A viewpoint on catalytic origin of boron nitride in oxidative dehydrogenation of light alkanes

Oxidative dehydrogenation of light alkanes to alkenes is an attractive alternative route for industrial direct dehydrogenation because of favorable thermodynamic and kinetic characteristics, but encounters difficulties in selectivity control for alkenes because of over-oxidation reactions that produce a substantial amount of undesired carbon oxides. Recent progress has revealed that boron nitride is a highly promising catalyst in the oxidative dehydrogenation of light alkanes because of its superior selectivity for and high productivity of light alkenes, negligible formation of CO2, and remarkable catalyst stability. From this viewpoint, recent works on boron nitride in the oxidative dehydrogenations of ethane, propane, butane, and ethylbenzene are reviewed, and the emphasis of this viewpoint is placed on discussing the catalytic origin of boron nitride in oxidative dehydrogenation reactions. After analyzing recent progress in the use of boron nitride for oxidative dehydrogenation reactions and finding much new evidence, we conclude that pure boron nitride is catalytically inert, and an activation period is required under the reaction conditions; this process is accompanied by an oxygen functionalization at the edge of boron nitride; the B-O species themselves have no catalytic activity in C-H cleavage, and the B-OH groups, with the assistance of molecular oxygen, play the key role in triggering the oxidative dehydrogenation of propane; the dissociative adsorption of molecular oxygen is involved in the reaction process; and a straightforward strategy for preparing an active boron nitride catalyst with hydroxyl groups at the edges can efficiently enhance the catalytic efficacy. A new redox reaction cycle based on the B-OH sites is also proposed. Furthermore, as this is a novel catalytic system, there is an urgent need to develop new methods to optimize the catalytic performances, clarify the catalytic function of boron species in the alkane ODH reactions, and disclose the reaction mechanism under realistic reaction conditions.