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Platinum Metals Rev., 1990, 34, (2), 98

ABSTRACTS: April 1990

of current literature on the platinum metals and their alloys

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PROPERTIES

The Adsorption of Nitric Oxide and Nitrogen Dioxide on Polycrystalline Platinum

d. t. wickham, b. a. banse and b. e. koel, Surf. Sci., 1989, 223, (l/2), 82-100

New temperature programmed desorption studies of NO and NO2 adsorption on polycrystalline Pt are reported. NO adsorption is irreversible for NO exposures <0.12L at 120K yielding only N2 and O2 upon heating. Reversible NO adsorption occurs at >0. 12L NO exposure. Two NO desorption states occur with peaks at 470 and 300K. No desorption of NO2 resulting from oxidation of NO was observed at any coverage. NO2 adsorption at 120K is largely irreversible below monolayer saturation coverages. However, a small NO2 desorption peak is observed at 300K at a monolayer coverage of NO2. NO and O2 TPD spectra following NO2 exposures are quite different from those spectra obtained following NO or O2 exposures.

Ethylene Adsorption and Decomposition on (2×1)Pt(110)

y. yagasaki, a. l. backman and r. i. masel, f. Phys.Chem., 1990, 94, (3), 1066-1072

The adsorption and decomposition of C2H4 on the (2×1) Pt(110) surface was examined by TPD and EELS. The C2H4 adsorbs molecularly to yield a mixture of di-σ and π-bound C2 H4. On heating some of the adsorbed C2H4 desorbs, some reacts to form ethane and some decomposes to yield a mixture of ethylidyne, ethan-1-yl-2-ylidyne and H2. Other changes occur upon further heating. This is a different chemistry to that on the closed packed faces of Pt, and other Pt faces. Thus the intermediates which form when C2H4 adsorbs on Pt depend strongly on the surface structure and are not simply a combination of the chemistry seen on the closed packed faces of this metal.

Anomalous Behavior of Magnetization for PtMnSb/CuMnSb Multilayer Films

k. takanashi, m. watanabe and h. fujimori, f.Appl. Phys., 1990, 67, (1), 393-397

Metallic multilayer films of ferromagnetic PtMnSb and antiferromagnetic CuMnSb were prepared by a rf sputtering method, making different thicknesses by using different numbers of Pt and Cu sheets. X-ray diffraction showed the films to have a [III] texture of the Clb-type Heusler structure. The magnetisation measured in the PtMnSb/CuMnSb multilayers was larger than that in PtMnSb. The temperature magnetisation dependence shows a bend at 50 K, near the Neel temperature of CuMnSb.

Brillouin Study of Spin Waves in Sputtered CoNiPt Alloy Films

a. murayama, m. miyamura, s. ishikawa and y. oka, J. Appl. Phys., 1990, 67, (1), 410-413

The characteristics of sputtered CoNiPt films for high-density longitudinal recording media have been studied by Brillouin scattering. The spin-wave spectra are broadened to a width of 13 GHz, which is much larger than the 3 GHz of a vapour deposited film. TEM shows the sputtered film consists of separated Co crystallites of diameter 50-100Å. Spin wave damping in the sputtered film is caused by the film structure. The film is elastically homogeneous. Segregation of the non-magnetic Pt-related alloys takes place between the Co crystallites. The exchange stiffness constant was 2.4 × 10-9 Oe cm2 in the sputtered film.

Characterization of (Methylcyclopentadienyl)trimethylplatinum and Low-Temperature Organometallic Chemical Vapor Deposition of Platinum Metal

z. xue, m. j. strouse, d. k. shuh, c. b. knobler, h. d. kaesz, r. f. hicks and r. s. williams, f. Am.Chem. Soc., 1989, III, (24), 8779-8784

5 -Methylcyclopentadienyl)trimethylplatinum, (η5 -MeCp)PtMe3 (MeCp=CH3C5H4) has been synthesised and its physical properties and structure determined. For deposition of metallic Pt, a stream of Ar gas at ambient pressure was first saturated with the vapour of (η5 -MeCp)PtMe3 at 23°C. This was then conducted into a chamber containing H2 such that the ratio Ar:H2 =4:1. A film of highly reflective Pt metal was deposited on a heated (120°C) substrate placed near the outlet of the saturated Ar gas stream. The films had high purity, containing <1 at.% C.

Dynamical Behaviour of Pt-Rh(100) Alloy Surface during Dissociative Adsorption of NO and Reaction of NO with H2

h. hirano, t. yamada, k.-i. tanaka, j. siera and b. e. nieuwenhuys, Surf. Sci., 1989, 222, (1), L804-L808

Exposure of a clean Pt0.25Rh0.75(100) alloy surface to NO or NO+H2 at > 440K produced a sequential change of the LEED pattern. Observations of the LEED patterns along with results of AES studies suggest that atomic N has equal affinity to Pt and Rh atoms so that the atomic N does not distinguish the Pt and Rh sites on the alloy surface. On the other hand atomic O makes a stronger bond with Rh atoms so that Rh atom segregation onto the surface is induced. By reacting randomly distributed Rh atoms on the Pt-Rh(100) surface with oxygen, a surface compound is built.

Pt2Si Formation: Diffusion Marker and Radioactive Silicon Tracer Studies

m. a. e. wandt, c. m. comrie, j. e. mcleod and r. pretorius, f. Appl. Phys., 1990, 67, (1), 230-236

The moving species during the formation of first-phase Pt2Si by thermal annealing has been identified using inert markers Ti, Co, Ge, As and radioactive 3l Si as a tracer. Experiments with thin-film structures using a reference marker at the substrate Si/amorphous Si interface and a mobile marker near the amorphous Si/Pt interface show a shift of the Pt marker towards the surface of the sample. The radioactive tracer, initially embedded in nonradioactive Si and metal, is moved from this position and concentrates at the sample surface.

Adsorption Kinetics of CO on Pd(100)-S Surface

r.-s. zhai, t. yamada and k. t amaru, f. Catal. (Dalian, China), 1989, 10, (4), 352-356

Studies of the adsorption kinetics of CO on the surface of Pd(100) modified by S showed the formation of CO precursor state molecules on the clean Pd(100) surfaces formed during CO adsorption. Addition of S adatoms on Pd(100) surface reduces the lifetime of precursor molecules. No precursor molecules are formed when S coverage on Pd(100) surface is >0. 16. The effect of S adatoms on Pd(100) surface is stronger than that on Ni surface.

Magneto-Optical Properties of Co/Pd Superlattice Thin Films

s.-c. shin and a. c. palumbo, f. Appl. Phys., 1990, 67, (1), 317-320

Co/Pd superlattice thin films were prepared by electron beam evaporation of Co and Pd on quartz substrates under vacuum, and the polar Kerr and ellipticity hysteresis loops at wavelengths 780nm were measured to assess their magneto-optical properties. The remnant Kerr rotation was strongly dependent on the Co and Pd sublayer thicknesses and on the total film thickness. The maximum polar Kerr rotation of 0.43° was observed at the film thickness of 110Å, where each bilayer was composed of 2Å thick Co and 9Å thick Pd sublayers.

Perpendicular Magnetic Anisotropy in Sputtered CoPd Alloy Films

s. hashimoto, y. ochiai and k. aso, fpn. f. Appl. Phys., 1989, 28, (9), I596-I599

Magnetic properties of CoPd alloy films prepared by rf magnetron sputtering have been studied as a function of the Pd content. CoPd films showed extraordinarily large magnetostriction constants of the order of 10-4 in a Pd-rich composition. The strong perpendicular magnetic anisotropy is related to the magnetostrictive effect. The CoPd films with perpendicular anisotropy can be used as perpendicular magnetic recording media. Furthermore, thin CoPd films of <100Å have high Kerr rotation and perfect squareness of Kerr loop suitable for magneto-optics.

Microscopic Properties of Co/Pd Multilayers Studied by Ferromagnetic and Nuclear Magnetic Resonance

h. a. m. de gronckel, c. h. w. swÜste, k. kopinga and w. j. m. de jonge, Appl. Phys. A, 1989, 49, (5), 467-472

The microscopic properties of Co/Pd multilayers have been studied by ferromagnetic and nuclear magnetic resonance. The anisotropy of the layer was found to decrease for decreasing Co sublayer thickness and a switching of the magnetic preferential direction occurred below 8Å. The anisotropy was also found to be a function of Pd layer thickness: below 20Å it increased with decreasing thickness-attributed to a decrease in the Pd/Co interface contribution to the anisotropy. Hyperfine field spectra showed that layers with [III] texture are mainly polycrystalline f.c.c. and that the Co “lattice” is stretched due to neighbouring Pd atoms when Co sublayer thickness is decreased. Comparison with studies of almost single phased [100] f.c.c. Co/Pd multilayers suggests that the expansion of the Co “lattice” is nearly isotropic.

