Alumina-supported silver (Ag/Al2O3) catalysts with different silver loadings were investigated for the selective catalytic reduction of NOx by ethanol. The catalytic role of silver in the formation of enolic species was studied by ultraviolet-visible spectroscopy, diffuse reflectance infrared Fourier transform spectroscopy combined with mass spectrometry, density functional theory calculations, and kinetic measurements. It was found that the enolic species originating from the partial oxidation of ethanol over Ag/Al2O3 prefer to adsorb on or close to silver sites, in intimate contact with the active phase. This adsorption behavior of this enolic species contributes to its high activity for the formation of isocyanate species (-NCO) and the final product N-2 during the NOx reduction by ethanol over Ag/Al2O3. Surface acetate also formed during this process, while only interacting with Al sites, resulting in a lower activity for -NCO formation. Meanwhile, the mechanism of the NOx reduction by ethanol was discussed. (C) 2012 Elsevier Inc. All rights reserved.