ABSTRACTS: July 1996
Journal Archive
ABSTRACTS: July 1996
of current literature on the platinum metals and their alloys
PROPERTIES
High Coercivity in Co/Pt Multilayers
j.-h. kim and s.-c. shin, Jpn. J. Appl Phys., 1996, 35, (1B), 342-345
The coercivity in a Co/Pt multilayer on a Si3N4 under-layer increased more than two-fold when using a rotating substrate. The increase was due to the enhance-ment of domain wall pinning effects caused by an increase of surface roughness in the Si3N4 underlayer. The Si3N4 underlayer surface prepared on a rotating substrate was rougher than that on a stationary substrate, which may be due to the oblique incidence of sputtered materials onto the rotating substrate.
Long-Range Order and Magnetic Properties Of MnxcPt1-x Thin Films
k. w. wierman and r. d. kkby, J. Magn. Magn. Mater., 1996, 154, (1), 12-16
Thin films of MnxPt1-x, (x = 0.18, 0.22, 0.25, 0.30, 0.34) prepared by magnetron sputtering onto quartz substrates were annealed in vacuum for 1 h at 850°C. After annealing, XRD showed the films to have the Cu3Au cubic structure and be highly textured with the (111) axis along the film normal. The films displayed a high degree of long-range order, shown by the ratio of the intensities of the superlattice (100) and fundamental (200) XRD reflections.
Growth of Ultrathin Pd Films on Al(001) Surfaces
v. shutthanandan, a. a. saleh, n. r. shivaparan and r.j. smith, Surf. Sci., 1996, 350, (1-3), 11-20
The growth mode and the interface structure of ultra-thin Pd films deposited on Al(OOl) surfaces were determined at room temperature. Pd atoms intermixed with and displaced Al substrate atoms. The mixing continued for Pd coverages from 0-5 monolayers, when a Pd metal film began to grow on the alloy surface. XPS indicated that AlPd formed during mixing, followed by the formation of Pd metal.
Effects of Y2BaCuO5 and Platinum Additions on the Unidirectional Solidification of YBa2Cu3O7-δ
l. durand, d. dierickx, p. regnier, o. van der biest and s. poissonnet, Supercond. Sei. Technol, 1996, 9, (4), 290-296
The effects of 211 and/or Pt additions on the solidification of YBaCuO was studied. Mixing the pure 123 powder with 20 wt.% very fine (1 |im) and regular sized Pt 211 particles strongly increased the viscosity of the peritectic liquid and resulted in a dramatic refinement in the distribution of the 211 particles trapped in the 123 matrix of the samples. Extra addition of 0.5 wt.% Pt further refined this distribution.
Magnetic Excitations and the Search for Crystal-Field Transitions in the Heavy-Fermion Superconductor UPd2Al3
a. krimmel, a. loidl, r. eccleston, c geibel and f. steglich. J. Phys.: Condens. Matter, 1996, 8, (11), 1677-1685
Crystalline-electric field (CEF) excitations in the anti-ferromagnetic heavy-fermion superconductor UPd2Al3 were studied by inelastic neutron scattering. UPd2Al3 is an example of 5/-electron systems with a residual line width which corresponds to the macroscopi-cally estimated Kondo lattice temperature. However, significant deviations from this suggest additional inelastic contributions that persist up to T = 150 K. This additional scattering could be due to CEF excitations or intersite magnetic correlations.
Superconductivity in Heavy-Fermion CeRh2Si2
r. movshovich, t. graf, d. mandrus, j. d. thompson, j. l. smith and z. fisk, Phys. Rev. B, 1996, 53, (13), 8241-8244
A superconducting transition in the heavy-fermion compound CeRh2Si2 was discovered under hydrostatic pressure of > ~ 9 kbar, near the critical pressure needed to suppress antiferromagnetic order (TN (P = 0) = 36 K). Superconductivity occurred at ~ 350 mK. Magnetic AC susceptibility showed a diamagnetic response corresponding to ~ 1% of perfect diamagnetism.
The Effect of Si/Ir Codeposition Ratio on the Ir Silicide/Si(100) Interface Roughness
c. k. chung and j. hwang, Mater. Chem. Phys., 1996, 43, (2), 191-194
The effect of the Si/Ir codeposition ratio on Ir silicide/Si(100) interface roughness was studied on Ir silicides grown on Si(100) by codeposition at Si/Ir atomic ratios of 0, 1 and 2 at 450°C under UHV. Epitaxial Ir3Si4 grew on Si(100) as pure Ir was deposited at all deposition ratios. The Ir3Si4/Si(100) interface remained smooth, although intermixing occurred during deposition, but at higher deposition ratios the Ir3Si4/Si(100) interface became rougher.
Electrical Conductivity and Superconductivity of Metal Phosphides with Skutterudite-Type Structure Prepared at High Pressure
i. shirotani, t. adachi, k. tachl s. todo, k. nozawa, t. yagi and m. kinoshita, J. Phys. Chem. Solids, 1996, 57, (2), 211-216
NiP35 LaRu4-xOsxP12 (x = 0, 1, 2, 3, 4) and CeRu4P12 phosphides with skutterudite (CoAs3)-type structure were prepared at around 1100°C and 4 GPa using a wedge-type cubic-anvil high pressure apparatus. Superconductivity was observed in LaRu4P12, LaRu3OsP12 and LaRu2Os2P12 at ~ 7 K. The upper critical field Of LaRu4P12 was 3.65 T at 0 K.
Quantum Oscillations in the Layered Perovskite Superconductor Sr2RuO4
a. p. mackenzie, s. r. julian, a. j. drver, g. j. mcmullan, m. p. ray, g. g. lonzarich, y. maeno, s. nishizaki and t. fujita, Phys. Rev. Leu., 1996, 76, (20), 3786-3789
A comprehensive study is presented of observed magneto-oscillatory phenomena in the normal state of Sr2RuO4, which is the first layered perovskite superconductor (Tc ≅1 K) not based on Cu. All sheets of the Fermi surface, including the large ones, have been observed, thus permitting consistent correlation of a number of physical properties. The observations are compatible with a Fermi liquid, which may be linked with coherent interplane transport at low temperatures.
