ABSTRACTS: July 1991
ABSTRACTS: July 1991
of current literature on the platinum metals and their alloys
Scanning Tunneling Microscopy of the Annealing of a Thin Platinum Film on Highly Oriented Pyrolytic Graphite
x. chuan zhou and e. gulari, Acta Cryst., 1991, A47, (1), 17–21
Scanning tunneling microscopy was used to study morphological changes in a thin Pt film deposited on highly oriented pyrolytic graphite (HOPG) during annealing. In air the film could be imaged with a vertical resolution of 0.5Å and a lateral resolution of 20Å. After annealing below 573 K surface morphology changed only slightly; at 573-873 K the originally uniformly distributed “rolling hills” of Pt coagulated into larger lumps. Above 873 K Pt crystal facets started to form on the surface. At 1123 K much of the surface turned into well defined Pt crystal facets. Above 1123 K the Pt film started to crack and formed scattered crystals on the HOPG surface. The crystallised Pt was preferentially oriented with the (111) plane parallel to the substrate graphite (0001) basal plane, indicating epitaxy of the Pt overlayer with tie graphite substrate underneath.
Kinetic Studies of the Chemical Vapor Deposition of Platinum
b. nixon, p. r. norton, e. c. ou, r. j. puddephatt, s. roy and p. a. young, Chem. Mater., 1991, 3, (2), 222–224
The chemical vapour deposition (CVD) of Pt was monitored by FTIR and UV spectroscopies using cis -[PtMe2(MeNC)2] as precursor in order to examine the effects of H2 and UV irradiation, which can enhance CVD. Pt deposition in a 2 cm pathlength UV cell under UV irradiation at <300 nm occurred on a pyrex target. Irradiation at longer wavelengths gave negligible deposition. The effect of H2 in a 10 cm pathlength pyrex cell was to accelerate the reaction.
Hydrogen, Hydrogen Sulfide and Hydrocarbon Coadsorption on Pt(111) and Pt(11O): Selective Formation of Alkylthiols
d. vassilakis, c.-m. pradier, y. berthier and j. oudar, Appl. Surf. Sci., 1991, 47, (3), 273–280
The simultaneous adsorption of diolefine, H2 and H2S on Pt single crystals forms mercaptan and alkanes. The nature, amount and temperature of desorption of these products depend on the size and configuration of the diolefine and on the structure of the surface. Mechanisms are proposed to explain the observed surface reactions. Some compounds are selectively produced when H2 S reacts firstly with the diolefine; this occurs with C4H6 on (111) and (110) orientations, and with C5H8 on Pt(110).
Magneto-Optical Kerr Effect and Perpendicular Magnetic Anisotropy of Evaporated and Sputtered Co/Pt Multilayer Structures
p. he, w. a. mcgahan, j. a. woollam, f. sequeda, t. mcdaniel and h. do, J. Appl. Phys., 1991, 69, (7), 4021–4028
Thin and ultrathin Co/Pt multilayered structures were prepared on glass substrates by electron-beam evaporation at room temperature and by sputtering at various substrate temperatures and sputtering pressures. Perpendicular magnetic anisotropy was found in samples with Co/Pt bilayer thicknesses near 3 Å/10 Å and total thicknesses of the layer stack of ≤300 Å. The effects of sputtering parameters, such as pressure and substrate temperature, on the magneto-optical Kerr effect were studied.
Perpendicular Magnetic Anisotropy in Pt/Fe Multilayers
t. katayama, y. suzuki, y. nishihara, t. sugimoto and m. hashimoto, J. Appl. Phys., 1991, 69, Part IIB, 5658–5660
Perpendicular magnetic anisotropy and related magnetic properties in Pt/Fe multilayers were investigated. Pt/Fe compositionally modulated films (CMFs) with ∼ an 18Å Pt layer and Fe layer <5Å become perpendicularly magnetised films. Surface magnetic anisotropy (Ks) was 0.46 erg/cm2 and volume anisotropy (Kv) was ∼ –2 x 10’ erg/cm3 at room temperature. The Ks is almost equivalent to that of Pt/Co CMFs and increases with decreasing temperature. The absolute value of Kv is much larger than that of the Pt/Co system. The effective magnetic anisotropy of [Fe(4.7Å)/Pt(18.5Å)]80 CMF changes from positive to negative at T∼200 K with decreasing temperature.
Permanent Magnetic Properties in Fe-Pt-Nb System Alloys
k. watanabe, J. Jpn. Inst. Met., 1990, 54, (11), 1284–1290
Magnetic properties and temperature dependence of Fe-Pt-Nb ternary alloys were investigated by various techniques. Permanent magnetic properties were obtained by water-quenching from the γ-phase region and tempering at ∼850–900 K in the γ1-phase region. A Fe-39.5 at.%Pt-0.75 at.%Nb alloy exhibits the maximum energy product of 167 kJ/m3, with a residual flux density of 1.05 T and a coercivity of 398 kA/m. These properties are superior to those of basic binary Fe-Pt. The Fe-Pt-Nb composition range is wider than that of Fe-Pt, so the heat-treatments can be easily controlled, and the reproducibility of the magnetic properties can be improved. Fe-38Pt-lNb has excellent rectangular hysteresis loops at 400 and 290 K with stable thermal properties.
Amorphous Phase Formation in an As-Deposited Platinum-GaAs Interface
d.-h. ko and r. sinclair, Appl. Phys. Lett., 1991, 58, (17), 1851–1853
A thin amorphous intermixed layer at the Pt-GaAs interface in as-deposited Pt/GaAs and Si/Pt/GaAs samples has been investigated by various techniques. The intermixed layer forms below the native oxide of the GaAs substrate and consists of the elements: Pt, Ga and As. It is suggested that this layer forms during the deposition process of the Pt.
High Temperature Reactions between SiC and Platinum
t. c. chou, J. Mater. Sci., 1991, 26, (5), 1412–1420
Solid state reactions between SiC and Pt were performed at 900-1100°C. In the reaction zones, alternating layers of Pt3 Si and C, and Pt2Si and C were formed at 900 and 1000°C, respectively. Both the Pt3Si and Pt2Si phases were stable at respective temperatures, but annealings at 1100°C produced alternating layers of mixed Pt silicides and C. The formation of Pt silicides gave rise to interfacial melting between SiC and Pt and SiC decomposed into C and Si at all the temperatures. The Si reacted with Pt and formed Pt silicides, while the carbon formed clusters and was unrective.
Solid State Reactions of SiC with Co, Ni, and Pt
t. c. chou, a. joshi and j. wadsworth, J. Mater. Res., 1991, 6, (4), 796–809
Solid state reactions between SiC ceramics and Pt, Ni and Co were studied at 800–1200°C for various times under He or vacuum. The Pt/SiC reactions at 900, 1000 and 1100°C were very similar to each other; interfacial melting was observed and Pt3Si, Pt2Si and a mixture of Pt silicides, respectively, were formed upon annealing. C precipitation behaviour, annealing conditions, diffusion phenomena and major reaction products for diffusion couples are given. A C-PFZ(C precipitation free zone) was generated in Ni/SiC and Co/SiC but not in Pt/SiC. While a CPZ(carbon precipitated zone) was formed in all the systems, both M-CPZ(modulated) and R-CPZ(random) were noted in the Pt and Ni systems, but only a R-CPZ in the Co system.
Magnetic-Field-Induced Strong Diamagnetic Transition in the Quasi-One-Dimensional Halogen-Bridged Platinum Complex [Pt(en)2][Pt(en)2I2](Cl04)4 (Where en Represents Ethylenediamine)
m. haruki and p. wachter, Phys. Rev. B, 1991,43, (7), 6273–6276
DC magnetisation measurements on the quasi-one-dimensional halogen-bridged Pt title complex show a magnetic-field induced strong diamagnetic transition at fields above 20 kOe. The diamagnetic signals are as large as 3.5-72% of complete diamagnetism and show large fluctuations. The transition temperature to paramagnetism is at ∼ 180 K.
Interfacial Reactions between Palladium Thin Films and InP
d. g. ivey, l. zhang and p. jian, J. Mater. Sci., Mater. Electron., 1991, 2, (1), 21–27
The reaction between a thin layer of Pd(≈100 run) and an InP substrate was studied at annealing temperatures of 250-450°C for up to 30 s, which are typical annealing conditions encountered during contact fabrication. Pd reacted readily with InP forming an amorphous ternary phase which later transformed to crystalline Pd2InP on annealing. Pd2InP had an ordered cubic structure, and microtwins, 2–3 atomic layers thick, were identified in the ternary phase and these formed along the (110) and (110) planes.
Comparative Study on Phase Formation in Al-Pd Thin Film by Ion Beam Mixing and Thermal Annealing
r. y. lee, j. h. park and c. n. whang, J. Mater. Sci., 1991, 26, (3), 721–725
Ion beam mixing and/or thermal annealing were conducted to study the phase formation and dissociation in Al-Pd thin films prepared by sequential evaporation. The intermetallic compounds formed by ion mixing with Ar+ were found to be Al3Pd2 and AlPd at a dose of 1.5 × 1016 Ar+/cm2. Thermal annealing after this radiation gave two new phases of Al3Pd and Al3Pd5 in addition to Al3Pd2 and AlPd. For an as-annealed sample without Ar+ bombardment, the observed phases are Al3Pd, Al3Pd2 and AlPd.
