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Platinum Metals Rev., 1996, 40, (4), 189

ABSTRACTS: October 1996

of current literature on the platinum metals and their alloys

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PROPERTIES

High-Temperature Creep of Pure Platinum

t. hamada, s.hitomi, y. ikematsu and s. nasu, Mater. Trans. JIM, 1996, 37, (3), 353–358

The creep behaviour of high purity Pt (99.999 mass%) was studied at 1373–1773 K. Pt showed the power-law creep with the stress exponent of the steady state rate being ∼ 6. Recrystallisation to bamboo-type grains from the initial polycrystalline micro-grains was observed. The creep rupture mechanism changed on recrystallisation from grain boundary fracture due to coalescence of the voids to rupture by necking or shear-ing-off. The activation energy for the steady state creep is (3.1 ± 0.3) x 105 J/mol.

Visualization and Analysis of Forced Diffusion of Hydrogen in Palladium by Electrotraneport

m. tamaki, s. hara, i. kondoh1k. yoneda, a. tsuruno and h. kobayashi, Nucl. Instr. Methods Pkys. Res. A, 1996, 377, (1), 166–169

Hydrogen was electrotransported in Pd hydride by an applied electric field to densify H at the cathodic side. The effectiveness of the electrotransportation was studied by neutron radiography. The H:Pd concentration was enhanced to 0.75 ± 0.05 at 395 K, after 100 days using 0.31 MPa H2, which is equivalent to a H2 equilibrium pressure of 100 MPa. The effective number of the electric charge of H in the Pd hydride (β) phase was 0.38 ± 0.08.

Properties and Structures of Cu-16.67Pd and Cu-37.5Pd Alloys

j. mu, Precious Met. (China), 1996, 17, (2), 12–17

Properties and structures of Cu-16.67Pd and Cu-37.5Pd alloys were studied by determining resistance, hardness, thermal analysis, TEM and XRD. The properties of the CuPd alloy were unusual. A Cu3Pd ordered compound with a tetragonal structure was formed after prolonged heat treatment and Cu-37.5Pd was transformed into the b.c.c. phase.

Development of Ir-Base Refractory Superalloys

y. yamabe, y. koizumi, h. murakami, y. ro, t. maruko and h. harada, scr. metall. mater., 1996, 35, (2), 211–215

A new class of Ir-base, refractory superalloys is described, which are alloys with γ-f.c.c. and γ′-L12 coherent structures similar to Ni-base superalloys, but with higher melting points. Ir-15 at.%Nb and Ir-15 at.%Ti refractory superalloys have γ/γ′ coherent two-phase structures, high compressive strengths and enhanced oxidation resistance. Their 0.2% flow stresses at 1800°C were 210-220 MPa, equivalent to those of the strongest W-base refractory alloys.

CHEMICAL COMPOUNDS

Patterns of Multiple Additions to Fullerene C70: Isolation and Structural Characterization of [C70{Pt(PPh3)2}4]

a. l. balch, l. hao and m. m. olmstead, Angevi. Chem., Int. Ed. Engl., 1996, 35, (2), 188–190

Addition reactions of Pt(PPh3)2 units to C70 are reported, which involve the successive formation of four adducts [C70{Pt(PPh3)2}], [C70{Pt(PPh3)2}2], [C70{Pt(PPh3)2}3] and [C70{Pt(PPh3)2}4] with the eventual addition of the four Pt atoms in a plane about the fullerene. The stepwise addition Of Pt(PPh3)2 groups occurs first to the most pyramidalised C-C bonds at the poles of the fullerene, with subsequent additions to the adjacent 6–6 ring junctions.

Synthesis and Characterization of Platina-β-diketones

d. steinborn, m. gerisch, k. merzweiler, k. schenzel, k. pelz, h. bÖgel and j. magull, Organometallics, 1996, 15, (10), 2454–2457

H2PtCl6 was reacted with n -butanol to give the but-2-ene complex H[PtCl32-C4H8)] as intermediate. This was further reacted with trimethylsilyl-substi-tuted acetylenes R′C;≡CSiMe3 (R′ = H, Me, SiMe3) with cleavage of the silyl groups to form Pt-β-dike-tones (Pt2(¼-CI)2{(COR)2H}2], R = Me, Et.