AES Characterization of the Oxides Formed on the Fe-40Cr-Pd and Pd-Implanted Fe-40Cr Alloys at 500°C

s. c. tjong and j. b. malherbe, Appl. Surf. Sci., 1989 40, (1/2), 1-7

Auger electron spectroscopic (AES) studies of the oxide films formed on Fe-4oCr-Pd alloys that have been oxidised in air at 500°C, showed that they consist of a very thin Fe oxide at the oxide/gas interface, intermediate Cr-rich oxide and innermost PdO layer next to the substrate alloys. Addition of 0.92 wt.% of Pd to the Fe-40Cr alloy was found to be very effective at promoting the formation of a thinner oxide film. High doses of Pd implantation (1015 ions/cm2) improved the oxidation resistance of the Fe-40Cr alloy by the formation of a thinner oxide scale.

Reduction and Cluster Growth of Palladium in Zeolite Y Containing Transition Metal Ions. X-ray Absorption Studies

k. moller and t. bein, f. Phys. Chem., 1990, 94, (2), 845-853

The effect of a second transition metal on the reducibility and agglomeration behaviour of Pd in zeolite Y was studied by EXAFS spectroscopy. Zeolite Y was co-exchanged with Fe2+ or Co3+ and Pd2+ and with each ion alone. Dehydration in O2 and reduction with H2 was performed at different temperatures up to 623K. Pd is partially reduced to Pd0 at room temperature and forms small metal clusters at higher temperatures. Only a small increase in the reducibility of Pd is observed if Fe is present in zeolite while co-exchange with Co results in a much higher dispersion of the Pd(o) phase after high temperature reduction. Diffusion of Pd ions into zeolite containing aqueous Fe(II) ions resulted in formation of a Pd(o) phase of larger crystallites at room temperature by a redox reaction with Fe(II).

Kinetics of Adsorption, Thermal Desorption and Dissociation of NO on Rhodium, Studied by Pulsed Field Desorption

n. kruse, g. abend and j. h. block, Colloq. Phys., Colloq. C8, 1989, 50, (11), 147-151

The interaction of NO with stepped surfaces of a Rh field emitter has been studied by pulsed field desorption (PFD) mass spectrometry. At 300< T < 550 K and pressure < 1.3 × 10-3 Pa, PFD mass spectra of the adsorbed layer were always dominated by NO+, RhxNn+ and RhOn+ ions (n,x = 1,2). It is concluded that part of the adsorbed NO undergoes dissociation with subsequent deposition of O and N atoms on the surface. At low coverages (θ<0.1 monolayer) NO adsorption was found to be predominantly molecular. Using a probe-hole technique the equilibrium between NO adsorption and thermal desorption was monitored. The temperature dependence of mean lifetimes before thermal desorption was measured and activation energy evaluated.

Morphology and Charge Capacity of Sputtered Iridium Oxide Films

j. d. klein, s. l. clauson and s. f. cogan, f. Vac Sci. Technol. A., 1989, 7, (5), 3043-3047

Iridium oxide films deposited on stimulation wires by rf-sputtering show markedly different surface morphologies and charge capacities in response to variations in deposition conditions. The morphology of sputtered Ir oxide films (SIROFs) on composite wire specimens consisted of well-defined closely packed ellipsoidal platelets with various degrees of alignment, which is not observed in SIROF-coated substrates having planar surfaces. The film appearance and electrochemical properties were found to be strongly dependent on the H2O:O2 ratio in the sputter gas. Increasing H2O:O2 from 0 to 0.22 resulted in a marked rotation of the direction of net alignment of the SIROF platelets and reduced anodic and cathodic charge capacities. The anodic charge capacities were remarkably linear with respect to the logarithm of the cyclic voltammetry sweep rate.

Solubility of Ruthenium Dioxide in Lead Borosilicate Glasses

p. palanisamy, d. h. r. sarma and r. w. vest, f. Am. Ceram. Soc., 1989, 72, (9), 1755-1756

The solubility of RuO2 in a Pb borosilicate glass and the effect of 2%, 4%, 6% and 10% A12O3 dissolved in the glass have been studied at 700-1000°C. The solubility showed an exponential dependence on temperature. The dissolved alumina decreased the solubility at any given temperature, however, the solubility was essentially the same in all of the Al2O3-containing glasses. The Kelvin equation was used to deduce the concentration of RuO2 in glass as a function of the curvature of the RuO2 particles, and the dependence was found to be quite small. The implications of the results in processing thick film resistors using RuO2 as the conductive phase and these glasses as insulating phases on an alumina substrate are discussed.

CHEMICAL COMPOUNDS

Transformation of O2S(C = CCMe3)2 to an Exoalkylidene Thiete 1,1-Dioxide Ligand by Pt-H Addition and Rearrangement Reactions

c. m. lukehart, a. t. mcphail, d. r. mcphail and m. d. owen, f. Chem. Soc., Chem. Commun., 1990, (3), 215-217

Addition of a Pt-H bond to the C ≡ C bond of an alkynyl substituent of a dialkynylsulphone occurred regioselectively to yield an exoalkylidene thiete 1,1-dioxide ligand following a subsequent insertion and rearrangement of the second alkynyl substituent. A proposed mechanism for the unusual formation of the heterocyclic ligand is presented.

Conversion of Aquapentammine Complexes of Ir(III), Rh(III) and Pt(IV) in Aqueous Acid Solutions at Higher Temperatures

n. ya. rogin, a. v. vershkov and g. d. mal’chikov, Izv. Vyssh. Uchebn. Zaved., Khim. Khim. Tekhnol., 1989, (8), 18-21

Studies of primary systems in acid solutions of [Pt(NH3)5OH](ClO4)3 [Rh(NH3)5H2O](ClO4)3 and [Ir(NH3)5H2O](ClO4)3, were performed at 130-200°C. In 0.1M solution of HClO4, two parallel aqueous processes were observed yielding internal ammine, and metallic Pt, Rh and Ir. In HCl solutions, however, the replacement of internal ammine occurred forming ammonia-chloride forms.

Preparation of Organopalladium Sols by Thermal Decomposition of Palladium Acetate

t. tano, k. esumi and k. meguro, f. Colloid Interface Sci., 1989, 133, (2), 530-533

It has been shown that the thermal decomposition of Pd acetate dissolved in various solvents with a boiling point > 110°C gives organo-Pd sol. In particular, using methylisobutylketone, uniform spherical particles with a diameter of 260nm are obtained for Pd acetate concentrations of 2-4×10-3 mol/dm3.

Mixed-Metal Carbido-Carbonyl Clusters. Part 4. Synthesis and Structural Characterization of [Rh6C(CO)13-{Au2(PPh3)2}]

a. fumagalli, s. martinengo, v. g. albano, d.braga and f. grepioni, f. Chem. Soc., Dalton Trans., 1989, (12), 2343-2346

The new mixed-metal carbido-carbonyl cluster species [Rh6C(CO)13{Au2(PPh3)2}] was prepared by reaction of [Rh6C(CO)13]2- with [Au(PPh3)Cl]. The crystal structure studies showed them to be orthorhombic with space group Fdd2, a = 22.335(4), b = 31.710(6), c = 14.947(7) Å, Z = 8, R = 0.045, and R’ = 0.047. The compound reacts easily with CO at 1 atm and room temperature, yielding the bicapped trigonal prism [Rh6C(CO)15{Au(PPh3)}2].

Extended Linear Metal-Metal Interactions in an Anionic Rhodium(I) Complex. X-Ray Structure of NMe4[Rh(ox)(CO)2] (ox = oxalato)

j. real, j. c. bayÓn, f. j. lahoz and j. a. lÓpez, f. Chem. Soc., Chem. Commun., 1989, (24), 1889-1890

In the search for new anisotropic materials, the complex NMe4[Rh(ox)(CO)2] (ox=oxalato) has been prepared by bubbling CO through NMe4[Rh(ox) (cod)] (cod = 1,5-cyclooctadiene). The latter complex was prepared from Rh2Cl2(cod)2, oxalic acid, and NMe4OH. The solid state structure of NMe4[Rh(ox) (CO)2] consists of infinite chains of metal atoms [Rh... Rh... Rh 175.01(3)°] with equal Rh-Rh distances of 3.243(1)Å, the shortest distance found in a stacked Rh complex.

