Seeds-induced fluoride media synthesis of nanosized zeolite Beta crystals

Abstract

This study reports on the seeded synthesis of zeolite Beta in fluoride media. Crystal growth kinetics of the material as a function of seed content, crystallization temperature and Si/Al ratio of the initial gel is studied. After the optimization of crystallization conditions a highly crystalline material with crystal size 100–300nm is synthesized. A counterpart zeolite Beta sample with similar characteristics is obtained in hydroxyl media. The physicochemical properties of fluoride and hydroxyl media syntheiszed zeolites are compared as particular attention is paid to the nature, number and distribution of their active sites. Zeolite Beta sample synthesized in fluoride media exhibits larger number of Broensted acid sites, while the concentration of Lewis acid sites is higher in the zeolite synthesized in hydroxyl media. The two materials are tested in m-xylene transformation, where zeolite Beta synthesized in fluoride medium shows superior performance. The set of experimental data unambiguously proves that seeded synthesis of zeolites in fluoride medium is a promising alternative of the conventional zeolite synthesis in hydroxyl medium.