A variable temperature infrared spectroscopy study of NaA zeolite dehydration

Variable temperature diffuse reflectance infrared spectroscopy is used to monitor the dehydration of sodium Linde type A zeolite (NaA). Between ambient temperature and 423 K, water desorbs from NaA α-cages. At 423 K, remaining NaA water molecules are primarily confined to β-cages. Variable temperature infrared difference spectra band shape and intensity trends reflect the influence of water-Na+ interactions and hydrogen bonding on α-cage water desorption mechanisms. Difference spectrum variations suggest that water loss is accompanied by rearrangement of the remaining NaA water molecules to establish new interactions and minimize potential energies. Water molecules that do not interact with Na+ form multiple water-water hydrogen bonds and attain near bulk water configurations. These waters desorb at the lowest temperatures. Most α-cage waters are involved in Na+ interactions. These water molecules participate in hydrogen bonding with neighboring water molecules, but opportunities diminish with increased dehydration, resulting in systematic temperature-dependent vibrational spectrum changes.