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.