ELECTROCHEMISTRY

Oxygen Exchange on Platinum Electrodes in Zirconia Cells: Location of Electrochemical Reaction Sites

n. l. robertson and j. n. michaels, f. Electrochem. Soc, 1990, 137, (1), 129-135

Oxygen exchange kinetics on porous Pt electrodes in a yttria-stabilised ZrO2 electrochemical cell have been measured at 600-800°C in 10-5-0.21 atm O2 by steady-state polarisation and potential-step chronoamperometric experiments. Results are compared with models from the literature which incorporate the two different locations of the electrochemicals reaction. The results indicate that O exchange becomes limited by surface diffusion of O and that charge transfer occurs at the three-phase boundary where the electrode, electrolyte and gas-phase intersect, and not in the two-phase interface between the electrode and electrolyte.

Activation Parameters for Oxygen Reduction Kinetics in Trifluoromethane Sulfonic Acid Systems

m. a. enayetullah, t. d. devilbiss and j. o’m.bockris, . f Electrochem. Soc, 1989, 136, (11), 3369-3376

The kinetics of O2 electroreduction on Pt in concentrated trifluoromethane sulphonic acid (TFMSA) have been studied at elevated temperatures up to ~90°C, using microelectrode techniques, in order to obtain data at conditions more appropriate to fuel cell operation. Results are compared with those for concentrated H3PO4. The activation energies for the reaction in ~9.5M, 6.0M and 3.0M TFMSA were 17, 20 and 29 kJ/mol, respectively, as compared to 66 kJ/mol in 98 wt.% (w/o) H3PO4. The exchange current densities in concentrated TFMSA were three orders of magnitude higher than in 98 w/o H3PO4, and diffusion-limiting current densities were two orders of magnitude higher. The solubilities and diffusion coefficients of O2 in TFMSA were evaluated, and their role in the current-potential for O2 reduction in these electrolytes is discussed.

Electrode Performance of a Thin-Film YSZ Cell Set on a Porous Ceramic Substrate by rf Sputtering Technique

n. nakagawa, h. yoshioka, c. kuroda and m. ishida, Solid State Ionics, 1989, 35, (3,4), 249-255

The performance of an electrode consisting of sputter-deposited Pt fixed between a yttria-stabilised zirconia (YSZ) film and a porous Al2O3 substrate was found to be superior to electrodes consisting of sputter-deposited Pt, or paste-baked Pt, on a YSZ film or pellet. The impedance measured in air for the superior electrode morphology was more than 3 orders of magnitude smaller than that of the others.

Titanium-Palladium Cathodes for Acid Media

v. n. fateev, k. o. ragimov, v. p. pakhomov, m.ya. bakirov, b. g. vladimirov and n. p. aparina, Electrokhimiya, 1989, 25, (11), 1455-1460

Studies of the effect of alloying of Ti electrodes with Pd- ions on the corrosion properties of the electrodes were performed in 1N H2SO, at 18°C. The Pd alloyed Ti electrodes were highly active and stable in H2 SO4, when the cathodic current density was 0. 1 A/cm2. The Pd alloyed Ti electrodes could be used therefore in electrolytic systems of low current density, such as photoelectrochemical apparatus based on electrolyser with solid polymer electrolytes.

Electrochemical and Surface Characterization of the Passive Film on Fe-Cr-Pd Alloys

s. c. tjong, Surf. Coal. Technol, 1989, 38, (3), 325-338

Electrochemical measurements have indicated that an Fe - 40Cr-0. 2Pd alloy undergoes spontaneous passivation in 0.5M HCl solution at 25-85°C. However, an Fe-40Cr-0-1Pd alloy showed spontaneous passivation in this solution only at 25-60°C. An Fe - 40Cr alloy implanted with Pd ions needed an implantation dose > 2.1×1015 Pd ions/cm2 for the maintenance of spontaneous passivation. AES studies showed that the spontaneously passivated film formed on the Fe - 40Cr-0. 2Pd alloy in o. 5M HQ at 25°C was enriched in Pd relative to Cr. However, the passivated film formed anodically at 220 mV was strongly enriched in Cr. XPS measurements indicated that the Pd is present as Pd2+, whereas Cr is present as Cr3+.

An Approach to the Cold Fusion through Hydrogen Isotopes Analysis by the Heavy Ion Rutherford Scattering

m. yanokura, m. minami, s. yamagata, s. nakabayashi, m. aratani, a. kira and 1. tanihata, Chem. Lett. fpn., 1989, (12), 2197-2200

Pd electrodes either etched with concentrated H2SO4 or loaded with D2 gas were ion beam analysed before and after electrolysis in different electrolytes to find any production of T and He-3, and to measure the H and D contents. The etched samples had only H peaks, while the loaded samples had only D peaks.

Electrocatalytic Properties of Ion-Implanted Oxide Films

l. elfenthal, t. patzelt, j. w. schultze and o. meyer, Mater. Set. Eng., 1989, A116, 71-77.

Studies have shown that the implantation of TiO2 films with Pd+ and Ru+ enhances the electrocatalytic activity due to the formation of surface states. Additionally, the electronic conductivity increases by the formation of defect states due to the radiation damage and metal states within the band gap. Xe+ implantation creates only defect states. At low potentials O2 reduction activity was enhanced, especially for the Ru+-implanted electrode. On the other hand, the anodic i/v curves of Cl2 evolution at Ru+-implanted TiO2 showed a small and decreasing activity caused by corrosion of the implanted metal. It is expected that a larger concentration of noble metals could yield a reasonable catalysis.

Electrocatalysis and Determination of Hydrazine Compounds at Glassy Carbon Electrodes Coated with Mixed-Valent Ruthenium(III,II) Cyanide Films

j. wang and z. lu, Electroanalysis., 1989, 1, (6), 517-521

Chemically modified electrodes, which were prepared by anodising glassy C electrodes in a Ru-Cl3/K4Ru(CN)6 solution are shown to enable the kinetically hindered oxidation of hydrazine compounds to proceed at significantly lower potentials than at the bare C surface. The mixed-valent Ru cyanide film offers improved stability and a broader operational pH range compared to previously described phthalocyanine-catalytic surfaces. The modified surfaces maintain long-term catalytic activity and are highly suitable for electrochemical detection of industrially and environmentally important hydrazine compounds in acidic and neutral solutions. Highly stable and sensitive flow injection measurements (with a relative standard deviation of 1.4% (n = 30) and a detection limit of 0.13 ng) are reported. Furthermore, a composite film with polyaniline offers additional advantages.

The Passivation of Fe-Cr-Ru Alloys in Acidic Solutions

a. higginson, r. c. newman and r. p. m. procter, Corros. Sci., 1989, 29, (11/12), 1293-1318

Electrochemical and surface analytical techniques have been used to study the spontaneous passivation of Fe-4oCr-Ru alloys in 0.5 M H2 SO4 and HCl. Passivation is achieved more readily in alloys with 0.2 w/o Ru than with 0.1 w/o Ru, and is more rapid in 0.5 M H2SO4 than 0.5 M HCl. Ru causes a positive shift in corrosion potential by the simultaneous catalysis of H, evolution and the inhibition of the anodic dissolution of Fe-40Cr. The enrichment and redistribution of Ru by a surface diffusion process occurs during this period of selective dissolution. The rate of this surface diffusion is an important factor in determining the geometry of the Ru distribution, and its efficiency in promoting spontaneous passivation.

PHOTOCONVERSION

Thermoelectrochemical Cell: A Newer Approach to Solar Energy Conversion

s. c. ameta, p. k. jain and d. sharma, Z. Phys. Chem. (Leipzig), 1989, 270, (6), 1242-1244

Different phase changing compounds have been used with methanol as solvent in a thermoelectrochemical cell containing a Pt electrode in one limb and a saturated calomel electrode in the other. When the limb containing the Pt electrode was illuminated with IR radiation, the thermopotential and thermocurrent generated were 267 mV and 38 μA, respectively, when Co chloride was used as phase changing compound. Current-voltage characteristics of 3 such cells, their power point, fill factors and conversion efficiencies were determined.

Mechanism and Quantum Yield of Hydrogen Photoevolution from a Suspension of Pt/TiO2 in Sacrificial Electron-Donor Solutions

s. sato, Shokubai, 1989, 31, (6), 469-472

The quantum yield of H2 photoevolution from a suspension of Pt/TiO2 was >100% in dialcoholic solutions, indicating that a current doubling effect is operative in semiconductor photocatalysis. Although anatase has 0.1eV more negative conduction band than rutile, they gave similar yield in alcoholic and EDTA solutions. Anatase showed higher photoactivity in the other electron-donor solutions. This result is discussed in relation to the results of IR spectroscopy and photoluminescence experiments. It is concluded that a direct, irreversible reaction of holes with adsorbed alcohol makes Pt/TiO2 particle potential so negative that electrons are inevitably used for hydrogen evolution.