Retardation of Grain Boundary Reactions in Ag-Pd-Cu Alloys by Additions of Small Amounts of Other Elements
i. kawashima, y. araki and h. ohno, J. Mater. Sci., 1991, 26, (4), 1113–1118
The grain boundary reactions in Ag-25%Pd-10%Cu (mass%) with 1% of Al, Co, Sn, Cr or In were studied. Addition of Sn and Cr retarded grain boundary reactions. Grain interior reactions were accelerated with Cr, Sn and In additions, with Cr being the most effective. The activation energies for the grain interior and grain boundary reactions were 192–196 and 144–208 kJ/mol, respectively. Additions retarded the growth but not the nucleation at the grain boundary.
Mechanical-Strain-Induced Influences on Hydrogen Diffusion within Pd77Ag23 Alloy Membranes
x. q. tong and f. a. lewis, J. Less-Common Met., 1991, 169, (1), 157–165
Sudden changes in H, gas pressure on the upstream side of tubular membranes of Pd77 Ag23 and Pd81 Pt19 alloys are known to produce complementary changes of H2 pressure on the downstream side; this has been attributed to “elastic dynamic” or “mechanically induced memory” effects. Further experiments show that such effects could be associated with combinations of Gorsky effect and self-strain-induced diffusion-elastic effect migrations of H interstitials in the walls of the membranes.
Hydrogen Permeable Palladium-Silver Alloy Membrane Supported on Porous Ceramics
s. uemiya, t. matsudaand e. kikuchi, J. Membrane Sci., 1991, 56, (3), 315–325
The H permeability and selectivity of a composite membrane consisting of miscible Pd-Ag alloy film supported on the outer surface of a porous alumina cylinder were investigated. The membrane had much higher flux than commercially obtained Pd-based membranes for H separation. The high H flux was due to the thinness of the film and its high H solubility. H embrittlement was suppressed by alloying the thin Pd film with Ag, and 100% H selectivity was retained even at relatively low temperatures.
On the Origin of a Lattice Expansion in Palladium and Pd-Au Vapour Deposits on Various Substrates
c. kuhrt and r. antqn, Thin Solid Films, 1991, 198–(1-2), 301–315
Vapour deposits of Pd and Pd-Au alloy particles and films were produced under UHV or in high vacuum, with and without the admission of H2O, on amorphous films of C and SiO2 and single crystal surfaces of NaCl and KBr. In all cases lattice expansions of up to 2.6% were measured, depending on the condition of degassing of the substrate and on the residual gas composition during deposition, especially with respect to water vapour. Lattice expansion correlated with the presence of H on or in the substrate materials, as detected by SIMS.
Mechanical Behavior of Nanocrystalline Cu and Pd
g. w. nieman, j. r. weertman and r. w. siegel, J.Mater. Res., 1991, 6, (5), 1012–1027
Bulk mechanical properties of nanocrystalline Pd and Cu samples, consolidated from powders prepared by inert gas condensation, were measured. Average grain sizes were 3–50 nm and mean lattice strains ranged from 0.02–3%. Densities range from 97–72% of that of a coarse-grained standard. Microhardness exceeds that of annealed, coarse-grained samples by a factor of 2–5, despite indications that sample porosity reduces hardness values below the ultimate value. Uniaxial tensile strength is also high.
The Palladium-Rich Pd-Ho(Er) Systems
y. sakamoto, k. takao and y. nagaoka, J. Mater. Sci., Lett., 1991, 10, (6), 341–344
Pd-Ho and Pd-Er alloys containing 10-21.0 at.% Ho(Er) prepared by arc-melting in Ar and heat treated to ∼ 1193 K for 10 min followed by quenching in iced H2O were studied by various metallographic, spectroscopic and electrical resistance measurements. It is concluded that the magnitude of the order-disorder transition temperature, Tc, for the reaction α-Pd + LI 2 -type Pd3RE (or Pd5RE where RE is Ce, Sm or Eu) = Pd7RE of the Pd-RE alloys is due to the magnitude of the metallic radius of the rare-earth metals.
A Contribution to Coupled Reduction of Rare Earth Oxides with Pd and H2
v. contardi, r. marazza, g. rambaldi, g. zanicchi and r. ferro, Z. Metallkd., 1991, 82, (3), 169–173
Stoichiometry and structural types of Pd-rare earth alloys are presented. Results from reacting Gd2O3-Pd mixtures with H2 are reported. For alloys containing up to 20 at.% Gd the reduction was nearly complete and Pd-rich Gd-Pd alloys were obtained. For Pd solid solutions containing up to ∼ 12 at.% Gd nearly single-phase samples of composition close to the nominal ones were obtained. For 10–22 at.% Gd when two solid phases, Pd and GdP3, are stable at temperatures over 537°C, two-phase alloys not too far from the nominal ones of eutectic appearance were obtained.
Kinetic and Thermodynamic Investigation of Hydrogen Absorption by Ternary LaNi4Al and LaNi4Al-Pd Alloys
m. v. susie and y. m. solonin, Int. J. Hydrogen Energy, 1991, 16, (4), 271–276
Differential scanning calorimetry and X-ray analysis of H2 absorption by ternary LaNi4Al and a LaNi4Al-Pd alloy containing <1% Pd showed that in a flowing H2 atmosphere H absorption by the first alloy took place exothermally at about 150 and 450°C. The alloys containing Pd behaved similarly with absorption facilitated by the presence of Pd, and the formation of a new phase with a phase transition at 150°C was observed.
Mechanical Alloying of the Pd-Si System. Investigation of the Early and Late Milling Stages
m. magini, n. basili, n. burgio, g. ennas, s. martelli, f. padella, e. paradiso and p. susini,Mater. Sci. Eng., 1991, A134, 1406–1409
Four Pd-Si compositions: Pd25Si, Pd3Si, Pd4Si and Pd5Si, have been processed by mechanical alloying. After the early milling stages, consisting of very fine fragmentation of the Si particles into a Pd matrix, the Pd2.5Si, Pd3Si and Pd4Si can nucleate intermetallic Pd3Si, depending on the milling conditions and/or the milling apparatus. Further milling seems to promote amorphisation, probably starting from the previously formed Pd3Si compound.
Standard Molar Enthalpies of Formation of Me5Ge3 (Me = Zr, Nb, Mo), MeGe (Me= Ru, Rh, Pd) and Pd2Ge by High-Temperature Calorimetry
w.-g. jung and o. j. kleppa, J. Less-Common Met., 1991, 169, (1), 93–103
The standard enthalpies of formation of the above 4d transition-metal germanides were determined using a high-temperature calorimeter at 1473±2 K. Liquid (Ni + Ge) alloys were used as solvents in the solute-solvent drop experiments, and values were obtained for Zr5Ge3 and NbsGe3. Values of –56.9±1.4 kJ/mol for RuGe, –113.8±2.1 kJ/mol for RhGe and –92.9±1.5 kJ/mol for PdGe were obtained.
Hydrazine Decomposition on a Clean Rhodium Surface: A Temperature Programmed Reaction Spectroscopy Study
j. prasad and j. l. gland, Langmuir, 1991, 7, (4), 722–726
The adsorption, desorption and decomposition of N2H4 on a Rh foil surface was studied as a function of its coverage by temperature programmed reaction spectroscopy. The gas-phase products observed depend markedly on the initial hydrazine coverage. At low coverage only H2 and N2 desorb from the surface, but at near monolayer coverage H2, NH3, N2 and diimide are observed. Simultaneous desorption of N2 and NH3 at 220 K for high coverages suggests the direct decomposition of hydrazine N2H4→N2+H(ad) and N2H4+H(ad)→NH3. Diimide formation was observed over a wide range of N2H4 coverages above 220K.
Dissociation of Nitric Oxide and Reaction with Hydrogen on Rh(lll) and Various Stepped Rh(111) Surfaces
r. m. wolf, j. w. barker and b. e. nieuwenhuys,Surf. Sci., 1991, 246, (1-3), 135–140
The reaction between NO and H2 was studied on Rh(111) and stepped surfaces: Rh(331), Rh(211) and Rh(321) by scanning field emission probe-hole microscopy. Reaction start-up temperature strongly depends on NO coverage, and is sensitive to surface structure. At low NO coverage the reaction starts by 240 K on Rh(321), and at a much higher temperature on Rh(211) and Rh(111). On Rh(321) characteristic features of both (100) and (111) steps are observed.
Infrared Spectroscopy at High Pressure. Interaction of N2 with Rh/Al203 at Ambient Temperature
j. p. wey, h. d. burkett, w. c. neely and s. d. worley, J. Am. Chem. Soc, 1991, 113, (8), 2919–2922
A new high-pressure infrared cell reactor capable of variable temperature operation was used to study the interaction of N2 with Rh/Al2O3 catalyst films in the pressure regime 1 × 10–6 to 9000 Torr at 298 K. The results were in good agreements with those previously obtained for similar catalysts at low temperatures and pressures. Infrared bands for chemisorbed and physisorbed N2 species were detected and assigned.
Solidification of Copper-Rhodium Alloy Single Crystals
m. p. delplancke, m. jardinier-offergeld and f.bouillon, Mater. Chem. Phys., 1991, 27, (3), 225–233
The preparation of Cu-Rh alloy single crystals by the vertical Bridgman method is described. Dendritic structures are formed during the solidification process of 1.5, 4, 8.75 and 15 at.%Rh alloys. Various methods are used to characterise the solute distribution. Formation conditions and the thermal stability of the structures are also discussed.
