Hiroyoshi Kanai

Analysis of XANES for identification of highly dispersed transition metal oxides on supports

XANES of vanadium and niobium oxide on silica or alumina have been analyzed quantitatively by a deconvolution technique. Based on the results for reference compounds, local structures of supported vanadium and niobium species were identified. The composition was estimated from difference spectra for the samples which consisted of two kinds of species.

The local structures and photo-catalytic activity of supported niobium oxide catalysts

Abstract Photo-oxidation of propene has been performed over Nb 2 O 5 /SiO 2 catalysts. By phosphorescence spectroscopy, it was concluded that the active species is a photo-excited Nbue5fbO bond dispersed on the catalyst surface. The oxygen of the Nbue5fbO bond was transferred to propene directly, producing ethanal as a major product, and acetone, propanal and propenal as minor products. XANES and EXAFS spectra indicate that the surface niobium oxide species is dominantly a tetrahedral species in a highly dispersed state, while an aggregated species of a square pyramidal cluster is dominant in a low dispersed state. The change in the selectivity of the photo-oxidation can be correlated with the dispersion. The difference in the selectivity between Nb 2 O 5 /SiO 2 and V 2 O 5 /SiO 2 is discussed from a quantum chemical view point.

Characterization of γ-Ga2O3-Al2O3 Prepared by Solvothermal Method and Its Performance for Methane-SCR of NO

The gamma-Ga(2)O(3)-Al(2)O(3) mixed oxides with a spinel structure were prepared by the solvothermal reaction of gallium acetylacetonate and aluminum isopropoxide in diethylenetriamine. In the crystal structures of the catalysts obtained by the calcination of these mixed oxides, Ga(3+) and Al(3+) ions preferentially occupied tetrahedral and octahedral sites, respectively. The catalysts with low Ga contents had a unique structure with high surface areas and a concentration gradient of decreasing Ga content from the surface to the bulk. In methane-selective catalytic reduction (SCR) of NO, higher NO conversion to N(2) was attained on the catalyst with high occupation of Ga(3+) ions at tetrahedral sites and Al(3+) ions at octahedral sites. For the gamma-Ga(2)O(3)-Al(2)O(3) mixed oxide with a charged Ga molar content of 0.3 (ST(0.3)), tetrahedral and octahedral sites were solely occupied by Ga(3+) and Al(3+) ions, respectively, and the catalyst exhibited the highest NO conversion to N(2). Therefore, it was concluded that the active site for methane-SCR of NO is tetrahedral Ga(3+) ion and octahedral Al(3+) ion, which are linked to each other. Nitrogen monoxide is adsorbed on the isolated hydroxyl group attached to Al(3+) ions and then oxidized by O(2) yielding surface nitrate species. Tetrahedral Ga(3+) ions work as Lewis acid sites for the activation of methane because of their coordinative unsaturation. The Ga(3+) ions in the gamma-Ga(2)O(3)-Al(2)O(3) catalyst have a redox property, which plays important roles in both the oxidation of NO to surface nitrate species and the activation of methane. The most important factor for this catalyst is that the sites for the formation of surface nitrate species reside next to the methane activation sites, which facilitates the reaction between surface nitrate species and the activated species derived from methane, thus mitigating the consumption of methane by simple combustion with O(2). Therefore, ST(0.3), which has the largest number of ensembles of the tetrahedral Ga(3+) ions and octahedral Al(3+) ions, shows the highest activity for methane-SCR of NO.

Asymmetric cyclopropanation of chiral fumarates with gem-dihalides catalyzed by Co(0) or Ni(0) complexes and zinc

Abstract Diastereoface differentiating cyclopropanation between fumarates derived from chiral alcohols and gem -dihalides has been carried out using cobalt(0) or nickel(0) complexes and zinc. The optical yields of the cyclopropane derivatives obtained from (−)-dimenthyl and (−)-dibornyl fumarate both exhibit maximum values at 23 °C. An approximate general linearity between the highest optical yield and the optical rotation of the chiral fumarate is observed except in the case of (−)-di-8-phenylmenthyl fumarate. The high asymmetric selection may be due to preferential coordination of a face of the chiral fumarate onto the metal center where the chirality has been determined by coordination of another molecule of the chiral fumarate.

Hydrodimerization of methyl vinyl ketone catalyzed by Co(I)-bipyridyl complexes

Abstract Methyl vinyl ketone was hydrodimerized to 2,7-octanedione in an alcoholic solution by CoX(bpy) 2 ( X = halogen, bpy = 2,2′-bipyridyl) prepared in situ from cobalt halides, 2,2′-bipyridyl, and zinc. The catalytic activity decreased in the order I > Br > Cl. The addition of alkali halides, of which sodium iodide was the most effective, gave higher yields of the hydrodimer in the presence of zinc. The cohydrodimerization between methyl vinyl ketone and excess methyl acrylate was carried out to yield methyl 6-ketoheptanoate and 2,7-octanedione in approximately equal ratio.

Selective hydrogenation of 1,3-diolefins catalyzed by cobalt(I)-bipyridyl complexes

Abstract Selective hydrogenation of nonbranched 1,3-diolefins mainly to cis-2-olefins was carried out in THF-ethanol by the catalysis of CoX(bpy)2 (X = halogen, bpy = 2,2′-bipyridyl) prepared in situ from cobalt halides, 2,2′-bipyridyl, and zinc. The induction period, the rate, and stereoselectivity depend on the time when 1,3-butadiene and hydrogen are introduced to the catalyst. The rate is proportional to the hydrogen pressure and to the catalyst concentration, and changes with the concentration of 1,3-butadiene. An excess of butadiene inhibits hydrogenation and leads to dimerization. A mechanism is proposed which involves an anti-1-methyl-π-allylcobalt complex as an intermediate.

Preparation of Amorphous Cu-Ti and Cu-Zr Alloys of High Surface area by Chemical Modification

Abstract Amorphous Cu-Ti and Cu-Zr alloys of high surface area (3–12 m 2 g −1 ) have been prepared by chemical modification; doping of Zn atoms into the surface layers and leaching the Zn atoms with a diluted NaOH solution. A treatment of the alloys with O 2 and H 2 under mild conditions were effective to obtain alloys of higher surface area and catalytic activity for methanol dehydrogenation