphine (~10 times more active and 10% more selective) and most importantly the Rh-TPP system seems to be insensitive to the P:Rh ratio.
Catalytic Properties of the Binuclear Rh(II) Complexes in Hydrogenation and Isomerisation of AHylbenzene
v. z. sharp, v. i. isaeve, a. n. zhilyaev and i. b. baranovskii, Izv . Akad. Nauk SSSR, Ser. Khim., 1989. (9), 1957-1961
Studies of the catalytic properties of binuclear Rh(II) complexes with acetonitrile and hexafluoroacetyl-acetonate ligands during hydrogenation and isomerisation of allylbenzene showed activity when isomerisation proceeded in Ar. The catalytic system [Rh2(hfacac)4(H2O)2]-Ph3P in allylbenzene conversion was considerably more active than other hexa-fluoroacetylacetonate Rh(II) complexes. Treatment of acetate complexes [Rh2(O2CCH3)4] with NaBH4 greatly increased their activity, which was probably due to the formation of [Rh2(O2CCH3)3l+ and [Rh2(O2CCH3)2]2+ complexes.
Rhodium(III) Complexes with O-Alkyl-S-Alkylthiocarbonates as Catalysts for the Homogeneous Hydrogenation of Unsaturated Compounds
v. n. maistrenko, i. a. rusakov. s. o. bondareva, i. yu. murinov and g. a. tolstikov, Izv. Akad. Nauk SSSR, Ser. Khim., 1989, (10), 2336-2338
Studies of catalytic activity of Rh3+ complexes with O-alkyl-S-alkylthiocarbonate (L) of general formula RhCl3L3 (where L = ROC(O)SR'; R = i -Pr, i -Bu, C7H15, Ph; R' = Me, Et, Pr, Bu, i -Bu) were performed during homogeneous hydrogenation of unsaturated compounds. Cyclic voltammetry studies showed the formation of Rh intermetallic hydrides during the process of alkene hydrogenation in the presence of these complexes.
Stoichiometric Reduction of Carbon Dioxide to HCHO and HCOOH by K[RuIII(EDTA-H)Cl].2H2O
m. m. taqui khan, s. b. halligudi and s. shukla, J. Mol. Catal, 1989, 53, (3), 305-313
The stoichiometric reduction of C02 by soluble K[RuIII(EDTA-H)Cl].2H2O complex at CO2 pressure of 5-70 atm and at 40-80°C gave formic acid and formaldehyde as “value added” reaction products. The rates of formation of HCHO and HCOOH were found to have first order dependence with respect to catalyst and dissolved CO2 concentrations.
Ruthenium Complex Catalyzed Benzyla-tion of Arenes with Benzyl Formates; Decarbonylation and Decarboxylation of Alkyl Formates
t. kondo, s. tantayanon, y. tsuji and y. watanabe, Tetrahedron Lett., 1989, 30, (31), 4137-4140
Ru3(CO)12-(CH3)3NO.2H2O showed high catalytic activity for the decarbonylation of alkyl formates to the corresponding alcohols at 150-200°C under Ar. Decarbonylation of β-phenetyl formate gave β-phenetyl alcohol in 82% yield.
Preparation and Characterization of SPE Composites for Electrolyzers and Fuel Cells
p. aldebert. f. novel-cattin, m. pineri. p. millet, c. doumain and r. durand, Solid State Ionics, 1989, 35, (1, 2), 3-9
Three different methods of the preparation of solid polymer electrolyte (SPE)-electrocatalyst composites are described, using Pt as a catalyst and Nafion 117 as SPE. First, a procedure based on the localised precipitation of Pt microparticles within a Nafion membrane is described. These composites showed no degradation of electrochemical performance over 15,000 hours of continuous H2O electrolysis. H2/O2 fuel cell performances are also reported. Second, composites were prepared by chemical transformation of Nafion which led to thermoplastic materials onto which were pressed Pt electrode structures. These were used in fuel cells. Third, the preparation, characterisation and use of solutions and gels of Nafion, leading to the realisation of Pt catalyst-based structures suitable for H2/O2 fuel cell applications, are described.
