An XPS study of La_2O_3 and In_2O_3 and In_2O_3 influence on the physicochemical properties of MoO_3/TiO_2 catalysts

摘要

To explore the influence of La_2O_3 and In_2O_3 doped TiO_2 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 La_2O_3-TiO_2 and the In_2O_3-TiO_2 binary oxide supports were prepared by a homogeneous coprecipitation method with in situ generated ammonium hydroxide and were deposited with MoO_3 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) La_2O_3-TiO_2 and In_2O_3-TiO_2 binary oxides are in X-ray amorphous state and exhibit reasonably high specific surface area. These supports also accommodate a monolayer equivalent of MoO_3 (12 wt.%) in a highly dispersed state on the surface. Both La_2O_3 and In_2O_3 dopants show a strong influence on the electronic properties of the MoO_3/TiO_2 catalysts as eyidenced 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.