Platinum Metals Rev., 1991, 35, (1), 32
ABSTRACTS: January 1991
of current literature on the platinum metals and their alloys
Electrical Properties, Stability, and Applications of Ultrathin Porous Pt Films on SiO2
r. nowroozi-esfahani and g. j. maclay, J. Vac. Sci Technol. A, 1990, 8, (4), 3591–3597
The morphology of 25 Å porous Pt films deposited on thermally grown Sio2 at room temperature and 250°C is presented. The impedance was measured over the range 100 Hz to 1 MHz. At 1 kHz, the impedance was measured in electric fields up to 250 V/cm at temperatures –192 to 140°C. The AC impedance of the 25 Å Pt film deposited at room temperature decreased by 25% in 21 days at 150°C in room air, but the AC impedance of the Pt film deposited at 250°C did not change.
Volatilization of Pt-Rh Alloys at High Temperature
y. ning, d. deng and y. wang, Guijinshu (Precious Met.), 1990, 11, (2), 12–17
Studies of the volatilisation of Pt-7Rh and Pt-Rh-Au alloys at high temperature showed that the volatilisation loss of the alloys at 1200–1350°C obey a parabola-straight line rule, and the transposition time from the parabola loss to straight line loss decreased with increasing temperature. The volatilisation loss increased with increasing Rh content and by addition of Au to Pt-Rh alloys. The activation energy of volatilisation of Pt-7Rh-3Au alloy is 167 kj/mol.
Columnar Epitaxy of PtSi on Si(111)
r. w. fathauer, q. f. xiao, s. hashimoto and c. w. nieh, Appl. Phys. Lett., 1990, 57, (7), 686–691
Columnar grains of PtSi surrounded by high quality epitaxial Si were obtained by ultrahigh vacuum codeposition of Si and Pt in an 8:1 ratio on Si(111) substrates heated to 610–810°C. The areal density of columns varied from 120 to 3.8/µ m2, and layers with thicknesses from 100 nm to 1 µm were displayed. The PtSi grains are also epitaxial and have one of three variants of the relation defined by PtSi(010)//Si(111), with PtSi//Si< 110 >.
Properties of a Platinum-Yttrium-Boron Alloy
k. schwarz and w. molle, Neue Hütte, 1990, 35, (10), 391–393
The properties of a Pt-0.03Y alloy was improved by adding a small amount of B. The addition of B resulted in an increase in the rate of internal oxidation and a fine dispersion of the Y oxide particles was obtained. High creep rupture strength, a high creep resistance and a decreased grain growth were found.
Magnetic and Transport Properties of the UTIn Series (T=Rh, Pd and Pt)
v. h. tran and r. troč, J. Magn. Magn. Mater., 1990, 88, (3), 287–294
Magnetic susceptibility, magnetisation, electrical resistivity and magnetoresistivity measurements have been performed for the U(Rh, Pd, Pt)In series crystallising in the hexagonal Fe2P type structure. Results for URhIn are reported for the first time. Antiferromagnetic ordering in URhIn and UPtIn with a Néel temperature of 7 and 22 K and metamagnetic transitions in fields of ~1.5 and 3.5 T at 4.2 K have been observed, respectively. Resistivity anomalies at low temperatures have been observed. UPdIn was antiferromagnetic with a Néel temperature of 20 K.
Effects of High Concentration CO and CO2 on Hydrogen Permeation through the Palladium Membrane
m. amano, c. nishimura and m. komaki, Mater. Trans., JIM, 1990, 31, (5), 404–408
The effects of high concentrations of CO and CO2 on the H permeation characteristics of a Pd membrane 0.7 mm thick, 12 mm diameter cut from cold-rolled Pd plate, followed by annealing were investigated using pure H2, H2-CO (10%,50%), and H2-50%CO2 at 423–723 K and pressures 0.9–250 kPa. Deterioration in H permeability and diffusivity in the Pd membrane occurred for H2-CO(10%,50%) gas below 523 K with a concentration dependence on CO, while only slight deterioration occurred for H2-50%CO2 gas below 473 K. Results are explained by different adsorption energies of CO and CO2 at the Pd surface. Deterioration in H2 permeability is attributed to a decrease in effective area for H2 dissociation by the weak adsorption of CO.
Kinetic Description of the Transition from a One-Phase to a Two-Phase Growth Regime in Al/Pd Lateral Diffusion Couples
b. blanpain, j. w. mayer, j. c. liu and k. n. tu, J. Appl. Phys., 1990, 68, (7), 3259–3267
The kinetics of the solid-state reaction between Al and Pd is studied in the geometry of a lateral Al-Pd diffusion couple at 250–430°C. The first reaction phase is the crystalline Al3Pd2 (δ) phase and after its growth to a critical length, the quasicrystalline decagonal Al3Pd(γ′) phase starts to grow in between the Al and the Al3Pd2 phases. The first-phase Al3Pd2 and second-phase Al3Pd grow simultaneously. Excellent agreement between the data and the model is found. From the analysis the effective interface growth constant for the Al3Pd is extracted as a function of temperature.
Electrical Resistivity Changes Due to Interstitial Hydrogen in Palladium-Rich Substitutional Alloys
k. baba, u. miyagawa, k. watanabe, y. sakamotoand T. B. FLANAGAN, J. Mater. Sci., 1990, 25, (9), 3910–3916
The changes in electrical resistivity of Pd solid solution alloys, alloyed with Ag, Au, Cu, Y, Ce, Ti, Zr, V, Nb and Ta, with H concentration were measured at 301 K up to r (H/M) = 1.5 x 10-2. The H was introduced by electrolysis and measurements of electrode potential were also made. The specific electrical resistivity of H-free Pd alloys increased with increasing solute contents.
Internal Oxidation of Pd-40Ag-lRE (RE = Sm, Eu, Gd) Alloys and Their Properties
y. li, h. dai and Y. NING, Guijinshu (Precious Met.), 1990, 11, (2), 18–22
The internal oxidation of Pd-40Ag-lRE (RE = Sm, Eu, Gd) alloy wires and their properties were studied in air at 800–1200°C. For the alloys containing Sm or Gd, the oxidation rate along the grain boundaries was higher than that of grains in some parts. It is concluded that the internal oxidation of Pd-40Ag-lRE alloys is controlled by volume diffusion.
Microstructural Stability of Diluted Pb-Cu-(Sn-Se-Pd) Alloys
a. de la torre, p. adeva, g. caruana and m. aballe,Z. Metallkde., 1990, 81, (8), 594–600
The evolution of microstructure was followed in homogeneous, fine grained Pb-Cu, Pb-Cu-Sn-Se and Pb-Cu-Sn-Se-Pd alloys optically, by SEM and by microanalytical identification of phases and measurement of several microstructural parameters, at temperatures between 323 and 423 K for 4 to 700 h. Small Cu and Se additions substantially reduce Pb grain size; Pd acts as a grain stabiliser during heat treatments. Grain size distributions in one or two dimensions are lognormal and invariant with treatment temperature and time. The Pd containing alloys have high microstructural stability at the temperatures studied, making them suitable for chemical plant application.
Magnetic Properties of Nonequilibrium Fe-Pd Alloys Produced by DC Triode Sputtering
k. sumiyama, h. fujimori, m. kataoka, j. y. kim ands. l. zhang, Jpn. J. Appl. Phys., Part 2, Lett., 1990, 29, (7), 1261–1265
Sputter-deposited Fe1-xPdx alloys of ~100µ m thickness were prepared by DC triode sputtering. The single b.c.c. phase was obtained for x= 0–0.25 in contrast to the narrow single b.c.c. of x=0–0.03 in the equilibrium phase diagram. The lattice constant and the magnetisation increased by annealing below 500 K and decreased by annealing above 500 K.
The(α +β) Hydrogen Miscibility Gaps in Hydrogenated Palladium-Rich Pd-Y(Gd)-Ag Ternary Alloys
y. sakamoto, f. l. chen, m. furukawa and k. mine, J. Less-Common Met., 1990, 166, (1), 45–56
Pd-rich Pd-Y(Gd)-Ag ternary alloys were investigated as possible diffusion membranes for H purification, and their alloying behaviour and the extent of (α + β) H miscibility gaps in hydrogenated alloys were studied. Metallographic and X-ray studies of annealed Pd100-x-y(Y(Gd))xAgy alloys with a Ag content y of 5–24 at.% and x in at.% giving the value of the content of Y and/or Gd, indicate that every one of these alloys forms as a single a-Pd phase. It was found that the (α + β) H miscibility gaps in the hydrogenated alloys with any given Ag content decrease gradually as the content of Y and/or Gd increases, and the critical compositions for the disappearance of the miscibility gaps are approximately isoelectronic.
Do Thermal Spikes Contribute to the Ion-Induced Mixing of Ni into Zr, Ti, and Pd?
p. borgesen, d. a. lilienfeld and h. h. johnson, Appl. Phys. Lett., 1990, 57, (14), 1407–1409
Low-temperature ion beam mixing rates for Pd-Ni, Ni-Ti and Zr-Ni bilayers greatly exceeded binary collision estimates, and appeared quite sensitive to thermodynamic driving forces. In the absence of a temperature dependence such a behaviour is usually ascribed to interdiffusion within thermal spikes. It is suggested that interdiffusion within a thermal spike of the Vineyard-Johnson type is not the dominant mechanism.
On the Constitution of the Pd-Te System up to 28 at.% Te
m. kelm, a. gortzen, h. kleykamp and h. pen-tinghaus, J. Less-Common Met., 1990, 166, (1), 125-133
The constitution of the Pd-Te system was completed in the Pd-rich range up to 28 at.% Te and at >600°C. The solid solution between Pd and Te has a maximum Te content of 16.3 at.% at ~770°C. The system shows a eutectic with 23.0 at.% Te at 773°C. Three phases Pd17Te4 (19 at.% Te), Pd20Te7 (26 at.% Te) and dimorphic Pd3Te (25 at.% Te) were observed in the subsolidus region.
