Insight into the Structural Evolution of the Cobalt Oxides Nanoparticles upon Reduction Process: An In Situ Transmission Electron Microscopy Study

As a prerequisite elementary step, the reduction of cobalt (Co) oxides to form metallic Co is essential to display activity in heterogeneous catalysis. Nevertheless, the intrinsic principle of phase and morphology evolution for Co oxides and formation mechanism of the active Co site remains unclear. Here, we resolve this decades‐long question by using a state‐of‐the‐art in situ transmission electron microscopy (TEM) to elucidate the multi‐role of initial crystalline phase and size of Co oxides in modulation of reduction rate, phase and morphology evolution under H2 atmosphere, by excluding the possible interference from promoter and support. We anticipate that this study enriches current understanding on the surface structure and morphology evolution of Co oxides, and provides reference for rational design of Co‐based catalytic material as well as its pretreatment protocol. In situ: The complex reduction process of the cobalt catalyst precursors has been observed by using a state‐of‐the‐art in situ transmission electron microscopy. In particular, the multi‐role of initial crystalline phase and size of cobalt oxides in modulation of reduction rate, phase and morphology evolution under H2 atmosphere has been elucidated, by excluding the possible interference from promoter and support.