Quantum chemical calculations have been performed using density functional theory to model the mechanism of selective catalytic reduction of NO by NH3 on vanadium oxide. The reaction is initiated by NH3 adsorption on a Bronsted site modeled as a dimer cluster model representative of vanadium oxide, containing a terminal V=O adjacent to a V-OH group. The calculations indicate that the adsorbed NH3 behaves as NH4+, which is supported by calculated LR spectra. Subsequently NO reacts with this activated NH3 to yield NH?NO and finally the reaction products N-2 and H2O. The present results give support to a dual-site Eley-Rideal-type mechanism involving a Bronsted site and agree with isotopic labeling studies.