Characterization of V2O5/TiO2-ZrO2 catalysts by XPS and other techniques

A high surface area titania-zirconia mixed oxide support was prepared by th e technique of precipitation from homogeneous solutions. Vanadia (12 wt %) was impregnated on TiO2-ZrO2 support by using an oxalic acid solution of NH 4VO3. The TiO2-ZrO2 binary oxide support and the V2O5/TiO2-ZrO2 catalyst we re then subjected to thermal treatments from 500 to 800 degrees C. The infl uence of thermal treatments on the dispersion and stability of the catalyst was investigated by X-ray diffraction (XRD), FT infrared (FTIR), UV-vis ab sorption, and X-ray photoelectron spectroscopy (XPS) techniques. The charac terization results suggest that the TiO2-ZrO2 binary oxide support is therm ally quite stable up to 800 degrees C. Calcination of the coprecipitated ti tanium-zirconium hydroxides at 500 degrees C result in the formation of an amorphous phase, and further heating at 600 degrees C converts this amorpho us phase into a crystalline ZrTiO4 compound. Impregnation of V2O5 and heati ng of the V2O5/TiO2-ZrO2 catalyst beyond 600 degrees C results in the forma tion of ZrV2O7, With the simultaneous presence of the TiO2 rutile phase. Ho wever, the vanadia is in a highly dispersed state on the TiO2-ZrO2 mixed ox ide support when calcined at less than 600 degrees C.