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Platinum Metals Rev., 1996, 40, (2), 88

ABSTRACTS: April 1996

of current literature on the platinum metals and their alloys

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PROPERTIES

Thermally Induced Structural Modification in Pt/C X-Ray Multilayer Mirrors Fabricated by Electron Beam Evaporation

g. s. lodha, s. pandita, a. gupta, r v. nandedkar and k. yamashita, Appl Phys., 1996, A62, (1), 29–32

The thermal stability of Pt/C multilayer mirrors with a bilayer spacing of 50 Å, fabricated in an UHV electron beam evaporator, was studied under vacuum annealing using X-ray reflectivity and XRD. At ≤ 450°C, the bilayer spacing increased monotonically giving a gradual increase in crystallite size and grain texture. At 500°C, multilayer reflection disappeared, the Pt crystallites grew rapidly and Pt in the [220]-plane had a strong texture.

Hydrogen-Induced Lattice Migration in Pd-Pt Alloys

h. noh, j. d. clewley and t. b. flanagan, Scr. Metall. Mater., 1996, 34, (4), 665–668

H2 solubilities were determined in ~100 µm thick foils of Pd-Pt alloys under H2 pressures of ≤ 100 MPa at temperatures ≤ 873 K. Pd-Pt alloys do not segregate at higher temperatures when little H2 dissolves; large amounts Of H2 are needed for segregation. The ternary (Pd + Pt + H) equilibrium causes a phase separation at 673 K. After H2 removal at ≤ 673 K and alloy cooling, metastable segregated Pd- and Pt-rich regions remain. Dissolved H2 catalyses the return of the segregated alloy to the homogeneous state.

Properties and Interface Diffusion of PdVNi Composite Wire

y. ningj h. dai and f. wen, Precious Met. (China), 1995, 16, (4), 25–30

Mechanical properties, interface diffusion and changes in Pd coating thickness were investigated in Pd/Ni composite wire. The thickness and weight percentage of the Pd coat were controllable on demand. The strength of the Pd/Ni composite wires, at ambient and high temperatures, is much higher than for pure Pd, and similar to that of Ni. The Ni diffusion rate from the interface to Pd is higher than that of Pd to Ni.

Magnetic Properties of U(Pd1-xFex)2Ge2

h. m. duh11. s. lyubutin, i. m. jiang, g. h. hwang and k. d. lain, F. Magn.& Magn. Mater., 1996, 153, (1–2), 86–96

Solid solutions of U(Pd1-xFex)2Ge2 with a mixture of 3d and 4d transition elements in one lattice site were prepared. Even very small Pd doping in UFe2Ge2 and Fe doping in UPd2Ge2 changed the magnetic state of the compounds dramatically. Coexistence between the antiferromagnetic ordering and Pauli paramagnetism was observed over the range 0.1 ≤ x ≤ 0.9.

Magnetism of Body-Centered Tetragonal FeRh1-xPdx Alloys. I. Magnetic Properties; II. Band Structure

s. yuasa, h. miyajima, y. otani and a. sakuma; a. sakuma, s. yuasa, h- miyajima and y. otani, F. Phys. SocJpn., 1995, 64, (12), 4906–4913; 4914–1922

Crystalline structures and magnetic properties of the FeRh1-xPdx system were studied and first-principle spin-polarised band calculations were performed for the b.c.t. FeRh1-xPdx alloys with x = 0, 0.5 and 1 as a function of the axial ratio c:a . A new ferromagnetic phase of orthorhombic structure with space group Cmmm was found in the b.c.t. alloys with x = 0.525 ~ 0.61 below room temperature. At a constant c:a value, substituting Pd for Rh raised the Fermi energy level.

Magnetic Structure and Physical Properties of the Heavy Fermion UIr2Si2

a. verniÈre, s. raymond, j. x. boucherle, p. lejay, b. fÅk, j. flouquet and j. m. mignot, F. Magn. & Magn. Mater., 1996, 153, (1–2), 55–62

Studies of the physical properties of a UIr2Si2 single crystal, which has CaBe2Ge2-type structure and very high residual resistivity values at low temperature, indicated that UIr2Si2 is antiferromagnetic with TN = 6 ?. A metamagnetic transition at a field of 1.5 T and heavy-fermion characteristics with a linear specific heat coefficient of γ~ 300 mj/mol K2 were measured. The antiferromagnetic structure Of UIr2Si2 was determined by neutron diffraction as (+,-,+,-).

Ruthenium and Sulphide Passivation of GaAs

s. t. ali, s. ghosh and d. n. bose, Appl. Surf. Sci., 1996, 93, (1), 37–43

The effectiveness of chemical surface treatment of GaAs using (NH4)2Sx, Na2S and RuCl, was studied. Modification involved the removal of native oxides and the consequent formation of bonds with Ru or S. Ga atoms were bonded more strongly with Ru or S than As. This reduced the surface recombination velocity and increased the photoluminescence intensity. S and Ru can be used to passivate the GaAs surface.

