AINbO oxides as new supports for hydrocarbon oxidation II. Catalytic properties of VOx-grafted AlNbO oxides

Abstract Vanadium oxides were immobilized by grafting VOCl 3 on AlNbO oxides calcined between 500 and 750°C. Chemical analysis, XPS, and STEM measurements suggest an incomplete but homogeneous stoichiometric reaction between superficial hydroxyl groups and vanadyl oxychloride. By FTIR studies, it is observed that the interaction involves preferentially basic hydroxyl groups bonded to aluminium cations. UV-visible spectra show that mainly V 5+ is present at the solid surface. Corresponding spectra are compatible with tetrahedral symmetry, in agreement with a previous 51 V NMR investigation. The acido-basic properties of the catalyst were tested by isopropanol decomposition and compared with the corresponding supports. It has been observed that basicity is higher for VO x grafted on AlNbO oxide calcined at high temperature and corresponding to the AlNbO 4 structure. VO x grafted on AlNbO oxides calcined at intermediate temperatures and corresponding to a AlNbO disorganized structure present a good selectivity for the oxidative dehydrogenation of propane into propene. It has been observed that, for both reactions, the turnover number increases with the temperature of calcination of the catalysts. The reactivity of the superficial VO x species is discussed in relation to the structure and chemical composition of the aluminium niobiate support.