ABSTRACTS: October 1991
Journal Archive
ABSTRACTS: October 1991
of current literature on the platinum metals and their alloys
PROPERTIES
Effects of Sputter Gas Medium on the Nanometer-Scale Surface Structures of the Pt/Co Multilayers
s. l. tang, p. f. carcia, a. j. mcghie and e. b. james, Appl. Phys. Lett., 1991, 59, (3), 289–291
The use of scanning tunnelling microscopy has enabled near atomic resolution images of the surface structure of polycrystalline Pt/Co multilayer thin films to be obtained. Surface relief structure was dependent on the sputter gas; Ar-sputtered films consisted of narrow, essentially flat terraces separated by monatomic steps while on Xe-sputtered films the step heights were close to the bilayer thickness, the difference being attributed to the energy distribution of the reflected sputter-gas neutrals that bombard the growing film. Surface structures were related to the magnetic coercivities of the films.
Reduced Hydrogen Embrittlement Susceptibility in Platinum Implanted High Strength Steel
j. g. cowie, l. j. lowder, r. j. culbertson and w. e. kosik, Nucl. Instrum. Method Phys. Res., 1991, B59/60, (Part II), 871–874
Pt was implanted into high strength electroslag remelted (ESR) 4340 steel samples to a dose of 1016 atoms/cm2. The samples implanted with Pt showed less diffusible H and were also able to sustain significantly higher loads before fracture than the unimplanted steel. SEM verified the presence of brittle cracking typical of H embrittlement type failures. Degradation of mechanical properties due to H embrittlement was thus significantly reduced.
In situ Electrochemical Scanning Tunneling Microscopy of Single-Crystal Surfaces of Pt(111), Rh(111), and Pd(111) in Aqueous Sulfuric Acid Solution
k. sashikata, n. furuya and k. itaya, J. Vac. Sci. Technol. B, 1991, 9, (2), 457–464
Electrochemical scanning tunnelling microscopy was applied to single crystal Pt(l11), Rh(l11) and Pd(l11) surfaces in aqueous H2SO4. Atomically flat Pt(111) surfaces became roughened in solution by the oxidation-reduction cycle. A single potential cycle causes the formation of many adatoms and very small clusters on the Pt(111) terrace. A steady state surface structure is seen after a few potential cycles. The STM image has regularly arrayed islands whose diameter and height are in the ranges 2–3 and 0.5–0.75 nm, respectively. Flame annealing can be successfully applied for Rh and Pd electrodes. Atomically flat terrace-step structures can be seen on Rh(111) and Pd(111) surfaces.
Investigation of FZ-Silicon Doped with Pt
j. prokes, Phys. Status Solidi A, 1991, 125, 263–272
Measurements were performed on n -Si crystals grown by the floating zone method and doped by diffusion with Pt. The parameters and distribution profiles of shallow and deep levels were investigated by capacitance methods. The levels at Ec –0.23 eV and Ev +0.33 eV were attributed to Pt, whereas those lying at Ec –0.32 eV and Ec –0.44 eV were probably not directly connected with Pt.
Paramagnetic Susceptibility of Quasibinary Pt3Mn-Pt3Fe Solid Solutions
n. i kourov, i. i. piratinskaya and yu. n. tsiovkin, Fiz. Metal. Metalloved., 1991, (5), 58–62
Studies of the paramagnetic susceptibility of Pt3MnxFe1-x in atomically ordered (300 < T < 800 K) and disordered (800 < T < 1200 K) states were performed. The concentration dependence of the paramagnetic state on the Curie temperature during transition from the ferromagnetic alloy Pt3Mn to antiferromagnetic Pt3Fe proceeded according to the Heizenberg model registered in two co-ordination spheres. The effect of a decrease in effective magnetic moment during atomic ordering and during transition into the antiferromagnetic state was discussed.
Formation of the PtMnSb Phase in Thin Multilayered Pt/Mn/Sb Films
n. hayashi, k. morii, t. matsui and y. nakayama, Mater. Trans. JIM, 1991, 32, (2), 195–198
Thin multilayered films of [Pt(1.2 nm)/Mn(1.2 nm)/Sb(2.6 nm)] and [Pt(1.0 nm)/Mn(2.0 nm)/ Sb(2.0 nm)] were prepared on glass substrates by an ion-beam sputtering method, and the formation of the Clb-PtMnSb phase in the as-deposited films was studied by XRD and TEM. The multilayered samples produced at room temperatue consisted of a layered structure of amorphous or nano-crystalline phases. However, as the substrate temperature increased up to ~ 473 K, inter-layer mixing among the constituent multilayers was found to occur and the PtMnSb phase was formed.
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 barrier heights of p -type <100> PtSi Schottky diodes prepared by sintering the samples at two different temperatures were studied using electrical forward I-V and IR photoresponse techniques. The results showed that there was a consistent difference of ~ 0.06 eV for two samples sintered at different temperatures.
Ordering and Magnetic Hyperfine Fields in Pt3Mn0.9Fe0.1 Studied by Mössbauer Spectroscopy
k. szymanski, l. dobrzynski, e. gerkema and a. m. van der kraan, J. Phys. Condens. Matter., 1991, 3, (29), 5469–5478
The effect of structural defects on the magnetic properties of Pt3Mn0.9Fe0.1 was studied. The magnetic hyperfine field distribution showed an in-homogeneous magnetisation distribution in the samples. The cold work gave a number of antiphase boundaries dividing the sample into subvolumes with the linear dimensions of 30–100 Å. The magnetisation of these subvolumes performed a superparamagnetic-like relaxation.
Effect of Pt Addition on Melt-Processed YBaCuO Superconductors
m. morita, m. tanaka, s. takebayashi, k. kimura, k. miyamoto and k. sawano, Jpn. J. Appl. Phys., Part II Lett., 1991, 30, (5A), L813–L815
A fine dispersion of Y2BaCuO5 (211) inclusions ~ 1 μm in size has been obtained in YBa2Cu3Ox matrix by the addition of Pt, as PtO2, to the precursor. Pt is considered to act as nucleation sites during the formation of 211 from Y 2O3; and liquid phase Ba-Cu oxide. The sample containing added Pt displayed a critical current density > 2 x 104 A/cm2 at 77 K and 1 T, as high as that of quench and melt growth processed material.
Palladium Clusters on Mica: A Study by Scanning Force Microscopy
j. colchero, o. marti and j. mlynek, J. Vac. Sci. Technol. B, 1991, 9, (2), 794–797
The study of clusters attached to surfaces is of interest because of their application to catalysis and their intermediate state between bulk and single atoms. A scanning force microscope equipped to measure topography and the friction force between sample surface and the tip has been used to study Pd clusters on cleaved faces of single crystal mica. The shape of clusters in the 50 nm range was found to be triangular with truncated edges.
Compound Formation at the Interaction of Pd with Strained Layers of Si1-xGex Epitaxially Grown on Si(100)
a. buxbaum, m. eizenberg, a. raizman and f. schaf-fler, Appl. Phys. Lett., 1991, 59, (6), 665–667
The interaction of thin Pd films deposited on strained layers of Si1-xGex epitaxially grown on Si(100) has been studied. The Ge concentration in the molecular beam epitaxy grown films of Si1-xGex was x = 0.16, and their thickness was 2300 Å. A highly textured ternary compound (Pd2Si1-yGey) formed concurrently with the PdGe phase, at annealing temperatures between 200 and 550°C. Above 500°C a region of Si1-xGex alloy with high Ge concentration formed between the fully reacted compound and the unreacted Si1-xGex layer.
The Effect of High Pressure upon the Valence Transition in EuPd2Si2
d. m. adams, a. e. heath, h. jhans, a. norman and s. leonard, J. Phys. Condens. Matter, 1991, 3, (29), 5465–5468
The so-called valence transition in EuPd2Si2 which was observed using energy-dispersive synchrotron X-ray powder diffraction at elevated pressures was centred at 8 kbar. The estimated increase in valence at the transition was 0.2 and was associated with crossover of 4f and 6d/s bands. It is concluded that both pressure and temperature changes induce same valence transition in the alloy.
Structural Analysis of a Novel Carbon Stabilized Mg-Pd Alloy: Mg2PdCx
d. norÉus, b. bogdanovic and u. wilczok, J. Less- Common Met., 1991, 169, (2), 369–373
The novel crystalline Mg-Pd alloy, Mg2PdCx, was initially isolated through dehydrogenation of an amorphous hydride, Mg2PdCxH2, which was prepared by solution techniques; but now it can also be obtained by heating Mg and Pd metals in the presence of graphite. Although the C atom position could not be refined, samples prepared by high temperature techniques indicated that the C content, x, could be as low as x = 0.1.
