Dispersion and Thermal Stability of MoO3on TiO2-ZrO2Mixed Oxide Support

Abstract

TiO2-ZrO2 mixed oxide support containing 1 : 1 mole ratio was prepared by the coprecipitation method and impregnated with MoO3. Ammonium heptamolybdate was used as source of MoO3, and molybdena contents were varied from 2 to 12 wt%. The TiO2-ZrO2 support and MoO3/TiO2-ZrO2 catalysts were subjected to thermal treatments from 773 to 1073 K and were investigated by X-ray diffraction, FT-infrared, oxygen uptake, and BET surface area measurements to establish the effects of molybdena loading and thermal treatments on the surface structure of dispersed molybdena species and thermal stability of the catalysts. Calcination of Ti- and Zr-hydroxides at 773 K result in the formation of an amorphous phase, and further heating to 973 K produces a crystalline ZrTiO4 compound. This compound is quite stable even up to 1273 K in the absence of MoO3. Impregnation of MoO3 and heating of the samples result in the formation of the ZrMo2O8 compound. This compound is highly sensitive to the concentration of MoO3 and calcination temperature.