Organopalladium and Platinum Complexes of C60 Bearing Isonitrile Ligands

h. nagashima, m. nakazawa, t. furukawa and k. itoh, Chem. Lett. Jpn., 1996, (5), 405–406

Organo Pd or Pt complexes, (η2-C60)M(CNR)2, where M = Pt or Pd, R = 1Bu, 2,6-Me2C6H3,2,4,6-Me3C6H2, cyclohexyl, were prepared from C60Mn, where n ∼ 1, and the corresponding isonitriles. Careful reaction of C60Ptn with CN(2,6-Me2C6H3) yielded 72% of (η2-C60)Pt[CN(2,6-Me2C6H3)]2. This further reacted with additional isonitriles to give (η2-C60)Pt[CN(2,6-Me2C6H3)], in 77% yield.

“Swollen” Macrocycles: Palladium(DI)-Directed Template Syntheses of Pendant-Arm 14-, 16-, and 18-Membered Macrocycles

m. rossignoli, c c. allen, t. w. hambley, g. a. lawrance and m. maeder, Inorg. Chem., 1996, 35, (17), 4961–4966

Bis(diamine)Pd(H) cations with varying chain lengths undergo condensation reactions with HCHO and nitroethane to produce macromonocycles, where each pair of cis -disposed primary amines is converted to a -NH-CH2-C(CH3)(NO2)-CH2-NH- strap. Use of the Pd(II)-template extends the synthesis to larger ring macrocycles. Increased distortion and a change in geometric isomer occurred with increasing ring size.

Preparation and Characterization of the Dicarbon Cluster Complex Ru55-C2)(μ-SMe)2(μ-PBu2)2(CO)11

c. j. adams and m. i. bruce, Aust. J. Chem., 1996, 49, (4), 517–520

Bis-tertiary phosphine C2(PBu2)2 (dbpa) was prepared and used to synthesise a Ru5 cluster containing a C2 ligand. Pyrolysis of the Ru carbonyl derivative {Ru3(CO)11}2(μ-dbpa) produced Ru55-C2PBu2)(μ-PBu2)(CO)13 in 41% overall yield from Ru3(CO)12. Further reaction with Me2S2 gave Ru55-C2) (μ-SMe)2(μ-PBu2)2(CO)11 in 19% yield.

ELECTROCHEMISTRY

Kinetics of Oxygen Reduction at IrO2-Coated Titanium Electrode in Alkaline Solution

c-c chang and t.-c. wen, J. Electrochem. Soc., 1996, 143, (5), 1485–1491

Cyclic voltammetry and rotating-disk electrode techniques were used to study O2 reduction at an IrO2-coated Ti electrode fabricated by thermal decomposition. O2 reduction on an electrode in alkaline solutions of pH 10.8-13.8 was catalysed by the Ir(III)/Ir(IV) transition on the IrO2-Coated Ti electrode. In the low polarisation region, O reduction with a Tafel slope of – 40 mV/decade depended on the solution pH and had a reaction order of-2 in OH-. In the high polarisation region, the process was nearly pH independent. Both cases were first order in the dissolved O2 concentration.

The Influence of Acetonitrile and Methanol on the Charge Transport Properties of [Os(bipy)2(PVP)10Cl] Cl Films

d. m. kelly and j. g. vos, Electrochim. Acta, 1996, 41, (11/12), 1825–1832

Addition of acetonitrile or MeOH to aqueous LiClO4 electrolyte solutions greatly changed the electrochemical behaviour of electrodes modified with [Os(bipy)2(PVP)10Cl]Cl films (bipy = 2,2′-bipyridyl; PVP = poly(4-vinylpyridine). The charge transport rate was enhanced 100-fold upon addition of 5-60% of the solvents. Polymer swelling is controlled by organic solvent content, and polymer chain motion becomes the rate limiting process, instead of ion movement.

PHOTOCONVERSION

Hydrogen Production by Water Photolysis Using Nitrilotriacetic Acid as Electron Donor

h. a. f. werner and r. bauer, J. Photochem. Photobiol., A: Chem., 1996, 97, (3), 171–173

H2 was photochemically produced in a system containing Ru(bipy)32+, methyl viologen, colloidal Pt catalyst and nitrilotriacetic acid (NTA), as sacrificial electron donor. The highest turnover numbers were ∼ 175 for both methyl viologen and Ru(bipy)32+, and > 250 for the Pt catalyst after 4 h irradiation at pH 4.5. Nearly 49% of NTA was oxidised after 6.5 h irradiation. The photochemical behaviours of di-(iminodiacetic) and mono-(aminoacetic) acids were also examined.

