Catalytic behavior of Pt single-atoms supported on CeO2

In this study, we demonstrate that the CO oxidation activity of Pt/CeO2 single-atom catalysts (≤0.4 Pt/nm2) is significantly low despite the increase in reducibility, which is associated with the formation of oxygen vacancies that are critical for oxygen activation, with increasing Pt surface density. This result can be related to the negligible amount of CO adsorbed onto the Pt/CeO2 single-atom catalysts. As the Pt surface density increases to 0.8 Pt/nm2, the activity sharply increases; at this loading, Pt clusters are formed and the interactions with CO are enhanced. Notably, after the controlled reduction treatment using CO, the catalytic activity of 0.4 Pt/CeO2 increases to the level of 0.8 Pt/CeO2. The sudden increase in activity can be explained by the formation of a partially reduced Pt cluster and the enhanced CO interactions with the Pt atoms of the cluster. These results indicate that Pt cluster formation and its partial reduction are essential for low-temperature CO oxidation. Our study explains the cause of the significantly low CO oxidation activity of Pt/CeO2 single-atom catalysts and how controlled reduction treatment of these catalysts enhances their activity.