Quantum Chemical Prediction of Pathways; and Rate Constants for Reactions of CO and CO2 with Vacancy Defects on Graphite (0001) Surfaces

Abstract

We present reaction pathways for adsorption of CO and CO2 molecules in the vicinity of monovacancy defects on graphite (0001) based on B3LYP and dispersion-augmented density-functional tight-binding (DFTB-D) studies of the potential energy surfaces (PES) of these reactions. To model the graphite (0001) monovacancy defects, finite-size molecular model systems up to the size of dicircumcoronene (C95H24) were employed. We find that the CO molecule reacts readily with the monovacancy defects and partially "heals" the carbon hexagon network leading to the formation of a stable epoxide, whereas CO2 oxidizes the defect via a dissociative adsorption pathway following CO elimination. We predict reaction rate constants in the temperature range between 300 and 3000 K using Rice-Ramsperger-Kassel-Marcus theory. Quantum chemical molecular dynamics simulations at 3000 K based on on-the-fly DFTB-D energies and gradients-support the results of our PES studies.