Toward Optimal Xenon Adsorption Capacity at Low Pressure on Silver-Exchanged Zeolites

Silver-exchanged zeolites are the most efficient materials for xenon adsorption at pressures in the ppm levels. It is widely accepted that silver moieties constitute the active phase in the adsorption. Among them, ZSM-5 appears to be the most efficient topology owing to its pore size and geometry. In this study, we fully exchanged seven different sodium-form zeolites (four ZSM-5, two BEA, and one MOR) to silver-form, characterized them, and compared their xenon adsorption capacities. Modeling the isotherms with a double-site Sips model allowed a quantitative comparison of their performances. The results confirmed a linear trend between the concentration of strong adsorption sites and the silver amount contained in the ZSM-5 and BEA zeolites. At the same time, it revealed that silver-exchanged MOR deviates from that trend and generates xenon adsorption sites in a higher-pressure range. Moreover, the 27 Al NMR measurements displayed a clear linear correlation between the amount of strong, silver-based, adsorption sites and the amount of exchangeable, framework aluminum-based, sites. Overall, this study revealed that an increase in the silver content leads to an increase in strong adsorption sites in a pressure range that depends on the zeolite structure. In addition, the tetra-coordination of aluminum must be checked to guarantee a high silver loading in pentasil-based zeolites.