Selective CO2 adsorption over alkali metal cation-exchanged UZM-9 zeolites

Adsorption on zeolites reduces CO 2 emissions and cuts the energy costs of processing gas mixtures, such as natural gas, biogas, and landfill gas (CO 2 /CH 4 of various concentrations). Among zeolite frameworks, LTA stands out for its CO 2 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 CO 2 over CH 4 . K + -exchanged UZM-9 reached the highest CO 2 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 CO 2 interactions, potentially via bridging CO 2 species. Due to partial pore blocking, the total uptake may decrease slightly, but the K-UZM-9 system effectively balances CO 2 /CH 4 selectivity and adsorption capacity. Therefore, K-UZM-9 emerges as a promising adsorbent for energy-efficient gas separation and carbon capture applications. • CO 2 adsorbs selectively over CH 4 on alkali-exchanged UZM-9 (LTA, Si/Al = 4.5). • K-exchanged UZM-9 exhibits the strongest interaction with CO 2 . • The CO 2 /CH 4 selectivity increase of K-UZM-9 is accompanied by only minor trade-offs. • This behavior is due to spatial distribution of the K + cations in the pores. • Medium-silica K-exchanged LTA exhibits a potential for natural gas/biogas upgrading.