Coordination of alkali metal ions in ZSM-5: A combined quantum mechanics/interatomic potential function study

Abstract

The siting and coordination of alkali metal ions (Li+, Na+, and K+) in zeolite ZSM-5 were studied by a combined quantum mechanics/interatomic potential function method, which employed the B3LYP density functional and core–shell model potentials. New interaction parameters for Li+ and K+ ions with the zeolite were parameterized based on ab initio data. Several different sites of extra-framework M+ ions in the ZSM-5 were found and classified. Relative stabilities of particular sites depend (i) on the location of the framework Al atom and (ii) on the size of the alkali metal ion. The Li+ ion preferably occupies the sites on top of the six-membered ring on the channel wall while K+ ion preferably binds on the channel intersection.