Photophysical Properties of (η2-C60)Pd(PPh3)2 Complex in Benzene. Picosecond and Nanosecond Laser Photolysis

n. n. denisov, a. s. lobach and v. a. nadtochenko, Izv. Akad. Nauk, Ser. Khim., 1996, (5), 1163–1166

The spectra of photoexcited (η2-C60)Pd(PPh3)2(1) complexes were studied in benzene by ps and ns laser photolysis, and compared with the photoexcited C60 spectra and charge transfer spectra of electron donor-acceptor complexes between C60 and ternary amines. The relaxation kinetics of excited (1) had three com-ponents with lifetimes τ1 = 43 ps, τ2 = 1500 ps and τ3= 1.17 μs. The fourth level of relaxation is discussed.

Catalytic and Photocatalytic Hydrogenation of Hexanal with Molecular Hydrogen in the Presence OfRhCl(PMe3)2CO

n. k. khannanov, g. n. menchikova and e. a. grigoryan, Kinet. Katal., 1996, 37, (1), 62–64

The Rh complex RhCl(PMe3)2CO was found to catalyse the hydrogenation of hexanal to hexanol at room temperature and H2 pressure of > 50 arm. The reaction occurred during exposure to light of wavelength λ > 340 nm. After 4 h at room temperature, hexanol production reached 30 mole/mole of Rh.

Time-Resolved Luminescence Investigation of the Adsorption of Ru(bpy)32+ onto Antimony-Doped SnO2 Colloidal Particles

w. e. ford, j. m. wessels and m. a. j. rodgers, Langmuir, 1996, 12, (4), 3449–3453

The adsorption of Ru(bpy)32+ (bpy = 2,2′-bipyridine) (1) onto negatively charged Sb-doped SnO2 colloidal particles ∼ 4 nm in diameter was monitored by time-resolved luminescence and was found to conform to the Frumkin isotherm. Electron injection from photoexcited (1) into the conduction band of the semiconductor particle resulted in luminescence quenching mainly within the laser pulse when the complex is bound to the particle, but the luminescence of the unbound complex decays with a lifetime of several hundred nanoseconds. The average maximum capacity of each particle for adsorbed (1) determined by the binding data, 29 ± 10, is in agreement with the value obtained by ion exchange, 30 ± 4, but is smaller than predicted for a close-packed monolayer.

Traws-Chromophore-Quencher Complexes Based on Ruthenium(II)

b. j. coe, d. a. friesen, d. w. thompson and t. j. meyer, Inorg. Chem., 1996, 35, (16), 4575–4584

A series of chromophore-quencher complexes (1), trans -tRu(bpy)2(pya)(pyb)]n+ (bpy = 2,2′-bipyridyl; pya, pyb = substituted pyridyl ligands; n = 2-4) containing combinations of the electron donor PTZ in py-PTZ (py-PTZ = 10-(4-picolyl)phenothiazine) and the electron acceptors MQ+ (l-memyl-4,4′-bipyridinium cation), etc., is described. At temperatures < 150 K the complexes display MLCT emission. At higher temperatures, visible light irradiation leads to photochemical decomposition, by crossing to a ligand-field state. This is important for the stereochemical design of Ru-based (1).

ELECTRODEPOSITION AND SURFACE COATINGS

Electroless Metal Plating on Carbonaceous Mesophase Spherules

t. teranishl k. takeda, y. yamazaki and m. miyake, Carbon, 1996, 34, (5), 589–594

Pd(NH3)42+ ions (1) were immobilised electrostatically on oxidised carbonaceous mesophase spherules, M6G, at pH 11. PdCl42- ions could not be immobilised. Ni was plated onto oxidised M6G, after immobilisation of 30 wt.% (1), at uniform thickness increasing from 0.8 to 2.0 μm, due to an increase in pH from 7–8 during plating. Cu plating was also performed.

APPARATUS AND TECHNIQUE

Double Electropolymer Modified Platinum Electrode to Follow the Kinetic Process H2O2 + Ascorbic Acid. Influence of the Reaction on Amperometric Biosensor Applications

i. losrro and c. g. zambonin, J. Elearoanal Chent., 1996, 410, (2), 181–187

The kinetics of ascorbic acid (AA) oxidation by H2O2 was studied on a Pt electrode modified by a polypyr-role/poly(orthophenylenediamine) bilayer membrane at 27°C and pH 7. Under AA:H202 ratios of 1000:1, pseudo-first-order kinetic constant values of 3.26 x 10-3 to 4.10 x 10-3/s were obtained at [AA] = 2 mM and initial [H2O2] = 2 ¼M. The sensitivity and reliability of H2O2 detectors, with AA present, are discussed.

