Vapour phase ammoxidation of toluene over vanadium oxide supported on Nb2O5–TiO2

Abstract

Vanadium oxide catalysts with V₂O₅ loadings ranging 1 to 9% (w/w) supported on 1∶1 wt% Nb₂O₅–TiO₂ mixed oxide have been prepared by the wet impregnation method. The calcined samples were characterized by X-ray diffraction (XRD), pulse oxygen chemisorption and temperature programmed desorption (TPD) of NH₃. Dispersion of vanadia was determined by oxygen chemisorption at 643 K in a dynamic method. At low V₂O₅ loadings, vanadia is found to be present in a highly dispersed state. X-Ray diffraction results also suggest that vanadium oxide exists in a highly dispersed state at lower loadings and in a crystalline V₂O₅ phase at higher vanadia loadings (5 wt% and above). The dispersion of vanadia was found to decrease with V₂O₅ loading due to the formation of V₂O₅ crystallites. The catalytic properties were evaluated for the vapor phase ammoxidation of toluene to benzonitrile and correlated with characterization results.