Polarized Single-Crystal Micro-RamanSpectroscopy of As-Synthesized Silicalite-1,Al MFI- and Fe MFI-Type Zeolites

Polarized single-crystal Raman spectra were collected from as-synthesized silicalite-1, Al MFI-type zeolites with different Si/Al ratios and Fe MFI-type zeolite using microspectrometry. These spectra are discussed in relation to the crystal structure of the as-synthesized materials. The assignment of the Raman bands to the zeolite framework and to the occluded tetrapropylammonium (TPA) ion templating the MFI structure was examined through the contribution of the different elements of the Raman tensors as functions of the Al or Fe content, respectively. The spectroscopic results are in good agreement with the conformation and location of the TPA ion in the as-synthetized MFI materials, and also with theoretical predictions of preferential substitution sites despite the low Al or Fe content of the zeolite framework.