Theoretical studies on carbon dioxide adsorption in cation-exchanged molecular sieves

The capture and storage of the greenhouse gas, CO(2), has attracted much interest from scientists in recent years. In this work, density functional theory (DFT) was used to study the adsorption of CO(2) in different cation-exchanged molecular sieves. The results show that for the monovalent metal (Li, Na, K, Cu) ion-exchanged molecular sieves (zeolite Y, ZSM-5, CHA and A), the adsorption capacities for CO(2) decrease in the order of Li(+) > Na(+) > K(+) > Cu(+). Cu(+)-exchanged zeolites are not suitable as adsorbents for CO(2). For the CO(2) adsorption capacities in different zeolites with the same exchanged cation, the adsorption energy decreases in the order of Y > A > ZSM-5 ≈ CHA for Li-exchanged zeolites, and ZSM-5 still has the lowest CO(2) adsorption energy for both Na- and K-exchanged zeolites. In the cation-exchanged Y zeolites with divalent metals (Be, Mg, Ca and Zn), the CO(2) adsorption performance increases in the order of Zn(2+) < Be(2+) < Ca(2+) < Mg(2+). Thus, Zn(2+)-exchanged zeolites are not suitable as adsorbents for CO(2).