Probing the Reactivity of Pt/Ceria Nanocatalysts toward Methanol Oxidation: From Ionic Single-Atom Sites to Metallic Nanoparticles

Single-atom catalysts represent the ultimate extreme in heterogeneous catalysis for the maximum dispersion of mononuclear catalytic metal particles on supporting surfaces. Ultralow Pt loading has been achieved on nanostructured ceria surfaces that allow for stabilizing metallic and ionic Pt sites that are anchored at surface defects. Here, we assess the chemical reactivity of these different Pt species, which are experimentally known to coexist on Pt-ceria nanocatalysts, by taking methanol oxidation as a chemical probe. Our density functional theory calculations demonstrate that Pt2+ and Pt4+ single-ion species do not promote methanol oxidation by themselves. Instead, metallic sites of supported sub-nanometer Pt particles are always required to promote the oxidation reaction. Our finding generalizes the conclusions of recent photoemission experiments in the context of H2 oxidation by ceria/Pt nanocatalysts. Moreover, the simulations predict that surface hydroxide groups may act as cocatalyst for the direct methanol oxidation to formaldehyde, thus proposing a viable strategy for catalyst design