Dispersion and reactivity of Mo/Nb2O5 catalysts in the ammoxidation of toluene to benzonitrile

A series of Mo/Nb2O5 catalysts were prepared with Mo loadings ranging from 2.5-15 wt% of Mo and characterized by X-ray diffraction (XRD), pulse oxygen chemisorption, temperature-programmed desoprtion of ammonia. Dispersion of molybdena was determined by oxygen chemisorption at 623 K in a dynamic method. At low Mo loadings molybdenum oxide is found to be present in a highly dispersed state. XRD results show the presence of crystalline MoO3 at higher Mo loadings (from 10 wt%). The dispersion of molybdena was found to decrease with increased Mo loading due to formation of MoO3. The catalytic properties were evaluated for the vapour phase ammoxidation of toluene to benzonitrile and are related to different characterization results.