Location of cations in synthetic zeolites X and Y. Part 4.—Exchange limiting factors for Ca2+ in zeolite Y

Abstract

The limit of exchange of NaY and KY zeolites with Ca²⁺ depends on the exchange temperature and the type of exchangeable cation. A variable mixed sample composition is obtained at room temperature, while a fully exchanged CaY sample was obtained by exchange at 368 K. The structures of CaNaY, CaKY as determined by X-ray powder methods are compared with those of NaY, KY and CaY. The electron density in the sodalite cage of incompletely exchanged CaNaY is identical to that of the original NaY sample. On the other hand, CaKY and CaY have a similar occupancy of the cubo-octahedron. The existence of stable structures formed with Na⁺ ions and water molecules inside the sodalite cages is thought to be the reason for the incomplete exchange of NaY. This effect is kinetic rather than thermodynamic.