Comparative study of Co/TiO2, Co–Mn/TiO2 and Co–Mn/Ti–Ce catalysts for oxidation of elemental mercury in flue gas

The Co–Mn/Ti–Ce catalyst prepared by sol–gel and impregnation method was evaluated for catalytic oxidation of Hg0 in the simulated flue gas compared with Co/TiO2 and Co–Mn/TiO2. The results showed that Co–Mn/Ti–Ce catalyst exhibited higher catalytic activity (around 93% Hg0 removal efficiency in the temperature of 150 °C with 6% O2, 400 ppm NO, 200 ppm SO2 and 3% H2O) than Co/TiO2 and Co–Mn/TiO2. Based on the characterization results of N2 adsorption–desorption, XRD, UV–Vis, XPS, H2-TPR and Hg-TPD, it could be concluded that the lower band gap, better reducibility and mercury adsorption capability and the presence of Co3+/Co2+, Mn4+/Mn3+ and Ce4+/Ce3+ redox couples as well as surface oxygen species contributed to the excellent Hg0 oxidation removal performance. In addition, well dispersion of active components and a synergetic effect among Co, Mn and Ce species might improve the activity further. A Mars–Maessen mechanism is thought to be involved in the Hg0 oxidation. The lattice oxygen derived from MnOx or CoOx would react with adsorbed Hg0 to form HgO and the consumption of lattice oxygen could be replenished by O2. For Co–Mn/Ti–Ce, MnOx−1 could be alternatively reoxidized by the lattice oxygen derived from adjacent CoOx and CeOx which is beneficial to the Hg0 oxidation.