Atomic-Scale Explanation of O₂Activation at the Au–TiO₂Interface

Abstract

By a combination of electron paramagnetic resonance spectroscopy, finite-temperature ab initio simulations, and electronic structure analyses, the activation of molecular dioxygen at the interface of gold nanoparticles and titania in Au/TiO₂ catalysts is explained at the atomic scale by tracing processes down to the molecular orbital picture. Direct evidence is provided that excess electrons in TiO₂, for example created by photoexcitation of the semiconductor, migrate to the gold particles and from there to oxygen molecules adsorbed at gold/titania perimeter sites. Superoxide species are formed more efficiently in this way than on the bare TiO₂ surface. This catalytic effect of the gold nanoparticles is attributed to a weakening of the internal O-O bond, leading to a preferential splitting of the molecule at shorter bond lengths together with a 70% decrease of the dissociation free energy barrier compared to the non-catalyzed case on bare TiO₂. The findings are an important step forward in the clarification of the role of gold in (photo)catalytic processes.