Enzyme Sensors Prepared by Electrodeposition on Platinized Platinum Electrodes

c s. kim and s. m. oh, Electrochint. Acta, 1996, 41, (15), 2433–2439

Platinised Pt(I) (Pt black) electrodes were used as the base electrodes for the immobilisation of glucose oxidase (GOD). The GOD sensors were made by electrodeposition of GOD/bovine serum albumin mixture on (1) and subsequent cross-linking with glutaralde-hyde. The roughness factors and morphologies of the (1) surfaces depended on the platinisation potential (0 to -0.25V). Pt black electrodes plated at more negative potentials gave high current signals to the GOD sensors. Adhesion of O2 bubbles can be greatly suppressed on the hydrophilic Pt surfaces, giving better S:N ratios in the current signals of these enzyme sensors.

Ammonia-Sensing Characteristics of Pt-Doped CdSnO3 Semiconducting Ceramic Sensor

t. zhang, y. shen, r. zhang and x. liu, Mater. Lett., 1996, 27, (4, 5), 161–164

Pt-doped mixtures of α- and β-CdSnO3 exhibited a high sensitivity and selectivity to NH3 gas. Mixtures of different ratios of β:α were obtained by calcining the raw CdSnO3 powder precursor. A 1 wt.% Pt doped mixture with β:α = 2.0 showed a very high sensitivity and selectivity to NH3 gas. At ∼ 240°C, the sensor can detect ppm of NH3 in air, while at higher tem-peratures it can selectively detect LPG or H2.

Current vs Voltage Characteristics of Al-Al2O3-Pd Tunnel Junction Hydrogen Sensor

s. okuyama, k. okuyama, n. takinami, k matsushita and y. kumagai, Jpn. J. Appl. Phys., 1996, 35, (4A), 2266–2270

The conduction mechanism of an Al-Al2O3-Pd MIM (metal-insulator-metal) junction, which can operate as a H2 gas sensor, displayed I-V characteristics that are typical of tunnelling conduction at > 3 V. The barrier height of the Pd-Al2O3 contact obtained from the position of the logarithmic derivative maximum of the current was 3.4 eV in vacuum and decreased to 2.7 eV under 40 Pa H2. The barrier height of the Al-Al2O3 contact was 1.8 eV in vacuum and did not change with increasing H2 pressure.

Iridium-Dispersed Carbon Paste Enzyme Electrodes

j. wang, g. rtvas and m. chicharro, Electroanalysis, 1996, 8, (5), 434–437

An Ir-dispersed C-paste transducer was successful as a very selective first-generation glucose biosensor. The Ir/C particles had excellent electrocatalysis for both reduction and oxidation of H2O2. This allows glucose biosensing at very low operating potentials, without interference. The Ir biocomposite had similar selectivity as its Rh and Ru counterparts and retained die sensing advantages of C paste enzyme electrodes.

Dissolved Oxygen Sensor Based on Fluorescence Quenching of Oxygen-Sensitive Ruthenium Complexes Immobilized in Sol-Gel-Derived Porous Silica Coatings

a. k mcevoy, c m. mcdonagh and b. d. maccratth, Analyst, 1996, 121, (6), 785–788

A sensor for dissolved O based on fluorescent quenching [Ru11tris(4,7-diphenyl-1,10-phenanthroline)] entrapped in a porous sol-gel SiO2 film is reported. The sol-gel films were prepared by dip-coating onto planar and optical fibre substrates. Surface modification of the sol-gel film enhanced sensor performance. By using organically modified precursors which impart surface hydrophobicity, the quenching response can be increased by a factor > 3.5. A very low detection limit of 6 ppb was determined for the modified films.

HETEROGENEOUS CATALYSIS

Hydrogenation of Naphthalene with Platinum-Aluminium Borate Catalysts

t.-c. huang and b.-c kang, Chem. Eng. J., 1996, 63, (1), 27–36

Aluminium borate (ABx) supported Pt catalysts were studied for hydrogenation activity using naphthalene dissolved in n -hexadecane to simulate the aromatics in diesel fuels. The aromatic hydrogenation activity of Pt-ABx (1) was higher than that of Pt/88-Al2O3 (2), but its os-decalin selectivity was lower, due to the higher acidity of the ABx support. Addition of B to (2) gave a better aromatic hydrogenation catalyst Pt-Bx-Al2O3, than (1). Hydrogenation and hydrogenolysis activities of (1) increased with a decrease in the A1:B atomic ratio.

Activity of Bifunctional Pt-Dy/Al2O3 Catalysts in Hydrocarbon Reactions

s. cheng, f. u and l. luo, React. Kinet. Catal. Lett., 1996, 57, (1), 119–125

The conversions of n -hexane and methylcyclopentane on 0.5 wt.% Pt-Dy/Al2O3 containing 0.1-1 wt.% Dy were studied on catalysts prepared by co-impregnation of γ-Al2O3 powders with an aqueous solution of H2PtCl6, Dy2O3 and HCl. The n -hexane conversions over Pt-Dy/Al2O3 catalysts were higher than over Pt/Al2O3, but hydrogenolysis activity was unchanged. The dehydrocyclisation of n-hexane to benzene over Pt-Dy/Al2O3 was greater than that of Pt/Al2O3.

