Role of the countercations on the molecular sieve properties of a clinoptilolite

Samples of clinoptilolite enriched with Na+, K+, Cs+, NH4+, Ca2+, Mg2+, and Ba2+ cations were prepared by ion-exchange. The degree of exchange for the different samples is discussed in terms of location and diffusivity of the cations. The thermal stability of natural clinoptilolite and of the enriched forms, as determined by XRD, is related to the nature and location of the major countercation in the zeolite framework. The specific retention volumes of O-2, N-2, CO and CH4 on each sample and the adsorption enthalpies of these gases were measured by a chromatographic method in the range of 298-393 K. The results are explained on the basis of the strength of the interaction molecule-adsorption sites of the zeolite, taking into account the diffusivity of gas molecules through the zeolite channels, and their accessibility to the adsorption sites, according to the more probable location of the cation in the lattice.