Platinum Metals Rev., 1989, 33, (3), 137
ABSTRACTS: July 1989
of current literature on the platinum metals and their alloys
Adsorption of Carbon Monoxide and Oxygen on Pt(110). Self-Oscillations in the Rate of CO Oxidation on Pt(110)
a. l. vishnevskii and v. i. savchenko, React. Kinet. Catal. Lett., 1989, 38, (1), 159–166; 167–173
Adsorption of CO and O2 on Pt(110) has been studied by X-ray photoelectron spectroscopy, low energy electron diffraction and thermal desorption spectroscopy techniques to elucidate the role of adsorbed O states and structural rearrangements of the surface under action of adsorbed CO in the appearance of self-oscillations in the rate of CO oxidation on Pt(110). The necessary condition for the appearance of self-oscillations in the system was the change in Pt surface properties under the action of reaction medium. Self-oscillations in the rate were maintained due to reversibility of these changes.
A Characterization of Heterogeneous Pt Surfaces by Work Function Measurements and Photoemission of Adsorbed Xenon
m. alnot, j. j. ehrhardt and j. a. barnard, Surf. Sci., 1989, 208, (3), 285–305
A Pt(111) single crystal surface was “artificially” disordered both by Pt deposition and by controlled doses of ion bombardment and the resulting defected surface was systematically characterised by work function measurements and by photoemission of adsorbed Xe. The effects of the Pt deposition were found to depend on substrate temperature. The Pt deposits on low temperature substrates of 130K, showed that a complex disordered surface is created probably dominated by Pt adatoms organised in very small clusters.
Microstructure of Pt-Rh Particles on SiO2
t. p. chojnacki and l. d. schmidt, J. Catal., 1989, 115, (2), 473–485
Transmission electron microscopy and electron diffraction studies on 20−200Å Pt-Rh alloy particles on amorphous SiO2 after heat treatment in H2 at 600−100°C revealed a two-phase microstructure. One phase was a section of a cube and the other was a highly twinned region usually with a single set of multiple twin bands <1Å wide. Heating these phaseseparated samples in N2 or He produced single-phase particles with shapes between polyhedra and spheres, which reverted to the two-phase morphology on subsequent heating in H2. Heating at 300°C in O2 produced breakup of the twinned regions without change to the cube-shaped regions.
The Transient Behaviour of Pt-Rh(410) Alloy Surfaces upon Interaction with O2, NO and CO
f. c. m. j. m. van delft, j. siera and b. e. nieuwenhuys, Surf. Sci., 1989, 208, (3), 365–382
The effect of the initial surface composition of Pt-Rh alloy (410) single crystal surfaces on their reactivity with O2, NO and CO was studied by AES, XPS and thermal reaction mass spectroscopy. The NO dissociation on the Pt-Rh (410) surface was found to depend on the surface composition and the reaction temperature. The Rh-rich surfaces showed a higher NO dissociation activity than the Pt-rich surfaces. However, the maximum CO2-production for the reactions of CO with O2 or NO occurs at a temperature (Tm), where NO dissociation is already complete on both Rh- and Pt-rich surfaces. The Tm appears to depend on the metal-O bond strength and on the CO:O2 or CO:NO molar ratios in the reaction mixture. This shows that CO2 is produced by the reaction of CO(ads) and O(ads).
Experimental and Theoretical Investigation of Hydrogen Diffusion on a Metal Surface
t. e. felter, r. h. stulen, m. l. koszykowski, g. e. gdowski and b. garrett, J. Vac. Sci. Technol., 1989, A7, (1), 104–107
Low-energy electron diffraction in combination with electron stimulation of the surface by the incident beam have been used to study H diffusion on Pd(111) surface. Rapid surface diffusion occurred at >55K. Two possible mechanisms, electron stimulated desorption and electron stimulated disordering, are presented. The results of theoretical calculations based on variational transition state theory of H/Ni(111) were in reasonable agreement with the experimental results for H/Pd(111) system.
Microcalorimetric Study of the Surface Structure of Graphite-Supported Iron/Rhodium Catalyst Particles
r. r. gatte and j. phillips, J. Catal., 1989, 116, (1), 49–60
Studies of the structure of the surface of the graphite-supported Fe-Rh bimetallic catalyst particles were performed by a Calvet-type differential adsorption microcalorimeter of a novel design and by transmission electron microscopy. The results showed that the two metals segregate locally on calcination at >200°C and do not form an alloy phase after a subsequent low temperature reduction. The 200°C calcination treatment resulted in Fe enrichment of the particle surface, which was also retained after the subsequent 100°C reduction.
Formation Specifics of IrO2 Powders during Thermal Transformations of Iridium(IV) Hydroxide
yu. s. shorikov, r. v. muzychuk and v. l. sbitnev, Izv. Akad. Nauk SSSR, Neorg. Mater., 1989, 25, (2), 289–293
Studies of the formation process of IrO2 powder during thermolysis of Ir(IV) hydroxide by various physico-chemical methods showed that heating of microporous amorphous Ir(IV) hydroxide to 220°C yielded Ir(OH)2 which has mesoporous adsorbent properties. Crystal lattice IrO2 with increased specific surface was formed at 450°C. The growth of microcrystals started at 450−800°C, followed by decrease in the level of defects until full recrystallisation was completed at 800°C and product became stoichiometric IrO2. This was accompanied by an increase in agglomerated sizes and poly-dispersion of powders, and rebuilding of porous structure. This is connected with a decrease in specific surface and a number of narrow and coarse mesopores.
High-Accuracy Capabilities of an OsO4 Molecular-Beam Frequency Standard
a. godone, m. p. sassi and e. bava, Metrologia, 1989, 26, (1), 1–8
Studies have shown that absorptions of OsO4 in coincidence with CO2 laser emissions have very attractive metrological characteristics. Results from using a Ramsey-type interaction technique showed the feasibility of a primary frequency standard at 30 THz, in the 10 μ m region, based on an OsO4 molecular beam with an accuracy level of 10−14 and satisfactory short-term frequency stability. The molecular flux was sufficiently high for the well-resolved OsO4 transitions to be observed with a relatively high signal to noise ratio. Interaction, detection techniques and sources of the uncertainty are discussed.
Preparation of a New Al-Cu-Ru Quasicrystal with Large Grain Sizes by Rapid Solidification
a. -p. tsai, a. inoue and t. masumoto, J. Mater. Sci., Lett., 1989, 8, (3), 253–256
The Al-Cu-Ru alloys were prepared by arc melting a mixture of pure Al, Cu and Ru in a purified Ar atmosphere and the as-solidified phase was studied by X-ray powder diffraction techniques. The results showed a new quasicrystal which was formed in the vicinity of Al65Cu20Ru15. The icosahedral structure in the Al-Cu-Ru alloy remained stable up to >1000K.
Corrigendum: Steady-State Kinetics of the Catalytic Reduction of Nitrogen Dioxide by Carbon Monoxide on Platinum
Ba3Y2Cu2PtO10: Newly Obtained Phase during Single Crystal Growth of Ba2YCu3O7−δ from Platinum Crucible
t. hibiya, y. nakabayashi, t. satoh and t. kawamura, Jpn. J. Appl. Phys., 1989, 28, (1), L63–L66
A new compound with chemical composition Ba3Y2Cu2PtO10 has been obtained as a single crystal during preparation of Ba2YCu3O7−δ single crystals from CuO flux melt using a Pt crucible. As-grown crystal is insulating or semiconducting, and has a room temperature resistivity of 3 MΩcm. The compound has monoclinic symmetry (space group: C2/m) and its lattice parameters are a0=12.333Å, b0=5.751Å and c0=7.247Å, and β =105°40′. The mechanism of incorporation of Pt ions is discussed.
