Triple-salt-promoted MgO composites (NaNO3, Na2CO3, and LiNO3) for precombustion CO2 capture were developed by a precipitation method with a controllable salt composition. MgO precursors were mixed and aged with salts to control the composition and morphology. The MgO composites exhibited a CO2 sorption capacity of 73 wt % in pure CO2 at 240 min and 300 degrees C and achieved a sorption capacity of 25 wt % within 10 min because of a high sorption rate. When a cyclic test was conducted with pure CO2 sorption for 60 min at 325 degrees C and N-2 regeneration for 15 min at 425 degrees C (60/15 min cycle) as a reference, the cyclic capacity was 45 wt % after 30 cycles. On the other hand, considering the applicable capture processes, the sorption capacity during a fast cycle (10/5 min cycle) was 18 wt % under the same gas and temperature conditions. Finally, the working capacity of the MgO composite was evaluated under a simulated emission gas (29% CO2, 3% H2O, and balance N-2) at 300 degrees C for sorption and CO2 at 450 degrees C for regeneration because of the importance of water vapor and CO2 regeneration in the evaluation. The rearrangement of the salts and the MgO grains during the initial cycles led to an enhanced working capacity. However, the working capacity declined along the subsequent cycles due to sintering, and it was severe under CO2 regeneration. However, the working capacity for the wet mixture sorption and CO2 regeneration stabilized after 20 cycles at 23 and 4.6 wt % for 60/15 min and 10/5 min cycles, respectively. The results indicate that the as-synthesized MgO composites are feasible for the practical application of precombustion CO2 capture.