DFT study on the reaction of NO oxidation on a stepped gold surface Original Research Article

The NO oxidation either with atomic or molecular oxygen on the stepped Au(3 2 1) surface was studied by means of DFT calculations (GGA/PW91). A periodic supercell approach was used to model the gold stepped surface and the kinetic profiles of the reactions were determined with the dimer approach. It was found that the co-adsorption of NO and O occurs preferentially with these species interacting with top and hollow sites nearby the steps, respectively. In the case of co-adsorbed NO and O2 species, the most stable configuration on the surface is a ONOO* intermediate. The NO2 product adsorbs strongly on the Au(3 2 1) surface (Eads = −1.10 eV) also nearby the step. The reaction of NO oxidation by atomic oxygen has an energy cost of 0.07 eV, whereas moderate-low energy barriers of 0.21 and 0.25 eV were computed for the reaction with molecular oxygen, via the ONOO* intermediate, following Elay–Rideal (ER) or Langmuir–Hinshelwood (LH) mechanisms, respectively. The reaction route following the ER mechanism is energetically more favorable since it is unnecessary to overcome the very high barriers (∼1 eV) needed for NO2 desorption and for dissociation of molecular oxygen in the cases of NO reaction via LH mechanism and NO oxidation with atomic oxygen, respectively.