Origin of Pt Nuclearity Dependence of CO Oxidation over Pt/TiO ₂ Catalysts in the Subnanometer Regime

Metal-oxide-supported Pt-group metal catalysts are essential for industrial reactions, including CO oxidation in automotive emission control. Maximizing the utilization of these metals is crucial for designing efficient catalysts. Therefore, understanding how the metal electronic properties and metal–support interactions change with metal nuclearity, especially in the subnanometer regime, is essential for advancing catalytic performance. This study investigates the reactivity of CO oxidation on Pt supported on anatase TiO 2 with varying Pt nuclearity from single atoms and 0.9 nm clusters to 1.8 nm nanoparticles. Kinetic measurements and in situ infrared spectroscopy reveal that CO oxidation activity and the Pt resistance to oxidation increase with nuclearity. Additionally, in situ infrared and X-ray absorption spectroscopy results show that the electron density on Pt under CO oxidation increases with Pt nuclearity. The reaction mechanism is shown to change as a function of nuclearity. For 0.9 nm clusters and 1.8 nm nanoparticles, TiO 2 lattice oxygen is involved in the reaction, likely via the Mars–van Krevelen mechanism. In contrast, on single atoms, oxygen from the lattice is not labile, and extra oxygen adatoms adsorbed on the Pt–Ti interface participate in CO 2 formation, leading to a significantly lower activity than 0.9 and 1.8 nm Pt. Kinetic analysis coupled with temperature-programmed reduction by CO and density functional theory calculations reveals that the higher activity is due to lower oxygen vacancy formation energy induced by larger Pt nuclearity. Overall, our study demonstrates that Pt nuclearity influences the reducibility of TiO 2 through electronic interaction, which gives rise to the structure sensitivity of CO oxidation on Pt/TiO 2 catalysts.