Al(2)O(3)-coated cordierite supported CuO catalyst shows high activities for selective catalytic reduction (SCR) of NO by NH(3) at 350-500 degrees C after being sulfated by SO(2). Its surface properties and reaction mechanism are elucidated in this paper by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) coupled with mass spectroscopy. Results show that the catalyst has both Lewis and Bronsted acid sites, the Bronsted acidity is far weaker than the Lewis acidity and the protonated ammonia on Bronsted sites is less stable than the coordinated ammonia on Lewis sites. Ammonia coordinated on sulfated CuAl(2)O(4) may transfer to NH(2)-NH(2), where aluminum species is responsible for NH(3) storage and copper species is responsible for activation of NH(3) to NH(2). The SCR reaction involves the adsorbed NH(2)-NH(2) and gaseous NO, following Eley-Rideal mechanism. When NH(3) is insufficient, NO may convert to NO(2) through oxidation by O(2) or to N(2)O and NO(2) through disproportionation. (C) 2010 Elsevier B. V. All rights reserved.