Light-assisted free radical initiation for efficient thermocatalytic propane oxidative dehydrogenation on defect-rich hexagonal boron nitride

Abstract

Oxidative dehydrogenation of propane (ODHP) offers a promising alternative to propane direct dehydrogenation. Hexagonal boron nitride (h-BN) has demonstrated high selectivity towards propylene, following a surface-mediated gas-phase radical mechanism. However, the initiation of radicals in this reaction requires high temperature. To tackle this challenge, we propose a novel approach of utilizing illumination to assist in radical initiation in the ODHP reaction. Here, we demonstrate that illumination enhances the activity of ODHP on the defect-rich h-BN. Specifically, propane conversion under illumination with an intensity of 800 mW cm⁻² at 450 °C nearly doubles compared to that in the non-illuminated condition, while maintaining a high propylene selectivity. Additionally, the apparent activation energy (E_a) was reduced from 192 kJ mol⁻¹ to 62 kJ mol⁻¹ with illumination. The effect of illumination on the E_a and product selectivity suggests that light does not change the fundamental characteristics of the reaction but lowers the E_a, thus promoting the reaction. Mechanistic investigations reveal that photo-induced electrons derived from h-BN are transferred to the BO_x active centers, facilitating radical initiation and enhancing the overall activity of ODHP. These findings not only offer valuable insights into the optimization of the ODHP reaction through light irradiation but also hold significant potential for other similar radical reactions.