Abstract
Highly crystalline pure silica MFI zeolites have been synthesized using tetraethylammonium (TEA), tetraethylphosphonium(TEP), or a mixture of both cations in different proportions as organic structure directing agents (OSDAs). The zeolites have been deeply characterized in order to get insight about the guest−guest interactions involving the OSDAs and the guest−host interactions involving the OSDAs and the inorganic framework, as well as the main features of the resulting materials. The results show that the average size of the MFI crystals decreases when TEP is present within the zeolite and that this cation is homogeneously distributed throughout the crystallites. The multinuclear NMR investigation (1H, 13C, 14N, 19F, 29Si, 31P) indicates that TEP interacts with the zeolite host creating higher heterogeneity of the SiO4 crystallographic sites and a diminution on the mobility of fluorine atoms incorporated into the zeolite. Moreover, the presence of TEP influences the dynamics of the nitrogen atoms of the TEA molecules, and 2D heteronuclear correlation experiments give evidence on the spatial proximity of the TEA and TEP molecules in the MFI zeolites. Then, it is concluded that TEA and TEP are intimately mixed within the zeolite voids of the pure silica MFI samples synthesized by the dual template route.