Platinum Metals Rev., 1991, 35, (2), 101
ABSTRACTS: April 1991
of current literature on the platinum metals and their alloys
Growth and Characterization of Reactively Sputtered Thin-Film Platinum Oxides
j. r. mcbride, g. w. graham, c. r. peters and w. h. weber, J. Appl. Phys., 1991, 69, (3), 1596–1604
Thin-film oxides of Pt prepared by reactive sputtering were studied by XRD and Raman scattering. Different phases of the Pt-O system were obtained by adjusting sputtering parameters, such as gas composition, deposition rate and substrate temperature. The Raman spectra from PtO show two broad peaks at 438 and 657 cm-1 and high resolution SEM and XRD line broadening indicates mean crystallite sizes of the order of 300Å. IR reflectivity spectra yield two of the three IR-active phonons, and along with scanning tunneling microscopy measurements suggest that PtO is a semiconductor. Thermoelectric measurements show that the predominant carriers are p -type, and IR reflectivity data indicate a carrier concentration of ∼4×1018/cm3.
The Equilibrium Shape and Surface Energy Anisotropy of Clean Platinum
w. h. lee, k. r. vanloon, v. petrova, j. b. woodhouse, c. m. loxton and r. i. masel, J. Catal., 1990, 126, (2), 658–671
The equilibrium shape of clean Pt was measured by following changes in shape of micrometre-sized Pt droplets during annealing at 1200°C and 10-7 Torr in O2. The Pt particles had a rounded shape with distinct (100) and (111) facets and stepped regions in between. At 1200°C only 16% of their surfaces is covered by the facets; the majority of the surface is stepped. The surface energy of Pt only varies by about 92 erg/cm2 with crystal face: Pt(100) has the lowest surface energy, Pt(111) has a slightly higher surface energy.
Oxidation of Clean and Pt-Covered Ni(111)
s. deckers, f. h. p. m. habraken, w. f. van der weg and j. w. geus, Appl. Surf. Sci., 1991, 45, 207–220
Clean and Pt-covered Ni(111) surfaces have been exposed to O2 at various temperatures. On clean Ni a closed oxide layer is formed at room temperature, and at 250 and 400°C, O2 penetrates into the bulk of the crystal. However, small amounts of Pt drastically decrease the extent of oxidation of Ni crystals at all temperatures. At room temperature, no oxidation occurs when the Pt coverage is > 1 monolayer. At 250°C, a Ni oxide layer forms on top of the Pt overlayer, but no O penetrates through the Pt layer into the bulk. At 400°C, a Ni oxide layer forms on top of the Pt and a small fraction of the O diffuses through the Pt layer into the bulk crystal.
Magnetic Phase Diagram of Ordered Fe(PdxPt1-x)3
m. kaburagi, t. tonegawa and k. ebina, J. Magn. Magn. Mater., 1990, 90&91, 161–162
Magnetic properties of the pseudobinary ordered alloy Fe(PdxPt1-x)3 are calculated on the basis of the localised moment model by noting the local environment effect on the Fe atom. The alloy exhibits a wide range of magnetic structures depending on Pd concentration. At high temperatures the phase is paramagnetic. At low temperatures there are three magnetically ordered phases depending upon x: an antiferromagnetic phase for 0≤x<x1 ∼0.53, intermediate magnetic phase for x1x<x2 ∼0.67 and ferromagnetic phase for x2<x≤l. The Néel temperature of 170 K is almost independent of x in the region of the antiferromagnetic phase. The Curie temperature of 530 K at x = 1, decreases monotonically with decreasing x until it reaches a quadruple point separating the above four phases.
Magnetic Properties of Co/Pd Multilayers Determined by Brillouin Light Scattering and SQUID Magnetometry
j. v. harzer, b. hillebrands, r. l. stamps, g. gÜntherodt, c. d. england and c. m. falco, J. Appl. Phys., 1991, 69, (4), 2448-2454
The saturation magnetisation and volume and interface anisotropics of Co/Pd multilayers with modulation wavelengths between 4 and 220 Å, prepared by magnetically enhanced DC-triode sputtering on single-crystal sapphire substrates, were studied by using Brillouin light scattering from collective spin waves and by SQUID magnetometry. A Pd polarisation was found and the polarisation depth was estimated. Samples with Co thickness of 2 atomic layers and Pd thickness of ≥ 5 atomic layers exhibited a perpendicular magnetisation.
Structural and Electrical Properties of Granular Palladium Cluster Films
a. carl, g. dumpich and e. f. wasserman, Thin SolidFilms, 1990, 193/194, (1–2), 1065–1072
Thin granular PdxC1-x films 10–70 nm thick were prepared by simultaneous co-deposition of pure Pd and high purity C on NaCl and quartz crystal substrates at room temperature under UHV. Different evaporation rates for Pd and C enable PdxC1-x films of metal volume fractions x = 0.1–1 to be made. TEM indicated networks of small Pd clusters embedded in amorphous C. Electrical resistance studies showed metallic resistance behaviour for films with 0.3<x<l and variable range hopping conductivity for x<0.3. The metal insulator transition is at x = 0.3.
Crystal Nucleation and Glass Formation in Undercooled Pd-Ni-P Melts
y. xu and w. wang, Mater. Sci. Eng., 1990, A130, (1), 93–100
Pd40Ni40P20 and Pd43.5Ni43.5P13 alloys were prepared and their undercooling was investigated in a 1.2 m drop tube filled with different inert gases at different pressures. As the cooling rates were reduced the crystal nucleation and growth processes were revealed, and the interior heterogeneous nucleation was found to be responsible for the solidification of the under-cooled melts. Time-temperature transformation curves allow predictions of the glass forming behaviour.
Magnetic Phase Diagram of Ge-Substituted CeRu2Si2 in an Applied Field
j.-m. mignot, p. boutrouille, l.-p. regnault, p. haen and p. lejay, Solid State Commun., 1991, 77, (5), 317–321
Long-range magnetic order can be induced in the heavy-fermion compound CeRu2Si2 by slighly expanding its lattice by substituting a few percent of Ge for Si. For a concentration of 10%, the material ordered in the same collinear, incommensurate, modulated structure as that already reported for (Ce, La) Ru2 Si2. The (H, T) phase diagram of this system was determined by elastic neutron scattering. The results were discussed in connection with the problem of magnetic correlations in pure CeRu2Si2.
Co-ordination of 3,3′-Bipyridazine with Bivalent Copper, Palladium and Platinum
h. a. goodwin, d. onggo, b. w. skelton and a. h. white, Aust. J. Chem., 1990, 43, (11), 1919–1928
Bis(ligand) complexes of the diimine 3,3′-bipyridazine (L) with bivalent Pt, Pd and Cu are described. Co-ordination of perchlorate in [PdL2][ClO4]2, was indicated but not in [PtL4][ClO4]2. Structure determination of the Pt complex showed a strictly planar PtN4 moiety, and the whole complex cation was approximately planar. The structure of [PtL2][ClO4]2 was determined at 295 K by single-crystal X-ray diffraction methods, and was refined to a residual of 0.033 for 1942 “observed” independent reflections.
The Preparation of Novel Ruthenium Complexes for Use in Langmuir-Blodgett Films
s. g. davies, a. j. smallridge, r. colbrook, t. richardson and g. g. roberts, J. Organomet. Chem., 1991, 401, (1–2), 181–186
A range of cationic cyclopentadienyl bisphosphine Ru nitrile complexes [(η 5-C5H5)L2RuNC-Aryl]+, where L = phosphine or phosphite, have been prepared and characterised for use with deposition for Langmuir-Blodgett films. The ready substitution of the phosphine ligands bound to Ru allows the complexes to be tailored for a wide range of properties.
The Stability of Hydrous Oxide Films on Platinum
l. d. burke and j. f. o’sullivan, J. Appl. Electrochem., 1991, 21, (2), 151–157
The stability of hydrous oxide films grown on Pt in both acid and base was studied as a function of holding potential in solutions of different pH. The stability of the bulk of the hydrous oxide deposits on Pt was not very dependent on solution pH, due to a rather facile rearrangement of the initially anionic Pt oxide species to a virtually neutral state. Reduction of the bulk hydrous oxide in base showed a marked degree of inhibition in the region of 0 V(RHE); the effect appeared to be related to the presence of weakly bound H2 on the Pt surface.
