Vapor-phase selective aerobic oxidation of benzylamine to dibenzylimine over silica-supported vanadium-substituted tungstophosphoric acid catalyst

Abstract

Silica-supported vanadium-substituted tungstophosphoric acid (TPAV_x, x = 0–3) catalysts were prepared by an impregnation method and their physico-chemical properties derived from different spectroscopic techniques. The characterization results confirmed the incorporation of vanadium into the framework of heteropoly tungstate anion and the Keggin structure remained intact on SiO₂. Vapor-phase aerobic oxidation of benzylamine was evaluated over these catalysts and dibenzylimine was obtained as the selective oxidative condensation product. Under optimized reaction conditions, 90% conversion of benzylamine with 95% selectivity to dibenzylimine was achieved over 20 wt% TPAV₁/SiO₂ catalyst. The catalyst showed constant activity, after an initial decrease by about 10%, during the time on stream analysis. Controllable acidity and redox properties of the catalyst were accountable for high catalytic activity and selectivity. A plausible reaction mechanism is also elucidated.