Stabilization of nanosized titania-anatase for high temperature catalytic applications

Abstract

M 2 O 3 -TiO 2 (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.% V 2 O 5 . The M 2 O 3 -TiO 2 and V 2 O 5 /M 2 O 3 -TiO 2 (M = Ga, In and La) 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 M 2 O 3 -TiO 2 composite oxides are in X-ray amorphous state and exhibit reasonably high specific surface area at 773 K calcination. The M 2 O 3 -TiO 2 mixed oxide supports also accommodate a monolayer equivalent of V 2 O 5 (12 wt.%) in a highly dispersed state. The V 2 O 5 /M 2 O 3 -TiO 2 catalysts are thermally stable up to 873-973 K calcination temperature. When subjected to thermal treatments beyond 873-973 K, the dispersed vanadium oxide selectively interacts with In 2 O 3 or La 2 O 3 portions of the respective mixed oxides and forms InVO 4 or LaVO 4 compounds. The remaining TiO 2 appears in the form of anatase or rutile phase. In the case of V 2 O 5 /Ga 2 O 3 -TiO 2 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% V 2 O 5 /La 2 O 3 -TiO 2 catalyst exhibited good conversion and product selectivity among various samples investigated.