Preparation of Al-rich hierarchical zeolites by conventional alkali treatment: Defects as mesopore directing agents

Abstract

In industry, it is highly desired to prepare Al-rich hierarchical zeolites by conventional alkali treatment without the use of costly chemical and special process. Here we provide an alternative strategy in which crystal defects are employed as mesopore directing agents. The effective elimination of the intracrystalline defects induces the generation of mesoporous structure in the alkali treatment process. Thus, the limitation originating from the framework Si/Al ratio of parent zeolite is circumvented. This strategy holds all merits of the conventional alkali treatment approach, which is industrially unfavorable. As an example, the Al-rich hierarchical ZSM-5 zeolites with very low Si/Al ratios were successfully prepared. The obtained Al-rich hierarchical zeolites were characterized by XRD, XRF, SEM, TEM, N₂ adsorption-desorption, in-situ IR, MAS NMR and NH₃-TPD. The results showed that Si/Al ratios of the prepared hierarchical ZSM-5 zeolites were around 10 and the increases of external surface area and mesoporous volume were up to 2.6 and 3.7 times respectively in comparison with parent zeolite. Moreover, the constructed mesopores were interconnected open channels. In the catalytic cracking of 1,3,5-triisopropylbenzene, the Al-rich hierarchical ZSM-5 zeolites exhibited an excellent performance because of the improved diffusion of reactant and product.