Oxygen Reduction in a Proton Exchange Membrane Test Cell
s. j. ridge, r. e. white, y. tsou, r. n. beaver and g. a. eisman, J. Electrochem. Soc, 1989, 136, (7), 1902-1909
Oxygen reduction in a gas-fed tetrafluoroethylene (Teflon®)-bonded Pt black porous electrode attached to a proton exchange membrane (PEM) is discussed. Experimental data and a mathematical model are presented for the test cell used. Various membrane and electrode assemblies were tested at different levels of Pt loading and Teflon® content. The model accounts for the diffusion and reaction of O and the diffusion and reaction of H ions. Based upon model predictions, it is shown that the transport of the protons in the active layer of the cathode is an important factor in the operation of the test cell.
A Project for the Electrochemical Production and Utilization of Hydrogen in Brazil
e. r. gonzalez. e. a. ticianelli, a. a. tanaka and l. a. avaca, Energy Sources, 1989, 11, (1), 53-58
Hydrogen production by H2O electrolysis and the development of H3PO4 fuel cells are described with reference to the development of a H2 economy in Brazil. Teflon-bonded gas diffusion electrodes have been developed with graphite paper substrate on which an active catalyst layer composed of 10% Pt, Shawinigan black C and PTFE (polytetrafluoroethene) binder was applied by a rolling process. Performances of these electrodes (prepared from “local” materials) were compared with commercially available electrodes. Bipolar separator plates, matrices and cell stack development are also described.
Morphological and Chemical Changes in Palladium Alloy Gauzes Used for Platinum Recovery in High-Pressure Ammonia Oxidation Plants
j. l. g. fierro, j. m. palacios and f. tomás, Surf. Interface Anal., 1989, 14, (9), 529-536
Platinum, evaporated from Pt-Rh catalyst gauzes during high-pressure NH, oxidation is efficiently recovered by catchment on a pack of Pd alloy gauzes placed at the outlet of plant. Studies of this process showed that, in general, the wire diameter increase due to Pt alloying depends on the gauze position in the pack and also on the initial wire diameter. Deep recrystallisation and faceting were observed with this diameter increase. Pt:Pd ratios depended markedly on the position in the catchment pack and also on the orientation with respect to the stream (front or back face). Nodular Rh2O3 particles randomly distributed over the Pd alloy surface have also been observed.
A Novel Method for Dehydrogenation of Cyclohexane with a Palladium Membrane
n. itoh, k.-i. miura, y. shindo, k. haraya, k. obata and k. wakabayashi, Sekiyu Gakkaishi, 1989, 32, (1), 47-50
The oxidative dehydrogenation of cyclohexane using a Pd membrane at 473 K under atmospheric pressure and using 10.1% O2-containing gas as a “sweep” gas, is reported. H2 produced by dehydrogenation of cyclohexane on Pd, permeates through the Pd membrane and reacts immediately with O2 on its opposite surface to produce H2O. Near 100% conversion can be obtained using this method, while equilibrium conversion is only 19%. This method is said to be much more efficient in obtaining higher rates of conversion than an alternate one in which permeated H2 is swept by inert gas.
ELECTRICAL AND ELECTRONIC ENGINEERING
Semiconductor Electrodes Modified by Electrodeposition of Discontinuous Metal Films. Part I. Role of the Film Morphology
p. allongue and e. souteyrand, J. Electroanal. Chem. Interfacial Electrochem., 1989,269,(2),361-374
The stability of semiconductor photoanodes modified by electrodeposition of discontinuous Pt films has been studied by measuring the shift ΔV in the flat-band potential with illumination. A simple model for ΔV shows that a quantitative determination is possible. The theory proposed explains the role of the film morphology and gives new insight into the potential distribution at the interface. Stabilisation is complete as soon as the main distance between the Pt islets is smaller than a distance of the order or magnitude of the mean free path of holes. The role of the metal-induced surface states are discussed.
Co/Pt and Co/Pd Ultrathin Multilayered Films as New Magneto-Optical Recording Materials
y. ochiai, s. hashimoto and k. aso, IEEE Trans. Magn., 1989, 25, (5), 3755-3757
Multilayer films of Co/Pt and Co/Pd have been prepared by magnetron type sputtering. Both multilayer films showed perpendicular magnetic anisotropy at Co layer ≤10Å. When film thickness became <1000Å, an enhancement of the Kerr rotation angle, an increase of the Kerr remanence to saturation ratio, and an increase of the coercive force were observed.
