Preparation of phthalimide by ammoxidation of <i>o</i>-xylene and characterization of V-Cr-O/SiO₂ catalyst

Abstract

Phthalimide, as an important intermediate of organic synthesis, has been prepared with high yield by ammoxidation of <i>o</i>-xylene over silica-supported vanadium-chromium oxide catalysts. Under suitable conditions, the molar yield of phthalimide can reach 89% with purity of 98.6%. The catalysts, prepared via wet impregnation method, have been characterized by BET, XPS and

XRD. Results show that vanadia and chromia form composite oxides, which exist mostly in the pores of silica. Their concerted catalytic function is the main reason for high activity. Vanadium exists mainly as pentavalent and chromium mainly as trivalent in the V-Cr-O/SiO₂ catalysts, with their oxidation states changing in the redox cycles. The additive chromium can interact with the

surface vanadium oxide phase and alter the structure of vanadia, which delays the formation of crystalline V₂O₅ and increases the catalytic activity and selectivity.