Effect of Aluminum Source on Hydrothermal Synthesis of High-Silica Mordenite in Fluoride Medium, and It's Thermal Stability

Effect of an aluminum source on the direct hydrothermal synthesis of high-silica mordenite-type zeolite in the presence of tetraethylammonium and fluoride ions was investigated. Highly crystalline MOR-type zeolites with a Si/Al ratio of approximately 30 were successfully prepared using Al(NO3)3 as an aluminum source. To clarify the role of fluoride ions, NaF as a fluoride source was added in the course of crystallization process. It was found that the crystallinity and the Si/Al ratio of MOR-type zeolite do not depend on the addition time of NaF. However, the content of fluorine in the as-synthesized zeolite decreased markedly when NaF was added in the course of crystallization process. The decrease in fluorine content improved considerably the thermal stability of the as-synthesized MOR-type zeolite.