Na2CO3 is one potential capture medium with the potential to decrease CO2 emission. Carbonation characteristics of four sodium-based sorbents were studied using thermogravimetric analysis (TGA), X-ray diffraction, scanning electron microscopy, and nitrogen adsorption apparatuses. Results show that, in TGA tests (carbonation atmosphere of 15% CO2 + 15% H2O(g) + 70% N-2 and carbonation temperature of 333 K), sorbent Na2CO3 [analytical reagent (AR)] is impervious, while sorbent Na2CO3 calcined from NaHCO3 (AR) reacts, mostly forming Na5H3(CO3)(4) instead of NaHCO3, corresponding to 72.87% conversion of Na2CO3 in about 140 min. With regard to the TGA tests of sorbent Na2CO3/Al2O3 and sorbent Na2CO3/Al2O3 calcined from NaHCO3/Al2O3, only NaHCO3 is generated and the carbonation conversions are both above 85% in about 55 min. The microstructure changes were observed to analyze the reaction mechanisms and carbonation characteristics. It is confirmed that, by loading active components on Al2O3, the microscopic structures can be significantly improved, contributing to the great improvement of carbonation characteristics of the latter two sorbents. On the other hand, there is little improvement of carbonation characteristics using NaHCO3 as precursors for sorbents supported on Al2O3.