Mesoporogen-Free Synthesis of Hierarchically Structured Zeolites with Variable Si/Al Ratios via a Steam-Assisted Crystallization Process

In the absence of additional mesoporous template, hierarchically structured zeolites (HSZs) with variable Si/Al ratios (30-150) have been successfully synthesized via a newly developed steam-assisted crystallization process. The synthesized materials were characterized with powder X-ray diffraction, nitrogen sorption measurement, scanning electron microscopy, transmission electron microscopy, inductively coupled plasma optical emission spectrometry, solid-state nuclear magnetic resonance, and ammonia temperature-programmed desorption. All these results prove that the synthesized materials feature high crystallinity (microporous framework) and auxiliary mesoporous structure. In the model reactions of isopropylbenzene and 1,3,5-triisopropylbenzene cracking, compared to purely microporous ZSM-5 counterparts, here synthesized HSZs exhibited markedly enhanced catalytic performances resulting from their enlarged external surface area and shortened diffusion length in the microporous system.