K2CO3 supported on activated carbon (K2CO3/AC) shows promise as a potential candidate for removing low-concentration CO2 from environmental control and life support systems (ECLSS). However, K2CO3/AC would suffer a decreased CO2 sorption capacity due to sorbent deactivation in acid impurities such as SO2 and NO2. To solve this problem, water vapor pretreatment, KOH addition and polyethyleneimine (PEI) modification were proposed as efficacious means for improving its CO2 sorption capacity and mitigating the sorbent deactivation in these acid impurities. CO2 sorption performances of the pretreated and modified sorbents were evaluated in a fixed-bed reactor under simulated ECLSS conditions of 20 degrees C, 1.0% CO2, 2.0% H2O, 30 ppm SO2, 20 ppm NO2 and balanced N-2. The mechanisms for sorbent deactivation inhibition by water vapor pretreatment, KOH addition and PEI modification were revealed by N-2 adsorption desorption, X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and Fourier transform infrared spectroscopy (FT-IR). Effects of water vapor pretreatment duration, KOH addition and PEI loading on sorbent deactivation inhibition performances were demonstrated. Furthermore, the long-term working stabilities of the pretreated and modified sorbents in impurities were evaluated. The results will provide fundamental support on practical application of K2CO3/AC for low concentration CO2 removal in ECLSS. (C) 2016 Elsevier B.V. All rights reserved.