Xenon adsorption in synthetic chabazite zeolites

Xenon adsorption has been studied in different ion-exchanged forms of synthetic chabazite zeolites, K–, Ca–, Li–, Rb– and Cs–CHA, at low pressures and variable temperature. The xenon adsorption capacities vary with the nature of the exchanged cation in a way that is consistent with the known cation locations in the zeolite. Highest uptake was found for Ca–CHA, and lowest for Cs–CHA. The xenon uptakes at room temperature were also consistent with differences in the nitrogen adsorption capacities at 77 K. Enthalpies of adsorption were estimated from the temperature dependence of the adsorption isotherms in Ca–CHA and K–CHA, and found to be very similar. The xenon adsorption was also compared with that of an aluminophosphate (ALPO-CHA) as well as a silicoaluminophosphate (SAPO-34), both having the chabazite-type structure. The high affinity of CHA for xenon is attributed in part to a close match between the size of the xenon atom and the pore dimensions of the CHA structure, the so-called confinement effect.