CHEMICAL COMPOUNDS
Size-Evolution Towards Metallic Behavior in Nano-Sized Gold and Platinum Clusters as Revealed by 197 Au Mössbauer Spectroscopy
f. m. mulder, r. c thiel, l. j. de jongh and p. c m. gubbens, NanoStructured Mater., 1996, 7, (3), 269-292
197Au Mössbauer spectroscopic studies were made on the large Pt309 cluster and four types of molecular Au55 clusters, with different types of ligands, using 197Au produced by neutron activation. The ligands had a large effect on the charge densities at the surface atoms of the cluster cores. For the Pt309 compound, the inner core atoms had the same charge density at the nucleus as in the bulk metal. The inner core of the Pt305 cluster is metallic, but the Au,, cluster is not.
On a New Oxoiridate(V) of the Sr4PtO6-Type: NaSr3IrO6
s. frenzen and h. müller-buschbaum, Z. Naturforsch.B, 1996, 51, (2), 225-228
X-ray studies were performed of single crystals of NaSr3IrO6 prepared by heating mixtures of Na2O2, SrO and Ir in closed Ag tubes. NaSr3IrO6 crystallises with trigonal (rhombohedral) symmetry in the space group D3d6 - R3c with a = 9.636(2), c = 11.556(3) Å, Z = 6, and is isotypic to compounds of the Sr4PtO6 type. The substitution of Sr2+ by Na+ in NaSr3IrO6 resulted in an ordered metal distribution and in an increase of the oxidation state from IrIV to IrV.
Synthesis and Spectral Studies of 1,3-Diketonate Derivatives of ortho -Palladated α-Arylalkylamines
v. v. dunina, o. a. zalevskaya, s. p. palii, d. v. zagorevskn and yu. s. nekrasov, IZV. Akad. Nauk, Ser. Khim., 1996, (3), 733-740
Acetylacetonato derivatives of a series of ortho -palla-dated secondary and tertiary α-arylalkylamines were prepared and characterised. An unusual rearrangement involving migration of an H atom from the alkyl aminoalkyl group to the Pd atom leading to a hydride intermediate and followed by PdH elimination was observed. This may be due to isomerisation of η2-O′.O′-co-ordinated β-diketonate ligand into the η1-C-bonded diketonyl form, to give the unsaturated metal centre.
Spectroscopic and Electrochemical Investigation of Mixed-Valence RhI-RhIII Complexes with Cyanide Bridge
t. v. magdesieva, s. i. gorel'sky, k. p. butin, a. a. bezrukova, v. s. khandkarova and ya. s. vygodskii, Izv. Akad. Nauk, Ser. Khim., 1996, (3), 726-731
New mixed valence RhI-RhIII complexes with cyanide bridges were studied using electronic spectra and redox potentials. Interaction between Rh atoms in the complexes is small (the “fixed valences” case). Intervalence transition from RhI to RhIII were not observed in the 7000-50,000/cm region. Some of the complexes in the solid state have additional absorption bands in diffuse reflectance spectra due to the interaction of the Rh(I) group orbitals of appropriate symmetry.
Synthesis and Characterization of Superstructured Rhodium Porphyrins
h. r. jiménez and m. momenteau, Inorg. Chim. Acta, 1996, 244, (2), 171-177
Three Rh “two-face” hindered porphyrins were synthesised by the metallation of “basket-handle” porphyrins in dimethylformamide, for example, [e-BHP(C12)2RhIII(L)(H2O)]Cl, etc., where e-BHP(C12)2 = α5,15 :β 10,20-bis [2,2′-(dodecamethyleneoxy)-diphenyl]porphyrinato dianion and L = dimethylamine. In these new neutral or cationic Rh porphyrins, the two faces of the porphyrin are protected by two chains linked at the opposite phenyl rings. Studies of the derivatives of these porphyrins show different reducing tendencies, which follow in general the order for the axial ligand NH(CH3)2 > H2O or Cl.
The Activation of C-H Bonds via Ru-Ru Bond Fission
a. j. blake, p. j. dyson, p. e. gaede and b. f. g. johnson, Inorg. Chim. Acta, 1996, 241, (2), 11-12
New metallacyclic cluster, Ru3(CO)8(C9H8) (1) is produced in low yield by heating the Ru3(CO)8(C9H10) cluster in heptane under reflux. In (1), the fission of σ Ru-Ru bond induced the cleavage of two C-H bonds with the concomitant formation of two Ru-C σ bonds. 1H NMR spectra show the two H atoms lost in the reaction are the most activated of those present on the ligand, giving resonances at 0.88 and 1.56 ppm, which are low compared with ~ 7 ppm for the free ligand.
A Chain Complex of Ruthenium(II,III) Cation Dimer Linked by a Nitroxide Radical, [Ru2(O2CCMe3)4(NITPh)]n(BF4)» (NTTPh = 2-Phenyl-4,4,5,5-tetrametbyl-4,5-dihydro-lH-imidazolyl-l-oxy-3-oxide)
m. handa, y. sayama, m. mikuriya, r. nukada, i. hiromitsu and k. kasuga, Chem. Lett. Jpn., 1996, (3), 201-202
The above Ru chain complex was characterised by the X-ray analysis, showing a structure with the alternated alignment of S = 3/2 (Ru(HjHI) core) and S = 1/2 (NITPh). The magnetic moment decreased mono-tonically with decreasing temperature. This chain complex has a paramagnetic dimetal centre with a metal-metal bond linked by the nitroxide radical.