Subsolidus Phase Equilibria in the RuO2-Bi2O3-ZnO and RuO2-Al2O3-ZnO Systems

m- hrovat, s. bernik, j. holc and d. kolar, J. Mater. Sci., Lett., 1996, 15, (4), 336–338

Phase diagrams of the ternary systems RuO2-Bi2O3-ZnO (I) and RuO2-Al2O3-ZnO (II) were constructed and showed that the RuO2-ZnO system contained no binary compound or liquid phase (eutectic) at < 1400°C, which is the temperature that RuO2 decomposes to metallic Ru and O2. Tie lines within the phase diagrams are discussed. The microstructure of a sample of nominal composition 5 mol%ZnO/50 mol%Bi203/45 mol%Ru02, fired at 700°C, is shown.

Superconducting Properties of CeRu2 Single Crystal

h. sugawara, h. sato, t. yamazaki, n. kimura, r. settai and y. onuki, J. Phys. Soc Jpn., 1995, 64, (12),4849–4855

Lower and upper superconducting critical fields at 0 K, of 250–400 Oe and 74 kOe, respectively, were measured on single crystals of superconductor CeRu2 grown by using a zone melting method. The upper critical field was slightly anisotropic, and was of size 64.8 kOe for the field along the <100> direction and 65.6 kOe along the <110> direction at 1.5K.A characteristic feature of the superconducting mixed state was also observed.

CHEMICAL COMPOUNDS

Ternary Thallium Platinum and Thallium Palladium Chalcogenides Tl2M4X6. Syntheses, Crystal Structures, and Bonding Relations

w. bronger and b. bonsmann, Z. Anorg. Allg. Chem., 1995, 621, (12), 2083–2088

The compounds Tl2Pt4S6, Tl2Pt4Se6, Tl2Pt4Te6 and Tl2Pd4Se6 were fabricated by melting the elements or by the reaction of Tl carbonate, Pt group metal and chalcogen powders at 400–950°C. X-ray studies on single crystals and powders showed a new type of structure, which is a stacking variant of the known atomic arrangement of the alkaline metal Pt chalco-genides. The short distances in Tl-Pt and Tl-Pd indicate covalent bonds between the main group and the Pt group metal atoms.

Evidence for a Hydrogen Insertion Compound of Novel Palladium Incorporated Vanadyl Hydrogen Phosphates

a. datta and r. y. kelkar, Chem. Commun., 1996, (1), 89–91

Pd was incorporated into the vanadyl H phosphate phase VOHPO4.0.5H2O in various ways depending on the medium used for preparation. In aqueous medium the incorporation of 0.61% Pd2+ changes the parent structure, so that Pd2+ ions appear to be located in the interlayer region. The relatively low reduction temperature of the incorporated Pd indicates it is located in the interlayer region. However, in an organic medium Pd is partially reduced to metal and partially introduced into the lattice of the parent compound.

Stable Carbonyl- and Thiocarbonyhhodium(I) Complexes Containing G-Bonded Phenyl and Vinyl Groups as Ligands

r. wiedemann, j. wolf and h. werner, Chem. Ber., 1996, 129, (1), 29–31

Rh(I) phenyl and vinyl complexes, trans -[Rh(R)(CO)(P2Pr3)2] (1, 2) were prepared from the chloro derivative and Grignard reagents. The corresponding thiocarbonyl trans -[Rh(CH=CH2)(CS)-(PiPr3)2] was obtained from trans -[RhCl(CS)(PiPr3)2] and CH2=CHMgBr. The carbonyl complexes (1) and (2) are inert in the presence of CO and do not react by migratory insertion to give acyl Rh derivatives.

Synthesis of the First Bimetallic Ruthenium-Iridium Cluster

i. a lobanova, i. t. chizhevskii, p. v. petrovskii and v. i. bregadze, Izv. Akad. Nauk Rosii, Ser. Khim., 1996, (1), 250–251

A new electron-deficient bimetallic cluster, (η4-C8H12)IrRu(μ-H) (PPh3)25-C2B9H11) was prepared by the reaction of exo-nido -5,6,10-[Cl(PPh3)2Ru]-5,6,10-(μ-H)3-10-H-7,8-C2B9H8 with dimeric or acetyl-acetonate complexes of Ir in the presence of KOH in EtOH at 22°C. Spectroscopic data are presented.

Formation of Ammonium Complexes during Interaction of Ruthenium Compounds with Hydrazine Chloride

yu. h. kukushkin, m. v. bavina and ?. v. zinchenko, Zh. Obshch. Khim., 1995, 65, (8), 1233–1235

The interaction of dimethylsulphoxide complexes [Ru(Me2SO4Cl2] (1) and RuCl3.2 Me2SO With N2H4. 2HC1 (2) produced ammonium Ru(III) compounds, [Ru(NH3)5Cl] Cl2 and fac -[Ru(NH3)3Cl3], depending on the length of heating. The interaction of RuCl3. n H20 with (2) resulted in the formation of isomeric compounds mer -[Ru(NH3)3Cl3]. After a short heat treatment of (1) with (2), the Ru complex [Ru(Me2SO)2-(N2H5)Cl3] was formed.