Structure Changes on Relaxation of Differently CooledPd0.835Si0.165 Alloy Glass
y. nishi, h. harano, s. uchida and k. oguri, J.Mater. Sci., 1990, 25, (10), 4477–4482
The radial distribution function (RDF) of X-ray diffraction was studied for liquid-quenched Pd0.835 Si0.165 alloy glasses in relation to cooling conditions. The atomic distance (r 1), total co-ordination number (n ) and volume (V ) were obtained by a first peak of RDF. The faster the cooling rate, the larger the r 1, n and V become. Based on the relaxation theory, it is shown that linear changes in r1, n and V with the thickness (D) indicate the reciprocal cooling rate.
High-Temperature Oxidation of Rhodium
l. a. carol and g. s. mann, Oxid. Met., 1990, 34, (1/2), 1–12
The oxidation kinetics of Rh were measured in air at 1 atm at temperatures 600–1000°C. The oxidation weight gain proceeds logarithmically at 600–650°C, followed by power law behaviour at >800°C. The logarithmic growth kinetics comes from thickening of hexagonal Rh2O3 scales. The transition reflects a thickening of hexagonal and orthorhombic Rh2O3 scales. Over 800°C the growth kinetics result from thickening of a predominantly orthorhombic Rh2O3 scale. At 1000°C the oxide becomes volatile.
The Controlled Oxidation of the High Chromium Steel Alloys Fe40Cr and Fe40Cr3Ru
m. j. van staden and j. p. roux, Appl. Surf. Sci., 1990, 44, (4), 263-269
Fe40Cr steel with and without 3% Ru added were exposed to O at different temperatures in an UHV system to find out how the Ru enhanced the corrosion resistance of the alloy. Cr was oxidised before Fe in both Fe40Cr and Fe40Cr3Ru, but only in the Ru alloy did the Cr also enrich the surface, at temperatures over 275°C, to form a substantial oxide, possibly because of an attractive interaction between Fe and Ru in the bulk.
New Compounds in the 30–40 at.% Ru Range of the Rare Earth-Ruthenium (R-Ru) Systems
a. palenzona and f. canepa, J. Less-Common Met., 1990, 162, (1), 267–272
New compounds were prepared and identified in the rare earth-Ru (R-Ru) systems and a complete compound formation scheme was constructed. Two new crystal structures were found and completely resolved. Y44Ru25 and Er3Ru2, while for a third one (RRux) the complexity of the structure prevented any structural determination.
Synthesis and X-Ray Crystal Structure of Trimesitylrhodium(III)
r. s. hay-moiherwell, b. hussain-bates, m. b.hursthouse and G. WILKINSON, J. Chem. Soc, Chem. Commun., 1990, (18), 1242–1243
The first neutral homoleptic aryl of Rh(III), Rh(2,4,6-Me3C6H2)3, was prepared by interaction of RhCl3(C4H8S)3 and mesitylmagnesium bromide. X-ray crystal studies showed that there is “agostic” interaction between Rh and an ortho-CH3 group in a distorted fac -octahedral geometry but no evidence for agostic H bonding was found. ‘ H NMR spectra over a temperature range indicate synchronised rotation of the mesityl group about the Rh-C bond.
A Novel Zwitterionicotho -Metallated Ruthenium(II) Phenolate
n. bag, s. b. choudhury, g. k. lahiri and a.chakravorty,J. Chem. Soc, Chem. Commun., 1990, (22), 1626–1627
Decarbonylative metallation of the dialdehyde by [Ru(PPh3)3Cl2] produced the unusual complex [Ru(MeL)(CO)(PPh3)2(Cl)]. X-ray crystallographic studies showed that the RuΙΙP2C2ClO co-ordination unit has a single net negative charge and the Ru(MeL) fragment incorporates a four-membered C,O-chelated phenolato function with a neighbouring monoprotonated azomethine moiety.
Preparation of Uniform Colloidal Metallic Ruthenium and Its Compounds
f. porta, w. p. hsu and e. matijevic, Colloids Surf., 1990, 46, (1), 63–74
Colloidal spherical particles with narrow size distribution of a Ru double salt, (NH3)2RuΙΙΙO(NO).2RuIVOCO3.5H2O were obtained by ageing solutions of RuCl3 containing K2 SO4 and urea at elevated temperatures. The amorphous product was readily converted to RuO2 by calcination at 400°C. The same original powder, dried and heated at 25O–30O°C in a stream of H2 yielded metallic Ru.
Complex Formation of Platinum with Tin(II) in Aqueous Solution of Malic Acid
p. g. antonov, t. p. lutsko and i. a. aganov, Zh. Obshch. Khim., 1990, 60, (8), 1846-1851
Studies of the interaction of K2PtCl4 with SnCl2.2H20 in 1 M malic acids at 20°C showed the formation of bimetallic Pt(II) complexes of anion type with maximum content of SnC4H3O5– ligands, with the molar ratio=5. Chloride ions in (Me4N)3[Pt(SnCl3)5] and (Me4N)6[Pt3(SnCl3)8] dissolved in the malic acid were completely replaced by malate-anions, thus preserving the Pt-Sn bond. During heating, Pt-Sn complexes undergo inter-molecular conversion, which result in the formation of bimetallic compounds with Pt oxidation order ~ 1.
Electrochemical Behaviour of Basal Single Crystal Pt Electrodes in Alkaline Medium
e. morall6n, j. l. vazquez and a. aldaz, J. Electroanal. Chem.Interfacial Electrochem., 1990, 288, (1&2), 217-228
The electrochemical behaviour of basal single crystal Pt electrodes in 0.1 M NaOH has been studied. The voltammogram for the Pt(111) surface orientation shows two clearly defined zones; one corresponds to weak H adsorption states and the other could tentatively be assigned to strong H adsorption states. The voltammogram for a Pt(100) surface shows four different H states while for the Pt(110) orientation only one H state is obtained.
Electrochemical Oxidative Cleavage of the Platinum-Hydrogen Bond in trans -[PtHCl(PEt3)2]
l. chen and j. a. davies, Inorg. Chim. Acta, 1990, 175, (1), 41–45
The electrochemical oxidation of the Pt(II) hydride, trans- [PtHCl(PEt3)2], in CH3CN containing NBu4ClO4 at a Pt gauze electrode produces almost exclusively Pt(II) complexes as products, none of which contain Pt-H bonds; trans -[PtCl(solvent) (PEt3)2]+ is the major oxidation product. Titrations on the electrochemically oxidised solutions show that Pt-H cleavage occurs with H+ formation. The overall oxidation process is therefore: H– → H+ and not Pt(II) → Pt(IV).
Reactor Control and Reaction Kinetics for Electrochemical Urea Oxidation
j. f. patzer, s. k. wolfson and s. j. yao, Chem. Eng. Sci., 1990, 45, (8), 2777–2784
The electrochemical oxidation of urea on anodic Pt surfaces to NH3 and CO2 was studied in the range 0.5–1.1 V relative to Ag/AgCl to develop a model to mimic the experimentally observed phenomena. The model indicates maximum urea current utilisation can be achieved by appropriately controlling the applied current density in the system. The absolute urea conversion rate can be maintained by increasing the available Pt surface area.
A New Fluoride Resistant Ceramic Electrode for Electrochemical Effluent Treatment Processes
s. k. harnsberger and i. romoda, Plat. Surf.Finish., 1990, 77, (7), 40–42
The effect of F ion on two inert anode materials, Pt-clad Nb and Ir oxide-coated Ti, and a new Ir oxide-coated Ti suboxide ceramic electrode was determined to find its effect when used for treating electrolyte effluent. The materials were tested under laboratory conditions in a H2 SO4 acid-based fluoride containing solution. The ceramic material had superior corrosion resistance and hence longer life than either of the metal oxides.
Corrosion Resistance and Electrochemical Behaviour of Platinised Porous Titanium Electrodes in Acid Media during Water Electrolysis
l. s. ivanova, t. g. bogatskaya, l. a. mikhailova, s. g. ogryz’ko-zhukovskaya, l. m. yakimenko, g. p. belyakov, a. g. vaganov and s. d. khodkevich,Electrokhimiya, 1990, 26, (6), 696–700
Studies were performed of the corrosion resistance of platinised porous Ti electrodes with a Pt layer deposited either galvanically or by ionic coverage using a magnetron, on thin (0.5 mm) porous (30%) Ti base during polarisation by a high density current of up to 1.0 A/cm2 in 10% H2 SO4 solution. Cumulative data of tested electrodes in a compartment with solid polymeric electrolyte are given.
Rectifying Bilayer Electrodes: Layered Conducting Polymers on Platinum
w. torres and m. a. fox, Chem. Mater., 1990, 2, (3), 306–311
The preparation of sequential bilayer structures made from any pair of polybithiophene, (I), polypyrrole, (II) and poly(3-bromothiophene), (III) by anodic electropolymerisation on Pt electrodes is described, and the electrochemical properties of the junction between the two conducting polymers are discussed. The polymers in the outer layers of the electrodes Pt/I/II and Pt/III/II can be trapped in the oxidised state for several hours and charge can be released from the outer layers via an appropriate redox couple in solution.
Hydrochloric Acid Electrolysis Using Solid Polymer Electrolytes. II. Gas Purity and Current Efficiency
i. uehara, y. kawami, n. wakabayashi, m. motone and h. takenaka, Denki Kagaku, 1990, 58, (5), 459–464
Current efficiencies and purities of H and CI in HC1 acid electrolysis by membrane-electrocatalyst composites of Ir-Pt/Nafion 117/Pt-Ir prepared by chemical plating were investigated over the range 1.7–12 mol/kg HC1 concentrations, and temperatures 25–75°C and current densities up to 100 A/dm2. Cathodic current efficiencies of 97–98% were found.
