Todorokite-type manganese dioxide (MnO2) is consisted of triple chains of edge-sharing MnO6 octahedra with a tunnel size of 0.69 nm × 0.69 nm (see Figure 1) and its possible uses as catalysts are of great significance to scientific research and practical application due to its special structure and abundance in nature. Herein, we report ozone (O3) decomposition over todorokite-type MnO2 for the first time, and the structure of the todorokite-type MnO2 is proposed to be modified by means of metal doping and post heat treatment in order to increase the specific surface area and selectively expose the reactive facets. Compared with the unmodified MnO2, the catalytic activity and stability were greatly improved over the cerium-modified MnO2 (Ce-MnO2). As revealed by the BET, XPS, H2-TPR, SEM and (HR)TEM characterizations, larger surface area and the exposed (004) facet of MnO2 together with the crystal boundaries between MnO2 and CeO2 accounted for the better activity of Ce-MnO2. Besides, it is also found that the improved catalytic stability was associated with the desorption of oxygen species occupying the positions of oxygen vacancies. Compared with the as-synthesized Ce-MnO2, whose O3 conversion decreased fast with reaction time, 300 oC treatment (Ce-MnO2(300)) greatly improved the catalyst stability and the Ce-MnO2(300) exhibited ~98% of removal efficiency for ~115 ppm of O3 within 5 h under the space velocity of 1200 L/g/h at room temperature. In addition, a surface hydroxyl species-involved deactivation mechanism was newly put forward. The present results should contribute to the development of a highly active O3 decomposition catalyst that has potential practical application in the future work.

Preparation of todorokite-type manganese dioxide and its application in gaseous ozone removal

253rd National Meeting (2017)

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