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.