The Electroxidation of Methanol in the Potential Region of Platinum-Oxygen Layer
h. matsui and a. kunugi, Bull. Chem. Soc. Jpn., 1990, 63, (5), 1427–1432
Methanol oxidation at a Pt electrode in 0.5 mol/dm3 H2 SO4 at high potentials was retarded by the formation of an O layer and a new type of retarding substance from MeOH. During retardation due to the formation of O layer, the rate of MeOH oxidation decreased and increased with increasing O coverage and potential, respectively. Reverse effects in O coverage and potential concurrently occurred when the potential was variable. At low O coverage, the decreased effect from O coverage was more notable than the increased effect from the potential, but this reversed at medium coverages.
Electrochemical Activity of Silicides of Some Transition Metals for the Hydrogen Evolution Reaction in Acidic Solutions
a. k. vijh, g. belanger and r. jacques, Int. J. Hydrogen Energy, 1990, 15, (11), 789–794
The H evolution reaction was examined on silicides of transition metals in H2SO4 solutions. The highest rates were observed on Pt and Pd silicides, followed by those of Cu, Cr and Ni. If Fe silicides are used as typical transition metal silicides their electrocatalytic activity for the H evolution reaction is enhanced considerably by electrodepositing traces of Ru, and especially Pt on their surfaces.
Morphological Changes in Silver Colloidal Particles during Oxidative Treatment in Complex Solutions of Cold and Palladium
m. v. artem’ev, g. a. bramtskii and b. d. stashonok, Vest. Akad. Navuk BSSR, Ser. Khim. Navuk, 1990, (3), 33–37
The treatment of polychromatic imaging Ag particles in H2PdCl6 and HAuCl4 solutions resulted in a change in the spectral and colour properties of an image. During the process, the spectral Ag particles transform to Ag shells with Pd and Au particles being ultradispersed on a surface.
Poly(pyrrole-2,2’-bipyridyl Rhodium (III) Complexes) Modified Electrodes: Molecular Materials for Hydrogen Evolution and Electrocatalytic Hydrogenation
i. m. f. de ohveira, j.-c. moutet and n. vlachopoulos, J. Electroanal. Chem. Interfacial Electrochem., 1990, 291, (1&2), 243–249
The synthesis and electropolymerisation of new [RhΙΙΙ(L)2 Cl2] + BF4– complexes, where L = 2,2’-bipyridine bearing pendant pyrrole units, and the electrochemical behaviour of the resulting polymers are examined. Films of this material are highly stable for bulk electrocatalytic reactions, especially for efficiently reducing water to H2 and for the hydrogenation of cyclohexanone to cyclohexanol.
The Electrochemical Reduction of Cp*Rh Complexes
u. koelle, J. Electroanal. Chem. Interfacial Electrochem., 1990, 292, (1&2), 217–229
The electrochemical reduction of [Cp*RhCl2]2(l) or [(Cp*Rh)(µ -Cl)3]PF6(2) in methylene chloride and acetone and of [(Cp*Rh)(µ -OH)3]PF6 and Cp*Rh(acetone)n2 + in acetone was investigated by cyclic voltammetry and coulometry. An involved stepwise reduction sequence with electron transfer, Cl– loss and disproportionation from (1) or (2) produces the novel blue, air-sensitive, binuclear RuΙΙ species [Cp*RhCl]2.
Application of Ion Implantation/RBS to the Study of Electrocatalysis
e. j. kelly, c. e. vallet and c. w. white, J. Electrochem. Soc, 1990, 137, (8), 2482–2491
Ir-implanted Ti near-surface alloys were prepared by ion implantation, characterised by Rutherford backscattering (RBS) and subsequently anodically oxidised to form electrocatalytically active IrxTi1_xO2/Ti electrodes, and their electrochemical behaviour in acidic chloride, sulphate and perchlorate solutions was studied. The specific catalytic activities (rate per catalyst surface site) of IrxTi1_xO2/Ti and RuxTi1_xO2/Ti and their relative catalytic activities were evaluated. IrxTi1_xO2/Ti was only 45% as effective a catalyst for Cl2 evolution as RuxTi1_x/Ti, but it was far more stable, with a corrosion rate of only 5% that of RuxTi1_xO2/Ti.
Catalytic Oxidation of Methanol by Ruthenium Oxides
b. j. kennedy, a. w. smith and f. e. wagner, AuSt.J. Chem., 1990, 43, (5), 913–921
The electrocatalytic behaviour of Ru oxide/C electrodes for O evolution and MeOH oxidation in acid solutions is reported. The electrodes were characterised by various techniques which showed the Ru to be present as a mixture of RuIV oxides, including the stable rutile phase. Electrochemical studies show that a RuIV species promotes the catalytic oxidation of MeOH, while surface-bound RuO4 is involved in the O evolution reaction.
Topotactic Two-Phase Reaction of Ruthenium Dioxide (Rutile) in Lithium Nonaqueous Cell
t. ohzuku, k. sawai and t. hirai, J. Electrochem. Soc, 1990, 137, (10), 3004–3010
Electrochemical and X-ray diffraction studies were performed for the reduction of RuO2 with rutile structure in 1M LiClO4 propylene carbonate: 1,2-dimethoxyethane (1:1) solution. Ruo2 was topotactically reduced to LiRuO2 which is othorhombic via an intermediate phase having a tetragonal lattice. The reaction was reversible. Although three phases coexisted during the reduction of RuO2 and oxidation of Li1 0RuO2 the reaction was classified as a topotactic two-phase reaction where an intermediate phase existed between the RuO2 and LiRuO2 phases.
An Ultramicrostructured Photoelectrode System Composed of TiO2 Single Crystal and Layered SiO2 and Pt Thin Film
m. htramoto, k. hashimoto and t. sakata, Chem. Lett. Jpn., 1990, (8), 1343–1346
An ultramicrostructured photoelectrode system composed of a TiO2 single crystal and thin films of SiO2 and Pt was prepared by exposing the vertical section of the layered SiO2 and Pt film. The SiO2 layer is ~140 nm thick. The electrode showed photoresponse under irradiation in the presence of NH3, water vapour, EtOH and acetone. This may be the first microphotoelectrode system which can work in the gas phase.
Photocatalytic One-Step Syntheses of Cyclic Imino Acids by Aqueous Semiconductor Suspensions
b. ohtani, s. tsuru, s.-i. nishimoto, t. kagiya and k. izawa, J. Org. Chem., 1990, 55, (21), 5551–5553
Photocatalytic cyclisation using aqueous suspensions of TiO2 or CdS loaded with Pt oxides under Ar at room temperature was applied to the one-step synthesis of optically active cyclic imino acids, pipecolinic acid and proline from the α,ω-diamino carboxylic adds and their Nω-substituted derivatives.
A Direct Absorber Reactor/Receiver for Solar Thermal Applications
r. e. hogan, r. d. skocypec, r. b. diver, j. d. fish, m. garrait and j. t. richardson, Chem. Eng. Sci., 1990, 45, (8), 2751–2758
A novel catalytic reactor concept of 3.5 kW is described where concentrated radiant solar energy is directly absorbed on Rh/Al2O3, thus avoiding the heat-transfer limitations of conventional tubular reactors for high-flux conditions.
Photocatalytic Asymmetric Reduction of 3-Methyl-2-Oxobutanoic Acid with Chiral Rh(I) Complexes and Powdery Semiconductors
h. wang, t. sakata, m. azuma, t. ohta and h. takaya, Chem. Lett. Jpn., 1990, (8), 1331–1334
Photocatalytic asymmetric reduction of the title acid giving 2-hydroxy-3-methylbutanoic acid has been performed at up to enantiomeric excess of 60% in aqueous MeOH with chiral BINAP-Rh(I) complexes and semiconductor photocatalysts, TiO2 or CdS. The efficiency of the asymmetric reduction is still low, but the asymmetric hydrogenation of α-ketocarboxylic acid has been obtained without using H2.
Simultaneous Photodissociation of H2 and PMe2 Ph from OsH4 (PMe2 Ph)3: Production of Dimeric and Paramagnetic Osmium Polyhydrides
j. w. bruno, j. c. huffman, m. a. green, j. d. zubkowski, w. e. hatfield and k. g. caulton,Organometallics, 1990, 9, (9), 2556–2567
Concurrent photodissociation of H2 and PMe2Ph (=P) from OsH4P3 in benzene, THF and EtOH has been proved by chemical trapping. It is the first polyhydride to undergo two distinct photoprocesses with comparable efficiencies. The final products observed on photolysis of OsH4P3 under vacuum is an equilibrium mixture of Os2H4P6 and Os2H4P5. The former is also photosensitive, leading to products of P-CH3 cleavage (Os2H4(PMe2Ph)4(µ -PMePh)2), as well as to a product of Os-H heterolysis, [Os2H3P6+] [trans -OsH4P2–], which contains a unique paramagnetic polyhydride anion.
Spectral, Photophysical and Photochemical Properties of Ru(bpy)32+ on Porous Vycor Class
h. d. gafney, Coord. Chem. Rev., 1990, 104, (1), 113–141
The properties of Ru(bpy)32+ adsorbed on porous Vycor glass have been characterised. The complex is immobilised on the glass surface and can be quenched by O2, N2O and SO2. Other forms of quenching are discussed, as are the few differences in behaviour due to the Ru being on a solid support and not in a fluid medium. The net photoredox chemistry initiates with a two-photon ionisation of Ru(bpy) 32+. Electron conduction may occur by a surface mechanism.
A Luminescence Quenching Study on the Localization Problem of Ru(bpy)32+ in Micelles and Hemimicelles
j. t. kunjappu, p. somasundaran and n. j. turro,J. Phys. Chem., 1990, 94, (1), 8464–8468
Quenching studies on the luminescence emission of compound Ru(bpy)32+ with ferrocyanide ion, 9-methylanthracene and dioxylstearic acids were carried out in hemimicellar and micellar aggregates to gain insight into the location of this Raman and luminescence probe. Ru(bpy)32+ is bound to a more nonpolar hemimicellar hydrophobic region. Stern-Volmer constants for the doxylstearic acid quenching of its luminescence in micelles indicated that the optical electron in the metal-ligand charge-transfer state of the probe molecule resides in a bipyridyl ring which appears to be close to position 7 of the stearic acid chain.