Diffusion of Ir-Dimers on Ir(llO) Surfaces by Atomic-Exchange and Atomic-Hopping Mechanisms
t. t. tsong and c.-l. chen, Surf. Sci., 1991, 246, (1–3), 13–24
On the Ir(110) surface, single Ir adatoms and Ir-dimers can diffuse along, as well as across, the  surface channels. The across-channel diffusion most probably occurs by an atomic-exchange mechanism. The visited-site-lattice for Ir and Ir2 is the (1 × 1) net of the substrate lattice. Atomic jumps are concluded to extend only to the nearest-neighbour sites. For single Ir-adatoms, diffusion across the channels is easier than along the channels. For Ir-dimers the along-channel diffusion is easier. The energies needed for single Ir-atoms and Ir-dimers to hop along the channel and to displace across the channel by atomic exchanges are derived. The binding energy of the dimer is 1.10±0.11 eV.
Structure and Magnetic Properties of FeRuGaSi Multilayer Thin Film
t. m. jagielinski, a. m. zeltser and c. f. brucker,J. Appl. Phys., 1991, 69, (8), Part IIB, 5628–5630
The structure and magnetic properties of FeRuGaSi thin films used in VHF (150 MHz) recording heads have been studied. The best soft magnetic properties of coercivity (0.2-0.3 Oe), permeability (2000 at 1 MHz and 400-500 at 150 MHz), and magnetostriction (<10–6), were obtained after annealing at 450-500°C. This magnetic behaviour is attributed to the phase transformations and the increase in the grain size of the films occurring during annealing.
Phase Equilibria in the Ru02-Bi203-CuO System
s. bernik, m. hrovat and d. kolar, J. Mater. Sci., Lett., 1991, 10, (2), 69–70
Studies of interactions between CuO and the conductive phases RuO, or Bi2Ru2O7 in thick-film resistors have been performed and the ternary phase diagram of the Ru02-Bi2O3-CuO system is presented. The phase equilibria indicate reactions between the conductive Bi2Ru2O7 phase in thick-film resistor material and the CuO, which was added as a temperature coefficient of resistivity modifier, with CuO being incorporated into the pyrochlore crystal structure, resulting in the Bi2–xCuxRu2O7–x/2 solid solution. When RuO2 was the conductive component, CuO did not react with it.
Growth and Characterization of RuSe2 Single Crystals
j.-s. sheu, y.-s.shffl, s.-s. lin and y.-s. huang, Mater. Res. Bull., 1991, 126, (1), 11–17
Single crystals of RuSe2, up to 10 × 8 × 6 mm3, were grown by an oscillating chemical vapour transport method using ICI3 as the transport agent. Optimum conditions for the growth of large single crystals are given. Crystal stoichiometry is discussed, and electrical resistivity and Hall effect measurement indicate n-type semiconducting properties.
Crystal Growth and Properties of R2Ba2CuPt08 (R = Ho, Er, Y), R2Ba3Cu2PtO10 and Ba4CuPt2O9
y. saito, t. shishido, n. toyota, k. ukei, t. sasaki and t. fukuda, J. Cryst. Growth, 1991, 109, (1–4), 426–431
Three new Pt complex oxides have been identified as products of the CuO-flux growth of R-Ba-Cu-O (R = Ho, Er, Y) superconducting oxides in Pt crucibles. These oxides are formed under normal atmospheric conditions and a growth mechanism for the compounds involving incorporation of Pt from the crucible is proposed. The crystal structure of R2Ba2CuPtO8 has been determined. The T–1/2 temperature dependence of the conductivity is explained by a -Cu2+-O2–-Pt4 +-O2– conduction chain model. The magnetic susceptibility measurements reveal an antiferromagnetic interaction of spins Ho3+, Er3+, and Cu2 +.
High-Nuclearity Platinum-Osmium Alloy Cluster Complexes. Synthesis and Structural Characterizations of Pt4Os6-(CO)22(COD) and Pt5Os6(CO)21(COD)2
r. d. adams, j.-c. lii and w. wu, Inorg. Chem., 1991, 30, (10), 2257–2258
The first example of a possible series of new high-nuclearity Pt-Os carbonyl cluster complexes having structures based upon alternating layers of Pt and Os are reported. The clusters were formed when Pt2Os3(CO)10(COD)2, where COD is 1,5-cyclo-octadiene, was refluxed under N2 for 30 min.
The Synthesis of Os3Pt Clusters. X-ray Crystal Structure of 083Pt(CO)u(PPh3)2
d. h. farrar, r. r. gukathasan and j. a. lunniss,Inorg. Chim. Acta, 1991, 179, (2), 271–274
The reaction of Os3(CO)11(NCMe) (1) with sources of PtL2 gave new clusters Os3Pt(CO)11L2 as major products, where L is PPh3 or PtBu2Ph. Each Os-Pt edge was bridged by a carbonyl ligand, while the remaining nine carbonyl ligands were terminally bound to Os atoms. The minor products from the reaction of (1) and PtL2 were phosphine-substituted derivatives of Os3(CO)12 and the raft clusters Os6(CO)21–n(NCMe)n with n = 1, 2. Crystal structures of the products are given.
Syntheses and Crystal Structures of [Pd9Asg(PPh3)g] and [Pd9Sb6(PPh3)8]
d. fenske and c. persau, Z. Anorg. Allg. Chem., 1991, 593, (2), 61–68
A new cluster [Pd9Asg(PPh3)8] which was prepared by reaction of [PdCl2(PPh3)2] with As(SiMe3)3 was characterised by X-ray crystal structure analysis. The cluster molecule has four [Pd2(PPh3)2] units bridged by As2 units with a further Pd atom being located in the centre of the cluster. The reaction of [PdCl2(PPh3)2] with Sb(SiMe3)3 yielded [Pd9Sb4(PPh3)8] which has a b.c.c. Pd9-cluster.
Structural, Magnetic, and Charge Transport Properties of Bis[(5,10,15,20-Tetramethylporphyrinato)Palladium(n)] Perrhenate, [Pd(tmp)] 2[ReO4]
e. m. mcghee, b. m. hoffman and j. a. ibers, Inorg.Chem., 1991, 30, (9), 2162–2165
Electrochemical oxidation was used to produce the new molecular conductor [Pd(tmp)]2[Re04], which is composed of partially oxidised Pd(tmp) cations stacked metal-over-metal and surrounded by chains ofReO4 anions. Single crystal room temperature conductivity along the needle axis averages 30/Ω cm, and can be fitted to an expression that describes a semiconductor with temperature-dependent carrier mobility, and is comparable with that of the best Pt-spine conductors, despite the interplanar separation being ∼3.38 A, compared to that for Pt-Pt of 2.95 Å. This conductor is isostructural with [Ni(tmp)]2[ReO4] and [Cu(tmp)]2[ReO4].
Ring Migration Reactions of (C5Me5)Rh(PMe3)H2. Evidence for η3 Slippage and Metal-to-Ring Hydride Migration
w. d. jones, v. l. kuykendall and a. d. selmeczy,Organometallics, 1991, 10, (5), 1577–1586
The reactions of (C5Me5)Rh(PR3)H2 (PR3 = PMe3, PMe2Ph, PMePh2, PPh3) with D2 gas occurred quickly at 25°C, leading to the stepwise exchange of H for D. Kinetic studies showed a second-order reaction mechanism involving Rh and D. (C3Me5)Rh(PMe3)H2 also reacted with PMe3 at 40°C to yield C3Me3H and HRh(PMe3)4 in a reaction displaying bimolecular kinetics. Isotope effect studies showed no rate difference with the dideuteride Rh complex.
Synthesis and Reactivity of Rhodium(I) Complexes of the Type Rh(L-L)(CO)[P(OPh)3] and Rh(L-L)[P(OPh)3]2
e. kwaskowska-chec and a. m. trzeoak, Transition Met. Chem., 1991, 16, (2), 212–214
The carbonyl ligands in the RhI complexes Rh(L-L)(CO)2 (L-L is anthranilate (AA) or N -phenylanthranilate (FA) ions) were replaced by P(OPh)3 to form the mono- or disubstituted products. Under Ar at [P(OPh)3]/[Rh]≥4 the ortho -metallated RhI complex Rh[P(OPh)3]3-[P(OC6H4)(OPh)2] was formed. The Rh(AA)(CO)2 complex was used as a catalyst precursor in hydro-formylation of olefins.
Reaction of Ru(η/-RC5H4)Cl(PPh3)2 with Carbon Disulfide
a. gutierrez-alonso and l. ballester reventos, J. Coord. Chem., 1991, 22, (4), 255–258
The reaction of CS2 with Ru(η-C3H3)Cl(PPh3)2 produced [Ru(η/-C5H5)(CS2)(PPh3)2]+ by two different routes. Results suggest that the formation of the CS2 derivatives is related to the partial dissociation of the Ru-Cl bond, which increases with the basicity of the phosphine attached to the metal.
Electrocatalytic Properties of Ultrafine Platinum Particles for Oxidation of Methanol and Formic Acid in Aqueous Solutions
k. yahikozawa, y. fujii, y. matsuda, k. nishimura and y. takasu, Electrochim. Acta, 1991, 36, (5/6), 973–978
The effect of size of ultrafine Pt particles prepared by vacuum evaporation onto a glassy C rod, on the electrochemical oxidation of MeOH and HCOOH acid was examined by cyclic voltammetry. The specific activity for the oxidation of MeOH decreased by decreasing the Pt panicle size, whereas that of the HCOOH acid increased as the particle size decreased.
