Reaction mechanism for the influence of SO2 on Hg0 adsorption and oxidation with Ce0.1-Zr-MnO2

•SO2 had different effects on Hg0 adsorption and oxidation process.•Active sites was deactivated by SO2 resulting in a bad Hg0 adsorption efficiency.•The forming sulphates acted as new active sites in Hg0 oxidation process.•Catalysts still had good Hg0 oxidation efficiency in the presence of SO2.

The removal of Hg0 from flue gas has been one of the primary challenges in the control of mercury emission. The presence of even small amounts of SO2 has a significant influence on the Hg0 removal process, and the mechanism of this process has not been thoroughly explained to date. To understand the mechanism for SO2 influence, the influence of SO2 on the Hg0 adsorption and Hg0 oxidation components of the Hg0 removal process were investigated separately based on Ce0.1-Zr-MnO2. SO2 was shown to have serious negative effects on the Hg0 adsorption process due to the reaction between SO2 and Mn-based active sites, as determined by TGA and XPS results. In contrast, for the Hg0 oxidation process Mn-SO42− formed through the reaction between SO2 and Mn-based active sites, and Mn-SO42− had a certain contribution to Hg0 oxidation. Moreover, XPS results indicated that SO2 reacts with O2 to form SO3 which adsorbed on the catalyst surface and act as new active sites, promoting Hg0 oxidation via: Hg + SO3 + 1/2O2 → HgSO4. This phenomenon caused the catalyst to retain Hg0 oxidation activity in the presence of SO2 for a relatively long time.

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