ELECTROCHEMISTRY
Electro-oxidation of Cl Molecules at Pt-Based Catalysts Highly Dispersed into a Polymer Matrix: Effect of the Method of Preparation
w. t. napporn, h. laborde, j.-m. léger and c lamy, J. Electroanal. Chem., 1996, 404, (1), 153-159
Highly dispersed Pt-based electrodes modified with Ru and/or Sn inserted in a conducting polymer matrix exhibited weak poisoning effects compared with pure Pt particles. The Pt-Ru alloy was the most promising catalyst for the electro-oxidation of MeOH, while Pt-Sn electrodes gave a very significant negative shift to the oxidation potentials during electro-oxidation of formaldehyde and formic acid. An important decrease in poisoning was found mainly with Pt-Sn electrodes, but also with Pt-Ru and Pt-Ru-Sn electrodes.
The Electrooxidation of Formaldehyde on Pt(100) and Pt(110) Electrodes in Perchloric Acid Solutions
p. oltvi, l. o. s. bulhöes, j.-m. léger, f. hahn, b. beden and c lamy, Electrochim. Acta, 1996, 41, (6), 927-932
Studies of the electro-oxidation of formaldehyde on Pt(IOO) and (110) electrodes in a perchloric acid medium showed both undergo two oxidation processes involving either methylene-glycol oxidation or adsorbed CO formation. The Pt(IOO) electrode is more active for the methylene-glycol oxidation. The CO species were adsorbed linearly on both electrode surfaces, but multibonded and bridge bonded CO forms were only present on the Pt(100). The adsorbed CO species block the surfaces during methylene-glycol oxidation, with Pt(110) being more blocked than Pt(100).
Hydrogen Evolution Reaction in Alkaline Solution. Catalytic Influence of Pt Supported on Graphite vs. Pt Inclusions in Graphite
j. fournŒr, l. brossard, j.-y. tilqutn, r. côté, j.-p., dodelet, d. guay and h. menard, J. Electrochem. Soc., 1996, 143, (3),919-926
Electrochemical behaviour of Pt having graphite powders bonded by polymerised LaPO4 was studied for the HER in 1 M KOH solution. Pt-supported electrodes, Pt(s)/C/LaPO4 (1) were more active than those containing Pt inclusions in graphite, Pt(i)/C/LaPO4 (2). In high-current-density conditions of 0.25 A/cm2, (2) was stable while (1) disintegrated after 24 h.
Fabrication of Pt/(Ta2O5+Pt) Coated Titanium Electrodes Using Combination of Partial Thermal Decomposition and Electrolytic Reduction of Pt and Ta complex
y. kamegaya, j. saito, h. kobayashi, m. okuyama and t. mttamura, Denki Kagaku, 1996, 64, (2), 138-142
A three-layered Pt/(Ta2O5H-Pt)/Ti electrode was fabricated, to protect the Ti substrate from corrosion, by partial thermal decomposition (1) and electrolytic reduction of Pt(NO2)2(NH3)2, and (1) OfTa(OC2H5)5. The interlayer is amorphous Ta2O5, and Pt, with a Pt top layer. It has excellent stability during anodic O2 evolution in H2SO4, high conductivity and durability.
A New Successive System for Hydrogénation of Styrene Using a Two-Compartment Cell Separated by a Pd Sheet Electrode
c. iwakura, t. abe and h-inoue, J. Electrochem. Soc., 1996, 143, (4),L71-L72
A new successive system for the hydrogénation of styrene using a Pd sheet electrode is reported. The activated H atoms are electrochemically produced at the front side of the Pd sheet electrode and supplied through it to be used for hydrogénation at the back surface of the Pd sheet electrode. Only ethylbenzene was produced, and the production rate depended on the applied current. The current efficiency of < 93% occurred at an applied current of 10 mA.
Voltammetric Study of the Immobilization of Palladium at the Surface of Carbon Paste Electrodes
k.-h. lubert, m. guttmann and l. beyer, Electroanalysis, 1996, 8, (4), 320-325
Cyclic voltammetric studies were performed of Pd immobilisation at the surface of unmodified C paste electrodes. During pretreatment at 0 V, Pd was bound at the surface of the C paste, and the amount of immobilised Pd depended on the composition of the solution, polarisation time, electrode potential and stirring. During an anodic scan, the surface-bound Pd was oxidised at ~ + 0.6 V and the well-shaped peaks could be utilised for the determination of the immobilised Pd. The detection limit was ~ 5 × 10 -6M Pd2+ after 5 min polarisation at 0 V with stirring. Pd and H can be “deposited” simultaneously at the C paste surface through cathodic polarisation.
Rapid Oxidation of Ru(NH3)6 3+ by Os(bpy)33+ within Nafion Coatings on Electrodes
m. shi and f. c. anson, Langmuir, 1996, 12, (8), 2068-2075
When Ru(NH3)63+ (1) and Os(bpy)33+, (2) reactants are incorporated in Nafion coatings on electrodes, the oxidation of (1) by (2), which is normally a very slow process, can proceed much more rapidly, especially with Nafion coatings that are not fully hydrated. The Ru(NH3)63+ is oxidised to Ru(VII) at a rate that is first order in Ru(NH3)63+ and Os(bpy)33+, and inverse first order in H+. The higher reaction rate obtained upon incorporation of the reactants into Nafion results from their higher concentrations rather than from enhancement in the intrinsic redox reactivity of either cation.
Electrochemical Behavior of the RuO2/TiO2 Anodes during the Electrolysis of Sea Water
c. liang and q. gu, Corros. Sei. Prot. Technol. (China), 1996, 8, (2), 125-129
Studies of the electrochemical behaviour of the anode RuO2/TiO2 during the electrolysis of sea water showed that use of the anode could improve current efficiencies and decrease energy consumption. The best results were obtained at current density of 100 mA/cm2 and electrode gap of 5 mm. The cathode was electrochemically protected at potentials from - 820 to —1450 mV (SCE).