Conversion of Light into Electricity with Trinuclear Ruthenium Complexes Adsorbed on Textured TiO2 Films
m. k. nazeeruddin, p. lbka, j. moser, n.vlachopoulos and m. grxtzel, Helvetica Chim. Acta, 1990, 73, (6), 1788–1803
A series of CN-bridged trinuclear Ru complexes of structure [RUL2(µ -(CN)RU(CN)L2′)2], where L=2,2’-bipyridine-4,4-dicarboxylic acid and L’=2,2’-bipyridine (1), and other bipyridines, etc, have been synthesised. The two carboxylic functions act as interlocking groups through which the dye is attached at the TiO2 film surface. The interlocking groups provide strong electronic coupling, allowing charge injection to proceed at quantum yields close to 100%. Monochromatic incident photon-to-current conversion efficiencies are >80% in some cases. Regenerative cells with these trinuclear complexes and ethanolic triiodide/iodide redox electrolyte have optimal results with (1), giving a fill factor of 75% and a power conversion efficiency of 11.3% at 520 nm.
Design of Antenna-Sensitizer Poly-nuclear Complexes. Sensitization of Titanium Dioxide with [Ru(bpy)2 (CN)2]2Ru(bpy(COO)2)22-
r. amadelli, r. argazzi, c. a. bignozzi and f. scan dola, J. Am. Chem. Soc., 1990, 112, (20), 7099–7103
The use of antenna-sensitiser molecular devices is proposed as a possible strategy to increase the light harvesting efficiency of sensitised semiconductors. The cyano-bridged trinuclear complex [Ru(bpy)2(CN)2]2Ru(bpy(COO)2)22– was prepared and studied. The complex adsorbs on TiO2 via the negatively charged -Ru(bpy(COO)2)22– central unit. Photophysical and photoelectrochemical studies were performed and emission and excitation spectra showed that in this complex the light energy absorbed by the terminal Ru(bpy)2(CN)2 (antenna) groups is efficiently funnelled to the central -Ru(bpy(COO)2)2-(sensitiser) fragment.
Electrodeposition and Surface Coatings
Deposition of Transition Metal and Mixed Metal Thin Films from Organometallic Precursors
h. d. kaesz, r. s. williams. r. f. hicks, j. i. zink. y.-j. chen, h.-j. muller, z. xue, d. xu, d. k. shuhand y. k. kim, New J. Chem., 1990, 14, (6/7), 527–534
High purity films of Pt, Ir, Rh, Ni and Re have been grown by organometallic chemical vapour deposition OMCVD (a), while thin films of Pt, Rh or Ir have been grown by photo-assisted OMCVD of volatile hydrocarbon precursors, but these contained more C than films grown under (a). Short-path OMCVD for organometallic precursors of limited volatility was used to deposit films of intermetallic compounds, PtGa2 and CoGa. Substrates to be coated are placed in the reaction tube at the temperature needed for controlled decomposition of the precursor complexes. The various hydrocarbon derivatives, carrier gases, substrates, light sources, temperatures and means of producing thin films are discussed.
Preparation of Thin Palladium Films by Use of an Electroless Plating Technique
s. uemiya, h. sasaki, t. matsuda and e. kikuchi, Nippon Kagaku Kaishi, 1990, (6), 669–675
An electroless plating technique was used to prepare supported thin Pd films permeable only to H. Before plating, Pd nuclei were depositied on the outer surface of a porous tube by sensitisation and activation treatments with Sn(II) chloride and Pd(II) chloride solutions, respectively. The rate of Pd deposition during plating was related to the Pd nuclei concentration, which increased with repeated number of treatments. Sn deposition retarded Pd deposition, but treating with AgNO3 solution before activation promoted the formation of Pd nuclei. An alkaline solution was used to plate the Pd on the porous glass tube, twice as fast as conventional plating methods.
Apparatus and Technique
An Oxygen Sensor Composed of Tightly Stacked Membrane/Electrode/Electrolyte
k. katakura, a. noma, z. ogumi and z.-i. takehara, Chem. Lett. Jpn., 1990, (8), 1291–1294
An O2 sensor which operates at room temperature has been constructed using Nafion, a porous Pt cathode directly deposited on Nafion and a polyethylene (PE) film directly covering the cathode surface. The sensor is amperometric and all the components are tightly stacked. The O2 reduction current is limited by the O diffusion rate through the diffusion-limiting PE film and it changes in proportion to O concentration of gases up to 100%.
Platinum Metal Etching in a Microwave Oxygen Plasma
c. h. chou and j. phillips, J. Appl. Phys., 1990, 65, (5), 2415–2423
The etching of Pt foils in an O plasma generated in a flow-type microwave system was studied as part of a general effort to understand the etching of metals in both plasma and chemical systems. It was found that very rapid etching (~6 Å/s) took place even at low power inputs of 200 W. The principal plasma parameters, including oxygen atom and ion concentrations, and electron temperature, were measured as a function of distance below the microwave coupler. Etching of Pt in an O plasma jet resulted from the concomitant action of O atoms and high energy electrons.
Use of Oxide Electrodes for Proton-Conductor Gas Sensor
n. miura, k. kanamaru, y. shimizu and n. yamazoe, Solid State Ionics, 1990, 40/41, (Part I), 452–455
An amperometric proton-conductor CO sensor operative at room temperature was developed by using a Pt/SnO2 and a Pt/WO3 electrode. The CO sensitivity of this sensor was about 7 times higher than the H2 sensitivity and the 90% response time was ~ 3 minutes. The sensor became H2 selective when a Pt-black electrode was combined with a Pt/WO3 electrode. Sensing mechanisms are discussed.
The Hydrolysis Products ofcis -Dichloro-diammineplatinum(II). 3. Hydrolysis Kinetics at Physiological pH
s. e. miller and d. a. house, Inorg. Chim. Acta, 1990, 173, (1), 53–60
The rate of hydrolysis of cis -PtCl2(NH3)2 has been measured in non-buffered aqueous solutions at I = 0.2 M NaCIO4 and T=45°C at constant pH over the range 4.0–8.5; the reverse reaction was also monitored. This allowed models for the hydrolysis of cis -PtCl2(NH3)2 under physiological conditions to be tested, and shows that the Rosenberg model for Pt(II) transport in vivo may need modification.
Study by UV-Visible Potential-Modulated Reflectance Spectroscopy of the Chemisorption of CO, Methanol and Ethanol on Several Noble Metal Electrodes
j. a. caram and c. gutierrez, J. Electroanal. Chem. Interfacial. Electrochem., 1990, 291, (1&2), 289–294
The title method has been used as a technique to determine the energy of electronic transitions in chemisorbed carbonyls and the type of bonding of CO. This was used to examine the electroadsorption of CO, MeOH and EtOH on Pt, Pd, Rh, Ru and Au electrodes. A maximum is reported, which depends only on the type of bonding of CO to the surface, i.e. linear, bridge-bonded or multiply bonded.
Manufacture and Performance of Rhodium/Carbon Multilayer X-Ray Mirrors
p. boher, p. houdy, p. kaikati, m. ouahabi and r. barchewitz,Appl. Phys. Lett., 1990, 57, (8), 834–836
A diode r.f. sputtering technique was used to produce Rh/C multilayers for application in the soft X-ray region. In situ kinetic ellipsometry, grazing X-ray reflectivity and absolute soft-X-ray reflectivity are used to make measurements. A model assuming a quasi-sharp C-Rh interface (4 Å thick) and a diffused Rh-C interface (22 Å) in the stack is used to fit the reflectivity curves at three experimental wavelengths. Reflectivities as high as 22% at 13.3 Å and 24% at 44.7 Å were measured on a 17-period multilayer structure having a period of =69 Å. One interface is relatively ideal and it is sufficient to give good reflectivities.
The Use of RuO4 in Studies of Polymer Blends by Scanning Electron Microscopy
b. ohlsson and b. tÖrnell, J. Appl. Polym. Sci., 1990, 41, (5/6), 1189–1196
Flat samples of blends of polypropylene (PP) and styrene-ethylene-butylene-styrene (SEBS) were contrasted with RuO4 and studied by SEM having a back-scattering electron (BSE) detector. The SEBS phase had bright areas with dark dots and the PP phase was dark. The dots were unstained EB-domains of the triblock SEBS polymer. This method gave high resolution images due to the intrinsic electrical conductivity on the surface from the deposited Ru species; the RuO4 vapour gave electrical conductivity to the stained areas. This method allows a BSE detector to be used in morphological studies.
A Heterogeneous “Ligand-Accelerated” Reaction: Enantioselective Hydrogenation of Ethyl Pyruvate Catalyzed by Cinchona-Modified Pt/Al2O3 Catalysts
m. garland and h.-u. blaser, J. Am. Chem. Soc, 1990, 112, (19)7048–7050
The effect of low modifier concentrations on the rate and enantioselectivity of ethyl pyruvate hydrogenation catalysed by Pt/Al2O3 modified with 10,11-dihydrocinchonidine (HCd) was studied in order to test the concept of “ligand-accelerated” catalysis for a modified heterogeneous system. The reaction mechanism was found to be in complete agreement with a simple two-cycle mechanism. The adsorption of HCd on the Pt surface must be reasonably strong and/or only a small fraction of the surface Pt is modifiable. Simple geometric considerations indicate that a modified ensemble should be one adsorbed cinchona molecule and 10–20 Pt atoms.
Sulphur-Resistant Character of Titania-Supported Platinum Catalysts
y. chen, y. chen, w. li and s. sheng, Appl. Catal., 1990, 63, (1), 107–115
The resistance of Pt/TiO2 catalysts to H2S was studied by pulse reactions with Pt/Al2O3 as a reference. Pt/TiO2 was found to be much more resistant than Pt/Al2O3 to H2S poisoning. The results showed that in TiO3 there is labile O that can react with H2S to form SOx or SO2, which leave the catalyst. Thus, with the Pt/TiO2 system a considerable part of S contamination is “auto-regenerated” and the poisoning effect of S on Pt is therefore mitigated. However, for the Pt/Al2O3 system, H2S decomposes on Pt giving H2 and PtS.
