Carbon dioxide and water co-adsorption on the low-index surfaces of TiC, VC, ZrC and NbC: a DFT study.

We present a theoretical DFT study into the activation of CO by TiC, VC, ZrC and NbC. Particular focus is given to the study of CO/HO co-adsorption and interaction on four carbide low-index surfaces: {001}, {011}, carbon-terminated {111} and metal-terminated {111}. The adsorption and activation of CO is shown to be most exothermic and indeed barrierless on the metal-terminated {111} surfaces, whilst adsorption on the {001} and {011} planes occurs via a small activation energy barrier. In contrast, the carbon-terminated {111} surface proves to be unstable in the presence of the adsorbates. Both water and carbon dioxide adsorb most strongly on TiC and most weakly on NbC, with the strongest co-adsorption interactions being seen in conformations that maximise hydrogen-bonding.