Understanding the Key Role of Cations in Water Tolerance during the CO2/CO Separation Process under Low-Humidity Conditions.

The efficient separation of CO2 and CO under low-humidity conditions is crucial for ensuring the long-term operational stability of industrial applications. While the number of adsorbent cations plays a key role in separation, their influence on purification under low humidity remains insufficiently understood. The breakthrough results indicate that, even under extremely low humidity, the adsorption capacity of CO2 and CO can decrease by up to 6 and 24%, respectively. It is found that the presence of water could increases the CO2/CO separation factor from 6.91 to 9. This enhancement occurs because CO, with its lower quadrupole moment, experiences a more significant reduction in adsorption capacity than CO2. The quantity and accessibility of cations significantly influence the water tolerance in adsorption processrs. As the number of cations decreases, CO adsorption stabilizes due to the associated hydrophobicity. However, for CO2, the high accessibility of cations at the S3 site in NaX(88) facilitates its conversion to stable carbonates and bicarbonates in the presence of water, enabling exceptional water resistance. These findings offer valuable insights into designing high-performance adsorbents for efficient CO2 capture and separation from industrial flue gas under low-humidity conditions.