Study of Pt-Ga/Al2O3Catalysts. I. The Reaction of n-Hexane over Pt-Ga/Al2O3
y.-h. sun, s.-y. chen and s.-y. peng, J. Catal.(Dalian, China), 1990, 11, (4), 259–264
The reduction and chemisorption properties of the Pt-Ga/Al2O3 catalysts were studied during n-hexane conversion in a flow microreactor. The addition of Ga into Pt/Al2O3 improved its stability, and the catalyst containing >3.5% Ga promoted n-hexane conversion. The selectivity for aromatisation, isomerisation and hydrocracking could be adjusted by changing the Ga content of the catalyst.
Role of Sulfur in Catalytic Reforming of Hydrocarbons on Platinum-Rhenium/ Alumina
g. m. bickle, j. n. beltramini and d. d. do, Ind.Eng. Chem. Res., 1990, 29, (9), 1801–1807
Cyclohexane and n-heptane reforming were studied on 0.3–0.3% Pt-Re/Al2O3-0.95% Cl catalyst in the presence of S. The combined effect of Re-S and Pt-Si (where Si is the irreversible form of Pt) that modified the Pt ensemble size and the electronic interactions caused the hydrogenolysis and dehydrocyclisation activities to decrease. Due to the added effect of Re-S decreasing the ensemble size, the fewer “available” free Pt crystallites on Pt-Re/Al2O3 compared to Pt/Al2O3 means the toxicity of reversible S was greater for the bimetallic catalysts.
XPS Studies of Pt-Sn Naphtha Reforming Catalysts
y.-x. li, j. m. stencel and b. h. davis, Appl. Catal., 1990, 64, (1-2), 71–81
XPS studies of Pt-Sn catalysts with porous and non-porous Al2O3 and SiO2 gel surface areas of 250 m2/g and 110 m2/g, and 700 m2/g, respectively, were performed. Both Pt(0) and Sn(0) were observed in the reduced samples. Sn(0), and alloy formation, occurs when Pt and Sn are added as a complex dissolved in acetone. The ratio of Pt(0) to Sn(0) varies, at constant Pt loading, with the total amount of Sn added in the preparation. This Pt:Sn ratio varies from about 0.4 to about 6 for the catalysts studied.
Molecular Die Catalysis: Hexane Aromatization over Pt/KL
s. j. tauster and j. j. steger, J. Catal., 1990, 125, (2), 387–389
Studies of n-hexane aromatisation over 0.6–0.8% Pt/KL, prepared by exchanging zeolite L powder with Pt(NH3)4Cl2 solution at room temperature for 20 h, and l%Pt/SiO2 catalysts were performed at 510°C, 100 psig pressure, with a H2/hexane mole ratio of 6. Pt/KL catalysts showed a much greater selectivity for hexane aromatisation than Pt/SiO2 catalysts and a strong preference for cracking the terminal C-C bond as opposed to interior bonds.
Preparation of Platinum Cluster Catalyst Supported on Porous Chelate Resin-Metal Complexes for Hydrogenation of Olefin and Diene
n. toshima, t. teranishi, h. asanuma and y. saito, Chem. Lett. Jpn., 1990, (5), 819–822
Catalysts of Pt clusters/chelate resin-metal complexes of Na(I), Mg(II), and Al(III) were prepared by reduction of Pt ions immobilised on the high porosity supports. The catalytic activity of the supported clusters increased in the order: Na(I)<Mg(II)<Al(III), which is consistent with increase in surface area of the resin.
Kinetics of Liquid-Phase Hydrogenation of Cinnamaldehyde over a Pt-Sn/Nylon Catalyst
e. tronconi, c. crisafulli, s. galvagno, a. donato, g. neri and r. pietropaolo, Ind. Eng.Chem. Res., 1990, 29, (9), 1766–1770
The kinetics of liquid-phase hydrogetion of cinnamyl alcohol and cinnamaldehyde over Pt/nylon and Sn-Pt/nylon catalysts were studied. The kinetics of cinnamaldehyde hydrogenation over Sn-Pt/nylon at 10–60°C were interpreted on the basis of a two-site model, where B sites, associated with Sn, were involved in hydrogenation of cinnamaldehyde and hydrocinnamaldehyde, whereas A sites, associated with Pt, catalysed cinnamyl alcohol hydrogenations. The results show strong adsorption of cinnamyl alcohol on Pt sites, which also explains the apparent negative activation energies of some rate constants.
Carbon Monoxide Restructuring of Palladium Crystallite Surfaces
r. f. hicks, h. qi, a. b. kooh and l. b. fischel, J.Catal, 1990, 124, (2), 488–502
Six Pd/Al2O3 catalysts, with dispersions ranging from 3 to 86% were studied during repeated cycles of exposure to CO at 25°C and reduction at 300°C. CO cycling lowers the dispersion of all the samples by 20 to 50%. The loss of surface sites was higher on the small crystallites. The adsorption capacity recovered with oxidation at 550°C and reduction at 300°C. The H solubility in the bulk of the Pd crystallites was not affected by CO cycling. Surface restructuring may be used to enhance the catalytic activity of Pd.
Selective Acetylene Hydrogenation in Mixtures with Ethylene in the Presence of a Palladium Catalyst
i. m. zhvanetsky and a. s. berenblyum, Neftekhimiya, 1990, 30, (4), 453–457
Studies of hydrogenation of C2H2-C2H4 mixture on Pd/γ-Al2O3 catalyst performed at 311–373 K in a wide range of reagents concentrations showed the formation of C2H6 from the intermediate compound systems ZH2-C2H4 (where Z are new active centres of the catalyst) which proceeds in two paralled routes. It is shown that in the case of C2H2-C2H4 interaction, the mechanism of ethylene and acetylene with H2 is the same as that during hydrogenation of individual hydrocarbons.
The Effect of Bismuth on the Selective Oxidation of Lactose on Supported Palladium Catalysts
h. e. j. hendriks, b. f. m. kuster and g. b. marin, Carbohydrate Res., 1990, 204, 121–129
The selective oxidation of lactose by O2 has been studied in a batch reactor containing an aqueous slurry of 0.5 kmol/m3 and 1.0 kg/m3 of Pd/C promoted by Bi. This resulted in 100% selectivity to Na lactobionate up to conversions of 95% in the pH 7–10 range and at up to 333K. A maximum initial reaction-rate of 0.47 mol/kg s occurred at molar Bi:Pd of 0.5–0.67. Other aldoses could be oxidised with similar selectivities.
Activity and Selectivity of 1-Hexene Conversion on SAPO-11 and Pd/SAPO-11
s. j. choung and j. b. butt, Appl. Catal., 1990, 64, (1–2), 173–189
The activity and selectivity patterns for 1-hexene reactions were compared at 150–450°C for four different kinds of acidic zeolites (H-mordenite, HZSM-5, SAPO-11 and Pd/SAPO-11) with different acid properties and geometric structure. The Pd/SAPO-11 catalyst gave enhanced double bond shift (DBS) selectivity and less cracking at higher temperatures in comparison to unloaded SAPO-11. There was a strong correlation between the shift from DBS to cracking with total acidity.
An Infrared Study of the Hydrogenation of Carbon Monoxide and Carbon Dioxide at High Pressure over Pd/La2O3
h. d. burkett, s. d. worley and c. h. dai, Chem.Phys. Lett., 1990, 173, (5,6), 430–434
A new high-pressure IR cell reactor has been used to study the reactions of CO and CO2 with H2 over Pd/La2O3 films at a pressure of 8300 Torr. The activation energy for the CO2 hydrogenation (25.1 kcal/mol) which produces MeOH is higher than that reported elsewhere for the analogous CO hydrogenation reaction. The CO2 reaction may proceed through hydrogenation of adsorbed CO, rather than by direct hydrogenation of CO2 over Pd/La2O3.
Structure-Sensitivity of the Deactivation of Pd/SiO2 for Methylcyclopropane Hydrogenolysis by CO
j. b. butt and c. l. m. joyal, J. Chem. Soc, Faraday Trans., 1990, 86, (16), 2911–2917
Pd/SiO2 catalysts with 5–80% metal exposed have been characterised for reactivity for methylcyclopropane hydrogenolysis as a function of CO poisoning. The CO surface coverage and metal crystallite size are important in the deactivation behaviour of the catalyst. Pretreatment conditions help to determine reaction and deactivation structure sensitivity patterns. As CO coverage increases a monotonic decrease in activity occurs for large Pd particles, while catalysts with >40% metal exposed have a near-step drop in activity between 20–30% coverage.
Effects of Promoters of Palladium/Silica Catalysts for the Synthesis of Methanol
h. s. hahm and w. y. lee, Appl. Catal., 1990, 65, (1), 1–9
Methanol synthesis from syngas on promoted Pd/SiO2 catalysts was carried out at 1–20 atm (H:CO = 2) and 230–310°C. The effects of Ca, K or La promoters on the activity and selectivity for methanol formation were studied. The highest methanol activity was achieved with 0.5wt.% Ca promoted Pd/SiO2 catalysts and was about four times higher than that of non-promoted catalyst.
Effects of Cerium Addition on the CO-NO Reaction Kinetics over Alumina-Supported Rhodium Catalysts
s. h. oh, J. Catal., 1990, 124, (2), 477–487
Laboratory reactor studies showed that the addition of Ce to a low-loaded Rh/Al2O3 catalyst resulted in changes in CO-NO reaction kinetics, mainly suppression of N2O formation, decreased apparent activation energy, and a shift to a positive-order dependence of the rate on NO partial pressure. The Ce-induced modification of the kinetics leads to increases in the NO reduction activity at low temperatures.
