Dealumination and surface fluorination of H-ZSM-5 by molecular fluorine

At room temperature, framework aluminum (FAl) is extracted rapidly from the lattice of H-ZMS-5 by molecular fluorine. Ionic fluoro-complexes containin g octahedral aluminum are formed within the micropores of the zeolite. The structure remains intact while the Si/FAl increases, for instance from 27 t o 233 or from 55.2 to 382. As shown previously, the behavior of HY with res pect to molecular fluorine is similar. The terminal SiOH in H-ZSM-5 are also fluorinated. The extent of this react ion was negligible in the case of HY. The quantitative distinction between the fluorine atom in SiF and the aluminum fluoro-complexes is possible usin g F-19 MAS NMR, HETCOR and TRAPDOR. The good agreement between Al-27 and F-19 NMR data and the quantitative ana lysis of the infrared spectra in the OH stretching region is outlined. In p articular, the disputed assignment of the 3700 cm(-1) band to OH on non-fra mework aluminum moieties is elucidated. (C) 2001 Elsevier Science B.V. All rights reserved.