Confinement effects facilitate low-concentration carbon dioxide capture with zeolites

Engineered systems designed to remove CO(2) from the atmosphere need better adsorbents. Here, we report on zeolite-based adsorbents for the capture of low-concentration CO(2). Synthetic zeolites with the mordenite (MOR)-type framework topology physisorb CO(2) from low concentrations with fast kinetics, low heat of adsorption, and high capacity. The MOR-type zeolites can have a CO(2) capacity of up to 1.15 and 1.05 mmol/g for adsorption from 400 ppm CO(2) at 30 °C, measured by volumetric and gravimetric methods, respectively. A structure–performance study demonstrates that Na(+) cations in the O33 site located in the side-pocket of the MOR-type framework, that is accessed through a ring of eight tetrahedral atoms (either Si(4+) or Al(3+): eight-membered ring [8MR]), is the primary site for the CO(2) uptake at low concentrations. The presence of N(2) and O(2) shows negligible impact on CO(2) adsorption in MOR-type zeolites, and the capacity increases to ∼2.0 mmol/g at subambient temperatures. By using a series of zeolites with variable topologies, we found the size of the confining pore space to be important for the adsorption of trace CO(2). The results obtained here show that the MOR-type zeolites have a number of desirable features for the capture of CO(2) at low concentrations.