Abstract: To study the effects of HNO₃ modification on NO reduction over activated carbon (AC) at low temperatures, the AC was modified using HNO₃ at different temperatures. The activity of the resulted activated carbons towards NO reduction with NH₃ was investigated in a temperature range of 30−250 ℃. The temperature programmed desorption (TPD) and transient response experiments were used to study the mechanism of NO reduction. The results reveal that the NO conversion decreased with temperature at the initial stage and then kept stable. The adsorption of reactants was the rate-determining step. The increase of oxygen groups on the catalyst surface enhanced NH₃ adsorption. The adsorbed NH₃ hardly reacted with NO at 30 ℃. With increasing temperature, the adsorbed NH₃ was gradually activated. In the temperature range of 30−90 ℃, the adsorption of reactants was rate-determining step of NO reduction. When the temperature was higher than 90 ℃, the reaction was dominated by the activation of adsorbed NH₃.