Effects of Adsorbed CO on the Electrode Reactions at a Platinum Electrode
h. kita, s. ye and k. sugimura, J. Electroanal. Chem. Interfacial Electrochem., 1991, 297, (1), 283–296
Studies of the behaviour and poisoning effects of the CO adsorbed at 50 and 500 mV (vs. RHE) on Pt performed in 1M HClO4 at room temperature showed that the CO adsorbed on a Pt electrode stays immobile and does not migrate onto a bare surface. The adsorbed CO has a physical poisoning effect on the H evolution reaction. At a high CO coverage, the lack of a nearest pair of CO-free reaction sites causes a change in the reaction mechanism of H evolution.
Early Stages of Growth of Hydrous Platinum Oxide Films
m. farebrother, m. goledzinowski, g. thomas and v. i. birss, J. Electroanal. Chem. Interfacial Electrochem., 1991, 297, (2), 469–488
The growth of thin hydrous Pt oxide (β -oxide) films by the rapid potential cycling method was studied. β -Oxide formation began in only a few cycles of potential to an extent which was dependent on the sweep rate used during oxide growth. Its properties vary greatly after ca. 20–30 cycles of potential, and then become constant. The compact α-oxide, present along with the β -oxide at all times, could be reduced and reformed in potential sweep studies, as well as thickened under potentiostatic conditions in the presence of the β -oxide, as at a bare Pt surface.
Study of the Characteristics of Electrochemical Cell Pt|CaF2|Pt in an Atmosphere of the Free Oxygen
i. a. zaks and m. v. glumov, Elektrokhimiya, 1990, 26, (11), 1473–1479
A study of the polarisation of a porous Pt electrode in contact with CaF2 in partial oxygen pressure 10–104,3 Pa was performed in a Pt|CaF2|Pt electrochemical cell, in the solid electrolyte, at 1100–1200 K. The resistance of the electrolyte is directly proportional, and the polarisation of the electrolyte is reversibly proportional to the O2 pressure.
The Structure and Activity of Pt-Co Alloys as Oxygen Reduction Electro-catalysts
b. c. beard and p. n. ross, J. Electrochem. Soc., 1990, 137, (11), 3368–3374
Bimetallic C supported Pt-Co (3:1 atom ratio) catalysts were prepared from a commercial 10% Pt/C catalyst with Pt particle sizes of 15–30Å, in both acid and alkaline aqueous media, followed by heat treatments to promote alloy formation. Greater alloying was observed in the catalyst prepared in the acid medium. X-ray diffraction studies of the acid-prepared catalyst showed lattice parameters tending away from Pt (3.927Å) and toward that for Pt3Co (3.83lÅ), greatly increased particle sizes and significant ordering demonstrated by the presence of super-lattice reflections. Loss of Co in a fuel cell phosphoric acid environment was the lowest in catalysts which were the most alloyed, and where the Pt3Co ordered phase was present.
Electrolytically Co-deposited Platinum-Palladium Electrodes and Their Electro-catalytic Activity for Ethylene Glycol Oxidation: A Synergistic Effect
n dalbay and f. kadirgan, Electrochim. Acta, 1991, 36, (2), 353–356
The electrocatalytic oxidation of ethylene glycol has been investigated on Pt-Pd solid solution alloy electrodes of different compositions in alkaline aqueous solution. Cyclic voltammetry was used to find the surface characteristics and X-ray diffraction studies were used to verify homogeneity of electrolytically co-deposited alloys.
Electrocatalytic Hydrogenation Using Precious Metal Microparticles in Redox-Active Polymer Films
l. coche, b. ehui, d. limosin and j.-c. moutet, J.Org. Chem., 1990, 55, (23), 5905–5910
Glassy C felt electrodes were modified by electrodeposition of poly(pyrrole-viologen) films followed by electroprecipitation of Pt, Pd, Rh or Ru micro-particles. The electrodes were active for the electrocatalytic hydrogenation of conjugated enones, styrene and benzonitrile in aqueous media of pH = 1. Although the metal loadings were low, the electric and product yields were high, and the cathodes had long term stability.
A Complex Formation of Palladium with Tin(II) in a Solution of Sulphuric Acid
p. g. antonov, i. a. agapov and m.n. maksimov, Zh. Obshch. Khim., 1990, 60, (11), 2421–2425
The interaction of K2PdCl4 with SnSO4 in H2SO4 resulted in the formation of bimetallic Pd(II) complexes, which convert into compounds according to the degree of oxidation of Pd, near to one. Chloride ions in Sn chloride Pd complexes totally mix with sulphate ions in the H2SO4 solution without breaking the Pd-Sn bond. This effect is used for the preparation of new Pd-Sn complexes.
The Properties of Palladium Electrodes for Electrooxidation of Ethylene Glycol
n. dalbay and f. kadİrgan, J. Electroanal. Chem. Interfacial Electrochem., 1990, 296, (2), 559–569
Mechanistic studies were performed in alkaline medium, in order to interpret the electrocatalytic properties of Pd for the oxidation of ethylene glycol. The kinetic parameters, estimated from electrochemical data, suggest a one electron step to be rate determining and the rate of the reaction depends directly on the pH.
Cathodic Behaviour of Palladium in Electrolyte Solutions Containing Alkali Metal Ions
v. e. kazarinov, i. i. astakhov, g. l. teplitskaya, i. g. kiseleva, a. d. davydov, n. v. nekrasova, d. yu. kudryavtsev and t. b. zhukova, Eletrokhimiya, 1991, 27, (1), 9–14
Studies of the cathodic implantation of Li and also to a lesser degree of K, in Pd electrodes were performed during cathodic polarisation in aqueous or aprotonic electrolytes. In aprotonic electrolyte the formation of Li with Pd intermetals occurred during implantation; these can actively react with H2O and solid Pd based solutions. In aqueous electrolyte, on a Pd electrode of 0.5 mm thickness after 74 h polarisation, formation of solid electrolyte occurred with average concentration of 5%, while the electrode was gradually dissolving during the polarisation.
Boundary Conditions in Electrochemical Measurements of Diffusion Coefficients of Hydrogen in α-Palladium
h. hagi, Mater. Trans. JIM, 1990, 31, (10), 842–847
Studies of the boundary conditions in electrochemical H permeation through α-Pd showed that the variations in electrode potential and current density at the cathode surface corresponded to those in the dissolved H concentration and H entry flux at the cathode surface, respectively. The diffusion coefficients of H at 278–333 K and the temperature dependence of the diffusion of H free from the trapping effect and the surface effect in annealed α -Pd were given.
Electrochemical Behaviour of RuTi
r. manoharan and j. b. goodenough, Electrochim. Acta, 1991, 36, (1), 19–26
The electrochemical properties of RuTi alloy in acidic solution were investigated by cyclic voltammetry and steady-state polarisation measurements. The I-V profiles for the formation/reduction of surface oxides and the deposition/dissolution of H at a RuTi electrode are similar to those at a Ru electrode. The O evolution and Ru corrosion reactions occur at nearly the same potential on Ru, but on RuTi the reactions are well resolved. RuTi does not catalyse MeOH oxidation; it forms a hydride on cycling negative of the normal H potential. Although hydride appears to suppress the H evolution reaction, H evolution activity remains relatively high. A model has been developed with two-step oxidation of the surface.
Effect of Composition on the Electro-catalytic Activity of the Ternary Oxide Ru0 3Ti(0 7-x)SnxO2. I. Oxygen Evolution from HCIO4 Solutions
i. f. c. boodts and s. trasatti, J. Electrochem. Soc, 1990, 137, (12), 3784–3789
The electrocatalytic activity of ternary oxides of general formula Ru0.3 Ti(0.7 –x)SnxO2 for O2 evolution from 1 mol/dm3 HClO4 solution was studied as a function of x by current-potential curves and reaction order determination. The mechanism of O2 evolution was found not to depend on oxide composition, whereas the electrocatalytic activity was observed to increase with the increase in SnO2 content. The surface charge drops dramatically after extensive O2 evolution thus indicating collapse of the surface morphology. The present results show that SnO2 activates RuO2 +TiO2 electrodes, decreasing their stability.
Photochemical Reactivity of Diplatinumμ -Alkenylidene Complexes: Evidence of Atom-Transfer Chemistry
e. baralt and c. m. lukehart, Inorg. Chem., 1991, 30, (2), 319–320
Complex [Pt2(μ -C = CHPh)(C = CPh)(PEt3)4 ] BF4 (1) reacts under photolysis with Li halide or KSCN salts, I2 and alkyl or aryl halides to give mono- or dihalide (or SCN) complexes of types [Pt2(μ - C = CHPh)(C = CPh)(Pet3)3X] or [Pt2,(μ - C = CHPh)(PEt3)3X2]. 2-Propanol is also catalytically oxidised to acetone and H2 by (1) or selected derivatives upon irradiation. Thus (1) represents another type of system that exhibits photochemical atom-transfer reactivity.