Low-Frequency Internal Friction of Pd40Ni40P20 Near the Glass Transition
h.-r. sinning, Acta Metall. Mater., 1991, 39, (5), 851–858
The internal friction of amorphous Pd40Ni40P20 near the glass transition was studied at oscillation frequencies of ~ 0.1 Hz. The glass transition manifested itself by a characteristic increase of viscoelastic damping measured at 550–600 K. Above 575 K, the metastable equilibrium value of internal friction obeys an Arrhenius equation with an apparent activation energy of 2.77 eV. An apparent acceleration of the relaxation kinetics due to a pre-annealing treatment to past the glass transition is not understood.
Atomic Structure of the Crystalline/Amorphous Interface in a Directionally Crystallized Pd80Si20 Alloy
w. h. brearley, p.-c. shieh and j. m. howe, Metall. Trans. A, 1991, 22, (6), 1287–1298
An amorphous ribbon of Pd80Si20 alloy was directionally crystallised under an imposed temperature gradient of 25 K/mm and a growth rate of 0.0785 mm/s; and the surface structure of the crystalline/amorphous interface was studied. The amorphous Pd80Si20 crystallised into a broken-lamellar eutectic of Pd3Si and Pd9Si2 equilibrium phases. The Pd3Si phase is faceted and grows by the nucleation and propagation of ledges on the (010) planes, while the Pd9Si2 phase is largely coherent with the Pd3Si phase. The directional crystallisation apparatus that was developed can produce crystalline/amorphous interfaces, under carefully controlled conditions, which are suitable for TEM.
Early and Late Mechanical Alloying Stages of the Pd-Si System
m. magini, n. burgio, s. martelli, f. padella, e. paradiso and g. ennas, J. Mater. Sci., 1991, 26, (14), 3969–3976
Four Pd-Si compositions (Pd:Si = 2.5:1; 3:1; 4:1 and 5:1) were mechanically alloyed by ball-milling. The first step of the milling process consisted of a very fine fragmentation of the Si particles into the Pd matrix, followed by the formation of the intermetallic line compound Pd3Si which could occur for the 2.5:1, 3:1 and 4:1 compositions. Long milling times, up to 56 h, promoted a demixing process towards the parent elements for the 2.5:1 and 4:1 compositions.
Electromigration and Diffusion of Hydrogen in Amorphous Alloys of Pd82Si18-Type
r. pietrzak, r szatanik and b. rozenfeld, J. Mater. Sci. Lett., 1991, 10, (8), 455–458
The direction of electromigration and the values of the effective valency of H in amorphous alloys Pd82Si18Hy, were investigated for different H concentrations and for alloys Pd82-xNixSi18Hy at 368 K, in order to assess the value of PdSi alloys as radiation shields. It was found that H migrates in amorphous alloys in the direction of the external electric field. The effective H valency in amorphous alloy Pd82Si18 increases simultaneously with the increase in H concentration, and the chemical diffusion coefficient increases with the increase in H concentration. In Pd82Si18 substitution of Pd with Ni results in a decrease in the value of the chemical diffusion coefficient and effective valency.
Properties of Conductive Films Made from Fine Spherical Silver-Palladium Alloy Particles
k. nagashima, t. himeda and a. kato, J. Mater. Sci., 1991, 26, (6), 2477–2482
Ag-Pd alloy films 2–3μ m thick were made by a thick-film technique using Ag-15 mol% Pd and Ag-30 mol% Pd alloy powders and mixtures of Pd and Ag powders prepared by the spray-pyrolysis method. The alloy particles sintered uniformly on firing, whereas the metal particles had uneven particle growth and large voids were formed in the fired films. Alloy films had better conductive properties and their resistivities were close to the intrinsic values for Ag-Pd alloys. Pd oxidation during heating in air was suppressed in the powders at Pd content < 30 mol%.
Enrichment of Deuterium with Tritium in the Presence of a Palladium-561 Giant Cluster
d. i. kochubey, v. p. babenko, m. n. vargaftik and i. i. moiseev, J. Mol. Catal., 1991, 66, (1), 99–104
A giant cluster of Pd561Phen60(OAc)160 idealised formula was contacted with gaseous deuterium at room temperature and atmospheric pressure. The content of T in D was increased after contact at room temperature and atmospheric pressure for 5–10 days.
Ultrathin Films of Rh on Au{001} and Rh on Ag{001}: Growth Mode and Magnetism
h. li, s. c. wu, d. tian, y. s. li, j. quinn and f. jona, Phys. Rev. B, 1991, 44, (3), 1438–1441
Deposition of minute amounts of Rh on a clean and reconstructed Au{001} surface destroyed the reconstruction and yielded a 1 × 1 structure. Deposition of Rh on a clean Ag{001} surface produced overlayers which were partially covered by or intermixed with Ag, but which were pseudomorphic with the Ag{001} substrate. Photoemission experiments in the very early stages of overlayer growth revealed a 4.1±0.3 eV splitting of the 4s levels of Rh, which was not observed in thick Rh films.
The High-Temperature Work Function Behavior of Polycrystalline Osmium
r. n. wall and d. l. jacobson, Metall. Trans. A, 1991, 22, (7), 1609–1613
Studies of the thermionic emission behaviour of randomly oriented polycrystalline Os showed its low thermionic work function of 4.68 eV at 1800 K which increased rapidly to 5.21 eV at 2600 K. The high temperatures and low pressures of these tests were designed to minimise any residual gas interactions with the sample surface. An allotropic phase transformation may explain the varying work function.
Interface Structure and Misfit Dislocations in Thin Cu Films on Ru(0001)
g. o. pötschke and r. j. behm, Phys. Rev. B, 1991, 44, (3), 1442–1445
Scanning tunnelling microscopy measurements showed that the strain at the interface between Cu films and a Ru(0001) substrate was reduced by a structural transformation from a more tightly bound, strained pseudomorphic first Cu layer to a unidirectionally contracted second Cu layer with periodic partial misfit dislocations. These results for a two-dimensional structure confirm the mechanism of stress accommodation in strain layers predicted in the dislocation model of Frank and Van der Merwe.
Site of Ruthenium in Icosahedral Al-Mn-Ru-Si
y. sakurai, y. tanaka, y. watanabe, s. nanao, h. kawata and m. ando, Mater. Sci. Eng., 1991, A134, 896–899
The sites occupied by Ru atoms in Al76Mn14Ru7Si3 and Al68Mn20Ru8Si4 icosahedral alloys were investigated by the anomalous X-ray scattering technique with synchrotron radiation. Assuming that Ru atoms occupy Al or Mn sites in the atomic structure model (quasiperiodic configuration of icosahedral clusters) of the Al-Mn icosahedral phase, it is concluded that Ru atoms are preferentially substituted at Mn sites, which almost correspond to the vertices of the three dimensional Penrose tiling in i -Al76Mn14Ru7Si3. For i -Al68Mn20Ru8Si4 Ru atoms are substituted at the Mn site and at the site of Al atoms at the innermost shell of the model icosahedra.
Changes in the Electrical Resistivity of Fe-C/Al2O3/Fe-Ru Multilayered Films Due to a Magnetic Field
r. nakatani and m. kitada, J. Mater. Sci., Lett., 1991, 10, (14), 827–828
Studies of the Fe-2.0 at.% C/Al2O3/Fe-1.7 at.% Ru junctions for obtaining a high relative resistivity change showed that the relative resistivity changes were between 0.2 and 1.0% in the prepared tunnelling junctions. The electrical resistivity change was caused by the tunnelling between two ferromagnetic layers. The area of the applied field, where the electrical resistivity was high, was broader than the area of the applied field where the magnetisation directions were thought to be antiparallel from the magnetisation curve.
CHEMICAL COMPOUNDS
Platinum Complex Structure and Regularities of Trans-Effect
y. van and y. han, Vestn. Mosk. Univ., Ser. Khim., 1991, 32, (3), 302–305
Structures of Pt(II) complexes of the types cis -[PtCl2(PPh3)2] and trans -[Pt(H)X(PPh3)2] where X is Cl, Br or I, were studied by various NMR and spectroscopic techniques. The results showed the order of trans -effect ligands for Pt(II) complexes: H > H2C=CH2> PMe3 > PPh3 > I > Br > CI > NH3.
Novel Platinum(II)-Diaminobiotin Complexes. Their Synthesis and Characterisation
a. f. noels, n. nihant and a. j. hubert, Bull. Soc. Chim. Belg., 1991, 100, (7), 497–502
The diaminobiotin ligand (cis -3,4-diamino-2-tetrahydrothiophene valeric acid) was reacted with K chloroplatinate and with a diaquodiammine Pt(II) cation. The reaction yielded new Pt complexes which were co-ordinated in a bidentate fashion through the diamine function of the ligand and had [PtN2Cl2] and [PtN4] geometries, respectively.
