Au (Core)–Pt (Shell) Nanocatalysts with the Shell Thickness Controlled at a Monolayer Level: Extremely High Activity for Hydrogen Peroxide Decomposition

Au and Pt nanoparticle-loaded anatase TiO2 particles (Au/TiO2 and Pt/TiO2) were separately prepared by the deposition–precipitation method. Also, selective Pt photodeposition on the Au surface of Au/TiO2 yielded Au (core)–Pt (shell) bimetallic NP-loaded TiO2 particles. In Au (core)–Pt (shell)/TiO2, the mean Pt-shell thickness was controlled at an atomic layer level by irradiation time. The thermocatalytic activities of Au/TiO2, Pt/TiO2, and Au (core)–Pt (shell)/TiO2 for the decomposition of H2O2 were evaluated in the dark at 25 °C. Au (core)–Pt (shell)/TiO2 exhibits a much higher activity than that of Au/TiO2 and even Pt/TiO2 in spite of that Pt has the highest activity among the metals. The turnover frequency depends on the mean number of Pt layers, reaching a maximum of 1.1 × 106 around the monolayer. Density functional theory simulations were performed to analyze the potential-energy surfaces in metal-cluster-catalyzed H2O2 decomposition with Au50, Pt50, and Au14 (core)–Pt36 (shell) used as model metal clusters. The results explain the relative catalytic activities of Au/TiO2 ≪ Pt/TiO2 < Au@Pt/TiO2, further indicating the affinity of the metal clusters for oxygen atom produced in the course of reaction.