Abstract Adsorption on zeolites reduces CO2 emissions and cuts the energy costs of processing gas mixtures, such as natural gas, biogas, and landfill gas (CO2/CH4 of various concentrations). Among zeolite frameworks, LTA stands out for its CO2 adsorption and/or separation potential, particularly the Na-LTA zeolite with a Si/Al ratio of ∼5. However, the impact of different cations on the separation efficiency of this system remains unknown. In this study, we tested various alkali-metal-exchanged UZM-9 zeolites (Si/Al = 4.5) for their selective adsorption of CO2 over CH4. K+-exchanged UZM-9 reached the highest CO2 affinity, isosteric heat of adsorption, and selectivity, outperforming more commonly used Na+ forms. This enhanced performance likely stems from the predominant location of K+ in the 8-ring window, which fosters strong CO2 interactions, potentially via bridging CO2 species. Due to partial pore blocking, the total uptake may decrease slightly, but the K-UZM-9 system effectively balances CO2/CH4 selectivity and adsorption capacity. Therefore, K-UZM-9 emerges as a promising adsorbent for energy-efficient gas separation and carbon capture applications.

Acknowledgement The authors acknowledge the DESIRED project within the Horizon Europe Research (project code: 101083355). MK and BK acknowledge the Ministry of Education, Youth and Sports of the Czech Republic through the ERC_CZ project LL 2104. JC acknowledges the ERDF/ESF project TECHSCALE (No.CZ.02.01.01/00/22_008/0004587). JH and RB acknowledge support from the Czech Science Foundation under project no. 25–16013S. The authors acknowledge Charles University Centre of Advanced Materials (CUCAM—OP VVV Excellent Research Teams, no. CZ.02.1.01/0.0/0.0/15_003/0000417) for providing instrumental facilities enabling this research.

https://doi.org/10.1016/j.jcou.2025.103305