Investigation of the Formation Of RuO2-Based Mixed Oxide Coatings by Secondary Ion Mass Spectrometry
s. daolio, j. kristóf, c. piccirillo, c. pagura and a. debattisn, J. Mater. Chem., 1996, 6, (4), 567-571
The evolution of a RuO2-TiO2 film electrode with temperature was studied using a coating mixture prepared on a Ti support from an isopropyl alcohol solution of hydrated Ru chloride and Ti diisopropoxide bispentane-2,4-dionate precursors. Concentration depth profiles monitored film evolution and identified surface segregation phenomena resulting from the increased metal dispersity.
PHOTOCONVERSION
The Role of Acidity in the Photoreaction of Carboplatin
w. iju1y. yang, h. xiong and z. que, Precious Met. (China), 1996, 17, (1), 19-22
Photochemical studies of acidic solutions of carboplatin on irradiation at 313nm showed that the photolytical product is cis -[Pt(NH3)2.(H2O)2]2+ and the quantum yield is 0.89. Acidity is a major factor in the photoreaction of carboplatin and the mechanism is discussed.
Vibrational Sidelines in the Localized 3MLCT Emission of [Ru(bpy)2(bpz)]2+ in [Zn(bpy)3] (CIO4)2 (bpy = 2,2-Bipyridine, bpz = 2,2'-Bipyrazine)
h. riesen, l. wallace and e. krausz, J. Phys. Chem., 1996, 100, (11), 4390-4394
The luminescence spectrum of [Ru(bpy)2(bpz)]2+ (1) and [Ru(bpy-d8)2(bpz)]2+ complexes in the host [Zn(bpy)3] (ClO4)2 (2) was studied and sidelines asso-ciated with the spectator bpy/bpy-d8 ligands were identified over the entire vibrational frequency range. Although the lowest excited 3MLCT states in Ru diimine systems are localised, the coupling in the 1MLCT excitations is 3–4 orders of magnitude larger. Dominant sidelines reported earlier for (1) in (2) are caused by contamination by [Os(bpy)2(bpy-d8)]2+.
Photosensitization of Nanocrystalline Semiconductor Films. Modulation of Electron Transfer between Excited Ruthenium Complex and SnO2 Nanocrystallites with an Externally Applied Bias
p. v. kamat, i. bedja1 s. hotchandani and l. k. patterson, J. Phys. Chem., 1996, 100, (12), 4900^908
The charge injection from excited Ru(bpy)2(dcbpy)2+, Ru(II), into SnO2 nanocrystallites was studied by in situ spectroelectrochemical measurements. Laser flash photolysis of Ru(U)-modified SnO2 nanocrystalline film was used to record the transient absorption spectra at different applied potentials. The yield of electron transfer product, Ru(III), decreased as the applied bias was switched to negative potentials. At a bias of –0.7 V, Ru(II)* was the only observed transient.
ELECTRODEPOSITION AND SURFACE COATINGS
Characterization of a Colloidal Pd(II)-Based Catalyst Dispersion for Electroless Metal Deposition
w. j. dressick, l. m. kondracki, m.-s. chen, s. l. brandow, e. matuevic and j. m. calvert, Colloid. Surf. A: Physicochem. Eng. Aspects, 1996, 108, (1), 101-111
An aqueous Pd(II) dispersion for the selective electroless deposition of Ni at ligand-bearing surfaces, was prepared by hydrolysis of PdCl42 at pH 5 in NaCl solution. The dispersion comprised anionic and uncharged Pd(II) species, from monomelic to colloidal, with colloidal species starting the electroless metal deposition. The colloidal catalysts have a diameter ~ 4—53 nm, with an average size of 30 ± 12 nm.
Electroplated Palladium Coating as a Nickel Migration (Thermal) Barrier
j. k. lim, j. s. russo and e. antonier, Plat. Surf. Finish., 1996, 83, (3), 64-67
Ni-Co plated chip carriers were coated with an acid Pd strike and electrolytic Pd deposits, using three different plating combinations: Ni-Co/Au (Pd strike), Ni-Co/Pd and Ni-Co/Pd/Au. Ni-Co/Au plated carriers were the standard. The tested samples showed equivalent or better Ni migration and solderability than the standard, that is, less than 10 at.% Ni migration and nearly 100% solder flow.
APPARATUS AND TECHNIQUE
Flow Injection Amperometric Detection of Ammonia Using a Polypyrrole-Modified Electrode and Its Application in Urea and Creatinine Biosensors
m. trojanowicz, a. lewenstam, t. krawczynski, v. krawczyk, i. lähdesmäki and w. szczepek, Electroanalysis, 1996, 8, (3), 233-243
Amperometric NH3 detection, using an anodically polarised Pt electrode, modified with PPy, was used in biosensors. NH3 detection in a flow injection system with ≤ 100 μM of analyte at a detection limit of 0.6 μM was used to detect urea and creatinine by immobiling urease and creatinine iminohydrolase, respectively, at the PPy surface. A biosensor of very low sensitivity was obtained by urease entrapment in the PPy layer during electropolymerisation.
Effect of Electrode Materials on the Sensitive Properties of the Thick-Film Ceramic Humidity Sensor
w. qu, Solid State Ionics, 1996, 83, (3, 4), 257-262
A thick-film humidity sensor with excellent stability was produced by depositing a humidity sensitive layer between two metal electrodes on an Al2O3 substrate. The sensor response depended on the sensing layer and the properties of the electrode material. Pt electrodes gave higher sensitivity over the whole humidity range, and faster response than Ag/Pd electrodes.
Composite Pd/Ta Metal Membranes for Hydrogen Separation
n. m. peachey, r. c snow and r. c dye, J. Membrane Sci., 1996, 111, (1), 123-133
A composite metal membrane was fabricated by vapour deposition using 13 μm Ta foils cleaned by ion milling, then coated with 1 μm of Pd metal on each side. The membrane of area ~ 2 cm2, gave exceptionally high H gas fluxes from 18.7 standard cm3/min (sccm) at 300°C to 27.4 sccm at 365°C with a H differential pressure of ~ 355 torr. The deposited Pd films were oriented along the (111) crystal axis.