A Comparative Study of Semiconductor Photocatalysts for Hydrogen Production by Visible Light Using Different Sacrificial Substrates in Aqueous Media

j. sabatÉ, s. cervera-march, r. simarro and j. gimenez, Int. f. Hydrogen Energy, 1990, 15, (2), 115-124

Three types of semiconductor photocatalytic systems have been tested for H2 productivity: Pt/TiO2 plus sensitisers like Ru(bipy)3 2+ and RuL32+, where L is 2,2’-bipyridine-4,4’-dicarboxylate; naked CdS, Pt/CdS and RuO2/CdS; and mixtures of CdS + Pt/TiO2 and CdS and ZnS coprecipitated on 7-A12O3. Systems with sensitisers had poor stability and only gave H2 with EDTA present. CdS + Pt/TiO2 gave highest reaction rates for H2 production in isopropanol medium, and CdS, naked or with Pt deposits gave the best results when sulphide or sulphide/sulphite were sacrificial agents. Adding sulphite to sulphide aqueous solution increased H2 production rate 4 times. Maximum photochemical and energy efficiencies of 13.2 and 5.0%, respectively, occur for 300-520 nm wavelengths.

Analytical TEM Study of the Selective Photocatalytic Deposition of Platinum on Titania-Silica Mixtures and Silica-Supported Titania

j.-m. herrmann and j.-l. mansot, f. Catal., 1990, 121, (2), 340 - 348

The selectivity of the photodeposition of Pt in the case of two biphasic supports (TiO2 and SiO2 mechanical mixture and SiO2-supported TiO2) containing only one photosensitive constituent (TiO2), has been studied. For both kinds of support, the photodeposition of Pt corresponding to 1 wt.% Pt was complete, and exclusively on the TiO, constituent of the biphasic supports. This method of metal deposition could be used to decorate a multicomponent support with a noble metal, the metal being exclusively deposited on the photo sensitive parts or constituents. The method has possible application in the preparation of a metal catalyst on a highly divided supported support.

Rate-Determining Step in Photocatalytic Production of Hydrogen

z. x. he, w. pong, n. priyantha and d. root, Int. f. Hydrogen Energy, 1990, 15, (2), 99-103

Measurements of photocurrent and dark current were made using n-type and p-type Si electrodes with thin Pd overlayers to find the rate-determining step in photocatalytic H2 production. For Si/SiOx/Pd electrodes the onset potential for photocurrent before and after exposure to H2 showed that at low light intensity the results support the metal/semiconductor interface model. However at high light intensity (34mW/cm2) the p -type electrodes agree with the metal/solution interface model. The dependence of the photocurrent change on light intensity suggests that the magnitude of the surface recombination rate constant is important in locating the rate-determining step in the photoelectrochemical system.

Photoinduced Charge Separation across the Solid-Liquid Interface of Porous Sol-Gel Glasses: Catalyzed Hydrogen Generation from Water

a. slama-schwok, d. avnir and m. ottolenghi, f. Phys. Chem., 1989, 93, (22), 7544-7547

Photoinduced electron transfer between [Ir(bpy)2(C3,N’)bpy]3+ (Ir111) trapped in a porous SiO2; glass generated by the sol-gel process, and 1,4-dimethoxybenzene (DMB) dissolved in a water phase in the pores of the glass, has been observed. For this heterogeneous (two-component) donor-acceptor system a retardation of 4 orders of magnitude of the back-electron-transfer process, with respect to homogeneous solutions, was observed at neutral pH. At acidic pH, retardation of the back-reaction along with a surface catalytic effect led to H2 evolution from water. The effective retardation is attributed to the combined effects of trapping of one reactant (Ir11) and adsorption of the second (DMB+), leading to long-lived separation of the two species.

The Life and Times of [Ru(bpy)3]2+: Localized Orbitals and Other Strange Occurrences

m. k. de armond and m. l. myrick, Acc. Chem. Res., 1989, 22, (10), 364-370

A discussion of research on the photophysics of [Ru(bpy)3]2+ is presented, and concludes that for Ru(II) diimine complexes (mono, bis and tris) the emission is a phosphorescence localised on a single RuL unit, with potential barriers existing between the adjacent spatially isolated optical orbitals. Multiple state emission occurs for all [RuL3]n+ and many [RuL2L’]n+ complexes, since the individual RuL units have near degenerate emitting energy levels. Other conclusions on the MLCT states, fast, intrinsic localisation in the triplet manifold, and the behaviour of the emitting triplet spin levels are drawn.

Temperature-Dependent Lifetimes, MCPL and Shifts of the Luminescence in the Materials [Ru(bpy)x(bpy-d 8)3 _x]2+, x = 0—3, in Dilute Systems

e. krausz, g. moran and h. riesen, Chem. Phys. Lett., 1990, 165, (5), 401-406

The emission lifetime variations in the series [Ru(bpy)x(bpy-d 8)3-x]2+ (where bpy = bipyridyl and bpy-d 8 = deuterated bipyridyl; x = 0-3) have been studied as a function of temperature and in a range of host environments. Luminescence decay kinetics, measured after quasi-steady-state excitation, were found to be first order under all conditions. The decay rates of the x= 1 and x = 2 partially deuterated complexes were approximately evenly spaced between the x = 0 and x = 3 values. Luminescence profiles were almost identical for the series, but with the low temperature x=0 luminescence shifted ~40 cm-1 to a higher energy relative to the x= 1,2,3 spectra. Analysis of the temperature dependence of the lifetimes in polyvinyl alcohol) indicates an 8.2±0.2 cm-1 lowest energy gap for all 4 complexes.

ELECTRODEPOSITION AND SURFACE COATINGS

Chemical Vapor Deposition of CoGa and PtGa2 Thin Films from Mixed-Metalorganometallic Compounds

y.-j. chen, h. d. kaesz, y. k. kim, h.-j. mÜller, r. s. williams and z. xue, Appl. Phys. Lett., 1989, 55, (26), 2760-2762

A new process for deposition of PtGa2 and CoGa thin metal films from organometallic precursors of limited volatility is reported. Short path vapour transport of the complexes Pt{N2C2(CH3)2O2) (GaMe2)}2 or (CO)4CoGaCl2(THF), each under a stream of H2, leads to the films of the intermetallic compounds PtGa2 and CoGa, respectively, on the substrates of Si(100) wafer or a glass slide at 500°C. The films are crystalline and highly reflective. The PtGa2 film shows a minor constituent of Pt2Ga3.

APPARATUS AND TECHNIQUE

Copper Determination in Urine by Flow Injection Analysis with Electrochemical Detection at Platinum Disk Microelectrodes of Various Radii

d. l. luscombe, a. m. bond, d. e. davey and j. w. bixler, Anal. Chem., 1990, 62, (1), 27-31

The incorporation of Pt disk microelectrodes of various radii (2.5-50μm) in a wall-jet flow cell was shown to considerably improve the detection limits for the determination of Cu in urine by flow injection analysis, compared with standard methods based on a conventional sized glassy C disk macroelectrode (radius 1.5 mm), in a thin layer cell. The radius of the Pt microelectrode was critical with respect to both the detection limits and flow rate dependence. An optimal radius of 28μm was found; detection limits increased with both larger and smaller radii. In contrast, as theoretically expected, flow rate dependence diminished with decreasing radius of the Pt microelectrode.

In-Line Monitor for Electrical Conductivity of High-Temperature, Aqueous Environments

y. asakura, m. nagase, m. sakagami and s. uchida, f. Electrochem. Soc., 1989, 136, (11), 3309-3313

An in-line monitor to determine electrical conductivity of aqueous solutions at elevated temperatures up to 300°C has been developed. The main feature of the monitor is that by analysing the frequency dependence between three Pt electrodes, the water resistivity can be estimated separately from the impedance due to the surface reactions. The effects of aqueous impurities, H2SO4, NaOH, and Na2SO4 on the electrical conductivity have been determined up to 300°C using this monitor. The measurement of the electrical conductivity of high temperature water is useful for both the precise determination of water qualities and determination of the effects of impurities on corrosion behaviour.

The Sensing Mechanism in a Semiconducting Humidity Sensor with Pt Electrodes

y. shimizu, m. shimabukuro and h. arai, .f Electrochem. Soc., 1989, 136, (12), 3868-3871

The sensitivity of Sr0.95 La0.05SnO3 semiconducting humidity sensors was found to increase with a rise in firing temperature when Pt electrodes were used; this sensitivity enhancement was not observed for sensors with RuO2 electrodes. The results of this study indicate that the sensitivity of the semiconducting humidity sensor may be modified by selecting the deposition conditions of Pt particles. A sensitisation model based on the variations in the amount of oxygen adsorbed on the Pt particles, which were deposited on the surface of grain boundaries in the interior part of the Sr0 95La0.05SnO3 by thermal diffusion, with the electrode firing temperature is given.

