First-principles study on cerium ion behavior in irradiated cerium dioxide

In order to clarify, from the electronic structure, the origin of the appearance of the tri-valent Ce state in irradiated cerium dioxide with swift heavy ions, we performed comprehensive first-principles calculations on various defective structures in cerium dioxide. The calculated results show that an oxygen mono-vacancy or an oxygen Frenkel pair can induce two tri-valent Ce states neighboring the oxygen vacancy. The calculation of the oxygen Frenkel pair further reveals that an interstitial oxygen atom that moves from the lattice position and an oxygen atom on the lattice can form a dimer that behaves as an oxygen molecule of negative di-valence. This bonding state can also produce excess electrons and the tri-valent Ce state in cerium dioxide.     

Preparation of supported gold catalysts from gold complexes and their catalytic activities for CO oxidation

A phosphine-stabilized mononuclear gold complex Au(PPh₃)(NO₃) (1) and a phosphine-stabilized gold cluster [Aug(PPh₃)₈](NO₃)₃ (2) were used as precursors for preparation of supported gold catalysts. Both complexes 1 and 2 supported on inorganic oxides such as -Fe₂O₃, TiO₂, and SiO₂ were inactive for CO oxidation, whereas the 1 or 2/ oxides treated under air or CO or 5% h₂/Ar atmosphere were found to be active for CO oxidation. The catalytic activity depended on not only the treatment conditions but also the kinds of the precursor and the supports used. The catalysts derived from 1 showed higher activity than those derived from 2. -Fe₂O₃ and TiO₂ were much more efficient supports than SiO₂ for the gold particles which were characterized by XRD and EXAFS.     

Energy-dispersive XAFS study on the decarbonylation process of Mo(CO)6 in NaY zeolite

The temperature-programmed decarbonylation process of Mo(CO)₆ in NaY zeolite was studied by means of a time-resolved energy-dispersive XAFS method. The XANES analysis demonstrated that the decarbonylation proceeded by two successive steps via a stable intermediate which existed between 440 and 490 K. The curve fitting analysis of the EXAFS data revealed that the intermediate was a molybdenum monomer subcarbonyl species Mo(CO)₃(O_L)₃ coordinated by three CO ligands and three oxygen atoms of zeolite framework (O_L). Molybdenum dimer subcarbonyl species were not observed. This study demonstrated that the DXAFS technique is a powerful method to study the dynamic behavior of the Mo carbonyl species during decarbonylation process.     

Development of an X-ray photoemission electron microscopy system with multi-probes, and its application to surface imaging at static and dynamic states

We have developed a new X-ray photoemission electron microscopy system combined with low energy electron microscopy, photoemission electron microscopy, mirror electron microscopy (MEM), secondary electron emission microscopy (SEEM) and Auger electron emission microscopy, which provides multi-angle information on the distribution and change of element, chemical state, structure, etc. at solid surfaces under the working conditions such as high temperature and gas atmosphere. The performance of each microscopical method was examined and typical images are presented. The dynamic behaviour of fabricated surfaces has been imaged in real time by SEEM and MEM.     

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.     

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 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.