HETEROGENOUS CATALYSIS
Deep Hydrodesulfurization of DBT and Diesel Fuel on Supported Pt and Ir Catalysts
r. navarro, b. pawelec, j. l. g. fierro, p. t. vasudevan, j. f. cambra and p. l. arias, Appt. Catal. A: Gen., 1996, 137, (2), 269-286
Deep hydrodesulphurisation (HDS) of dibenzothio-phene (DBT) and diesel fuel (with 0.08 wt.% S) was performed using Pt/- and Ir/amorphous SiO2-Al2O, (ASA) and on a stabilised HY zeolite. The normalised activities of Pt/ASA and Pt/HY catalysts were better than those of the Ir catalysts, with the HDS being dominant over hydrogénation. In HDS of diesel fuel (at 623 K), both Pt catalysts were a little more active than a commercial Co-Mo/Al2O3 catalyst. The normalised activity for HDS of DBT (593 K) increased as: Pt/HY > Pt/ASA >> Ir/HY >Ir/ASA, and the HDS of diesel fuel (623 K) increased as: Pt/HY >> Pt/ASA >> Ir/HY > Ir/ASA.
Regioselective Hydrogénation of Alkenes over Pt-Loaded Zeolite BEA
e. j. creyghton, r. a. w. grotenbreg, r- s. downing and h. van berkum, J. Chem. Soc., Faraday Trans., 1996, 92, (5), 871-877
The hydrogénation of dec-l-ene (1) and (J2)-dec-5-ene (2) was studied over Pt/Na-BEA and non-zeolitic Pt catalysts. Under specific conditions using Pt/Na-BEA, (1) is hydrogenated 18 times faster than (2), whereas the ratio is only ~ 2 for Pt on non-micro-porous supports. Compared with Pt/Na-BEA, Pt/ amorphous meso/macroporous support shows a higher activity in the catalytic hydrogénation of (1) and (2) but a much lower regioselectivity. The hydrogénation over Pt/Na-BEA deviates from zero-order kinetics.
Kinetic Modeling of CO Oxidation on Pt/CeO2 in a Gradientless Reactor
m. a. shalabi, b. h. harji and c. n. kenney, J. Chem. Tech. Biouchnol., 1996, 65, (4), 317-324
Pt/CeO2 was studied in order to understand the promoting effects Of CeO2 in the CO oxidation reaction, at 100-170°C. At low concentrations of reactants, Pt/CeO2 exhibited multiple steady states, similar to the multiplicity behaviour of Pt/Al2O3. CeO2 lowers the activation energy for CO oxidation, increases the activity of the reaction by being a good O2 store and suppresses the usual CO inhibition effect.
Synthesis and Characterization of Sol-Gel Pt/TiO2 Catalyst
e. sánchez, t. lópez, r. gómez, bokhimi, a. morales and o. novaro, J. Solid Stau Chem., 1996, 122, (2), 309-314
Pt/TiO2 catalysts with 1.0 wt.% Pt were prepared in a one-step operation by the sol-gel technique with Ti(OBut)4 and Pt acetylacetonate, without any reduction of the sample in H2. The fresh samples had three nanophases: rutile (the majority), anatase and Pt. Pt promoted the formation of rutile, either due to the presence of an intermediate PtO2 phase, having the rutile structure, or to the Pt-catalysed dehydroxylation of anatase. Pt atoms do not enter into the crystalline structure of rutile, despite both PtO2 and rutile having the same crystalline structure.
Crotonaldehyde Hydrogénation over Bimetallic Pt-Sn Catalysts Supported on Pregraphitized Carbon Black. Effect of the Sn/Pt Atomic Ratio
f. coloma, a. seplveda-escribano, j. l. g. fierro and f. rodrguez-reinoso, Appl. Catal. A: Gen., 1996, 136, (2), 231-248
Three bimetallic Pt-Sn/C catalysts, prepared by successive impregnation of pregraphitised C black with an aqueous solution of hexachloroplatinic acid and Sn(II) chloride, were studied during crotonaldehyde hydrogénation. When Sn was added to the samples, the amount of surface Pt was greatly reduced. Both Pt0 and PtII were detected by XPS in the fresh bimetallic catalysts. After reduction in flowing H2 at 623 K, Pt was completely reduced to metal, and some Sn was reduced to Sn0, possibly allowing Pt-Sn alloy formation. Catalytic activity for gas phase hydrogénation of crotonaldehyde was greatly improved by Sn.
A Pt-Rh Synergism in Pt/Rh Three-Way Catalysts
z.hu, Chem. Commun., 1996, (7), 879-880
Performances of Pt, Rh and Pt/Rh catalysts were assessed after ageing in exhaust to mimic in-use catalyst operation. The activity of the Pt/Rh catalyst was about one order of magnitude higher than either a Pt or an Rh catalyst for HC/CO/NO three-way con-versions. This high activity of the Pt/Rh three-way catalyst is attributed to a Pt-Rh synergism. The Pt/Rh/Al catalyst also gives HC/CO conversions of 50% at tem-peratures 70 K lower than the Pt/Al catalyst and lower than the Rh/Al catalyst by 100 K.
Structure and Catalysis of a SiO2-Supported Gold-Platinumauster [(PPh3)Pt(PPh3Au)6]-(NO3)2
y. yuan, k. asakura, h. wan, k tsai and y. iwasawa, Chem. Lett. Jpn., 1996, (2), 129-130
A Pt catalyst [(PPh3)R(AuPPh3)6] (NO3)2 (1)/SiO2 was very active for H2-D2 equilibration with a TOF of 29.8/s, but had low activity for ethene hydrogénation and CO oxidation at 303 K. Pt atoms bonded to Au atoms in the cluster. The cluster framework of (1)/SiO2 was stable during the reactions at 303 K. The number of Au-Pt bonds fell after heat treatment.
