Reversible Multi‐Complexation of CO₂ to Alkaline Earth Metal Ion‐Pair at 400 ppm and 298 K

The efficient capture of low-pressure CO₂ remains a significant challenge due to the lack of established multi-complexation of CO₂ to active sites in microporous materials. In this study, we introduce a novel concept of reversible multi-complexation of CO₂ to alkaline earth metal (AEM) ion pairs, utilizing a host site in ferrierite-type zeolite (FER). This unique site constrains two AEM ions in proximity, thereby enhancing and isotopically spreading their electrostatic potentials within the zeolite cavity. This electrostatic potential-engineered micropore can trap up to four CO₂ molecules, forming M²⁺-(CO₂)_n-M²⁺ (n=0-4, M=Ca, Sr, Ba) complexes, where each CO₂ molecule is stabilized by interactions between terminal oxygen (O_t) in CO₂ and the AEM ions. Notably, the Ba²⁺ pair site exhibits higher thermodynamic stability for multiple adsorptions due to the optimal binding mode of Ba²⁺-O_t-Ba²⁺. Through high-accuracy energy calculations, we have established the relationship among structure, CO₂ uptake, and operating temperature/pressure, demonstrating that the Ba²⁺ pair site can capture four CO₂ molecules even at concentrations as low as 400 ppm and at 298 K. Three of the four molecules of CO₂ trapped were removable at room temperature and under vacuum. The findings in the present study provide a new direction for developing efficient CO₂ adsorbents.