K2CO3-doped CaO-based sorbent for CO2 capture: Performance studies and promotion mechanisms

Calcium looping (CaL) represents a promising technology for CO2 capture from flue gas. Nevertheless, CaO-based sorbents, characterized by high theoretical absorption capacities and low costs, experience significant degradation in CO2 capture capacity during continuous cycling. In the present study, a novel K2CO3-doped CaO sorbent was synthesized through a concurrent hydrophilic impregnation process, and the performance of consecutive cyclic CO2 capture was evaluated. The optimal 0.05 K-CaO demonstrated the highest CO2 sorption (12.4 mmol/g), maintaining about 64 % of the initial sorption after 20 repetitive cycles under N2 calcination atmosphere, which is 6.6 times greater than that of CaO. These findings indicated that K2CO3 can regulate the particle size and the state of surface oxygen species in CaO-based sorbents while simultaneously enhancing CO2 diffusivity on the sorbent surface. The DFT calculations indicated that the incorporation of K2CO3 improved the mechanism of CaO chemisorption of CO2. Additionally, the vacancies and CO 3 2- generated by K2CO3 doping can enhance the CO2 sorption energy and reduce the system's energy level. Notably, the net charge transfer for CO2 sorption from K2CO3 doping is greater than that from pure CaO, and the O atoms on the surface of K2CO3-CaO (001) exhibit strong covalent interactions with the C atoms in CO2, both of which facilitate CO2 chemisorption. This study offers a comprehensive theoretical mechanism for the incorporation of K-based alkali metals to enhance the CO2 capture performance of CaO sorbents.