An XPS study of La2O3 and In2O3 influence on the physicochemical properties of MoO3/TiO2 catalysts

To explore the influence of La2O3 and In2O3 doped TiO2 support on the dispersion and chemical nature of Mo-oxide species an investigation was undertaken by using XPS and other techniques. In this study, the La2O3-TiO2 and the In2O3-TiO2 binary oxide supports were prepared by a homogeneous coprecipitation method with in situ generated ammonium hydroxide and were deposited with MoO3 by adopting a wet impregnation technique. The Mo-containing catalysts and the corresponding supports were characterized by means of XRD, FTIR, XPS, and BET surface area methods. Characterization results suggest that the calcined (773 K) La2O3-TiO2 and In2O3-TiO2 binary oxides are in X-ray amorphous state and exhibit reasonably high specific surface area. These supports also accommodate a monolayer equivalent of MoO3 (12 wt.%) in a highly dispersed state on the surface. Both La2O3 and In2O3 dopants show a strong influence on the electronic properties of the MoO3/TiO2 catalysts as evidenced by a change in the XPS binding energies of these metal oxides. The XPS binding energy values further indicate that the dispersed molybdenum oxide is in Mo(VI) oxidation-state. However, the maximum broadening of Mo 3d as observed from full width at half-maximum values indicates that the presence of different Mo(VI) species on both the support surfaces. (C) 2001 Elsevier Science B.V All rights reserved.