Ternary Intermetallic Compounds Synthesized by Molten-Metal-Solution Growth
j. p. a. westerveld, d. m. r. lo cascio, m. o. doornik, p. i. loeff, h. bakker, h. j. m. heijligers and g. f. bastin, J. Less-Common Met., 1989, 146, 189–195
Several new ternary compounds including Sn4.68Pt1.37Yb1.00, Sn4.65Pd1.34Ca1.00 and In5.06Pd1.17La1.00, four different compositions of GaPtSc, and GaPdX where X is Ca, Pr, Yb, Y and Sc, have been synthesised by growing crystals of metallic compounds in a molten-metal solution.
New Family of 2Hb-Type Layered Diselenides: Preparation of 2Hb-Re1/2Ta1/2Se2 and 2Hb-Os1/3Ta2/3Se2
k. hayashi, m. hyoma, h. yamanaka and h. nishihara, J. Less-Common Met., 1989, 147, (1), 19–26
Samples of MxTa1−xSe2, where M is Pt, Ir, Os or Re, have been prepared from the elements by reaction at 850 and 950°C. Only two compounds Os1/3Ta2/3Se2 and Re1/2Ta1/2Se2 crystallised in the 2Hb-polytype structure, and are semiconductors which show weak paramagnetism. No anomalies of the resistivity or magnetic susceptibility were observed in the temperature range 10−290K.
The Prediction and Synthesis of Some New Intermetallic Compounds between Transition Metals and Rare Earth Metals
y. -t. ning, x. -m. zhou, y. zhen, n.-y. chen, h. xu and j. -z. zhu, J. Less-Common Met., 1989, 147, (2), 167–173
Six new intermetallic transition metal-rare earth compounds with various crystal structures have been synthesised, including NdIr3, GdIr3 and DyIr3 with the AuCu3-type structure, and LaPd5 with the CaCu5-type structure. The crystal structures of these new compounds coincided with those predicted using computer pattern recognition of chemical bonds.
Preparation, Crystal Structure and Magnetic Properties of Dy5Ru19P12 and Isotypic Lanthanoid Ruthenium Phosphides
v. ghetta, p. chaudouët, r. madar, j. p. senateur and b. lambert-andron, J. Less-Common Met., 1989, 146, 299–307
A new series of phosphide compounds Ln5Ru19P12, where Ln is Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er and Yb, have been prepared by reacting the elemental components and annealing at 1700K. From single crystal X-ray data the structure of Dy5Ru19P12 was determined as a hexagonal type derived from Hf2Co4P3 with one formula unit per cell and the lattice constants a=12.465 Å and c=3.940 Å. The Ln5Ru19P12 compounds were isotypic with Dy5Ru19P12, and their lattice constants are reported. Studies of magnetic properties have shown that compounds with a magnetic rare earth have a spontaneous magnetisation at low temperature and then follow a paramagnetic Curie-Weiss law.
The Electrocatalytic Reactions of Oxidation, Evolution and Adsorption of Hydrogen on Partially Sulphurized Platinum
e. lamy-pitara, l. lghouzouani, y. tainon and j. barbier, J. Electroanal. Chem. Interfacial Electrochem., 1989, 260, (1), 157–166
Studies of the effect of S adsorbed on Pt have shown that H2 oxidation is slightly inhibited, while the evolution of H2 is enhanced at small S coverages. At low S coverages and for negative overpotentials this observed synergetic effect is explained by a favourable electronic effect which appears to be stronger than the geometric inhibition effect. In the range of positive overpotentials, different H sites, more sensitive to the S inhibition effect, were probably involved. The strong inhibition effect due to high S coverages was observed in the same coverage range where polymeric S species are formed. Gibbs energy of adsorption showed that the natures of the two main kinds of adsorbed H were different.
Oxygen Reduction on Platinum in Borate-Buffered Saline Solutions
s. m. kaska, s. sarangapani and j. giner, J. Electrochem. Soc., 1989, 136, (1), 75–83
Studies of the effect of Cl− adsorption on a rotating Pt ring disc electrode on the kinetics of O2 reduction in alkaline solutions showed that the polarisation curves for O2 reduction on Pt in buffered 0.5M NaCl were shifted cathodically relative to those in buffered 0.5M NaClO4 of pH 8−10 due to Cl− ion adsorption. In alkaline solutions of pH 7−9, Cl− specific adsorption inhibited Pt-OH formation. During O2 reduction, Cl− adsorption resulted in an increase in H2O2 generation. Triangular sweep cyclic voltammetry showed Cl− adsorption on Pt at pH 8−12.
Pd-Catalysed Reaction of Allylic Acetates with Carbonyl Compounds via Electrochemical Reduction
w. qiu and z. wang, J. Chem. Soc., Chem. Commun., 1989, (6), 356–357
Electroreductive addition of allylic acetates to carbonyl compounds proceeded smoothly at room temperature on Pt electrode in the presence of Zn chloride and a catalytic amount of PdCl2(PPh3)2 to yield the corresponding homoallylic alcohols. This reaction provided a novel method for allylic acetates, as the allylic carbanion synthon equivalent, to react with carbonyl compounds to form C-C bonds.
High Resolution Deposition of Polyaniline on Pt with the Scanning Electrochemical Microscope
y. -m. wuu, f. -r. f. fan and a. j. bard, J. Electrochem. Soc., 1989, 136, (3), 885–886
A method for the high resolution deposition of polyaniline on a Pt substrate is based on the scanning electrochemical microscope (SECM) which gives a constant faradaic current between a tip electrode made of Pt or W, and Pt substrate electrode. The electrodes are separated by a thin layer of an ionically conductive polymer, which works as the electrolyte and contains cations that are free to move within the polymer matrix. The current is driven by application of a potential between the tip and the metal. The SECM can deposit polyaniline on a substrate by using Nafion films coated on a Pt surface.
New Solid Polymer Electrolyte Composites for Water Electrolysis
p. millet, m. pineri and r. durand, J. Appl. Electrochem., 1989, 19, (2), 162–166
A new procedure for the preparation of solid polymer electrolyte (SPE) electrocatalyst composites is reported, in which Pt and Ir cationic species are chemically reduced within the SPE. These electrocatalysts were used in SPE H2O electrolysis using Nafion membranes and showed good electrochemical properties, with low catalyst loadings, long-time stability and high energetic efficiencies. Microscopy techniques showed that the metallic particles were not homogeneously distributed across the SPE thickness but predominated near its surface.
Oxidation of CH3OH by Molybdenum-Modified Platinized Pt and Pt-SPE Electrodes
h. kita, h. nakajima, k. shimazu and j. wang, Shokubai, 1988, 30, (6), 448–451
Studies of CH3OH oxidation on Mo-modified platinised Pt and Pt bonded solid polymer electrolyte (SPE) membrane electrodes have shown an acceleration in CH3OH oxidation by 102 and 5×102 times at 25°C and 5×102 and 1.5×104 times at 82°C, respectively. Detailed analysis of voltammograms showed that the adsorbed redox couple, Mo(IV)/(III) catalyses CH3OH oxidation but Mo(VI) was inactive.
High Power Density Performance of WPt and WRh Electrodes in Alkali Metal Thermoelectric Converter
r. m. williams, b. jeffries-nakamura, m. l. underwood, b. l. wheeler, m. e. loveland, s. j. kikkert, j. l. lamb, t. cole, j. t. kummer and c. p. bankston, J. Electrochem. Soc., 1989, 136, (3), 893–894
Studies of high power density performance of WPt and WRh electrodes in the alkali metal thermoelectric converter (AMTEC) showed sustained power densities of ∼0.7W/cm2 through partial optimisation of WPt and WRh alloy electrodes. Electrode maximum power vs. time for the electrodes operated at 1150−1200K showed that the best electrodes of both kinds exhibit low porosity and thicknesses of >0.8μ m. The morphology of WPt and WRh electrodes after AMTEC cell operation showed quite small grain size of 0.1−0.4μ m which suggests that grain growth at elevated temperature is slow and that these electrodes will have long term stability.
