Li3NaSiO4 as reversible CO2 absorbent: elucidation of performance-governing factors and regeneration mechanism

In situ reversible CO2 capture by thermally stable materials such as oxides has drawn much attention because of the high operation temperatures of the main CO2 sources, namely thermal power plants and internal combustion engines. In particular, Li4SiO4 features a high CO2 absorption capacity but suffers from slow CO2 absorption at practical CO2 partial pressures (P(CO2)), which can be mitigated through the incorporation of Na to afford Li3NaSiO4. Given that the Li3NaSiO4 regeneration kinetics and the possibility of the corresponding absorption/desorption cycling based on temperature or P(CO2) control remain underexplored, we herein characterized Li3NaSiO4 as a material for reversible CO2 absorption at high temperatures in response to CO2/N-2 gas switching, achieving excellent cycling performance at 750 degrees C. CO2 desorption (i.e., Li3NaSiO4 regeneration) was concluded to occur at the interface between solid Li2SiO3 and molten LiNaCO3, generating a Li3NaSiO4 layer that prevented further desorption at a thickness of > 1 mu m and thus resulted in the saturation of the CO2 desorption reaction in the middle. The lack of such saturation during cycling was attributed to the formation of needle-like (short side length approximate to 2 mu m) Li2SiO3 particles upon the absorption of CO2 by Li3NaSiO4. Thus, this work paves the way for the development of industrially applicable high-temperature CO2 capture/release materials and thus contributes to the establishment of a greener society.