Why Boron Nitride is such a Selective Catalyst for the Oxidative Dehydrogenation of Propane.

In recent years, boron-containing materials and in particular boron nitride, have been identified as highly selective catalysts for the oxidative dehydrogenation of alkanes such as propane. Until now, no mechanism exists that can explain both the unprecedented selectivity, the observed surface oxyfunctionalization, as well as the peculiar kinetic features of the reaction.  In this contribution we combine catalytic activity measurements with quantum chemical calculations to put forward a bold new hypothesis. Based on our results, we argue that the remarkable product distribution 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. Indeed, although the mechanism of this benchmark catalyst is also not yet unambiguously established, it is generally assumed that radical intermediates are rapidly converted to stable molecular products on the catalyst surface before they can desorb. The new insights obtained in this work highlight the importance of the mechanistic differences between these two catalyst families which could lead to better design principles and improved catalytic systems.