In-Situ X-Ray Diffraction Study of Metal Hydride Formation in Palladium and Palladium-Based Alloy Electrodes under Cathodic Hydrogen Charging
k.-i. machida and m. enyo, Bull. Chem. Soc. Jpn., 1989, 62, (2), 415–418
An in situ X-ray diffraction technique has been developed and used to study the phase changes during metal hydride formation in Pd and Pd-Au alloy foil and amorphous Pd-Zr ribbon electrodes. The α- to β -PdHx phase transformation in the Pd electrode, accompanied by an increase in cell volume, was shown by formation of a β -phase domain in the bulk during cathodisation. A discontinuous change in lattice constant was observed for Pd and Pd90Au10 alloy. No phase transformation was observed for Pd-Au alloys with Pd content 70at.% and the lattice constant increased continuously with an increase in negative potential for cathodic polarisation.
Hydrogen Evolution on Iridium Oxide Cathodes
j. c. f. boodts and s. trasatti, J. Appl. Electrochem., 1989, 19, (2), 255–262
Studies of changes in surface conditions and H2 evolution from 1 mol/dm3 constant ionic strength perchlorate solutions at pH 0−1 on IrOx electrodes, prepared by thermal decomposition of IrCl3 at 300−500°C, are reported. A Tafel slope close to 40mV and a reaction order of 1.5 with respect to H+ are explained by a mechanism involving a step of reduction of active sites and a pH dependence of potential at the reaction plane which is typical of the acid-base properties of the oxide surface. Wetting-dewetting phenomena of the electrode surface, depending on the magnitude of the current, operate during H2 evolution. The oxide surface was never reduced down to metal, while no bulk reduction whatsoever took place. This work starts a series of systematic studies on the cathodic behaviour of oxides.
Preliminary Investigation on the Corrosion Behavior of Amorphous (Ti90Ru10)87Si13 in Saline Solutions
j. l. carbajal, r. e. white, r. b. griffin and j. n. dubrouillet, Electrochim. Acta, 1989, 34, (3), 317–320
Studies of the corrosion characteristics of a new (Ti90Ru10)87Si13 amorphous alloy in 0.5M NaCl and in artificial seawater (ASW) saturated with O2 were made by linear polarisation resistance, AC impedance and small amplitude cyclic voltammetry. Results show a low corrosion rate of the alloy in these media, with the rate of corrosion in seawater slightly faster than the rate of corrosion in NaCl.
Investigation of the Functions of CdS Surface Composite Layer and Pt on Treated Pt/CdS for Photocatalytic Dehydrogenation of Aqueous Alcohol Solutions
j. zhensheng, l. qinglin, f. liangbo, c. zhengshi, z. xinhua and x. chanjuan, J. Mol. Catal., 1989, 50, (3), 315–332
Studies of the activity of Pt/CdS in the photocatalytic dehydrogenation of aqueous alcohol have shown that initially photodeposited Pt exists as a sulphide, but after heat treatment is converted into Pt and PtO, which act as the catalyst for H+ reduction and OH + CH3CH2OH reaction, respectively. Surface Cd(OH)2 in the surface composite layer Cd(OH)2-CdO-CdS generated by the heat treatment reacted with H+ or OH− to give two kinds of surface active sites which were oxidised by a photon to give the OH radical. “Two-photon action” model is given.
Rate-Controlling Steps in a Three-Phase (Solid-Liquid-Gas) Photoreactor: A Phenomenological Approach Applied to Hydrogen Photoproduction Using Pt-TiO2 Aqueous Suspensions
j. s. escudero, r. simarro, s. cervera-march and j. giménez, Chem. Eng. Sci., 1989, 44, (3), 583–593
Water photolysis has been studied using a three-phase solid-liquid-gas photoreactor, continuous with respect to the gas phase, and with Pt-TiO2 powders as catalysts. These were kept suspended in H2O by means of gas bubbling through the liquid. In this case, the H2 production rate could be controlled by the luminic step and dark (chemical or mass-transfer) steps. The relative importance of each of these steps depended on the lamp-photoreactor system used, the nature and physical characteristics of the photocatalysts, and the operating (fluidodynamic) conditions. A description of the steps involved in this photocatalytic process is given. The importance of mass transfer in limiting the process yield is shown and this step has to be considered in the development of photocatalysts even at early stages.
Photoreactions of Organic Halides, Alcohols, and Olefins with Tetrakis(pyrophosphito)diplatinate(II)
c.-m. che, w.-m. lee, k.-c. cho, p. d. harvey and h. b. gray, J. Phys. Chem., 1989, 93, (8), 3095–3099
Studies of the photoreaction of [Pt2(P2O5H2)4]4− (Pt2) with organic halides (RX), alcohols (RR′CHOH) and olefins by steady-state photolysis, Stern-Volmer quenching and transient-absorption showed that the 3A2u, excited state of Pt2 (3Pt2★) readily cleaves both C-X (X = Cl, Br, I) and C-H bonds. With RX the second-order rate constant (kq) values increased with decreasing C-X bond strength and the primary step of the photoreactions of Pt2 was halogen atom transfer. Broad-band irradiation of alcohols in the presence of Pt2 yielded an aldehyde or ketone and H2. The reported kq values for aliphatic and benzylic alcohols are 104 – 106/Ms and are highest for benzyl alcohol.
Characterization of Pd-β -Cyclodextrin Colloids as Catalysts in the Photosensitized Reduction of Bicarbonate to Formate
i. willner and d. mandler, J. Am. Chem. Soc., 1989, 111, (4), 1330–1336
The kinetic characterisation of the catalytic activity of Pd-β -cyclodextrin colloids in the photosensitised reduction of HCO3− to HCO2− using N,N′-dimethyl-4,4′-bipyridinium (methyl viologen, MV2+) as primary electron acceptor, MV+ radical as electron carrier, deazariboflavin as photosensitiser, and oxalate as sacrificial electron donor, is reported. The reaction proceeded with quantum efficiency, φ = 1.1. Active sites for HCO3− activation and reduction were detected and were specifically inhibited by thiols. Catalytic sites for H2 evolution were also identified. The catalyst for reduction of HCO3− to HCO2− and reverse oxidation of HCO2− mimiced enzymic activities, with high specificity and effectiveness.
Photoenhanced Homogeneous Catalytic Hydrogenation of Olefins Following XeCl Excimer Laser Excitation of RhH(CO)(PPh3)3
h. moriyama, a. yabe and f. matsui, J. Mol. Catal., 1989, 50, (2), 195–202
Irradiation of RhH(CO)(PPh3)3 by XeCl excimer laser (308nm) accelerated the homogeneous hydrogenation of olefins under mild conditions. Significantly enhanced dark reactions were observed after periods of laser irradiation. The laser produced a highly active catalyst species, producing product at high turnover. The apparent quantum yield has been estimated at greater than unity (2.4) under appropriate conditions (pulse cycle 1Hz and catalyst concentration of 10−3M). XeCl excimer laser-induced acceleration of homogeneous hydrogenation was also observed for RhCl(PPh3)3 and IrCl(CO)(PPh3)2. Lasers allow the use of strong, monochromatic and coherent light pulses in the field of homogeneous catalysis to activate molecules via their excited states.
Hydrogen Photoevolution from Water-Methanol on Ru/TiO2
a. sobczynski, t. jakubowska and s. zielinski, Monatsh. Chem., 1989, 120, (2), 101–109
In situ photodeposition of Ru on anatase TiO2 from RuCl3 solution was found to efficiently produce Ru/TiO2 powders highly active in H2 photoevolution from H2O-CH3OH. The most active sample was 0.75 wt.% Ru/TiO2. Electron microprobe analysis and SEM showed that Ru distribution was inhomogeneous on porous TiO2. The size of Ru islets influenced the stability of the Ru/TiO2 catalyst. Enhanced efficiency was obtained when TiO2 was subjected to cation exchange prior to illumination in H2O-CH3OH.