Pt-SnAAl2O3 Sol-Gel Catalysts: Catalytic Properties

r. gÓmez, v. bertin, t. lÓpez, i. schifter and g. ferrat, J. Mol. Catal. A: Chem., 1996, 109, (1), 55–66

Pt-Sn supported catalysts, containing various amounts of Pt and Sn, were prepared by the sol-gel method by adding tetrabutyltin to a homogeneous solution containing Al tri-sec-butoxide, followed by drying, calcination and impregnation with aqueous H2PtCl6. The catalysts had specific BET areas of ∼ 270 m2/g and Pt dispersions up to 90%, with fewer acidic sites being observed in Sn-Al2O3 sol-gel preparations than in sol-gel Al2O3. The catalysts had 54% lower selectivity to benzene formation and higher selectivity to acetone. High tolerance to thiophene poisoning during n -heptane dehydrocyclisation was also found.

HCN Synthesis by Ammoxidation of Methane and Ethane on Platinum Monoliths

s. s. bharadwaj and l. d. schmidt, Ind. Eng. Chem. Res., 1996, 35, (5), 1524–1533

HCN synthesis by the ammoxidation of CH4 (1), C2H6 and CH4/C2H6 mixtures in air or O2 at atmospheric pressure on ±-Al2O3 foam monoliths coated with 1–10 wt.% Pt and on Pt-10% Rh gauzes was studied. On Pt monoliths for ammoxidation of (1), HCN yields > 63% were achieved, which is comparable to yields on industrial Pt-10%Rh gauzes. Large improvements in yields were obtained by exposing the catalyst to high temperatures for several hours. Ammoxidation of C2H6 yielded ∼42% HCN on Pt monoliths during HCN synthesis conditions. At richer C2H6 compositions, C2H4 was the dominant product.

Durability of Automotive Pd 3-Way Catalyst Added Ba or La

h. shinjoh, t. suzuki, n. takahashi, k. yokota, m. sugiura and s. matsuura, Nippon Kagaku Kaishi, 1996, (5), 433–440

The effects of adding La or Ba to a three-way Pd car catalyst were studied and compared with activities and durabilities of Pa/γ-Al2O3 after ageing in simulated exhaust gases at 600-900°C. Modified catalysts had improved NOx reduction. After ageing at > 800°C, the NOx reduction activities of the PdVBa catalyst were superior to those of Pd/La under reducing conditions, and maintained high NOx reduction, as Ba was more difficult to react with γ-Al2O3 than La.

Development of Supported Thin Palladium Membrane and Application to Enhancement of Propane Aromatization on Ga-Silicate Catalyst

k. kusakabe, s. yokoyama, s. morooka.j.-i. hayashi and h. nagata, Chem. Eng. Sci., 1996, 51, (11), 3027–3032

A high performance thin Pd membrane was formed by Pd acetate sublimation at reduced pressure at 400°C through the macropores of an ±-Al2O3 support tube. H2 permeance and selectivity to N were > 10-6 mol/m2/ s/Pa and 1000, respectively. The membrane was resistant to H embrittlement and poisoning by S and Cl. Ga/SiO2 catalyst was prepared and fitted in a tubular reactor with the Pd membrane. Propane conversion and aromatics selectivity were improved by removal of H.

Promotion Effect of Polymer-Immobilized Neodymium Ions on Catalytic Activity of Ultrafine Palladium Particles

t. teranishi, k. nakata, m. miyake and n. toshima, Chem. Leu. Jpn., 1996, (4), 277–278

Monodispersed ultrafine Pd particles protected by polyacrylate (PA)-Nd3+ complexes had catalytic activity for acrylic acid hydrogenation. The acrylic acid may be concentrated around ultrafine Pd particles by co-ordinating to Nd ions bound to the protecting polymer. A promotion effect was observed for (PA)-pro-tected Pd particles, but not for colloidal dispersions of poly(N -vinyl-2-pyrrolidone)-protected particles.

