Supported gold catalysis derived from the interaction of a Au–phosphine complex with as-precipitated titanium hydroxide and titanium oxide

Supported gold catalysts derived from interaction of a Au–phosphine complex Au(PPh₃)(NO₃) (1) with conventional titanium oxide TiO₂ and as-precipitated titanium hydroxide (*, as-precipitated) have been characterized by means of XRD, XPS, EXAFS, and CP/MAS–NMR. The Au complex 1 was supported on TiO₂ and without loss of Au–P bonding at room temperature. The Au complex 1 on TiO₂ was readily and completely decomposed to form metallic gold particles by calcination at 473 K, whereas only a small part of the complex 1 on was transformed to metallic gold particles. By calcination of 1/ at 573 K the formation of both metallic gold particles and crystalline titanium oxides became notable as evidenced by XRD, XPS and CP/MAS–NMR. The mean diameter of Au particles in 1/ calcined at 673 K was less than 30 Å as estimated from Au(2 0 0) diffraction, which was about one-tenth of that for the corresponding 1/TiO₂. Thus the as-precipitated titanium hydroxide was able to stabilize the Au complex 1 to lead to the simultaneous decomposition of Au complex and . The catalyst 1/ calcined at 673 K afforded remarkably high catalytic activity for low-temperature CO oxidation at 273–373 K as compared to the catalyst 1/TiO₂.     

Dependences of the Oxygen Reduction Reaction Activity of Pd–Co/C and Pd–Ni/C Alloy Electrocatalysts on the Nanoparticle Size and Lattice Constant

Carbon-supported Pd-based binary alloy electrocatalysts (Pd–Co and Pd–Ni) with different particle sizes for polymer electrolyte fuel cells were prepared by a NaBH₄ reduction method and investigated to examine effects of the size and lattice constant of the Pd alloy nanoparticles on the oxygen reduction reaction (ORR) activity. The particle size and lattice constant were controlled in the wide ranges 4.2–12.1 and 0.3802–0.3948 nm, respectively by heating the catalysts in specific atmospheres. The alloy structures were characterized by X-ray diffraction, transmission electron microscopy and X-ray absorption fine structure. The electrochemical tests of the Pd–Co/C and Pd–Ni/C catalysts were performed by cyclic voltammetry and rotating disk electrode in 0.1 M HClO₄. Nearly linear relationship between the lattice constant and nanoparticle size was observed with the Pd–Co and Pd–Ni nanoparticles. The nanoparticle sizes and lattice constants of the Pd–Co/C and Pd–Ni/C electrocatalysts, which influence the Pd d-band center, showed positive and inverse relations with the ORR specific activities, respectively. The mass activities of the Pd–Co/C and Pd–Ni/C electrocatalysts showed an increasing trend with the lattice expansion.     

Zinc-Accelerated Cycloaddition of Carbon Dioxide to Styrene Oxide Catalyzed by Pyrrolidinopyridinium Iodides

The addition of ZnI₂ drastically accelerated the cycloaddition of carbon dioxide to styrene oxide catalyzed by pyrrolidinopyridinium iodides. In the presence of ZnI₂, the styrene carbonate yield reached up to 89 % in 7 h at 100 °C under 1 atm of CO₂. The rate constant increased by greater than three-fold by the addition of ZnI₂. Studies of reaction kinetics in addition to high resolution mass and NMR analysis demonstrated that the primary active species consists of two or more pyrrolidinopyridinium cations combined with ZnI₄ ^2? anion.     

Quantitative analysis of hydrogen adsorbed on Pt particles on SiO2 in the presence of coadsorbed CO by means of L3-edge X-ray absorption near-edge structure spectroscopy

X-ray absorption near-edge structure (XANES) spectra at the Pt L₃-edge for Pt particles supported on SiO₂ under CO adsorption and CO+H₂ coadsorption were recorded to analyze the amount of adsorbed hydrogen in the coadsorbed state on the Pt particles. Adsorbed CO on the Pt particles revealed a new peak at 6 eV above the Pt L₃-edge in the difference spectra before and after CO adsorption in the coverage range 0.10-0.51. Subsequent adsorption of hydrogen at various coverages on the CO-preadsorbed Pt particles broadened and shifted the peak to the higher energy side. The peak was deconvoluted to two components due to adsorbed hydrogen and CO by a linear least-squares fitting technique. It was found that the fitting coefficient with respect to adsorbed hydrogen was proportional to the amount of adsorbed hydrogen. The XANES difference spectra provide a quantitative analysis method for adsorbed hydrogen on supported Pt particles in the presence of coadsorbates like CO. This revised version was published online in July 2006 with corrections to the Cover Date.     

