Manganese Catalysts for the Ozone-Assisted Oxidation of Volatile Organic Compounds: Effect of the Mn3+/Mn4+ Active Site Ratio on Catalytic Properties

The catalytic properties of supported Mn/carrier catalysts (carriers: Al2O3, SiO2, SiO2–Al2O3) in the ozone-assisted oxidation of volatile organic compounds (using the example of n-С4Н10) in a temperature range of 25–350°С have been studied. X-ray diffraction analysis and H2-TPR have shown that the carrier has a significant effect on the valence state of manganese in the supported oxide: on the SiO2 surface, manganese is present mostly in the form of Mn3+ (Mn2O3, Mn3O4), whereas in the Mn/Al2O3 and Mn/SiO2–Al2O3 catalysts the dominant species is Mn4+ (MnO2). Comparison of data on the composition of MnOx active phases and catalytic properties in the ozone-assisted oxidation of n-С4Н10 has revealed that an increase in the content of Mn3+sites contributes to an enhancement of the catalytic activity of Mn/support. However, an excess amount of Mn3+ leads to the consumption of ozone in a side reaction to form O2, which leads to a significant decrease in the n-С4Н10 oxidation efficiency. The data suggest that the maximum activity of the catalyst in the ozone-assisted oxidation of n-С4Н10 can be achieved via providing an optimum Mn3+/Mn4+ ratio.