Metallation of a Crown Thioether Ligand. Synthesis, Structure and Reactivity of [Pt(L1)][BF4] and Structure of [PtI2(L1)][BF4] (L1 =2,6,10-Trithia[11]-m -benzenophane)
g. s. hanan, j. e. kickham and s. j. loeb, J. Chem. Soc., Chem. Commun., 1991, (13), 893–895
The first example of a metallated crown thioether and a rare example of a macrocyclic complex containing a direct M-C bond is reported. The formation of square-planar crown thioether complex [Pt(L1)][BF4l occurs by the metallation of L1; and the versatility of this S3C donor ligand is demonstrated by substitution for the central S donor and oxidative-addition to octahedral complexes of PtIV. Complexes of L1 with RhI, RuII and IrI have the potential for exhibiting catalytic chemistry employing a thioether macrocycle.
Effects of Perturbed Symmetry: Low-Melting Stable Mesogens Based onortho- Palladated Imines
m. j. baena, p. espinet, m. b. ros and j. l. serrano, Angew. Chem. Int. Ed. Engl., 1991, 30, (6), 711–712
The symmetry of the ligand sphere was lowered in a dinuclear metallomesogen by replacement of PdCl2 -azomethine by acetyl acetonate with formation of a mononuclear complex. The temperature range in which the mesophase existed was thereby reduced by around 100 K to 80–130°C.
Metal Complexes of Benzodiazepines.Part 2. The Reaction of 1,4-Benzodiazepines with Halide-Bridged Complexes of Palladium(II) [Pd2X4(PPrn3)2] (X = Cl or I)
m. cusumano, a. giannetto, p. ficarra, r. ficarra and s. tommasini, J. Chem. Soc., Dalton Trans., 1991, (6), 1581–1584
1,4-Benzodiazepines cleaved the halide-bridged complexes [Pd2X4(PPrn3)2] (X = CI or I) to yield monomeric complexes where the benzodiazepine is co-ordinated through N(4) of the heterocyclic ring. The reactions between the Pd complex containing I and five 1,4-benzodiazepines were studied kinetically and thermodynamically in CHC13. The stability of the monomeric complexes formed varied considerably and is attributed mainly to the difference in the rate constants corresponding to the reverse reaction.
Synthesis and Characterization of Palladium(II) Complexes Derived from Aromatic Thiosemicarbazide Derivatives
m. m. bekheit, y. a. elewady, f. i. taha and s. i. mostafa, Bull. Soc. Chim. Fr., 1991, 128, (2), 178–183
The reaction of aromatic thiosemicarbazides with Pd(II) yielded three types of Pd complexes with the compositions PdLCl2, Pd(L-H)2 and Pd(L-2H), where L are aromatic thiosemicarbazides. The IR spectroscopic data showed that the aromatic thiosemicarbazides behaved as neutral, mononegative and binegative ligands and co-ordinate in a bidentate or bridging tetradentate way.
Aspects ofη2 Binding by Osmiumammines
h. taube, Pure Appl. Chem., 1991, 63, (5), 651–664
The chemistry of osmiumammines is examined. The strong tendency of Os(II), when the auxiliary ligands are saturated, for back-bonding interactions accounts in large part for the stability of a large number of new organometallic species. In most cases, the one-electron oxidation of the Os(II) complexes takes place at potentials of < 1 V, and the resultant species have enough kinetic stability to be characterised. Because of the different requirements of Os(II), with its tendency for electron donation to p acids, and Os(III), which acts mainly as a s acceptor, the oxidation is often accompanied by dramatic changes.
A Stable Os° 16-Electron Complex: Synthesis and Structure of [OsCl(NO)(Pi Pr3)2 ]
h. werner, a. michenfelder and m. schulz, Angew. Chem. Int. Ed. Engl., 1991, 30, (5), 596–598
The Os complex [OsCl(NO)(Pi Pr3)2] which is the first structurally characterised [OsL4] complex (L = monodentate ligand) was synthesised. Its reactivity toward Lewis acids and Lewis bases makes it a valuable building block in the synthesis of Os° and Os11 complexes.
Proof of Strong S-H...S Bridges in [Ru(SH2)(PPh3)(′S4′)]. THF, the First H2S Complex Characterized by X-Ray Crystallography
d. sellman, p. lechner, f. knoch and m. moll, Angew. Chem. Int. Ed. Engl., 1991, 30, (5), 552–553
The H2S complex [Ru(SH2)(PPh3)(′S4′)] (1) which was obtained from [Ru(PPh3)(′S4′) precipitated as (l).THF on recrystallisation from H2S-saturated THF as yellow-orange crystals. X-ray structural analysis was performed on the Ru complex (l).THF. The H2S ligand in the (l).THF complex was found to be stabilised by strong S-H...S bridges. On exposure to air the Rh complex was rapidly oxidised.
ELECTROCHEMISTRY
Electrooxidation of Dissolved CO on a Platinum Electrode Covered with a Monolayer of the Chemisorbed CO Formerly Considered to be a Poison
c. gutiÉrrez and j. a. caram, J. Electroanal. Chem. Interfacial Electrochem., 1991, 308, 321–325
Studies showed that under certain conditions, CO electro-oxidation took place on Pt at 0.6 V and in the presence of a full monolayer of adsorbed CO ‘poison’. A smooth Pt electrode held at a potential lower than 0.22 V, placed in an electolytic cell in which CO was bubbled for 1 h, showed in a subsequent voltammogram, under quiescent conditions two anodic peaks whose simultaneous existence was considered to be imposssible. One of them was the well known peak of chemisorbed CO at 0.94 V, which up to the present was considered to be a poison for the oxidation of dissolved CO.
Electrocatalytic Effect of Phenanthroline Iron Complexes on Oxygen Reduction in Sulfuric Acid Media
l. galicia, i. gonzalez and y. meas, React. Kinet. Catal. Lett., 1991, 44, (1), 109–114
A study of O2 reduction on a Pt rotating disk in 1 M H2SO4 at different pHs showed an increase in the reaction velocity on addition of 2 × 10-3 M Fe(II) and 0.1 M 1,10-phenanthroline. The increase depended on the pH of the solution; at pH < 0.5 it was ~ 100 fold while at pH > 0.5 it was greater by a factor of 600. The change at pH = 0.5 was explained by a change in the co-ordination sphere of electrogenerated Fe(II).
Electrocatalytic Activity of a Graphite-Based Pt Electrode Modified with Metal Oxides towards Methanol Oxidation
p. c. biswas, t. ohmori and m. enyo, J. Electroanal. Chem. Interfacial Electrochem., 1991, 305, (2), 205–215
The electro-oxidation of CH3OH was carried out on oxide-modified Pt electrodes using graphite as the substrate in 0.5 M H2SO4. A more negative zero-current potential (~ 70 mV vs. RHE) was achieved on a graphite-based Pt electrode modified with In + Pb mixed oxide and Au as compared with ~ 400 mV on an ordinary Sn-modified Pt electrode. However, the oxidation current did not increase rapidly with the electrode potential and the oxides were not sufficiently stable in the solution of 0.5 M H2SO4.
On the Electrocatalytic Activity of Platinum Catalysts on Carbon Carriers
v. s. gatotskii, g. v. shteinberg and n. a. urisson, Elektrokhimiya, 1991, 27, (5), 563–570
Studies of electrochemical activity of Pt/C catalysts containing various structural supports were performed during ionisation reaction and separation of H from the model electrode. The results showed that the specific activity of Pt/C catalysts during oxidation of H2 was higher on non-porous supports than on highly porous supports even when the specific surface of Pt on highly porous supports was 3–4 times higher than on non-porous support.
In Situ Infrared Studies of Glucose Oxidation on Platinum in an Alkaline Medium
i. t. bae, e. yeager, x. xing and c. c. liu, J. Electroanal. Chem. Interfacial Electrochem., 1991, 309, (1 and 2), 131–145
The oxidation of α -D( +)-glucose on a Pt electrode in 0.1 M NaOH was studied by in situ Fourier transform IR reflection-absorption spectroscopy in the potential range of –0.76 to +0.46 V vs. Hg/HgO, OH–. The linear CO persisted on Pt in the entire potential range with gradual shifts to higher frequencies, ca. 70 cm-1/V, while the bridged CO disappeared as the electrode potential reached –0.05 V. A potential excursion up to +0.46 V was found to cause a pH swing of more than 8 in the spectroelectrochemical thin layer due to glucose oxidation.
Anodic Oxidation of Phenol for Waste Water Treatment
ch. comninellis and c. pulgarin, J. Appl. Electrochem., 1991, 21, (8), 703–708
The electrochemical oxidation of phenol for use with waste water treatment has been studied in a two compartment cell at a cylindrical Pt anode of surface area 35 cm2 and 4 cm2 Pt spiral cathode, enclosed in a porous porcelain pot. The reaction was found to occur by two parallel pathways, chemical oxidation with electrogenerated hydroxyl radicals and direct combustion of adsorbed phenol and/or its aromatic intermediates to CO2.
