The influence of Mn species on the SO2 removal of Mn-based activated carbon catalysts

- Mn2O3 is the major species in Mn/NAC-500.
- MnO and Mn3O4 coexist in the Mn/NAC-650 and Mn/NAC-800.
- The coexistence of MnO and Mn3O4 helps to improve SO2 removal ability.
- Nitric acid treatment can increase CO and decrease the crystal size of MnO.
- Mn2O3 and Mn3O4 are gradually transferred into MnO2 in SO2 removal process.

Using Mn(NO3)2 as precursor, a series of Mn-based activated carbon catalysts were prepared by ultrasound-assisted excessive impregnation method and characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and temperature programmed reduction (TPR). The influences of Mn species and nitric acid pretreatment on the removal role of SO2 were investigated. MnO and Mn3O4 coexist in catalysts calcined at 650 and 800 °C and exhibit best SO2 removal ability, whereas Mn2O3 formed in the catalyst calcined at 500 °C and shows poor activity. After treatment by nitric acid, the CO of activated carbon support increases and the crystal size of MnO decreases, resulting in the enhancement of the catalytic activity. During reaction process, manganese oxides are gradually transferred into MnO2. And this change directly results in a decrease of activity. But the SO2 removal rate has been maintained in the range of 30-40%, indicating that MnO2 still has a certain SO2 removal ability.