Phase transformation study of titania in V2O5/TiO2 and MoO3/TiO2 catalysts by X-ray diffraction analysis

Abstract

The effect of the presence of vanadia or molybdena and the thermal treatment on the phase transformation of titania in V2O5/TiO2 and Mo03/Ti02 catalysts was investigated using X-ray powder diffraction (XRD) analysis. The titania support used was a commercial sample from Harshaw containing anatase together with a small quantity of graphite. The XRD results suggest that when the TiO2 support is calcined at 973 K, anatase is partially transformed into rutile, whereas at 1273 K it is totally converted to rutile. In the presence of V2O5 the temperature of partial conversion is reduced to 813 K, and a total transformation is noted already at 973 K. MoO3 also induces this transformation, but is less effective than V2O5. XRD results further show that when the V2O5/TiO2 catalyst is subjected to calcination at 973 K, no crystalline V2O5 phase is present. The same is not true for MoO3, which is present in a crystalline state at this calcination temperature. This study reveals clearly that vanadia and molybdena behave differently when impregnated on the same titanium dioxide support.