XPS Analysis of Amorphous Ni-Nb-Sn-Pt Alloy Catalysts for Electro-Oxidation of Formaldehyde
a. kawashima, k. asami and k. hashimoto, Mater.Sci. Eng., 1991, A134, 1070–1073
Amorphous Ni-40Nb-xSn-(3-x)Pt alloy ribbons were prepared and used for the electrooxidation of HCHO after surface activation by HF. Maximum activity was observed at ∼ 0.4 at.%Sn. XPS revealed that the surface layer was rich in Pt and deficient in Ni, but that the surface concentration decreased continuously with increasing Sn content.
Electrochemical Properties of Ultra-Fine Palladium Particles for Adsorption and Absorption of Hydrogen in an Aqueous HC104 Solution
n. tateishi, k. yahikozawa, k. nishimura, m. suzuki, y. iwanaga, m. watanabe, e. en ami, y.matsuda and y. takasu, Electtockim. Acta, 1991, 36, (7), 1235–1240
Ultra-fine Pd particles were prepared by vacuum evaporation onto a plane of glassy C (GC) rod. Then-diameters were estimated to be 2-10 nm by SEM. Properties of Pd/GC electrodes in H adsorption and absorption were characterised by cyclic voltammetry. Adsorption strength of H species on the Pd particles of Pd/GC did not depend on the particle size, whereas amounts of the adsorbed H species and the absorbed ones into the Pd particles were dependent.
Electrochemical Hydrogen Insertion into Palladium and Palladium-Nickel Thin Films
j. m. rosamilia, j. a. abys and b. miller, EUc- trochim. Acta, 1991, 36, (7), 1203–1208
A generator-detector mode with the rotating ring-disk electrode was used to determine the difference between Pd and Pt electrode behaviour and the origin of the larger overpotentials at Pd-H evolving cathodes. The use of thin film (1-10μm) Pd disk electrodes has allowed full H or D charging of the metal phase in short times. This electrode system enables measurements of the H uptake in PdHx films to be made, with PdH0.81 being the maximum.
The Role of the Electrolyte Anion in Anodic Dissolution of the Pd(100) Surface
t. solomun, J. Electroanal. Chem. Interfacial Electrochem., 1991, 302, (1 and 2), 31–46
Electrodissolution of Pd during its electro-oxidation in H2SO4 was studied by XPS, LEED, cyclic voltammetry and IR spectroscopy. At the beginning of the surface electro-oxidation reaction Pd species, showing a rather large shift of the (3d) core levels (2.5 eV towards the high binding-energy site), were electrogenerated at the surface in H2SO4 but not in HCIO4 electrolyte. Their concentration was directly related to the anion surface concentration. A surface complex of the type PdO(HS04) acted as a precursor in the formation of highly soluble PdSO4.
Adsorption Properties of an Iridium Oxide Electrode: A Thermodynamic Approach
o. a. petrh and a. vitin’sh, Elektrokhimiya, 1991, 27, (4), 461–476
Adsorption properties of electrodes made of thermally prepared IrOx, deposited on Ti layers were studied by potentiometric titration during isoelectric conditions in 0.1 M KNO3. A strong dependence of the acid-oxidation properties of the IrOx/Ti electrode on the stoichiometry of the active oxidation surface, characterised by the value of the electrode potential at the determined pH of the solution, was observed.
Characterization of DSA-Type Oxygen Evolving Electrodes. Choice of Base Metal
g. p. vercesi, j. rolewicz, c. comninellis and j.hinden, Thermachim. Acta, 1991, 176, 31–47
The effect of the base metals: Ti, Ta, Zr, Nb and some of their alloys, on the performance of IrO2-Ta2O5 coated DSA-type O2-evolving electrodes was investigated. The thermal behaviour and O affinity sequence of the metals in relation to the electrode preparation procedure were determined ther-mogravimetrically. The chemical and electrochemical stability of the base metal was directly related, through the wear mechanism, to the service life of the electrode, measured in 30% H2S04 at 80°C and 750 mA/cm2. Ti-based electrodes have the longest service life of 1700 h, compared to 120 h for Ti-based electrodes.
Morphological and Microstructural Study of the Ti/Ir02-Ta205 Electrode: Effect of the Preparation Temperature
g. p. vercesi, j.-y. salamin and c. comninellis,Electrochim. Acta, 1991, 36, (5/6), 991–998
Morphological and structural examinations of dimen-sionally stable electrode coatings (Ir02-Ta205) (70:30 mol %) show that at moderate firing temperatures, ∼550°C, separation of phases occurs with the formation of agglomerates of IrO2 crystals and amorphous Ta2O5. At ∼750°C both crystalline IrO2 and Ta2O5 are present.
Reaction between [(TPP)Ru(CO)] – and Methyl Iodide. Evidence for Formation of a Ruthenium(II) Carbonyl Methylated Tetraphenylchlorin Derivative
y. j. deng, x. h. mu, p. tagliatesta and k. m.kadish, Inorg. Chem., 1991, 30, (8), 1957–1960
This study provides the first example for electrogeneration of a methylated chlorin. The reaction between [(TPP)Ru(CO)] –, where TPP is the dia-nion of tetraphenylporphyrin, and CH3I differs from that of reduced Co, Fe, and Rh porphyrins because a stable σ-bonded CH3 derivative is not formed.
Photocatalytic Dehydrogenation of Pen-tane in the Presence of RhCl(CO)(PR3)2 (R = CH3, iso-C3H7 and n -C4H9)
n. k. khannanov, e. a. kochetkova, g. n. men-chikova, e. a. grigoryan, a. o. borisov and v. d.makhaev, Kinet. Kami, 1991, 32, (2), 473–477
Studies of the effect of the nature of phosphine ligands on the activity and selectivity of the process during dehydrogenation of pentane solutions in the presence of RhCl(CO)(PR3)2 (R = CH3, iso-C3H7 and n-C4 H9) were performed in the IR spectra region on >270nm light exposure.
Luminescence Quenching of Tris(2,2’-bipyridine) Ruthenium(II)Complex by Viologens in Anionic Micellar and Poly electrolyte Solutions:Variation with Alkyl Chain of Viologens
j. w. park, m. y. suk and b.-t. ahn, Bull. Korean Chem. Soc, 1990, 11, (6), 552–557
Luminescence quenching reactions of photoexcited tris(2,2’-bipyridine)Ru(II) complex cation, Ru(bpy)3 2+, by dialkylviologens were studied in Na dodecyl sulphate (SDS), poly(styrenesulphonate) (PSS) and poly(vinylsulphonate) (PVS) solutions. The relative quenching rate varies widely with the microheterogeneous media used. The highest quenching rate was observed for methyldodecylviologen in homogeneous aqueous medium, dibenzylviologen in SDS and PVS and dimethylviologen in PSS.
Preparation and Photochemical Characteristics of the Copolymer Pendant Tris(2,2’-bipyridine)Ruthenium-Mercury [Ru(bpy)32 +.Hg2Cl62–] Complex
r. ramaraj, a. kira and m. kaneko, J. Photochem. Pkotobiol. A: Chem., 1991, 56, (2-3), 287–293
The title Ru-Hg copolymer pendant complex was prepared and characterised by IR, visible absorption and emission spectroscopies and emission decay measurements. The solubility and excited state lifetime both in DMF solution and the film state were quite different from those of the low molecular Ru-Hg complex reported before. The emission from the excited poly-Ru-Hg was much longer than that from the poly-Ru in DMF solution.
APPARATUS AND TECHNIQUE
Preparation of an Oxygen Sensor Composed of Tightly Stacked Membrane/-Electrode/Electrolyte
k. katakura, a. noma, z. ogumi and z. takehara,Denki Kagaku, 1991, 58, (12), 1184–1189
An amperometric O sensor operating at room temperature was constructed using a porous Pt cathode on Nafion and perfluoropolymer as the O transport limiting membrane, which was directly bound on the cathode by plasma polymerisation. The O reduction current increased with increasing O concentration, from 0 to 30 ppm. A microsized O sensor can be prepared in principle.
Kinetics of Oxygen Interaction with Pt/CeO2 Sensors: Application of a New Pressure Modulation Spectroscopy
a. dubbe, h. d. wiemhofer, k. d. schierbaum andw. gopel, Sens. Actuators B, 1991, 4, (1 & 2), 23–28
A new method for characterisation of the dynamic response of the electrode potential upon sinusoidal O2 partial-pressure variations, and its powerful application was demonstrated in a study of the kinetics of different Pt electrodes on CaO-doped CeO2 electrolytes. Surface diffusion effects play a major part in the overall kinetics of the O2 response of their microstmctures. Gradients of the O2 surface concentration were analysed in an independent spectroscopic study on CeO2 samples with Pt contacts.
A Laser Power Detector Built Up by Application of Thick-Film Technology
j. nicolics and w. smetana, Sens. Actuators A, 1991, 25, (1–3), 235–239
A structure for a laser power detector using thick-film technology was developed. The incident laser radiation caused a heat flow in a metal plate where the resultant temperature differences, detected by thick-film Pt sensor elements, acted as a measure of the laser power. The sensitivity of the sensor was calculated and experimentally determined. The indicated laser power was independent of the radial intensity distribution of the laser beam.
Schottky-Barrier and Conductivity Gas Sensors Based upon Pd/SnO, and Pt/Ti02
k. d. schierbaum, u. k. kirner, j. f. geiger and w.gopel, Sens. Actuators B, 1991, 4, (1 & 2), 87–94
Electronic conductivity, mixed conductivity and Schottky-barrier sensors based on SnO2 and TiO2 modified by Pt and Pd metals can be used to detect CO, CH4, H2 and O2 gases. Sensor response signals result from changes in surface and bulk conductivities or in Schottky-barrier heights, which are measured using different geometric arrangements of Pt or Pd metal contacts. Studies showed that reliable sensor properties can only be achieved either by forming stable metal/oxide interfaces or by adjusting a stable dopant distribution.
