Tailoring the CO2 selective adsorption properties of MOR zeolites by post functionalization

A wide range of organic molecules covering benzene, dimethylbenzene, methoxybenzene, and dimethoxybenzene, isopropylbenzene with different molecular diameters were covalently attached to the interior micropore walls of mordenite (MOR) zeolites to enable the systematic tuning of adsorption properties. The formation of covalent bonds between internal oxygens of MOR and benzene carbon atoms were confirmed via Rietveld refinement. The adsorption properties of the functionalized MORs were studied using CO2, CH4, and N2 adsorption isotherms under static conditions, and ideal adsorbed solution theory was used to predict MOR selectivities for CO2 over CH4 and N2. The results showed that post-functionalization with organics remarkably improved CO2/CH4 and CO2/N2 selectivities, albeit at the expense of a slight concomitant partial loss of CO2 adsorption capacity. Among the functionalized zeolites, the MOR functionalized with isopropylbenzene (the bulkiest moiety introduced) exhibited the highest selectivities (CO2/CH4 = 18.3, CO2/N2 = 59.9), which were 2.8 and 4.3 times higher, respectively, than those of pristine MOR (CO2/CH4 = 6.6, CO2/N2 = 14). Reduction of effective micropore diameters by isopropylbenzene is responsible for the improved CO2 adsorption selectivity. We believe that the concept of tailoring the molecular-sieve properties of zeolites by organic functionalization will open new opportunities for developing efficient molecular sieves for chemical separation processes.