Design of a Novel Pd Three-Way Catalyst: Integration of Catalytic Functions in Three Dimensions

z. hu, c z. wan, y. k. lui, j. dettling and j. j. steger, Catal. Today, 1996, 30, (1–3), 83–89

Pd catalysts for three-way conversion of HC/CO/NO were studied using simulated auto exhaust gas at 423–823 K. When CeO2 was introduced into the Pd catalysts, NO conversion at ∼ 600 K was reduced, while NO conversion at ∼ 770 K increased. An integrated Pd-only catalyst washcoat was designed, consisting of a top Pd and a bottom Pd-Ce layer, to maximise HC/CO/NO performance. Engine and vehicle evaluation showed that this catalyst, which integrates Pd sites and O2 storage components in three dimensions, has superior three-way performance.

Synthesis of Ru, Rh and Pd Complexes Immobilized on Modified Supports. Investigation of the Hydrogenation of Cinnamaldehyde

v. isaeva, a. derouault and j. barrault, Bull. Soc. Chim. Fr., 1996, 133, (4), 351–357

Cinnamaldehyde was hydrogenated over complexes, such as Rh2(O2CCH3)4 (1), Ru2(O2CCH3)4 (2), Pd(NH3)4Cl2, PdCl2 or Ru2(O2CCH3)4, immobilised on modified supports, such as SiO2 gels or resins. The selectivity to unsaturated alcohol was improved by using weak base supports containing aliphatic or heterocyclic amino groups; immobilised (2) was the best. Immobilised (1) catalysed C=C bond hydrogenation.

CO2 Hydrogenation to Ethanol over Promoted Rh/SiO2 Catalysts

h. kusama, k. okabe, k. sayama and h. arakawa, Catal. Today, 1996, 28, (3), 261–266

Hydrogenation of CO2 to EtOH was performed over Rh/SiO2 based catalysts promoted with various metal oxides, Li salts had the most prominent effect on EtOH formation. Under optimised reaction condi-tions, the highest EtOH selectivity obtained over Rh-Li/SiO2 was 15.5% with a CO2 conversion of 7.0% at 5 MPa and 513 K in a flow OfH2-CO2 premixed gas with a flow-rate of 100 cm3. In-situ FT-IR studies suggest that CO2 was hydrogenated to EtOH via CO intermediate(s).

Catalytic Activity of Perovskite-Type La0.8JiSr0.2M1-2yCuyRuyO3 (M = Al, Mn, Fe, Co) for CO Oxidation and NO-CO Reactions. Influence of the Simultaneous Substitution of Cu and Ru

y. teraoka, h. nil, s. kagawa, k. jansson and m. nygren, Chem. Lett. Jpn., 1996, (4), 323–324

The catalytic activity of the ABO3 perovskite-type title compound for CO oxidation and NO-CO reactions was greatly changed by the simultaneous substitution of Cu and Ru for M at the B sites. The effect was dependent on the host M cations. The simultaneous incorporation of Cu and Ru gave a very active catalyst Lao0.8Sr0.2Al0.8Ru0.1O3 (1) for both CO-NO and CO-O2 reactions, at a substitution level (y-value) of 0.1. The activity of (1) was comparable to that of 0.5 wt.% Pt/Al2O3, or La0.8Sr0.2CoO3, which is one of the most active perovskite catalysts.

HOMOGENEOUS CATALYSIS

An Improved Synthesis of 1,4-cis,exo -Hexa-or Tetrahydromethano- or -ethanobiphenylene Derivatives Catalyzed by Palladium Complexes

m. catellani and l. ferioli, Synthesis, 1996, (6), 769–772

A direct method for the preparation of exo-disubsti-tuted benzocyclobutenes based on the use OfK2CO3 in DMF in the presence of Pd(PPh3)4 catalyst is reported. The reaction, performed at 105°C for 12-24 h, with a Pd(PPh3)4:substrate:K2CO3 molar ratio = 1:20:24 gave good to excellent yields, particularly when ortho -substituents were present in the aromatic ring. The exo orientation of the cycloaliphatic substituents on the cyclobutene ring was confirmed by 1H and 13C NMR spectroscopic measurements.

Allylic Alkylation with a Supported Aqueous Phase Palladium Catalyst

p. schneider, f. quignard, a. choplin and d. sinou, New J Chem., 1996, 20, (5), 545–547

The allylic alkylation of (E)-Cinnamyl ethyl carbonate was catalysed by SiO2 supported aqueous phase Pd/tppts, where tppts is P(C6H4-m -SO3Na)3. The water soluble catalyst was prepared in situ from Pd(OAc)2 and tppts. The stability of the complex and the absence of metal leaching allowed easy catalyst recycling.

