(688f) Experimental and Theoretical Investigations of Propene Ammoxidation to Acrylonitrile over Bismuth Molybdate
Propene ammoxidation over Bi2Mo3O12 was investigated to elucidate product (acrylonitrile, acetonitrile, HCN, acrolein, N2, etc.) formation pathways. Propene consumption rate is first order in propene and zero order in ammonia and oxygen partial pressures, has an activation energy (Ea = 22 kcal/mol) comparable to that for propene oxidation, suggesting that the rate-limiting step for both reactions is the same. Two N-containing species are relevant at ammoxidation conditions: adsorbed NH3 on surface Bi3+ ions that reacts with vinyl alkoxide species to form products with C-N bonds, and metastable Mo-NH2 groups that are responsible for NH3 oxidation to N2. The proposed reaction mechanism and model of the reaction kinetics captures the experimental trends in product distribution as a function of partial pressures and temperature. DFT calculations of the elementary steps comprising the reaction pathway support the proposed mechanism, as well as revealing what processes control product selectivity.