Amorphous high-surface-area vanadium aluminum oxynitrides (VAlON) prepared by nitridation of an amorphous oxide precursor exhibit a high acrylonitrile yield in propane ammoxidation at very low contact time, indicating the participation of ammonia dehydrogenated species in the ammoxidation of alkanes. The productivity of the VAlON catalysts (1 of ACN/kg catalyst/h) was markedly improved as compared with known oxide systems.