Cr Doping MnOxAdsorbent Significantly Improving Hg0Removal and SO2Resistance from Coal-Fired Flue Gas and the Mechanism Investigation

A series of binary Mn-based materials (Fe-MnOx, Cu-MnOx, Cr-MnOx, and Mo-MnOx) were prepared by the coprecipitation method, and the mechanism for elemental mercury (Hg0) removal of Cr-MnOxin the absence and presence of SO2was investigated. The physicochemical structure properties of the fresh as well as spent Cr-MnOxsamples were well characterized by the methods of N2physisorption, XRD, SEM-EDS, FTIR, H2-TPR, XPS, and TPD. The experiment results revealed that the loading of Cr into/onto MnOxyielded above 90% of Hg0removal efficiency in the presence of SO2at 120 °C. However, the appearance of SO2would lead to the formation of chromium sulfate/sulfite and manganese sulfate/sulfite although much superior SO2resistance was obtained. According to the N2physisorption and XRD characterization results, Cr doping can enlarge the BET surface area of MnOxwhen Cr was doped into/onto MnO2, and the MnCrO4mixed oxide material was produced. Moreover, the H2-TPR result exhibited that Cr loading into/onto MnOxenhanced the redox property of Cr-MnOxmixed oxides and many more easily reduced species appeared in the mixture. The larger surface area and an abundance of reactive species could benefit from excellent performances of Hg0removal and superior SO2resistance although the DFT calculation showed almost the same adsorption energies of Hg0on MnO2(110) and Cr-MnO2(110) surfaces. The DFT calculation exhibited that the adsorption energy of SO2on the surface of Cr-MnO2(110) was much lower than that on MnO2(110), implying that Cr doping into MnO2would decrease the adsorption behavior of SO2, thereby improving its SO2resistance performance.