Interaction of O2 and N2 molecules with Au deposited on regular and defective CaO (001) surfaces: Density functional calculations

The adsorption of O2 and N2 on gold atoms deposited at regular O2 −site and neutral oxygen vacancy (Fs site) that is the most reactive sites of the CaO (001) surface, has been studied by means of the density functional theory calculations and embedded cluster model. Two different orientations, perpendicular and parallel, for the O2 and N2 molecules approaching the surface have been considered. Fundamental aspects such as adsorption energy, natural bond orbital, charge transfer, band gaps, the spin densities, the densities of states, total charge-density contours, pairwise and non-pairwise additivity are elucidated to analyze the adsorption properties of O2 and N2. It is observed that the adsorption of O2 is stronger at the Au atom that is supported on the Fs site than on the anionic site. Therefore, the presence of supported Au particle strongly stabilizes the adsorption of O2. The molecular bonding mechanism to these complexes involves charge transfer to the oxygen molecule with a concomitant activation of the OO bond to a superoxo-like state. On the contrary, Au deposited at CaO (O2 −) and CaO (Fs) sites does not exhibit any tendency to bind N2. The charge transfer between Au atom and N2 molecule is not significant in these adsorption systems. The binding of O2 precursor is mostly dominated by the metal EiAu−O2 pairwise additive contributions, and the role of the CaO is not restricted to supporting the metal.