Interplay of On- and Off-Surface Processes in the B2O3-Catalyzed Oxidative Dehydrogenation of Propane: A DFT Study

Metal-free boron-based catalytic systems are growing to be promising choices in the oxidative dehydrogenation (ODH) of light alkanes to olefins. However, the ambiguity in the understanding of the mechanism has impeded the improvement of novel catalytic systems. Herein, by using density functional theory (DFT), we mapped a complex reaction network for the B2O3-catalyzed ODH of propane, which displayed a typical feature of interplay between the on-surface and off-surface channels through the whole reaction from the initiation stage to the termination stage. The results showed that the interplay between the channels in the two regimes was necessary in two aspects: On one hand, to guarantee high selectivity for olefin products, the gaseous channels need the intervention of the surface sites to eliminate the oxygenated intermediates, for example, alkoxyl radicals, that would otherwise evolve into deep oxidation products. On the other hand, to maintain the high conversion of propane, the catalyst surface needs gaseous radicals to regenerate reactive >BO· species. The mechanism also well explained the catalytic role of trace water and addressed the surface dynamical restructuring, thus constituting a plausible comprehensive understanding of the ODH of propane catalyzed by an oxygenated boron system.