se of an activated carbon (AC) with high ash content (15.92%) for SO2 removal was investigated during adsorption‒desorption cycles. Significant deterioration in both dynamic and equilibria adsorption processes during the cycles was observed. To investigate causes of deactivation, SO2 temperature-programmed desorption (SO2‒TPD) experiments were conducted. The results indicated that most stored sulfur-containing species were released in the form of SO2 when the temperature was below 400°C. In addition to SO2, traces of CO were also detected, but abundant release of CO required higher temperatures. A Fourier-transform infrared spectrometry (FTIR) experiment was used to investigate changes in the oxygen-containing groups, and the results confirmed the formation of stable C‒O complexes. These formations were tentatively attributed to the CO precursor’s occupation of active sites. Based on the formation of C‒O complexes, two deactivation pathways in the cycles were proposed. The adsorption‒desorption cycles also have affected the AC ash. The formation of sulfur-containing species in the ash was confirmed through thermodynamic calculation and powder X-ray diffraction.