To determine the nature of oxygen groups for the selective catalytic reduction (SCR) of NO with NH3 over activated carbon (AC), coal-based AC was oxidized by HNO3 to suitable degrees. Resulted carbons were characterized by N-2 adsorption, elemental analysis, X-ray photoelectron spectroscopy, diffuse reflectance infrared Fourier transform spectroscopy, and temperature programmed desorption. Changes in surface properties were compared with the variation in the SCR activity in the temperature range of 100-250 degrees C. Carboxyl, anhydride, and phenol groups were found to be most likely responsible for the promoted catalytic activity of AC towards NO reduction mainly because of enhanced NH3 adsorption. (C) 2015 Published by Elsevier B.V.