Tuning the oxidative dehydrogenation of propane mechanism by Pd–B/Al2O3 bifunctional catalysis through suppression of gas-phase radicals and enhancement of surface-mediated pathways

Abstract

Boron-based catalysts typically promote the oxidative dehydrogenation of propane through a gas-phase radical mechanism, achieving high propylene selectivity but limited propane conversion. In this study, palladium is incorporated into B/Al₂O₃ to construct a bifunctional Pd–B/Al₂O₃ catalyst that shifts the reaction pathway from a radical-dominated route to a surface-catalyzed Langmuir–Hinshelwood mechanism. This cooperative effect increases propane conversion while maintaining the propylene selectivity. Quantitative analysis of both gaseous and surface H₂O₂ indicates a likely shift in the reaction mechanism from a gas-phase radical pathway to a surface-catalyzed process. Combined in situ EPR, DRIFT, and XPS analyses, along with DFT calculations, reveal that Pd sites promote propane adsorption and substantially lower the dehydrogenation barrier of C₃H₇, while adjacent BO_x(OH)_3−x species selectively oxidize hydrogen to H₂O, mitigating over-oxidation. The presence of surface B–OH groups further improves performance, increasing propylene selectivity by approximately 5% under humidified conditions. These findings highlight a new strategy for designing efficient ODHP catalysts by harnessing bifunctional active sites to promote surface-mediated reaction pathways.