X-ray photoelectron spectroscopy study of V2O5 dispersion on a nanosized Al2O3-TiO2 mixed oxide

The Al2O3-TiO2 (1:1.3 mole ratio) was obtained from dilute mixture solution s of sodium aluminate and titanium tetrachloride by hydrolysis with in situ generated ammonium hydroxide. The calcined (773 K) mixed oxide powder was constituted from nanosized anatase crystallites and amorphous alumina. A no minal 16 wt % V2O5 was impregnated on the calcined Al2O3-TiO2 support by us ing an oxalic acid solution of NH4VO3. To investigate thermal stability of Al2O3-TiO2 and the dispersion of vanadia on its surface these samples were subjected to thermal treatments from 773 to 1073 K and were examined by X-r ay photoelectron spectroscopy, X-ray diffraction, FT-infrared, and Oz chemi sorption techniques. The physicochemical characterization results revealed that the Al2O3-TiO2 mixed oxide is homogeneous and accommodates a monolayer equipment of V2O5 in a highly dispersed state when calcined at 773 K. The Ti/Al atomic ratio as determined by XPS suggests a coverage of Al2O3 by TiO 2. However, at higher calcination temperatures surface enrichment of alumin a occurs due to a concentration gradient. In the case of the V2O5/Al2O3-TiO 2 sample, an increase of calcination temperature also resulted in the decre ase of specific surface area and the dispersion of vanadium oxide. The impr egnated vanadium oxide also exhibited a noticeable influence on the phase t ransformation of titania anatase. The V/Ti and V/Al atomic ratios revealed that vanadium oxide is distributed equally on both tiania and alumina surfa ces when calcined at 773 K; however, surface segregation of vanadium oxide occurred on the titania surface at higher calcination temperatures.