Exploring a Novel Adsorbent for CO2 Capture and Gas Separation

The urgent need to mitigate carbon emissions has spurred research into small-pore zeolites as cost-effective options for CO2 capture by solid adsorbents, particularly in postcombustion and biogas separation applications. In this study we investigate levyne (LEV-type) zeolite, a largely unexplored material for CO2 adsorption, as a novel adsorbent for CO2 capture and gas separation. Using seed-assisted synthesis approaches and different synthesis conditions, nanosized and micron-sized LEV zeolites were synthesized and characterized in terms of synthesis pathways, morphology, crystal size, and chemical composition. The variation of the Si/Al ratios and chemical compositions of the synthesized LEV zeolites resulted in significant differences in their CO2 adsorption capacity and separation selectivity. Micron-sized LEV, with a lower Si/Al ratio = 3.5 and a higher Na+ content, exhibited superior CO2 uptake and stronger interactions with CO2 than the nanosized LEV (Si/Al = 6.6). Dynamic adsorption measurements using breakthrough curve analysis revealed that the micron-sized LEV exhibited twice the CO2 adsorption capacity of its nanosized counterpart, along with higher CO2/N2 and CO2/CH4 selectivities. This enhanced performance, including better cyclability, emphasizes the critical role of the zeolite Si/Al ratio in improving adsorption and separation properties. In situ FTIR measurements supported these findings, showing that the nanosized LEV predominantly adsorbs CO2 by physisorption, allowing efficient desorption using He flow only. In contrast, micron-sized LEV primarily physisorbs CO2 but also exhibited chemisorbed CO2, reflective of the more highly charged framework (higher Al content) and extra-framework cation content. These results highlight the importance of synthesis strategies in optimizing the properties of LEV zeolite, making them promising candidates as physical adsorbents for gas separation applications.