Atmosphere-pretreatment-induced structural reorganization of Al2O3-supported phosphorus oxynitride for enhanced catalytic activity in ethylbenzene direct dehydrogenation

Non-metallic materials have attracted continuous interest in the direct dehydrogenation (DDH) of ethylbenzene due to their coke resistance and environmental friendliness. However, the catalytic activity was limited by the exposed density of active sites in non-metal catalysts. Herein, we report an atmosphere-pretreatment strategy using H₂ or O₂ at 350 ℃ to improve the exposure of active sites in Al₂O₃-supported phosphorus oxynitride (PNO) catalysts, thereby enhancing their catalytic performance in DDH of ethylbenzene. XPS, FTIR, and in situ DRIFTS analyses demonstrated that H₂ or O₂ pretreatment partially cleaved P–N bonds in the P₃N₅ framework, inducing structural reorganization and exposing the inner N₂P = O groups, thereby increasing the active site density. Among them, the H₂-pretreated PNO/Al₂O₃ catalyst (PNO/Al₂O₃-H) exhibited the highest N₂P = O content (a 74.2 % increase compared with PNO/Al₂O₃), which resulted in the highest catalytic activity (X_EB=58.5 %) under high-concentration ethylbenzene feed (12.2 vol%). This work demonstrates, for the first time, the application of atmosphere pretreatment to phosphorus-nitrogen catalysts and proposes a novel strategy for regulating the active site in dehydrogenation catalysis.