EFFECT OF CATION SUBSTITUTION ON THE ADSORPTION OF XENON ON ZEOLITE NAY AND ON THE XE-129 CHEMICAL-SHIFTS

A comprehensive study of the effect of cation substitution on the adsorption of xenon on NaY zeolites and on Xe-129 chemical shifts has been made. The cations studied include H+, alkali (Li+, K+, Rb+, Cs+), alkaline earth (Mg2+, Ca2+, Sr2+, Ba2+) and transition metal (Co2+, Ni2+, Cu2+, Zn2+), each with varied degree of exchange with Na+. The results of the adsorption isotherms were analyzed by the use of a Langmuir-type equation. It was found that the adsorption strength for the Y-zeolites follows the trend Ba > Cs greater than or equal to Rb > K greater than or equal to Sr > Ca > Na greater than or equal to Co greater than or equal to Ni greater than or equal to Li greater than or equal to Zn > Cu similar or equal to H > Mg. The observed Xe-129 chemical shifts of the adsorbed xenon were interpreted by a newly developed virial expansion model; an equation relating the Xe-129 chemical shift and the amount of xenon atoms adsorbed per cage has been derived and used to fit the experimental data of all the systems studied, and the results are quite satisfactory. It is suggested that the adsorption strength and the Xe-129 chemical shift are dependent on the location of the cation in the supercage as well as on various interactions of the xenon atoms with each other and with the zeolite walls. The van der Waals interaction, which is determined by the polarizability of the interacting species, is the major interaction. The Coulombic interaction of the cations plays a secondary role.