Interface Reactions Dominate Low-Temperature CO Oxidation Activity over Pt/CeO2

First-principles-based kinetic Monte Carlo simulations and kinetic experiments are used to explore CO oxidation over Pt/CeO2. The simulations compare CO oxidation over a ceria-supported ∼1 nm particle with simulations of a free-standing particle and Pt(111). The onset of the CO oxidation over ceria supported Pt is shifted to lower temperatures compared to the unsupported systems thanks to a Mars–van Krevelen mechanism at the Pt/CeO2 interface perimeter, which is not sensitive to CO poisoning. Both the Mars–van Krevelen mechanism and the conventional Langmuir–Hinshelwood mechanism over the Pt nanoparticle are contributing to the conversion after the reaction onset. The reaction orders in CO and O2 are compared experimentally for Pt/CeO2 and Pt/Al2O3. The reaction orders over Pt/CeO2 are close to zero for both CO and O2, whereas the corresponding reaction orders are −0.75 and 0.68 over Pt/Al2O3. The measured zero orders for Pt/CeO2 show the absence of CO/O2 site competition and underline the relevance of interface reactions. The measurements for Pt/Al2O3 indicate that the main reaction path for CO oxidation over Pt is a conventional Langmuir–Hinshelwood reaction. The results elucidate the interplay between condition-dependent reaction mechanisms for CO oxidation over Pt supported on reducible oxides.