ELECTRODEPOSITION AND SURFACE COATINGS
Structure and 900°C Hot Corrosion Behavior of Chromium-Modified Platinum Aluminide Coatings
r. e. malush, p. deb and d. h. boone, Surf. Coat. Technol., 1988, 36, (1–2), 13–26
Of ten coating types on Ni-base superalloy substrate IN738 tested in accelerated hot corrosion environments at 900°C for 200h, Pt-Al (produced by an intermediate temperature, intermediate activity process) and Cr-Pt-Al (two step Cr + Pt + Al process) showed excellent high temperature hot corrosion (HTHC) resistance. The average measured depth of attack rate was ∼0.025μ m/h, slower than previously reported low temperature (700°C) data. In general the addition of Pt to an aluminide coating improved its HTHC resistance when the PtAl2 was present as a high density layer (18μ m thick in Cr-Pt-Al) near the outer zone of the coating, together with a deep reservoir of Pt (distribution of PtAl2 phase in β -NiAl matrix) beneath the surface.
APPARATUS AND TECHNIQUE
Ion Selectivity of a Polypyrrole Coated Pt Electrode for Hydronium Ion
j. -d. kim, k. -s. lee and k. -j. kim, Bull. Korean Chem. Soc., 1989, 10, (1), 119
The first use of a polypyrrole (PPy) electrochemically modified Pt electrode as a potentiometric sensor for hydronium ion (H3O+) is reported. Potentiometric responses to H3O+ were nearly Nernstian with slopes of 59.9 and 58.7mV for PPy modified-Pt and typical glass electrodes, respectively, over pH 2 to 12. The slopes remained fairly constant with an increase in ionic strength from 0.01 to 0.30M. The PPy coated Pt electrode was almost comparable with a typical glass electrode in potentiometric response and had better selectivity coefficients for the other cations studied, Li+, K+ and Na+. Response times and stability of the electrode are also reported.
Fabrication and Testing of Subminiature Multi-Sensor Hot-Wire Probes
p. m. ligrani, r. v. westphal and f. r. lemos, J. Phys. E, 1989, 22, (4), 262–268
Subminiature single-sensor and crossed hot-wire probes have been fabricated using an improved method which allows accurate control of sensor orientation and etched (active) sensor length. The sensor incorporates a Wollaston-type wire with core material of 90%Pt-10%Rh of diameter 0.625μ m. The outer jacket is Ag. The new procedure eliminates the final Cu plating step employed to achieve desired active length. The subminiature probes gave more accurate measurements in boundary layers than conventional sized probes.
Membrane Reactor Using Microporous Glass-Supported Thin Film of Palladium. Application to the Water Gas Shift Reaction
e. kikuchi, s. uemiya, n. sato, h. inoue, h. ando and t. matsuda, Chem. Lett. Jpn., 1989, (3), 489–492
A composite membrane consisting of a Pd thin film and a microporous-glass tube has been applied to a membrane reactor. In the water-gas shift reaction, the membrane reactor attained high conversion levels of CO, exceeding the equilibrium level for the closed system as a result of the separation of H2 produced. The rate of H2 permeation was evaluated to be almost of the same order as the rate of reaction by considering initial reaction rate of 1 × 10−2 mol g-catalyst−1 min−1, with the effective area for H2 separation of 25.1cm2.
In Situ Concentration of Metallic Hydrides in a Graphite Furnace Coated with Palladium
l. zhang, z.-m. ni and x.-q. shan, Spectrochim. Acta, 1989, 44B, (3), 339–346
A method has been developed for, and satisfactorily applied to, the ultrasensitive determination of As, Sb and Se in urine and various H2O samples at ng/ml levels, by hydride generation with subsequent trapping and atomisation in the Pd-coated graphite furnace. Surface Pd (0.25−1.0μ g) acted as an efficient adsorber for the metallic hydrides. Sensitivities, accuracies and precisions were significantly improved compared with the uncoated tube, and the sorption temperatures of the metal hydrides were lower.
Electret and Rhodium Gas Sensors
c. f. klein and p. e. thoma, Sens. Actuators, 1989, 16, (4), 325–334
The organic gas-sensing characteristics of an electret and a Rh probe are presented and discussed. A dome-shaped, circular, 500 μ inch-Rh-plated probe sensed changes in organic gas concentration due to electron donor/acceptor interactions between adsorbed gas and the surface of the probe. The Rh probe distinguished between strong and weak electron donor gases by the polarity of the response signal.
Periodic Operation Effects in Propane and Propylene Oxidation over Noble Metal Catalysts
h. shinjoh, h. muraki and y. fujitani, Appl. Catal., 1989, 49, (2), 195–204
The oxidation of propylene and propane over Pt, Pd and Rh catalysts supported on α -Al2O3 was studied under static and periodic conditions. Catalytic activities decreased in the order Pd>Pt>Rh for propylene oxidation and Pt>Rh>Pd for propane oxidation. The conversion of hydrocarbon (HC) was improved by the cycling feed in comparison to a static feed. This periodic operation effect was dependent on both catalyst species and temperature. The optimum period for the maximum conversion decreased with increasing temperature. The periodic operation effect arises from the difference in adsorption capability between HC and O2 on the catalyst surface. The order of the periodic operation effect corresponds to the order of the catalyst sensitivity to self-poisoning by HC and O2.
Evidence for Multiple CO Hydrogenation Pathway on Pt/Al2O3
j. l. robbins and e. marucchi-soos, J. Phys. Chem., 1989, 93, (8), 2885–2888
Studies of the reactivity of CO toward H2 over 12%Pt/Al2O3 were performed by temperature programmed reduction of adsorbed CO (CO TPR) and i.r. spectroscopy. The CO TPR spectra showed two CH4 formation rate maxima at 490 and 613K and their relative intensities depended on the CO adsorption temperature and the extent of surface hydroxylation. The i.r. spectra showed that CO chemisorbed molecularly on Pt at 300K, but some bound CO was converted to Al2O3-bound methoxy species as the sample was heated to 400K in H2. The support played a part in defining both CO TPR behaviour and steady-state CO hydrogenation rates over Pt.
Influence of pH on the Preparation of Monometallic Rhodium and Platinum, and Bimetallic Rhodium-Platinum Catalysts Supported on γ -Alumina
j. h. a. martens and r. prins, Appl. Catal., 1989, 46, (1), 31–44
Raman and 195Pt NMR studies have shown that H2PtCl6 adsorbs monomolecularly on the surface of γ -Al2O3 up to a loading of 1 μ mol/m2 during pore volume impregnation. Adsorption studies showed that RhCl3 behaves the same, with an even larger monomolecular coverage. The coverages decreased with decreasing pH due to a shift in bonding equilibrium between the metal complexes in solution and the complexes adsorbed on the surface of the support. The amount of co-adsorbed Pt and Rh was smaller than their amounts when separately adsorbed, due to the acidic nature of H2PtCl6 and RhCl3. The reduction of RhCl3 + H2PtCl6 was governed by mobile Rh atoms and small bimetallic clusters.
Effect of Steam on the Coking of Platinum Catalysts. I. Inhibiting Effect of Steam at Low Partial Pressure for the Dehydrogenation of Cyclopentane and the Coking Reaction. II. Kinetics
d. duprez, m. hadj-aissa and j. barbier, Appl. Catal., 1989, 49, (1), 67–74; 75–82
The effect of steam on the coking of Pt/Al2O3 has been studied at 400°C under 1 atm pressure in the presence of cyclopentane in dry or wet (0.67kPa of H2O) N2. Steam decreased the coking rate, owing to inhibition of the dehydrogenation of cyclopentane to cyclopentadiene, the main coke precursor. Temperature programmed oxidation showed a peak ascribed to C deposited on metal and 2 peaks for 2 different forms of coke deposited on the support. Kinetic studies at temperature of 400−520°C, partial pressures of cyclopentane from 12–80kPa and H2O from 0–35kPa showed that the inhibiting effect of steam on coking depends on the partial pressure. At low partial pressure (Pw<2.5kPa) H2O decreased the rate of dehydrogenation of cyclopentane whereas when Pw>2.5kPa polymerisation was inhibited.
