FTIR/ATR study of water encapsulated in Na-A and Mg-exchanged A-zeolites

FTIR–ATR spectroscopy has been applied to follow the evolution of intramolecular HOH bending vibrational mode of water in fully hydrated Na-A and various Mg-exchanged A zeolites. The measurements have been performed as a function of temperature and for different percentages of induced ion-exchange. The observed changes have been justified by taking into account the population of water molecules that do not lie in a symmetric tetrahedral environment and the force constants associated to the mode. The data, compared with previous FTIR–ATR O–H stretching spectra for the same samples, give new information to confirm, in the whole explored T-range, the ‘‘structure-maker’’ role played by zeolitic surface on chemisorbed water. It appears systematically enhanced by increasing the percentage of induced ion-exchange.