Alkali Metal–Based Adsorbents for Direct Air Capture

Direct air capture (DAC) technology employs adsorbent materials to selectively extract carbon dioxide (CO2) directly from ambient atmospheric air. The development of high-efficiency and energy-efficient adsorbents is pivotal to the successful deployment of DAC. In this study, sodium- and potassium-based adsorbents were synthesized via the equal volume impregnation method, employing γ-Al2O3 and TiO2 as supports and Na2CO3 and K2CO3 as active components, respectively. The CO2 adsorption performances of the as-prepared adsorbents were systematically evaluated using a fixed-bed reactor system. Thermodynamic analysis indicated that the Langmuir isothermal adsorption model accurately described the equilibrium CO2 adsorption behaviors of four kinds of adsorbents. Additionally, use of the Avrami model enabled accurate analysis of the associated kinetic mechanisms. The environmental relative humidity (RH) and desorption temperature affected CO2 adsorption capacities. Notably, a maximum CO2 adsorption capacity of 1.19 mmol/g was achieved at 78.7% RH during 10 adsorption–desorption cycles by forming KHCO3 using K/TiO2 powder materials. The CO2 adsorption capacity of 0.409–0.507 mmol/g was acceptable for K/TiO2 pellets during 20 adsorption–desorption cycles, demonstrating good prospects for industrial DAC application.