Location and Structure of Coke Deposits on Alumina-Supported Platinum Catalysts by EELS Associated with Electron Microscopy
p. gallezot, c. leclercq, j. barbier and p. marecot, J. Catal., 1989, 116, (1), 164–170
The location and structure of carbonaceous deposits formed during coking Pt/Al2O3 catalysts with cyclopentane were studied by TEM and by electron energy loss spectroscopy (EELS). The results showed patches of amorphous coke covering the support surrounding each metal particle and that the coke coverage could extend up to 20nm from a given particle. The local structure of coke was not graphitic or pregraphitic but could consist of a disordered arrangement of polyaromatic molecules. After partial combustion at 563K, the coke on the metal particles was removed but still present on the support.
Thioresistance of Supported Metal Catalysts. Hydrogenolysis of Cyclopentane on Pt/Al2O3 and Ir/Al2O3
p. marecot, l. tifouti, m. guenin and j. barbier, Bull. Soc. Chim. Fr., 1988, (5), 817–820
Different series of Pt/Al2O3 and Ir/Al2O3 catalysts have been characterised by their activities in hydrogenolysis of cyclopentane and by their S resistances. At 300°C, Pt/Al2O3 with large metallic particles was more active for cyclopentane hydrogenolysis. On Ir/Al2O3 at 170°C, activity was independent of structure, while at 240°C smaller Ir particles showed higher activity. Deactivation of Pt/Al2O3 by thiophene is explained by selective adsorption of S on the hydrogenolysis sites. However, this explanation is insufficient for Ir/Al2O3 at 240°C, where it is thought that the large electron affinity of S induces a partial oxidation of Ir.
Automotive Exhaust Gas Catalysts: Surface Structure and Activity
b. engler, e. koberstein and p. schubert, Appl. Catal., 1989, 48, (1), 71–92
The effect of CeO2 promotion with a standard set of three-way automotive emission control catalysts with and without Pt or Rh, and with γ -Al2O3 to CeO2wt.% ratios of 100:0, 70:30, 30:70 and 0:100, has been studied by surface analytical methods, and performance and activity measurements. Although providing valuable qualitative results, the surface analytical methods available do not allow a surface characterisation sufficient to be related to elementary catalytic steps. Catalyst surfaces were found to be extremely variable.
Platinum Dispersion and Valence State of Chromium in the Pt+Re+Cr/γ -Al2O3 Catalysts during Dehydrocyclisation of n-Heptane
e. a. skrigan, g. m. sen’kov, l. a. kupcha, m. f. gorgatsevich and n. s. kozlov, Vest. Akad. Navuk BSSR, Ser. Khim. Navuk, 1989, (1), 9–14
The dispersion of Pt metal and changes in the valence states of Cr in Pt+Re+Cr/γ -Al2O3 were studied and correlation between these factors and their activity, selectivity and stability in dehydrocyclisation of n-heptane was explained. A dependence on the preparation method and Cr content was established.
The Role of Tellurium and Antimony in PtTe/Al2O3 and PtSb/Al2O3 Reforming Catalysts
c. h. cheng, k. m. dooley and g. l. price, J. Catal., 1989, 116, (2), 325–337
Bimetallic PtTe/Al2O3 and PtSb/Al2O3 catalysts have been studied using the model n-hexane isomerisation, aromatisation and hydrocracking reactions at 673K, and cyclohexane dehydrogenation at 573K, under 1 atm pressure in a recirculation batch reactor. These co-impregnated catalysts showed increased isomerisation selectivity and reduced hydrocracking selectivity, compared to Pt/Al2O3. An electronic effect caused by electron donation from Te to Pt increased the specific activities of isomerisation and dehydrogenation for low Te:Pt ratio of <0.06.
Effect of CO Addition on Propene-Deuterium Exchange Reaction and Mechanism of Hydroformylation over Supported Pd, Rh and Ru Catalysts
s. naito and m. tanimoto, Shokubai, 1988, 30, (6), 488–491
Microwave spectroscopy has been used to study the effect of CO addition on propene-D exchange over SiO2-supported Pd, Rh and Ru. Hydroformylation of propene proceeded simultaneously to form butyraldehyde and butylalcohol, via similar σ-alkyl intermediates in the exchange process. The addition of Na+ caused considerable changes in activity and selectivity of the catalysts.
Influence of Intercrystalline Mass Transfer on Catalytic Properties of Pt.H-ZSM-5.Al2O3 Catalyst
v. r. choudhary and d. b. akolekar, J. Catal., 1989, 116, (1), 130–143
Effect of intercrystalline (macropore) mass transfer on the catalytic activity and product selectivity in oxylene isomerisation, isooctane cracking and methanol-to-aromatics conversion reactions on Pt.H-ZSM-5.Al2O3 was studied by using different sizes of catalytic particles. The effective intercrystalline diffusivity of the zeolite catalyst was studied by using a first-order reaction cracking of isooctane. The results showed that both the activity and the selectivity of the catalyst in the studied reactions are strongly affected by the intercrystalline mass transfer.
Hydroisomerization of Branched-Chain Olefins over Pt/H-ZSM-5 Zeolite
t. behrsing, h. jaeger and t. mole, Appl. Catal., 1989, 47, (1), 67–73
The first example of shape-selective hydroisomerisation has been observed in the hydrogenation of branched-chain olefins to alkanes over Pt on the proton form of ZSM-5 zeolite. The results are temperature dependent. At 150°C alkanes of unrearranged skeleton were mainly formed, and at >300°C cracked products were formed. At intermediate temperatures there was extensive formation of alkanes with straightened chains.
Effect of Pd and Pt Additives on the Activity of Ni-Cr Catalysts in Reaction of CO with H2
v. l. kuznetsov, s. p. noskova, i. l. kuznetsova and yu. i. yermakov, React. Kinet. Catal. Lett., 1989, 38, (2), 411–416
Introduction of small amounts of Pt or Pd, such as 0.1wt.%, into unreduced Ni-Cr catalysts decreased the temperature of their reduction with H2, and enhanced their methanation activity and stability to carbonisation. These results are interpreted in terms of spillover of extra H from Pt or Pd which participates in the hydrogenation of active C species on the Ni surface.
Polymerization and Decarbonylation Reactions of Aldehydes on the Pd(III) Surface
j. l. davis and m. a. barteau, J. Am. Chem. Soc., 1989, 111, (5), 1782–1792
The adsorption and reaction of formaldehyde, acetaldehyde and propanal have been compared by temperature programmed desorption and spectroscopy studies on clean Pd(111). The presence of alkyl substituents had a dramatic effect on aldehyde reaction. Formaldehyde either decomposed to adsorbed CO and H or underwent polymerisation to paraformaldehyde upon adsorption at 170K. Adsorbed η 2-acetaldehyde and η 2-propanal underwent decarbonylation to give CO, H2 and a hydrocarbon with one C atom less than the parent aldehyde.
Nitric Oxide Reduction Performance of Automotive Palladium Catalysts
h. muraki, k. yokota and y. fujitani, Appl. Catal., 1989, 48, (1), 93–105
Studies have shown that NO reduction by Pd/α -Al2O3 catalysts is significantly inhibited by hydrocarbons (HC), due to a self-poisoning effect. However, NO reduction activity was improved by both a periodic operation effect and the addition of La2O3 to the Pd catalyst. The mechanism of the periodic operation effect was interpreted in terms of the strong adsorption of HC. The addition of La2O3 substantially moderated this HC poisoning. Reduction of NO by Pd/La2O3 with a cycled feed stream was similar to that on a Rh catalyst.
Isomerisation of m-Xylene on Palladium-Containing Superhigh-Silicon Zeolites
l. p. shirinskaya and v. s. komarov, Dokl. Akad. Nauk BSSR, 1989, 33, (3), 230–232
Effect of Pd on activity of decationation of superhigh-Si zeolites TSVM and TSVK with ratios SiO2:Al2O3=31.9:62.3, during isomerisation of mxylene was studied with respect to methods of Pd introduction into the zeolites and conditions of preliminary activation of the catalysts. The results showed that depending on the electronic state of Pd and its position on the surface or inside of the zeolite structure, catalysts with different activity and selectivity can be obtained.
