Quantum chemical calculations using the density functional theory were performed to model the mechanism of selective catalytic reduction of NO by NH3 on a supported vanadium oxide monolayer. In the first step, the adsorption of NH3 on a bimetallic cluster representative of vanadium oxide, containing a terminal VO adjacent to a VOH group, was investigated. The calculations indicate that NH3 may be strongly adsorbed on VOH (Brönsted acid site) as NH+4(ads); subsequently, NO reacts with this activated NH3 to yield the reaction products N2 and H2O. The present results give support to a dual-site Eley-Rideal-type mechanism involving a Brönsted site.