Taming Gas-Phase Radical Contributions to the Oxidative Dehydrogenation of Propane by Tailoring Defect Structures in Boron Nitride

Abstract

Hexagonal boron nitride (h-BN) is a promising catalyst for highly selective oxidative dehydrogenation of propane (ODHP). Defect engineering exposes unsaturated boron (B) sites, which form oxy/hydroxylated B-based active ensembles (i.e., B(OH)xO3–x) that are crucial for ODHP. The reaction proceeds via both surface and gas-phase radical pathways, making it critical to clarify the gas-phase contribution over N-defective h-BN. Here, we synthesized a series of N-defective BN (BN-x) samples via an N-repair strategy. Catalytic evaluation and in situ diffuse reflectance Fourier transform infrared spectra (DRIFTS) reveal that BN-1, with the highest N defect density, achieves enhanced ODHP activity by exposing more B(OH)xO3–x active ensembles, as corroborated by X-ray absorption near edge structure (XANES). Kinetic studies, void-space filling, and water co-feeding experiments collectively demonstrate that the number of defects in BN-1 helps tame the gas-phase pathway contribution in the ODHP. Density-functional theory (DFT) calculations confirm that N-defect sites promote O2 dissociation, thereby inducing active >B–B–O• sites that increase the reactivity and stabilization of radicals (e.g., HOO•, C3H7•, and CH3•), leading to an increase in the contribution of the gas-phase pathway. Additionally, >B–B–O• facilitates i-C3H7 generation and initiates a gas phase reaction with a lower dehydrogenation barrier, and water-assisted active site regeneration is thermodynamically more favorable.