Mechanistic Insights into CO2 Adsorption of Li4SiO4 at High Temperature

The development of materials with high adsorption capacity for capturing CO2 from industrial exhaust gases has proceeded rapidly in recent years. Li4SiO4 has attracted attention due to its low cost, high capture capacity, and good cycling stability for direct high-temperature CO2 capture. Thus far, the CO2 adsorption mechanism of Li4SiO4 is poorly understood, and detailed phase transformations during the CO2 adsorption process are missing. Here, aided by in situ X-ray diffraction and in situ Raman spectroscopy, we find that Li4SiO4 reacts with CO2 to form Li2SiO3 and Li2CO3 in CO2 atmosphere at 973 K, with no detectable involvement of crystalline Li2O during the adsorption process. Moreover, we observe a formation of stepped structures in the Li4SiO4 surface after CO2 adsorption by scanning electron microscopy. To illustrate the formation of stepped structures, we propose a modified double-shell mechanism, suggesting a possible two-dimensional nucleation and growth of Li2CO3. This work provides a deeper understanding of the CO2 adsorption mechanism and paves a way for further optimization of Li4SiO4-based adsorbents.