A density functional theory study for the adsorption of various gases on a caesium-exchanged trapdoor chabazite

Rational design and development of porous materials for adsorptive gas separation gains ever-increasing attention as industrial applications, such as carbon capture and natural gas purification, always require more energy-efficient processes with adsorbents providing high selectivity. Zeolite molecular sieves represent a class of such desirable adsorbents. Our recently discovered molecular trapdoor mechanism in zeolites allows for unprecedented high selectivity and affords designability for versatile adsorbents. In this work, we presented a route for identifying the molecular trapdoor mechanism and predicting the gas separation feasibility using density functional theory calculations, based on a typical molecule trapdoor zeolite - caesium-exchanged chabazite with silicon to aluminium ratio of 3. We established criteria to assess the viability for "door-open" process by examining the dependence of energy barriers for the movement of "door-keeping" cation in the presence of different gases. Calculations at the standard PBE level and the van der Waals DFT levels were carried out. This theoretical route could serve as a standard method to study and develop other molecular trapdoor zeolites.