Infrared spectroscopic study on the cation distribution in calcium-exchanged erionite

Abstract I.r. spectroscopy of OD vibration, lattice vibration, and CO adsorption, together with near-infrared measurements in the combination vibration range, were used to study the cation distribution in NaK—, NH 4 — and Ca—erionite. It is shown that in dehydrated Ca—erionite the calcium ions were selectively located in the supercage at positions in front of oxygen six-rings. The strong interaction of calcium ions with lattice oxygen has the following effects: (i) the water dissociation does not take place, and therefore structural hydroxyl groups were not formed in erionite as observed in CaNaY zeolites; and (ii) the exchange degree of calcium ions does not exceed 50% because divalent cations in contrast to monovalent ions cannot migrate into the gmelenite cage caused by different Si >Al ratio of various T sites.