Wu and Lan [20] developed a kinetic model for CaO reaction with CO2, a fast surface reaction regime followed by a slow diffusion-controlled regime. In practical application, the fast reaction regime is more important. The CaO conversion in the fast reaction regime is defined as Xu, which is equal to two times the CaO conversion X1 at the maximum reaction rate (Xu = 2X1) [20]. In this work, the CO2 capture capacity Cu at the point of Xu is calculated and shown in Fig. 8. In the first cycle, the order of Cu for three sorbents is: CA-91> untreated CaO > CA-82. At the 13th cycle, untreated CaO is sintered seriously and Cu value is decreased to 0.1 g/g, and the synthetic CaO–Al2O3 sorbents still have the higher CO2 capture capacities, whose Cu values are 0.14 g/g (CA-82) and 0.22 g/g (CA-91), respectively, and the order of Cu for three sorbents is changed as: CA-91 > CA-82 > untreated CaO. In the slow diffusion-controlled stage, CA-91 sorbent has the higher reaction kinetics. After 13th carbonation, the reaction rates of the synthetic CaO–Al2O3 sorbents are still higher than that of untreated CaO at the slow diffusion-controlled regime even though the CaO contents in CA-91 and CA-82 sorbents are less than that in untreated CaO. Therefore, the porous structures formed in the synthetic CaO–Al2O3 sorbents are beneficial to the intraparticle CO2 diffusion. From Fig. 7 and Fig. 8, it can be found that the CO2 capture capacity of CA-91sorbent is the highest, so that the synthetic CaO–Al2O3 sorbent with 9% Al2O3 additive can be a promising Ca-based sorbent material in the Ca-looping CO2 capture system.