Unprecedentedly High Selective Adsorption of Gas Mixtures in rho Zeolite-like Metal-Organic Framework: A Molecular Simulation Study

We report a molecular simulation study for the separation of industrially important gas mixtures (CO2/H-2, CO2/CH4, and CO2/N-2) in rho zeolite-like metal-organic framework (rho-ZMOF). Rho-ZMOF contains a wide-open anionic framework and charge-balancing extraframework Na+ ions. Two types of binding sites for Ne ions are identified in the framework. Site I is in the single eight-membered ring, whereas site II is in the a.-cage. Na+ ions at site I have a stronger affinity for the framework and thus a smaller mobility. The binding sites in rho-ZMOF resemble those in its inorganic counterpart rho-zeolite. CO2 is adsorbed predominantly over other gases because of its strong electrostatic interactions with the charged framework and the presence of Na+ ions acting as additional adsorption sites. At ambient temperature and pressure, the CO2 selectivities are 1800 for the CO2/H-2 Mixture, 80 for the CO2/CH4 mixture, and 500 for the CO2/N-2 mixture. Compared with other MOFs and nanoporous materials reported to date, rho-ZMOF exhibits unprecedentedly high selective adsorption for these gas mixtures. This work represents the first simulation study to characterize extraframework ions and examine gas separation in a charged ZMOF. The simulation results reveal that rho-ZMOF is a promising candidate for the separation of syngas, natural gas, and flue g as.