It’s a Gas: Oxidative Dehydrogenation of Propane over Boron Nitride Catalysts

Boron nitride and related boron-containing materials have recently been suggested as very promising catalysts in the oxidative dehydrogenation of propane. The high selectivity toward propylene at comparably high conversion significantly exceeds the performance of established vanadium-based catalysts. In the current work we show that the high selectivity toward propylene and ethylene is fully consistent with a gas-phase conversion mechanism and that it can be modeled reasonably well by the recent detailed microkinetic reaction mechanism of Hashemi and co-workers [Proc. Combust. Inst. 2019, 37, 461]. Our analysis, using six heterogeneous catalytic reaction pathways, each representing a hypothetical limit case, shows that the boron nitride catalyst is responsible for initiating the gas-phase chemistry. The increased conversion of propane in cases with water cofeed, as well as the trends in the selectivities of minor species upon dilution of the catalytic bed and upon varying the C3H8/O2 inlet ratio, as observed by Venegas and Hermans [Org. Process Res. Dev. 2018, 22, 1644], are here explained as gas-phase phenomena. Hence, the oxidative dehydrogenation of propane over boron nitride catalysts is an example of a coupled gas and catalytic chemistry system. The current work also highlights the importance of modeling of the complete heated zone, including the rear heat shields and reactor padding if present.