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.