On the Mesoporogen-Free Synthesis of Single-Crystalline Hierarchically Structured ZSM-5 Zeolites in a Quasi-Solid-State System

Hierarchically structured zeolites (HSZs) have gained much academic and industrial interest owing to their multiscale pore structures and consequent excellent performances in varied chemical processes. Although a number of synthetic strategies have been developed in recent years, the scalable production of HSZs single crystals with penetrating and three‐dimensionally (3‐D) interconnected mesopore systems but without using a mesoscale template is still a great challenge. Herein, based on a steam‐assisted crystallization (SAC) method, we report a facile and scalable strategy for the synthesis of single‐crystalline ZSM‐5 HSZs by using only a small amount of micropore‐structure‐directing agents (i.e., tetrapropylammonium hydroxide). The synthesized materials exhibited high crystallinity, a large specific surface area of 468 m2 g−1, and a pore volume of 0.43 cm3 g−1 without sacrificing the microporosity (≈0.11 cm3 g−1) in a product batch up to 11.7 g. Further, a kinetically controlled nucleation–growth mechanism is proposed for the successful synthesis of single‐crystalline ZSM‐5 HSZs with this novel process. As expected, compared with the conventional microporous ZSM‐5 and amorphous mesoporous Al‐MCM‐41 counterparts, the synthesized HSZs exhibited significantly enhanced activity and stability and prolonged lifetime in model reactions, especially when bulky molecules were involved. Full steam ahead! Based on the steam‐assisted crystallization (SAC) approach, ZSM‐5‐type single‐crystalline hierarchically structured zeolites with penetrating and three‐dimensionally well‐interconnected mesoporosity have been obtained by using no mesoporogens and a minimized amount of microporous‐structure‐directing agent, tetrapropylammonium hydroxide (see figure).