Enhanced hydrothermal stability and propylene selectivity by e-beam irradiation-induced hierarchical HZSM-5 additives

Abstract

In this work, hierarchical H-ZSM-5 catalysts (Si/Al molar ratio = 20, 30) with different levels of mesoporosity and acid strength were prepared via e-beam irradiation post-synthesis treatment and tested as propylene-increasing FCC additives. It was found that higher specific surface areas and highly accessible porous systems were obtained among the irradiated samples. Combination of ²⁷Al, ¹H MAS NMR and NH₃-TPD methods showed that upon irradiation, part of framework tetrahedral Al atoms was removed as non-framework Al in flexible coordination with the Si-OH groups (either framework or non-framework defects), manipulating the acidic strength and the stability against hydrothermal dealumination. The enhanced selectivity and stability towards propylene production over the irradiated H-ZSM-5 samples were attributed to an integration of the reserved population of medium acid sites into the highly accessible hierarchical network.