Figure 7 . Ozone conversion over different MnOxcatalysts (MnO2-H-200, MnO2, Mn2O3 and Mn3O4)
MnO2, Mn2O3 and Mn3O4 showed distinctly different performance on ozone decomposition, although they had almost the same Oads/Olatt ratio. As it is recognized that the improvement in catalytic performance may be due to higher surface area, BET surface area were obtained for the catalysts as shown in Table 2 and Figure S2. To exclude the influence from surface area, specific surface reaction rates of different MnOx were shown in Table 2, in the following order: MnO2>Mn2O3> Mn3O4. It indicated that their catalytic performances of O3 decomposition were not likely dependent on their surface area among MnO2, Mn2O3 and Mn3O4. The related study reported that the desorption of peroxide species O2*was the rate-limiting step during ozone catalytic decomposition. And the desorption procedure is a reduction process, in which electrons were transferred to the manganese center by O2* to form O2. That is to say, the easier MnOx reduces, the better the catalytic activity is. XPS results showed that the O1s binding energy of Olatt decreased in the following order: MnO2(529.5eV) < Mn2O3(529.9eV) < Mn3O4(530.2eV), suggesting that MnO2 had the most loosely bound of Mn-O or the highest mobility of oxygen, which was consistent with the results of H2-TPR and O2-TPD. Since the three catalysts had comparable Oads/Olattratio values, the nature of oxygen vacancies may play a crucial role in the desorption of O2*. However the gap on the nature of oxygen defects still needed to be elucidated by DFT calculation.
Table 2. Reaction rate after 3h time-on-stream test