Formation of Aromatic Hydrocarbons in CO Hydrogenation over Silica Gel-Supported Palladium
g. v. filonenko, yu. i. pyatnitskii, t. m. shaprinskaya, v. p. stasevich, v. i. gritsenko, g. i. girushtin and v. l. struzhko, React. Kinet. Catal. Lett., 1989, 38, (1), 39–44
It has been shown that several aromatic hydrocarbons are formed in CO hydrogenation over SiO2-gel supported Pd catalysts. A mechanism for the formation of reaction products is proposed. The enhancing effects of Cl− ions and small Al2O3 additions on CH3OH formation are also noted.
Hydrogenation of Carbon Monoxide, Aldehydes, and Unsaturated Hydrocarbons on Titania-Supported Palladium Catalysts
j. wu, m. funakoshi, h. nagamoto, h. komiyama and h. inoue, Bull. Chem. Soc. Jpn., 1989, 62, (2), 493–498
The catalytic properties of Pd/TiO2 catalysts prepared by different methods have been studied in the hydrogenation of CO and other unsaturated compounds. Catalysts prepared by coprecipitation contained smaller Pd particles than those in catalysts prepared by impregnation. Catalyst activities increased with increasing Pd dispersion for CO hydrogenation. Coprecipitated catalysts were more active and showed higher activity for CH3OH formation.
Comparison of Microstructures in Oxidation and Reduction: Rh and Ir Particles on SiO2 and Al2O3
j. burkhardt and l. d. schmidt, J. Catal., 1989, 116, (1), 240–251
Studies of microstructure and fractions of metal and oxide formed in oxidation and subsequent reduction of 100 Å particles of Rh and Ir on SiO2 and Al2O3 supports were performed by X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) and their results were compared. XPS studies showed that both metals were oxidised at ∼200°C higher temperatures on SiO2 than on Al2O3, and reduction in H2 occurred at a slightly lower temperature on Al2O3. Rh oxidised at 300−400°C on Al2O3 and at 400−500°C on SiO2. Ir oxidised at 500−600°C on Al2O3 and at 600−700°C on SiO2.
Influence of the Support on the Catalytic Properties of Bimetallic Ru-Cu Samples
c. crisafulli, r. maggiore, g. schembari, s. sciré and s. galvagno, J. Mol. Catal., 1989, 50, (1), 67–80
Propane hydrogenolysis has been studied on a series of Ru-Cu catalysts supported on SiO2, Al2O3 and MgO. On SiO2 the activity of Ru decreased continuously on addition of Cu. On Al2O3 and MgO, Cu addition caused an initial decrease in activity reaching a minimum at intermediate Ru:Cu ratios, then increased with higher Cu content. For each support, less active samples were the most selective toward ethane formation. The lower activity and higher selectivity observed was due to a Ru-Cu interaction.
Synthesis of Highly Calorific Gaseous Fuel from Syngas on Cobalt-Manganese-Ruthenium Composite Catalysts
t. inui, a. sakamoto, t. takeguchi and y. ishigaki, Ind. Eng. Chem. Res., 1989, 28, (4), 427–431
The composite catalyst system of Co-Mn-Ru supported on Al2O3 calcined at 1060°C has been used to synthesise a highly calorific gaseous fuel from syngas, and has been studied by a continuous flow reactor under pressure of 10kg/cm2. A CH4-rich gas containing significant concentrations of C2-C4 paraffins and comparable to natural gas with added C2-C4 paraffins, was obtained. Pilot plant tests using a fluidised bed showed the satisfactory conversion of coke oven gas into a highly calorific gas for >3000h.
Selective Hydrogenation of Methyl Oleate to Oleyl Alcohol on Mixed Ruthenium-Tin Boride Catalysts
c. s. narasimhan, v. m. deshpande and k. ramnarayan, Appl. Catal., 1989, 48, (1), L1–L6
Selective hydrogenation of the saturated fatty acid ester, methyl oleate, to oleyl alcohol, which is used extensively to make surfactants, has been achieved using Ru-Sn-B/Al2O3 catalysts. Maximum yield of oleyl alcohol (60.4%) and maximum selectivity to oleyl alcohol (74.7%) was obtained using a catalyst with Ru:Sn atomic ratio of 1:2.
Intramolecular, Stoichiometric (Li, Mg, Zn) and Catalytic (Ni, Pd, Pt) Metallo-Ene Reactions in Organic Synthesis
w. oppolzer, Angew. Chem., Int. Ed. Engl., 1989, 28, (1), 38–52
The potential of Pt-, Pd- and Ni-catalysed versions of the metallo-ene reaction is discussed with respect to new methods of organic synthesis. An almost 100% stereospecific C-O → C-Pd → C-C chirality transfer permits simple and selective cis- or trans-annelation processes. The mild cyclisation conditions are compatible with various functional groups, such as N moieties and offer routes to heterocycles such as alkaloids, difficult to prepare by other methods. CO insertion reactions of the cyclised σ -metal intermediates gave concomitant stereocontrolled formation of 4 C-C bonds. Applications and potential of this powerful method in organic synthesis are discussed.
Hydrogen Production from Ethanol Catalysed by Group 8 Metal Complexes
d. morton, d. j. cole-hamilton, i. d. utuk, m. paneque-sosa and m. lopez-poveda, J. Chem. Soc., Dalton Trans., 1989, (3), 489–495
Studies of various platinum group metal catalysts for H2 production from EtOH in the presence of added base have shown that where the metal has low affinity for CO, in [PtH(PEt3)3]+ for example, simple dehydrogenation to give ethanal and aldol condensation products takes place. Metals with high CO affinity bring about CO abstraction and can poison the reaction, but in the absence of base and irradiated with visible light produced H2, CH4 and CO. Water-gas shift type chemistry was observed in reactions catalysed by [Rh(bpy)2]Cl, so that EtOH was converted to 2H2, CH4 and CO2. For [Rh(bpy)2]Cl and [RuH2(N2)(PPh3)3], H2 production rates of >100 catalyst turnovers per hour were readily sustained over long periods.
Platinum Complex Catalyzed Carbonylation of Organic Iodides: Effective Carbonylation of Organic Iodides Having β -Hydrogens on Saturated sp3 Carbons
r. takeuchi, y. tsuji, m. fujita, t. kondo and y. watanabe, J. Org. Chem., 1989, 54, (8), 1831–1836
Studies of the Pt-catalysed carbonylation of organic iodides using PtCl2(PPh3)2 and Pt(CO)2(PPh3)2 catalysts showed that this novel system gives effective carbonylation of organic iodides with β -H on saturated sp3 C, as well as the carbonylation of alkenyl and alkynyl iodides. The carbonylation under CO pressure in the presence of alcohol gave esters, and aldehydes were obtained by the reaction under CO and H2 pressure. Heptanal was formed in 86% yield from 1-iodohexane at 120°C under CO and H2, and 1-iodohexane was carbonylated to methyl heptanoate in 79% yield in the presence of methanol at 120°C under 70kg/cm2 of the initial CO pressure.
Kinetics of Ethylene Oxidation to β -Halogenoethylalkyl Esters and Acetaldehyde Dialkylacetals in Methanol and Ethanol Solutions of Pd(II) and Cu(II) Complexes
a. b. pshenichnikova, s. m. brailovskii and o. n. temkin, Kinet. Katal., 1989, 30, (1), 92–97
Effect of Pd halide, HCl and C2H4 pressure on the rate of the formation of β -halogenoethylalkyl esters and acetaldehyde dialkylacetals was studied in three catalytic systems: PdCl2-CuCl2-LiCl-LiClO4-methanol, PdCl2-CuCl2-LiCl-ethanol and PdBr2-CuBr2-LiBr-methanol. The results showed that in the studied catalytic systems equation of formation rates of the products is of first order with respect to Pd(II) halide and HCl concentrations, and C2H4 pressure, with high rate constants in ethanol.
