Synergetic role of photogenerated electrons and holes in the oxidation of CO to CO₂ on reduced TiO₂(110): A first-principles study

We present the role of photogenerated charge carriers in the oxidation of CO by O₂ on reduced, rutile TiO₂(110) based on first-principles DFT calculations. Our calculations show that hole-trapped O₂ at the O vacancy site adopts a tilted open ring configuration, while an additional electron preferentially localizes at the CO-bound Ti site. The electron-hole separated configuration likely converts to the O-O-C-O complex with a small barrier of around 0.1 eV. From the neutral intermediate state, CO₂ is predicted to desorb off the surface with a barrier less than 0.2 eV if another hole is available. For comparison, we also look at both thermally activated and hole-mediated CO oxidation processes, but the predicted overall barriers of around 0.9 and 0.5 eV, respectively, appear to be high for facile CO oxidation at low temperatures. Our findings clearly highlight that excess electrons and holes can synergetically contribute to CO photooxidation, which is consistent with a recent experimental study by Petrik and Kimmel that provides evidence for involvement of multiple nonthermal reaction steps.