This study investigated the selective catalytic reduction of NOx over alumina-supported silver catalyst by butyl alcohol isomers. Butyl alcohol (BA), sec-butyl alcohol (SBA), and isobutyl alcohol (IBA) showed similarly high efficiency for NOx reduction at low temperatures, while tert-butyl alcohol (TBA) exhibited a much lower performance. In situ diffuse reflectance infrared Fourier transform spectroscopy was used to clarify the remarkable influence of the alcohol structure on NOx reduction. A high surface concentration of enolic species was observed during the partial oxidation of BA, IBA, and SBA, leading to a high concentration of isocyanate species and high NOx conversion. However, due to the absence of alpha-H, it was difficult to partially oxidize TBA to form the enolic species, which resulted in its low efficiency for NOx reduction. Based on the results obtained, a mechanism was proposed to explain the close relationship between the structure feature of alcohols and NOx reduction efficiency. (C) 2010 Elsevier Inc. All rights reserved.