Hydrogen Evolution at a Pt-Modified InP Photoelectrode: Improvement of Current-Voltage Characteristics by HCl Etching
h. kobayashi, f. mizuno, y. nakato and h. tsubomura, J. Phys. Chem., 1991, 95, (2), 819–824
H photoevolution at p -InP electrodes coated with Pt and Pd was studied before and after etching with concentrated HCl. Before etching electrodes with a continuous Pt layer have poor I-V behaviour, due to defect states in InP, and the photocurrent density decreases with illumination, due to increased defect density. After etching, stable efficient solar-to-chemical energy conversion was achieved. The barrier height increased to 1.0 V and the I-V characteristics improved remarkably with no degradation on illumination. The HCl dissolved the InP substrate in the InP/Pt interracial region, simultaneously removing part of the Pt from the InP surface. A structural model of the etched electrode is proposed with the InP surface in direct contact with the solution due to minute Pt island formation. The cell characteristics of Pd deposited electrodes are poor and become worse on H2 bubbling.
Supramolecular Photochemistry and Photophysics. Mutual Inhibition of Host and Guest Photochemistry and Luminescence in the Adduct of an Anthraceno-Crown Ether with Pt(bpy)(NH3)22+
l. prodi, r. ballardini, m. t. gandolfi, v. balzani, j. p. desvergne and g. bouas-laurent, J. Phys. Chem., 1991, 95, (5), 2080–2083
Pt(bpy)(NH3)22+ forms a 1:1 adduct with the anthraceno-crown ether (1). The adduct formation causes strong changes in the absorption spectra, luminescence behaviour and photoreactivity. It is suggested that the adduct shows a sandwich-type conformation in which the Pt complex is inserted between the two aromatic moieties of (1). Such a structure allows the stabilisation of the adduct via both H bonds and π-π interactions and accounts for the mutual protection of the two components toward their luminescence and photoreactivity.
Investigation of the Relation between the Photogenerated Intermediate Radicals and the Photocorrosion of CdS in Aqueous and Aqueous Ethanol Dispersions of Pt/CdS
l. feng, h. wang, z. jin, q. li and m. shi, J. Photochem. Photobiol. A: Chem., 1991, 56, (1), 89–100
The spin-trapping technique showed that OH and CH3CHOH radicals can be generated in the visible-light-illuminated dispersions of H2O/Pt/CdS/POBN (or PBN) and C2H5OH-H3O/Pt/CdS/POBN (or PBN), where POBN = α -(4-pyridyl-N -oxide) N -tert-butyl nitrone and PBN = α -phenyl N-tert-butyl nitrone. OH radicals attack the surface of air-treated Pt/CdS to create photocorrosion, which destroys the surface composite layer, but this can be suppressed by addition of C2H5OH.
Stepwise Reduction of Coordinated Dinitrogen to Ammonia Via Diazinido and Hydrazido Intermediates on a Visible Light Irradiated Pt/CdS.Ag2S/RuO2 Particulate System Suspended in an Aqueous Solution of K[Ru(EDTA-H)Cl]2H20
m. m. taqui khan and n. nageswara rao, J. Photochem. Photobiol. A: Chem., 1991, 56, (1), 101–111
The photocatalytic fixation of co-ordinated N2 to NH3 in aqueous solution at 30°C and 1 atm N2 is reported in the presence of modified semiconductor particulate system Pt/CdS.Ag2S/RuO2 catalysed by K[Ru(EDTA-H)Cl]2H,0. Doping of CdS with Ag2S enhances the rate of NH3 production at 505 nm. The quantum yields of the product were obtained at 5 monochromatic absorption lines between 450 and 550 nm. Illuminating the system with light of wavelength 505–525 nm gives the highest quantum yield of 0.35. A mechanism for NH3 formation is proposed and the source of the N atom in NH3 is N2.
Photospillover of Hydrogen in the Semiconductor-Palladium Membrane System
a. yu. graifer, a. p. koshcheev and i. a. myasnikov, Kinet. Katal., 1990, 31, (6), 1493–1501
Studies of H2 photospillover in the dispersed ZnO/Pd membrane semiconductor system prepared by the deposition of ZnO onto a thin Pd membrane were performed during the photocatalytic decomposition of H2O, and also, directly during the reaction by thermodesorption mass-spectrometric method. The results showed the effect of spillover (mass-transfer) of H atoms with the surface of Pd membrane after stimulated UV light exposure of the semiconductor. The H atoms were either adsorbed from gaseous phase or formed during heterogeneous photo-gaseous decomposition of H2O molecules.
Changes in the Redox State of Iridium Oxide Clusters and Their Relation to Catalytic Water Oxidation. Radiolytic and Electrochemical Studies
g. s. nahor, p. hapiot, p. neta and a. harriman, J. Phys. Chem., 1991, 95, (2), 616–621
Radiolytically prepared IrOx.n H2O clusters for the photochemical oxidation of H2O were oxidised and changes in optical absorptions and redox states were studied. The clusters contain 4 or 5 Ir atoms in IrIII and IrIV states, formerly described as Ir3.2+. Pulse radiolytic studies revealed 3 processes in the subse-cond time scale: a short-lived intermediate such as an OH adduct, transforming to more stable oxidised species, and a rise in the 580nm absorption. The initial IrOx cluster is oxidised in 2 stages from Ir3.2+ to Ir3.8+ and then to Ir4+. Further cluster oxidation oxidises H2O to O2. The Ir4+ clusters decay to regenerate IrOx clusters of lower oxidation state.
Luminescent and Redox-Reactive Building Blocks for the Design of Photochemical Molecular Devices: Mono-, Di-, Tri-, and Tetranuclear Ruthenium(II) Polypyridine Complexes
g. denti, s. campagna, l. sabatino, s. serroni, m. ciano and v. balzani, Inorg. Chem., 1990, 29, (23), 4750–4758
Mono-, di-, tri-, and tetrametallic complexes of general formulae RuL2(BL)2+, L2Ru(μ -BL)RuL24+, LRu[μ -BL)RuL2]26+ and Ru[μ -BL)RuL3]38+ (L = bpy or biq, BL = 2,3- or 2,5-dpp) showed very intense absorption bands in the UV and visible regions, relatively long lived luminescence both in a rigid matrix at 77 K and in fluid solution at room temperature and a very rich electrochemical behaviour. The electrochemical, spectroscopic and photophysical properties of this family can be tuned by a suitable choice of L, BL and number of metal ions. These complexes are good candidates for light absorption and/or light emission sensitisers, for luminescent probes and photochemical cleavers of DNA.
The First Report of the Isolation and Characterisation of an Intermediate Formed upon Photolysis of a Ruthenium(II) Diimine Compound, in which One of the Chelating Ligands is Bound in a Monodentate Fashion
b. e. buchanan, h. hughes, j. h. van diemen, r, hage, j. g. haasnoot, j. reedijk and j. g. vos, J. Chem. Soc, Chem. Commun., 1991, (5), 300–301
The isolation and characterisation of an intermediate produced upon photolysis of [Ru(bipy)2(L-L′)I(PF6)2 in MeCN (where bipy = 2,2′-bipyridyl and L-L′ = 4-methyl-3-(pyridin-2-yl)-l,2,4-triazole) in which L-L′ is co-ordinated to the metal centre in a monodentate fashion, via the N of the triazole ring, is reported. It is shown that the photochemically induced ligand dissociation can be reversed thermally. A mechanism for the photoinduced ligand exchange in these compounds in which monodentate intermediates are formed upon photolysis of Ru polypyridyl compounds, and thermal ring closure regenerates the starting compound, is confirmed.
ELECTRODEPOSITION AND SURFACE COATINGS
Electroless Deposition of Pure Nickel, Palladium and Platinum
p. steinmetz, s. alperine, a. friant-costantini and p. josso, Surf. Coat. Technol., 1990, 43/44, (1–3), 500–510
A new process for the electroless deposition of Pt, Pd and Ni was designed using hydrazine as the reducing agent. Electrochemical measurements for a wide range of bath compositions were performed and several were examined which gave high purity deposits of these metals. Bath composition and conditions leading to adherent and defect-free ductile coatings with purity higher than 99.9% were found. Long term stability of the baths was achieved as well as bath replenishment. For the Pd and Ni the level of contaminants was very small with no significant effect on the hardness of the coatings. Coatings of Pt, Pd and Ni were dense and regular.
