DISPERSION AND THERMAL-STABILITY OF MOO3 ON TIO2-ZRO2 MIXED-OXIDE SUPPORT

TiO2-ZrO2 mixed oxide support containing 1:1 mob ratio was prepared by the coprecipitation method and impregnated with MoO3. Ammonium heptam olybdate was used as source of MoO3, and molybdena contents were varie d 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 inve stigated by X-ray diffraction, FT-infrared, oxygen uptake, and BET sur face area measurements to establish the effects of molybdena loading a nd 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 format ion of the ZrMo2O8 compound. This compound is highly sensitive to the concentration of MoO3 and calcination temperature. (C) 1998 Academic P ress.