ELECTROCHEMISTRY

Oxygen Reduction on Weil-Defined Platinum Nanoparticles inside Recast Ionomer

a. gamez, d. richard, p. gallezot, f. gloaguen, r. faure and r. durand, Electrochim. Acta, 1996, 41, (2), 307–314

The effect of particle size on the catalytic activity of the O2 reduction reaction at a Pt/recast ionomer interface was studied by TEM and H and CO electrosorption, using porous graphite electrodes of well-defined geometry carrying well calibrated Pt particles. The catalytic powders were prepared by cationic exchange. For O reduction, the loss of catalytic activity with decreased Pt particle size is correlated with the stronger adsorption of oxygenated species under an inert atmosphere. No interparticle distance effects were seen, even for particles of 1.2 nm, 10 nm apart.

ElectrocataIytic Activities of Graphite-Supported Platinum Electrodes for Methanol Electrooxidation

p. c biswas, y. nodasaka and m. enyo F. Appl. Electrochem., 1996, 26, (1), 30–35

Electrooxidation of MeOH in 1 M NaOH at 30°C was studied on graphite-supported Pt electrodes prepared both in H2 and in air at various temperatures. Heating in H2 produced Pt of higher surface area with greater mass activity, than in air at a specific temper-ature.The electrodes had nearly the same specific activity as a smooth Pt electrode for MeOH electrooxidation regardless of the preparation conditions. The difference in mass activity is due to different surface areas resulting from different preparations. The first charge transfer process was the rate-determining step.

Pt-Base Electrodes and Effects on Phase Formations and Electrical Properties of High-Dielectric Thin Films

w.-j. lee, y.-m. kim and h.-g. kim, Thin Solid Films, 1995, 269,(1–2),75–79

Structvires and properties of Pb(Zr, Ti)03 PZT, and (Ba, Sr)TiO3 BST, thin films deposited on Pt/SiO2/Si substrates by MOCVD and r.f. sputtering were studied. Pt films sputter-deposited at 400°C had perfect (111) preferred orientation and a dense surface. A 130 nm PZT film deposited on Pt at 400°C had dielectric constant, ε = 1300 and remanent polarisation = 32 μC/cm2; a 100 nm BST film had ε = 575 and leakage current density at 2 V = 1.8 × 10-7 A/cm2.

Oxygen Evolution and Hypochlorite Production on Ru-Pt Binary Oxides

c.-c. hu, c-h. lee and t.-c. wen, F. Appl Electrochem., 1996, 26, (1), 72–82

The effects of varying coating solutions on the OER and the hypochlorite production ability of Ru-Pt oxide electrodes were studied. Maximum apparent activity occurred for coatings of 60 and 20 mol.% Pt for the OER and the Cl evolution reaction, respectively. Freshly prepared electrodes had lower current efficiencies for hypochlorite production than those treated by repetitive cyclic voltammetry, but both types were stable in 0.5 M NaCl at 300 mA/cm2 for a 480 h test.

Structural Effects in Electrocatalysis: Electrooxidation of Carbon Monoxide on Pt3Sn Single-Crystal Alloy Surfaces

h. a. gasteiger, n. m. markovic and p. n- ross, Catal. Lett., 1996, 36, (1, 2), 1–8

The electrochemical oxidation of CO and CO:H2 mixtures in H2SO4 was studied on clean annealed and sputtered cleaned non-annealed (110) and (111) surfaces of single crystal Pt2Sn. Annealed (111) and sputtered non-annealed (110) surfaces had very different activities. Relative to pure Pt surfaces, a potential shift > 0.5 V was observed for CO oxidation, which implies catalytic activity of four orders of magnitude higher. This high catalytic activity for the Pt3Sn surface is attributed to a unique adsorbed CO state.

Reactivity of 17- and 19-Electron Organometallic Complexes. Formation of Bent Sandwich 19-Electron Radical Cation Complexes of Ruthenium and Osmium

s. v. kukharenko, v. v. strelets, l. i. denisovich, m. g. peterleitner, a.z. kreidlin, a. r. kudinov and m. i. rybinskaya, Izv. Akad. Nauk, Ser. Khim., 1995, (12), 2394–2399

The redox behaviour of sandwich indenyl complexes (η5-C9H7)ML, M = Ru or Os, L = η5-C9H7, etc., was studied by cyclic voltammetry at a Pt electrode at -85 to 20°C and by controlled potential electrolysis. The complexes underwent reversible one-electron oxidation to the corresponding radical cations. A fast interaction of the 17-electron radical cations with nucle-ophiles yielded bent sandwich 19-electron radical cations [(η5-C9H7)M(L)(Nu)]+, Nu = Cl-, MeCN, etc.

High Sensitivity of Electron Transfer Rates within Nafion Coatings Saturated with to the Extent of Hydration of the Coating

m. shiandf. c. anson, F. Electrochem. Soc., 1995, 142, (12),4205–4214

Hydration effects on Nation coatings on glassy C disk electrodes showed that when only one electroactive counterion is present in the coating the electrochemical response is enhanced. Nafion coatings fully saturated with but containing little H2O had Nafionate salt properties; these are low ionic and electronic conductance and a high affinity for H2O, which occurs when some of the counterions are ejected from the coating allowing H2O to enter. Hydrated and unhydrated coatings are compared.