Hydrogenation of Olefins on Platinum
c.-m. pradier and y. berthier, J. Catal., 1991, 129, (2), 356–367
The hydrogenation of buta-l,3-diene and isoprene was studied on three Pt planes. The reaction for butadiene was structure sensitive, with an increase in the turnover frequency by a factor of 5 from the denser to the rougher planes: Pt(111)<Pt(100)<Pt(110). There is a remarkable correlation between variations of the reaction orders and changes in the selectivity. The surface works as a bi-functional catalyst: hydrogenation and exchange seem not to occur upon the same kind of sites. The catalytic surfaces works with a HC layer present, not identical on the three studied surfaces.
Hydrocracking and Isomerization of n-Octane and 2,2,4-Trimethylpentane over a Platinum/Alumina-Pillared Clay
c. doblin, j. f. mathews and t. w. turney, Appl. Catal., 1991, 70, (2), 197–212
The hydrocracking and isomerisation of n-octane and 2,2,4-trimethylpentane (TMP) over an Al2CO3 pillared clay (Al-PILC), containing 0.16% Pt were studied in a microreactor at atmospheric pressure, at 175-325°C and weight hourly space velocity of 0.48-7.5/h. The Pt/Al-PILC catalyst underwent an initial stabilisation period of ∼30 h, resulting in changes in the physical structure of the catalyst. The catalyst showed ideal hydrocracking behaviour for nC8 giving high isomerisation yields, with a maximum isomer yield of 64% at 80% conversion. For hydrocracking 2,2,4-TMP, the major reaction was A type β-scission giving a product with >96% isobutane at all conversions.
Platinum-Tin Complexing and Its Application to Catalysis
l. y. jin, Appl. Catal., 1991, 72, (1), 33–38
Catalysts for the dehydrogenation of long chain alkanes were prepared by impregnating a γ-Al203 support with a [PtCl2(SnCl3)2]2– complex using H2PtCl4 and SnCl2 solutions in an acidic medium. The catalytic performance of the catalyst prepared by the complex method was remarkably improved compared to the Pt-Sn dehydrogenation catalyst prepared by non-complex methods.
Infrared Study of CO Adsorption on Pt-Rh/Al203 Catalysts
j. a. anderson and c. h. rochester, J. Chent. Soc.,Faraday Trans., 1991, 87, (9), 1479–1483
Studies of CO adsorption on Pt/Al2O3, Rh/Al2O3 and Pt-Rh/Al2O3, at 303-573 K were performed by FTIR spectroscopy. Catalysts containing Rh were precalcined at either 673 K or 873 K before reduction in H2 and exposure to CO. The intensities of IR bands due to gem-dicarbonyl and linear carbonyl species were a function of both the precalcination temperature and the temperature of contact with CO.
Improved Higher Alcohols Selectivity in Syngas Reaction (CO + H2) over Platinum Deposited on Rare Earth Oxides of the Fluorite Structure
j. el fallah, f. le normand, s. boujana and a.kiennemann, Eur. J. Solid State Inorg. Chem., 1991, 28, Suppl., 433–436
The effect of rare earth oxide as support on the reactivity of Pt in syngas conversions was tested. A chain growth process, giving up to C7 alcohols is observed on Pt deposited on rare earth oxides of the fluorite type (CeO2, Pr6O11, Tb4O7). This remarkable selectivity is explained by the creation of anionic vacancies at the interface of the metallic particle and the support, similar to that previously reported for Pd. On such catalytic sites both the dissociation of the CO molecule and the chain growth process occurs. Praseodymia gives the most effective support for improved higher alcohol formation.
Hydrogenation of Acetylene over Various Group VIII Metals: Effect of Particle Size and Carbonaceous Deposits
a. j. den hartog, m. deng, f. jongertus and v. ponec, J. Mol. Catal., 1990, 60, (1), 99–108
Supported Pt, Pd, Rh and Ir catalysts were studied for the hydrogenation of C2H2 and the effect of the particle size on this reaction was established. Rh and Ir show effects that can most probably be explained by the influence of the particle size on the intermediate of direct hydrogenation to C2H6 while for Pt and Pd the effect of deposition of carbonaceous layers prevails.
Gas-Phase Hydrogenation of Styrenes by Transfer over Pd/AlPO4 Catalysts
m. a. aramendla, v. borau, c. jimenez, j. m.marinas and m. e. semfere, React. Kinet. Catal. Lett., 1991, 43, (1), 1–6
The hydrogenation of styrene and α-methylstyrene over Pd/AlP04, using cyclohexene as donor is reported. The catalysts were activated in the pulse reactor and retained H, which was subsequently used to reduce the olefins. The amount of ethylbenzene produced from the styrene can be accounted for by H transferred by cyclohexene and H stored over the catalyst surface during treatment with cyclohexene, intended to reduce the impregnating metal salt.
Kinetics of Liquid-Phase Hydrogenation of Hexene-1 on Palladium Sulphide Catalyst
l. v. shalimova, a. d. berents, s. v. popov and o.v. chebaeva, Kinet. Katal., 1991, 32, (1), 55–59
Studies of the kinetic dependence of hexene-1 hydrogenation in benzene solution in the liquid phase in a flow system over a Pd sulphide/A12O3 catalyst were performed at 50-150°C and H2 pressure of 5 MPa. Intermediate adsorption stages were calculated and an equation for the rate of change of the concentrations of basic components was obtained.
A New Palladium-Catalyzed Coupling Reaction of Vinyl and Allylic Triflates with Pyrimidine Nucleosides
m. e. hassan, Can. J. Chan., 1991, 69, (2), 198–200
Vinyl trifluoromethane sulphonates (triflates) form Pd intermediates which react with pyrimidine nucleosides to yield C-5 alkyl substituted nucleosides, after hydrogenation of the vinylic coupling products with H2 and Pd/C in MeOH under mild conditions. The reaction is a general one since mono-,disubstituted and cyclic vinylic triflates give high yields of the corresponding C-5 alkyl-substituted nucleoside.
Oxidation State of the Surface of Palladiuni in the Catalytic Combustion of Hydrogen
m. g. jones, t. g. nevell, r. j. ewen and c. l.honeybourne, Appl. Catal., 1991, 70, (2), 277–286
The activity of supported Pd catalysts for the oxidation of H2 was studied at 80-500°C using a microcalorimetric technique and XPS. The reaction involved a surface layer of O2, and was inhibited by adsorbed H2O. Palladium(II) oxide was formed on the surface of metallic Pd under O2 at 450°C. Heating in H2 at 250°C reduced this surface layer and produced deactivated catalyst but the activity was subsequently restored by exposure to O2.
Methylcyclopentane Conversion Catalysis by Zeolite Encaged Palladium Clusters and Palladium-Proton Adducts
x. bai and w. m. h. sachtler, J. Catal, 1991, 129, (1), 121–129
The conversion of methylcyclopentane (MCP) was studied over the prototype catalysts HY, Pd/HY, Pd/NaHY and proton-free Pd/NaY. Ring opening of MCP to hexane isomers was catalysed by Pdn clusters, but ring enlargement (RE) of MCP to cyclohexane and benzene required metal sites and protons. The RE of MCP was catalysed by the “electron-deficient” [PdnH]+ adducts more effectively than by separate metal and acid sites. The catalysts containing Pd and protons in the same zeolite cavity, were dramatically more active for RE than a mixture of HY and proton-free Pd/NaY.
Direct and Indirect Promotion of Pd/Y and Ca2+ Ions
x. bai, z. zhang and w. m. h. sachtler, Appl. Catal, 1991, 72, (1), 165–178
Studies of Pd in NaY or CaY zeolites tested as catalysts for HC conversion reactions showed that the pre-exchanged Ca2+ cations in Y zeolite increase the concentration of [PdnH]+ adducts and subsequently improve the rate and stability of the catalyst for ring enlargement, while decreasing the ring opening rate of methylcyclopentane. The results suggest a direct interaction of the charge compensating ions (Ca2 + or Na+) with Pd particles and an indirect effect viz. by affecting the concentration of electron-deficient Pd-proton-adducts.
Liquid-Phase Oxidation of Propylene on Supported Palladium Mono- and Bimetallic Catalysts in Acetic Acid
a. v. karandin, e. v. gusevskaya, v. a. likholobov,a. i. boronin and e. m. moroz, Kinet. Kami, 1991, 32, (2), 367–374
Studies of the oxidation of propylene and propylene glycol and their acetates in acetic acid solutions, in HNO3 were performed in the presence of heterogeneous Pd, Pd-Pt and Pd-Rh catalysts deposited on C, SiO2 and TiO2 supports. The Pd-Pt catalysts were found to be most resistant to deactivation in the presence of reactive S. One of the reasons for deactivation of the catalysts was the formation of cyanide metal complexes on the support surfaces.
Effect of Promoters on the Catalytic Activity of Rh4(CO)12/Ti02 for CO Hydrogenation
y. chen, j. du, y. chen and z. du, J. Fuel Chem. TechnoL, 1991, 19, (1), 1–7
The activities for CO hydrogenation in a continuous flow microreactor of promoted Rh catalysts were in the order Rh4/V-TiO2>Rh4/TiO2>Rh4/Mg-TiO2. On the Rh,/V-Ti02 catalyst CO was completely converted to CH4 at 200°C, while for CO hydrogenation at various H2:CO ratios on Rh4/Mg-TiO2, CO2 was always present in the product. Catalyst dispersions were determined by H2-O2 titrations. A high H:M ratio occurred for Rh4 (CO)12/V2O5-TiO2, which was caused by the low temperature reduction of V20, catalysed by metallic Rh. The H:Rh ratio was in the same order as their activities. Only a twin CO band without linear or bridged CO was found during temperature programmed adsorption and desorption of CO.
