The Standard Oil of Ohio Company (SOHIO) process is the oxidation/ammoxidation of propene over bismuth/molybdate catalysts. Studies in the heterogeneous systems show that bismuth is involved in the rate-determining hydrogen abstraction from propene in both cases, and may be involved in later steps of the process as well. Model studies support the intervention of bismuth(III) in the rate-determining step and molybdenum(VI) in later steps. Few model studies with bismuth-containing compounds have been reported. (C) 2004 Elsevier B.V. All rights reserved.