Stabilization of nanosized titania-anatase for high temperature catalytic applications

Abstract

M2O3–TiO2 (M = Ga, In and La) composite oxides were prepared by a co-precipitation method with in situ generated ammonium hydroxide and were impregnated with 12 wt.% V2O5. The M2O3-TiO2 and V2O5/M2O3-TiO2 (M = Ga, In and La) samples were subjected to thermal treatments from 773 to 1073K 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 M2O3–TiO2 composite oxides are in X-ray amorphous state and exhibit reasonably high specific surface area at 773K calcination. The M2O3-TiO2 mixed oxide supports also accommodate a monolayer equivalent of V2O5 (12 wt.%) in a highly dispersed state. The V2O5/M2O3-TiO2 catalysts are thermally stable up to 873–973K calcination temperature. When subjected to thermal treatments beyond 873–973 K, the dispersed vanadium oxide selectively interacts with In2O3 or La2O3 portions of the respective mixed oxides and forms InVO4 or LaVO4 compounds. The remaining TiO2 appears in the form of anatase or rutile phase. In the case of V2O5/Ga2O3-TiO2 sample, no such surface vanadate compound formation was observed. All 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/La2O3-TiO2 catalyst exhibited good conversion and product selectivity among various samples investigated.