Controlled synthesis of ZSM-5 zeolite with an unusual Al distribution in framework from natural aluminosilicate mineral

摘要

Precisely tuning the location of Al atoms in zeolite framework that plays a critical role in determining the catalytic performance of zeolite based catalysts has attracted considerable attention. In this article, we present an organotemplate-free approach for the controllable synthesis of ZSM-5 zeolite with a high content of Al pairs selectively located at the channel intersections, which is achieved by using a submolten salt (SMS) depolymerized rectorite as both the Al source and heteropical crystalline seeds. The quasi in-situ characterizations tracking the zeolite crystallization process reveal that the depolymerized rectorite with abundant oligomeric aluminosilicate species and Al-O-(Si-O)(1,2)-Al sequences plays dual roles in the synthesis of ZSM-5 zeolite. These oligomeric aluminosilicate species like 5- and 6-membered ring structures serve as the crystalline seeds to promote the zeolite nucleation; simultaneously, the Al-O-(Si-O)(1,2)-Al sequences are in-situ transformed into the final zeolite framework leading to the generation of numerous Al pairs selectively located at the channel intersections. Such an unusual Al distribution endows the synthesized ZSM-5 zeolite with excellent catalytic performance in methanol to aromatics (MTA) reaction. Our strategy provides a sustainable and efficient way to design and synthesize high-performance zeolites with special framework Al distributions for catalytic applications.