Molecular Simulations and Experimental Studies of CO2, CO, and N2 Adsorption in Metal-Organic Frameworks

Atomistic grand canonical Monte Carlo simulations were performed to understand the interplay of factors (pore size, heat of adsorption, open metal sites, electrostatics, and ligand functionalization) contributing to adsorption of CO2, CO, and N-2 in MOFs. Four MOFs-IRMOF-1, IRMOF-3, Cu-BTC, and Zn-2[bdc](2)-[dabco]-were chosen for comparison. Binary mixtures (CO2/CO) and (CO2/N-2) containing 5%, 50%, and 95% CO2 were examined. CO2 is preferentially adsorbed over CO and N-2 in all MOFs. Cu-BTC displays higher selectivities for CO2 over CO at lower pressures and CO2 over N-2 at all pressures for all mixtures due to the increase in electrostatic interactions of CO2 with the exposed copper sites. However, IRMOF-3 shows surprisingly high selectivities for CO2 over CO for 50% and 95% mixtures at higher pressures due to the presence of amine-functionalized groups and high pore volume. CO2 selectivities increase with increasing CO2 concentration in the gas mixtures at total pressures above 5 bar. On the basis of the results obtained, it can be concluded that construction of smaller pore size MOFs relative to sorbate size with embedded open metal sites or functionalized groups can lead to greater enhancement of these adsorption separation systems.