The specific surface area and pore size distribution of the synthetic CaO–Al2O3 sorbents were analyzed by Micrometrics ASAP 2010 apparatus, as listed in Table 2. Since the synthetic CaO–Al2O3 sorbents are activated with a four-step heating mode, heating at 170 °C for 0.5 h, at 340 °C for 0.5 h, at 440 °C for 0.5 h, and at 720 °C for 0.5 h, the mild calcination condition favors the formation of porous structure in sorbents. The BJH adsorption average pore diameter of CA-91 sorbent is as small as 5 nm and the pore volume is as high as 0.85 cm3/g, so the synthetic CaO–Al2O3 sorbent with 9% Al2O3 additive has an amazingly high BET surface area (958 m2/g), which is far higher than that of untreated CaO sorbent (5 m2/g), as shown in Fig. 5. Comparing with CA-91 sorbent, when the CaO–Al2O3 sorbent is synthesized with a higher Al2O3 content, such as CA-82 sorbent with 18% Al2O3, the mean pore diameter is increased to 36 nm and the pore volume significantly is decreased to 0.06 cm3/g, which results in a decrease of the BET surface area to 11 m2/g for CA-82 sorbent.