High Temperature Air Cathodes Containing Ion Conductive Oxides
t. kenjo, s. osawa and k. fujikawa, J. Electrochem. Soc., 1991, 138, (2), 349–355
Ion conductive oxides were introduced into Pt electrodes to see if they would behave as liquid electrolyte penetrating the porous electrodes. The mixed electrodes were expected to operate as a pore whose inner wall was covered with a gas permeable electrolyte film, in which the electrode performance should increase with increasing electrode thickness. However, (ZtO2)0.92(Y2O3)0.08 and (CeO2)0.8(SmO1.5)0.2 additions produced no marked improvement, while (Bi2O3)0.7(Er2O3)0.3exhibited the expected trend, giving a much higher performance than simple Pt/ZrO2 electrodes.
Electrochemical Charging of Pd Rods
s. szpak, c. j. gabriel, j. j. smith and r. j. nowak, J. Electroanal. Chem. Interfacial Electrochem., 1991, 309, (1 and 2), 273–292
A model describing the electrochemical charging of Pd rod and featuring the coupling of the interfacial processes with the transport of interstitials in the Pd electrode interior is presented. It is shown that boundary conditions arise from the solution of equations governing the elementary adsorption-desorption and adsorption-absorption steps and electrode symmetry.
The Indirect Anodic Oxidation of 2-Methylnaphthalene. Part 1. Ruthenium Compounds as Catalysts
s. chocron and m. michman, J. Mol. Catal., 1991, 66, (1), 85–98
The indirect anodic oxidation of 2-methylnaphthalene and naphthalene to 2-methylnaphthoquinone-l,4 and naphthoquinone, respectively, was carried out with RuCl3.3H2O, Ru(acac)3 and Ru(NH4)2Cl6 as catalysts, in an undivided cell using Pt electrodes. RuCl3.3H2O or Ru(NH4)2Cl6 increased the selectivity for quinone formation, whereas Ru(acac)3 had no effect. Voltammetry showed that RuCl3.3H2O and Ru(acac)3 oxidised H2O and not the hydrocarbon.
PHOTOCONVERSION
Hydrogen Evolution over a Powdered Semiconductor Photocatalyst
t. maruyama and t. nishimoto, Ind. Eng. Chem. Res., 1991, 30, (7), 1634–1638
The rates of H2 evolution from a H2O-MeOH mixture containing a dispersed semiconductor Pt/TiO2 photocatalyst of colloidal, porous particle or thin film forms were compared with catalyst morphology. A porous particle catalyst has increased surface area compared to its light absorbing area, with decreased particle size, which increases the duration of the initial high H2 evolution rate. The porous catalyst maintains high catalyst activity for a long period of time, and H2 evolves in the solar collector.
Linear Chains of Pt(bpy)(CN)2 at Electrode Surfaces by Partial Reduction of the Bipyridineπ System
j. b. cooper, s. m. rhodes and d. w. wertz, J. Phys. Chem., 1991, 95, (12), 4800–4803
Spectrochemical properties of Pt(bpy)(CN)2 (1) are reported on both polished Pt and roughened Ag electrodes. There is a weak emission and a very strong resonance Raman spectrum (RRS) with visible excitation, and (1) may form linear chains on both surfaces. The emission and RRS are very potential dependent (–500±50 mV), the approximate E 1/2 of the bpy reduction and the RRS consist exclusively of bpy modes; thus linear chain growth may be due to partial reduction of the bpy π system, and visible absorption to a π→π* transition.
Preparation of Ruthenium(II) Complex-Containing Polymer Monolayers and Langmuir-Blodgett Films
t. miyashita, h. saito and m. matsuda, Chem. Lett. Jpn., 1991, (5), 859–862
Studies of the spreading behaviour of the copolymers of [Ru(bpy)2(Vbpy)]2+ (Vbpy = 4-vinyl-4’-methyl-2,2’-bipyridine) and N -dodecylacrylamide (DDA) showed that they form a stable condensed monolayer on a H2O surface. The monolayers could be transferred onto solid supports, yielding the Y-type (bilayer type) Ru(II) complex contained in polymer Langmuir-Blodgett films.
Kinetics and Mechanisms of the Photo-Induced Oxidation of Ascorbic Acid by Molecular Oxygen Catalyzed by Ruthenium(II) Complexes Containing 2,2’-Bipyridine and 2,2’-Bipyrazine
k. tsukahara, y. wada and m. kimura, Bull. Chem. Soc. Jpn., 1991, 64, (3), 908–915
H2O2 was efficiently produced by the irradiation of visible light on aqueous acid solutions containing ascorbic acid, O2 and Ru(II) complexes: [Ru(bpy)x(bpz)3–x]2+ (X = 0–3, bpy = 2,2’-bipyridine and bpz = 2,2’-bipyrazine). The formation of H2O2 and the decay of ascorbic acid were followed by polarography during continuous irradiation of the solution by visible light.
Chemically Initiated Electron-Exchanged Luminescence of Ru(bpy)3Cl2 in Catalytic Reaction with 1,2-Dioxetane
a. i. voloshin, g. l. sharipov, v. p. kazakov and g. a. tolstikov, Izv. Akad. Nauk SSSR, Ser. Khim., 1991, (6), 1316–1321
Studies of activated Ru(bpy)3Cl2 chemiluminescence during decomposition of 1,2-dioxetane were performed. The results showed that kinetics and activity of chemiluminescence of 1,2-dioxetane chemically initiated by the Ru complex proceeded according to the mechanism of chemical initiation of electron-exchange, thus effectively exciting Ru(bpy)3Cl2 and giving an excited ϕ*RU yield of 0.20 ± 0.05.
Laser-Induced Modulation of Second-Harmonic Light Emission from Ru(II)-Bipyridine Metal Complex in Langmuir-Blodgett Film
h. sakaguchi, t. nagamura and t. matsuo, Jpn. J. Appl. Phys., Part II Lett., 1991, 30, (3A), L377–L379
When a Langmuir-Blodgett film containing Ru(II) bipyridine metal complex was irradiated by a Nd-YAG laser, strong second-harmonic light of 532 nm was observed. However, the intensity of this light is remarkably suppressed when the Ru complex is excited by either 355 or 460 nm laser pulses, just before laser irradiation at 1064 nm. This is ascribed to the reduction in hyperpolarisability on going from the ground state to a metal-to-ligand charge transferred excited state. Thus optical modulation of second harmonic light on this film by laser light provides a novel way of achieving an optical switch.
ELECTRODEPOSITION AND SURFACE COATINGS
Preparation of a Pt-GaAs Schottky Contact by Ion Plating
g. peto and t. andersson, Solid-State Electron., 1991, 34, (6), 591–592
A tentative investigation has been made to determine if superior intimate metal-semiconductor contact can be achieved by ion plating, and if the negligible surface damage caused would improve the quality of Schottky contacts. A 5000 Å Pt layer was evaporated onto a Si doped GaAs wafer, which was subjected to an ion accelerating negative bias voltage (UB) during evaporation. I-V curves for 4 values of UB are given; increasing UB improves the characteristics of Schottky contacts, and ion plating improved the diode.
Sputter Deposition of Cobalt-Palladium Multilayers
r. j. highmore, w. c. shih, r. e. somekh and j. e. evetts, J. Vac.Sci. Technol.A,1999, 9, (4), 2123–2127
Ultrahigh vacuum DC magnetron sputtering has been used to deposit Co-Pd multilayers onto unhealed (111) Si substrates; and the films have been characterised. Variations in the microstructure and magnetic properties of the films as the sputtering pressure was altered have been observed; changes in magnetic properties are related to microstructure.
Galvanic Ni/PdNi/Au Laminar Composite for Electrotechnical Applications
g. bÄr and d. rÜhlicke, Metall, 1991, 45, (7), 668–673
The electroplated layer combination: Ni/PdNi/Au, containing 80 wt.% Pd–20 wt.% Ni, which is used as a contact material for connectors and contacts in electronic applications is investigated. The coating is performed on previously punched contact strips in a continuous electroplating process, by dip and spot plating. Applications for Ni/PdNi/Au are discussed.
APPARATUS AND TECHNIQUE
STM Fabrication of Platinum Disks of Nanometer Dimensions
n. casillas, s. r. snyder and h. s. white, J. Electrochem. Soc., 1991, 138, (2), 641–642
Inlaid Pt disks of 5–36 nm radius were fabricated using scanning tunneling microscopy and tunneling spectroscopy. The Pt was deposited on mica, then a Ti film was electron beam deposited onto the substrate, and exposed to air. A small area of the TiO2 layer was selectively removed from the underlying Pt surface by placing the STM tip at a fixed distance above the surface and a voltage bias was linearly cycled (80 V/s) between positive and negative limits. The Pt disk size can be controlled by changing the tip to surface distance and/or the voltage scanned.
