Self-reactivated mesostructured Ca-Al-O composite for enhanced high-temperature CO₂ capture and carbonation/calcination cycles performance

In this study, highly efficient high-temperature CO₂ sorbents of calcium aluminate (Ca-Al-O) mesostructured composite were synthesized using presynthesized mesoporous alumina (MA) as a porous matrix to react with calcium nitrate through a microwave-assisted process. Upon annealing at 600 °C, a highly stable mesoporous structure composed of poorly crystalline Ca₁₂Al₁₄O₃₃ phase and the CaO matrix was obtained. The Ca-Al-O mesostructured sorbents with a Ca²⁺/Al³⁺ ratio of 5:1 exhibit an enhanced increasing CO₂ absorption kinetics in the CO₂ capture capacity from 37.2 wt % to 48.3 wt % without apparent degradation with increasing carbonation/calcination cycling up to 50 at 700 °C due to the strong self-reactivation effect of the mesoporous Ca-Al-O microstructure. Remarkable improvements in the CaO-CaCO₃ conversion attained from the mesostructured Ca-Al-O composite can be explained using the concept combined with available mesoporous structure and Ca₁₂Al₁₄O₃₃ phase content. However, a high Ca²⁺/Al³⁺ =8:1 Ca-Al-O composite causes degradation because the pores become blocked and partial sintering induces CaO agglomeration.