Control of Zeolite Local Polarity toward Efficient Xenon/Krypton Separation

Abstract

The inherent inertness and striking physicochemical similarities of krypton and xenon pose significant challenges to their separation. Reported herein is the efficient xenon capture and xenon/krypton adsorptive separation by transition metal-free zeolites under ambient conditions. The polarized environment of zeolite, denoted as local polarity, can be tuned by changing the topology, framework composition, and counter-cations, which in turn correlates with the guest-host interaction and separation performance. Chabazite zeolite with a framework Si/Al ratio of 2.5 and Ca²⁺ as the counter-cations, namely, Ca-CHA-2.5, is developed as a state-of-the-art zeolite adsorbent, showing remarkable performance, <i>i.e.</i>, high dynamic xenon uptake, high xenon/krypton separation selectivity, and good recyclability, in the adsorptive separation of the xenon/krypton mixture. Grand Canonical Monte Carlo simulation reveals that extraframework Ca²⁺ cations act as the primary binding sites for xenon and can stabilize xenon molecules together with the chabazite framework, whereas krypton molecules are stabilized by weak guest-host interaction with the zeolite framework.