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

Abstract

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.

Synergetic NOx Removal and Hg0 Oxidation over V2O5–WO3/TiO2 Catalysts in a Simulated Fast SCR Atmosphere: Catalytic Performance and Hg0 Oxidation Mechanism

“…The ratio of O α exhibited slightly decrease after the catalyst pretreated under N 2 /O 2 /Hg 0 , indicating that the Hg 0 oxidation process consumed the chemisorbed oxygen species. Researchers have found that the chemisorbed oxygen species is more active than the lattice oxygen species because of its superior mobility. , Our previous study also found that the chemisorbed oxygen species was responsible for Hg 0 oxidation. , However, the O α ratio increased when the catalyst was pretreated in the presence of NO. This might be because the gaseous NO could adsorb on the catalyst surface to form adsorbed NO or other substance containing O species, thus increasing the chemisorbed oxygen species. , This is also the main reason why NO can promote the Hg 0 oxidation in the presence of O 2 .…”