Characterization of La2O3-TiO2 and V2O5/La2O3-TiO2 catalysts and their activity for synthesis of 2,6-dimethylphenol

The La2O3-TiO2 (1:5 molar ratio) mixed oxide was prepared by a co-precipita tion method with in situ generated ammonia and was impregnated with various amounts of vanadia (4-12 wt.%). The La2O3-TiO2 and the V2O5/La2O3-TiO2 cat alysts were subjected to thermal treatments from 773 to 1073 K and were inv estigated by X-ray diffraction, FT-infrared, BET surface area, and O-2 chem isorption methods to establish the effects of vanadia loading and thermal t reatments on the surface structure of the dispersed vanadium oxide species and the temperature stability of these catalysts. Conversion of cyclohexano l to cyclohexanone/cyclohexene was investigated as a model reaction to asse ss the acid-base properties of these materials. The catalytic property was evaluated for a single step synthesis of 2,6-dimethylphenol from cyclohexan one and methanol in the vapor phase at normal atmospheric pressure. Charact erization results suggest that the co-precipitated La2O3-TiO2 when calcined at 773 K is in X-ray amorphous state and exhibits reasonably high specific surface area. The amorphous La2O3-TiO2 is converted into crystalline compo unds La2Ti2O7 and La4Ti9O24 at 873 and 1073 K, respectively. The La2O3-TiO2 also accommodates a monolayer equivalent of V2O5 (12 wt.%) in a highly dis persed state on its surface. The V2O5/La2O3-TiO2 catalyst is thermally quit e stable up to 873 K calcination temperature. When subjected to thermal tre atments beyond 873 K, the dispersed vanadium oxide selectively interacts wi th La2O3 portion of the mixed oxide and forms a LaVO4 compound. The remaini ng TiO2 appears in the form of anatase phase. The La2O3-TiO2 and the V2O5/L a2O3-TiO2 differ in terms of acid-base properties and the 12% V2O5/La2O3-Ti O2 catalyst provided a maximum yield of 2,6-dimethylphenol among various ca talysts investigated. (C) 2001 Elsevier Science B.V. All rights reserved.