Electrooxidative Fission of Carbon-Carbon Double Bond in a K2OSO2(OH)4/HIO4 Double Mediatory System

h. tanaka, r. kikuchi, m. baba and s. torii, Bull. Chem. Soc. Fpn., 1995, 68, (10), 2989–2992

Electrooxidative C-C double bond fission of olefins occurred in the presence of catalytic amounts of K osmate and periodic acid. Corresponding carbonyl compounds were produced in moderate to good yields, when the turnover number of periodic acid reached ~ 3. The oxidative fission occurred by dihydroxylation of olefins followed by glycol cleavage. High selectivity to ketones showed that the regeneration of periodic species can occur in this electrooxidative media.

Surface Characterization Of RuO2-SnO2 Coated Titanium Electrodes

m. ito, y. murakami, h. kaji, k. yahikozawa and y. takasu, F. Electrochem. Soc., 1996, 143, (1), 32–36

Studies of the morphology of RuO2-SnO2 coatings supported on Ti showed that Ru is segregated in island-like deposits for RuO2-rich electrodes (1). For SnO22-rich electrodes, where Sn is localised in the macroscopically flat plane of ultrafine particles, Ru was segregated along cracks. The ultrafine particles on the SnO2-rich electrodes were smaller than those found for (1) and contributed to the large active surface area of the electrode. Only particles < 10 nm will give more active electrodes.

PHOTOCONVERSION

Effect of re-Si on the Photocatalytic Production of Hydrogen by Pt-Loaded CdS and CdS/ZnS Catalyst

g. c de, a. m. roy and s. s. bhattacharya, Int. J. Hydrogen Energy, 1996, 21, (1), 19–23

Studies of H2 production on illuminated CdS suspensions in Na2S/Na2SO3 solution showed that the maximum rate occurred with a photocatalyst of 1.5 wt.% Pt/CdS/n -Si (6–7 wt.%)/ZnS in a 1.5:1 weight ratio. An increased H2 rate was achieved by incorporating P-doped n -type Si in CdS. Combining small-bandgap semiconductor particles and larger-bandgap semiconductor particles increases photocatalytic efficiency.

Rigid Multinuclear Arrays Assembled Around Platinum Centres

a. harriman, m. hissler, r. ziessel, a. de cian and j. fisher, F. Chem. Soc., Dalton Trans., 1995, (24), 4067–4080

A series of cis - and trans -Pt(II) acetylide complexes of type where L = 2,2′-bipyridin-4-ylethynyl or 2,2′:6′52″-terpyridin-4′-yl-ethynyl or -butadiynyl, were prepared and their photophysical properties were measured at 293 and 77 K. The peripheral metal complexes of these PtII systems have relatively long-lived excited triplet states, and could function as effective photosensitisers. Photons collected by the central Prn site are quantitatively transferred to the terminal metal complexes. The PtII centre thus acts as a light-harvesting antenna, for near-UV light.

Photoreactions of Metal Complexes with DNA, Especially Those Involving a Primary Photo-Electron Transfer

a. kirsch-de me smaeke r, j.-p. lecomte and j. m. keixy, Topics Current Chem., 1996, 177, 25–76

Photochemical reactions induced by Ru(II), Rh(III) and Co(III) polypyridyl complexes, porphyrins and uranyl ions with DNA are reviewed. Electron transfer reactions are examined. Evidence for direct oxidation of the DNA bases, production of DNA-dam-aging reactive species, direct H abstraction from the DNA ribose and formation of adducts between the metal complex and DNA is provided. The use of metal complexes as photoprobes for studying nucleic acids and photo-therapeutic applications is discussed.

APPARATUS AND TECHNIQUE

Development of a Micro Glucose Sensor Using an Electrodeposited Platinum Black with Mechanical Stability

s. ikeda, h. watanabe and i. igarashi, Denkt Kagaku, 1995, 63, (12), 1138–1140

A glucose sensor has been fabricated from a Pt wire, sealed in the capillary of a 23-gauge needle with epoxy resin and electrodeposited with stable Pt black by ultrasonic irradiation from a solution containing H2PtCl6.6H2O. The sensor responds to glucose concentration of ≤ 50 mg/dl within a few minutes and its output current varies with O2 partial pressure. The sensor can be implanted via a semipermeable membrane.

In-situ Modification of the NO* Sensitivity of Thin Discontinuous Platinum Films as Gates of Chemical Sensors

j. zubkans, a. l. spetz, h. sundgren, f. winquist, j. kleperis, a. lusis and i. lundstrÖm, TAin Solid Films, 1995, 268, (1–2), 140–143

A sensor of improved NOx sensitivity, optimum at ~ 125°C, was obtained by modifying a thin discontinuous Pt gate MOSFET with NH3 at 150°C for 10 min. NOx exposure increases the threshold voltage but exposure to H2, NH3, alcohols and unsaturated hydrocarbons decreases it. The sensor was stable to NOx for one month without more NH3 treatment.