Problems in DSA® Coating Deposition by Thermal Decomposition
c. comninellis and g. p. vercesi, J. Appl. Electrochem., 1991, 21, (2), 136–142
Several dimensionally stable anodes, made up of an electrochemically active coating deposited on a base metal, were prepared by thermal decomposition of Ir, Ta, Sn, Ru and Pt chloride salts on Ti base. The initial coating composition does not necessarily correspond to the final coating. IrO2, RuO2 and Ta2O5, compounds can be deposited with almost 100% yield, while SnO2 and Pt precursors give high material losses. The thermal deposition technique is sensitive to the geometry of the sample, the solvent that is used, and also the concentration and nature of the metal salts.
Hydrogen Codeposition in Palladium Plating
s. jayakrishnan and s. r. natarajan, Met. Finish., 1991, 89, (1), 23–25
Hydrogen codeposition from ammonia complexed Pd plating solutions and the determination of the H:Pd ratio in the deposited metal were studied. The quantity of codeposited H retained by electrodeposited Pd depends on the time lapsed after deposition. The stress and crack-free nature of electroplated Pd can be attributed to the Pd being in the thermodynamically stable alpha phase.
Electrodeposition of Ni-Transition Alloys for the Oxygen Evolution Reaction
h. j. miao and d. l. piron, J. Appl. Electrochem., 1991, 21, (1), 55–59
Electrodes for the O evolution reaction (OER) were prepared by electrodeposition of Ni, Ni-Ru and Ni-Ir alloys in an attempt to find new electrocatalytic material for long-lasting, economic high performance electrodes. The electrodes were activated by anodic polarisation at 100 mA/cm2 to form an oxide layer. Ni-Ir alloys had better corrosion resistance and provide greater electrocatalytic activity for the OER than Ni-Ru alloys in alkaline solution.
APPARATUS AND TECHNIQUE
A New Hydrogen Sensor Based on a Pt/GaAs Schottky Diode
l. m. lechuga, a. calle, d. golmayo, p. tejedor and f. briones, J. Electrochem. Soc, 1991, 138, (1), 159–162
H sensors based on a Pt/GaAs Schottky barrier have been fabricated with stable, sensitive and reproducible characteristics. Dark I-V and C-V measurements as a function of temperature have been used to characterise the devices. At 150°C a minimum of 6 ppm of H2 in N2, and 200 ppm of H2 in synthetic air can be detected. In air, a linear response is found up to 3000 ppm H2. The sensitivity to H2 is explained by Schottky barrier reduction. The sensor can operate over a wide temperature range and is sensitive even at room temperature. The diodes recover easily in air at 190°C and show long-term stability.
Low-Level Moisture Generation
f. mermoud, m. d. brandt and j. mcandrew, Anal. Chem., 1991, 63, (3), 198–202
Two complementary methods for generating moisture concentrations in the 0.02–50 ppm-v range in various gaseous media have been developed. The first method uses catalytic recombination of H2 and O2: over a hot Pt/Rh catalyst using air as the balance gas, while the second is based on permeation of water through a membrane, using any gas compatible with the membrane material. This moisture generation system can be used to calibrate hygrometers and moisture generators, and study the behaviour of components used in high purity gas installations.
Conductance Response of Pd/SnO2 (110) Model Gas Sensors to H2 and O2
t. b. fryberger and s. semancik, Sens. Actuators B, 1990, 2, (4), 305–309
Surface analytical and in situ conductance measurements showed that the H response of Pd/SnO2 model sensors at moderate temperatures (400 K) was dominated by surface reactions. In the absence of O2, H2 increases the sensor conductance via chemisorption and dissociation on the Pd clusters followed by “spill-over” to the SnO2, substrate. When O2 was available, the conductance was modulated by the reaction between chemisorbed H2 and O2, to form volatile H2O. The chemisorption and dissociation of O2 occurred on the Pd clusters.
Effects of Thickness and Additives on Thin-Film SnO2 Gas Sensors
j. klӦber, m. ludwig and h. a. schneider, Sens. Actuators B, 1991, 3, (1), 69–74
The effect of reducing gases on the electrical conductivity or gas sensitivity of thin-film Sn oxide sensors was studied as a function of the Sn oxide film thickness and the Pd concentration. The dependence on the film thickness showed a maximum at ∼ 30–45 nm for H detection. It also depended on the Pd concentration. For CO a decrease of the sensitivity with increasing Pd thickness was observed at > 30 nm.
Electrocatalysis and Flow Detection of Alcohols at Ruthenium Dioxide-Modified Electrodes
d. leech, j. wang and m. r. smyth, Electroanalysis, 1991, 3, (1), 37–42
A highly stable sensitive flow detection system for simple alcohols with a constant potential operation is described; it uses RuO2 containing C paste electrodes. The optimisation of the system for Ru loading, pH, flow rate and operating potential is reported. The electrode response was stable over 2 weeks with a signal loss of 6%; repeated MeOH injections over a 2 h period gave a relative standard deviation of 3.4%. Detection limits for the alcohols depend on the number and position of the hydroxyl groups, with 30 ng for glycerol to 3 μ g for EtOH.
Perfluorinated Membranes as Catalyst Supports
a. m. hodges, m. linton, a. w.-h. mau, k. j. cavell, j. a. hey and a. j. seen, Appl. Organomet. Chem., 1990, 4, (5), 465–473
Perfluorinated polymer Nafion and porous PTFE/Nafion composite membranes have been employed as supports for Pt and Pd metal particles and Ni complexes to be used as olefin conversion catalysts. For cyclohexene hydrogenation, the Pt and Pd supported systems had turnover numbers in excess of 6000, with no apparent poisoning, and could be easily regenerated.
Stoichiometric Composition of Platinum, Iridium and Platinum-Iridium Catalytic Precursors
s. subramanian and j. a. schwarz, Appl. Catal., 1991, 68, (1–2), 131–147
The stoichiometry of A12O3), TiO2 11.4%TiO2-Al2O3 and 0.87% Al2O3-TiO2 supports for Pt, Ir and Pt-Ir precursors were assessed by temperature-programmed reduction and thermogravimetry. The H consumed and the observed weight change result from precursor reduction and support reduction. PtCl4, IrCl3) and PtCl4-IrCl3 exist as supported entities after the catalysts, prepared from H2PtCl6 and H2IrCl6, are dried at 423 K in air. The metal-support interactions for a given metal are stronger for A12O3 than for TiO2. Bimetal formation in the Pt-Ir system does not occur during drying.
Competition between Ethyne, Ethene and Carbon Monoxide for the Active Sites during Hydrogenation at Transient Conditions over Supported Metal Catalysts
l. cider and n.-h. schÖÖn, Appl. Catal., 1991, 68, (1–2), 191–205
The effect of CO on the hydrogenation of ethene over Pt/Al2O3, Pd/α-Al2O3 and Rh/Al2O3 was temporarily eliminated after a short pulse of ethyne, propadiene or butadiene. The very slow thermal desorption of CO increased, an effect which is similar to the “cross-desorption” and “adsorption-assisted desorption”. The same phenomenon occurred for the reverse process; increased desorption of ethyne after a pulse of CO.
The Aromatisation of re-Heptane on Pt-Sn/Al2O3 and Pt-Ir/Al2O3 Catalysts
m. wilde, r. feldhaus, k. anders and h.-d. neubauer, Z. Phys. Chem. (Leipzig), 1990, 271, (5), 919–925
The aromatisation of n -heptane and methylcyclopentane was investigated at normal pressures over Pt-Ir and Pt-Sn catalysts supported on Al2O3. Pt-Sn/Al2O3 had high activity and outstanding selectivity for dehydrogenation and dehydrocyclisation via 1,6 ring closure.
A Chemisorption and XPS Study of Bimetallic Pt-Sn/Al2O3 Catalysts
k. balakrishnan and j. schwank, J. Catal., 1990, 127, (1), 287–306
Bimetallic 1 wt.%Pt-(0–3.25 wt.%)Sn/Al2O3 catalysts, prepared by co-impregnation of non-porous Al2O3, were studied by chemisorption of H2, O2 and CO at room temperature. Addition of Sn to Pt resulted in significant differences in the gas uptake characteristics of the three adsorbates. Both H2 and CO showed an initial increase in gas uptake with addition of small amounts of Sn, and then the chemisorbed amount dropped off with further addition of Sn. XPS of the reduced catalysts showed that in Al2O3 supported samples most of the Sn was in a valence state of either Sn(II) or Sn(IV).
