With the support of the National Natural Science Foundation of China (Grant No.: 52025011, 51390474), the team led by Prof. Ze Zhang (张泽) and Prof. Yong Wang (王勇) at Center of Electron Microscopy, School of Materials Science and Engineering, Zhejiang University, unveiled the reversible epitaxialrotation of Au nanoparticles (NPs) on a TiO₂ surface during CO oxidation via environmental transmission electron microscope (ETEM). Taking the advantage of this reversible rotation, the team  further realized in situ manipulation of interface active sites of Au-TiO₂ catalyst by changing environments for the first time. This work was a collaboration between Yi Gao’s group from Shanghai Advanced Research Institute, Chinese Academy of Sciences, and the team of Prof. Wagner and Dr. Hansen from Technical University of Denmark. These results were published in Science on January 29^th, 2021 (2021, 371: 517-521.), titled “In-situ manipulation of the active Au-TiO₂ interface with atomic precision during CO oxidation”. Website link: https://science.sciencemag.org/content/371/6528/517.

Visualizing the catalytic reactions occurring at active sites and unveiling the catalytic mechanism is of great significance, which is the foundation for precise design and control of active sites at the atomic level. For a long period, gold was believed to be chemically inert. However, when AuNPs are loaded on titanium dioxide support, it exhibits excellent catalytic performance in many catalytic reactions, in which the Au-TiO­₂ interface plays the role of active center. While at the atomic scale, the catalytic process is still a mysterious "black box", and researchers have never seen the dynamic evolution of active interface at the atomic level during the catalytic reaction. It is more challenging to further accurately control the interface active sites.

Employing the advanced spherical aberration corrected ETEM, the researchers studied the dynamic evolution of the Au-TiO₂ interface at the atomic scale under the environment of CO catalytic oxidation. Different from the conventional understanding that the Au NPs are fixed on TiO₂ surface, they found the AuNPs loaded on TiO₂ surface underwent reversible in-plane (epitaxial) rotation during the catalytic process. As a result, with the rotation, the atomic structure of the Au-TiO₂interface changed, and thus correspondingly altered its catalytic activity. Therefore, by controlling the catalytic reaction conditions, the researchers realized in situ manipulation of the active Au-TiO₂ interface by changing gas and temperature. This work demonstrated the possibility of real-time design of the catalytic interface in operating conditions, which may help to develop better catalysts through the in-situ "intelligent manufacturing" at the atomic level.

Figure 1. The rotation of Au NPs on the (001) surface of TiO₂ support observed from both side (left) and top (right) views, via environmental transmission electron microscope.