Oxidative co-dehydrogenation of ethane and propane over h-BN as an effective means for C-H bond activation and mechanistic investigations

Hexagonal boron nitride (h-BN) is a highly selective catalyst for oxidative dehydrogenation of light alkanes to produce the corresponding alkenes. Despite intense recent research effort, many aspects of the reaction mechanism, such as the observed supra-linear reaction order of alkanes, remain unresolved. In this work, we show that the introduction of a low concentration of propane in the feed of ethane oxidative dehydrogenation is able to enhance the C2H6 conversion by 47%, indicating a shared reaction intermediate in the activation of ethane and propane. The higher activity of propane makes it the dominant radical generator in the oxidative co-dehydrogenation of ethane and propane (ODEP). This unique feature of the ODEP renders propane an effective probe molecule to deconvolute the two roles of alkanes in the dehydrogenation chemistry, i.e., radical generator and substrate. Kinetic studies indicate that both the radical generation and the dehydrogenation pathways exhibit a first order kinetics toward the alkane partial pressure, leading to the observed second order kinetics of the overall oxidative dehydrogenation rate. With the steady-state approximation, a radical chain reaction mechanism capable of rationalizing observed reaction behaviors is proposed based on these insights. This work demonstrates the potential of ODEP as a strategy of both activating light alkanes in oxidative dehydrogenation on BN and mechanistic investigations. (c) 2022, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.