Surface Characterization of Ga₂O₃−TiO₂ and V₂O₅/Ga₂O₃−TiO₂ Catalysts

Abstract

The techniques of X-ray photoelectron spectroscopy, X-ray diffraction, FT-infrared, and O₂ chemisorption\nwere employed to characterize a specially obtained Ga₂O₃−TiO₂ mixed oxide and V₂O₅/Ga₂O₃−TiO₂ catalyst\ncalcined at different temperatures from 773 to 1073 K. The Ga₂O₃−TiO₂ (1:5 mole ratio based on the oxides)\nmixed oxide was synthesized by a homogeneous coprecipitation method with in situ generated ammonium\nhydroxide, and a nominal 4 wt % V₂O₅ was impregnated over the calcined support (773 K) by adopting a wet\nimpregnation technique. A commercial TiO₂ (anatase) sample was also used in this study for comparison\npurposes. The characterization results suggest that the Ga₂O₃−TiO₂ mixed oxide, calcined at 773 K, primarily\nconsists of a mixture of TiO₂ anatase and α-Ga₂O₃. In the case of the V₂O₅/Ga₂O₃−TiO₂ catalyst, the\nimpregnated V₂O₅ is in a highly dispersed state on the surface of the mixed oxide. Under the influence of\nthermal treatments from 773 to 1073 K, the dispersed vanadium oxide promotes the transformation of anatase\nto rutile and α-Ga₂O₃ to β-Ga₂O₃ and is accompanied by a loss in the specific surface area of the samples.\nIn particular, the gallia in the V₂O₅/Ga₂O₃−TiO₂ catalyst retards the transformation of anatase into rutile.\nThe Ti 2p, Ga 3d, and V 2p photoelectron peaks of the V₂O₅/Ga₂O₃−TiO₂ sample are highly sensitive to the\ncalcination temperature. The intensity of the Ti 2p line increased with increasing calcination temperature and\nan opposite trend was noted in the case of Ga 3d and V 2p lines. The XPS line shapes and the corresponding\nbinding energies indicate that the dispersed vanadium oxide in the V₂O₅/Ga₂O₃−TiO₂ catalyst interacts\npreferably with the gallium oxide. The V/Ti and V/Ga atomic ratios as determined by XPS measurements\nreveal that more vanadium is confined to Ti than Ga at 773 and 873 K and almost equally at 973 and 1073\nK calcination temperatures, respectively.