On the Importance of Benchmarking the Gas‐Phase Pyrolysis Reaction in the Oxidative Dehydrogenation of Propane

Abstract

The oxidative dehydrogenation of propane (ODP) proceeds catalytically on a gas-solid interface (heterogeneous reaction) and/or in the gas phase (homogeneous reaction) via a radical chain process. ODP may therefore combine interrelated contributions from the heterogeneous dehydrogenation and gasphase reactions, which can be initiated by a catalyst. This study demonstrates that relatively high propene and ethene selectivities (ca. 80 % and 10 %) and propane conversions (viz., 10 % at 500 °C) can be achieved with an empty quartz reactor, which is comparable to the performances of state-of-the-art ODP catalysts (boron-based or supported VO x ). Optimization of the post-catalytic volume of a h-BN catalyst bed tested at 490 °C allows to increase the conversion of propane from 9 % to 15 % at a propene selectivity of 77 %, highlighting this parameter as an important variable for improving catalytic ODP performances.

Kinetic Insights into Boron-Based Materials Catalyzed Oxidative Dehydrogenation of Light Alkanes

“…However, due to the overoxidation of propylene to carbon monoxide and carbon dioxide, the propylene selectivity of vanadium-based catalysts decreases rapidly with the increase in the propane conversion, limiting the propylene yield to below 20%. 54 In comparison, the drop in the propylene selectivity with an increase in propane conversion is much less steep on boron-based catalysts (Figure 1d). This difference indicates that the activated oxygen species on boron-based catalysts cause less overoxidation of propylene at iso-conversion, compare to transitional metal oxides which follow the Mars-van Krevelen mechanism.…”

“…The selectivity-conversion relationship of boron-based catalysts is quite different from that on conventional vanadium-based ODH catalysts, but similar to the noncatalytic alkane oxidative pyrolysis, as reported by Müller and co-workers (Figure d) . Supported vanadium-based catalysts also exhibit a linear relationship between propylene selectivity and propane conversion.…”

“…The selectivity-conversion relationship of boron-based catalysts is quite different from that on conventional vanadium-based ODH catalysts, but similar to the noncatalytic alkane oxidative pyrolysis, as reported by Muller and coworkers (Figure 1d). 54 Supported vanadium-based catalysts also exhibit a linear relationship between propylene selectivity and propane conversion. However, due to the overoxidation of propylene to carbon monoxide and carbon dioxide, the propylene selectivity of vanadium-based catalysts decreases rapidly with the increase in the propane conversion, limiting the propylene yield to below 20%.…”

“…In comparison, the drop in the propylene selectivity with an increase in propane conversion is much less steep on boron-based catalysts (Figure d). This difference indicates that the activated oxygen species on boron-based catalysts cause less overoxidation of propylene at iso-conversion, compare to transitional metal oxides which follow the Mars-van Krevelen mechanism. , Revealingly, the linear selectivity-conversion relationship of boron-based catalysts coincides with that of noncatalytic propane oxidative pyrolysis . This implies that the reaction scheme of the ODH catalyzed by boron-based catalysts is analogous to noncatalytic alkane oxidative pyrolysis, which occurs through a gas-phase radical reaction pathway.…”

“…55,56 Revealingly, the linear selectivity-conversion relationship of boron-based catalysts coincides with that of noncatalytic propane oxidative pyrolysis. 54 This implies that the reaction scheme of the ODH catalyzed by boron-based catalysts is analogous to noncatalytic alkane oxidative pyrolysis, which occurs through a gas-phase radical reaction pathway.…”