New Insight into Hg0 Oxidation over a Mn-Doped VWTi Catalyst at a Wide Temperature Window

A series of Mn-doped VWTi (Mn-VWTi) catalysts were prepared and used for simultaneous NO removal and Hg0 oxidation at a wide temperature window of 200–400 °C for the first time, and the catalytic activity of the Mn-VWTi catalysts was investigated. The results indicated that Mn doping could notably improve the NO removal activity at 200–300 °C and the Hg0 oxidation activity at 200–400 °C, and the catalyst with 3% Mn loading exhibited superior catalytic activity. The relationship between NO removal and Hg0 oxidation and the effects of NO and NH3 concentrations on Hg0 oxidation over a Mn3-VWTi catalyst were also explored to verify the possibility of synergistic NO removal and Hg0 oxidation on a Mn-VWTi catalyst at a wide temperature window of 200–400 °C. In addition, several characterization methods, including Brunauer–Emmett–Teller, X-ray diffraction, H2 temperature-programmed reduction, X-ray photoelectron spectroscopy, and Hg temperature-programmed desorption, were used to characterize the catalyst, and the Hg0 oxidation mechanism over the Mn3-VWTi catalyst was also investigated based on the experimental data and characterization results. It was revealed that Mn species with higher valence states (Mn4+/Mn3+) played a major role during the Hg0 oxidation process at the lower temperature of 250 °C, while the synergistic interaction between Mn and V species (Mn4+/Mn3+ + V4+ ↔ Mn2+ + V5+) showed a dominant role in Hg0 oxidation at the higher temperature of 350 °C. Moreover, the oxidized mercury species mainly existed in the form of HgO on the catalyst surface.