Effect of Tungsten on Hg⁰ Removal by W–Mn–Mo/CNT During Oxy-Fuel Combustion Simulated Flue Gas

A new type of tungsten-doped Mn–Mo/CNT catalyst (CM₅Mo₅W_x) is prepared by the impregnation method, and their surface properties and mercury removal ability during oxy-fuel combustion simulated flue gas are investigated in this study. It indicated that the addition of tungsten to Mn–Mo/CNT significantly changed the surface structure of the catalyst. The Brunauer–Emmett–Teller surface areas of CM₅Mo₅ and CM₅Mo₅W₆ are 209 and 172 m²/g, respectively. However, the addition of tungsten expands pore volume of the catalyst. In addition, less Mn⁴⁺ is found on the surface of the tungsten-doped catalyst. Mercury removal ability of the tungsten-doped catalyst is stronger than that of CM₅Mo₅, especially the mercury removal ability of CM₅Mo₅W₆. Its mercury removal efficiency is 98% at 100 °C, while that of CM₅Mo₅ is lower than 70%. Under different flue gas conditions, O₂ and NO can significantly enhance Hg⁰ removal, but SO₂ decreases mercury removal efficiency. However, H₂O slightly suppresses the mercury removal by this catalyst. Moreover, combining the Hg-TPD and kinetic analyses, it was revealed that chemisorption is crucial for Hg⁰ removal. Hg⁰ is more easily adsorbed by CM₅Mo₅W₆ through the results of kinetic analysis.