Determination of Mercury by Atomic Absorption Spectrometry Using a Platinum-Lined Graphite Furnace for In Situ Preconcentration

d. c. baxter and w. frech, Anal. Chim. Acta, 1989, 225, (1), 175-183

Mercury in water samples was reduced by SnCl2 and the generated vapour swept in a flow of Ar through a Pt-lined graphite tube to permit in situ preconcentration. The Hg was then atomised under essentially gas-stop conditions to maximise sensitivity. The use of Pt permits amalgamation directly in the absorption cell. Relatively high temperatures can be applied to clean the Pt surface thoroughly. The system was optimised and for 50 ml artificial sea water samples detection limits of <2 ng/1 Hg were obtained, based on twice the standard deviation of the blank. The Hg generator can be easily constructed and connected to available graphite atomic absorption spectrometers.

Gas-Sensing Characteristics of SnO2_x Thin Film with Added Pt Fabricated by the Dipping Method

d.-d. lee and w.-y. chung, Sens. Actuators, 1989, 16, (3), 301-305

Pt-SnO2-x thin films were prepared by reactive electron beam evaporation of sintered pellets of SnO2 powder and dipping the films into an aqueous solution of H2PtCl6.6H2O. Pt particles dispersed onto SnO, 2-x films are oxidised passivatingly after decomposition from H2PtCl6.6H2O so that the bulk of them remain unoxidised. The samples were studied by Auger electron spectroscopy and X-ray diffractometry and the results thus obtained showed that the Pt-SnO2-x thin films have relatively high sensitivity to CO gas and sufficient stability at 150°C. This technology for Pt-SnO2-x fabrication could be applied therefore to the development of a CO-detecting microsensor system.

Ultrathin (1 nm) Vertically Shadowed Platinum-Carbon Replicas for Imaging Individual Molecules in Freeze-Etched Biological DNA and Material Science Metal and Plastic Specimens

g. c. ruben, f. Electron Microsc. Tech., 1989, 13, (4), 335-354

A high-resolution vertical Pt-C replica technique for transmission electron microscopy, which can image in the context of solutions, gels, or solids, single molecular chains 3-7 Å wide, their associations, and their conformation, is reported. Previously, the granularity of the metal film replicas limited their resolution to ≥ 20 Å. This paper demonstrates that Pt-C film granularity and resolution are a function of method of replication and other controllable factors. Comparing low-angle 20° rotary, 45° unidirectional, and vertical 9.7±1 Å Pt-C films deposited on mica, the vertical replication had a 5 Å granularity, the highest resolution, and evenly coated the whole surface. Various examples using the technique are given.

A DNA Probe of Ruthenium Bipyridine Complex Using Photocatalytic Activity

h. kojima, n. sato, y. kawamoto and j. iyoda, Chem. Lett. fpn., 1989, (10), 1889-1892

A method for labelling DNA and for detection of the complementary sequence using the photocatalytic activity of tris-(2,2’-bipyridine)Ru(II) is presented. The cis-Ru(bipy)2Cl2 can co-ordinate to a single-stranded DNA under reflux with DNA in water-EtOH solution, and Ru is recoverable as Ru(bipy) 32+ when the Ru-DNA was refluxed with an excess of 2,2’-bpy. Plasmid DNA of ~0.6 µg can be detected.

HETEROGENEOUS CATALYSIS

The Low-Pressure Reaction of Carbon Monoxide with Nitrogen Monoxide in the Presence of Oxygen on Polycrystalline Platinum, Palladium and Rhodium. I. Binary Mixtures of Reactants. II. Intrinsic Selectivities

l. m. carballo, t. hahn and h.-g. lintz, Appl. Surf. Sci., 1989, 40, (1/2), 53-58; 59-63

The experimental results of the study of binary systems (CO/O2 or CO/NO) on polycrystalline ribbons of Pt, Pd, and Rh have been used to partially interpret the intrinsic selectivities measured in the study of catalytic reduction of NO by CO in the presence of O2, over the same catalysts. Intrinsic selectivities were measured in an open gradientless system at a stationary state in large domains of temperature (250<ν<600°C) and reactant partial pressures (10-7< Pi<5×10-4 mbar).

Activity and Surface Composition of Sputter-Deposited Pt/γ-Al2O3 Catalysts

a. licciardello, f. iacona, s. pignataro, a. parmaliana f. frusteri and n. giordano, Mater. Sci. Eng., 1989, A116, 65-70

A comparison is made between Pt/γ-Al2O3 hydrogenation catalysts prepared by simple and dual-ion-beam sputter deposition and conventionally impregnated catalysts. The sputter-deposited catalysts were characterised by electron spectroscopy for chemical analysis. The ion-beam-assisted chemical reaction led to species in which Pt-0 bond was formed, and so in this case, the dual-ion-beam sputter-deposited catalyst showed lower activity than the simple sputter-deposited catalyst.

Redispersion of Platinum on Pt/Al2O3 Model Catalyst in Oxygen Studied by Transmission Electron Microscopy

j. m. rickard, l. genovese, a. moata and s. nitsche, f. Catal., 1990, 121, (1) 141-152

A model Pt/Al2O3 catalyst was studied by TEM and AES, and regenerated in O2 (500°C, 20 Torr for 1 h). This resulted in two phases: a bimodal distribution consisting of a phase of particles 40-100 Å in diameter and a phase of very small clusters (<10 Å).

A New Method for the Immobilization of Polymer-Protective Colloidal Platinum Metals via Co-ordination Capture with Anchored Ligands. Synthesis of the First Example of a Mercapto-Containing Supported Metallic Catalyst for Hydrogenation of Alkenes with High Activity

y. wang, h. liu and y. jiang, f. Chem. Soc., Chem. Commun., 1989, (24) 1878-1879

A poly (N-vinyl-2-pyrrolidone) (PVP)-protective metallic Pt or Rh colloid interacts at room temperature with a suspension of silica gel, bearing mercapto ligands, in a 1:1 methanol-water system to give a well dispersed heterogeneous metallic catalyst which shows excellent activity for the hydrogenation of alkenes. The catalysts were 100-300 times more active than commercial Rh/C and Pt/C catalysts.

Hydrogenation of Butadiene in Liquid Phase on Palladium Catalysts

p. s. ivanov, v. d. stytsenko, i. a. eigenson, a. ya. rozovskii and kh. dimitrov, Neftekhimiya, 1989, 29, (6), 762-767

Studies of hydrogenation of butadiene in liquid phase on modified and unmodified Pd/Al2O3 catalysts containing 0.67 and 0.3% Pd were performed under H2 pressure of 0.5-2.0 MPa at 20-60°C. Hydrogenation of butadiene proceeds in parallel in 1,2- and 1,4-positions while the isomerisation of butene-1 to butene-2 was insignificant. Surface modified Pd/Al2O3 catalysts showed higher selectivity to butene (specially to butene-1) and high stability to S. Kinetics of catalyst deactivation by H2S were found.

Hydrogenation of CO on Group VIII Metals Supported on Carbon Fibres

a. yu. krylova, o. a. malykh, g. i. emel’yanova and a. l. lapidus, Kinet. Katal, 1989, 30, (6), 1495-1498

Studies of the activity and selectivity of Pd, Co, Ni and Fe catalysts deposited on C fibres were carried out during hydrocarbon synthesis from CO and H2. The results showed that reaction temperature and concentration of active metal greatly affect the activity of the catalysts. Selectivity of the metal/C fibre catalysts depends on the nature of the metal, the method of deposition the C fibre and on H2: CO ratio.

Autocatalytic Reduction of Metal Ions, Initiated by Irreversible Oxidation of Reducing Agent

g. a. ragoisha and v. v. sviridov, Vest. Akad. Navuk BSSR, 1989, (6), 44-49

Studies of the thermodynamic characteristics of the Pd2+/Pd-Ag+/Ag-H2PO2- systems were performed in order to illustrate the difference in two ways of initiating autocatalytic reduction of metal ions by quasi-equilibrium and non-equilibrium. Initial stages of a spontaneously initiated and electrostimulated autocatalytic reduction of Pd2+ with H2PO2- ions on the SnO2 film surface were studied.

Studies of Ethylene Polymerization over Exchanged Zeolites. VI. The Promotive Effect of Alkali Metal and Alkaline Earth Metal Cations on Palladium Ions in Fau-jasite Zeolite for Ethylene Dimerization

x.-l. bai, g.-w. wang and l.-b. zheng, f. Catal. (Dalian, China), 1989, 10, (4), 396-401

The effect of the pre-evacuation temperature on the activity of LiPdY, NaPdY and KPdY for ethylene dimerisation was studied. The results show that along with the increase of evacuation temperatures, the activity of these catalysts increases first and then decreases, and passes a maximum. It is suggested that the effect of alkali metal cations on Pd2+ ions is to regulate the location of Pd2+ in zeolite cages and the reducibility of Pd2+ ions. The reducibility of Pd2+ increases in the order of LiPdY<NaPdY<KPdY. An induction period of ethylene dimerisation appears on LiPdY and NaPdY, but not on KPdY and CaPdY.

