Adsorption of NO on Au atoms and dimers supported on MgO(1 0 0): DFT studies

The adsorption of NO on single gold atoms and Au2 dimers deposited on regular O2− sites and neutral oxygen vacancies (Fs sites) of the MgO(1 0 0) surface have been studied by means of DFT calculations. For Au1/MgO the adsorption of NO is stronger when the Au atom is supported on an anionic site than when it is on a Fs site, with adsorption binding energies of 1.1 and 0.5 eV, respectively. In the first case the spin density is mainly concentrated on the metal atom and protruding from the surface. In such a way, an active site against radicals such as NO is generated. On the Fs site, the presence of the vacancy delocalizes the spin into the substrate, weakening its coupling with NO. For Au2/MgO, as this system has a closed-shell configuration, the NO molecules bonds weakly with Au2. Regarding the N-O stretching frequencies, a very strong shift of ∼340-400 cm−1 to lower frequencies is observed for Au1/MgO in comparison with free NO.