Effect of Temperature on the Rate and Selectivity of Styrene Hydrocarboxylation Catalysed by Pd(II) Complexes
yu. g. noskov, m. i. terekhova and e. s. petrov, Kinet. Katal., 1989, 30, (1), 234–239
Studies of the temperature dependence of the rate of hydrocarboxylation of styrene in the presence of PdCl2(PPh3)2 showed that effective activation energy (E) for the formation of the isomers of phenyl propionic acid differs by 80kJ. Excess of PPh3 did not affect the value E and in the presence of SnCl2 the difference decreased. The results showed that the reaction proceeds by two routes yielding various types of Pd-containing intermediates.
Palladium-Catalyzed Vinylation of Alkyl Vinyl Ethers with Enol Triflates. A Convenient Synthesis of 2-Alkoxy 1,3-Dienes
c.-m. andersson and a. hallberg, J. Org. Chem., 1989, 54, (7), 1502–1505
Reaction of cyclic or acyclic enol triflates with alkyl vinyl ethers in the presence of Pd(PPh3)4 or Pd(OAc)2 catalysts yielded 2-alkoxy 1,3-dienes as the major products. The regioselectivity for α -substitution was higher than 90% and the products could be isolated in synthetically useful yields.
Some Problems of the Mechanism of Catalyst Formation by Carbalkoxylation of Acetylene in the System PdBr2-P(OPh)3-n-BuOH
n. g. mekhryakova, a. n. nyrkova, n. f. alekseeva, g. m. shulyakovskii and o. n. temkin, Kinet. Katal., 1989, 30, (1), 98–105
Studies of the catalyst formation by carbalkoxylation of acetylene in the system PdBr2-P(OPh)3-n-BuOH showed the catalytically active complex cis-Pd[P(OPh)n(OBu)3−n]2Br2 with ligands which re-esterify to 30−60%, needing 0.95 M of H2O in contact solution for this formation. In the systems containing 0.1M H2O, a non-catalytically active complex was formed in the analogue systems, which had trans-configuration and re-esterified to 70−95%.
Role of the Reactions of the First and Second Orders with Respect to Pd(II) in Oxidation of Thiophene by Pd(II) Salts in Aqueous Solutions. III. Oxidation by Aquachloride Complexes at High Concentrations of Pd(II) and Cl−
v. m. ignatenko and e. s. rudakov, Kinet Katal., 1989, 30, (1), 44–49
Studies of the kinetics of oxidation of thiophene (TH) with Pd(II) complexes of high Pd content (>0.05M), 0.3-1M of Cl− and 0.05-0.2M of H+ at concentration of TH<<Pd(II) were performed under conditions which in previous studies were of second order with respect to Pd(II) during oxidation of ethylene, propylene and butene-1. A mechanism was determined involving formation of π -thiophene Pd(II) complex and its conversion to thienyl Pd compounds with subsequent splitting of thienol and three kinetically indistinguishable routes yielding binuclear (TH)Pd2Cl5(OH)2−, (TH)Pd2Cl5− and mononuclear (TH)PdCl3−−π -thiophene Pd(II) complexes. In the last stage, the second Pd(II) takes part in decomposition of thienyl Pd(II).
Palladium Catalyzed Coupling of Organostannanes with Vinyl Epoxides
d. r. tueting, a. m. echavarren and j. k. stille, Tetrahedron, 1989, 45, (4), 979–992
Studies of the coupling reaction of organo-Sn reagents with vinyl epoxides, catalysed by various Pd catalysts showed that it takes place at ambient temperatures, regioselectively, giving predominantly the 1,4-addition product. Both aryl- and vinylstannanes underwent coupling in high yields while acetylenic, allylic and benzylic Sn reagents either gave low yields or failed to couple. In coupling reactions with cyclic 1,3-diene monoepoxides, the reaction was stereospecific.
Studies of Catalytic Activity of Metal Complexes Fixed on Solid Substrate. Part 6. Reduction of Nitrobenzene and Its Halogen Derivatives by Chemically Bonded Hydrogen in the Presence of Immobilised Rhodium Complex
v. z. sharf, v. f. dovganyuk, v. i. isaeva and b. i. maksimov, Izv. Akad. Nauk SSSR, Ser. Khim., 1989, (3), 534–539
Catalytic properties of Rh complexes [RhCl(COD)]2 (where COD is cyclooctadiene), RhCl(PPh3)3 and RhCl3, which were immobilised on SiO2 modified by amino- and aminophosphine groups, prepared by precipitation at room temperature, were studied during reduction of nitrobenzene and various halogen derivatives. The rate of reduction of nitrobenzene by NaBH4 increased by one to two orders than the rate of reduction by propanol-2. The addition of halogen to benzene rings leads to a decrease of reduction rates of nitro-groups. Reduction of halogenated nitrobenzene by NaBH4 proceeded via the reduction of NO2-groups followed by the splitting of the halogen.
The First Catalytic Hydrogenation of Natural Oils at Ambient Condition by an Intercalated Ruthenium Complex in Montmorillonite
m. m. taqui khan, s. a. samad and m. r. h. siddiqui, J. Mol. Catal., 1989, 50, (1), 97–102
The dihydrido Ru(IV) species [H2RuCl2(AsPh3)2] obtained by the hydrogenation of RuCl3(AsPh3)2·CH3OH intercalated in the interlamellars of montmorillonite clay, catalysed the hydrogenation of long chain jojoba oil and castor oil at room temperature and 1 atm H2. The catalytic species could be regenerated over many hydrogenation cycles without loss of efficiency.
Catalytic Synthesis of Vinyl Carbamates from Carbon Dioxide and Alkynes with Ruthenium Complexes
r. mahé, y. sasaki, c. bruneau and p. h. dixneuf, J. Org. Chem., 1989, 54, (7), 1518–1523
Studies of the terminal alkynes reaction with CO2 and secondary amines in the presence of Ru complex catalysts showed yields of vinyl carbamates in one step. Mononuclear Ru complexes such as RuCl2(PR3)(arene) and RuCl2(norbornadiene) (pyridine)2 for monosubstituted alkynes at 100−125°C and [RuCl2(norbornadiene)]n or even RuCl3.3H2O for acetylene at 90°C were found to be the best catalyst precursors.
Selective Oxidation of Alkanes and Ethers Mediated by Ruthenium(II) Complexes
m. bressan and a. morvillo, J. Chem. Soc., Chem. Commun., 1989, (7), 421–423
Selective hydroxylation or ketonisation of cyclic alkanes and conversion of ethers to esters and of secondary alcohols to ketones, with significant rates were achieved by using hypochlorite as oxidant and a number of Ru(II) complexes as catalysts, in a biphasic H2O-dichloromethane system. The presence of soft atom-donors (S and P) in the coordination sphere of Ru(II) appears to increase the catalytic ability of the metal in the oxidation of activated and unactivated C-H bonds.
Performance Evaluation of Platinum Catalysed Hydrogen Gas Diffusion Electrodes for Alkaline Fuel Cells
r. pattabiraman, r. chandrasekaran, s. muzhumathi, i. arulraj and s. dheenadayalan, Bull. Electrochem., 1988, 4, (9), 807–811
The promoting effect of Pt when incorporated in the matrix of porous H2 gas diffusion electrodes which employ skeletal Ni as catalyst, has been studied with Pt content from 0.5 to 2.0mg/cm2. At a potential of −800mV vs. Hg/HgO, current densities increased from 30−35mA/cm2 to more than 50mA/cm2 for Pt-promoted electrodes.
