Oxidation of Gas-Phase and Supported Pt Nanoclusters: An Ab Initio Investigation

Heterogeneous catalysts based on Pt nanoparticles supported on oxides are used in a number of important catalytic processes, including oxidation of hydrocarbons and redox reactions in PEM fuel cells. The interaction with gas-phase oxygen is often a key component of the target chemistry and can affect the reactivity of the clusters because of their oxidation. Recent experiments have shown that the oxidation of Pt nanoparticles is influenced by a number of factors, including the clusters size and the interaction with the support, leading to properties that can differ substantially from those of larger samples. Here we combine density functional theory, the genetic algorithm, and ab initio thermodynamics to investigate the structure and the oxidizability of small Ptx(x = 1-8) nanoparticles. We find that the interaction of oxygen with Pt depends strongly on the size of the clusters, leading to facile oxidation of Pt nanoparticles. The interaction with the oxide supports studied in this work, brookite TiO2and Co3O4, hinders the oxidizability compared to the gas phase. At conditions of temperature and pressure typically encountered in catalytic oxidation reactions, Pt nanoparticles are predicted to be oxidized, at variance with the bulk counterpart. Our results highlight the importance of low Pt-Pt coordination in the interaction with oxygen and the role of the interaction with oxide supports.