A variable temperature infrared spectroscopy study of NaY zeolite dehydration.

Abstract

Variable temperature diffuse reflection infrared spectroscopy is used to monitor molecular vibration changes associated with water molecules and zeolite framework during thermal dehydration of NaY zeolite. Absorbance bands are assigned to three unique water molecule environments. These three water types exhibit different temperature-dependent band intensity profiles. A band at 3700 cm-1 is assigned to framework acid sites. The intensity of this band was found to vary with temperature in a manner consistent with the occupancy of sodium cations in II' unit cell locations. Specific framework vibrations exhibit temperature-dependent intensity change profiles. Band intensities at 1190, 1060, and 960 cm-1, associated with Si-O-Si and Si-O-Al asymmetric stretching vibrations, are sensitive to water content. Band intensity at 800 cm-1, assigned to Si-O-Si symmetric stretching, is inversely correlated with temperature-dependent unit cell volume changes. All framework band intensity changes detected during heating are reversible after re-hydration during sample cooling.