The relationship between surface open cells of α-MnO2 and CO oxidation ability from a surface point of view

Abstract

α-MnO₂ is a widely reported material for catalysis reactions. However, due to its complicated structure with 2 × 2 tunnels, knowledge of the surface structure and its relationship with the catalytic performance for α-MnO₂ is limited, even though the understanding of this is key for developing better catalysts. Herein, a surface-focused structure–performance relationship regarding the oxidation of CO is established in this work. It is shown that the 2 × 2 tunnels are open at the surface {100} planes via transmission electron microscopy (TEM), TEM simulation, and CeO₂ probe deposition experiments. Since α-MnO₂ is rod-like and wrapped with {100} planes, the surface of α-MnO₂ consists mainly of this open cell structure. The open cells are rich in adsorption sites for O₂. Furthermore, these surface sites are also highly oxidative in nature. Owing to the fact that CO can react with surface oxygen species to yield CO₂, the promoted adsorption of O₂ and the oxidative surface sites will benefit CO oxidation over α-MnO₂. Thus, the superior performance for CO oxidation can be related to the open cell structure. This work not only establishes the surface structure–performance relationship, but also provides a new point of view for the understanding of the structure of α-MnO₂ by emphasising the surface open cells.