Direct Observation of Interfacial Au Atoms on TiO₂ in Three Dimensions

Interfacial atoms, which result from interactions between the metal nanoparticles and support, have a large impact on the physical and chemical properties of nanoparticles. However, they are difficult to observe; the lack of knowledge has been a major obstacle toward unraveling their role in chemical transformations. Here we report conclusive evidence of interfacial Au atoms formed on the rutile (TiO₂) (110) surfaces by activation using high-temperature (∼500°C) annealing in air. Three-dimensional imaging was performed using depth-sectioning enabled by aberration-corrected scanning transmission electron microscopy. Results show that the interface between Au nanocrystals and TiO₂ (110) surfaces consists of a single atomic layer with Au atoms embedded inside Ti-O. The number of interfacial Au atoms is estimated from ∼1-8 in an interfacial atomic column. Direct impact of interfacial Au atoms is observed on an enhanced Au-TiO₂ interaction and the reduction of surface TiO₂; both are critical to Au catalysis.