Access to sodalite cages in ion-exchanged nanosized FAU zeolites probed by hyperpolarized 129Xe NMR and DFT calculations

Abstract

The accessibility to sodalite (SOD) cages in nanosized zeolite X (FAU-type framework) is tuned by varying the nature and location of extra-framework exchangeable cations (Na+, Li+, Cs+, K+ and Rb+). Hyperpolarized (HP) and EXchange SpectroscopY (EXSY) 129Xe NMR experiments highlight the connectivity between SOD- and super (SUP)-cages, in particular that its diffusion pathway from sodalites to supercages depends mainly on the size and location of extra-framework cations present in the zeolite. These 129Xe NMR results are supported by DFT simulations. Based on the computed adsorption energies of Xe in both SOD and SUP cages of zeolite X with different cationic compositions, it is concluded that xenon penetration in SUP cages is always favorable while the adsorption in the SOD cages is possible only if small cations (Na+, Li+, K+) are present.