Effect of Potassium on the Formation of Isocyanate Species in the NO + CO Reaction on Rhodium Catalyst
ě. novák and f. solymosi, J. Catal., 1990, 125, (1), 112–122
Adsorption and IR spectroscopic studies of the effect of K on the formation of isocyanate species in the NO + CO reaction on supported Rh catalysts showed that the addition of K to 5% Rh/Al2O3 significantly decreased the uptake of H2, CO and NO at 300 K. Preadsorbed K caused a significant increase in the formation of the NCO complex, with the maximum intensity obtained for a sample containing 2.5% K. The same effect was observed on Rh/SiO2 catalyst where two NCO species were identified (2180cm–1 for Rh-NCO and 2310cm–1 for Si-NCO).
CO Adsorption on Rhodium(I) and on Metallic Rhodium Supported on Titanium Dioxide
j. herrero, c. blanco, a. r. gonzález-elipe, j. p.espinós and l. a. oro, J. Mol. Catal., 1990, 62, (2), 171–177
The interaction between a cationic organometallic Rh(I) compound and TiO2 in acetone leads to Rh(I)/TiO2. The reduction with H2 at atmospheric pressure and ambient temperature yields a supported metallic Rh catalyst which is active in 1-hexene hydrogenation. The precursor and catalyst have been characterised, and the predominant species is dicarbonyl on both. Dissociative CO adsorption is discussed.
Selectivity Changes in the Ring-Opening Reaction of Methylcyclopentane over Rhodium Catalysts Caused by the Addition of Silver and Metal-Support Interactions
r. j. fenoglio, g. m. nuñez and d. e. resasco, Appl. Catal., 1990, 63, (2), 319–332
The hydrogenolysis of methylcyclopentane (MCP) was studied over Rh-Ag/TiO2 catalysts after various reduction/oxidation treatments. The addition of Ag resulted in a decrease in activity, accompanied by an increase in the selectivity toward n-hexane (n-Hx). This increase in selectivity was enhanced when Ag and Rh are impregnated simultaneously and when the catalysts are reduced at 773 K. The selectivity changes can be interpreted in terms of a shift in the ring-opening mechanism. This shift is caused by a blockage of large ensembles required to constitute the multi-site complexes. This blockage would be more effective when Ag and TiOx species are simultaneously present on the Rh surface.
Carbon Dioxide Hydrogenation on Rhodium Supported on Transition Metal Oxides. Effect of Reduction Temperature on Product Distribution
a. trovarelli, c. mustazza, g. dolcetti, j. kašparand m. graziani, Appl. Catal, 1990, 65, (1), 129–142
Studies of the effects of metal reduction conditions during CO hydrogenation on Rh/TiO2 and Rh/Nb2O5 catalysts showed the presence of C1-C6 hydrocarbons which followed Anderson-Schulz-Flory statistics. For Rh/TiO 2, the role of CO as an intermediate in CO2 hydrogenation was clearly evident. In both catalysts, the formation of the SMSI state (strong metal-support interaction) during high temperature reduction greatly affected catalytic activities and selectivities. The differences in the general behaviour of the two oxides as far as the reversibility of the SMSI in the reaction conditions was concerned was ascribed to thermodynamic and/or kinetic constraints in the formation of SMSI during high temperature reduction.
Synthesis of Hydrocarbons and Alcohols from CO and H2 over Co-Rh Catalysts
a. l. lapidus, z. novak, m. m. savel’ev, b. lyukke, t. zimmerman, s. d. pirozhkov, kh. e. manek, s. d.sominskii and l. f. rar, Izv. Akad. Nauk SSSR, Ser. Khim., 1990, (8), 1707–1709
Studies of synthesis of hydrocarbons and alcohols from CO and H2 (CO:H2 = 1:2) over Co catalysts promoted by addition of Rh and Cu were performed at 250–300°C and pressure of 0.1–6.0 MPa. The results show that 4.5% Co-0.1% Rh-5:10% Cu/TiO2 catalysts are highly active in the above synthesis and have much higher selectivity in regards to the formed alcohols as compared to the traditional Co-catalysts.
Immobilization of Rhodium Complexes with Chiral Cationic Water Soluble Ligands on Nafion-H and Other Strongly Acidic Cation Exchange Resins
i. tóth, b. e. hanson and m. e. davis, J. Organomet. Chem., 1990, 397, (1), 109–117
Rhodium complexes of the chiral cationic water solubleligands,[(S, S)-2,4-bis[-bis(-p -N, N -dimethyl-ammoniumphenyl)phosphino]pentane]4 +, etc., were immobilised on cation exchange resins. All these supported complexes catalyse the asymmetric hydrogenation of dehydroaminoacid derivatives with no detectable loss of Rh into the substrate phase. Rates and enantioselectivities depend on the ligand and the nature of the exchange resin.
IR Study of CO Adsorption and Its Interaction with Oxygen over Ir/Al2O3 Catalyst
h.-y. lou, y.-z. chu, c.-i. xu and y.-s. zhou, J.Catal, 1990, 11, (4), 284–289
An IR study of the behaviour of CO adsorption and its interaction with O over Ir/Al2O3 catalyst showed that CO adsorption on Ir/Al2O3 with high Ir loading was an activation process, and the intensity of the adsorbed CO band increased with the increase in adsorption temperature from ambient to 300°C. The amount of adsorbed CO at 150°C was approximately one half that of the maximum. The migration of adsorbed CO and O was increased by increasing the temperature.
Zeolite A-Supported Ru Catalysts
j. c. s. wu, j. g. goodwin and m. davis, J. Catal., 1990, 125, (2), 488–500
A number of zeolite A-supported Ru catalysts were prepared either by addition of Ru precursor to the zeolite A synthesis gel [ZS] with resulting metal being dispersed intrazeolitically, although not uniformly, or by surface deposition of Ru on zeolite A with metal particles primarily on the external surfaces of the zeolite crystallites. With the exception of the strong molecular sieving effect on the reaction of cyclopropane found for RuNaA[ZS], the most important effect on the catalysis was Ru particle size.
Surface Structure and Catalysis for CO Hydrogenation of the Supported Ru Species Derived from the Ru3 (CO)12 Inorganic Oxides
k. asakura and y. iwasawa, J. Chem. Soc, Faraday Trans., 1990, 86, (14), 2657–2662
Supported Ru cluster particles were prepared by the surface reaction of Ru3(CO)12 with inorganic oxides followed by H2 reduction at 723 K. On V2O5 the cluster was converted to three-atomic-layer Ru metal particles, while one-atomic-layer [Ru]n clusters were formed on SiO2 (n=12) and TiO2 (n = 6). Clusters [Run(OZ)x] (Z=A1 or Mg) with Ru-O surface bonds were formed on Al2O3 (n=6), K-doped Al2O3 (n = 6) and MgO (n = 3). CH4 was predominantly formed on [Ru] 12/SiO2. The 6-Ru atom clusters with Ru-Ru distances of 0.262–0.265 nm had the highest selectivity for C2-C4 hydrocarbon formation. Metallic [Ru]6 clusters on TiO2 had higher activity than [Ru6(OAl)x] clusters bonded to the surface through O atoms. The smallest surface-bound clusters on MgO produced mainly CH4 and CO2.
A New Platinum-Based Catalyst System for Olefin Asymmetric Homogeneous Hydroformylation
s. paganelli, u. matteoli and a. scrtvanti, J. Organomet. Chem., 1990, 397, (1), 119–125
A number of Pt(II) diphosphino complexes in combination with SnCl2 are known to be active in olefin hydroformylation. It is now reported that the complex [Pt(C2H4)((+)–DIOP)] interacts with [PtCl2((+)–DIOP)] to give catalysts active in the hydroformylation of styrene and 1-hexene. The activities of the systems depend upon the molar ratio of the two Pt complexes and the nature of the substrate. The systems display good chemioselectivity and induce asymmetry in the branched aldehydes formed. 2-Phenylpropanal can be isolated in ~27% optical purity from styrene hydroformylation.
Evidence for a Bis(alkylidene) silacyclopropane Intermediate in the Platinum-Mediated Formation of a Silacyclobutene
a. c. dema, c. m. lukehart, a. t. mcphail and d. r. mcphail, J. Am. Chem. Soc, 1990, 112, (20), 7229–7233
The treatment of Ph 2 Si(C = CCMe 3) 2 with a cationic Pt-H reagent resulted in the formation of a 4-alkylidene-l-silacyclobutenyl ring system. Acetic acid cleaves at Pt-C bond to yield alkenylsilane products, showing the intermediate formation of a Pt, Si-µ -alkenylidene complex. ROH reagents react with a proposed bis(alkylidene)silacyclopropane intermediate to initiate ring opening and to form η3- butadienyl complexes (where R=H, Me, Et or Ph). The R = H complex ion structure was confirmed.
Hydroformylation with Platinum Phosphinito Complexes
p. w. n. m. van leeuwen and c. f. roobeek, New J. Chem., 1990, 14, (6/7), 487–493
Pt complexes containing phosphinito ligands afford active hydroformylation catalysts at 30–100 bar and 80–100°C. The hydroformylation rates for α -alkenes are the same as those obtained with Pt-trichlorostannate catalysts. Products are a mixture of alcohols and aldehydes with linearities in excess of 90%. Internal alkenes can also be hydroformylated with linearities as high as 70%.
Homogeneous Catalysis of Platinum Blue Related Complexes in Photoreduction of Water into Hydrogen
k. sakai and k. matsumoto, J. Mol. Catal, 1990, 62, (1), 1–14
The evolution of H2 is reported on dissolving platinum blues [Pt2(NH3)4(C4H6NO)2]2(PF6)4, [Pt4(NH3)8(C4H6NO)4](NO3)2(PF6)3.5H2O, etc. in water. The H2 seems to be due to an interaction between [Pt4(NH3)8(C4H6NO)4]6+ (1) and proton. A homogeneous photochemical H-producing catalyst system is made with (1) or [Pt4(NH3)8 (C5H4NO)4l5+, using EDTA as sacrificial electron donor, and Ru(bpy)32+ as photosensitiser and MV2 + as electron relay. Quantum yields for their H2 production are 0.022 and 0.11, respectively.
