UC Berkeley

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 (for NH3/C3H6 = 0-2) and oxygen (for O2/C3H6 ≥ 1.5) partial pressures, with an activation energy (Ea = 22 kcal/mol) comparable to that for propene oxidation, suggesting the same rate-limiting step for both reactions. We propose two N-containing species are relevant at ammoxidation conditions: adsorbed NH3 on surface Bi3+ ions that reacts with a propene derivative to form products with C-N bonds, and a few metastable M-NHx (M = Mo, Bi; x = 1, 2) groups that are very sensitive to destruction by water, but that are responsible for NH3 oxidation to N2. A proposed reaction mechanism and model that captures the experimental trends in product distribution as a function of partial pressures and temperature are presented.