Takashi Ushikubo

Catalytic properties of hydrated tantalum oxide

Abstract The hydrated tantalum and niobium oxides display strong acid properties in their amorphous form. TheH0 value of these hydrated oxides was less than −8.2. The acid property of the hydrated tantalum oxide was maintained to higher temperatures than that of the hydrated niobium oxide. The hydrated tantalum oxide catalyzed not only some gas-phase reactions, including the esterification of methacrylic acid with methanol, the alkylation of benzene with ethene, and the isomerization of 1-butene, but also some liquid-phase reactions, such as the aldol condensation of acetone and the hydration of isobutene. The hydrated tantalum oxide showed mainly Lewis acidity in the absence of water. Bronsted acidity was regenerated by steam treatment, confirmed by infrared spectroscopy and the isomerization of 1-butene. The hydrated tantalum oxide was activated to a solid superacid by treatment with sulfuric acid.

The preparation of and water adsorption on thin films of niobium oxide on Pt(111)

Abstract Three types of thin films of niobium oxide on Pt(111): NbO x , Nb 2 O 5 and Ar + -bombarded Nb 2 O 5 were studied. The thin films were made up of a high density of small crystallites on an epitaxial monolayer. AES, ILS and UPS showed that the NbO x thin film had an electronic structure that is a composite of those of NbO, NbO 2 and Nb 2 O 5 , while the Nb 2 O 5 thin film had an electronic structure similar to Nb 2 O 5 . LEED and HREELS showed that the surface periodicities and crystal structures differ from those of the bulk oxides. HREELS indicates a structural similarity with some supported two-dimensional Nb oxide monolayers with Nb=O surface sites of highly distorted NbO 6 octahedra. Ar + bombardment decreased the proportion of surface oxygen. Water adsorption at room temperature, studied by HREELS and UPS, was associative on Nb 2 O 5 and dissociative on Ar + -bombarded Nb 2 O 5 . It was associative on NbO x but dissociates on heating.

Catalytic activities of niobium oxide for the liquid-phase hydrogenation of maleic anhydride and hydration of succinonitrile

Abstract Co and Pd supported on Nb 2 O 5 catalyst was active for the hydrogenation of maleic anhydride to γ-butyrolactone and tetrahydrofuran in the liquid-phase. The catalyst was more active than Co and Pd supported on diatomaceous earth, SiO 2 and Al 2 O 3 . Co and Pd seem to be stable on Nb 2 O 5 . Nb 2 O 5 · nH 2 O was active for the hydration of succinonitrile to β-cyanopropionamide, that is an intermediate for α-pyrrolidone, in the liquid-phase. Niobium oxide showed unique catalytic activities, especially, in the presence of water.