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

The capture and storage of the greenhouse gas, CO₂, has attracted much interest from scientists in recent years. In this work, density functional theory (DFT) was used to study the adsorption of CO₂ 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 CO₂ decrease in the order of Li⁺ > Na⁺ > K⁺ > Cu⁺. Cu⁺-exchanged zeolites are not suitable as adsorbents for CO₂. For the CO₂ 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 CO₂ adsorption energy for both Na- and K-exchanged zeolites. In the cation-exchanged Y zeolites with divalent metals (Be, Mg, Ca and Zn), the CO₂ adsorption performance increases in the order of Zn²⁺ < Be²⁺ < Ca²⁺ < Mg²⁺. Thus, Zn²⁺-exchanged zeolites are not suitable as adsorbents for CO₂.

Density functional theory was used to study the adsorption of CO₂ in cation-exchanged zeolite Y, ZSM-5, CHA and A. The adsorption energies and the interactions of cations on various zeolitic topologies towards CO₂ molecule was discussed.