Abstract
A detailed i.r. study has been performed in the silanol frequency range of silica, silica-alumina, and modified zeolites with different structures. Three different types of silanol groups have been found in dealuminated zeolites: (i) a first band at 3747–3749 cm −1 sensitive to pyridine (adsorption and desorption at 423 K), which corresponds to SiOH groups attached to amorphous silica-alumina debris; (ii) a second band at 3744–3746 cm −1 unsensitive to pyridine corresponding to silanol groups attached to extraframework silicon-rich debris; and (iii) a third component at 3738 cm −1 unsensitive to pyridine, assigned to terminal framework silanol groups. The silanol bands present in modified zeolites provide information on the nature of the extraframework debris and on framework structural defects. After steaming, the extraframework phase is alumina-rich, whereas after a subsequent acid leaching, it becomes richer in silica as the strength of leaching increases.
Published Version
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