Direct Organotemplate-Free Synthesis of Nanorod-Assembled Mordenite: Nucleation-Inducing Mechanism of Activated Natural Aluminosilicate Minerals

Abstract

Nanosized hierarchical zeolites, combining the advantages of both nanoscale crystal and hierarchical pore structure, exhibited superior catalytic performance due to their shorter diffusion paths, reduced mass resistance, and more accessible active sites. Here, different from the traditional synthesis methods that create nanocrystals by using crystal growth modifiers, inhibitors, and/or zeolite seeds, we report a sustainable and simple method, characterized by kinetically modulated crystallization, for synthesizing nanosized hierarchical mordenite (HR-MOR) from quasi-solid-phase activated kaolin (QSP-kaolin) and thermally activated diatomite (TAD). Benefiting from the self-assembled nucleation-inducing property of QSP-kaolin and the progressive dissolution characteristics of TAD, a nanorod-assembled HR-MOR was synthesized neither using any Al- and Si-containing chemical reagents nor involving any growth modifier and organic structure-directing agents (OSDAs). Compared to conventional mordenite, the HR-MOR has a larger external surface area, enhanced acid site accessibility, and framework Fe species, which endows it with the superior catalytic performance in benzylation reaction of benzene with benzyl alcohol. Our work provides a sustainable and low-cost alternative for the direct synthesis of nanosized zeolites, entirely eliminating the need for Al- and Si-based chemical reagents, zeolite seeds, growth modifiers, and OSDAs.