Alumina-S upported Platinum-Rhenium Dehydrogenation Catalysts: Influence of Metal Ratio and Precursors on Catalytic Behavior
m. garland, a. baiker and a. wokaun, Ind. Eng. Chem. Res., 1991, 30, (3), 440–447
Two series of Pt-Re/Al2O3 dehydrogenation catalysts with 0.5 wt.% loading were prepared by incipient wetness from H2PtCl6 and Re2O7 with nominal Pt/Re atom ratios of 100/0, 75/25, 50/50 and 25/75, and the second series was prepared from H2Pt(OH)6 and Re2O7 with atom ratios of 100/0, 75/25, 50/50, 25/75 and 0/100. During dehydrogenation, nearly constant activity was observed on the 50/50, 75/25 and 100/0 Pt/Re first series catalysts for the conversion of cyclic C6 hydrocarbons whereas for the dehydrogenation of cyclic C5 hydrocarbons activity continually increased with increasing Pt/Re ratio. Unchlorinated 75/25 and 50/50 Pt-Re/Al2O3 catalysts showed most promise for the highly selective dehydrogenation of methylcyclohexane.
Hydroconversion of n-Heptane on Platinum/H-Mordenite Catalysts Prepared via Different Routes
a. k. aboul-gheit, m. f. menoufy and a. k. elmorsi, J. Chem. Technol. Biotechnol., 1991, 50, (2), 227–237
Two Pt/H-mordenite catalysts were prepared by impregnating H2PtCl6 in (a) H-mordenite (HM) and (b) NH4HM, followed by drying, calcination and reduction. Catalyst (a) was found to be more active for n- heptane hydroconversion, more selective for its isomerisation, and it encountered more diffusion limitation as it yielded a larger Thiele modulus. The catalyst also gave a lower effectiveness factor and lower activation energy, Ea, values than catalyst (b). An increase in the catalytic activities was observed to a maximum at 3.0 MN/m2, followed by a decrease. High selectivities for central hydrocracking of heptane components and high iso-butane to n -butane ratios were obtained on both catalysts.
Characterization Study of Silica-Supported Platinized Tin Oxide Catalysts Used for Low-Temperature CO Oxidation: Effect of Pretreatment Temperature
s. d. gardner, g. b. hoflund, d. r. schryer and b. t. upchurch, J . Phys. Chem., 1991,95, (2), 835–838
Pt/SnO2 surfaces supported on SiO2 used for low temperature CO oxidation in CO2 lasers have been characterised before and after reduction in CO at 125 and 250°C by various techniques. Pt was present initially as PtO and PtO2, small amounts of Pt(OH)2 and metallic Pt. Reduction at 125°C converts most of the Pt to Pt(OH)2 while reduction at 250°C converts most of the Pt to metallic Pt. SnO2 is partially reduced to SnO. At 250°C the outermost Pt and Sn are covered by impurities from the SiO2 substrate, while at 125°C the outermost atomic layers are enriched in Pt and Sn. IIS and XPS data suggest that a Pt/Sn alloy may form during the reductions.
Microstructure and Reactivity of Pt-Ce and Rh-Ce Particles on Silica
t. chojnacki, k. krause and l. d. schmidt, J. Catal., 1991, 128, (1), 161–185
The interactions of Ce with 20–200 A diameter particles of Pt and Rh on planar SiO2 were studied using TEM and reactivity measurements following treatment in H2 and O2. After heating Pt-Ce in H2 at 650°C, Ce formed a thin amorphous film on the SiO2, and the only crystalline phase observed was Pt metal for low Ce loadings. For high Ce loadings a phase was detected with a diffraction pattern of Ce hydride, and dark field imaging showed that this formed as cubes near the Pt particles. When Rh-Ce was heated in H2 a Ce film formed on the SiO2.
Non-Faradaie Electrochemical Modification of Catalytic Activity. III. The Case of Methanol Oxidation on Pt
c. g. vayenas and neophytides, J. Catal., 1991, 127, (2), 645–664
The catalytic activity and selectivity of polycrystalline Pt for the oxidation of methanol to formaldehyde and CO2 can be dramatically and reversibly affected when O2– anions are electrochemically pumped to or from the Pt catalyst surface via the NEMCA effect. The studies were performed using stabilised ZrO2 solid electrolyte at 600–900 K. The increases in the catalytic rate of H2CO and CO2 formation were 103–104 times higher than the rate of O2– transport to or from the catalyst, and exceed the regular open-circuit catalytic rates by up to a factor of 15.
Mechanism of Sulfur Poisoning of Supported Pd(Pt)/Al2O3 Catalysts for H2-O2 Reaction
l.-d. an and y. q. deng, Appl. Catal., 1990, 66, (2), 219–234
Spent commercial Pd(Pt)/Al2O3 catalysts used in the elimination of H from CO2 feed gas in the synthesis industry and deactivated by S poisoning were characterised by chemical analysis, XPS, IR, XRD and TPR. The negative charged S ions existed mainly as noble metal sulphides on/in the surface of the catalysts. Under industrial reaction conditions, S6+ is the main state of S in the poisoned catalysts.
Catalytic Combustion of Methane over Supported Palladium Catalysts. I. Alumina Supported Catalysts. II. Support and Possible Morphological Effects
t. r. baldwin and r. burch, Appl. Catal., 1990, 66, (2), 337–358; 359–381
A series of Pd/Al2O3 catalyst were tested under continuous-flow conditions, for their activity towards CH4 combustion in an O2 rich atmosphere and the effects of various precursor Pd salts and different supports in the preparation of Pd catalysts for CH4 combustion were studied. Catalytic activities were found to increase dramatically after heating in a 1% CH4/air reaction mixture.
Catalytic Oxidation of Methane over Palladium Supported on Alumina. Effect of Aging under Reactants
p. briot and m. primet, Appl. Catal., 1991, 68, (1–2), 301–314
After ageing a Pd/Al2O3 catalyst at 600°C under a CH4-O2-N2 mixture with a O2:CH4 = 4, it was found that the aged catalyst was more active than the fresh one, especially below 400°C. Ageing decreased metal dispersion and increased Pd particle size from 7–16 nm, and turnover was strongly enhanced. The reactivity of adsorbed O towards H increased with metal particle size. Pd may be in the form of bulk Pd oxide for reaction temperatures of >400°C and for CH4:O2 mixtures rich in O2. The formation of bulk PdO appears to be metal particle size dependent.
Influence of Oxidation of Pd/Al2O3 for the Reactions of CO with NH3 and For-mamide Decomposition
d. k. paul and s. d. worley, J. Phys. Chem., 1990, 94, (26), 8956–8959
The reaction of CO with NH3 and the decomposition reactions for HNCO and formamide over Pd/Al2O3 films were studied by IR spectroscopy. The formation of isocyanate species (NCO) was observed during all of these reactions over pre-oxidised Pd/Al2O3, but not over pre-reduced surfaces. The NCO species were formed on Pd but spilled over to the Al2O3 support. Pd became reduced during the course of the reaction of CO with NH3.
Effect of Preparation Conditions on the Structure and Properties of Palladium-Aluminosilicate Catalysts
e. m. moroz, s. d. mikhailenko, a. k. dzhunusov, l. v. pavlyukevich and a. b. fasman, Kinet. Katal., 1990, 31, (6), 1506–1510
Studies of the effect of preparation conditions of deposited Pd catalysts on the structure and activity during 2-ethylanthraquinone hydrogenation were performed on Pd catalysts supported on aluminosilicates containing 86.5% SiO2, 13% A12O3 and oxides of Na, Fe and Mn. The results showed that part of the metal interacts with the support, forming Pd2Si compounds in amount depending on preparation conditions. The effect of structural factors on the activity and selectivity of catalysts during the reaction was analysed.
Bulk Alloy Formation during Metal Ion Poisoning of Palladium
t. mallÁt, z. bodnÁr, s. szabÓ and j. petrÓ, Appl. Catal., 1991, 69, (1), 85-95
Studies of the phase structure of Pd catalysts poisoned by metal ions, performed by XRD, electrochemical polarisation and AAS methods, showed bulk alloy formation during liquid phase hydrogenation at 295–350 K. Both ordered: Pd3,Pb, Pd5Ge, PdGe, PdHg, Pd2Hg5, and disordered: Pd-Sn, Pd-Cd, Pd-Hg, alloys were identified.
CO Oxidation over Pd and Cu Catalysts. I. Unreduced PdCl2 and CuCl2 Dispersed on Alumina or Carbon. II. Unreduced Bimetallic PdCl2-CuCl2 Dispersed on A12O3 or Carbon
k. i. choi and m. a. vannice, J. Catal., 1991, 127, (2), 465–488; 489–511
CO can be oxidised at 300–400 K by O2 over dispersed, unreduced PdCl2 or CuCl2, but specific activities for CO oxidation by O2 over unreduced PdCl2-CuCl2 catalysts were higher than on the reduced bimetallic catalysts. PdCl2 was more active than CuCl2 and the addition of H2O vapour to the feed greatly enhanced the activity of the PdCl2 catalysts. The activity of PdCl2-CuCl2 catalysts can also be enhanced by 1–3 orders of magnitude by addition of H2O vapour to the feed, thus producing very active catalysts at 300 K. A reaction model that involves H2O as a reactant with the PdClCO species is proposed.