Highly Stereoselective Palladium-Catalyzed Coupling Reactions of Captodative Olefins Acetylvinyl Arenecarboxylates

l. villar, j. p. bullock, m. m. khan, a. nagarajan, rw. bates, s. g. bott, g. zepeda, f. delgado and j. tamariz, J Organomeu Chem., 1996, 517, (1–2), 9–17

The reaction of the captodative olefin 3-(p -nitroben-zoyloxy)-3-buten-2-one with aryl and vinyl halides was catalysed by (Ph3P)2PdCl2 to give coupled products 4-aryl- and 4-vinyl-3-(p -nitrobenzoyloxy)-3-buten-2-ones, respectively, with high Z stereoselectivity. Catalytic cross-coupling alkylation, phenylation and vinylation with trialkylorganostannanes and bromo olefin (Z)-4-bromo-3-(p -nitrobenzoyloxy)-3-buten-2-one) gave the corresponding trisubstituted alkenes.

Transition Metal Complexes of Diazenes XXXVI. [la] : Formation of Indoles from Azobenzene and Diphenylacetylene through Supported Aqueous Phase Catalysis by Rhodium(I) Complexes

s. westernacher and h. kisch, Monatsh. Chem., 1996, 127, (5), 469–73

The addition of diphenylacetylene to azobenzene was catalysed by Rh(I) trisulphonated triphenylphosphine supported on SiO2, in refluxing butanol in the presence of triphenylphosphine to give AT-anilino-2,3-diphenylindole and 2,3-diphenylindole with turnover numbers of 80 and 20, respectively. This supported aqueous phase system retained a constant turnover frequency throughout the reaction and could be partially recycled.

Rhodium-Catalyzed Carbonylation of 2-Alkynylbenzaldehyde under Water-Gas Shift Reaction Conditions: Formation of Novel Tricyclic Lactones

t. sugioka, s.-w. zhang, n. morii, t. joh and s. takahashl, Chem. Lett. Jpn., 1996, (4), 249–250

A tricyclic lactone was prepared by the carbonylation of 2-alkynylbenzaldehyde under water-gas shift reaction conditions in the presence OfRh6(CO)16 in a chloroform solvent. The lactone was the major product with ≤ 59% yield. The reactions of 2-phenylethynyl-benzaldehyde derivatives with a substituent at the 4-position of the phenyl group gave the corresponding tricyclic products in 54% and 44% yields.

Hydrogenation of Organic Substrates by Isocyanide Polymer-Bound Rh(PPh3)3Cl

r. giannandrea, p. mastrorilli, g. zaccaria and c. f. nobile, J. Mol. Catal. A: Chem., 1996, 109, (2), 113–117

Isocyanide polymer-bound Rh(PPh3)3Cl was prepared by quantitative co-ordination to hydrophilic macro-molecular isocyanides. The organic support was obtained by copolymerisation of 3-isocyanopropyl acrylate with oxytriethylene glycol methacrylate, in the presence of methylene glycol dimethacrylate as cross-linker. At 50°C under 1 arm H2, the complex became a versatile and recyclable catalyst for the hydrogenation of alkenes, alkynes, nitriles and nitrocompounds.

Ruthenium-Catalyzed Allylic Substitution of AUylic Cyclic Carbonates

s.-k. rang, d.-y. kim, r.-k. hong and p.-s. ho, Synth. Commun., 1996, 26, (17), 3225–3235

(E)-Allylic alcohol and erythro -β-hydtoxy thiophe-noxide or phenoxide were prepared by allylic substitution of allylic cyclic carbonates with PhSH or PhOH, respectively, in the presence of CpRu(PPh3)2Cl (5 mol%), via external attack of nucleophiles to π;-allyl Ru complex. For the methyl-substituted allylic cyclic carbonate, only β-hydroxy sulphide was obtained after refluxing for 48 h, which indicated that the substitution reaction was very sensitive to steric effects.

Ruthenium-Catalyzed cis-Dihydroxylation of Alkenes: Scope and Limitations

t. k. m. shing, e. k. w. tam, v. w.-f. tai, i. h. f. chung and q.jiang, Chem. Eur. J., 1996, 2, (1), 50–57

Oxidative Ru-catalysed dihydroxylation of a wide range of alkenes with EtOAc or CCl4, acetonitrile, and H2O in the ratio 3:3:1, or with acetonitrile and H2O in the ratio 6:1 in the presence of 0.07 mol equiv. of RuCl3. (H2O)3 and 1.5 mol. equiv. OfNaIO4, at 0-5°C gave syn-diols rapidly and efficiently. With substrates containing electron-withdrawing group (s), the reactions were slower but gave better yields. Cyclohexene derivatives had better diastereoselectivities for syn -dihydroxylation anti to the existing a-stereogenic centre than acyclic alkenes.