Voltresistometry of Noble Metals and Extension of Measuring Capability of the Contact EJectroresistance Method by Using Iridium Reference Electrodes

v. a. marichev and l. a. charny, Surf. Sei., 1996, 347, (1/2), 228–236

The potential dependence of the contact electrore-sistance (CER) of Pt, Ir, Ag and Au was studied in borate buffer solutions of pH 1–14. Ir has the lowest CER by 3–14 mΩ and can be used as the reference electrode for measuring high CER values of the oxides of metals, such as Ti, Zr and Cr. The CER of oxidised metal surfaces was non-ohmic. Thus, a new method is proposed for an in situ evaluation of the specific area of defects in oxide films on metals.

HETEROGENEOUS CATALYSIS

Adsorbate-Assisted NO Decomposition in NO Reduction by C3H6 over Pt/Al2O3 Catalysts under Lean-Burn Conditions

r. burch and t. c watling, Catal. Lett., 1996, 37, (1–2), 51–55

The rates and product selectivities of the C3H6-NO-O2 (1) and NO-H2 reactions over a Pt/Al2O3 catalyst, and of the NO decomposition over the reduced catalyst were compared at 240°C. The NO decomposition rate over reduced catalyst was 7 times greater than the NO decomposition rate in reaction (1). The (extrapolated) rate of the NO-H2 reaction at 240°C was ~ 104 times faster than the rate of the NO decomposition. NO decomposition may be assisted by Hads.

Nitric Oxide and Carbon Monoxide Adsorption on Lanthana-Supported Platinum and Rhodium Catalysts

h. cordatos and r j. gorte, Appl. Catal. B: Environ., 1995, 7, (1–2), 33–48

CO and NO adsorption studies by TPD on model Rh/lanthana and Pt/lanthana catalysts showed that the Ianthana surface can be reduced in CO by forming the carbonate which decomposes at 650 K. The reduced lanthana has similar adsorption and decomposition properties for NO as those seen for Pt and Rh. Adding Pt and Rh promotes the CO reduction of the lanthana surface, possibly by migration of the O from the lanthana to the metal surfaces.

Control of the Efficiency of Low-Percentage Pt-Cu/Al2O3 Catalysts in the Activation of CH and C-C Bonds in Light Alkanes

d. b. furman and a. p. barkova, Kinet. Katal., 1995, 36, (6), 878–882

The effects of preliminary preheating Cu(NO3)2/Al2O5 on Pt metal deposition and on C-H and C-C bond activation by Pt-Cu/Al2O3 catalysts were studied in ethane and propane. Treating Cu(NO3)/Al2O3 in H2 at 300–900°C produced catalysts which activate the ethane C-H bond, and form C2H4 selectively in 92–85% yield. Preliminary heat treating the support in air gave catalysts which activate the C-C ethane bond, and form CH4 selectively in > 60% yield.

Stationary Kinetics of Essential Reactions on Automobile Exhaust Pt-Rh/Al2O3 Catalyst

p. mannila, t. salmi, h. haario, m. luoma, m. hÄrkÖnen and j. sohlo, Appl Catal. B: Environ., 1996, 7, (3–4), 179–198

Oxidation and reduction reactions of three-way catalysts were studied over CeO2-promoted Pt-Rh/Al2O3 at 100–400°C. The concentrations of CO, CO2, total hydrocarbons, NO/NOx and O2 at the monolith outlet were measured for different gas feeds. When H2O was present, oxidation reactions were enhanced at low temperatures, while the H2O-gas shift reaction and steam reforming occurred at higher temperatures.

Aromatics Reduction over Supported Platinum Catalysts. 2. Improvement in Sulfur Resistance by Addition of Palladium to Supported Platinum Catalysts

t.-b. lin, c.-a. jan and j.-r. chang, Ind. Eng. Chem. Res., 1995, 34, (12), 4284–4289

Effects on the S resistance of a supported Pt catalyst on adding Co, Mo, Ni, Re, Ag and Pd, were studied by accelerated ageing reactions on tetralin hydrogenation with 1000 ppm S at 280°C, 380 psig and H2:oil = 2.7. Pd-Pt had the highest S resistance. Pd-Pt had the best catalytic performance for aromatic reduction, hydrodesulphurisation and hydrodenitrogenation of diesel. Pd-Pt bimetallic interactions lower the Pt electron density and inhibit H2S adsorption.

Surface Structure Change of a [Pt4(µ-CH3COO)8]/SiO2 Catalyst Active for the Decomposition of Formic Acid

w.-j. chun, k. tomishige, m. hamakado, y. iwasawa and k. asakura, F. Chem. Soc., Faraday Trans., 1995, 91, (22),4161–1170

Studies of catalytic properties of Pt4-cluster/SiO2 (1) prepared from the (Pt4(µ-CH3COO)8] cluster showed that it is highly active for HCOOH decomposition giving 100% selectivity to CO2 and H2, compared with the Pt-particle/SiO2 catalyst, which also gives CO and H2O. Reaction on (1) involved: an induction period; a slow reaction period; a catalytic high-rate reaction period; and deactivation. The surface structure of (1) changed from tetramer to dimer during induction, then to monomers which were active for catalysis.