Hydroconversion of n-Nonane Catalyzed by PdHY Zeolites. I. Influence of Catalyst Pretreatment. II. Effect of the Chromium Promoter
j. leglise, a. chambellan and d. cornet; j. leglise, j. m. goupil and d. cornet, Appl. Catal., 1991, 69, (1), 15–31; 33–47
Pd/HY catalysts reduced at 573–873 K were studied during n -nonane hydroconversion at 473 K and 0.1 MPa. The catalyst reduced at 573 K had a stable activity and a high selectivity for isomerisation, but samples reduced at 773 K initially favoured cracking at the expense of isomerisation. 3% Cr was added to Pd/SY zeolites to maintain a good dispersion of the noble metal upon reduction at elevated temperature. Catalysts reduced at 573 K showed a promoter effect limited to a change in reaction selectivity. However, if Cr was properly introduced in catalysts reduced at 773 K, it improved the dispersion of Pd and hence the hydrogenation function.
Catalysis with Palladium Deposited on Rare Earth Oxides: Influence of the Support on Reforming and Syngas Activity and Selectivity
f. le normand, j. barrault, r. breault, l. hilaire and a. kiennemann, J. Phys. Chem., 1991, 95, (1), 257–269
The effect of the support was tested on the reactivity of Pd/rare earth oxide catalysts (La2O3, CeO2, Pr6O11, Nd2O3 and Tb4O7) by measuring BET surface area, chemisorption, TPR and TPO, XRD and XPS. The catalysts were put into three classes according to their ability to create anion vacancies: (a) oxides of the type Re2O3 which are unreducible, (b) CeO2 where anion vacancies can be created extrinsically by the reduction process, and (c) Pr6O11 and Tb4O7 where anion vacancies exist due to the nonstoichiometric nature of these oxides. In syngas conversion the production of high alcohols at the metal-support interface is favoured by the presence of intrinsic anion vacancies on Pr6O11 and Tb4O7.
Preferential Site Displacement of Carbon Monoxide by Phosphine on Rh/Al2O3 Surfaces
g. lu, j. e. darwell and j. e. crowell, J. Phys. Chem., 1990, 94, (21), 8326–8328
Transmission IR spectroscopic studies showed that specific bonding sites of CO are preferentially displaced upon exposure of a CO-saturated Rh/Al2O3 surface to PH3. CO is bound in three primary adsorption states on Rh/Al2O3, with bridged, atop, and gem -dicarbonyl bonding. At all adsorption temperatures studied (90–300 K), exposure to PH3 readily leads to removal of CO bound in gem -dicarbonyl sites. Production of Rh(CO)PH3 was verified upon PH3 exposure of a Rh/Al2O3 surface containing only the gem -dicarbonyl species.
Protection of a Rh/Al2O3 Catalyst under Extreme Environmental Conditions
d. k. paul and j. t. yates, J. Phys. Chem.., 1991, 95, (4), 1699–1703
The removal of isolated Al-OH groups by the silation of Rh/Al2O3 catalysts is effective in preventing catalyst degradation under conditions where CO adsorption occurs. The functionalisation of isolated Al-OH species by (CH3)3SiCl led to the formation of very stable (CH3)3Si-O-Al= (alumasiloxane) surface species. Silation by alkyl halosilanes may provide a practical route for the protection of Rh/Al2O3 catalysts from oxidative degradation under the conditions encountered in automotive catalysts.
Membrane-Supported Rhodium Hydroformylation Catalysts
j. feldman and m. orchin, J. Mol. Catal., 1990, 63, (2), 213–221
Films prepared from the THF solutions containing cellulose acetate, [HRh(CO)(PPh3)3] and PPh3 were tested for catalytic activity in the vapour phase hydroformylation of C2H4 and C3H6 at 800 Torr and 80°C, giving RCH2CH2CHO. Turnover rates were about 25 mol propanal/mol Rh/h. No loss of Rh or PPh3 was noted from the film. The turnover rates with the films were equal to or even slightly higher than when using homogeneous [HRh(CO)(PPh3)]. Films prepared from poly(phenylsulphone) were also active catalysts. The absence of O2 enabled the system to retain its activity for more than 13 days.
Carbon Monoxide Hydrogenation on Supported Rh-Mn Catalysts
s. lisitsyn, s. a. stevenson and h. knÖzinger, J. Mol. Catal., 1990, 63, (2), 201–211
Rh/SiO2 catalysts promoted with Mn show a higher specific activity for CO hydrogenation than unpromoted catalysts. This results in increased C2+ product formation. Activation energy for chain growth is significantly higher on the Mn promoted catalysts, possibly because promoted catalysts provide more active sites and the insertion mechanism may be different to that for unpromoted catalysts.
Catalytic Properties of Well Dispersed Supported Ruthenium Alloys
b. coq, a. bittar, r. dutartre and f. figueras, J. Catal., 1991, 128, (1), 275–286
Small particles of Ru alloyed with Sn, Pb, Sb, Ge or Si were prepared by reacting a well dispersed Ru/Al2O3 parent sample with an organometallic compound of the desired modifier, by the so-called controlled surface reaction method. The results showed that a topological segregation of Sn, and to a lesser extent Pb, takes place at the bimetallic surface, with the second metal occupying sites of lower coordination, displacing Ru onto the facets. Ge seems more randomly distributed at the surface.
Hydrogenation Pathway of Quinolines over Raney Nickel and Ru/C
h. okazaki, k. onishi, m. soeda, y. ikefuji, r. tamura and i. mochida, Bull. Chem. Soc. Jpn., 1990, 63, (11), 3167–3174
Quinoline, together with 2-methylquinoline and 8-methylquinoline were hydrogenated over Ru/C and Raney Ni catalysts, under 100 atm H2 at 150°C and 10 atm H2 at 200°C, respectively. All the substrates were commonly hydrogenated into the initial products, 1,2,3,4-tetrahydroquinolines. Ru/C promoted exclusively the direct hydrogenation of 1,2,3,4-tetrahydro derivatives to the final products. The effects of methyl substituent and different reactivities of quinoline and isoquinoline are discussed.
Catalysis of the Water-Gas Shift Reaction by Supported Ru3(CO)12 with 2,2'-Bipyridine
u. kiiski, t. venÄlÄinen, t. a. pakkanen and o. krause, J. Mol. Catal., 1991, 64, (2), 163–169
The water gas shift reaction was studied on RU3(CO)12 with 2,2'-bipyridine on silica gel, Mg silicate and X- and Y- mordenite zeolites in Na form supports, in a flow reactor at 100–150°C and CO partial pressure of 7 bar. The highest activity of 8170 mol H2/mol Ru3(CO12)/24 h was obtained with a Mg silicate support at 150°C, and its activity was stable for long periods. The metal catalyst was well retained on the support during flow operation.
Homogeneous Hydroformylation of Olefins by cis-[PtCl2(PPh3)2]/SnCl2
g. muller, d. sainz and j. sales, J. Mol. Catal., 1990, 63, (2), 173–180
The catalytic activity of cis- [PtCl2(PPh3)2]/SnCl2 for the hydroformylation of various olefins was studied. For 1-pentene and cyclohexene, conversions and hydroformylations are higher than for other Pt/Sn systems. The results obtained with cyclopentene (79% hydroformylation and TOF 180/h) and allyl benzene (87% hydroformylation and TOF of 220/h) were among the best yet reported.
Metal Colloid Morphology and Catalytic Activity: Further Proof of the Intermediacy of Colloids in the Platinum-Catalyzed Hydrosilylation Reaction
l. n. lewis, r. j. uriarte and n. lewis, J. Catal., 1991, 127, (1), 67–74
The Pt colloids formed during hydrosilylation reactions were studied by TEM and high-resolution electron microscopy (HREM). Reaction solutions were analysed for the addition of Et3SiH to either n -hexene or neohexene catalysed by bis(l,3-diviny1,1,1,3,3,-tetramethyldisiloxane)Pt0 (Karstedt’s catalyst) and showed dramatic differences between the morphology of the Pt colloid formed in each case. The neohexene reaction which gave 62% conversion to products in 1 h contained polycrystalline, 2.5 nm diameter Pt particles.
