A high surface area titania−silica binary oxide support was prepared according to the homogeneous precipitation method and was coated with a monolayer of vanadium oxide. The TiO2−SiO2 support and the V2O5/TiO2−SiO2 catalyst were then subjected to thermal treatments from 773 to 1073 K. The influence of heat treatments on the dispersion and thermal stability was investigated by X-ray diffraction, FT infrared, X-ray photoelectron spectroscopy, oxygen uptake, and BET surface area methods. The results suggest that TiO2−SiO2 is quite thermally stable even up to 1073 K calcination temperature. However, the V2O5/TiO2−SiO2 catalyst is stable, in terms of dispersion and surface area, only up to a calcination temperature of 873 K. Thermal treatments beyond this temperature transformed vanadia and titania into crystalline phases and then titania anatase into rutile phase.

A high surface area titania-zirconia mixed oxide support was prepared by the technique of precipitation from homogeneous solutions. Vanadia (12 wt %) was impregnated on TiO 2 -ZrO 2 support by using an oxalic acid solution of NH 4 VO 3 . The TiO 2 -ZrO 2 binary oxide support and the V 2 O 5 /TiO 2 -ZrO 2 catalyst were then subjected to thermal treatments from 500 to 800 °C. The influence of thermal treatments on the dispersion and stability of the catalyst was investigated by X-ray diffraction (XRD), FT infrared (FTIR), UV-vis absorption, and X-ray photoelectron spectroscopy (XPS) techniques. The characterization results suggest that the TiO 2 -ZrO 2 binary oxide support is thermally quite stable up to 800 °C. Calcination of the coprecipitated titanium-zirconium hydroxides at 500 °C result in the formation of an amorphous phase, and further heating at 600 °C converts this amorphous phase into a crystalline ZrTiO 4 compound. Impregnation of V 2 O 5 and heating of the V 2 O 5 /TiO 2 -ZrO 2 catalyst beyond 600 °C results in the formation of ZrV 2 O 7 , with the simultaneous presence of the TiO 2 rutile phase. However, the vanadia is in a highly dispersed state on the TiO 2 -ZrO 2 mixed oxide support when calcined at less than 600 °C.

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