Direct air capture of CO2 by metal cation‐exchanged LTA zeolites: Effect of the charge‐to‐size ratio of cations

Abstract Direct air capture of CO 2 (DAC) has been increasingly recognized as a promising carbon‐negative technology. The challenge in deploying energy‐efficient DAC lies in effective sorbent materials. In this research, we comprehensively investigated the DAC behavior of LTA zeolites exchanged with different metal cations (Na + , K + , Mg 2+ , Ca 2+ , Mn 2+ , Co 2+ , Ni 2+ , Cu 2+ , Zn 2+ , Y 3+ , La 3+ , Ce 3+ , Eu 3+ , Tb 3+ , and Yb 3+ ) by both static single‐component gas adsorption and dynamic mixture gas adsorptive separation tests. We found that a large charge‐to‐size ratio of cations is critical to imparting a high DAC capacity of LTA zeolites, which is ascribed to the enhanced electrostatic interaction and/or π‐back bonding toward CO 2 . Meanwhile, a detrimental effect is associated with an excessively large charge‐to‐size ratio, that is, a significant “shielding effect” of (pre‐) adsorbed contaminants (e.g., H 2 O and CO 2 ) on cations (e.g., Mn 2+ and Mg 2+ ) reduce the accessible CO 2 capacity. Ca‐LTA featuring Ca 2+ with an appropriate charge‐to‐size ratio exhibits the highest DAC capacity (350 ppm CO 2 in the air, 1.20 mmol/g) with fast kinetics and good reusability. These results provide valuable insights for the design of zeolites‐based physisorbents for DAC.