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 H 2 or O 2 at 350 ℃ to improve the exposure of active sites in Al 2 O 3 -supported phosphorus oxynitride (PNO) catalysts, thereby enhancing their catalytic performance in DDH of ethylbenzene. XPS, FTIR, and in situ DRIFTS analyses demonstrated that H 2 or O 2 pretreatment partially cleaved P–N bonds in the P 3 N 5 framework, inducing structural reorganization and exposing the inner N 2 P = O groups, thereby increasing the active site density. Among them, the H 2 -pretreated PNO/Al 2 O 3 catalyst (PNO/Al 2 O 3 -H) exhibited the highest N 2 P = O content (a 74.2 % increase compared with PNO/Al 2 O 3 ), 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.