Scattering of CO from Vacant-MoSe$_2$ with O Adsorbates: Is CO$_2$ Formed?

TL;DR

This study uses ab initio molecular dynamics to investigate CO oxidation on MoSe$_2$ with oxygen adsorbates, finding that CO$_2$ formation is highly unlikely despite being energetically favorable.

Contribution

It provides the first detailed AIMD analysis showing the improbability of CO$_2$ formation on MoSe$_2$ with oxygen vacancies, challenging assumptions based solely on thermodynamics.

Findings

CO$_2$ formation is energetically favorable but rarely occurs in simulations.

Most CO molecules are reflected or trapped without reacting.

Recombination of CO with adsorbed O is highly unlikely in this system.

Abstract

Using ab initio molecular dynamics (AIMD) simulations, based on density functional theory that also accounts for van der Waals interactions, we study the oxidation of gas phase CO on MoSe$_2$ with a Se vacancy and oxygen coverage of 0.125~ML. In the equilibrium configuration, one of the O atoms is adsorbed on the vacancy and the other one atop one Se atom. Recombination of the CO molecule with the second of these O atoms to form CO$_2$ is a highly exothermic reaction, with an energy gain of around 3~eV. The likeliness of the CO oxidation reaction on this surface is next examined by calculating hundreds of AIMD trajectories for incidence energies that suffice to overcome the energy barriers in the entrance channel of the CO oxidative recombination. In spite of it, no CO$_2$ formation event is obtained. In most of the calculated trajectories the incoming CO molecule is directly reflected and in some cases, mainly at low energies, the molecules remain trapped at the surface but without reacting. As important conclusion, our AIMD simulations show that the recombination of CO molecules with adsorbed O atoms is a very unlikely reaction in this system, despite its large exothermicity.