HCN Synthesis from NH3 and CH4 on Rh and Ir
m. p. suarez and d. g. loffler, React. Kinet. Catal Lett., 1991, 43, (1), 195–199
The synthesis of hydrocyanic acid from CH4 and NH3 on Rh and Ir wires was studied at temperatures between 1200 and 1500 K, at a pressure of one atmosphere. Activation energies and pre-exponential factors are reported.
The Effect of CeO2 Support upon Activity and Selectivity of Ru and Co Fischer Tropsch Catalysts
a. f. y. al-shammary, i. t. caga, a. y. tata and j. m. winterbottom, Eur. J. Solid State Inorg. Chem., 1991, 28, (2), 453–456
5% Ru and Co catalysts supported on CeO: were prepared by impregnation and characterised by TPR. Their catalytic activities and selectivities were tested in H2 and CO reactions and compared with a Ru/SiO2 catalyst in the range 1–9 atm and 260°C. Ru/SiO2 and Co/SiO2 catalysts gave CH4 only at I atm and 70% CH4 at 9 atm, while Ru/CeO2 and Co/CeO2 gave significantly smaller quantities (20-80%) of CH4 over the same pressure range.
Substitution of Halogen in Vinylbromide and Reduction of Vinylhalogenides to Ethylene in the System Pt(II)-NaI-HClO4-H2O
s. a. mitchenko, v. v. zamashchikov and a. a.shubin, Kinet. Katal, 1991, 32, (2), 343–345
Studies of the kinetics of the Nal (2.5 M)-HClO4(0-2.5 M)-H20 system at 80°C catalysed by Pt(II) (0.004-0.06 M) showed the substitution of B by iodine in vinylbromide (RBr). When [HCIO4] > 0, parallel substitution of RBr occurred by reduction to ethylene, and in acid solutions the formed vinyliodide also reacted with Pt(II) yielding ethylene. A phase mechanism is provided which includes oxidative addition of vinylhalogenide to Pt(II) with the intermediate formation of σ-vinyl Pt(IV) complexes.
H-NMR-Study of Deuterium Exchange in Styrene under the Conditions of Hydrocarboxylation Catalysed by Palladium Complexes
yu. g. noskov, n. a. novikov, m. i. terekhova and e. s. petrov, Kinet. Ratal, 1991, 32, (2), 331–335
A study of the hydrocarboxylation of styrene catalysed by PdCl2(Ph3P)2 at 110°C and CO pressure of 2.0 MPa by the deuterium exchange method showed that terminal protons of unreacted substrate were noticeably substituted by D, but that proton exchange in the a-position of phenyl groups was not observed. When the pressure was decreased and SnCl2 was added, proton exchange occurred in both C atoms of the vinyl styrene group.
Homogeneous Catalytic Hydrogenation of Alkenes by Zero-Valent Palladium Complexes of cis-Fixed Dinitrogen Ligands
r. van asselt and c. j. elsevier, J. Mol. Catal., 1991, 65, (3), L13–L19
Zero-valent Pd complexes (DIAN)Pd(olefin) containing a cis-fixed dinitrogen ligand (DIAN) (N,N ’-diaryl-diiminoacenaphthene) are active as catalysts in the homogeneous hydrogenation of various unsaturated substrates. The title hydrogenation can be performed under mild conditions (THF, 20°C and 1-1.5 bar of H2 pressure). This results in complete conversion of various substituted alkenes to the corresponding alkanes.
Palladium-Catalyzed Coupling Reactions of Trifluoroacetimidoyl Iodides with Olefins and 1-Alkynes
k. uneyama and h. wat an abe, Tetrahedron Leu., 1991, 32, (11), 1459–1462
Pd-catalysed coupling of trifluoroacetimidoyl iodides with olefins and also 1-alkynes produced trifluoromethylated α,β -unsaturated imines which were transformed into N heterocycles bearing CF3-group. N-aryl trifluoroacetimidoyl iodides underwent smooth palladation with Pd2(dba)j.CHCl3.
Palladium Catalysed Tandem Cyclisation-Anion Capture Processes Initiated by Alkyl- and π -Allyl-Palladium Species
r. grigg, s. sukirthalingam and v. sridharan, Tetrahedron Lett., 1991, 32, (22), 2545–2548
Palladium catalysed tandem cyclisation-anion capture processes initiated by oxidative addition of benzylic or allylic halides or acetates to Pd(0) occurred regio-and stereo-specifically in good yield. The benzylic halide reacted with Na tetraphenylborate in the presence of Pd(0) to yield 69 % of the organic species. Examples of “anion” capture involving formate (H–), and organo- Sn, -Zn and -B species are described.
Palladium-Catalyzed β-Vinylation of Vinyl Acetate with Enol Triflates. An Entry to 1-Acetoxy-l, 3-Dienes
p. g. ciattin1, e. morera and g. ortar, Tetrahedron Lett., 1991, 32, (12), 1579–1582
Reaction of enol triflates with vinyl acetate in the presence of Pd(OAc)2 catalyst produced 1-acetoxy-l, 3-dienes as the major products in 40-79% isolated yields. Formation of the β-vinylated product was significantly favoured. The results showed that steric effects prevail over electronic factors in these organo-Pd reactions, in contrast to the corresponding reactions with enol ethers where electronic factors predominate.
Synthesis of Carboxylic and Phosphonic α-Amino Acids Using Palladium Allylic Alkylation
j. p. genet, s. juge, i. besnier, j. uziel, d. ferroud, n. kardos, s. achi, j. ruiz-montes and s.thorimbert, Bull. Soc. Chim. Fr., 1990, 12, (6), 781–786
Schiff bases derived from glycine and alanine esters were alkylated in the presence of Pd catalysts under neutral or basic conditions using allylic carbonates, esters or halides. Asymmetric Pd allylic alkylation of the benzophenone inline glycine methyl ester using Pd(OAc)2 + (+)DIOP was achieved with up to 70% ee. After hydrolysis, several functionalised α- aminoacids-enzyme inhibitors-were obtained.
Cationic PaUadium(II)-Diphosphine Complexes as Catalysts for the Carbonylation of Alkenes to Ketones
c. pisano, g. consiglio, a. sironi and m. moret, J.Chem. Soc, Chem. Commun., 1991, (6), 421–423
Cationic Pd complexes of the type [(dppp)Pd (solvent)2][X] 2, where X = a non or weakly co-ordinating anion and dppp = l,3-bis(diphenyl-phosphino)propane, are active catalysts for the carbonylation to ketones, for the selective formation of E-l,5-diphenylpent-l-en-3-one from styrene. In the presence of water and depending on the acidity conditions dimerisation to the much less catalytically active [(dppp)Pd(μ-OH)2Pd(dppp)]X2 takes place, the structure of which has been determined by X-ray crystallography.
New Highly Water-Soluble Surfactants Stabilize Colloidal Rhodium(O) Suspensions Useful in Diphasic Catalysis
c. larpent, f. brise-le menn and h. patin, J. Mol.Caul., 1991, 65, (3), L35–L40
New highly water-soluble trisulphonated surfactants C18H37 and C16H33 efficiently stabilise suspensions of colloidal (20-30Å) Rh(0) particles. These novel protective-colloid agents provide the means to perform catalytic hydrogenations of alkenes without cosolvents in real biphasic liquid-liquid conditions, and to recycle the aqueous colloidal suspensions after decantation.
Selective Catalytic Reduction of Aromatic Nitro Compounds Using CO and Water with Highly Active Rhodium-Phosphine Chelate Complexes
k. nomura, m. ishino and m. hazama, J. Mol.Caul., 1991, 65, (3), L5–L7
The reduction of aromatic nitro compounds, such as nitrobenzene, nitroanilines, chloronitrobenzenes, etc., was found to proceed at significant rates with remarkably high nitro-group selectivities under extremely mild reaction conditions of room temperature, and atmospheric CO pressure, using Rh phosphine chelate complexes. The reduction was complete in the case of p -nitroaniline. 1-Nitro-anthraquinone was also converted to 1-amino-anthraquinone with extremely high selectivity.
Homogeneous Catalytic Asymmetric Hydrogenolysis of Sodium Epoxysuc-cinate: the First Example of Asymmetric Hydrogenolysis of an Epoxide
a. s. c. chan and j. p. coleman, J. Chem. Soc, Chem. Commun., 1991, (7), 535–536
The first example of the asymmetric catalytic hydrogenolysis of an epoxide, Na epoxysuccinate, is discussed in which the chiral product is formed via a critical bond-breaking process using Rh catalysts containing chiral phosphine ligands. The enantioselectivity of the catalyst system was found to be independent of the H2 pressure, and the reaction rate is faster under higher H2 pressure, while the enantioselectivity is lower at higher reaction temperatures.
Regioselective Rhodium-Catalysed Hydroformylation of Olefins: Efficient Synthesis of Ethyl 2-Formylpropanoate from Ethyl Acrylate
d. neibecker and r. reau, New J. Chem., 1991, 15, (4), 279–281
Ethyl acrylate hydroformylation was performed using in situ generated catalysts from [Rh(CO)2Cl]2 and a phosphole or phosphanorbomadiene at 40°C and 20 bar syngas pressure and was compared to the Rh/l,4-bis(diphenylphosphino)butane system. The hydroformylation of ethyl acrylate was brought about under mild reaction conditions by a Rh-monophosphane system. The phosphanorbomadienes were superior ligands for this reaction.
