Deconstructing the black box of zeolite crystallization gels by species-specific isolation

Abstract

The crystallization of zeolites in gel-based systems, the cornerstone of their industrial synthesis, has long remained a “black box” due to the inability to characterize specific aluminosilicate species within the amorphous network. This obscurity precludes rational design. Herein, we report a deconstruction-dialysis methodology that disassembles the gel and isolates the entire suite of particulate intermediates. Applying this to the MTW-type zeolite, we quantitatively identify a hierarchy of species: long-range-ordered crystals (MTW-t-C), short-range but highly ordered precursors (MTW-t-HOP), poorly ordered particles (POPs), and monomers/oligomers. We demonstrate that HOPs are the primary building blocks for crystal growth via nonclassical particle attachment. More importantly, by tracking the evolution of these species and combining with the Kolmogorov–Johnson–Mehl–Avrami (KJMA) model, we delineate the crystallization into three stages: nucleation, particle attachment, and molecular addition. We reveal that the final properties of the zeolite are governed by a dynamic competition between the rate of HOP attachment and that of structural/elemental maturation (dealumination). This competition dictates the temporal evolution of defects, porosity, and composition. Our work dismantles the gel black box by establishing a species-resolved crystallization pathway, offering a universal strategy for mechanistic understanding in complex media and thereby paving the way for the precise synthesis of zeolites.