Quantum chemical prediction of pathways and rate constants for reactions of CO and CO₂ with vacancy defects on graphite (0001) surfaces

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.