Dynamic switch of CTAB as the sole template for the synthesis hierarchically porous ZSM-5 through a straightforward conventional static hydrothermal method

Abstract

At present, the construction of hierarchically porous ZSM-5 molecular sieves using only cetyltrimethylammonium bromide (CTAB) as the template represents a major challenge in the field of molecular sieve synthesis. In this work, hierarchically porous ZSM-5 zeolite was synthesized via a straightforward conventional static hydrothermal method, employing CTAB as the sole template agent derived from CTAB-encapsulated silica sphere precursors. By controlling the dissolution rate of silica spheres, the release rate of CTAB is regulated, enabling the synthesis of pure-phase hierarchical porous ZSM-5 zeolite. The influences of alkalinity, aging time, Si/Al ratio, CTAB content and addition method, and crystallization time on the construction of hierarchically porous ZSM-5 molecular sieves were examined. The experimental results indicate that the crystallization process in this system proceeds in the order: MFI → MFI + kenyaite → MFI + quartz. Additionally, by managing the crystallization process, we systematically examined the formation process of impurities and established the optimal conditions for synthesizing pure-phase hierarchically porous ZSM-5 molecular sieves in this system. Moreover, the as-prepared hierarchically porous ZSM-5 molecular sieves demonstrated enhanced selectivity towards light olefins in the MTP reaction.