Portablein situ Wall-Rock Thermal Conductivity Meter for Mine Pits
x.-j. shen, s.-z. yang and w.-r. zhang, Rev. Sci. Instrum., 1991, 62, (6), 1581–1586
A novel ring heat source probe, based on three-dimensional transient heat conduction from a point source, is incorporated in a device modified for the in situ measurement of wall-rock thermal conductivity in coal mines, following minimal preparation of the rock surface. Measuring, controlling and power supply systems are enclosed in a sealed container into which thermal conductivity and environmental temperature probes are plugged. The latter consists of a mini Pt resistor.
How a Limited Mass Transfer in the Gas Phase May Affect the Steady-State Response of a Pd-MOS Hydrogen Sensor
u. ackelid and l.-g. petersson, Sens. Actuators B, 1991, 3, (2), 139–146
The H2 sensitivity of Pd MOS sensors in an O2 containing atmosphere is shown to depend on the area of the Pd film, the rate of the gas flow, the total pressure and the type of carrier gas. Limited mass transfer in the gas phase can explain all the observations, and is confirmed by mass spectrometric studies using a local gas-sampling technique. It is suggested that such sensors be calibrated in situ under realistic conditions, since the larger the Pd area the more important this will be.
Progress in Hydrogen Detection: A New Photopyroelectric Device
c. christofides and a. mandelis, Int. J. Hydrogen Energy, 1991, 16, (8), 577–578
A new and inexpensive H2 detector has been developed which can operate through a broad range of low temperatures (–190 to +53°C). The structure contains a Pd-polyvinylidene fluoride detector. The thickness of the Pd layer evaporated on the PVDF film plays an important role in determinimg sensitivity and durability of the H sensor. The detector is very sensitive, even for concentrations down to 40 ppm.
Reduction of the Interference Caused by NO and SO2 in the CO Response of Pd-Catalysed SnO2 Combustion Gas Sensors
h. torvela, j. huusko and v. lantto, Sens. Actuators B, 1991, 4, (3 & 4), 479–484
Studies of SnO2-based semiconductor gas sensors containing 0.05, 0.1, 1 and 3 mol % Pd showed that they can be used to monitor the concentration of CO in combustion gases in the presence of NO and SO2. By increasing the sensor temperature to > 500°C the interference effects of NO and SO2 on the conductance response to CO could be nearly eliminated. The best conductance response to CO was obtained with sensors containing ~ 0.5 mol % Pd. The best response characteristics for thick film paste was obtained on adding Pd to SnO2 in the chloride form followed by calcination at 900°C.
Detection of Hydrogen from the Photodissociative Splitting of Water through Hydrogen-Oxygen Separation over a Thin Film
h. dannetun, i. lundstrӦm and L.-G. PETERSSON, J. Appl. Phys., 1991, 70, (1), 453–456
The photodissociative splitting of water was studied in the gas phase under UV on a plane solid surface of 1–2 nm of TiOx coating on Pd-MOS. A natural separation of the produced H and O occurs over the Pd film; H diffuses to the Pd/SiO2 interface and O stays at the TiOx-Pd surface. The H was monitored by the electric behaviour of the MOS device. Thus suitably treated thin Pd membranes may be used to study the continuous photodissociation of water.
A Model for Sheet Resistivity of RuO2 Thick Film Resistors
r. w. vest, IEEE Trans. Components, Hybrids, Manuf. Technol., 1991, 14, (2), 396–406
A study of the microstructure composition relationship of RuO2 -based thick film resistors has been carried out using the results of recent investigations, in order to develop an improved loading curve model. Five types of microstructure are possible, depending upon the volume fraction (Vc ) of RuO2. A theoretical loading curve model has been developed for 0.032 < Vc < 0.24, which is in excellent agreement with the results for a system using glass with high RuO2 solubility.
JOINING
Platinum Silicide Fusion Bonding
m. s. ismail and r. w. bower, Electron. Lett., 1991, 27, (13), 1153–1154
Silicide direct bonding between PtSi coated Si wafers and both PtSi coated and uncoated silicon wafers has been successfully carried out after the PtSi surface had been rendered hydrophilic by a selective etching and cleaning process. The PtSi conductive medium provides relatively low resistance interconnections between circuit elements on the bonded pair of wafers, and the technique has potential for 3D ICs.
HETEROGENEOUS CATALYSIS
Morphology and Site Blocking Effects on Chemisorption Properties and Reactivity of Pt/TiO)2 and Sulfided Pt/Al2O3 Catalysts
l. bonneviot and g. l. haller, J. Catal., 1991, 130, (2), 359–373
Surface inhibition effects due to S poisoning or strong metal-support interaction were compared on small Pt particles supported on A12O3 and TiO2. The change in properties was monitored either by H2 or CO chemisorption at room temperature or by n -butane hydrogenolysis and isomerisation. The surface inhibition took place in two steps; first, an apparent flattening of the particles that leads to less active, low-index-planes-exposure to reactants and to a compensation effect. This occurs at 773 K on Pt/η -Al2O3 and at 573 K in the presence of S or TiO2. Then, following a high temperature reduction, the second step takes place by simple site blocking by S or TiOx moieties and does not lead to compensation.
Kinetics of Deactivation of Bifunctional Pt/Al2O3-Cl Catalysts by Coking
j. n. beltramini, t. j. wessel and r. datta, AIChE J., 1991, 37, (6), 845–854
The catalytic activity, product selectivity and coke deposition were studied during methylcyclopentane (MCP) reforming on bifunctional Pt/Al2O3-Cl catalysts with different metal loadings, but constant Pt dispersions and constant Cl loading. The overall conversion of MCP decreased as the metal content of the catalyst increased. The change of activity of the metal and acid functions with time was monitored by following the rates of hydrogenolysis and hydrocracking, respectively. A mechanistically based dual site model for the kinetics of coke formation and the resulting deactivation was developed, which accounts for the deactivation of both the metal and the acid functions.
CH3 and CH3I Chemistry on Pt(111): The Influence of CO
m. a. anderson, g. e. mitchell and j. m. white, Surf. Sci., 1991, 248, (3), 279–286
The surface chemistry of CH3I alone and coadsorbed with CO on Pt(111) was studied by various techniques. CH3I bonds to Pt(111) through lone pair electrons on the halide with a molecular symmetry less than C3v and is not significantly affected by coadsorbed CO. On a clean surface CH3I decomposes to CH3 and I at ~ 250 K. CH4 is formed at 290 K from the hydrogenation of CH3 groups using H from the decomposition of other CH3 groups. The competition between CH3 hydrogenation and dehydrogenation depends on coverage. For a surface dosed with CH3I, then saturated with CO, more thermal energy must be added to break the C-I bond. If CH3 is formed first, followed by CO to saturation, CH4 formation occurs at 40 K lower and with a higher yield than in the absence of CO.
Process Gas Filtration in Nitric Acid Production
e.baurand f. k. pethick, Nitrogen, 1991, (192), 19–22
A discussion of process gas filtration units and their behaviour upstream of the catalyst in nitric acid plants is presented. It is suggested that stainless steel filters are beneficial in protecting the catalyst from contaminants. Fe, either bonded to the Pt catalyst or as loose fine particles, catalyses the competing reaction in which the NH3 feed is oxidised to N2 and water vapour. This reaction releases much more heat than the desired reaction and wastes NH3. Si acts as a catalyst poison and deactivates the surface. Other contaminants include phosphates, Pb, Ni and Cr and to a much smaller extent Ca, Mg and Ba.
Effects of Acidic and Basic Properties on Selectivity in the Reforming of n-Hexane over a Binary Oxide of Titanium and Zirconium Supporting a Platinum Catalyst
k. hashimoto, t. masuda and h. kashihara, Appl. Catal., 1991, 75, (2), 331–342
A Pt catalyst on a binary oxide support, TiO2-ZrO2, having both acid and base sites, was used in reforming n -hexane. When the distance between acid and base sites is shorter than the length of the reactant molecule, the active sites on the support are: an adjacent pair of acid-base sites and a lone acid site. The rates of the cyclic and aromatisation reactions increase linearly with the number of adjacent pairs of acid-base sites. Reaction rates for cracking and isomerisation are proportional to the number of lone acid sites. The selectivity in the cyclic and aromatisation reactions therefore can be enhanced by increasing the number of adjacent pairs of acid-base sites and decreasing the number of lone acid sites. The support with a 50% content of TiO2 has more adjacent pairs of acid-base sites and fewer lone acid sites than does a commercial catalyst. Hence the selectivity of the sum of the cyclic and aromatisation reactions over the 50% catalyst is higher (62%) than that of the commercial catalyst.
