Surface Characterization of La2O3−TiO2 and V2O5/La2O3−TiO2 Catalysts

The techniques of X-ray diffraction, O 2 chemisorption, FT-Raman, and X-ray photoelectron spectroscopy were utilized to characterize La 2 O 3 −TiO 2 composite oxide and V 2 O 5 /La 2 O 3 −TiO 2 catalyst calcined at 773 and 1073 K temperatures. The investigated La 2 O 3 −TiO 2 (1:5 mole ratio) mixed oxide was obtained by a homogeneous coprecipitation method with in situ generated ammonium hydroxide. A nominal 12 wt % V 2 O 5 was impregnated over the calcined (773 K) composite oxide by adopting a wet impregnation method from ammonium metavanadate dissolved in aqueous oxalic acid solution. The characterization results suggest that the calcined La 2 O 3 −TiO 2 mixed oxide primarily consists of a mixture of TiO 2 anatase and La−Ti oxides. The La 2 O 3 −TiO 2 also accommodates a monolayer equivalent of vanadia in a highly dispersed state. The O 1s, Ti 2p, La 3d, and V 2p photoelectron peaks of the V 2 O 5 /La 2 O 3 −TiO 2 sample are highly sensitive to the calcination temperature. The XPS line shapes and the corresponding binding energies indicate that the dispersed vanadium oxide interacts selectively with the lanthana portion of the La 2 O 3 −TiO 2 mixed oxide and readily forms a LaVO 4 compound. The XRD and FT-Raman techniques, in particular, provide direct evidence for the formation of LaVO 4 compound. Interestingly, the presence of lanthana in V 2 O 5 /La 2 O 3 −TiO 2 catalysts retards the phase transformation of anatase into rutile under the influence of vanadia.