Si/Al ratio induced structure evolution during desilication-recrystallization of silicalite-1 to synthesize nano-ZSM-5 catalyst for MTH reaction

Introducing mesopores into nano-ZSM-5 zeolite could further shorten its micropore length and significantly enhance its catalytic stability in methanol to hydrocarbons (MTH) reaction. In this work, a series of hierarchical nano-ZSM-5 were synthesized by desilication-recrystallization of silicalite-1. Through adjusting the NaAlO2 additive amount, SiO2/Al2O3 feed ratio was controlled to induce the structure evolution of ZSM-5. Hollow structured nano-ZSM-5 was synthesized at high SiO2/Al2O3 feed ratio, while mesopores were further created in the shell of hollow nano-ZSM-5 with low SiO2/Al2O3 ratio. The acid amount of ZSM-5 gradually increased from 0.13 to 0.91 mmol g(-1) and the acid strength also enhanced with decreasing the SiO2/Al2O3 ratio from 400 to 25. The strong acidity promoted aromatization reaction and the sample prepared with a SiO2/Al2O3 ratio of 25 showed the highest aromatics selectivity of 56.45%. Under suitable SiO2/Al2O3 ratio of 50, synthesized nanoZSM-5 possessed large external surface area of 133 m(2) g(-1) and proper acidity of 0.66 mmol g(-1), endowing it long lifetime of 132 h. The adjustable pore structure and acidity achieved by controlling the Si/Al ratio during the desilication-recrystallization of silicalite-1 provides possibility for the directional preparation of ZSM-5 with long lifetime and high selectivity for other MTH reaction.