Structure and Activity of Composite Oxide Supported Platinum-Iridium Catalysts
s. subramanian and j. a. schwarz, Appl. Catal., 1991, 74, (1), 65–81
Pt mobility, TiOx mobility and Al3+ readsorption were found to affect the structure and activity of Pt-Ir catalysts supported on A12O3, TiO2, Al2O3-TiO2 and TiO2-Al2O3 during study by TPRd/TPD and by ethane hydrogenolysis. TPRd and ethane hydrogenolysis suggest that bimetal formation occurs when pure oxide supports are used, and bimetal formation is suppressed when composite oxides are used. TiO2 acts as a ‘spacer’ and inhibits the mobility of Pt and thus prevents Pt and Ir from forming bimetallic clusters. Bimetal formation is assessed as a function of the support, and models for the structures of the calcined precursor and finished catalysts are proposed.
Heterogeneous Catalysis on Platinum and Self-Assembled Monolayers on Metal and Metal Oxide Surfaces
t. randall lee, p. e. laibinis, j. p. folkers and g. m. whltesides, Pure Appl. Chem., 1991, 63,(6), 821–828
A series of Pt complexes, CODPt(CD3)2, CODPt(CH2CD3)2 and CODPt(CH2C(CD3)3)2, CODPt(CH2C(CH3)2(CH2)nCD3)2 (n = l–3) were synthesised and then hydrogenated under mass-transfer limited conditions over Pt black in n -heptane. Heterogeneous Pt catalysts were used in the hydrogenation of diolefin(dialkyl)Pt(II) complexes. The incorporation of D from isotopically labelled protic solvents was particularly useful mechanistically.
Hydrogenation of Acetylene at Transient Conditions in the Presence of Olefins and Carbon Monoxide over Palladium/ Alumina
l. cider and n.-h. schӦӦn, Ind. Eng. Chem. Res., 1991, 30, (7), 1437–1443
An egg-shell Pd/α -Al2O3, catalyst in a well-mixed reactor, which behaved as an ideal tank reactor, was used in the hydrogenation of C2H2, C2H4 and propylene. The conditions used were transient, being caused by cross-desorption of CO due to a pulse of C2H2. A simple model can explain the competition for the active sites and the difference in reactivity. The propylene was added to make it possible to discriminate between the hydrogenation of the olefin (propylene) present in excess in the inflow gas and the olefin (C2H4) formed by the C2H2 hydrogenation.
Hydrogenation of Phenol to Cyclohex-anone over Pd/MgO
s. galvagno, a. donato, g. neri and r. pietropaolo, J. Chem. Tech. Biotechnol., 1991, 51, (2), 145–153
Hydrogenation of phenol to cyclohexanone on a series of Pd/MgO catalysts was studied at 160–250°C. At 160°C, the reaction orders found on all catalysts were ~ –1 with respect to phenol and ~ +1 with respect to H2. The kinetic data showed that the rate determining step is the surface reaction between phenol and H2 adsorbed on the catalyst. An increase in the reaction temperature decreased the rate of reaction.
Heterocyclization Reaction Sites on the Sulfided Pd(111) Surface
a. j. gellmann, Langmuir, 1991, 7, (5), 827–830
The sulphided Pd(111) surface can cyclise C2H2 to both benzene and thiophene. The reactions are sensitive to the temperature of preparation of the sulphided surfaces, giving the greatest yield on surfaces produced at temperatures > 1000 K. CO adsorption shows that heating the surface introduces defects at which CO can bind in bridging sites between exposed Pd atoms. This defect concentration, as determined by CO adsorption in bridging sites, is correlated with the amount of thiophene produced from C2H2. Heterocyclisation of C2H2 is thus a defect catalysed reaction.
Characterization of Rhodium Catalysts Supported on Various Inorganic Oxides for Carbon Monoxide Hydrogenation
r. m. sanyal, d. k. ghorai, d. r. dutta, s. k. adhya, b. sen and b. viswanathan, Appl. Catal., 1991, 74, (2), 153–161
Rh catalysts prepared by impregnation of Rh6(CO)16 on γ-Al2O3, ZrO2, ZnO and MgO have been characterised by IR, XPS, and UV-VIS. The Rh cluster is oxidatively degraded with time when kept exposed to air. On the first two supports [Rh(CO)2X] type dicarbonyl species are produced while on ZnO the Rh6(CO)16 keeps its nuclearity, and on MgO species of type [Rh(CO)yX3] are formed. Acidic oxides selectively form CH4, while basic oxides favour mainly MeOH on CO hydrogenation.
The CO/H2 Reaction on Rh/MgO Studied by Transient Isotopic Methods
a. m. efstathiou, J. Mol. Catal., 1991, 67, (2), 229–249
Various transient isotopic methods were used to study the CO/H2 reaction over 2.5 wt.% Rh/MgO at 493–573 K. The steps for CH4 formation pass through a large reservoir of surface CO and through a small reservoir of active C. Rate control is largely determined by the rate of CO dissociation on the metal surface. Formate on the support may be an active intermediate to make CO2. Two pools of surface CO, α -CO* which readily exchanges with gaseous CO, and β -CO* which does not, are present on Rh and take part in the methanation. β -CO* increases with time on stream at 563 K. Some α -CO* and β- CO* interact with -OH groups of the support to give CO2 and H2, probably via a formate intermediate.
Kinetics of Heterogeneous Catalytic Hydroformylation of Propylene on Rhodium-Cobalt Catalysts. Reaction Mechanism
s. i. reut, g. l. kamalov and g. i. golodets, React. Kinet. Catal. Lett., 1991, 44, (1), 191–195
Steady state kinetics of combined heterogeneous catalytic hydrogenation and hydroformylation of propylene on Rh-Co catalysts supported on Al2O3, MgO or SiO2, have been studied at atmospheric pressure and 140–170°C. A reaction mechanism is suggested.
Gas-Phase Hydroformylation of Propylene on Ru/SiO2 Catalysts
s. b. halligudi, m. m. taqui khan, b. l. moroz, a. l. chuvilin, i. p. prosvirin and v. a. likholobov, React. Kinet. Catal. Lett., 1991, 44, (1), 139–146
Studies of Ru/SiO2 catalysts performed during gas-phase hydroformylation of propylene showed that catalysts prepared by reduction of supported Ru-Cl3.xH2O were active at low pressure (~ 0.3 MPa) of H2 + CO + C3H6 mixture with very high selectivity towards unbranched oxo-products. The effect of electronic state and dispersity of Ru on their catalytic behaviour was studied.
Chemistry in Cages: Synthesis and Reversible Decarbonylation of [Ir6(CO)16] Isomers in NaY Zeolite
s. kawi and b. c. gates, J. Chem. Soc., Chem. Commun., 1991, (15), 994–995
A simple synthesis of two isomers of [Ir6(CO)l6] from [Ir(CO)2(acac)] in the supercages of NaY zeolite is reported. [Ir(CO)2(acac)] in NaY zeolite cages was convened in CO at a pressure of 1 bar to the isomer of [Ir6(CO)]6] with edge-bridging CO ligands and in CO + H2 at 20 bar to the isomer of [Ir6(CO)16] with face-bridging ligands.
HOMOGENEOUS CATALYSIS
Synthesis of Carbonyl-Olefin Complexes of Platinum(II), PtX2(CO)(olefin), and the Catalytic Hydrochlorination of Olefins
h. alper, y. huang, d. b. dell’amico, f. calderazzo, n. pasqualetti and c. a. veracini, Organometallics, 1991, 10, (6), 1665–1671
The mixed olefin-carbonyl complexes of Pt(II), PtX2(CO)(C6H10) (X = CI, Br) were prepared by the reaction of PtX2(CO)2 with cyclohexene, or from Pt2Cl4(CO)2 and the olefin. The olefin ligand was promptly displaced by CO. The chloro-carbonyl complex PtCl2(CO)(C6H10) reacted with dry HC1 to yield cyclohexyl chloride and Pt2Cl4(CO)2. The mixed carbonyl-cyclohexene complex, or PtCl2(CO)2 or Pt2Cl4(CO)2 were found to be effective catalyst precursors for the hydrochlorination with dry HCl of a number of symmetrical, terminal and internal olefins, in hydrocarbon or chlorinated solvents.
Palladium-Catalyzed Hetero-Cope Rearrangement of Alkyl AllylN- Aryldithiocarbonimidates
j. garin, e. melÉndez, f. l. merchan, t. tejero, s. uriel and j. ayestaran, Synthesis, 1991, (2), 147–149
Allyl methyl N -aryldithiocarbonimidates (1) were smoothly rearranged to methyl N-allyl-N- aryldithiocarbamates in the presence of PdCl2(PhCN)2 catalyst. Very high yields of rearranged products can be obtained depending on the substitution pattern of the allyl group.
