Propene ammoxidation over Bi2Mo3O12 was investigated to elucidate product (acrylonitrile, acetonitrile, HCN, acrolein, N-2, etc.) formation pathways. Propene consumption rate is first order in propene and zero order in ammonia (for NH3/C3H6 = 0-2) and oxygen (for O-2/C3H6 >= 1.5) partial pressures, with an activation energy (E-a = 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 N-2. A proposed reaction mechanism and model that captures the experimental trends in product distribution as a function of partial pressures and temperature are presented. (C) 2016 Elsevier Inc. All rights reserved.