Zeolite Synthesis by the Excess Fluoride Approach with Varying the Type and Concentration of Azonia-Spiro Compounds as Organic Structure-Directing Agents

Abstract

From a technological point of view, rationalizing a synthetic strategy is at the basis of routinely crystallizing zeolite materials with unknown compositions and/or structures. Here we searched for a way to extend the viability of the excess fluoride approach, which investigates the effects of fluoride concentration on the phase selectivity of zeolite materials. In that view, we tried controlling some conventionally applied synthesis parameters such as the type and the concentration of organic structure-directing agents (OSDAs) together with increasing the fluoride concentration, in this case, using N-alkyl substituted azonia-spiro ions as OSDAs and varying the concentration of OSDAs in somewhat wide range (0.125-0.50). As a result, it was found that the (alumino)silicate version of the ISV-type zeolite could crystallize only with the synthesis of zeolites using an ethyl-subtituted azonia-spiro ion as an OSDA and synthesis mixtures with the specific OSDA/Si ratio (0.25) under the excess fluoride condition (HF/OSDA = 2.0). We anticipate that the use of the approach is extendable by accumulating the knowledge of understanding various synthesis parameters. Our synthesis results also reveal that the STF and NES structures could be obtained with the normal F- concentration conditions (HF/OSDA = 1.0) by varying an organic synthesis parameter, in this case, the concentration of OSDAs.