Efficient Oxygen Reduction in Alkaline Solution with Platinum Phthalocyanine on Porous Carbon
a. k. shukla, c. paliteiro, r. manoharan, a. hamnett and j. b. goodenough, J. Appl. Electrochem., 1989, 19, (1), 105–107
Studies of O2 reduction on a porous C electrode prepared from pretreated coconut-shell charcoal and coated with various amounts of Pt phthalocyanine (PtPc) were performed in alkaline solutions. Electrodes coated with 5 wt.% PtPc sustained load currents up to 2A/cm2 at an overvoltage of 300 mV from its rest potential in 6M KOH at 35°C. They were also more active than thermally treated and untreated FePc, CoPc, NiPc and MnPc. The results showed that PtPc has the catalytic activity and stability suitable for its use as an O2-reducing catalyst with porous C electrode in alkaline fuel cells.
Phase-Transfer Catalysts in Extraction Kinetics: Palladium Extraction by Dioctyl Sulfide and KELEX 100
s. j. al-bazi and h. freiser, Inorg. Chem., 1989, 28, (3), 417–420
Studies of the role of the quaternary ammonium salts (C7H15)4N+Cl− and (C10H21)(CH3)3N+Cl− in accelerating Pd extraction from acidic Cl− solutions by dioctylsulphide in chloroform and also by 7-(1-vinyl-3,3,5,5-tetramethylhexyl)-8-quinolinol (KELEX 100) in chloroform, respectively, have shown them to be phase-transfer catalysts. Kinetic studies of the rate of Pd extraction as functions of the quaternary ammonium salt (Q+Cl−), extractant, aqueous Cl− concentrations and pH showed that the active metal complex was transformed from aqueous phase to bulk organic phase as an ion pair, Q+PdCl3−, where it reacted with the extractant.
ELECTRICAL AND ELECTRONIC ENGINEERING
X-Ray Photoelectron Spectroscopy of Pt/GaAs Interfacial Reactions
h. iwakuro and t. kuroda, Jpn. J. Appl. Phys., 1989, 28, (2), 223–228
Studies of Pt/GaAs interfacial reactions have shown that even at room temperature the reaction occurred to form a Pt-rich Pt-Ga compound and unreacted As. The top surface of the deposited Pt film was covered with As. Annealing at 200°C formed PtAs2 and the same Pt-Ga compound that was found in the as-deposited state. The top surface was covered with Ga because As and its oxides sublimated during annealing. Annealing at 450°C produced islands of Ga-rich Pt-Ga compound, surrounded by a ternary compound in the surface. This method which uses X-ray photoelectron spectroscopy combined with Ar+ sputtering is useful for in-depth monitoring of the binding energy for each element.
Annealing Effect of Magneto-Optical Kerr Rotation for PtMnSb Compound
k. takanashi, h. fujimori, j. watanabe, m. shoji and a. nagai, Jpn. J. Appl. Phys., 1988, 27, (12), L2351–L2353
The polar magneto-optical Kerr rotation angle (θ k) has been obtained in the 400−1000nm wavelength range for bulk PtMnSb, one of the Clb-type Heusler compounds. The values of θ k were strongly enhanced by annealing at temperatures >400°C, compared to as-polished PtMnSb, although the change in the spectrum of reflectance was very small.
Planar Ge/Pd and Alloyed Au-Ge-Ni Ohmic Contacts to n-AlxGa1−xAs (0 x 0.3)
e. d. marshall, l. s. yu, s. s. lau, t. f. kuech and k. l. kavanagh, Appl. Phys. Lett., 1989, 54, (8), 721–723
The functional dependence of the specific contact resistivity ϱ c of the planar Ge/Pd ohmic contacts to n-type AlxGa1−xAs on anneal temperature Tann was found to be the same for all AlAs mol fractions x, and decreased to a minimum at 275−325°C. Ohmic contact formation mechanism was independent of x (0x0.3). Compared with standard Au-Ge-Ni contacts, Ge/Pd showed a greater dependence of ϱ c on x and a much smoother morphology. An undoped 200 Å GaAs cap layer reduced ϱ c of Ge/Pd/AlxGa1−xAs (x=0.2 or 0.3) by ∼1 order of magnitude.
Tantalum Nitride as a Diffusion Barrier between Pd2Si or CoSi2 and Aluminum
m. a. farooq, s. p. murarka, c. c. chang and f. a. baiocchi, J. Appl. Phys., 1989, 65, (8), 3017–3022
Reactively sputtered Ta2N was studied as a diffusion barrier between Pd2Si and Al and CoSi2 and Al. Ta2N was found to give excellent metallurgical stability to Pd2Si and CoSi2 samples up to 555°C, when used as a diffusion barrier to Al penetration. Schottky barrier devices n-Si/Pd2Si/Ta2N/Al were excellent and showed no deterioration after annealing at 500°C for 60 min.
New Insights into the Mechanism of the cis-Platin-Guanosine 5′-Monophosphate Reaction
n. goswami, l. l. bennett-slavin and r. n. bose, J. Chem. Soc., Chem. Commun., 1989, (7), 432–433
Studies have shown that the reactions of cis-diamminedichloro-Pt(II) and cis-dichloroethylenediamine-Pt(II) with guanosine 5′-monophosphate (GMP) proceed through the formation of a N-7 bound mono(GMP) complex which further reacts with the initial Pt substrate and another GMP molecule to form a GMP-bridged di-Pt(II,II) species and bis(GMP) complex. The active drug is the Pt substrate and its monoaquated species.
In Vitro Antitumor Activity of Platinum Pyrimidine Greens Obtained by One-Pot Synthesis on L1210 Cells
h. okuno, t. shimura, t. uemura, h. nakanishi and t. tomohiro, Inorg. Chim. Acta, 1989, 157, (2), 161–163
A series of cis-diammine Pt green compounds with uridine, uracil, 5-fluorouracil, uridine 5′-monophosphate and thymidine have been prepared by a convenient one-pot synthesis, and their biological activity against mouse leukaemic L1210 cells in vitro, studied. All the Pt greens showed remarkable growth inhibitory activities against L1210 cells, the lower molecular weight Pt greens showing the higher inhibitory activity. Higher inhibitory activity values were also obtained when the ratio of pyrimidine substrate to Pt in the molecule was relatively low, and these complexes are promising chemotherapeutic agents.
Synthesis and X-Ray Crystal Structure Determination of 1,3-Bridged β -Lactams: Novel, Anti-Bredt β -Lactams
r. m. williams, b. h. lee, m. m. miller and o. p. anderson, J. Am. Chem. Soc., 1989, 111, (3), 1073–1081
A Rh(II)-catalysed carbene insertion of diazo keto esters into the N-H bond of β -lactams was shown to be the key cyclisation reaction in the synthesis of several 1,3-bridged β -lactams from alkyl acetoacetate in 11–14 steps. These are the first successful syntheses of 1,3-bridged β -lactams which may have importance as antibiotics. This new class of structurally unique bicyclic β -lactams has been characterised by X-ray crystallography.
Brain Affinity of Ruthenocene Compounds: Quinuclidinol-Ester
m. wenzel and d. preiss, J. Labelled Compd. Radiopharm., 1989, 27, (4), 369–376
The labelled ruthenocenoyl-ester has been prepared by heating 103RuCl3 with the ester of ferrocene carboxyl acid and quinuclidinol. The organ distribution of this ester and of 103Ru-labelled ruthenocenyl-N-(isopropyl)-ethyl-amine was studied in mice and rats and compared with the organ distribution of iodolabelled n-(isopropyl)-amphetamine. A high brain affinity was found and the ruthenocenyl-quinuclidinolester showed a remarkable heart to blood ratio.
Mixed-Ligand Complexes of Ruthenium(II): Factors Governing Binding to DNA
a. m. pyle, j. p. rehmann, r. meshoyrer, c. v. kumar, n. j. turro and j. k. barton, J. Am. Chem. Soc., 1989, 111, (8), 3051–3058
Binding and spectroscopic parameters for a series of mixed ligand Ru(II) complexes on binding to DNA have been determined. The complexes examined, except Ru(bpy)32+, all appeared to intercalate and surface-bind to DNA, and those binding appreciably showed enantioselectivity.