Mechanistic Study of CO2 Adsorption and Desorption on Li4SiO4

Abstract

Lithium orthosilicate (Li4SiO4) is considered as one of the promising material for high temperature CO2 capture. However, there is no clear understanding about the reaction mechanisms for adsorption and desorption processes, which include the formation of two solid phases (i.e. Li4SiO4(s) + CO2(g) ↔ Li2SiO3(s) + Li2CO3(s)). In this study, the CO2 adsorption and desorption mechanisms were investigated by density functional theory calculation. In the adsorption process, we explored the reaction pathways for the formation of thin bilayer structure consisting of Li2CO3 (above) and Li2SiO3 (below). After the thin bilayer formation, thermal diffusion of Li+ and O2- enabled the further reaction to occur and made a double shell for complete adsorption. In the desorption process, we observed the successive formation of Li4SiO4 nuclei at the Li2CO3-Li2SiO3 interface, which was induced by the desorption of CO2 from Li2CO3 layers. The detailed reaction energetics on each step were confirmed by Gibbs free energy calculation. These findings into underlying mechanisms for CO2 capture will provide a way to improve the catalytic performance for Li4SiO4-based sorbents at high temperature.