How PtO x /CeO ₂ Nanostructures Catalyze CO Oxidation at Very Low Temperatures

High Resolution Image Download MS PowerPoint Slide Nanomaterials based on Pt and ceria (CeO 2 ) that are subjected to oxidative pretreatments can catalyze the CO oxidation reaction at temperatures below 0 °C, which is relevant for the conversion of low-temperature combustion emissions. However, the mechanisms by which such systems catalyze the low-temperature CO oxidation reaction remain unclear; the apparent activation energies measured experimentally for Pt/CeO 2 catalysts active below 0 °C are low and inconsistent with the activation barriers calculated using density-functional theory (DFT) on various oxidized or reduced ceria-supported Pt models. This study demonstrates, by means of DFT modeling and kinetic Monte Carlo simulations, CO oxidation pathways on stable ceria-supported PtO x clusters involving activation energies, turnover frequencies, and reaction temperature onsets consistent with low-temperature experimental catalytic data. These reaction pathways involve the oxidation of CO with O atoms of the supported PtO x clusters instead of those from the CeO 2 support often suggested for Mars van Krevelen mechanisms on ceria-supported metal catalysts. In contrast to the often-assumed higher reactivity of interface sites, the low-temperature CO oxidation mechanism via top-layer O atoms of the Pt 6 O 9 cluster distant from the support exhibits higher turnover frequencies than the mechanism involving interface O atoms of the cluster. These mechanistic insights pave the way for designing very low-temperature oxidation catalysts based on stable supported metal-oxide clusters.