Tailored Cationic Palladium(II) Compounds as Catalysts for Highly Selective Linear Dimerization of Styrene and Linear Polymerization of p- Divinylbenzene
z. jiang and a. sen, J. Am. Chem. Soc, 1990, 112, (26), 9655–9657
The replacement of the weakly co-ordinating MeCN ligands in [Pd(MeCN)4](BF4)2 by more strongly ligating and bulkier pyridine and phosphine derivatives resulted in the formation of highly selective catalysts for selective linear dimerisation of styrene and linear polymerisation of p -divinylbenzene. The new catalyst systems differ from most existing systems in several important ways; specifically. (a) no indan derivative of higher oligomers are formed from styrene, (b) only styrene reacts when a mixture of styrene and α -methylstyrene is employed and (c) the ability to effect clean, linear dimerisation of styrene allowed the formation of a soluble, linear polymer from p -divinylbenzene.
Annulation via Alkylation-Alder EneCyclizations. Pd-Catalyzed Cyclo-isomerization of 1,6-Enynes
b. m. trost, m. lautens, c. chan, d. j. jebaratnam and t. mueller, J. Am. Chem. Soc, 1991, 113, (2), 636–644
A Pd(0)-catalysed alkylation of an allyl substrate with a nucleophile containing a double or triple bond to allow subsequent thermal Alder ene reactions gives a novel annulation process. For a triple bond, a Pd(2 +) complex catalyses an equivalent of an Alder ene reaction. This new cyclisation was studied in terms of the effect of substitution on the olefin, the acetylene, and the tether connecting the two. The Pd(2 + ) catalysed reaction showed an ability to interact with remote non-reactive parts of substrates to affect conformation and selectivity. A novel cyclopentannulation of allyl alcohols and related derivative evolves in which Pd(0) catalyses formation of the first bond and a simple electronic switch to Pd(2 + ) catalyses formation of the second bond.
Reactions of Cyclopalladated Compounds and Alkynes: New Pathways for Organic Synthesis?
m. pfeffer, Recl. Trav. Chim. Pays-Bas, 1990, 109, (12), 567–576
Cyclometallated compounds obtained by direct intramolecular C-H activation of a ligand by transition metals, and those derived from Pd(II) were found to be fairly reactive towards insertion of internal alkynes into their metal-C bond. This reaction led to either new organometallic compounds by inclusion of one to three alkynes into the M-C bonds, or organic compounds, which were either carbocyclic or heterocyclic.
Chiral Rhodium(II) Carboxamides. A New Class of Catalysts for Enantioselective Cyclopropanation Reactions
m. p. doyle, b. d. brandes, a. p. kazala, r. j. pieters, m. b. jarstfer, l. m. watkins and c. t. eagle, Tetrahedron Lett., 1990, 31, (46), 6613–6616
The preparation of an effective class of chiral catalysts, Rh2L4 where L=4-substituted oxazolidinones and methyl 2-pyrrolidone-5-carboxylate, based on the dirhodium(II) framework with two N-Rh bonds in the cis geometry at each Rh face, are effective catalysts for enantioselective intermolecular cyclopropanation reactions, such as for styrene.
Efficient Activation of Acetals, Aldehydes, and Imines toward Silylated Nucleophiles by the Combined Use of Catalytic Amounts of [Rh(COD)Cl]2 and TMS-CN under almost Neutral Conditions
t. soga, h. takenoshita, m. yamada and t. mukaiyama, Bull. Chem. Soc. Jpn., 1990, 63, (11), 3122–3131
Studies of the reaction of trimethylsilyl cyanide (TMS-CN) with acetals in the presence of a catalytic amount of [Rh(COD)Cl]2 Co(acac)2 or NiCl2 showed the smooth formation of α -methoxy carbonitriles in good yields. The co-existence of catalytic amounts of [Rh(COD)Cl]2 and TMS-CN, allowed silyl enol ethers or ketene silyl acetals to react with acetals, aldehydes or imines to yield the corresponding coupling products in good yields under almost neutral conditions.
Homogeneous Catalysis. Catalytic Production of Simple Enols
s. h. bergens and b. bosnich, J. Am. Chem. Soc, 1991, 113, (3), 958–967
Complexes of the type [Rh(diphosphine)(solvent)2] + in dry acetone or tetrahydrofuran solutions are effective catalysts for the production of synthetically useful quantities of simple enols from their corresponding allylic alcohols. A number of simple enols were produced, and the physical properties and stabilities were recorded. The mechanism of catalysis was inferred from specific isotopic labelling studies.
Poly-(l,4-Naphthalene) as Support of Catalytically Active Osmium Clusters for Olefin Isomerisation
h. p. fritz and t. trÜbenbach, J. Mol. Catal., 1991, 64, (2), 213–220
The complex [H2Os3(CO)9-(PPh2)x-Cl0H6-x] with x = 2-3 and n∼55, was synthesised and shown to have significantly higher catalytic activity for the isomerisation of 1-hexene than H,Osj(CO)»-polystyryl chain, or than free H2Osj(CO),„. It may be considered as a model system for comparing its ‘linear’ or rather non-coiled structure with polymer-supported catalysts with alkane backbones.
Ruthenium-Catalyzed Allylation of Primary Alcohols by Allylic Acetates: A Novel Synthesis of a,j3-Unsaturated Ketones
t. kondo, t. mukai and y. watanabe, J. Org. Chem., 1991, 56, (2), 487–489
A novel synthesis of α,β -unsaturated ketones from primary alcohols and allylic acetates via π-allylruthenium intermediates is described. The π-allylruthenium intermediates act as nucleophiles rather than as electrophiles in reactions with aldehydes to give homoallylic alcohols. This behaviour contrasts with that of π-allylpalladium complexes which usually act as electrophiles.
Selectivity in Catalytic Diol Electrooxida-tion Using A Polypyridine Ru(IV) Complex
m. navarro, w. f. de giovani and j. r. romero, Tetrahedron, 1991, 47, (4/5), 851–857
The polypyridine [(bpy)(trpy)RuO]2+ complex, (bpy is 2,2′-bipyridine, trpy is 2,2′:6′,2″-terpyridine) was systematically studied to explore its oxidising ability. 1,2-, 1,3- and 1,4-butanediols and phthalic alcohol were oxidised electrocatalytically with different concentrations of the catalyst, pH and temperature. By controlling the number of coulombs passed through the electrolytic cell, it was possible to obtain selective reactions. Products obtained by controlled potential electrolysis were l-hydroxy-2-butanone, l-hydroxy-3-butanone, γ -butyrolactone, phthalide, phthalic aldehyde and phthalic acid.
General Synthesis of Noval Chiral Ruthenium Catalysts and Their Use in Asymmetric Hydrogenation
j. p. genet, s. mallart, c. pinel, s. juge and a. laffitte, Tetrahedron: Asymmetry, 1991, 2, (1), 43–46
The first general synthesis of mononuclear hexaco-ordinate chiral Ru complexes is presented. Four chiral Ru(II)(2-methylallyl)2_, complexes containing. Diop, Chiraphos, Norphos and Binap were prepared in 50–71% yield under mild conditions, and were effective for asymmetric hydrogenation of unsaturated carboxylic acids to give the corresponding saturated derivatives attaining 90% optical purity.
Homogeneous Catalysis in Water: A Remarkable Salt Effect in the Hydrogenation of Propionaldehyde with RuCl2 (tppts)3 and Related Complexes [tppts = (m .NaS03C6H4)3P]
e. fache, f. senocq, c. santini and j.-m. basset, J. Chem. Soc., Chem. Commun., 1990, (24), 1776–1778
New water soluble Ru11 complexes such as RuHI(tppts)3, exhibit an extremely high catalytic activity in the presence of various salts during hydrogenation of aldehydes. Mechanistic studies showed clearly that the salt effect occurred both via the cation and the anion in the catalytic cycle. The electrophilic cation favoured an unusual type of aldehyde co-ordination and reaction mechanism as the anion modified the co-ordination sphere around the Ru atom.
Low Severity Coal Conversion by an Elec-troreduction Route
m. farooque, a. rush, h. maru and j. macdonald, J. Appl. Electrochem., 1991, 21, (2), 143–150
Electrochemical conversion of coal to low molecular weight hydrocarbons through an electroreduction route involves reaction of H+ with the coal surface leading to hydrogenation of coal molecules at low severity operating conditions. The type of cell used is the same as that used in H3PO4 fuel cells with the anode comprising a porous thin layer of supported Pt catalyst laminated on a porous, conductive graphite support layer. The matrix’ consisted of a thin porous layer of SiC soaked with H3PO4 electrolyte. The liquid product compositions were dependent upon the parent coal and comprised a variety of aliphatic and aromatic compounds.
