In order to investigate the selective catalytic reduction of NO by hydrocarbons, Ag/Al2O3 models were constructed by means of density functional theory (DFT) and experimental results. The geometrical structures and vibrational frequencies obtained at B3LYP levels of DFT were compared with the corresponding experimental results. EXAFS results suggest silver ion species were predominant on the Al2O3 surface. Two forms of interaction between Ag and the Al2O3 support can be deduced, namely Ag-O-Al-octa (octahedral, AlO6) and Ag-O-Al-tetra (tetrahedral, AlO4). The Ag-O-Al-octa interaction is energetically favorable, which can be corroborated by both NMR results and DFT calculation. However, vital NCO intermediate species prefer to adsorb on the Ag-O-Al-tetra entity. In the reduction of NO2, -NCO species close to Ag-O-Al-tetra are more favorable than those on Ag-O-Al-octa, both energetically and kinetically. Thus rather than Ag-O-Al-octa should be considered as the active site during the HC-SCR process. The CNO-species, as an isomer of -NCO, was also examined by theoretical methods, and it was found to be more kinetically favorable to reduce NOx over the site of the Ag-O-Al-tetra entity than -NCO species. (C) 2015 Elsevier B.V. All rights reserved.