Formation of V₂O₅-based mixed oxides in flames

V₂O₅–TiO₂ and V₂O₅–Al₂O₃ mixed oxide powders were synthesized in a hydrogen-oxygen flame using VOCl₃, TiCl₄, and Al(CH₃)₃ as precursors. The particle formation processes were investigated as a function of VOCl₃ concentration by laser light-scattering and by collecting particles directly onto transmission electron microscopy grids. In the V₂O₅–TiO₂ system, the oxides condense as an intimate mixture at all three VOCl₃ concentrations. Spherical particles, 40 to 70 nm in diameter, are obtained. In the V₂O₅–Al₂O₃ system, chain-like particles composed of an intimate mixture of V₂O₅ and Al₂O₃ form at the lowest VOCl₃ concentration. At high VOCl₃ concentrations, the chain-like particles have a core-mantle structure (a core mainly of Al₂O₃ and a mantle mainly of V₂O₅). The crystalline form and the surface area of these mixed oxides were determined by x-ray diffractometry, FT-IR spectroscopy, and BET analysis by nitrogen desorption. These measurements indicate that amorphous vanadium oxide forms at low VOCl₃ concentrations, and V₂O₅ is obtained at the higher VOCl₃ concentrations. The structure of the amorphous vanadium oxide matches that published for vanadium oxide “supported” catalysts.