Fluorine-containing organic molecules as structure-directing agents in the synthesis of crystalline microporous materials. Part II: Synthesis of all-silica zeolites from fluorine-containing derivatives of 1-benzyl-1-methyl-hexamethylenammonium cations

Abstract

We have used 1-benzyl-1-methyl-hexamethylenammonium cation (BMHM) and several fluorine-containing derivatives of this cation as novel structure-directing agents for the synthesis of all-silica zeolite crystals in fluoride media. It has been found that the non-fluorinated BMHM cation leads to all-silica zeolite beta under appropriate synthesis conditions, while the crystal size and morphology of the zeolite change as a function of these conditions. The 1-orthofluorobenzyl-1-methyl-hexamethylenammonium cation ( o-FBMHM) in the same synthesis conditions as those of the all-hydrogenated cation, also allows the crystallisation of all-silica beta zeolite, but with a very different crystal size and morphology. The metafluoro derivative ( m-FBMHM) leads to a mixture of beta, nonasil and a non-identified phase, whereas the parafluoro derivative ( p-FBMHM) only leads to the nucleation of the clatrasil nonasil. Therefore, the presence and position of the F in the aromatic ring influence the crystallisation pathway and the product obtained.