Towards understanding the interaction mechanism of Sintering, hydration and carbonation of calcium oxide during CO2 capture

Hydration activation is an effective approach to improve the cyclic reactivity and mitigate the sintering of CaO sorbents. However, the interaction mechanism between sintering, hydration and reactivity remains unclear. In this study, we conducted hydration experiments using ex-situ water treatment in a separate hydrator to investigate the role of sintering degree in the activation reaction, complemented by ReaxFF molecular dynamics simulations (ReaxFF-MD) to elucidate the underlying mechanisms. The results revealed that high-temperature calcination causes apparent sintering of CaO, leading to a decline in CO 2 adsorption capacity. Hydration treatment greatly enriches the specific surface area and pore structure, providing more active sites and channels for CO 2 adsorption, thereby enhancing carbonation performance. The hydration degree of CaO was found to be negatively correlated with the degree of sintering, but positively correlated with the improvement of pore structure and property activation. Two types of hydroxyl groups (direct hydroxyl O w H and indirect hydroxyl O s H) were rapidly generated. O w H can convert to O s H through re-decomposition, involving O* radicals and proton diffusion. The hydroxylation gradually weakened as the sintering intensified. During the CaO hydration reaction, three types of water were generated: free H 2 O, adsorbed H 2 O and dissociated H 2 O. Free H 2 O and adsorbed H 2 O continued to increase with the degree of sintering, while the associated H 2 O decreased. Sintering significantly limited the diffusion of H atoms and hindered O s H formation, resulting in an overall decline in hydroxylation. For hydrated samples, the evaporation of free water, desorption of adsorbed water, and decomposition of dissociated water occurred simultaneously during heating. These phase transitions directly impacted on the evolution of pore structure.