Organic Anions Facilitate in Situ Synthesis of Mesoporous LTA Zeolites

Abstract

The synthesis of hierarchical zeolites commonly relies on mesoscale templates such as surfactants or polymers to form mesopores during zeolite crystallization employing a space-filling strategy. Herein, we demonstrated a class of small anions as organic mesopore-generating agents (OMeGAs) including oxyanions, nitranions, and carbanions to create mesopores with average diameters 9–20 nm based on rationally designed experiments screening a wide range of acidic-proton-bearing molecules. The small organic molecules with pKa < ∼13.5 all facilitated mesopore formation in LTA zeolites, whereas those with higher pKa values did not. Density functional theory and molecular dynamics calculations unraveled dual roles of OMeGAs: chemical effect via SN2-type nucleophilic attack to cleave framework Si–O/Al–O bonds in situ and steric hindrance effect of molecular clusters formed via self-assembly of Ala– and Na+ ions in solution. Given the rich variety in the scope of organic anion precursors, the general synthetic process provides a new view for the synthesis and application of mesoporous zeolites.