Characterization of LTA- and CHA- type zeolites by means of solid state NMR

摘要

Pure silica LTA and CHA-type zeolites synthesized in fluoride media have been investigated by ~1H and ~(29)Si solid state (MAS) NMR spectroscopy. The ~1H spectra of the dehydrated samples reveal the presence of different silanol groups (1.5-2.5 ppm), while upon hydration they give a band of water at ca. 3 ppm and a weak peak at 7.5 ppm. The application of ~1H/~(29)Si cross polarization (CP MAS) two dimensional 2D-heteronuclear correlation technique supports the existence of a variety of Si-OH groups whose relative intensity changes. These groups interact in a different way with water. This type of interaction can be tentatively related with the location of the silanol groups in the crystals.