A crystalline SbRe2O6 catalyst active for selective ammoxidation of isobutylene and propene

This paper reports the first performance of a crystalline SbRe₂O₆ catalyst, which is a new family of Re mixed oxide, for the selective ammoxidation reactions of isobutylene to methacrylonitrile and propene to acrylonitrile. The SbRe₂O₆ with alternate (Re₂O₆)^3– and (SbO)⁺ layers showed much better performance than two other known Re–Sb–O compounds SbOReO₄2H₂O and Sb₄Re₂O₁₃ with tetrahedral (ReO₄)^– anions and cationic (SbO)⁺ layers. The SbRe₂O₆ catalyst was also much more active than a coprecipitated SbRe₂O_x catalyst, a supported Re₂O₇/Sb₂O₃ catalyst, and Re oxides such as Re₂O₇, ReO₃ and ReO₂ for the selective ammoxidation. Rhenium is prerequisite to the ammoxidation catalysis of the Re–Sb mixed oxides. Sb oxides such as Sb₂O₃ and Sb₂O₄ were inactive, but Sb in the SbRe₂O₆ catalyst contributes positively to the methacrylonitrile and acrylonitrile syntheses. Neither change nor modification of the surface composition, crystallinity and morphology of SbRe₂O₆ occurred under the ammoxidation reaction conditions, where the presence of NH₃ stabilized the crystalline SbRe₂O₆ structure.     

The Effect of ppm-Level Na Impurity on the Structure of SiO2-Supported Mo Catalysts Prepared in a Clean Room

To investigate the effect of alkali impurity in Mo/SiO₂ on the MoO _x structure on SiO₂ surfaces SiO₂-supported Mo oxides were prepared with various amounts of Na ions in a class-1 clean bench with a laminar flow in a class-1000 clean room. The Na concentrations were varied in the range 0-5000 ppm, while the Mo loading on SiO₂ was maintained at 0.7 wt%. The Mo-Na/SiO₂ samples obtained were characterized by diffuse reflectance UV-visible and Raman spectroscopy. Three types of Mo species were identified: octahedral monooxo Mo monomer species, Na₂Mo₂O₇ and MoO₃. At less than 100 ppm Na both octahedral Mo monomers and MoO₃ species were formed on SiO₂. The MoO₃ species was transformed to Na₂Mo₂O₇ at 2000 ppm Na, where the Na ions interact directly with the Mo species on the surface. The octahedral monooxo Mo monomer species seems not to be influenced significantly by Na impurity.     

Conceptual Integration of Homogeneous and Heterogeneous Catalyses

This article illustrates how bifunctional catalyst surfaces are created by modifying oxide surfaces with organic functional groups and/or with metal complexes, summarizing our previous reports and also presenting new data, which provide a new class of catalytic materials with a high complexity for selective catalysis including C–C coupling, hydroformylation, and asymmetric reactions. The catalyst surfaces are characterized by in situ physical analysis techniques such as time-resolved XAFS, FT-IR, solid-state MAS NMR and so on.     

The influence of basicity on the solubility of platinum in oxide melts

The solubility of platinum in molten BaO-CuO _x , BaO-MnO _x , CaO_satd-SiO₂-FeO _x , KO_0.5-SiO₂, NaO_0.5-SiO₂, and NaO_0.5-PO_2.5 fluxes has been measured in order to seek a measure of the basicity of highly basic fluxes containing transition metal ions and to clarify the chemical behavior of platinum in those melts. The solubility of platinum increases with increasing content of basic oxide in highly basic fluxes, suggesting that it may be a good indicator of the basicity of highly basic fluxes containing transition metal ions. The solubility of platinum in the KO_0.5-SiO₂, NaO_0.5-SiO₂, and NaO_0.5-PO_2.5 melts has a minimum value, and it is suggested that a platinum is amphoteric: it exists as a platinum cation in an acidic flux and does as a platinate ion in a basic flux.     

Plasma-Resistant Dense Yttrium Oxide Film Prepared by Aerosol Deposition Process

Dense yttrium oxide film was prepared on a quartz substrate by the aerosol deposition process at the room temperature. The deposition rate was very high, 60 m/h. Thick film of 10 m was easily achievable on the quartz substrate. Transmission electron microscopy showed that the film was highly dense without voids and was composed of randomly oriented Y₂O₃ crystallites of sizes smaller than 20 nm. The interface between the film layer and the quartz substrate was homogeneous. The film (2-m thick) had a high transmittance (55–85%) in the wavelength region of 250-800 nm. The mechanical properties of the film were very good. The adhesion force of the interface between the Y₂O₃ layer and the quartz substrate was over 80 MPa. The Vickers hardness of the film was 7.7 GPa. The film also had an excellent plasma resistance in a gas mixture of CF₄/O₂. Outstanding results were noted in eroded depth, surface roughness, nanostructure, and transmittance change after plasma exposure of the film.     

Identification of individual 4-methylpyridine molecules physisorbed and chemisorbed on TiO2(110)-(1 x 1) surface by STM

We succeeded in identifying geometries of 4-methylpyridine (4-MP) molecules adsorbed on a TiO₂(110)-(1 x 1) surface based on sequential STM imaging. Characteristics in mobility, topographic height, and location allowed us to distinguish three adsorption states at room temperature: a chemisorbed state with the upright geometry (A₁), a flat-lying state localized at specific sites (A₂), and a flat-lying physisorbed state mobile over the surface (B). The concentration of A₁ and A₂ species was restricted at an order of 0.01 ML. The A₂ state was related to the adsorption at oxygen vacancies resident on the vacuum-annealed surface. The present study demonstrates the promising ability of STM to identify the adsorption geometry of small probe molecules, 4-methylpyridine in the present case, and to provide atom-level information on the origin of acidic property of oxide surfaces. This revised version was published online in July 2006 with corrections to the Cover Date.