CO Adsorption on Molybdenum Nitride's γ-Mo2N(100) Surface: Formation of NCO Species? A Density Functional Study

Abstract

To gain insight into the electronic surface properties of γ-Mo2N(100) and the CO chemisorption, density functional calculations have been undertaken on periodic surface models using the generalized gradient approximation for the exchange-correlation functional. Structure relaxation of γ-Mo2N(100) has been performed for different models depending on the surface stoichiometry (Mo/N ratio, mimicking the nitridation effect) or composition (O adatom, mimicking the passivation effect). The reaction γ-Mo2N(100) + X2(g) → γ-Mo2N(100)−X, with X = N and O, is calculated to be exothermic. This suggests that stoichiometric (100) surfaces containing 4-fold vacancy sites are unstable with respect to the dissociative adsorption of N2 and O2 molecules. The chemisorption sites of CO and the associated CO vibrational frequencies have been determined for the Mo2N(100)−X/CO surfaces. On a stoichiometric (100) surface, a μ4-bonding mode of CO is localized on the potential energy surface with the same binding energy as the one...