Effects of Barium on NOx Reduction Activities of Palladium Three-Way Catalyst

h. shinjoh, k. yokota, h. doi, m. sugiura and s. matsuura, Nippon Kagaku Kaishi, 1995, (10), 779–788

Three-way automotive Pd/γ-Al2O3 catalyst modified with Ba was studied by NOx reduction using simulated exhaust gases, reaction gas chemisorption, H2O gas shift reaction, etc. A big improvement in the NOx reduction activity was seen at 100–500°C on adding Ba, under stoichiometric simulated exhaust gas (1) and under reduction conditions for the simulated exhaust gas (2). Under (1) NO was selectively reduced, rather than O2. Under (2), suppression of chemisorbed hydrocarbons allowed smooth NOx reduction.

Effect of Ceria Structure on Oxygen Migration for Rh/Ceria Catalysts

h. cordatos, t. bunluesin, j. stubenrauch, j. m. vohs and r. j. gorte, F. Phys. Chem., 1996, 100, (2), 785–789

The adsorption and reaction properties of Rh particles supported on a CeO2(100) surface and on poly-crystalline CeO2 film annealed at low (970 K) and high (1720 K) temperatures were studied. Significant growth of the CeO2 crystallite size and change in the surface morphology upon high-temperature annealing was found. High-temperature annealed CeO2 single crystals and polycrystalline films are relatively inert, but CO adsorbed on Rh/small CeO2 crystallites can be oxidised by CeO2. Thus, loss of O2 storage capacity in automotive catalysts may be due to changes in the CeO2 morphology and crystallite size.

Propionitrile Formation from Ethene and Ammonia over Rh/A-Zeolite

n. takahashi, h. sakagami, t. kamishima, s. azuma and t. matsuda, Catal. Lett., 1996, 36, (3,4), 241–244

Rh-Y zeolite catalyst was found to be very effective for C2H5CN formation from C2H4 and NH3. The catalyst was more active and selective than other transition metals supported on Y-zeolites. The reaction between C2H4 and HCN is proposed as a reaction route for C2H5CN formation.

One-Step Preparation of Highly Dispersed Supported Rhodium Catalysts by Low-Temperature Organometallic Chemical Vapor Deposition

p. serp, r. feurer, r. morancho and p. kalck, F. Catal., 1995, 157, (2), 294–300

A new method for preparing supported Rh catalysts using organometallic CVD, and contacting a Rh complex vapour with SiO2 in a fiuidised bed reactor at 50–100 Torr, is described. Adding small amounts of H2 allows Rh deposition at low temperature (100°C). Three Rh precursors, [Rh(μ-Cl)(CO)2]2, [Rh(η3-C3H5)3] and [Rh(acac) (CO)2], were used. Small aggregates of 1–2 nm with high dispersions of 0.95–0.70 were obtained. Rh(O) was detected on the surface, and Rh(I) and Rh(II) centres were found near the interface, covalently bound to the support. The catalyst showed greater hydrogenation activity than its counterpart prepared by conventional impregnation.

Ethanol Synthesis from Carbon Dioxide on TiO2-Supported [Rh10Se] Catalyst

h. kurakata, y. izumi andk.-i. aika, Chem. Commun., 1996, (3), 389–390

An efficient synthesis of EtOH from CO2/H2 over TiO2-supported [Rh10Se] clusters prepared from [Rh10Se(CO)22]2- is reported. Promoter effects of the interstitial Se inside the [Rh10] framework are discussed. [Rh10Se]/TiO2 converted CO2 into EtOH faster, 60 ×? 10-3 mol/h/g cat., and more selectively, ~83%, than other supported Rh clusters or [Rh10Se] clusters on other inorganic oxides. This may be due to effects from interstitial Se and the [Rh10Se]/TiO2 interface.

Redox and Carbonylation Chemistry of Iridium Species in the Channels of H-ZSM-5 Zeolite

t. v. voskobojnikov, e. s. shpiro, h. landmesser, ?. i. jaeger and g. schulz-ekloff, F. Mol. Catal. A: Chem., 1996, 104, (3), 299–309

Reduction of Ir/H-ZSM-5 by H2 yields Ir0 clusters with a large positive XPS shift and an upward IR shift of linearly bonded CO, which suggest a strong electron deficiency. Ir clusters (< 1 nm) can be rapidly reoxidised by the highly acidic hydroxyls with subsequent formation OfIr+(CO)2 gem-dicarbonyl even with residual CO. Displacement of NH3 ligands which were co-ordinated to unreduced Ir3+ cations formed Ir3+(CO)2. This species is reduced stepwise to Ir+(CO)2 and Ir0-CO via the H20-gas shift reaction.

Preparation of Ruthenium-Containing Polycarbonate Films and the Chemistry of Ruthenium in Polycarbonate

1. -w. shim, w.-s. oh, h.-c. jeong and w.-k. seok, Macromolecuks, 1996, 29, (4), 1099–1104

RuCl3.3H2O complexes were incorporated into polycarbonate (PC) using solvent. Interactions with CO,O2, H2 etc., effects of the Ru complexes and thermal properties of PC were studied in films. Catalytic activities were observed in various gas phase reactions under relatively mild conditions, such as NO reduction, H2O-gas shift reaction, etc.

