Surface characterization of Ga2O3-TiO2 and V2O5/Ga2O3-TiO2 catalysts

The techniques of X-ray photoelectron spectroscopy, X-ray diffraction, FT-i nfrared, and O-2 chemisorption were employed to characterize a specially ob tained Ga2O3-TiO2 mixed oxide and V2O5/Ga2O3-TiO2 catalyst calcined at diff erent temperatures from 773 to 1073 K. The Ga2O3-TiO2 (1:5 mole ratio based on the oxides) mixed oxide was synthesized by a homogeneous coprecipitatio n method with in situ generated ammonium hydroxide, and a nominal 4 wt % V2 O5 was impregnated over the calcined support (773 K) by adopting a wet impr egnation technique. A commercial TiO2 (anatase) sample was also used in thi s study for comparison purposes. The characterization results suggest that the Ga2O3-TiO2 mixed oxide, calcined at 773 K, primarily consists of a mixt ure of TiO2 anatase and alpha -Ga2O3. In the case of the V2O5/Ga2O3-TiO2 ca talyst, the impregnated V2O5 is in a highly dispersed state on the surface of the mixed oxide. Under the influence of thermal treatments from 773 to 1 073 K, the dispersed vanadium oxide promotes the transformation of anatase to rutile and alpha -Ga2O3 to beta -Ga2O3 and is accompanied by a loss in t he specific surface area of the samples. In;particular, the gallia in the V 2O5/Ga2O3-TiO2 catalyst retards the transformation of anatase into rutile. The Ti 2p, Ga 3d, and V 2p photoelectron peaks of the V2O5/Ga2O3-TiO2 sampl e are highly sensitive to the calcination temperature. The intensity of the Ti 2p line increased with increasing calcination temperature and an opposi te trend was noted in the case of Ga 3d and V 2p lines. The XPS line shapes and the corresponding binding energies indicate that the dispersed vanadiu m oxide in the V2O5/Ga2O3-TiO2 catalyst interacts preferably with the galli um oxide. The V/Ti and V/Ga atomic ratios as determined by XPS measurements reveal that more vanadium is confined to Ti than Ga at 773 and 873 K and a lmost equally at 973 and 1073 K calcination temperatures, respectively.