Zeolite synthesis by the excess fluoride approach in the presence of piperidinium-based structure-directing agents

Abstract

Here, we investigate the effects of fluoride concentration on the phase selectivity of crystallization in (alumino)silicate synthesis mixtures containing a series of N -alkyl- N -methylpiperidinium ions, where alkyl is methyl to hexyl, as organic structure-directing agents (OSDAs). Considerable diversity in the phase selectivity was observed when the HF/OSDA ratio in synthesis mixtures is 2.0 or higher. Using this excess fluoride approach, we synthesized five different aluminosilicate zeolites (i.e., EMM-10P, EU-1, MCM-22P, ZSM-12, and ZSM-58) that did not crystallize under the normal F − concentration conditions (HF/OSDA = 1.0). Our synthesis results also reveal that the same zeolite phase (i.e., levyne, nonasil, octadecasil, or ZSM-5) can crystallize over a wide range (0.5–2.0) of HF/OSDA ratios. More interestingly, F − concentration in the synthesis mixture was found to influence the crystal size and framework Al distribution of levyne. • Zeolite syntheses using piperidinium-based OSDAs in fluoride media are performed. • Notable changes in the zeolite product are observed at HF/OSDA ratios ≥ 2.0. • Zeolite crystal size varies with the F − concentration in synthesis mixtures. • F − concentration in the synthesis mixture is a zeolite framework Al distribution factor.