HOMOGENEOUS CATALYSIS

Polyketone Polymers Prepared Using a Palladium/Alumoxane Catalyst System

y. koide and a. r barron, Maeromoleeules, 1996, 29, (4), 1110–1118

The Pd-catalysed copolymerisation of CO and ethylene to give polyketone polymers was achieved using either (dppp)Pd(OAc)2 or (dppp)Pd[C(O)tBu] Cl in the presence of a tert -butyl alumoxane as a co-catalyst. The polymers were alternating ethylene/CO and had high molecular weights. No furanisation or cross-linking was found. The crystal structure of these poly-mers was that of the α-phase polyketone. The increased densities of these polyketones is due to a decrease in the interchain packing distances.

Unprecedented Intra- and Intermolecular Palladium-Catalyzed Coupling Reactions with Methylenecyclopropane-Type Tetrasubstituted Alkenes

s. brÄse and a. de meijere, Angew. Chem., Int. Ed. Engl., 1995, 34, (22), 2545–2547

A cascade of reactions consisting of a Heck coupling, cyclopropyl ring-opening and a domino Diels-Alder reaction proceeded in a one-pot synthesis in the presence Of Pd(OAc)2. The Pd-catalysed coupling of bicy-clopropylidene with vinyl iodide gave dendralene, even in the presence of dienophile, which then reacted with R1 = H, CO2Me or R2 = CO2Me to yield bisadducts. Carbopalladation of the tettasubstituted alkene proceeds faster than the Heck reaction with the dienophile.

A New, Highly Selective, Water-Soluble Rhodium Catalyst for Methyl Acrylate Hydroformylation

g. fremy, y. castanet, r. grzybek, e. monflier, a. mortreux, a. m. trzeciak and j. j. ziolkowski, J. Organomet. Chem., 1995, 505, (1), 11–16

Hydroformylation of methylacrylate to α-aldehyde was achieved in a two-phase system in the presence of two new H2O-Soluble Rh phosphine PNS and PC catalysts, prepared by reacting [Rh(acac) (CO2)] with various H2O-Soluble monodentate phosphines, such as Ph2PCH2CH(COOLi)(CH2COOLi) (PC), Ph2PCH2-CH2CONHC(CH3)2CH2SO3Li (PNS), P(CH2)n -C6H4SO3Na]3, etc. High yields and selectivities of α-aldehyde were obtained.

Substrate Selective Catalysis by Rhodium Metallohosts

h. k. a. c. coolen, j. a. m. meeuwis, p. w. n. m. van leeuwen and r j. m. nolte, F. Am. Chem. Soc., 1995, 117, (48), 11906–11913

A new supramolecular catalyst, consisting of a basket-shaped molecule with a catalytically active Rh(I) complex attached, is described. It functions according to the principles of enzymatic catalysis. The catalyst selectively hydrogenates and isomerises allyl-sub-stituted dihydroxyarene substrates bound in its cavity. The rate-limiting component of these catalysts is the metal centre and the process sequence there.

Ligand Effects in the Catalytic Hydrogenation of Carbon Dioxide to Formic Acid Using in situ Catalysts Formed from [{(cod)Rh(μ-Cl)}2] and Monodentate and Bidentate Phosphorus Ligands

e. graf and w. leitner, Chem. Ber., 1996, 129, (1), 91–96

Highly active catalysts for the hydrogenation of CO2 to formic acid in DMSO/NEt3 were formed in situ from [{(cod)Rh(μ-Cl)}2] and various monodentate or bidentate ligands with P as the donor atom. Formic acid concentrations of ≤ 2.3 ± 0.2 mol/1 were obtained in < 6 h at ambient temperature under a total initial pressure of 40 arm by using Rh concentrations of 5 × 10-3 mol/l. With bidentate ligand R2P(CH2)n PR2 the chain length n determines the activity of the catalysts.

Ligand-Induced Selectivity in the Rhodium(H)-Catalyzed Reactions of α-Diazo Carbonyl Compounds

a. padwa, d. j. austin and s. f. hornbuckle, F. Org. Chem., 1996, 61, (1), 63–72

The reaction of 3-allyl-2,5-diazopentanedione and 3-butenyl-2,5-diazopentanedione with traces of a Rh(H) catalyst in methylene chloride at room temperature gave products with internal trapping of a carbonyl ylide as well as intermolecular cyclopropanation. When the catalyst was changed from Rh2(OAc)4 to Rh2(cap)4 to Rh2(tfa)4, a significant change occurred in the product distribution. With Rh2(rfa)4, an unexpected regio-chemical crossover occurred in cycloaddition, due to complexation of the metal with the dipole.

Homogeneous Hydrogenation of Carbon Dioxide to Methanol Catalyzed by Ruthenium Cluster Anions in the Presence of Halide Anions

k.-i. tominaga, y. sasaki, t. watanabe and m. saito, Bull. Chem. Soc Jpn., 1995, 68, (10), 2837–2842

Detailed catalytic and mechanistic studies showed the first formation of MeOH, together with CH45 by homogeneous hydrogenation of CO2 using a system consisting of Ru3(CO)12 and alkaline iodides in N-methylpyrrolidone solution at 240°C. The successive formation of CO, MeOH, and then CH4 was indicated. An overall reaction mechanism is proposed.

