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