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

Abstract

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/CeO2interface 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 O2are compared experimentally for Pt/CeO2and Pt/Al2O3. The reaction orders over Pt/CeO2are 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/CeO2show the absence of CO/O2site competition and underline the relevance of interface reactions. The measurements for Pt/Al2O3indicate 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.