Rhodium(III) Biphasic and Phase-Transfer-Catalyzed Hydrogenolysis of Chloroarenes under Exceptionally Mild Conditions
v. v. grushin and h. alper, Organometallics, 1991, 10, (5), 1620–1622
The Rh(III) complexes L2Rh(H)Cl2 [L = tricyclohexylphosphine or triisopropylphosphine] were excellent catalysts for the hydrogenolysis of chloroarenes. The reaction proceeded under biphasic (40% NaOH, PhCH3) conditions, or giving higher product yields, under phase-transfer conditions, using benzyltriethylammonium chloride as the quaternary ammonium salt. The reaction occurred under mild conditions.
Catalytic Tail-to-Tail Dimerization of Methyl Acrylate Using Rh(IH) Catalysts
m. brookhart and s. sabo-etienne, J. Am. Chem. Soc, 1991, 113, (7), 2777–2779
Cp*(P(OMe),)Rh(C2H4)(H)+(l) (where Cp* is C5Me3) catalysed ethylene dimerisation and further treatment of (1) with methyl acrylate (MA) resulted in initial formation of Cp*(P(OMe)3)Rh(CH2CH2-Co2Me)+ followed by slow tail-to-tail dimerisation of MA. A much more reactive catalyst was prepared when Cp*(C2H4)RhCH2CH2CH2-μ-H+ (2) was used in which P(OMe)3 was replaced by a labile ethylene ligand. A long-lived catalyst system could be generated by adding neat MA to (2) under 1 atm of H2. Total turnover numbers of up to 1.3 × 104 were achieved with > 99% conversion of MA.
Rhodium(II) Perftuorobutyrate Catalyzed Hydrosilylation of 1-Alkynes. Trans Addition and Rearrangement to Allylsilanes
m. p. doyle, k. g. high, c. l. nesloney, t. w.clayton and j. lin, Organometallics, 1991, 10, (5), 1225–1226
Hydrosilylation of 1-alkynes catalysed by Rh(II) perfluorobutyrate or chloroplatinic acid formed either allylsilanes or vinylsilanes in moderate to high isolated yields, dependent on the mode of addition of react ants. The duality of these transformations depended on co-ordination of the organosilane or alkyne with the transition-metal catalyst.
Hydrosilylation of Phenylacetylene via an Os(SiEt3)(η-H2) Intermediate Catalyzed by OsHCl(CO) (PPr3)2
m. a. esteruelas, l. a. oro and c. valero, Organometallics, 1991, 10, (2), 462–466
The five-co-ordinated hydrido carbonyl complex OsHa(CO)(PiPr3)2 catalysed the addition of triethylsilane to phenylacetylene. Trans- and cis- PhHC=CH(SiEt3) were selectively obtained in high yields depending on the reaction conditions. Although the vinyl compound Os((E)-HC = CHPh)Cl(CO) (PiPr3)2 was the main species under hydrosilylation conditions, the reaction proceeded via the silyl dihydrogen intermediate Os(SiEt,)Cl (η2-H2)(CO)(PiPr3)2.
Ruthenium-Catalysed Aerobic Oxidation of Alcohols via Multistep Electron Transfer
j.-e.backvall, r. l. chowdhury and u. karlsson, J. Chem. Soc., Chem. Commun., 1991, (7), 473–475
The aerobic oxidation of primary alcohols occurs under mild conditions at 20°C in air via a triple catalytic system of RuCl(OAc) (PPh3)3-hydro-quinone-Co(salophen) (PPh3) [H2salophen = N, N ’-bis(salicylidene)-o-phenylenediamine]. The present multistep electron transfer system leads to a very mild aerobic process which can be run under a reduced partial pressure of O2(air).
Formaldehyde and Formates as Sources of Synthesis Gas via Ruthenium-Catalyzed Decomposition Reactions
g. jenner, e. m. nahme and s. libs-konrath, J.Mol. Catal., 1991, 64, (3), 337–347
Paraformaldehyde can be decomposed into mostly CO and H2 with a Ru phosphine catalytic system, and with the same catalyst HCOOH is fully decarbox-ylated into CO2 and H2. The best chemical systems for the generation of CO/H2 mixtures are aqueous methyl formate solutions. Ru3(CO)12-tricyclohexylphosphine decarbonylated methyl formate, and simultaneously catalysed the water gas shift reaction. The catalytic species is [HRu3 (CO)11]– formed by the reaction of Ru3(CO) 12 whh phosphine and water. The present process can be applied to hydrogenation and to hydrocarbonylation reactions.
Selective Reduction of Dimethyl Oxalate by Ruthenium Carbonyl Carboxylates in Homogeneous Phase. Part IV
u. matteoli, g. menchi, m. bianchi and f.piacenti, J. Mol. Catal., 1991, 64, (3), 257–267
Ethylene glycol can be selectively obtained from dimethyl oxalate by hydrogenation in homogeneous phase in the presence of Ru2(CO)4(CH3COO)2-(PiPr3)2. In order to avoid decomposing the substrate the hydrogenation must be performed at 120°C to completely convert the oxalic diester and then at 180°C to hydrogenate the intermediate methyl glycolate.
Catalytic Carbonylation of Acetone Oxime at Bisoximatodiruthenium Complexes: A Simple Access to Anhydrous Acetonine. Isolation and Molecular Structure of [Ru 2 (CO) 5 (Me 2 CNO) 2 (Me 2 CNOH)]
m. langenbahn, h. stoeckli-evans and g. soss-fink, Helv. Chim. Acta, 1991, 74, (3), 549–553
Acetone oxime reacted with CO in the presence of catalytic amounts of [Ru2(CO)4(Me2CNO)2-(Me2CNOH)2] (1) to yield 2,3,4,5,-tetrahydro-2,2,4,4,6-pentamethylpyrimidine (acetonine), CO2and NH3. The reaction may proceed via carbonylation of Me2C=NOH to the unstable intermediate Me 2 C=N - OCHO which undergoes decarboxylation to give the corresponding imine Me2C = NH.
Ruthenium Complex-Catalysed Highly Selective Codimerisation of Acetylenes and Alkenes
t.-a. mitsudo, s.-w. zhang, m. nagao and t. watanabe, J. Chem. Soc, Chem. Commun., 1991, (8), 598–599
2,4-Dienes were prepared in high yields with high regioselectivity by the codimerisation of acetylenes and alkenes in the presence of a catalytic amount of Ru(cod)(cot), where cod is cycloocta-l,5-diene and cot is cycloocta-l,3,5-triene, at 80°C. The best yield was obtained in pyridine, while in triethylamine, toluene and tri-n-butylamine as solvents, the yields were low.
Reactivity and Catalytic Activity of [RuBr2(Me2SO)3]
b. c. paul, u. c. sarma and r. k. poddar, Inorg.Chim. Acta, 1991, 179, (1), 17–23
[RuBr2(Me2SO)3] was used as precursor for the synthesis of many Ru(II) complexes containing bromide ion and other ligands. The complexes synthesised were of the types: [RuBr2L4] (L = PPh3; L2=phen or bpy), [RuBr2(Me2SO)2L2] (L=py, AsPh3; L2 =phen, bpy or o -phenylenediamine), etc. [RuBr2(Me2SO)3) was used as a catalyst for the oxidation of PPh3 by O2.
A Methanol Fuel CeU Having a Molybdenum-Modified Platinum-SPE Membrane Electrode
h. nakajima, J. Chem. Technol. Biotechnol., 1991,50, (4), 555–561
Studies of the modification of a methanol fuel cell made of a Pt-solid polymer electrolyte composite (Pt-SPE) with Mo showed that adsorption of Mo species on Pt enhances catalytic activity for MeOH oxidation both at Pt and Pt-SPE electrodes. The treatment with Mo increased the cell voltage by 100-200 mV at a current density lower than 2 mA per apparent unit area. MeOH permeated through the SPE membrane and reduced stability of the fuel cell.
Alloys Cathodically Modified with Noble Metals
j. h. potgieter, J. Appl. Electrochem., 1991, 21, (6), 471–482
Cathodic alloying platinum group metal additives to Cr greatly increases the corrosion resistance of Cr in non-oxidising acid environments. The corrosion resistance of Fe-Cr stainless steels was significantly increased by addition of <0.5% of platinum group metals. When Mo and platinum group metals occurred together in the alloy, a synergistic beneficial effect was exerted on the corrosion resistance. Alloying of stainless steels with Pd leads to a significant increase in the corrosion resistance of the steels.
New Methods of Uranium(IV) Production Using a Pt-Loaded Gas-Diffusion Electrode
m. shibata and n. furuya, J. Appl. Electrochem., 1991, 21, (3), 226–230
A local-cell mode and a fuel-cell mode are proposed as new methods for the production of uranous nitrate. In the local-cell mode the cell consists of a Pt loaded gas diffusion electrode and a system of circulation for uranyl nitrate solution and H gas, although H gas is required instead of the power source. H gas is the more economical method if it is easily obtained. In the fuel-cell mode the reduction can take place at a Pt gauze cathode in the catholyte, above the gas diffusion electrode. Uranyl ions are spontaneously reduced to 250-300 g/dm3 U(IV) using these methods and electrical energy is obtained by the fuel-cell mode.
