ESCA investigation of V2O5+TiO2 catalysts for the vapour phase oxidation of alkylpyridines

Abstract

Sensitivity factors for the quantitative analysis of vanadium- and titanium-oxide mixtures by ESCA have been determined from calibration curves of various V₂O₅+TiO₂ mixtures.

Sintered Ti(VO₃)₄ and sintered powder mixtures of V₂O₅ and TiO₂ in various ratios yielded a higher vanadium content than the bulk composition; this is caused by the TiO₂ particles being embedded in a matrix of V₂O₅. The unsintered Ti(VO₃)₄ and V₂O₅+TiO₂ mixtures, on the other hand, gave atom ratios in good agreement with the bulk composition.

The V 2p, Ti 2p and O 1s electron binding energies and half widths were measured for various oxides and oxide mixtures, both sintered and unsintered. The lower vanadium oxides were non-stoichiometric at the surface.

The V₂O₅+TiO₂ catalysts used in the oxidation of alkylpyridines were only reduced in a thin surface layer. The V₂O₅ was partially reduced to lower valence states while the TiO₂ was unchanged, as determined by the V 2p and Ti 2p signals. The degree of reduction varied throughout the catalyst bed, with the highest reduction nearest to the reactor inlet. It was strongly dependent upon the reaction temperature and a maximum was obtained at 455°C, the same temperature which gives maximum selectivity. Surface compositional changes in V, Ti and O, caused by participating in catalysis, were observed for all the catalysts used.