Palladium-Catalyzed Coupling of Aryl Iodides, Nonconjugated Dienes, and Carbon Nucleophiles by Palladium Migration
r. c. larock, y.-d. lu, a. c. bain and c. e. russell, J. Org. Chem., 1991, 56, (15), 4589–4590
Aryl iodides, non-conjugated dienes and C nucleophiles reacted in the presence of Pd catalysts (PdCl2, Pd(OAc)2, Pd(PPh3)4 and Pd(dba)2) at 60–120°C to give good yields of coupled products. The coupled products are apparently formed by aryl Pd generation and addition to the less substituted end of the diene, Pd migration down the C chain to form a π-allyl Pd intermediate and carbanion displacement of the Pd moiety.
Catalytic System PdCl2/Ph2PC6H4 SO3Na in the Hydrocarboxylation of 1-Heptene
l. f. starosel’skaya, t. e. kron, m. i. terekhova and z. e. petrov, Zh. Obshch. Khim., 1991, 61, (3), 736–739
Studies of the hydrocarboxylation reaction of 1-heptene catalysed by PdCl2 in the presence of Na salt m -sulphophenylene diphenylphosphine were performed, and reported. The catalytic system PdCl2/Ph2PC6H4SO3Na-m was more effective during hydrocarboxylation of olefine than the analogous system with Ph3 and it also allowed the reaction to proceed in media with high H20 content.
5-Vinyl-4-Pentynoic Acids through the Palladium-Catalyzed Reaction of 4-Pentynoic Acid with Vinyl Triflates
a. arcadi, s. cacchi, m. delmastro and f. marinella, Synlett, 1991, (6), 409–411
The reaction of vinyl triflates (1-cycloalkenyl trifluoromethanesulphonates) and 4-pentynoic acid at room temperature in dimethyl sulphoxide in the presence of diethylamine or diisopropylamine and catalytic amounts of [Pd(OAc)2(PPh3)2] and Cu(I) iodide, gave a high yield of a variety of 5-vinyl-4-pentynoic acids. The best results were obtained on addition of DMSO to the reaction mixture. Good results were also obtained in the absence of solvents or using MeCN and DMF.
Palladium-Catalyzed Coupling of Alkenyl lodonium Salts with Olefins: A MUd and Stereoselective Heck-Type Reaction Using Hypervalent Iodine
R. M. MORIARTY, W. R. EPA and A. K. AWASTHI, J. Am. Chem. Soc, 1991, 113,(16), 6315-6317
A catalysis using Pd(OAc) 2 and giving a variation of C-C coupling with phenyl(alkenyl)iodonium salts and various alkenes is presented. The reaction occurs at room temperature and polymerisation of activated olefins at > 100°C, which occurs in the Heck reaction, does not happen. A wide range of structural types are available and high yields are produced.
Palladium-Catalyzed Synthesis of N,N’-Diphenylurea from Nitrobenzene, Aniline, and Carbon Monoxide
j. s. oh, s. m. lee, j. k yeo, c. w. lee and j. s. lee, Ind. Eng. Chem. Res., 1991, 30, (7), 1456–1461
N,N’-Diphenylurea has been synthesised from nitrobenzene, aniline and CO at 80–160°Cand 15–75 bar. A homogeneous catalyst system of a Pd(II) salt, an onium salt and triphenylphosphine dissolved in xylene or toluene was highly efficient in giving isolated urea yields of up 98% at 100% nitrobenzene conversion. The reaction consumed more aniline than nitrobenzene on a molar basis, suggesting the existence of a new reaction path in addition to the usual path where equimolar amounts of aniline and nitrobenzene are consumed. Excess aniline enabled the catalyst system to be reused.
Facile Aryl-Aryl Exchange between the Palladium Center and Phosphine Ligands in Palladium(II) Complexes
k.-c. kong and c.-h. cheng, J. Am. Chem. Soc., 1991, 113, (16), 6313–6315
A facile two-way aryl migration between the metal centre and co-ordinated phosphine in Pd(II) complexes is reported. When Pd(PPh3)2(C6H4-p -CH3)I, after preparation from the oxidative addition of p- iodotoluene to Pd(PPh3)4, was heated at 50–60°C in THF or chloroform, a regiospecific exchange between the aryl on the Pd centre and the phenyls on the phosphine occurred. The reaction was monitored by 1H NMR spectroscopy.
Palladium-Catalyzed Oxyhexatriene Cyclization: A Novel Approach to Cyclohexenone Annulation
c. m. hettrick and w. j. scott, J. Am. Chem. Soc., 1991, 113, (13), 4903–1910
A general approach to the hexatriene cyclisation of dienone enolates or their derivatives is afforded by converting fully conjugated dienones to the kinetic enolates with kinetic silyl ethers and trapping as the silyl enol ethers; heating these in toluene or xylenes in the presence of 5 mol% Pd(PFu3)2Cl2, where Fu is furyl, gives the corresponding cyclohexenones in good yield. Thermal electrocyclisation of electron-rich hexatrienes may be difficult. Pd(PFu3)2Cl2 is proposed to mediate the cyclisation of [(trimethylsilyl)oxy] hexatrienes by causing Pd enolate formation, followed by addition across a C = C bond and trapping the annulated product as the silyl enol ether.
The Effect of Metal Colloid Morphology on Catalytic Activity: Further Proof of the Intermediacy of Colloids in the Rhodium-Catalyzed Hydrosilylation Reaction
l. n. lewis, r. j. uriarte and n. lewis, J. Mol. Catal., 1991, 66, (1), 105–113
The relative activity of different morphological forms of Rh colloids were examined by TEM and HREM. The degree of agglomeration of the Rh colloid was affected by either its storage or by the use of a vinyl silicone stabiliser. The smaller particle size (higher surface area) yellow Rh colloid was more active than the larger particle size red Rh colloid, but a black Rh colloid, which had no stabiliser, was most active.
Enantioselective Hydroborations Catalyzed by Rhodium( + 1) Complexes
k. burgess, w. a. van der donk and m. j. ohlmeyer, Tetrahedron: Asymmetry, 1991, 2, (7), 613–621
Enantioselective hydroborations of alkenes with catecholborane were performed via catalysis with complexes containing the chiral phosphine ligands DIOP, BINAP, CHIRAPHOS, DIPAMP, BDPP, 2-MeODIOP and 3-MeODIOP. Alkenes were also hydroborated with catecholborane derivatives in the presence of Rh( + )/DIOP catalysts.
Enantioselective Metal Complex Catalysis. 6. Rhodium Catalysts for Asymmetric Hydrosilylation Based on Chiral Phosphites
e. yu. zhorov, k. n. gavrilov, v. a. pavlov, a. t. teleshev, l. s. gorshkova, e. e. nifant’ev and e. i. klabunovskii, Izv. Akad. Nauk SSSR, Ser. Khim., 1991, (5), 983–988
Studies of asymmetric hydrosilylation of acetophenone by diphenylsilane in the presence of a Rh complex catalyst containing chiral phosphates were performed. Enantioselectivity of the catalyst depended on phosphite formation, on the ratios of acetophenone: Rh and ligand: Rh and on the temperature of the reaction.
Colloidal Rhodium Suspensions Stabilized by Various Hydrotropic or Surface Active Triphenylmethyl Trisulfonates and Their Use in Biphasic Catalysis
c. larpent, f. brisse-le menn and h. patin, New J. Chem., 1991, 15, (15), 361–366
Highly water soluble trisulphonated compounds R-C(p -C6H4SO3Na)3 bearing polar, non-polar or lipophilic R substituents have been used to stabilise a catalytically active colloidal suspension of polyhydroxylated Rh particles, thus allowing the hydrogenation of liquid alkenes in biphasic media. Stabilisation occurs via adsorption of the polyanionic head group on the polar surface of the hydroxylated Rh particles, affording electrostatic or electrosteric repulsions. The catalyst can be recycled.
Extremely Efficient Catalytic Reduction of Aromatic Nitro Compounds Affording Amines Using Amine-Added Rh6(CO)16 Catalyst Systems under CO/H2O Conditions
k. nomura, m. ishino and m. hazama, J. Mol. Catal., 1991, 66, (2), L11–L13
Rh6(CO)l6 catalysts with added small amounts of amines or diamines in 2-methoxyethanol/5 N NaOH aqueous solution exhibit remarkably high activities for the reduction of aromatic nitro compounds: p- nitrotoluene and p -nitroanisole. The reaction conditions are 25°C and 1 atm CO.