Palladium-Catalyzed Hetero- and Carboannulation of Vinylic Cyclopropanes and Cyclobutanes
r. c. larock and e. k. yum, Synthesis, 1990, (9), 529–530
ortho -Functionally substituted aryl iodides react under mild conditions with vinyl- and isopropenylcyclopropane and isopropenylcyclobutane in the presence of Pd(II) acetate and an appropriate base, K acetate, triethylamine or Na carbonate to give 2-(I-alkenyl)-substituted 2,3-dihydrobenzofurans, indolines and indans in good yield. This gives a novel versatile route to a variety of heterocycles and carbocycles, amenable to unsaturated cycloalkanes, 1,2-, 1,3- and 1,4- dienes as well as alkynes.
Carboxylic Acid Transvinylation as Catalysed by Complexes of Palladium Acetate with Phenanthroline-Like Ligands
a. a. ketterling, a. s. lisitsyn, a. v. nosov and v.a. likholobov, Appl. Catal., 1990, 66, (1), 123–132
The complexing of Pd acetate with di-imine ligands results in a promotion effect on the vinyl exchange processes and ensures excellent selectivity and stability of the catalyst under reaction conditions. Vinylation of both saturated and unsaturated carboxylic acids by vinyl acetate proceeds smoothly even at an increased concentration of H2O in the mixture.
Heteropoly Anion-Modified Palladium Catalyst for Reductive Carbonylation of Nitrobenzene
y. izumi, y. satoh and k. urabe, Chem. Lett. Jpn., 1990, (5), 795–796
An efficient catalyst system of PdCl2 and Keggin-type heteropoly anions containing Mo and V which had a noticeable promoting effect on the Pd, were used in a reductive carbonylation of nitrobenzene to form N-phenylcarbamate in the presence of alcohol in dimethoxyethane solvent. Turnover numbers were 98 and 196 in terms of moles of Pd and heteropoly anion.
π-Olefin-Palladium-Copper Complexes as Intermediates in Formation of Propylene Glycol Monoacetate during Oxidation of Propylene in the System PdCl2/CuCl2/HOAc
a. v. karandin, e. v. gusevskaya, v. a. likholobov, a. g. stepanov and e. p. talzi, Kinet katal, 1990, 31, (3), 580–584
Studies of the kinetic and physical-chemical mechanisms during propylene oxidation by O2 in the system PdCl2/CuCl2/HOAc were performed by various electron spectroscopic techniques. The contact of propylene-oxygen gaseous mixture with acetate solutions of PdCl2, CuCl2, LiCl and LiOAc resulted in a catalytic reaction yielding propylene glycol monoacetate and acetone.
Phase Transfer Pd(0) Catalyzed Polymerization Reactions. III. Polymerization by Cross-Coupling of Alkyl-Boron Compounds and Aromatic Halides Catalyzed by PdCl2(dppf) and Bases
e. cramer and v. percec, J. Polym. Sci.: Part A:Polym. Chem., 1990, 28, (11),3029–3046
A novel one flask polymerisation of a sequence of hydroboration of a diolefin with 9-borabicyclo[3.3.1]nonane followed by the inter-molecular cross-coupling of the resulting α -ω -bis(B-alkanediyl-9-borabicyclo[3.3.1] nonanes with dihaloarenes is described. The reactions are catalysed by PdCl2(dppf) and a base and are performed in a two-phase (organic liquid-liquid or solid-liquid) phase transfer catalysed system. This provides unique synthetic routes to the preparation of functional polymers containing C-C bonds in the main chain.
Hydrodechlorination of CCl4 in the Presence of Pd(OAc)2
g. s. dasaeva, s. m. velichko, yu. a. treger and i.i. moiseev, Kinet. katal., 1990, 31, (4), 858–862
Methane was produced by the reaction of H 2 on CC14 in acetic acid in the presence of Pd(OAc)2 catalyst under 0.1 MPa and at 20–80°C. In the presence of aliphatic alcohols, CH4 content in the reaction products decreased sharply yielding chloroform and ethyl chloride as main hydrodechlorination products.
Synthetic Methodology Involving the Carbopalladation of Allenes
b. cazes, Pure Appl. Chem., 1990, 62, (10), 1867–1878
Carbopalladation of allenes by vinylic or arylic Pd species (vinylic or arylic halides+ Pd(0)Ln catalyst) gives new 2-substituted η -allyl Pd complexes, which have interesting stereochemical properties due to the conjugated unsaturated system on the central C atom of the η 3 -allyl ligand, and react with high regio and stereoselectivities with delocalised carbonucleophiles. The overall process creates two new C-C bonds in a single reaction and leads to functionalised 1,3-dienic (or styryl) compounds of known stereochemistry.
Expanding Industrial Applications of Palladium Catalysts
j. tsuji, Synthesis, 1990, (9), 739–749
A review of Pd in industry as homogeneous and heterogeneous catalysts classifies them into having oxidative reactions with olefins and aromatic compounds and oxidative carbonylation, by Pd(II) salts and appropriate reoxidants; and Pd(0) complexes for reactions of organic halides and reactions via π-allylPd complexes. Careful selection of reaction conditions, solvents, choice of ligand and catalyst modifiers are necessary to achieve long catalyst life and high selectivity. (89 Refs.)
Rhodium Phosphine Complexes as Acetalization Catalysts
j. ott, b. schmid, l. m. venanzi, g. wang, t. r.ward and g. m. ramos tombo, New J. Chem., 1990, 14, (6/7), 495–498
Complexes containing Rh(III) triphos moieties as catalyst precursors have been studied for acetalisation and trans -acetalisation reactions. The complexes are reactive under mild conditions and give a high turnover rate and induce interesting diastereoselectivities. For methyl-substituted acetals [RhCl3(triphos )l (1) with substrate:catalyst ratio 2000:1 can be used, though a ratio of 10,000:1 may be possible. Proton-sensitive substrates can be acetalised with (1), giving products with yields of 80–90%.
Asymmetric Metal Complexes Catalysis. 5. Asymmetric Hydrosilylation on the Phosphine Complex [Rh(COD)Cl]2(S)-Phephos
e. yu. zhorov, v. a. pavlov, yu. d. koroshkov ande. i. kladunovskii, Izv. Akad. Nauk SSSR, Ser. Khim., 1990, (9), 1951–1955
Studies of the asymmetric hydrosilylation of acetophenone by diphenylsilane in the presence of [Rh(COD)Cl] 2 (S)-Phephos showed high activity and enantioselectivity of the catalysts. Enantioselectivity of the catalyst increased with increase in the reaction temperature, and the reaction still proceeded at acetophenone:Rh ratio of up to 20,000.
Optically Active Phenanthrolines in Asymmetric Catalysis. III. Highly Efficient Enantioselective Transfer Hydrogenation of Acetophenone by Chiral Rhodium/3-Alkyl Phenanthroline Catalysts
s. gladiali, l. pinna, g. delogu, s. de martin, g.zassinovich and g. mestroni, Tetrahedron:Asymmetry, 1990, 1, (9), 635–648
The in situ catalysts prepared from [Rh(Diol)Cl]2 (Diol = l,5-hexadiene or 1,5-cyclooctadiene) and 3-alkylphenanthrolines display extremely high catalytic activity in the transfer hydrogenation of acetophenone. Turnover rates up to 10,000 cycles/h have been recorded in 2-propanol solution at 83°C, with KOH as promoter. Asymmetric inductions up to 65% e.e. have been obtained, using a ligand with a chiral trimethylpropyl substituent. In the asymmetric process the most active and stereoselective catalytic species might be a Rh hydride complex containing two phenanthroline ligands in a chiral C2 array.
An Experimental and Modelling Study of Polybutadiene Functionalization to Polyaldehydes Using a Homogeneous Rhodium Catalyst
s. j. tremont, e. e. remsen and p. l. mills, Chem.Eng. Sci., 1990, 45, (8), 2801–2808
The liquid-phase hydroformylation of a polybutadiene containing 1,2 and 1,4 olefin units can be performed using a homogeneous Rh-phosphine ligand catalyst (Wilkinson’s) with excess phosphine ligand at mild reaction temperatures. The product is a polybutadiene whose degree of olefin unit functionalisation can be controlled through use of proper reaction conditions. The olefin units in the polybutadiene are selectively hydroformylated to the 1,2 terminal branched and 1,4 internally branched aldehyde products. The aldehyde addition is reasonably uniform in the range of polymer molecular weight.
Unusual Activity and Selectivity in Alkyne Hydrosilylation with an Iridium Catalyst Stabilized by an O-Donor Ligand
r. s. tanke and r. h. crabtree, J. Am. Chem. Soc, 1990, 112, (22), 7984–7989
Studies of alkyne hydrosilylation by Ir in the O-donor ligand environment of Grim’s triso ligand (=tris(diphenyloxophosphoranyl)methanide) showed that the reaction is selective for 1-alkynes and regioselective for β -products. However, it gave the thermodynamically less favoured cis -vinylsilane products by an unexpected anti addition of Si-H to the triple bond. Mechanistic studies suggest that the alkyne first inserts into the M-Si, not the M-H, bond and that a trans to cis rearrangement occurs via an η2 - vinyl intermediate before reductive elimination. A number of Rh and Ir complexes of the type [(triso)ML2] are prepared.”
Selective Oxygenation of Aliphatic Ethers Catalyzed by Ruthenium(Il) Complexes
m. bressan, a. morvillo and g. romanello, Inorg. Chem., 1990, 29, (16), 2976–2979
Studies of selective and fast conversions of primary ethers to esters (or lactones) were performed using Li hypochlorite in the presence of catalytic amounts of Ru(II) complex catalysts RuX2L4 (L is (CH3)2SO and (L)2 is l,3-bis(diphenylphosphino)propane). Isopropyl ether undergoes oxidative cleavage to acetone, while secondary ethers bearing methylene groups in the β -position are converted into β -keto ethers. Methyl ethers are unaffected by the oxidation.
