Preparation and characterization of M2O3-TiO2 and V2O5/M2O3-TiO2 composite oxides for catalytic applications

In2O3-TiO2 (1: 13 mole ratio) mixed oxide was prepared by a co-precipitation method with in situ generated ammonium hydroxide and was impregnated with various amounts Of V2O5 (4-12 wt.%). The In2O3-TiO2 and V2O5/In2O3-TiO2 samples were subjected to thermal treatments from 773 to 1073 K and were investigated by X-ray diffraction, FT-infrared, and BET surface area methods to establish the effects of vanadia loading and thermal treatments on the surface structure of the dispersed vanadium oxide species and temperature stability of these catalysts. Characterization results suggest that the co-precipitated In2O3 -TiO is in X-ray amorphous state and exhibits reasonably high specific surface area. The In2O3-TiO2 also accommodates a monolayer equivalent Of V2O5 (12 wt.%) in a highly dispersed state. The V2O5/In2O3-TiO2 catalyst is thermally stable up to 873 K calcination temperature. When subjected to thermal treatments beyond 873 K, the dispersed vanadium oxide selectively interacts with In2O3 portion of the mixed oxide and forms InVO4 compound. The remaining TiO2 appears in the form of anatase or rutile phase. These samples were evaluated for one step synthesis of 2,6-dimethylphenol from cyclohexanone and methanol mixtures in the vapour phase at normal atmospheric pressure. The 12% V2O5/In2O3-TiO2 catalyst exhibits good conversion and product selectivity among various samples investigated. (C) 2003 Elsevier Science B.V. All rights reserved.