Phase structures, morphologies, and NO catalytic oxidation activities of single-phase MnO2 catalysts

•γ-MnO2 showed superior NO oxidation activity in comparison to α-, β- and δ-MnO2.•γ-MnO2 had a special random-tunnel structure which easily created structural faults.•The structural faults in γ-MnO2 facilitated the adsorption and activation of NO and O2.

The NO catalytic oxidation activities of single-phase α-, β-, γ-, and δ-MnO2 were investigated. All the catalysts were systematically characterized using various techniques. The results showed that the catalytic activities were significantly affected by the MnO2 phase structures. Among the four catalysts, the urchin-like γ-MnO2 showed the best NO catalytic oxidation activity across the studied temperature range, with the largest NO conversion, namely 88%, at 280 °C. This is good activity, even compared with those of noble-metal-based catalysts. It also displayed the best activity during long reaction times. The NO catalytic oxidation activities of the other three catalysts decreased in the order α- > β- > δ-MnO2. The various phase structures of MnO2 contain the same [MnO6] octahedral units, but with different linking modes. γ-MnO2 has a disordered structure, resulting in larger numbers of active oxygen species, leading to a better catalytic performance.

Graphical abstractγ-MnO2 displayed the best NO catalytic oxidation activity, especially in the low temperature range. The large specific surface area and pore volume of the γ-MnO2 were supposed to have beneficial effect, besides, the active oxygen in the γ-MnO2 resulted from the random structure of γ-MnO2 was also responsible for the superior activity.Figure optionsDownload full-size imageDownload high-quality image (113 K)Download as PowerPoint slide