Synthetic and structural studies of high silica MFI zeolites

Abstract

A systematic series of high-silica fluoride MFI zeolites were efficiently synthesised using a variety of shape and size structure directing agents. The effects of these structure directing agents on the zeolite synthesised have been studied by the complementary use of X-ray diffraction and solid state NMR. These 14N, 13C and 29Si NMR experiments yield information about the orientation of the structure directing agent within zeolite pores. They also identify covalently bonded fluoride in the form of pentacoordinated silicon whereby the first case of static and dynamic ordering of fluoride in the same zeolite is discovered by changing the structure directing agent.

A two-dimensional solid state NMR experiment has also been used to study 13C isotopically labelled silicalite-1 synthesised using n-methyltributylammonium iodide. The double cross polarisation (DCP) experiment allows the distance to be determined between the structure directing agent and silicon framework for the first time in a zeolite system using NMR. This experiment has the potential to be replicated for silicalite-1 zeolites synthesised using alternate structure directing agents or for other zeolites systems.

Citation

(2017). Synthetic and structural studies of high silica MFI zeolites