The formation of active species for oxidative dehydrogenation of propane on magnesium molybdates

Pure and mixed magnesium molybdate phases (MoO3, MgMoO4, and MgMo2O7) have been examined for the oxidative dehydrogenation reaction of propane. The re sults are very sensitive to the stoichiometry and method of preparation. Th e catalysts exhibiting superior activity and selectivity are characterized by a unique temperature-programmed reduction peak that is not present for t he poorly active or selective catalysts. Mixtures of MgMoO4 and MoO3 or MgM oO4 and MgMo2O7, materials that perform poorly by themselves, show signific ant improvements in performance upon heating. The solid-state interactions leading to these improvements correspond to the appearance of the character istic reduction peak. The results suggest that the beneficial synergistic e ffects seen with mixtures of inactive phases are due to formation of a new phase or species, rather than remote communication between phases (e.g., ox ygen spillover).