- Chen, Yizhen;
- Rana, Rachita;
- Zhang, Yizhi;
- Hoffman, Adam S;
- Huang, Zhennan;
- Yang, Bo;
- Vila, Fernando D;
- Perez-Aguilar, Jorge E;
- Hong, Jiyun;
- Li, Xu;
- Zeng, Jie;
- Chi, Miaofang;
- Kronawitter, Coleman X;
- Wang, Haiyan;
- Bare, Simon R;
- Kulkarni, Ambarish R;
- Gates, Bruce C
Supported noble metal catalysts, ubiquitous in chemical technology, often undergo dynamic transformations between reduced and oxidized states-which influence the metal nuclearities, oxidation states, and catalytic properties. In this investigation, we report the results of in situ X-ray absorption spectroscopy, scanning transmission electron microscopy, and other physical characterization techniques, bolstered by density functional theory, to elucidate the structural transformations of a set of MgO-supported palladium catalysts under oxidative treatment conditions. As the calcination temperature increased, the as-synthesized supported metallic palladium nanoparticles underwent oxidation to form palladium oxides (at approximately 400 °C), which, at approximately 500 °C, were oxidatively fragmented to form mixtures of atomically dispersed palladium cations. The data indicate two distinct types of atomically dispersed species: palladium cations located at MgO steps and those embedded in the first subsurface layer of MgO. The former exhibit significantly higher (>500 times) catalytic activity for ethylene hydrogenation than the latter. The results pave the way for designing highly active and stable supported palladium hydrogenation catalysts with optimized metal utilization.