NH3-efficient ammoxidation of toluene by hydrothermally synthesized layered tungsten-vanadium complex metal oxides

Abstract

Hydrothermally synthesized WVO layered metal oxides (WVO) are studied for the vapor phase ammoxidation of toluene to benzonitrile (PhCN). Under similar conversion levels at 400°C, WVO shows higher selectivity (based on toluene) to PhCN and lower selectivity to COx than conventional V-based catalysts (V2O5 and VOx/TiO2). Under the conditions of high contact time, WVO shows 99.7% conversion of toluene and 93.5% selectivity to PhCN. Another important feature of WVO is high NH3-utilization efficiency in ammoxidation, which originates from the lower activity of WVO for NH3 oxidation than that of V2O5. In situ infrared (IR) study shows that toluene is oxidized by the surface oxygen species of W83V17 to yield benzaldehyde which undergoes the reaction with adsorbed NH3 to give benzonitrile. Model reaction studies with WVO suggest that the rate of NH3 conversion to PhCN in the benzaldehyde+NH3+O2 reaction is 3 times higher than the rate of NH3 oxidation to N2 in the NH3+O2 reaction. It is shown that the high NH3-efficiency of WVO is caused by the preferential reaction of NH3 in PhCHO+NH3+O2 over NH3+O2 reaction.