Insights into the structural requirements for oxidative dehydrogenation of propane on crystalline Mg-V-O catalysts

Abstract

MgV2O6, α-Mg2V2O7 and Mg3V2O8 model catalysts with high phase purity were prepared and studied in the oxidative dehydrogenation (ODH) of propane to determine the active and selective Mg-V-O crystalline structures required for the propane ODH reaction. Initial activities and selectivities, and rate constants for the propane ODH (k1), propane combustion (k2) and propylene combustion (k3) reactions were rigorously measured within the kinetically controlled regime. MgV2O6 exhibited the highest propane turnover rates, but it was not a selective phase for the formation of propylene, due to the favorable propylene combustion on its surface reflected by the high k3/k1 ratio. α-Mg2V2O7 exhibited both superior propane ODH rates and propylene selectivity relative to Mg3V2O8, indicating that α-Mg2V2O7 consisting of dimeric V2O7 units is intrinsically more active and selective than Mg3V2O8 containing isolated VO4 tetrahedra in the ODH of propane, consistent with the smallest k2/k1 and k3/k1 ratios measured for α-Mg2V2O7 among the three pure Mg vanadates. Moreover, a detailed comparison between the crystalline Mg-V-O catalysts and their physical mixtures in terms of the intrinsic activities and selectivities demonstrated no synergetic effects between either α-Mg2V2O7 and Mg3V2O8 or Mg3V2O8and MgO phases in the ODH of propane. This study provides directions for optimization of compositions and design of new structures based on the well-studied Mg-V-O catalysts towards the efficient synthesis of propylene from the ODH of propane.