Crucial role of blocking inaccessible cages in the simulation of gas adsorption in a paddle-wheel metal–organic framework

Abstract

A molecular simulation study is reported to investigate the adsorption of CO₂ and H₂ in a recently synthesized paddle-wheel Cu-based metal–organic framework (Cu–MOF). The Cu–MOF consists of three types of cages; the type-III cages are restricted by narrow windows and inaccessible to gas molecules. By blocking the inaccessible type-III cages, the simulated adsorption isotherms for pure CO₂ and H₂ agree well with experimental data. Ideal-adsorbed solution theory (IAST) is used to predict the adsorption of a CO₂/H₂ mixture, and the predicted isotherms and selectivities are consistent with simulated results. Furthermore, the breakthrough profiles are evaluated for a CO₂/H₂ mixture in a fixed-bed packed with the Cu–MOF. The breakthrough times are estimated to be 2.8 and 85.2 for H₂ and CO₂, respectively, implying the efficient separation of the CO₂/H₂ mixture. The simulation study reveals the crucial role of blocking inaccessible cages in the proper simulation of gas adsorption in the Cu–MOF, and the capability of IAST applied to the Cu–MOF with inaccessible cages.