Water Gas Shift Reaction Assisted by a Palladium Membrane Reactor
s. uemiya, n. sato, h. ando and e. kikuchi, Ind.Eng. Chem. Res., 1991, 30, (3), 585–589
The water gas shift reaction was operated at 673 K in a double tubular type membrane reactor, the inner tube of which was Pd membrane of thickness 20 μm, supported on a porous glass cylinder. The membrane reactor gave higher levels of CO conversion beyond the equilibrium attainable in a closed system, resulting from a shift of thermodynamic equilibrium toward the product side, caused by the selective and rapid removal of H from the reaction system. The amount of steam needed to achieve reasonable levels of conversion could be reduced, and from computer simulation, the high reaction efficiency attained by this membrane reactor is credited to the thinness of the Pd film.
Heterogeneous Platinum Nucleation and Crystallization of a Heavy-Metal Fluoride Glass
j. m. jewell, j. jaganathan and i. d. aggarwal, J.Am. Ceram. Soc., 1991, 74, (4), 788–796
The effect of controlled heterogeneous nucleation by Pt on the crystallisation of a ZrF^BaFi-LaFj-AlFj-NaF glass was studied, using various levels of Pt doping introduced into the glass by a combination of PtCl2 doping and melting-atmosphere variation. The effect of doping levels and melting conditions on the incorporation of Pt and the subsequent nucleation of crystals was studied by optical microscopy, SEM, DSC and XRD. Increased Pt in the glass increased the number of nucleation sites for the growth of β-ZrF4-BaF2 crystals. The crystallisation of this glass changed from surface controlled to bulk controlled with an mcreased number of nuclei. An accurate approximation of the number of nuclei in the glass was also found.
ELECTRICAL AND ELECTRONIC ENGINEERING
Conduction Mechanism in PtSi/Si Schottky Diodes
m. wittmer, Phys. Rev. B, 1991, 43, (5), 4385–4395
The conduction mechanism in PtSi/Si Schottky diodes was studied over temperatures 80-300 K. Above 100 K the forward current-voltage (I/V) characteristic of the diodes is highly ideal and obeys the thermionic-emission theory, including image-force lowering of the barrier. Some diodes show a deviation from this behaviour, due to carrier recombination in the depletion region. Carrier recombination is also responsible for the soft behaviour of the reverse I/V characteristic. The temperature dependence of the barrier height and the bias-independent position of the quasi-Fermi-level at the interface are associated with a high density of interface states. The activation energy for current transport at low temperatures suggests that these states are due to substitutional Pt atoms on the Si.
The Effect of Sintering Temperature on the Barrier Height of p-Type PtSi Schottky Diodes
v. w. l. chin, s. m. newbery, j. w. v. storey and u. theden, Aust. J. Phys., 1991, 44, (1), 67-72
The effect of sintering temperature on the barrier height of p -type <100> PtSi Schottky diodes was studied by various means. The diodes sintered in a furnace under foaming gas at 350°C for 40 min had a barrier height of 0.235 eV, which is lower than diodes sintered at 475°C for an additional 20 minutes (0.290 eV). For IR detection a low barrier height and high IR responsivity are necessary. Thus sintering by the first method is preferable, giving a cutoff wavelength of 5.3 μm at a reverse bias of 2 V, and a Schottky emission coefficient of -0.5 eV–1/2.
Ultraviolet, Visible, and Infrared Response of PtSi Schottky-Barrier Detectors Operated in the Front-Illuminated Mode
c. k. chen, b. nechay and b.-y. tsaur, IEEE Trans. Electron Devices, 1991, 38, (5), 1094–1103
The quantum efficiency of PtSi Schottky barrier detectors was measured as a function of wavelength, from 0.23-7 μm. For front-illuminated PtSi/p -Si devices at low temperatures, quantum efficiencies of 40-70% are obtained for the UV and visible regions with little loss of the IR photoresponse that is obtained for operation in the conventional back-illumination mode. At room temperatures for front-illumination the quantum efficiencies are ∼ the same in the UV and visible regions, but the IR response decreases abruptly beyond the Si absorption edge. Calculated quantum efficiencies in the UV and visible regions agree well with measured efficiencies. The temporal response of front-illuminated PtSi/p -Si was fast enough for operation at video frame rates.
Wear Reliability of Gold-Flashed Palladium vs. Hard Gold on a High-Speed Digital Connector System
e. j. kudrak, j. a. abys, i. kadija and j. j. maisano, Plat. Surf. Finish., 1991, 78, (3), 57–63
The wear characteristics of Au-flashed Pd and hard Au terminals in high-speed digital connector systems were evaluated after 60, 125, 250, 375, 500 and 1000 insertion and withdrawal cycles for thicknesses in the range 1.25 to 2.5 μm. Contact areas and wear tracks were examined by various techniques. The location, size, shape and depth of wear tracks were quantitatively examined and compared.
Thermal Stability of Pd-In Ohmic Contacts to n-GaAs Formed by Scanned Electron Beam and Rapid Thermal Annealing
k. prasad, l. faraone and a. g. nassibian, Electron. Lett., 1991, 27, (2), 149–151
Thermally stable and low resistance Pd-In ohmic contacts to n -GaAs were formed using scanned electron beam (SEB) and rapid thermal annealing (RTA). A specific contact resistance ϱc of – 10–6 Ω cm2 was obtained using both techniques with the SEB annealed contacts exhibiting a superior surface morphology. High temperature ageing of the contacts showed that the SEB annealed contacts were more stable than RTA contacts, as displayed by an increase in their respective ec values, a factor of ∼5 for SEB annealed contacts, against an increase by a factor of ∼ 8 for RTA contacts after 25 h of ageing.
Thermally Stable and Nonspiking Pd/Sb(Mn) Ohmic Contact to p-GaAs
c. c. han, x. z. wang, s. s. lau, r. m. potemski, m. a. tischler and t. f. kuech, Appl. Pkys. Lett., 1991, 58, (15), 1617–1619
A thermally stable, nonspiking Pd/Sb(Mn) ohmic contact to p -GaAs was developed based on the solid-phase regrowth mechanism. The contact metallisation consisted of a layered structure of Pd(250 Å)/Sb(100 A)/Mn(10 Å)/Pd(250 Å)/p -GaAs. Rapid thermal annealing of the contact at 500°C for 10 s yielded contact resistivities of ∼ 2 × 10-6 Ω cm2 and 4 × 10–7 Ω cm2 on substrates doped to 2.5 × 1018/cm3 and 4 x 1019/cm3, respectively.
Temperature Cycling Effects between Sn/Pb Solder and Thick Film Pd/Ag Conductor Metallization
b.-s. chiou, k. c. liu, j.-g. duh and p. s. palanisamy, IEEE Trans. Components, Hybrids, Manuf. Technol, 1991, 14, (1), 233–237
Thermal cycling effects on the solder joint between thick film mixed Pd/Ag conductor and Sn/Pb solder are investigated. Microstructural evolution of the in-terfacial morphology, elemental and phase distribution are probed by electron microscopy and XRD. Microstructural analysis reveals the formation of in-termetallic compounds: Pd3Sn, Pd2Sn, Pd3Sn2, PdSn, Pd3Pb, Ag5 Snand Ag3 Sn after thermal cycles from –55 to +125°C.
Contact Resistance Characteristics of Noble Metal Alloys for Connector Contacts
s. umemura, k.-i. yasuda and t. aoki, IEEE Trans. Components, Hybrids, Manuf. Technol, 1991, 14, (1), 181–186
Contact resistance characteristics, corrosion characteristics and the degradation mechanism for Pd, Ag, Au and Ni containing binary and ternary alloys were investigated to find useful lower cost noble metal alloy for connector contacts. The test conductor contacts are clad inlays mated with each other, clad inlays mated with hard gold plating and clad inlays with hard gold flash mated with inlays of the same material. Air mixed with SO2, N02, CI2, or H2S were the test gases. The following alloys are listed in order of increasing contact resistance: Au-Ag, Ag-Pd, Au-Ag-Pd, Au-Pdand Pd-Ni. The dominant corrosion products causing an increase in contact resistance were the chlorides in Pd alloys.
A Study of the Discharge Phenomena of Rhodium-Plated Contact Reed Switches
t. kobayashi, k. hinohara and c. kawakita, IEEE Trans. Components, Hybrids, Manuf. Technol., 1991, 14, (1), 20–22
The discharge phenomena of high breakdown voltage reed switches, such as the pressurised reed switch and vacuum reed switch, and the discharge phenomena of general purpose reed switches, with respect to their basic mechanism and reactions were studied. Rh-plated reed switches with contacts treated with high temperature O for surface deactivation were used in the study. The contacts were analysed after discharge, and it was found that the N cation and O anion serve as carriers in the discharge for the pressurised reed switch and general purpose reed switch, and a nitride is formed on the cathode and oxidation increases on the anode. In the vacuum reed switch, the O anion triggers the discharge as a carrier, and oxidation increases on the anode.
Screening of a Stable Cholesterol Oxidase for the Fabrication of Microbiosensor of Cholesterol by the Embodiment of Cholesterol Oxidase and a Platinized Platinum Electrode
s. yamauchi, m. yaoita, r. nagai, y. yoshida and y.ikariyama, Denki Kagaku, 1990, 58, (12), 1103–1106
Microbiosensors for cholesterol of diameter 100 μm were fabricated by direct immobilisation of cholesterol oxidases from different sources on a platinised Pt electrode. The response current of the cholesterol sensor decreased gradually at +0.6 V (vs. Ag/AgCl), however, reproducible, stable responses were obtained at +0.5 V. The response of the microbiosensor for cholesterol determination was very rapid, the response time being 20 s. This sensor detects cholesterol contents of 1.3-52 μM.