Effect of crystallinity on CO2 adsorption performance of CaO prepared from different precursors by thermolysis: The key to obtain equimolar capture materials

The development of efficient carbon dioxide (CO 2 ) adsorbents is crucial for the carbon capture, storage and utilization (CCSU) as well as carbon neutrality targets. Calcium oxide (CaO) has attracted intensive attention due to its low cost and high CO 2 adsorption capacity at high temperature. In the present work, various CaO samples were prepared by simple calcination of different calcium-based precursors with different molecular weight. The CO 2 adsorption performance of these CaO had a tendency to increase at first, and then decrease as the molecular weight of the precursors further increases, which were attributed to differences in their crystallinity. More precisely, there is a negative correlation between the crystallinity of the CaO (200) peak and CO 2 adsorption capacity, i.e. the crystallinity of CaO from different precursors increase according to the order of CaC 4 H 6 O 4  < CaC 2 O 4  < CaCO 3  < Ca(OH) 2  < CaC 36 H 70 O 4, but their adsorption capacity is CaC 4 H 6 O 4 (0.907 mol/mol) > CaC 2 O 4 (0.84 mol/mol) > CaCO 3 (0.64 mol/mol) > Ca(OH) 2 (0.61 mol/mol) > CaC 36 H 70 O 4 (0.30 mol/mol). Additionally, the reaction between CaO and CO 2 followed the Type I Langmuir adsorption isotherm and adhered to a pseudo-second-order kinetic model. Moreover, the optimal adsorption temperature of CaO from CaC 4 H 6 O 4 was around 650°C, where the maximum adsorption capacity nearly reached 1 mol/mol at the pressure of 0.1 bar. It was also determined that CaO from CaC 4 H 6 O 4 had good cyclic adsorption capacity.