Molecular Simulation Study on CO2 Capture by Li4SiO4 at High Temperature

Abstract

Lithium orthosilcate, Li4SiO4, is now considered as a plausible candidate for a high-temperature CO2 sorbent. In this study, the CO2 adsorption/desorption mechanism was investigated by the multi-scale simulation combining density functional theory(DFT) with molecular dynamics(MD). In the periodic slab model, the most physicaly adsorbed site was found in MD and from that site, the chemisorption proces was continuously calculated by DFT. In the reaction, Li4SiO4+CO2↔Li2SiO3+Li2CO3, we observed the onset of the formation of two product crystals of the double-shel structure. To understand this proces in detail, the reaction pathways and transiton states of adsorption/desorption proceses were investigated and identified. We also found that the existence of Li atom in the intervals of SiO4 tetrahedra plays a key role in reactivity. Because of strong interaction of Li with SiO4 tetrahedra, CO2 can not penetrate but reacts only at the surface. Especialy, the Li difusion into CO3 2- makes the reaction ocurs further. Besides these observation, we compared the adsorption amount and energy to know the surface selectivity.