Controlling Crystallization Pathways: A Universal Na+/K+ Ion Switch for Mesostructure Engineering of Zeolites

Abstract

Precise mesostructure engineering of zeolites remains a formidable challenge due to the complexity of crystallization and precursor heterogeneity. Conventional methods often rely on costly organics or destructive post-synthetics, lacking simplicity and scalability. Herein, we report a facile and universal "Na⁺/K⁺ ion switch" strategy to precisely tailor the mesostructure of zeolite beta in a seed-induced system. Merely switching Na⁺ to K⁺ without altering other parameters redirects the crystallization pathway, yielding unique mulberry-like hollow nanocrystal assemblies (beta-K) instead of conventional dense single crystals (beta-Na). Through multi-curve kinetic analysis and visual tracking, we elucidate that K⁺ fosters moderately aggregated gels that evolve into semi-crystalline nanoparticles for oriented attachment, whereas Na⁺ promotes excessive gelation leading to classical dissolution-recrystallization. This ion switch effect, synergistically modulated by inorganic alkalinity, proves universally applicable, enabling predictable "dense-loose" morphology control across diverse zeolites (ZSM-5, ZSM-11, zeolite L and mordenite). The hollow, mesopore-rich beta-K mesocrystals demonstrate superior catalytic performance in macromolecular conversion (e.g., low-density polyethylene cracking), achieving a tenfold faster rate than beta-Na due to enhanced mass transfer and acid site accessibility. This work provides a green, mechanism-driven paradigm for designing functional crystalline materials with tailored architectures.