Scattering of CO\nfrom Vacant-MoSe<sub>2</sub> with\nO Adsorbates: Is CO<sub>2</sub> Formed?

Using ab initio molecular\ndynamics (AIMD) simulations, based on\ndensity functional theory that also accounts for van der Waals interactions,\nwe study the oxidation of gas-phase CO on MoSe<sub>2</sub> with a\nSe vacancy and oxygen coverage of 0.125 ML. In the equilibrium configuration,\none of the O atoms is adsorbed on the vacancy and the other one atop\none Se atom. Recombination of the CO molecule with the second of these\nO atoms to form CO<sub>2</sub> is a highly exothermic reaction, with\nan energy gain of around 3 eV. The likeliness of the CO oxidation\nreaction on this surface is next examined by calculating hundreds\nof AIMD trajectories for incidence energies that suffice to overcome\nthe energy barriers in the entrance channel of the CO oxidative recombination.\nIn spite of this, no CO<sub>2</sub> formation event is obtained. In\nmost of the calculated trajectories, the incoming CO molecule is directly\nreflected, and in some cases, mainly at low energies, the molecules\nremain trapped at the surface but without reacting. As an important\nconclusion, our AIMD simulations show that the recombination of CO\nmolecules with adsorbed O atoms is a very unlikely reaction in this\nsystem, despite its large exothermicity.