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

Pure silica LTA and CHA-type zeolites synthesized in fluoride media have been investigated by lH and 29Si solid state (MAS) NMR spectroscopy. The lH 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 lH/29Si 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.