| Abstract
| - The techniques of X-ray photoelectron spectroscopy, X-ray diffraction, FT-infrared, and O2 chemisorptionwere employed to characterize a specially obtained Ga2O3−TiO2 mixed oxide and V2O5/Ga2O3−TiO2 catalystcalcined at different temperatures from 773 to 1073 K. The Ga2O3−TiO2 (1:5 mole ratio based on the oxides)mixed oxide was synthesized by a homogeneous coprecipitation method with in situ generated ammoniumhydroxide, and a nominal 4 wt % V2O5 was impregnated over the calcined support (773 K) by adopting a wetimpregnation technique. A commercial TiO2 (anatase) sample was also used in this study for comparisonpurposes. The characterization results suggest that the Ga2O3−TiO2 mixed oxide, calcined at 773 K, primarilyconsists of a mixture of TiO2 anatase and α-Ga2O3. In the case of the V2O5/Ga2O3−TiO2 catalyst, theimpregnated V2O5 is in a highly dispersed state on the surface of the mixed oxide. Under the influence ofthermal treatments from 773 to 1073 K, the dispersed vanadium oxide promotes the transformation of anataseto rutile and α-Ga2O3 to β-Ga2O3 and is accompanied by a loss in the specific surface area of the samples.In particular, the gallia in the V2O5/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 sample are highly sensitive to thecalcination temperature. The intensity of the Ti 2p line increased with increasing calcination temperature andan opposite trend was noted in the case of Ga 3d and V 2p lines. The XPS line shapes and the correspondingbinding energies indicate that the dispersed vanadium oxide in the V2O5/Ga2O3−TiO2 catalyst interactspreferably with the gallium oxide. The V/Ti and V/Ga atomic ratios as determined by XPS measurementsreveal that more vanadium is confined to Ti than Ga at 773 and 873 K and almost equally at 973 and 1073K calcination temperatures, respectively.
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