Synthesis of high silica zeolites using a combination of pyrrolidine and tetramethylammonium as template

Abstract

High silica ZSM-39 (MTN structure), ZSM-35 (FER structure) and ZSM-5(MFI structure) zeolites were successfully synthesized using pyrrolidine and tetramethylammonium as structure directing agents (SDAs), in absence of alkaline cation and fluoride medium. The effect of the relative amount of tetramethylammonium and pyrrolidine, and Si/Al molar ratio on the crystalline phases was investigated. All structures could be synthesized using pyrrolidine as solely SDA. On the other hand, when a mixed template system being used, the crystallization was accelerated by a factor of 2 times, TMA+ would then play a generally beneficial but structurally non-specific role in the crystallization spicily for FER and MFI zeolites. The obtained products were characterized by XRD, 13C solid-state CP MAS NMR, TGA and SEM techniques. The XRD patterns confirmed the formation of pure zeolites with high crystallinity.13C CP MAS NMR spectroscopy confirmed the incorporation of pyrrolidine and tetramethylammonium in the structure of Al-ZSM-5 and Al-ZSM-35 zeolites. These two kinds of SDAs played a cooperative role in the crystallization of these zeolites. The role of pyrrolidine was to provide the initial nucleation and tetramethylammonium to provide both space-filling and basicity capacities.