Stress-Induced Perpendicular Magnetic Anisotropy in PtMnSb Thin Films
n. sugimoto, t. inukai, m. matsuoka and k. ono, Jpn. J. Appl. Phys., 1989, 28, (6), 1139-1140
The inducement of perpendicular magnetic anisotropy in PtMnSb thin films is required for the application of PtMnSb as magneto-optical recording media. Stress-induced perpendicular magnetic anisotropy has been studied for PtMnSb thin films deposited on various substrates having different expansion coefficients. The magnetostriction constant λ of PtMnSb thin films was determined as -30×10-6.
Effects of Pt and Zr on the Oxidation Behavior of FeTbCo Magneto-Optic Films: X-Ray Photoelectron Spectroscopy
d. majumdar and t. k. hatwar, J. Vac. Sci. Technol. A, 1989, 7. (4), 2673-2677
X-ray photoelectron spectroscopy has been used to study in situ the effects of addition of 10 at.% Pt or Zr on the oxidation behaviour of FeTbCo magneto-optic films under 5×10-7 Torr of O2 at room temperature. Environmental stability was increased and pinhole formation was reduced without significantly affecting the magneto-optical properties. In (FeTbCo) 0.9Pt0.1, Pt decreased the oxygen uptake at the surface and retarded the oxidation kinetics of Fe. No oxidation of Pt was observed.
Perpendicular Magnetic Anisotropy of Pd-Co Alloy Films and Related Multilayers
s. tsunashima, k. nagase, k. nakamura and s. uchiyama, IEEE Trans. Magn., 1989 25, (5), 3761-3763
Extremely large perpendicular anisotropy is reported for PdCo alloy films, potential magneto-optic recording media. Vacuum deposited PdxCo1-x (0.3≤x≤o.85) films have large uniaxial anisotropy ku with the easy axis perpendicular to the film plane. Maximum ku was 5×106 erg/cm3 for x= 0.35-0.5. Compositional dependence of ku is similar to that of the magnetostriction constant λ111, which suggests magnetostrictive origin. In multilayer films, PdCo/Pt and PdCo/Pd showed positive ku while PdCo/Cu showed negative.
Optical Recording Materials Based on TeOx Films
k. kimura, Jpn. J. Appl. Phys., 1989, 28, (5), 810-813
Electron-beam co-evaporation of Te, TeO2 and additional elements has been used to prepare TeOx films containing Pd, Ge or Sn. Since these films exhibited large differences in optical constants between the amorphous and crystalline states, they are thought to be potentially useful for optical recording media. TeOx films with Pd, in particular, showed rapid crystallisation speed as well as high stability against humidity and oxidation. The optical property changes in Te48Pd24O28 are attributed to the amorphous-to-crystalline transformation of the PdTe component. The single phase of PdTe was observed on the recorded mark after laser irradiation. In general, addition of Pd, Ge or Sn increased the transformation temperatures and reduced the time for crystallisation from 30 s to 300 ns.
New Method for the Synthesis of Boron-10 Containing Nucleoside Derivatives for Neutron-Capture Therapy via Palladium-Catalyzed Reaction
y. yamamoto, t. seko and h. nemoto, J. Org. Chem., 1989, 54, (20), 4734-4736
The Pd-catalysed coupling reaction of halogenated nucleoside derivatives with an aryltin compound having a boronic moiety proceeded chemoselectively at the C-Sn bond rather than the C-B bond to give B-containing nucleoside derivatives in good yields, for use in neutron-capture therapy for treatment of cancer. A systematic procedure for the synthesis of a number of B-containing nucleosides has been developed through the proper choice of catalyst (Pd(PPh3)4) and protecting group of the boronic moiety, and the protection of the sugar portion.
Coordination Compounds and
Microorganisms, Part 12. Rhodium Compounds of S-Nicotine and Their Bacterial Activity
r. d. gillard, j. d. pedrosa de jesus and a. y. a. mohamed, Transition Met. Chem., 1989, 14, (4), 258-260
The activities of the S-nicotine (nic) complexes of Rh(III), [RhCl3(nicH+)3](PF6)3 and trans-[RhCl2(nic)4](PF6) have been studied on Escherichia coli B growing on a minimal glucose medium in both lag- and log-phases. [RhCl3,(nicH+)3](PF6)3 at 50 ppm caused bacteriostasis, and at 100 ppm or more was bactericidal, whereas trans -[RhCl2(nic)4(PF6) at 50 ppm or more was bactericidal in the lag-phase. However [RhCl3(nicH+)3](PF6)3 delayed cell division of Escherichia coli B just entering the log-phase by two generation times, whereby the bacteria transformed from the normal unicellular shape to filamentous forms. Cytotoxicities are reported.