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

Graphical abstract Highlights • Intrinsic catalytic performances of MgV 2 O 6 , α-Mg 2 V 2 O 7 , Mg 3 V 2 O 8 and their biphasic mixtures were obtained in the ODH of propane. • α-Mg 2 V 2 O 7 consisting of corner-shared V-O-V units is the most selective Mg-V-O phase for the ODH of propane to propylene. • No synergetic effect exists between either α-Mg 2 V 2 O 7 and Mg 3 V 2 O 8 or Mg 3 V 2 O 8 and MgO in the ODH of propane to propylene. Abstract MgV 2 O 6 , α-Mg 2 V 2 O 7 and Mg 3 V 2 O 8 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 (k 1), propane combustion (k 2) and propylene combustion (k 3) reactions were rigorously measured within the kinetically controlled regime. MgV 2 O 6 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 k 3 / k 1 ratio. α-Mg 2 V 2 O 7 exhibited both superior propane ODH rates and propylene selectivity relative to Mg 3 V 2 O 8 , indicating that α-Mg 2 V 2 O 7 consisting of dimeric V 2 O 7 units is intrinsically more active and selective than Mg 3 V 2 O 8 containing isolated VO 4 tetrahedra in the ODH of propane, consistent with the smallest k 2 / k 1 and k 3 / k 1 ratios measured for α-Mg 2 V 2 O 7 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-Mg 2 V 2 O 7 and Mg 3 V 2 O 8 or Mg 3 V 2 O 8 and 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. [ABSTRACT FROM AUTHOR]