Reduction of crystal size of silicalite-1 synthesized in fluoride-containing media via multi-stage heating with intermediate stirring

Abstract

When zeolites are synthesized in fluoride-containing media, large crystals tend to be obtained. In this research, we present a multi-stage synthesis strategy for size reduction of silicalite-1 synthesized in fluoride-containing media. Increase of the number of effective nuclei was crucial for the size reduction since, in dense hydrogel systems, only a limited number of nuclei can grow due to the hindrances in solid–liquid contacts. Small crystals are obtained by enhancing such contacts which aids in effective growth of nuclei. An intermediate low-temperature treatment coupled with stirring enhances the contact between the solid and liquid phases. Subsequent high-temperature heating completes the crystallization. The obtained silicalite-1 exhibits characteristics such as large micropore volumes and low number of defects comparable to the samples obtained from a single-stage synthesis.