The Shape-Selectivity of Activated Carbon Fibers as a Palladium Catalyst Support
h. jin, s.-e. park, j. m. lee and s. k. ryu, Carbon, 1996, 34, (3),429-431
Activated C fibre (ACF) was used as a shape-selective catalyst support for Pd. Pd was deposited on pitch-based ACF and was used as the catalyst in the liquid-phase heterogeneous hydrogénation of olefinic C6 hydrocarbons. As the adsorption capacity increased, the pore size distribution became wider, and meso-pores and wider micropores increased. HNO3 treatment and Pd loadings did not greatly affect the types of adsorption isotherm. For 1-hexene, the hydro-génation rate was a function of mean pore radius: the reaction does not occur at a mean pore radius of < 0.9, but for > 0.9 the reaction rate increased considerably. Shape-selectivity occurs inside the pores.
Liquid Phase Hydroformylation of Ring Substituted Styrenes Catalyzed by Rh-B and Rh-Zn-B Systems Supported on Silica
m. lenarda, r. ganzerla, s. paganelli, l. storaro and r. zanoni, J. Mol. Catal. A: Chem., 1996, 105, (3), 117-123
Rh based catalysts/SiO2 were prepared by low temperature reduction of the preadsorbed salts with NaBH4 and Zn(BH4)2. A remarkable B and Zn surface enrichment was observed from ESCA data in both catalysts. Both catalysts were active in the hydro-fbrmylation of liquid phase ring-substituted styrenes. The resulting reaction was really heterogeneous as no catalyst leaching occurred. The chemoselectivity was always close to 100%, and regioselectivity appeared to be controlled by the nature of the ring substituents.
Synthesis of Cyclopentanone Derivatives with Polystyrene-Supported Cyclopentadienyl Rhodium Catalysts
d. p. dygutsch and p. eilbracht, Tetrahedron, 1996, 52, (15), 5461-5468
A polystyrene-supported η5-cyclopentadienyl Rh catalyst was applied to two different methods of cyclopen-tanone synthesis. The synthesis of subsumed cyclopen-tanones was performed either by hydrocarbonylative cyclisation, starting from 1,4-dienes or from allyl vinyl ethers via tandem Claisen rearrangement, and intramolecular hydroacylation of the 4-pentenal intermediates. The polymer-attached CpRh(cod) complex was a very efficient and reusable hydroformylation catalyst.
Ruthenium Catalyst Supported on CeO2 for Ammonia Synthesis
y.ntwa and k.-i.aika, Chem. Lea. Jpn. 1996, (1), 3-4
Lanthanide oxides, Sm2O3, La2O3, especially CeO2, were more effective, when supporting Ru catalysts, rather than being a dopant during NH3 synthesis. The activity of Ru/La2O3 catalyst was superior to other metal oxide-supported Ru catalysts, such as Ru/MgO. The activity, Ru dispersion, BET surface area and the amount of H consumption by Ru/CeO2 depended on H2 treatment, thus suggesting a SMSI phenomenon. Partially reduced CeO2 donated electrons to Ru atoms, which then formed the active sites.
A Novel Basic Alkaline-Earth Zeolite-Supported Ruthenium Catalyst for Ammonia Synthesis
c t. fishel, r. j. davis and j. m. garces, Chem. Commun., 1996, (5), 649-650
Studies of the promotional effect of alkaline-earth cations on the catalytic activity of Ru/zeolites during NH3 synthesis showed an increase in the reaction rates that exceeds those for analogue catalysts containing only alkali-metal cations. The Ru clusters were supported on basic zeolite using as a starting material KX, CsX, CaX, BaX and MgO. Ru/BaX and Ru/CaX catalysts were three times more active than Ru/CsX; this is the highest value for zeolites in NH3 synthesis.
Carbon Monoxide Hydrogénation on Supported Manganese-Ruthenium Catalysts
t. tercioglu and j. f. akyurtlu, Appl. Catal. A: Gen., 1996, 136, (2), 105-111
CO hydrogénation over 6.3% Mn-2.5% Ru/Al2O3 catalyst was studied in a flow system with a differential fixed-bed reactor operating under atmospheric pres-sure at 553-613 K, H2:CO = 1:3 and space velocity 5100-27,600 cm3/gh. Modification with Mn resulted in a shift of the product distribution to lower olefins. The activity and selectivity of the catalyst changed at/below and above 573 K. It is suggested that at/below 573 K, monolayer C deposits and > 573 Kmultilayer C deposits affect the performance of the catalyst.
Hydrogénation of Citral and Cinnamaldehyde over Bimetallic Ru-Me/Al2O3 Catalysts
g. neri, l. mercad ante, c milo ne, r. pietropaolo and s. galvagno, J. Mol. Catal. A: Chem., 1996, 108, (1), 41-50
Hydrogénations of citral and cinnamaldehyde were studied over Ru-Me/Al2O3 catalysts, where Me = Ge, Sn or Pb. Two series of catalysts were prepared by using the controlled surface reaction (CSR) technique (RuEC series) and the more conventional co-impregnation method (RuNI series). Addition of Ge increased the catalytic activity of the RuEC series, but had no effect on RuNI series. Addition of Sn universally increased both activity and selectivity. The Pb present did not modify the selectivity and slighdy decreased the catalytic activity on RuNI series samples.
HOMOGENEOUS CATALYSIS
Intramolecular Heck-Type Reactions in Aqueous Medium. Dramatic Change in Regioselectivity
s. lemaire-audoire, m. savignac, c. dupuis and j.-p. genÉt, Tetrahedron Lett., 1996, 37, (12), 2003-2006
Intramolecular Heck-type cyclisations promoted by Pd(OAc)2/TPPTS and PdCl2/TPPTS catalytic systems, in CH3CN/H2O medium, are reported. The cyclisations were efficiently performed in aqueous medium. Unexpected endo selectivity was observed rather than the usual exo process, the reaction reversing in favour of the endo cyclised compounds. Either endo or exo-ring closure can be obtained from the same substrate.
