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

Abstract

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.