Hydroformylation of Oct-1-ene with Extremely High Rates Using Rhodium Catalysts Containing Bulky Phosphites
a. van rooy, e. n. orij, p. c. j. kamer, f. van den aardweg and p. w. n. m. van leeuwen, J. Chem. Soc., Chem. Commun., 1991, (16), 1096–1097
A Rh complex containing tris(o-tert-butyl-p-methylphenyl )phosphite as a ligand catalyses the hydroformylation of oct-1-ene with good selectivity and at extremely high rates. The rate constant is pseudo first order in [H2] and 1/[CO] and shows that the reaction of H is the rate determining step. The observed rates are at least 10 times higher than those observed for the Rh triphenylphosphine catalyst.
Hydroformylation of Styrene Catalyzed by Rhodium Complexes with 2 -Diphenylphosphinopyridine
s. gladiali, l. pinna, c. g. arena, e. rotondo and f. faraone, J. Mol. Catal, 1991, 66, (2), 183–190
Mono- and binuclear Rh complexes containing 2-(diphenylphosphine)pyridine, Ph2PPy (1) as ligand, have been examined as catalysts for styrene hydroformylation. All were good catalysts and the formation of the expected aldehydes took place selectively within several hours in mild conditions. The binuclear catalyst was efficient only under high pressure, whereas the in situ system obtained by addition of (1) to RhH(CO)(PPh3)3 (2) had a pronounced activity even in the low pressure reaction. In solution (1) can easily displace one or two moles of PPh3 from (2) giving rise to mixed mononuclear phosphine-Rh complexes, the most active catalytic species.
Efficient Low-Temperature Thermal Functionalization of Alkanes. Transfer Dehydrogenation Catalyzed by Rh(PMe3)2Cl(CO) in Solution under a High Pressure Dihydrogen Atmosphere
j. a. maguire and a. s. goldman, J. Am. Chem. Soc., 1991, 113, (17), 6706–6708
An efficient catalytic system for alkane dehydrogenation is described which requires an added H2 atmosphere; this is because the thermodynamic barrier to CO loss from the Rh(PMe3)2Cl(CO) catalyst is overcome by its being coupled with alkene hydrogenation. This affords the reactive fragment Rh(PMe3)2Cl, which thermally dehydrogenates alkanes in accordance with photocatalytic behaviour.
Ruthenium Catalyzed Hydroformylation Reactions Using in Situ Generation of Synthesis Gas from Aqueous Methyl Formate
g. jenner, Appl. Catal., 1991, 75, (2), 289–298
Aqueous methyl formate was used as a source of CO and H2 via catalysis with Ru3(CO)12 + tricyclohex-ylphosphine in the hydroformylation of cycloalkenes and linear alkenes. The hydroformylation reaction involved [HRu3(CO)11]–. The best results for formation of higher alcohols were obtained with lower alkenes. The addition of Pd(acac)2 was able to modulate the selectivity with respect to the alcohols.
Efficient Ruthenium-Catalysed Transfer Hydrogenation of Ketones by Propan-2-ol
r. l. chowdhury and j.-e. bÄckvall, J. Chem. Soc, Chem. Commun., 1991, (16), 1063–1064
In the presence of co-catalyst NaOH, RuCl2(PPh3)3 catalyses the efficient transfer hydrogenation of both aliphatic and aromatic ketones by propan-2-ol, at rates of up to 900 turnovers/h at 82°C. No hydrogenation occurs in the absence of NaOH. Using NaOH dramatically improves such reported hydrogenations, run under neutral conditions.
FUEL CELLS
Dependence of Performance of Solid Polymer Electrolyte Fuel Cells with Low Platinum Loading on Morphologic Characteristics of the Electrodes
e. a. ticianelli, j. g. beery and s. srinivasan, J. Appl. Electrochem., 1991, 21, (7), 597–605
Pt electrocatalysts supported on C and also low catalyst loading gas-diffusion electrodes used in proton-exchange-membrane (PEM) fuel cells were studied by TEM and SEM and/or Rutherford backscattering spectroscopic analyses. The results showed an increase in Pt crystallite sizes when the Pt:C weight ratio increases in the order 10, 20 and 40 wt.% Pt/C electrocatalyst; and that the Pt:C ratio is 1:2.4:4 for the electrodes with 10, 20 and 40 wt.% Pt/C, respectively. It is concluded that the use of electrodes with thin catalyst layers, of high Pt:C ratio, with Pt localised near the front surface had the effect of diminishing the overpotentials in PEM fuel cells.
ELECTRONIC AND ELECTRICAL ENGINEERING
Thermal Stability of Au-Sn/Near Noble Metal Barrier Metallization Systems
o. wada and t. kumai, Jpn. J. Appl. Phys., Part II Lett., 1991, 30, (6A), L1056–L1058
The reaction barrier characteristics and thermal stability of evaporated Pt, Pd and Rh films when used with Au-30 wt.% Sn were studied. Sn in Au-Sn diffused preferentially into a barrier metal uniformly for all three metals; the diffusion coefficients are sufficiently thermally stable over a temperature range relevant for chip bonding and device operations. Rh has the smallest diffusion coefficient between 200 and 400°C, with the highest activation energy, 1.95 eV, below the melting point of Au-Sn of 280°C. Thus Pt and especially Rh are useful in highly stable metallisation systems applicable to flip-chip integration.
Low-Temperature Formation of the PtSi Layer by Codeposition of Pt and Si in a Molecular Beam Epitaxy System
k. fujii, h. kanaya, y. kumagai, f. hasegawa and e. yamaka, Jpn. J. Appl. Phys., Part II Lett., 1991, 30, (3B), L455–L457
Pt and Si were codeposited on Si(100) to form polycrystalline PtSi layers in a molecular beam epitaxy system. Properties of codeposited Pt silicide layers depend on the substrate temperature and the evaporated Pt:Si ratio. The film codeposited at the substrate temperature of 200°C with the stoichiometric ratio of Pt:Si = 1:1 had a similar crystallised grain structure, (oriented to [110]), and the same resistivity, ~ 35 μΩ cm, as those of the PtSi layer formed by the thermal reaction at 500°C. The film codeposited at 80°C and Pt:Si = 1:1 or at Pt:Si = 3:4 and 200°C showed a smaller grain size and a higher resistivity.
Preparation of YBa2Cu3Oy Superconducting Thin Films on Metallic Substrates by Excimer Laser Ablation
j. saitoh, m. fukutomi, k. komori, y. tanaka, t. asano, h. maeda and h. takahara, Jpn. J. Appl. Phys., Part II Lett., 1991, 30, (5B), L898–L900
Superconducting thin films of YBa2Cu3Oy on metallic substrates were obtained by a pulsed laser ablation technique. The growth quality of the films was compared on YSZ/Hastelloy substrates with and without a Pt underlayer. A thin Pt film between YSZ and Hastelloy changed into a PtCr2 layer on reaction with Cr, and was very effective in suppressing inter-diffusion between YSZ and Hastelloy and in stabilising the YSZ buffer layers, giving well-crystallised YBa2Cu3Oy films on them.
Barrier Metals for ULSI: Processing and Reliability
d. pramanik and v. jain, Solid State Technol., 1991, 34, (5), 97–102
Problems encountered in applying barrier metal technology to Si ULSI processing is discussed. Barrier metal films separate two materials, such as Al/Si, Au/Si, Au/Si, Al and noble metal silicides such as PtSi, Pd2Si and NiSi2. Very low contact resistances to n+ and p+ can be obtained by forming PtSi or Pd2Si in the contacts prior to the barrier metal deposition. For PtSi contacts the Al reacts with PtSi at temperatures as low as 300°C; above 400°C the PtSi is a strong sink for Al atoms, and once Al penetrates the TiW barrier, contact failure occurs.
Pd-on-GaAs Schottky Contact: Its Barrier Height and Response to Hydrogen
h.-y. nie and y. nannichi, Jpn. J. Appl. Phys., 1991, 30, (5), 906–913
A Pd-on-GaAs Schottky contact was prepared by depositing Pd using a W heater, instead of electron beam heating, onto a GaAs surface, and the interface composition was investigated. A reacted interface in the Pd-on-GaAs system characterised a barrier height of 0.88–0.92 eV insensitive to H2. The response to H2 was correlated with the barrier height, and the device was sensitive to H2 when barrier height was higher than a critical value of ~ 0.96–0.99 eV.
Size Effects in Ruthenium-Based Thick-Film Resistors: Rutile vs. Pyrochlore-Based Resistors
m. prudenziati, f. sirotti, m. sacchi, b. morten, a. tombesi and t. akomolafe, Active Passive Elec. Comp., 1991, 14, (3), 163–173
The change of sheet resistance, Rs, as a function of resistor length has been investigated in resistive layers whose conductive phase evolves from Pb-rich pyrochlores to Pb2Ru2O6 5 and finally to RuO2 on increasing the firing temperature. Bi diffusion lowers the sheet resistance values in shorter resistors, while Ag diffusion has this effect in shorter resistors only for ruthenate conductive grains, the reverse being noted in RuO2-based layers.
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