Formation of nitric oxide dimers on MgO-supported gold particles

We present density functional theory (DFT) calculations on the formation of nitric oxide dimers (N2O2) on Au atoms, dimers and trimers adsorbed on regular O2 − sites and neutral oxygen vacancies (Fs sites) of the MgO(100) surface. The study of the N2O2 species is of great interest since it has been detected in the NO reduction reaction as an intermediate towards the formation of N2O. We found that the coupling of a NO molecule with a previously adsorbed one on Au/MgO is energetically favorable on Au1 and Au3, but unfavorable on Au2. The stability of N2O2 is in direct relation with the amount of charge taken from the support. Furthermore, one of the N―O bonds can be activated as a result of the attraction between the negatively charged NO dimer and the ionic oxide surface. In fact, for Au1 anchored on the Fs site a barrierless reaction occurs between N2O2 and a third NO molecule, forming adsorbed N2O and NO2.