A SPECTROSCOPIC STUDY OF SURFACE ZEOLITE Y .2. INFRARED SPECTRA OF STRUCTURAL HYDROXYL GROUPS AND ADSORBED WATER ON ALKALI ALKALINE EARTH AND RARE EARTH ION-EXCHANGE ZEOLITES

Infrared spectra of alkali, alkaline earth, and rare earth Y zeolites have been observed during dehydration and subsequent rehydration at various temperatures. No structural hydroxyl groups were observed for the alkali cation Y zeolites. Readsorbed water simply physically adsorbed by association with the exchangeable cations. No new structural hydroxyl groups were formed. The frequency of the absorption bands of the adsorbed water varied with the cation radius and hence with the calculated electrostatic field and potential and with the ionization potential. The results were similar to those found for alkali cation X zeolites by Habgood. An examination of NaX zeolite confirmed the results of Habgood in most respects. The adsorption of water on the alkali cation zeolites is highly reversible. Barium Y zeolite dehydrated and rehydrated analogous to the alkali cation forms. Spectra of magnesium, calcium, and strontium Y zeolites all showed structural hydroxyl groups. The absorption bands near 3640 and 3540 cm-1 are considered to be the same as observed in decationized zeolites and represent silanol groups. An absorption band in the 3600-3560-Cm-1 region is identified with hydroxyl groups associated with the divalent cations, while a band near 3690 cm-1 is due to adsorbed undissociated water. Rehydration produces a strong band near 3690 cm-1, which, when the zeolite is heated above 200°, disappears simultaneously with the growth of bands near 3640 and 3600-3560 cm-1. The latter band is very sensitive to the hydration level, probably indicating that the MOH+ species is readily converted to the oxide. Confirmation of this band representing attachment to the cation is shown by the regular variation of its frequency with cation. Spectra of the rare earth Y zeolite showed two dominant hydroxyl bands at 3640 and 3522 cm-1 assigned to silanol groups and MOH groups. Water adsorbed in a highly reversible manner. No new structural hydroxyl groups were formed.