Cycloaddition of Carbon Dioxide to Propyne over Supported Rh4 and Fe2Rh4 Carbonyl Cluster-Derived Catalysts

s. m. pillai, r. ohnishi and m. ichikawa, f. Chem. Soc., Chem. Commun., 1990, (3), 246-247

Studies of Rh4 and Fe2Rh4 carbonyl cluster-derived catalysts supported on A12O3, SiO2, TiO2 and ZrO2 showed that they are active in the formation of 4,6-dimethyl - 2-pyrone by the cycloaddition of CO2 to propyne under moderate conditions. It is suggested that pyrone is produced on a cationic Rh metal centre bound to a basic site (O2- or OH-) on the oxide support.

The Interaction of Synthesis Gas (CO-H2) with Small Rhodium Particles

p. johnston, r. w. joyner and p. d. a. pudney, f. Phys.: Cond. Mater. (Suppl. B), 1989, 1, SB171-SB176

In situ EXAFS spectroscopy studies of small Rh particles in a 1% Rh/Al2O3 catalyst have shown that, after reduction in H2, the average diameter is ~ 8Å and the Rh-Rh interatomic distance is ~0.03Å shorter than in the bulk metal (R = 2.69Å). After exposure to CO at 1 bar marked changes were seen similar to those reported by other authors. On subsequent exposure to H2-CO (2:1) at 1 bar and 373K the catalyst structure reverted to that of the metal, although the Rh-Rh distance increased to 2.74Å.

The Surface Chemistry of Isolated and Aggregated Silica-Bound Rhodium Complexes

k. c. cannon and j. m. white, f . Catal., 1989, 120, (2), 314-324

Aggregation of SiO2, bound molecular Rh complexes and their activity for the formation of isocyanate species during reaction with NO and CO is reported. From studies it is concluded that isocyanate formation depends strongly on the form of Rh. A µ-oxo Rh carbonyl did not give bis(nitrosyl) Rh complexes but a nitrite/nitrate complex on NO treatment.

Quantum Chemical Study on the Mechanism of CO Hydrogenation to Oxygenates over Vanadium-Promoted Rhodium Catalyst

r.-h. wang and y.-s. xu, f. Mol. Catal., 1989, 54, (3), 478-483

Extended Hückel calculations of the elementary step of carbonyl insertion in the process of CO hydrogenation over a V-promoted Rh catalyst in the synthesis of oxygenates is reported. The results of these calculations show that the barrier for CH3 migration to Rh-CO to form Rh-COCH3 species is decreased in the case of the V-promoted catalyst. A discussion attempts to explain the role of the promoters.

Effect of Oxide Promoters on the Surface Characteristics of Carbon-Supported Co and Ru Catalysts

i. rodriguez-ramos, a. guerrero-ruiz and j. l. g. fierro, Appl. Surf. Sci., 1989, 40, (3), 239-247

The effect of promoters MgO, CeOx and VOx on the surface characteristics of C-supported Ru or Co catalysts has been studied by H2 and CO chemisorption, X-ray diffraction and X-ray photoelectron spectroscopy. Both metals and oxide promoters were found to be well dispersed within the porous structure of C, although they are not uniformly distributed across the catalysts pellets. The effect of the different precursors on the location and dispersion of the active phases in the C porous structure was also studied.

Fischer-Tropsch Synthesis over Ruthenium/Y-Zeolite Catalysts: Effects of the Neutralizing Cations of Zeolites

y. -w chen, w.-c. hsu and c.-s. lin, React. Kinet. Catal. Lett., 1989, 40, (2), 301-306

Alkali and alkaline earth neutralising cations in zeolites were found not to significantly influence H chemisorption of a series of Ru/Y-zeolite catalysts. However, the turnover frequencies of Ru in the CO/H2 reaction were enhanced when the neutralising Na cations were replaced by alkaline earth cations. This effect is attributed to an increase in electron deficiency of the metal crystallites due to the higher acid strength of alkaline earth Y-zeolites.

Effects of Presulfidization on the Selectivity and Surface Structure of Ruthenium Catalysts

r. a. cocco and b. j. tatarchuk, Langmuir, 1989, 5, (6), 1309-1315

The adsorption sites and surface phases which are formed on Ru catalysts following pretreatment in H2-rich or H2S-rich sulphidisation mixtures have been studied by XPS and static SIMS. It was found that while sulphidisation in as little as 29ppm H2S/H2 at 673K can be used to produce the bulk sulphide, RuS2, the surface instability of S- -S- anion pairs, found in the pyrite-RuS2 lattice, requires that >80% H2S/H2 be used at 673K before these species are stabilised at the surface.

HOMOGENEOUS CATALYSIS

Palladium(II)-Mediated Carboxylation of Cyclohexane with CO via C-H Bond Activation

y. fujiwara, t. jintoku and y. uchida, New f. Chem., 1989, 13, (10/11), 649-650

The carboxylation of cyclohexane with 1 atmosphere of CO in the presence of Pd(OAc)2 and CF3COOH at reflux temperature without irradiation gives benzoic acid and cyclohexanecarboxylic acid in the ratio - 3:1 by C-H aliphatic bond activation.

Hydrogenolysis of α, β-Epoxyketone and Ester to Aldol in Pd(O)/HCOOH/Et3N and H2/Pd/C Reduction Media

s. torii, h. okumoto, s. nakayasu and t. kotani, Chem. Lett. fpn., 1989, (11), 1975-1978

Simple procedures for reducing epoxyketones and esters to the corresponding aldols by two different methods are presented. One is the reduction with triethylammonium formate in the presence of Pd catalysts, such as Pd acetate and dppe, and the other is a hydrogenation in a Pd/C-THF system.

Formylation of Aryl Chlorides Catalysed by a Palladium Complex

y. ben-david, m. portnoy and d. milstein, f. Chem. Soc., Chem. Commun., 1989, (23), 1816-1817

The complex (dippp)2Pd, where dippp is 1,3-bis(di-isopropylphosphino)propane, is an efficient catalyst for the direct formylation of aryl chlorides to aldehydes with CO and NaHCO2, under mild pressures. In a typical example, chlorobenzene was completely converted to benzaldehyde (95% yield) and benzene (5% yield).

Organo-Palladium Compounds in Oxidation of Styrene by Palladium(II)

L. m. martynova and e. a. katsman, Kinet. Katal., 1989, 30, (6), 1489-1491

Studies of the reaction changes of α-phenyl-β -chloromercury ethanol (Ph-CH(OH)CH2 Hg Cl) with PdCl2 in chloroform and acetone were performed at 20°C. The reaction mainly yielded phenylacetaldehyde and acetophenone, that is, the same compounds formed during styrene oxidation by PdCl2 in aqueous solution.

Selective Synthesis of Unsymmetrical Biaryls via Palladium-Catalyzed Cross-Coupling of Arylfluorosilanes with Aryl Iodides

y. hatanaka, s. fukushima and t. hiyama, Chem. Leu. fpn., 1989, (10), 1711-1714

In the presence of KF/Pd catalyst the cross-coupling reaction of arylsilanes with aryl iodides gives a straightforward route to highly functionalised unsymmetrical biaryls which have hardly been accessible by conventional methods.

Hydroformylation of Allyl Alcohol in the Presence of Rhodium Catalysts Modified with Bicyclophosphite Ligand

g. a. korneeva, e. v. slivinskii, m. m. potarin, n. a. kibasova, r. v. chekhova and s. m. loktev, Neflekhimiya, 1989, 29, (6), 818-823

Studies of hydroformylation of allyl alcohol in the presence of Rh catalysts Rh4CO)12 and Rhacac(CO2) modified with bicyclophosphite ligand and PPh3, during butane-1,4-diol production showed that activity and selectivity of the reaction is analogous with PPh3 but its stability was superior. Bicyclophosphite in the free state is subjected to hydrolysis, but its co-ordination with Rh atom suppresses the reaction thus allowing recycling of Rh complex catalytic system with bicyclophosphite during hydroformylation of allyl alcohol. The hydroformylation reaction occurs at CO + H2 pressure of 0.6-1.0 MPa, at 60-70°C and P:Rh ratio of 3-4 in toluene solution, after which aqueous extraction of products from the reaction media is carried out.

