The bulk structure and catalytic behavior of bulk mixed Mo-V-Sb-Nb-O catalysts in propane ammoxidation were investigated. These mixed oxides were prepared via a redox reaction between V5+ and Sb3+ in the presence of Mo6+ and Nb5+. The catalytic performance of these model catalysts exhibited a strong dependence on the phases present. The catalysts showing significant amounts of alpha-MoO3 phase exhibit low selectivity/yield in propane ammoxidation to acrylonitrile, while the presence of SbVO4 phase resulted in high activity and selectivity to acrylonitrile. It was demonstrated that the SbVO4 is the active phase in the formation of acrylonitrile while it is inefficient for propane oxidation to acrylic acid. (C) 2003 Elsevier B.V. All rights reserved.