Mild Azide-Mediated Palladium-Catalysed Cleavage of Allyloxycarbonyl Protected Alcohols in Aqueous Media
s. sigismondi and d. snsiou, J. Chem. Res. (S), 1996, (1),46-47
The deprotection of allyloxycarbonyl-protected alcohols was efficiently performed under neutral conditions using Pd(OAc)2-tppts catalyst in MeCN-H2O, in the presence OfNaN3 as allyl scavenger. The deprotection reaction proceeded smoothly with alloc-pri-mary and alloc-secondary alcohols, giving quite good yields. The H2O-Soluble catalyst can be easily reused without the addition of more nucleophile.
An Improved Procedure for the Synthesis of Substituted Acetylenes from the Reaction of Acetylene Gas with Aryl Iodides under Palladium-Copper Catalysis
m. pal and n. g. kundu, J. Chem. Soc., Perkin Trans. I, 1996, (5), 449-451
The use of dimethylformamide (DMF) as a solvent promoted the Pd-Cu catalysed reaction of acetylene gas with aryl iodides in a closed system to give disub-stituted acetylenes in fair to excellent yields. The reaction was carried out in the presence of [Pd(PPh3)2] Cl2, Et3N and CuI in DMF in acetylene gas. When chloroform was used as the solvent, mixtures of monoand disubstituted acetylenes were produced; some of these have biological interest.
Synthesis and Characterization of Poly(ethynyltrimethylsilane) Containing Pd(DI) Coordination Sites
m. v. russo, a. furlanl m. cuccu and g. polzonetti, Polymer, 1996, 37, (9), 1715-1722
Polymerisation reaction of ethynyltrimethylsilane (HC≡C-Si(CH3)3) are reported in the presence of the bis(acetiylide) complex {Pd[OC≡Si(CH3)3]2(PPh3)2} in 1:100; 1:50 and 1:25 catalyst : monomer ratios. The catalyst plays different roles, such as activation by Pd of the triple C≡C bond of the monomer and insertion into the Pd-C s-bond with growth of the polymer chain; oxidation Of PPh3 to OPPh3 which can be released leaving free co-ordination sites on Pd followed by crosslinking with the C=C bonds of neighbouring polymer chains; and in the presence of NH(C2H5)2, the C-Si bond is activated followed by substitution of some Si(CH3)3 groups with N(C2H3)2.
Hydroformylation of Unsaturated Alcohols Catalyzed by Rh(acac)(CO)2 Modified with Different Phosphorus Ligands
a. m. trzeciak, e. wolszczak and j. j. ziÓlkowski, New J. Chem., 1996, 20, (3), 365-370
The activity of Rh(acac)(CO)2 catalysts modified with mono- and diphosphorus ligands of different electronic and steric properties was studied during hydro-formylation of unsaturated alcohols at 60-80°C under 10 atm H2/CO = 1. The reaction of the 3-buten-2-ol and l-octen-3-ol yielded the cyclic 2-hydroxy-5-methyltetrahydrofuran and 2-hydroxy-5-pentyl-tetrahydrofuran, respectively. Ph2P(CH2)4PPh2 and P(O-m -MeC6H4)3 gave the highest catalytic activity.
Direct Formation of Alcohols by Hydrocarbonylation of Alkenes under Mild Conditions Using Rhodium Trialkylphoephine Catalysts
j. k. macdougall, m. c simpson, m. j. green and d. j. cole-hamilton, J. Chem. Soc., Dalwn Trans., 1996, (6), 1161-1172
The hydroformylation of hex-1-ene to heptanal and 2-methylhexanal in toluene was catalysed by the complex [RhH(PEt3)3], while in tetrahydrofuran signifi-cant amounts of heptanol and 2-methylhexanol were formed, especially over long reaction times. In pro-tic solvents only alcohols were produced even after short reaction times. The reactions were very rapid and occurred readily with alkenes. The highest rates were observed for ethene (54,000 turnovers/h) and the products were always alcohols. A new mechanism for this direct hydrocarbonylarion is proposed.
Catalytic Alkane Dehydrogenation by IrClH2(PPri3)2: Evidence for an Alkane Associative Mechanism
j. belu and c. m. jensen, Organometallics, 1996, 15, (6), 1532-1534
The dehydrogenation of alkanes to alkenes was catalysed by IrClH2(PPri3)2 in the presence of the H acceptor, tert -butylethylene, at 150°C. Mechanistic studies, including labelling experiments with IrClD2(PPri3)2, showed that reversible co-ordination and hydride migration to tert -butylethylene is facile and that the slower, subsequent elimination of rerr-butylethane required prior co-ordination of alkane.
Ru-CataIyzed HydrogenoIysis of Chiral AUylic and Propargylic Cyclic Carbonates: Synthesie of Optically Active (E)-AUyIic and Allenic Alcohols
s.-k. rang, d.-y. kim, h.-s. rho, s.-h. yoon and p.-s. ho, Synth. Commun., 1996, 26, (8), 1485-1492
Optically active (E )-allylic, (E,E )-dienylic and allenic alcohols were synthesised with excellent regioselectivity by RuH2(PPh3)4 (1) catalysed reductive cleavage of chiral allylic cyclic carbonates with NH4 formate. Also, hydrogenolysis of propargylic cyclic carbonates by (1) afforded only allenic alcohols.
FUEL CELLS
The Chemical State of Sulfur in Carbon-Supported Fuel-Cell Electrodes
k. e. swider and d. r. rolison, J. Electrochem. Soc., 1996, 143, (3), 813-819
The chemical state of S in Pt/C electrocatalysts, using vulcan C, was studied by measuring its oxidation state by XPS during the preparation of a “mock” fuel-cell electrode to find if the S from the C affects the electrocatalyst. Pt catalytically oxidised some of the covalent S in the vulcan C to sulphate when H2O, heat and strong physical contact between Pt and C were all present. However, most of the zero-valent S remained in the C after treatment, without any initial contact with Pt, so may be a source of Pt poisoning.