The pH Dependence of the Ruthenium-Catalysed Ferricyanide Oxidation of Cyclohexanol

r. w. kaziro and j. k. beattie, Aust. f. Chem., 1989, 42, (8), 1273-1279

The oxidation of cyclohexanol(1) to cyclohexanone by ferricyanide(2) in alkaline aqueous solutions is catalysed by the addition of K3[RuCl6].At pH < 11 the reaction is limited by decomposition of the reduced catalyst, but catalyst lifetime can be increased by increasing the concentration of (2). For pH 11.3-11.9 the oxidation or the reduction step in the catalytic cycle can be made rate determining by adjusting the relative concentrations of (1) and (2). The pH dependence of the oxidised catalyst reaction affects the rate constant of the reaction between pH 11.3 and 11.9.

Reduction of CO2 by Molecular Hydrogen to Formic Acid and Formaldehyde and Their Decomposition to CO and H2O

m. m. taqui khan, s. b. halligudi and s. shukla, f.Mol. Catal., 1989, 57, (1), 47-60

Carbon dioxide can be reduced to HCOOH and HCHO as initial product using the catalyst K[Ruln(EDTA-H)Cl ]. 2H2O in aqueous media at mild pressures (1-4 arm CO2 and H2) and 40°C. The initial products, HCOOH and HCHO, decompose later to give CO and H2O as the final products, the reactions thus constituting a reverse water-gas shift reaction. The rates of formation of HCOOH and HCHO were first order with respect to catalyst and dissolved CO, and H2 concentrations, respectively, as were the rates of HCOOH and HCHO decomposition. Activation energies have been evaluated from studies of the effect of temperature on the rates of formation and decomposition of HCOOH and HCHO. Based on the kinetic data, a mechanism is proposed for the reactions.

FUEL CELLS

Photoelectrolysis and In Situ Storage of Solar Energy

s. chandra and n. khare, f. Electrochem. Soc., 1989, 136, (10), 2856-2857

The feasibility of developing a solar energy storage device by coupling a photoelectrolysis cell and a proton conductor H2/O2 fuel cell is demonstrated. Thermally grown TiO2 film was used as a photoelectrode and Pt wire was used as a counter electrode in the photoelectrolysis cell. The fuel cell consisted of Pd hydride/hydrogen uranyl phosphate (HUP) solid electrolyte/air (O2). An initial layer of Pd film was vacuum coated on the pellet of HUP.

Effects of Surface-Active Agents on Platinum Dispersion Supported on Acetylene Black

a. honji, s. takeuchi, t. mori and y. hishinuma, J. Electrochem. Soc., 1989, 136, (12), 3701-3704

From the evaluation of 14 nonionic surface-active agents, sorbitan monolaurate, sorbitan mono-oleate, sorbitan trioleate, and polyoxyethylene(20)sorbitan trioleate were found to give highly dispersed Pt particles (~30Å diameter, Pt specific surface area ~150m2/g) on acetylene black when chloroplatinic acid was reduced by methyl alcohol at 70°C. The double bond in the oleic group exercised the dominant effect on Pt dispersion.

Characterization of Platinum-Ruthenium Catalyst for the Methanol Electrodes of Methanol-Air Fuel Cells

t. horiba and k. tamura, Denki Kagaku, 1989, 57, (7), 712-717

The deposition states and catalytic activities of Pt-Ru binary methanol electrodes of methanol-air fuel cells have been studied. The catalysts were prepared by three methods: Willstätter (W-method), Adams (A-method) and NaBH4 (S-method). The catalyst prepared by the W-method was formed by the coprecipitation of Pt black and Ru black. The A-method catalyst contained PtO2 and RuO2 and the S-method catalyst consisted of Pt-Ru binary alloy.

One-Step Oxidation of Benzene to Phenol Applying a Fuel Cell System

k. otsuka, k. hosokawa, i. yamanaka, y. wada and a. morikawa, Electrochim. Acta, 1989, 34, (10), 1485-1488

The fuel cell system, [O2, benzene, FeCl3, (FeSO4, CuCl2, CuSO4 or SnCl2) in HCl or H2SO4(aqueous), Pd (or Au)/Nafion-H/Pt, H2], produced phenol selectively while continuously generating electricity. H2O2 is generated by the fuel cell reaction of O2 and H2. Fenton’s reagent (Fe11-H2O2) or Cu1-H2O2 are generated when Fe111 or Cu11 salts are added initially in the solution of the cathode compartment. Thus the fuel cell system generates Fenton’s type reagents continuously, producing phenol.

CHEMICAL TECHNOLOGY

Methane Polymerization with a Hollow Cathode: Influence of the Cathode Metal

p. meubus, h. lange and g. jean, Plasma Chem. Plasma Process., 1989, 9, (4), 527-543

Methane, mixed with Ar, has been polymerised using two hollow-cathode discharge systems. Under identical operating conditions a cathode made of a solid solution of 81% W and 19% Pt gave a higher polymer yield (90%) than a cathode made of pure W (70% yield). The work function for the solid solution was estimated to be 6.3 eV, compared with 4.4 eV for W. The concentration of CH- radicals was 5 times higher in the W-Pt cathodes. This was attributed to a surface catalytic effect inside the cathode, as no Pt vapour was detected in the gas phase. The plasma polymer deposition rate was evaluated as 70 nm/s for W-Pt compared with 42 nm/s for pure W.

Production of Hydrogen from the Na/NaH-Process

f. herzog and d. glaubitz, Int. f. Hydrogen Energy, 1990, 15, (1),13-19

Metal/metal hydride (Na/NaH) processes produce H2 from water through the direct employment of high-temperature heat, and have considerably higher overall efficiencies compared with purely electrolytic processes. Following studies of an a-iron membrane for the H2 -permeable membrane cathode required by the process, a double-layer membrane of V and Pd/Ag foil was tested in the laboratory plant. On the Na side the membrane consists of V foil which is corrosion resistant to the H2 acceptor. This foil is coated with a layer of β -Pd-Cu on the side facing the Na, which serves to catalyse the H2 input. The V foil is protected from the electrolyte by a Pd/Ag foil coated with Pd black. Measurements of the permeation rates using the double-layer membrane were carried out at 288°C and H2 admission pressures between 10 and 130 mbar, and show the suitability of the membrane.

ELECTRICAL AND ELECTRONIC ENGINEERING

Selective Copper Film Growth on Platinum Clusters

b. lecohier and h. van den bergh, Appl. Surf. Sci., 1989, 43. (1-4), 61-67

In order to grow spatially delineated Cu lines from a solid Cu formate layer on a surface, a localised Pt film, <10Å high, was first deposited. Subsequently the whole surface was covered by a few ftm of Cu(HCOO)2.2H2O. Heating to about 70°C caused the formate to decompose exclusively where the surface had been seeded with the thin Pt clusters. Line heights up to 0.3 µm were developed with resistivity ratios of 2-4, i.e. resistivities of about twice that of pure bulk Cu. In principle this method should permit direct writing of metal stripes at very high speeds and of good resolution.

Interconnection Lines of Pt Induced by Laser Direct Writing

c. garrido, d. braichotte, h. van den bergh, b. leÓn and m. piÉrez-amor, Appl. Surf. Sci., 1989, 43, (1-4), 68-73

Laser chemical vapour deposition has been used to produce Pt interconnection lines for microelectronic applications. The influence of the laser power as well as the vapour pressure of the precursor (Pt bishex-afluoroacetylacetonate) upon the geometry, the morphology and the line resistivity, was studied. The vapour pressure seems to be the key parameter to produce excellent interconnection lines at relatively high writing speeds. All the lines were essentially 100% Pt and resistivities close to that of pure Pt were achieved depending on the morphology. Line widths < the laser spot diameter were obtained.

Comparison of Au/Ni/Ge, Au/Pd/Ge, and Au/Pt/Ge Ohmic Contacts to n-type GaAs

c. lin and c. p. lee, f. Appl. Phys., 1990, 67, (1), 260-263

The electrical properties of Au/Ge-based ohmic contacts to n-type GaAs with an addition of Pt, Pd or Ni were studied by TEM and AES after thermal alloying. Au/Pt/Ge had the best surface morphology, while Au/Ni/Ge had the roughest one. The electrical characteristics of Au/Pt/Ge are also superior to those of Au/Pd/Ge (which had the highest contact resistance) and Au/Ni/Ge.

Effect of Conventional and Rapid Thermal Annealing on Platinum Silicide Schottky Barrier Diodes

c. a. dimitriadis, Appl. Phys. Lett., 1990, 56, (2), 143-145

The effects of rapid thermal annealing (RTA) on the material properties and on the performance of Pt Schottky barriers on Si were studied and compared with the effects of corresponding furnace annealings. Best performance of Pt Si/Si Schottky diodes prepared by RTA was achieved for annealing temperature 400°C which is much lower than the corresponding temperature of furnace annealing of 550°C. The results of the diode electrical properties in combination with the diffusion length measurements showed that RTA is superior as it is a nondestructive process without degradation of the diffusion length.