Catalytic Activities of New Arsine-Dihydrido Ruthenium(II) Complexes in the Homogeneous Hydrogenation of Aldehyde

j.-y. kim, m.-j. jun and w.-y. lee, Polyhedron, 1996, 15, (21), 3787–3793

A number of arsine-dihydrido Ru(II) complexes, [RuH2(CO)(AsPh3)3] (1) and [RuH2(CO) (AsPh1) (L-L)], where L-L = diars (2), arphos (3), diphos (4), were prepared. Their catalytic activities for the hydrogenation of propionaldehyde to yield propan-l-ol were studied at 130°C and 30 arm H2, and compared with the catalytic activity of [RuH2(CO)(PPh3)3] (5). Complexes with a chelate ring had higher catalytic activities than (1). The catalytic activities decreased in the order: (4) > (3) > (2) > (5) > (1).

FUEL CELLS

Development and Electrochemical Studies of Cas Diffusion Electrodes for Polymer Electrolyte Fuel Cells

v. a. paganin, e. a. ticianelli and e. r. gonzalez, J. Appl. Electrochem., 1996, 26, (3), 297–304

Low catalyst loading gas diffusion electrodes for polymer electrolyte fuel cells were studied electrochemi-cally. The best performance was obtained with an electrode formed from 20 wt.% Pt/C, 0.4 mg Pt/cm2 and 1.1 mg Nafion /cm2 in the catalyst layer and 15% PTFE in a 50 μm thick diffusion layer. Optimum operating conditions for PEFC occurred at a cell temperature of 80°C and H and O/air humidifiers at 15 and 5°C above the cell temperature, respectively.

Conversion of Methane to Synthesis Gas over Pt Electrode in a Cell with Solid Oxide Electrolyte

v. v. gal’vita, v. d. belyaev, v. n. parmon and v. a. sobyanin, Catal. Lett., 1996, 39, (3, 4), 209–211

Electrochemical oxidation of CH4 to syngas was studied over a Pt electrode-catalyst in a SOFC at 800°C with a solid oxygen conducting electrolyte, such as yttria stabilised zirconia (YSZ). The Pt electrode was found to be active for the partial oxidation of CH4 to syngas. CO selectivity and yields of 85 and 65%, respectively, were obtained. The Pt electrodes, porous and of thickness ∼ 10 μm, were prepared by calcination of a Pt paste, containing 5 wt.% of YSZ in air at 950°C. For stable electrochemical characteristics, the electrodes were pretreated with both the anodic and cathodic current in air at 850°C for 20 h.

ELECTRICAL AND ELECTRONIC ENGINEERING

Electroplated, High Hc CoPt Films: ÓM Magneto-Optical Measurements

l. callegaro, e. puppin, p. l. cavallotti and g. zangari, J. Magn. Magn. Mater., 1996, 155, (1–3), 190–192

Co-rich CoPt and CoPtP alloy thin films were obtained by electrodeposition. Adding a P compound to the electrolyte for CoPt deposition resulted in P code-position and improved the hard magnetic properties of the film, giving coercive forces ≤ 5500 Oe. Óm curves, to characterise interactions in ferromagnetic material, revealed exchange coupling in CoPt, but mainly magnetostatic interactions in CoPtP films.

Excellent Au/Ge/Pd Ohmic Contacts to n-Type GaAs Using Mo/Ti as the Diffusion Barrier

c.-y. chai, j.-a. huang, y.-l. lai, j.-w. wu, c.-y. chang, y.-j. chan and h.-c cheng, Jpn. J. Appl. Phys., 1996, 35, (4A), 2110–2111

The Au/Ge/Pd ohmic metallisation system on n-type GaAs is significantly improved by using an additional Mo/Ti bi-layer as the diffusion barrier. Optimum conditions were achieved in the annealing temperature range of 325–400°C for 60 s. The minimum specific contact resistivity achievable was 1.2 x 10-7 Ω cm2. The improvements are attributed to the effective retardation of As-outdiffusion by the Mo/Ti barrier.

Ohmic Contacts to re-Type GaN Using Pd/Al Metallization

a. t. ping, m. asif khan and i. adesida, J. Electron. Mater., 1996, 25, (5), 819–824

Ohmic contacts to n -type GaN grown by metalor-ganic CVD were formed using a Pd/Al based metallisation. As-deposited Pd/Al produced rectifying contacts while subsequent annealing at ≥ 400°C produced ohmic contacts; contact resistance decreased with decreasing Pd interlayer thickness. A minimum contact resistance and specific contact resistance of 0.9 Ω mm and 1.2 x 10-5 Ωcm2, respectively, were obtained after rapid thermal annealing at 650°C for 30 s.

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