ELECTRICAL AND ELECTRONIC ENGINEERING
Focused Ion Beam Induced Deposition of Platinum
t. tao, j.-s. ro, j. melngaius, z. xue and h. d. kaesz, J. Vac. Sci. Technol. B, 1990, 8, (6), 1826–1829
Focused ion beam induced deposition of Pt film, using Ga+ ions, from a precursor gas of (methylcyclopentadienyl)trimethyl Pt, which is solid at room temperature, has been performed. The resulting film has a resistivity of 70–700 μΩ cm, depending on conditions. The resistivity and impurity C content dropped as the ion current increased. The Pt film is amorphous and of composition 46%Pt, 24%C, 28%Ga and 2%O. Adding H2 to the same area by a nozzle has little effect on the yield or resistivity. Pt formed in this way can fill trenches, while at near grazing incidence on a cleaved Si surface it forms discrete islands of size 0.25 μ m. It may find applications in IC chip repair.
Dielectric Enhancement Layers for a Pt/Co Multilayer Magneto-Optical Recording Medium
p. f. carcia, m. reilly, w. b. zeper and h. w. vankesteren, Appl. Phys. Lett., 1991, 58, (2), 191–193
Studies showed that a transparent ZnO dielectric layer, with refractive index n∼2, not only enhanced the Kerr rotation of the Pt/Co recording layer, but also substantially increased its magnetic coercivity (Hc). Coercivhies of up to 3kOe were obtained in Pt/Co multilayers Kr sputtered on a ZnO layer, while maintaining square hysteresis loop shape for an applied magnetic field perpendicular to the thin film.
Thermal Stability of PtSi Contact to GexSi1-x
q.z. hong, j. g. zhu, c. b. carter and j. w. mayer, Appl. Phys. Lett., 1991, 58, (9), 905–907
Studies of the thermal stability of PtSi contact to epitaxial Ge0.5Si0 5/(100)Si showed that the PtSi layer remained structurally and morphologically intact on the epitaxial Ge-Si alloy at ∼650°C. When annealed at higher temperatures, PtSi penetrated locally into the alloy, although no chemical reaction was observed.
Barrier Layers for Realization of High Capacitance Density in SrTiO3 Thin-Film Capacitor on Silicon
t. sakuma, s. yamamichi, s. matsubara, h. yamaguchi and y. miyasaka, Appl. Phys. Lett., 1990, 57, (23), 2431–2433
High dielectric constant SrTiO3 thin films were sputter deposited on barrier layers/Si substrate to produce a capacitor for dynamic random access memories. Dielectric constant (ϵ ) values of 140–210 were achieved for the 150 nm thick SrTiO3 films using a Pt/Ti or Pt/Ta double-layer barrier. In the Pt(50 nm)/Ti(10 nm), Pt(50 nm)/Ti(50 nm) and Pt(50 nm)/Ta(10 nm) barrier, effective ϵ decreased on annealing at 450–550°C. In the Pt(50 nm)/Ta barrier, increasing the Ta thickness from 10 to 50 nm remarkably improved the endurance to high-temperature annealing.
Preferential Reaction and Stability of the Au-Sn/Pt System: Metallization Structure for Flip-Chip Integration
o. wada and t. kumai, Appl. Phys. Lett., 1991, 58, (9), 908–910
Studies of thermal reactions of a metallisation system consisting of Au-Sn solder, Pt/Ti barrier, and Au/Zn/Au contact layers formed on an InP substrate were performed by AES, SEM and XRD. On heating to 400°C a moderate reaction was observed between Au-Sn and Pt, with a characteristic feature of preferential Pt-Sn interdiffusion to produce an intermediate layer involving the PtSn phase. The effective diffusion coefficient had an activation energy of 1.35 eV, and the lifetime of the Pt barrier was found to be in excess of 108 h for 50°C, which is sufficient for the application of this structure in devices.
Stress Migration Resistance and Contact Characterization of Al-Pd-Si Interconnects for Very Large Scale Integrations
y. koubuchi, j. onuki, m. suwa, s. fukada, s. moribe and y. tanigaki, J. Vac. Sci. Technol. B, 1990, 8, (6), 1232–1238
Stress induced migration resistance and contacts to Si of Al-0.3%Pd-1%Si interconnections for submicron process integrated circuit devices were investigated and compared to those of Al-0.5%Cu–l%Si. From creep tests, Fd addition to Al reduced the grain boundary diffusion. Pd improved the stress-induced migration resistance and reduced void and hillock formation in Al-Si conductors. AlPd precipitates in Al-Pd-Si alloys formed at higher temperatures than AlCu compounds and may explain the improvements. Contact resistances were similar, but reliability and yield data from 1.2 μ m ROM devices using Al-Pd-Si conductors were better than that from Al-Cu-Si conductors. Thus Al-Pd-Si metallisation is promising as an interconnection for submicron VLSIs.
Probe Beam Deflection Investigation of the Charge Storage Reaction in Anodic Iridium and Tungsten Oxide Films
r. kÖtz, c. barbero and o. haas, J. Electroanal. Chem. Interfacial Electrochem., 1990,296, (1), 37–49
The electrochromic charge storage reaction in anodic Ir oxide films (AIROF) was studied in aqueous electrolytes using the probe beam deflection (PBD) technique in combination with cyclic voltammetry. In acid electrolyte, of 1 M HClO4 for Ir and 1 M H2SO4 for W, the sign of the PBD signal showed clearly that protons were ejected from the oxide film into the bulk electrolyte during oxidation. In basic electrolyte of 1 M LiOH, 1 M NaOH, OH– ions were consumed during the oxidation reaction in the AIROF. The change in sign of the beam deflection signal, indicative for one or the other reaction, occurred at ∼pH4 (±0.5).
Structural and Electrical Evolution of the Al/Ru02 Interface upon Thermal Annealing
q. t. vu, e. kolawa and m.-a. nicolet, Solid-State Electron., 1991, 34, (3), 271–278
The behaviour of the Al/RuO2 interface was monitored by various techniques as a function of the annealing temperature: 450–550°C and the duration. An interfacial Al-O compound layer grew with concurrent reduction of a thin layer of RuO2. This result does not depend on the deposition conditions. Structures of the type <Si>/SiO2/Al/RuO2/Al were annealed, and the. specific contact resistance between Al and RuO2 was derived, and shown to decrease with annealing duration at 500°C. This evolution of the specific contact resistance indicated that the interfacial reaction does make an insulating interface, as expected if the interfacial growth were pure and dense A12O3. RuO2 can be used as a diffusion barrier between Si and Al.
Reactively Sputtered RuO2 Thin Film Resistor with Near Zero Temperature Coefficient of Resistance
q. x. jia, z. q. shi, k. l. jiao, w. a. anderson and f. m. collins, Thin Solid Films, 1991, 196, (1), 29–34
Ru oxide thin film resistors with near zero temperature coefficients of resistance (TCR) were successfully deposited on SiO2/Si substrates by reactive DC magnetron sputtering. The TCR was a strong function of substrate temperature during sputtering. Around 80°C a critical temperature was found where the TCR changed signs, between a temperature dependence of semiconductor-like behaviour and metal-like behaviour. Films with amorphous structure usually had a negative TCR, but films with a polycrystalline structure had a positive TCR. Resistors with near zero TCR may have a microcrystalline structure.
Temperature Measurement under Extreme Conditions
r. mӦbius, p.-e. nau and r. wahren, Chem. Tech. (Leipzig), 1991, 43, (1), 26–29
The temperature of the reactors during the production of syngas from fuel oil was controlled by temperature measurement thermocouples (PtRh 30/PtRh 6), which were protected by sintered corundum conduits. At temperatures up to 1800 K and pressure up to 4 MPa the thermocouples and conduits were exposed to extreme conditions from the gas atmosphere and the oil ash. Accuracy of the measurements and the life of the thermocouples depend very much on the quality of the sintered corundum conduits and on stable plant operation.
Magneto-Resistance of a Highly Stable Industrial-Grade Platinum Resistance Thermometer between 20 and 240 K
k. nara, h. kato and m. okaji, Cryogenics, 1991, 31, (1), 16–20
The stability and magneto-resistance of a new Pt resistance thermometer made to the Japanese Industrial Standard were studied. The stability was estimated from the change in resistance at the triple point of water after thermal cycles between room temperature and liquid N2 temperature. The variation in the resistance values at 20, 50 and 100 cycles was < 1 mK. The magneto-resistance was measured between 20 and 240 K in a field of up to 8 T. The relative resistance increase, ϵ, obeyed the equation ϵ = D(T)B2/[1+E(T)B]. The fitting error in the field dependence was < 15 mK at >30 K and ∼0.1 % of the correction for a magnetic field of 8 T – which is a better fit than the previously reported equation. An extremely reliable screening procedure has been established to characterise long-term stability of small sensors for thermometry in magnetic fields.