Silica aerogel supported K2CO3 sorbents with different K2CO3 loadings were synthesized by sol-gel and wet impregnation processes. The sorbents were characterized by N-2 adsorption-desorption, X-ray diffraction (XRD), and field emission scanning electron microscopy (FESEM) techniques. CO2 capture performances of the sorbents were tested in a simulated ultra-dilute flue gas stream of 1.0% CO2 and 2.0% H2O at 20 degrees C, using a fixed-bed reactor coupled with an online infrared gas analyzer. Sorbent regeneration performances of the samples were evaluated in a pure N-2 atmosphere at 200 degrees C with a heating rate of 10 degrees C/min. CO2 capture capacity and K2CO3 utilization efficiency increased first and then decreased with the increase in K2CO3 loading. The desired sorbent with 20 wt% K2CO3 was screened for investigating the effects of acid impurities. The presence of 500 ppm SO2 and 500 ppm NO in the simulated flue gas stream was found to adversely affect the CO2 capture, sorbent regeneration and multiple cyclic performances. Detailed mechanisms of the irreversible sorbent deactivation process were discussed. SO2 could be chemically absorbed by K2CO3 under a moist condition to form by-product of K2SO3 center dot H2O, and the byproduct was stable and would be accumulated in the sorbent during the repeated cycles. This further attenuated the physical properties and K2CO3 utilization efficiency of the sorbent. These results would lay a solid foundation for further application of the sorbent in ultra-dilute flue gas treatment.