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

The techniques of X-ray photoelectron spectroscopy, X-ray diffraction, FT-infrared, and O 2 chemisorption were employed to characterize a specially obtained Ga 2 O 3 −TiO 2 mixed oxide and V 2 O 5 /Ga 2 O 3 −TiO 2 catalyst calcined at different temperatures from 773 to 1073 K. The Ga 2 O 3 −TiO 2 (1:5 mole ratio based on the oxides) mixed oxide was synthesized by a homogeneous coprecipitation method with in situ generated ammonium hydroxide, and a nominal 4 wt % V 2 O 5 was impregnated over the calcined support (773 K) by adopting a wet impregnation technique. A commercial TiO 2 (anatase) sample was also used in this study for comparison purposes. The characterization results suggest that the Ga 2 O 3 −TiO 2 mixed oxide, calcined at 773 K, primarily consists of a mixture of TiO 2 anatase and α-Ga 2 O 3 . In the case of the V 2 O 5 /Ga 2 O 3 −TiO 2 catalyst, the impregnated V 2 O 5 is in a highly dispersed state on the surface of the mixed oxide. Under the influence of thermal treatments from 773 to 1073 K, the dispersed vanadium oxide promotes the transformation of anatase to rutile and α-Ga 2 O 3 to β-Ga 2 O 3 and is accompanied by a loss in the specific surface area of the samples. In particular, the gallia in the V 2 O 5 /Ga 2 O 3 −TiO 2 catalyst retards the transformation of anatase into rutile. The Ti 2p, Ga 3d, and V 2p photoelectron peaks of the V 2 O 5 /Ga 2 O 3 −TiO 2 sample are highly sensitive to the calcination temperature. The intensity of the Ti 2p line increased with increasing calcination temperature and an opposite 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 vanadium oxide in the V 2 O 5 /Ga 2 O 3 −TiO 2 catalyst interacts preferably with the gallium 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 almost equally at 973 and 1073 K calcination temperatures, respectively.