New Route to Pentasil-Type Zeolites Using a Non Alkaline Medium in the Presence of Fluoride Ions

TLDR: In this article, high resolution 29 si-, 27 Al- and 11 B magic angle spinning NMR evidences Si substitution by Al and B in the zeolite framework, showing that the presence of fluoride in the as-synthesized samples leads to organic fluro compounds formation on calcination.

Abstract: Silica-rich, Al-, B- and (Al + B) MFI zeolites called Zeosilites, Aluzeosilites, Borozeosilites and Aluborozeosilites respectively were obtained by hydrothermal crystallization at 60–200°C from mixtures containing F anions and tetra-, tri- and di-propylamraonium cations as templates; pH values were 3–10. Crystal size is a function of the Si substitution degree, it may reach 800 um in some cases. DSC, DTA and TG curves corresponding to the decomposition of the templates occluded as fluoride salts are different from those observed for samples obtained in alkaline medium. Mass spectrometer analysis shows that the presence of fluoride in the as-synthesized samples leads to organic fluro compounds formation on calcination. High resolution 29 si-, 27 Al- and 11 B magic angle spinning NMR evidences Si substitution by Al and B in the zeolite framework.