Elucidating the promotion of Na₂CO₃ in CO₂ capture by Li₄SiO₄

Although Li₄SiO₄-based sorbents are candidates for CO₂ capture at high temperatures, it is still necessary to improve their kinetic activation for adsorption and desorption. Carbonate doping to Li₄SiO₄ is considered as one of the effective means to improve CO₂ capture by Li₄SiO₄. In this study, Li₄SiO₄ was synthesized using Li₂CO₃ and SiO₂ at 900 °C, and mixed with different amounts of Na₂CO₃ as CO₂ sorbents. The effects of Na₂CO₃ on the absorption and desorption were characterized using thermal analyses in an atmosphere of 80 vol% CO₂-20 vol% N₂. In situ Raman and XRD were used for the characterization of the structural transformations and phase evolution during the CO₂ capture. The activation energy of both chemisorption and diffusion in adsorption dropped significantly. The additive Na₂CO₃ can react with CO₂ and produce the pyrocarbonate, which is favorable for CO₂ capture of Li₄SiO₄ and CO₂ diffusion. The doped Na₂CO₃ served two functions: producing the intermediate product and forming the melt with the product Li₂CO₃ to accelerate CO₂ transport. The Na₂CO₃-doped Li₄SiO₄ exhibits stable cyclic durability with conversions of 75% in 20 adsorption-desorption cycles.