A New Ruthenium(VI) Oxidant: Preparation, X-Ray Crystal Structure, and Properties of (Ph4)[RuO2(OAc)Cl2]
w. p. griffith, j. m. jolliffe, s. v. ley and d. j.williams, J. Chem. Soc, Chem. Commun., 1990, (18), 1219–1221
The title compound was obtained by the addition of RuO4 inCCl4 to a slight excess of PPh4 Cl and glacial acetic acid in acetonitrile, followed by recrystallisation or by recrystallisation from dichloromethane-CC14. The compound has a quasi-trigonal bipyramidal structure with a symmetrically bound acetato ligand and cis -dioxo ligands in the trigonal plane. It is an effective oxidant for halides, alcohols, sulphides and phosphines, functioning catalytically in the presence of N -methylmorpholine-N -oxide.
Autocatalysis and Free Radical Mechanism in a Ruthenium Cluster Catalysed Hydrogen Transfer Reaction
s. bhaduri, d. mukesh and k. sharma, J. Chem. Soc, Chem. Commun., 1990, (21), 1506–1508
The mechanisms of the [(Ph3P)2N][H3Ru4(CO)12] (1) catalysed disproportionation and transfer-hydrogenations of cyclohex-2-en-l-one have been shown to involve free radicals. In the latter reaction (1) is converted to other carbonyl species via autocatalysis. Spectroscopic analyses at the end of a catalytic run at 82°C and 5h, and > 100 turnovers of cyclohexanol with (1) as the precatalyst showed that all of (1) was converted into a mixture of soluble carbonyl and hydridic species.
Ruthenium-Catalysed C-H Bond Activation. Evidence for a Concerted Mechanism in Oxyfunctionalization of Cyclic Saturated Hydrocarbons
a. tenaglia, e. terranova and b. waegell, J. Chem. Soc, Chem. Commun., 1990, (19), 1344–1345
Oxidation of bridged polycyclic alkanes with in situ generated RuO4 occurred by a concerted mechanism involving interaction of the highly electrophilic oxo Ru species with tertiary unhindered C-H bonds. However, it is not yet clear whether an alkoxyhydroxo- or alkoxyhydrido-oxo Ru species was involved as a key intermediate.
Oxo Transfer and Metal Oxidation in the Reaction of [Ru(PPh3)3Cl2] with m -Chloroperbenzoic Acid; Structure of [Ru(PPh3)2(m -ClC6H4CO2)Cl2]
s. chattopadhyay, n. bag, p. basu, g. kumar lahiri and a. chakravorty, J. Chem. Soc, Dalton Trans., 1990, (11), 3389–3392
One mol and 0.5 mol of peracid were consumed for oxo transfer to PPh3 and oxidation of metal, respectively, in the reaction of [Ru(PPh3)3Cl2] with m-ClC6H4CO3H. X-ray studies of the product [Ru(PPh3)2(m-ClC6H4CO2)Cl2] showed that after oxo transfer the carboxylate residue remains chelated to the metal centre. The trans,cis,cis-RuP2O2Cl2 co-ordination sphere has two-fold symmetry. The complex undergoes one-electron quasi-reversible reduction but only at low potentials.
“Development of Advanced Noble Metal-Alloy Electrocatalysts for Phosphoric Acid Fuel Cells (PAFC)”
p. stonehart, Ber. Bensenges. Phys. Chem., 1990, 94, (9), 913–921
Highly dispersed Pt and Pt alloys for PAFC electrocatalysts of crystallite size 12 Å diameter are discussed. For the cathodes advanced alloys have been developed of higher performance than Pt. For anodes diluting the Pt with less expensive materials gives a superior performance to Pt alone. For O reduction modifications to produce ordered alloys have given stability for over 9000 hours in the hot PAFC environment, as have alloys of Pt-Co and/or Cr containing Ga additions. For H oxidation Pt-Pd alloys show greater tolerance to poisoning and greater stability against crystallite growth. For successful commercialisation fuel cells must achieve high performance, low cost and long life.
Electrical and Electronic Engineering
Display of Wide Dynamic Range Infrared Images from PtSi Schottky Barrier Cameras
j. silverman, j. m. mooney and v. e. vickers, Opt. Eng., 1990, 29, (2), 97–104
Twelve-bit digitised infrared images taken with PtSi Schottky barrier detector arrays have been processed on work stations. Two techniques for 8-bit global display are compared. The projection technique gives superior results based on an extensive set on indoor, day and night imagery. The new projection algorithm can be used as a powerful and robust local contrast enhancement technique. A real-time implementation of the projection alogrithm is now incorporated into a specially designed camera and gives a very satisfactory automated alternative to the offset/gain controls.
Temperature Dependence of the Resistance in the Pt/Ti Nonalloyed Ohmic Contacts to p-InAs Induced by Rapid Thermal Processing
a. katz, s. n. g. chu, b. e. weir, w. c. dautremont-smith, r. a. logan, t. tabun-ek, w. savin and d. w.harris, J. Appl. Phys., 1990, 68, (8), 4141–4150
The temperature dependence of the resistance in the Pt(60 nm)/Ti(50nm) nonalloyed ohmic contacts to p- InAs (Zn doped 1 x 1018 to 1 x 1019/cm3) induced by rapid thermal processing at 300–600°C was studied. The ohmic nature of these contacts was attributed to both the low metal-semiconductor interfacial barriers and to the heavily doped semiconductor contacting layers. The results showed conversion from thermionic emission as the dominant carriers transport mechanism across the interfacial barrier for the as-deposited sample to a combination of thermionic and field emission mechanisms for the heat-treated samples.
Electrical and Structural Properties of Pt/Ti/p+-InAs Ohmic Contacts
a. katz, s. n. g. chu, b. e. weir, w. savin, d. w. harris, w. c. dautremont-smith, t. tanbun-ek andr. a. logan, J. Vac. Sci. Technol. B, 1990, 8, (5), 1125–1127
The thermally stable Pt/Ti metallisation scheme was applied to Zn doped p +-InAs layers to evaluate the influence of the outstanding electrical properties of the p +-InAs, such as the narrow band gap and the surface Fermi level pinning in the conduction band on the ohmic contact performance. Zn doping was 1×1018 to 1x1019/cm3. After rapid thermal processing for 30 s the specific contact resistances were lowered to <6 × 10–7 Ωcm2 for a 450°C anneal. This heat treatment enhanced limited reactions in both the Pt/Ti and Ti/InAs interfaces, but did not degrade the stable microstructure.
Hole Trap Level in Pt-Ti/p -InGaAs/n -InP Heterostructures Due to Rapid Thermal Processing
k. l. jiao, a. j. soltyka, w. a. anderson and a.katzs, Appl. Phys. Lea., 1990, 57, (18), 1913–1915
Deep level transient spectroscopy and I-V-T measurements were performed on Pt-Ti/p -InGaAs/n -InP heterostructure mesa diodes annealed by rapid thermal processing (RPT). Four electron trap levels with activation energies of 0.61, 0.45, 0.35 and 0.30 eV were observed which are believed to be native defects in InP, and they were independent of RTP conditions. A new hole trap, with an activation energy of 0.89 eV was found only for samples annealed at >500°C and thought to be introduced by Ti diffusion at high temperature. I-V-T data were consistent among all samples, indicating that the hole trap level is not dominant in the current mechanism.
Stability of Amorphous Ir-Ta Diffusion Barriers between Cu and Si
r. de reus, r. j. i. m. koper, h. zeijlemaker and f.w. saris, Mater. Lett., 1990, 9, (12), 500–505
Thin film amorphous Ir-Ta (a-IrTa) was tested as a diffusion barrier between (100) Si and Cu. Sandwich structures of (100) Si/a-IrTa/Cu/a-IrTa were stable during annealing in vacuum up to 700°C. At 750°C interdiffusion of Cu and Si occurred. The crystallisation temperature of thin film a-Ir45Ta55 was reduced from 900 to 750°C in the presence of Cu. The high stability of the metallic a-IrTa buffer layer makes it useful for application in miniaturisation of very large scale integrated electronics.
Metal Complexes as Anticancer Agents. The Future Role of Inorganic Chemistry in Cancer Therapy
b. k. kepler, New J. Chem., 1990, 14, (6/7), 389–403
A review of the background and reasons for the success of cisplatin in the treatment of various tumours is discussed. Other metal complexes with cancer inhibiting properties for chemotherapy are examined; these include Ru compounds, Ti compounds and possibly Au and Sn compounds; as well as drug targetting with Pt complexes showing affinity to hormone receptors and osteotropic properties. (77 Refs.)
[Bis(aminomethyl)dimethylsilane] platinum(II)dichloride: A Potential Antitumor Agent
r. d. haugwitz, w. k. anderson, j. plowman, r. kaslinal, d. m. houston and v. l. narayanan, Appl. Organomet. Chem., 1990, 4, (4), 375–378
The tide compound was synthesised by a three-step procedure and its anti-tumour activity was investigated against L1210 leukaemia in mice. With suitable dosing it extended the life span by at least 100% and resulted in 40–50% survivors (day 30) in two experiments. It appeared to be as least as active as cisplatin under these conditions.
Effect of Palladium Addition on the Tarnishing of Dental Cold Alloys
m. ohta, m. nakagawa and s. matsuya, J. Mater. Sci.: Matter. Med., 1990, 1, (3), 140–145
Tarnishing tests were performed on Au-Cu-Pd and Au-Cu-Ag alloys. Tarnish resistance was almost perfect for the alloys with nobility of >50%, but it seemed to relate to the Pd:Au atomic ratio for the alloys with low nobility. Pd inclusion reduced the tarnish susceptibility up to ~ 10 at. %. Tarnishing of the alloy with low nobility was very sensitive to its microstructure. Pd-bearing alloy showed no increase in the degree of tarnishing by phase separation. This may be attributed to the enrichment of Pd in the Cu-rich phase.