Coupling H2 to Electron Transfer with a 17-Electron HeterobimetalUc Hydride: A “Redox Switch” Model for the H2-Activating Center of Hydrogenase

r. t. hembre, j. s. mcqueen and v. w. day, F. Am. Chem. Soc., 1996, 118, (4), 798–803

The preparation of a meta-stable heterobimetallic mixed-valence ion, [Fe(II),Ru(III)], formed by one-electron oxidation of Cp*(dppf)RuH (1), where dppf = 1,1’-bis (diphenylphosphino) ferrocene and Cp* = pentamethylcyclopentadienide, is reported. Cyclic voltammetry of (1) showed that there was great stability for one-electron oxidation. Two reversible oxidations at +0.073 and +0.541 V and a quasireversible oxidation at +0.975 V (vs NHE) appeared and were assigned to Ru(III/II), Ru(IWIII) and Fe(IIMI), respectively. Compound (1) is the first homogeneous catalyst to reduce methyl viologen with H2.

Amino Alcohol Effects on the Ruthenium(H)-Catalysed Asymmetric Transfer Hydrogenation of Ketones in Propan-2-ol

j. takehara, s. hashiguchi, a. fujii, s.-i. inoue, t. ikartyaandrnoyori, Chem. Commun., 1996, (2), 233–234

A Ru(IT) complex, generated in situ from [{RuCl26-C6Me6}]2], (IS, 2S)-2-methylamino-l,2-diphenyl-ethanol and KOH was found to be an efficient catalyst for asymmetric transfer hydrogenation of acetophe-none derivatives in propan-2-ol. The catalyst had high reactivity at room temperature. (S)-enriched alcohols in ≤ 92% ee and in > 90% yield are produced.

FUEL CELLS

A New Fuel Cell Electrocatalyst Based on Highly Porous Carbonized Polyacrylonitrile Foam with Very Low Platinum Loading

s. ye, a. k. vtjh and l. h. dao, F. Electrochem. Soc., 1996, 143, (1), L7–L9

A carbonised polyacrylonitrile (PAN) microcellular material of high porosity with incorporated Pt loading of ~ 13 µg/cm2 was prepared, characterised and used as the electrode material for O2 reduction. It has excellent electrocatalytic activity which is attributed to the highly homogeneous distribution of the small Pt particles in the carbonised PAN foam surface.

Improved Pt Alloy Catalysts for Fuel Cells

a. freund, j. lang, t. lehmann and k. a. starz, Catal. Today, 1996, 27, (1–2), 279–283

Electrode catalysts, Pt-Co-Cr/C black, with increased activity and stability for the O2 reduction reaction in phosphoric acid fuel cells were developed by co-precipitation of the corresponding metal nitrates. A tetragonal ordered structure was formed at > 873 K. This method will allow preparation of more efficient catalysts of small Pt-Co-Cr alloy particle size.

CORROSION PROTECTION

Effect of Mo and Pd on Corrosion Resistance of V-Free Titanium Alloys for Medical Implants

y. okazaki, k. kyo, y. ito and t. tateishi, F. Jpn. Inst. Met., 1995, 59, (10), 1061–1069

The corrosion resistance of Ti-15%Zr-4%Nb-4%Ta-0.2%Pd-0.2%O-0.05%N and Ti-15%Sn-4%Nb-2%Ta-0.2%Pd-0.2%O alloys, for medical implants, were compared with pure Ti Grade 2 alloys, Ti-6%A1-4%V ELI (Extra low interstitial), etc., by anodic polarisation and immersion testing at 310 K in various pseudo saline solutions. The rate of Ti ion released by Ti alloys in a deaerated 5% HCl solution decreased with increasing Zr, Nb, Ta and Pd contents.

ELECTRICAL AND ELECTRONIC ENGINEERING

Improved p-Channel InALWGaAsSb HIGFET Using Ti/Pt/Au Ohmic Contacts to Beryllium Implanted GaAsSb

k. g. merkel, c l. a. cerny, v. m. bright, f. l. schuermeyer, t. p. monahan, r t. lareau, r. kaspi and a. k. rai, Solid-State Electron., 1996, 39, (2), 179–191

Ti/Pt/Au metallisation produces an extremely low contact resistance on Be implanted GaAs1-xSbx. The contact is thermally stable at 250°C for ~ 500 h and can withstand thermal cycling to 450°C. The use of Ti/Pt/Au as the source, drain and gate metallisation produced a single, conventional metallisation for the In0.52Al0.48As/GaAs0.51Sb0.49 p -HIGFET, which is improved with respect to ohmic contact reliability, etc. Using Be implantation with Ti/Pt/Au metallisation directly enhances future device designs.

Bias and Thickness Dependence of the Infra-Red PtSi/p-Si Schottky Diode Studied by Internal Photoemission

v. w. l. chin, j. w. v. storey and m. a. green, Solid-StateElectron., 1996, 39, (2), 277–280

IR PtSi/p -Si diodes with different metal thicknesses were studied at ~ 80 K by internal photoemission as a function of reverse bias. The zero-bias barrier height of PtSi/p -Si was found to increase only marginally with metal thickness. The main lowering of the Schottky barrier height is at low to moderate electric fields. The carrier mean free path in Si decreased with an increase in the semiconductor acceptor density.

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