(740h) Investigating Surface and Gas-Phase Chemistries during the Boron Nitride-Catalyzed Oxidative Dehydrogenation of Propane
Over the last years, we have identified boron-based materials, such as hexagonal boron nitride, as a new class of ODH catalysts. These materials offer improved selectivity towards propylene during the ODH of propane and show decreased yields of combustion side products. While spectroscopic characterization has identified BO3-type surface structures as possible active sites, the reaction mechanism that affords the unique selectivity of boron-based catalysts remains unknown. In this contribution, we combine catalytic activity measurements with quantum chemical calculations to propose that the remarkable product distribution during boron-catalyzed ODH can be rationalized by a combination of surface-mediated formation of radicals over metastable sites and their sequential propagation in the gas phase. Based on known radical propagation steps, we quantitatively describe the oxygen pressure-dependent relative formation of the main product propylene and by-product ethylene. The free radical intermediates are most likely what differentiates this catalytic system from less selective vanadium-based catalysts. Furthermore, this work also highlights the role of water, formed during the reaction, in modulating the reactivity of boron nitride catalysts. These investigations provide a new paradigm that considers gas phase chemistry for the design of improved ODH catalysts.