Fifteen distinct MgO-V2O5, MgO-MoO3, MgO-V2O5-MoO3, and V2O5-MOO3 compositions were prepared using sol-gel chemistry and their selectivities and conversions for propane oxidative dehydrogenation (ODH) to propylene were measured. The vanadates were more active than the molybdates at lower temperatures; however, the molybdates exhibited higher selectivities at similar conversions. An increase in both ODH conversion and selectivity with molybdenum substitution on vanadium sites was also observed. These results demonstrate the importance of the bulk structure on the ODH reaction. In general, propylene selectivities increased with increasing conversions at temperatures above 673 K when oxygen depletion in the reactant stream occurred. Visible and UV Raman spectroscopy corroborates this result and helps focus attention on critical surface-specific information. A new Raman peak was observed for the partially reduced MgMoO4 and is associated with a three-coordinate surface oxygen. (C) 2004 Elsevier Inc. All rights reserved.