Improved Uniformity of PtSi Schottky Barrier Diodes Formed Using an Ion Mixing Scheme

c. a. hewett, m. g. fernandes and s. s. lau, f. Appl. Phys., 1990, 67, (1), 524-527

Low dose ion implantation through the PtSi/Si interface prior to annealing has been used to prepare Schottky barrier diodes with a more planar PtSi/Si interface. The electrical characteristics of such devices are more uniform from device to device and more nearly approach theoretical performance than conventionally prepared devices.

Evaporated Metal Films as Substrates for Hydrogenated Amorphous Silicon

s.-i. ishihara, Thin Solid Films, 1989, 182, 229-236

Evaporated Pt, Ni, Ag, Al, and Cu films have been studied for use as substrate metals for hydrogenated amorphous (a -) Si p-i-n diodes. The forward current of a- Si:H p-i-n diodes on Pt or Ni film was 60-180 mA/cm2 with a +1 V bias applied, and the diode quality factor was about 1.6. Pt and Ni as the substrate metal did not degrade the a -Si:H p-i-n diode at a -Si:H deposition temperature Ts <300°C. The Ag produced a large scattered leakage current from the diode. Al and Cu were not suitable as substrate metals for a -Si:H deposition. These metals diffused throughout the a -Si:H films during the a -Si:H deposition.

Oxygen Sensitivity of a Pt-Pd/p-Type CaFe2O4 Diode

y. matsumoto, j. hombo and f. nitta, f. Appl.Phys., 1989, 66, (10), 5109-5110

Studies of the O2 sensitivity of Pt-Pd/p -type CaFe2O4 and Pt-Pd/Rh/p -type CaFe2O4 diodes, where CaFe2O4 exhibits Fermi-level pinning, showed reversible O2 responses for both diodes at 100°C, when current under bias increased with increasing O, concentration. Response time was decreased by Rh doping. The Schottky barrier height, ø, determined from the measured photocurrent-bias curve, decreased with an increase in O2 concentration.

Use of Au-In-Pd and Pd-In Electroless Deposits for Ohmic Contacts on n-GaAs

g. stremsdoerfer, j. r. martin, p. clechet and nguyen-du, f. Electrochem. Soc., 1990, 137, (1), 256-259

Electroless codeposition of Au-In-Pd and Pd-In alloys onto n -GaAs substrates in an acidic medium is shown to give a high quality ohmic contact having ϱ = 6 × 10-6 Ωcm2 on annealing. The addition of Pd ions to In and Au-In acidic electroless deposition baths allows the deposition of these metals which does not otherwise occur. For the Pd-In alloys, a crystalline refractory In3Pd compound was initially formed, whereas after a 2 min annealing treatment at 470°C traces of InAs and PdGa were found.

Epitaxially Grown Pd2InP on InP

d. g. ivey and p. jian, Mater. Lett., 1989, 8, (10), 389-395

In a Au/Pd/Zn/Pd contact metallisation to p -type InP, Pd was found to react with InP during deposition to form an amorphous phase with the approximate composition, Pd2InP. After annealing at 300-350°C, Pd2InP crystallises and grows epitaxially on InP with the relationship: (100)Pd2InP ‖ (110)InP and [001]Pd2InP ‖ [001]InP. The solid-state epitaxial growth of a uniformly thick, dislocation free layer of Pd2InP on InP is of interest from a device standpoint: incorporation of Pd2InP in Au/Zn-based p -type ohmic contacts may improve device performance and reliability, particularly as device scale decreases.

A STM Study of Pd-Catalyst for Electroless Cu Deposition on Nonconductors by Means of a Modified Graphite Substrate

j. o. besenhard, u. krebber, j. k. h. hÖrber, n. kanani and h. meyer, f. Electrochem Soc., 1989, 136, (12), 3608-3610

Highly dispersed Pd is the preferred catalyst for the activation of electroless deposition of Cu from Cu2 +/formaldehyde on glass fiber reinforced epoxy printed circuit boards. Using highly oriented pyrolytic graphite (HOPG) as a model substrate, scanning tunnelling microscopy (STM) images of Pd clusters (typical size 1-5nm) have been obtained. The initial mechanism of Pd-catalysed electroless Cu deposition is an electrochemical one, with spatial separation of oxidation (anode) and reduction (cathode) reaction. Formaldehyde oxidation on Pd occurs at the anode, whereas the cathode reaction is Cu deposition.

Fast Laser Writing of Copper and Iridium Lines from Thin Solid Surface Layers of Metalorganic Compounds

p. hoffmann, p. lecohier, s. goldoni and h. van den bergh, Appl. Surf. Sci., 1989, 43, (1-4), 54-60

Laser direct writing of Cu lines from a Cu formate film is compared with direct writing of Ir lines from two Ir-cluster films [Ir4 (CO)11Br] [N(C2H5)4] and [Ir6CO)15] [N(CH3)3]C8H17]2. The Ir system showed several advantages over the Cu system: (a) improved homogeneity of the precursor film; (b) lower laser powers could be used to obtain relatively good electrical resistivity; (c) the limiting line width obtained was 2 μm, narrower than in the Cu system; (d) significantly less sputtering of metal to the near surroundings of the Ir lines as compared to Cu; (e) the Ir precursor films are compatible with high vacuum apparatus, so that in situ processing with charged particle beams seems to be feasible. Laser writing of Ir at several cm/s gave lines of about 10 μm width, with electrical resistivities of ~ 10 times the bulk.

The Influence of Substrate Bias on the Morphology and Charge Capacity of rf-Sputtered Iridium Oxide Films

j. d. klein, s. l. clauson and s. f. cogan, J. Mater. Res., 1989, 4, (6), 1505-1510

Studies have shown that the morphologies of sputtered Ir oxide films deposited on Ti-alloy stimulation electrode wires can be actively and repeatedly controlled through the application of a DC substrate bias. Film morphology gradually progressed from relatively smooth and featureless films deposited with a - 20 V bias to films comprised of closely packed 1 μm long platelets on sputtering with a + 20 V bias. Cyclic voltammetry studies showed that the electrochemical properties of the films are strongly dependent on the substrate bias employed during deposition. As the DC bias increased from -20 to + 20 V the anodic and cathodic charge capacities decreased linearly from 36 to 12 mC/cm2.

TEMPERATURE MEASUREMENTS

Measurement of Low Temperatures in Magnetic Fields with Platinum Resistance Thermometers

g. s. abilov, i. a. razhba and d. n. astrov, Instr. Exp. Tech., 1989, 32, (2), 500-503

The characteristics of TSPN-3 and TSPN-4 resistance thermometers made of P1-0 Pt wire of 50/un diameter, in their working temperature range in magnetic fields of up to 6.6 T, are described. A standard function has been determined for calculation of temperature corrections for the effect of a magnetic field with an error of μ≤± 0.02 K in the range 30-190 K. An auxiliary equation to the standard function is used to extend this accuracy in the range 14-30 K.

MEDICAL USES

Chemical Properties and Antitumor Activity of Complexes of Platinum Containing Substituted Sulfoxides [PtCl(R’R”SO) (diamine)]NO3. Chirality and Leaving-Group Ability of Sulfoxide Affecting Biological Activity

n. farrell, d. m. kiley, w. schmidt and m. p. hacker, Inorg. Chem., 1990, 29, (3), 397-403

A novel set of Pt complexes [PtCl(R’R”SO) (diam)] NO,, where diam = bidentate amine, and R’R’SO = substituted sulphoxides such as Me2SO, MePhSO, MeBzSO, Ph2SO and Bz2SO was prepared and the anti-tumour activity of the complexes towards L1210 leukaemia was tested. The complexes are the first Pt well defined anti-tumour complexes containing S ligands. The anti-tumour activity is high and dependent on the natures of the amine and sulphoxide.

Electronic Structure of Platinum(II) Antitumor Complexes and Their Interactions with Nucleic Acid Bases. Part II

j. lipinski, f. Mol. Struct. (Theochem.), 1989, 201, 295-305

Based on calculations of solvation (hydration) energies and formation energies in the gas phase, the formation of Pt dimers and some possible interactions of Pt(II) anti-tumour complexes with guanine, thioguanine and the phosphate group are discussed. It is concluded that: (a) the solvent more strongly stabilises the Pt(II) 06-N7 chelate than it does the intrastrand N7-N7 crosslink, but the latter is enthalpy favoured; (b) binding of Pt(II) to the phosphate group is less likely than binding to the guanine N7 region; (c) Pt dimers, if formed, react with guanine and will disappear from solution under normal conditions; and (d) the solvent effect does not change the main conclusions obtained for the gas phase in cases of the interaction of cis -Pt(II) with thioguanine and trans -Pt(II) with guanine.

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