Analysis of Reaction Kinetics for Carbon Monoxide and Carbon Dioxide on Polycrystalline Platinum Relative to Fuel Cell Operation
r. j. bellows, e. p. marucchi-soos and d. t. buckley, Ind. Eng. Chem. Res., 1996, 35, (4), 1235-1242
Hydrogen can be produced in a polymer electrolyte fuel cell by reforming hydrocarbons or alcohols. Such H2 contains CO and CO2 (COx) impurities which adsorb onto the Pt anode electrocatalyst, reducing the efficiency for H2 electro-oxidation. Studies showed that the rate of CO electro-oxidation is an important factor in determining the CO tolerance of Pt anodes. It is suggested that for CO tolerance, all CO in the feed must be effectively consumed during electro-oxidation at low potentials; CO adsorption fluxes will be much faster than CO2 electroreduction on Pt.
Work Function Variations and Oxygen Conduction in a Pt|ZrO2(Y2O3)|Pt Solid Electrolyte Cell
n. g. torkelsen and s. raaen, Appl Surf. Sei., 1996, 93, (3), 199-203
The working electrode in a Pt|ZrO2(Y2O3) |Pt solid electrolyte cell was studied by photoelectron spectroscopy in UHV, and changes in the electrode work function were correlated with the O ion transport through the cell. The change in work function was independent of the cell temperature, when the cell operated as an O conductor. Negative O species at the working electrode during O pumping were indicated.
CHEMICAL TECHNOLOGY
Preparation of Pd/Ceramic Composite Membrane. 1. Improvement of the Conventional Preparation Technique
a. li, g. xiong, j. gu and l. zheng, J. Membrane Sci., 1996, 110, (2), 257-260
An improved method of making Pd/ceramic composite membranes has been developed. Thin Pd films were deposited on the surface of a porous ceramic substrate by the conventional and the improved electroless plating technique. The improved method pre-seeds Pd nuclei in a new way: Pd2+ modified by γ-AlOOH sol is deposited on the surface of the porous Al2O3 disk support by a slip-casting process, calcined in air, then the Pd ion in the top layer is reduced to metallic Pd in H2 for 2 h at 400°C. The Al2O3 membrane + Pd nuclei is then electrolessly plated in a Pd bath.
Sonochemical Preparation of Ultrafine Palladium Particles
k. okitsu, h. bandow and y. maeda, Chem. Mater., 1996, 8, (2), 315-317
Ultrafine Pd particles were prepared by using ultrasound to reduce tetrachloropalladate ions in aqueous solutions. Stable fine particles of Pd were readily pro-duced in the presence of a protective agent, such as a surfactant or a H2O-Soluble polymer. The Pd particles obtained were very fine and their sizes had only a nar-row distribution in the range of several nanometres.
ELECTRICAL AND ELECTRONIC ENGINEERING
Pt/PZT/n-SrTiO3 Ferroelectric Memory Diode
k. gotoh, h. tamura, h. takauchi and a. yoshida, Jpn. J. Appl Phys., 1996, 35, (1A), 39-43
A non-volatile ferroelectric memory was fabricated from vertical metal-ferroelectric-semiconductor diodes with simpler structure than a ferroelectric random access memory (FRAM) cell. It operates at a lower voltage than metal ferroelectric semiconductor field effect transistors or flash memories. The correct nonvolatile and non-destructive memory read-outs were shown with the Pt/PZT/n -SrTiO3 diode. The write voltages were – 5 V to write a logic “0” and > 2.5 V to write a logic “1”. The read voltage was 0.8 V.
Material and Electrical Characteristics of Iron Doped Pt-InAlAs Schottky Diodes Grown by LP-MOCVD
k. hong, d. pavlidis and f. sÉjalon, J. Electron. Mater., 1996, 25, (4), 627-632
The effect of Fe doping on electrical properties and on noise characteristics of devices was studied using Pt-Schottky diodes fabricated on undoped and Fe-doped InAlAs. Fe-doped InAlAs showed a Lorentzian component in the noise spectra not found in undoped materials. An activation energy of ~ 0.77 eV was found for traps due to Fe incorporation, using temperature dependent low frequency noise measurements.
Barrier Characteristics of PtSi/p-Si Schottky Diodes as Determined from I-V-T Measurements
p. g. mccafferty, a. sellai, p. dawson and h. elabd, Solid-StateElectron., 1996, 39, (4), 583-592
The current-voltage-temperature characteristics of PtSi/p -Si Schottky barrier diodes were measured at 60–115 K. Deviation of the ideality factor from unity below 80 K was modelled using the so-called Ti parameter with T 0 = 18 K as an inhomogeneous Schottky contact. A mean barrier height at T = 0 K, øb0 = 223 mV, with an assumed Gaussian distribution of standard deviation, σø = 12.5 mV was determined.
TEMPERATURE MEASUREMENT
Progress on Fabrication of Iridium-Gold Proximity-Effect Thermometers
j. höhne, g. forster, c. absmaier, p. colling, s. cooper, f. v. feilitzsch, p. ferger, j. igalson, e. kellner, m. koch1 m. loidl1 u. nagel, f. pröbst, a. rulofs and w. seidel, Nucl Instr. Methods, Phys. Res. A, 1996, 370, (1), 160-161
Ir-Au proximity-effect bilayers with critical temperatures 20–100 mK were made as superconducting phase transition thermometers for low temperature calorimeters. Film thickness for the Ir and Au films is controlled during evaporation to ± 3% and varies < 15 À at different positions on the film. The measured residual resistivity ratio of the Ir films is ~ 2 for substrate temperatures of300°C and ~ 8 for 630°C.
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