Manganese doped CeO2-ZrO2 catalyst for elemental mercury oxidation at low temperature

Abstract

To develop an efficient catalyst used for elemental mercury (Hg0) oxidation at low temperature in coal-fired power plant, Mn doped CeO2-ZrO2 catalysts were synthesized and studied concerning their performance on Hg0 oxidation. Under the atmosphere of simulated coal-fired flue gas, Ce0.47Zr0.23Mn0.3O2 (CZM0.3) exhibited the best activity at 150°C. It was found that Hg0 oxidation performance over CZM0.3 was determined by the flue gas compositions. Gaseous O2 was important for the oxidation process, because it regenerated the lattice oxygen and replenished the chemisorbed oxygen, which boosted Hg0 oxidation. HCl and NO could improve the Hg0 oxidation efficiency slightly, respectively. In N2+HCl+O2 atmosphere, the Hg0 oxidation efficiency observed was significantly higher than those in N2+O2 or N2+HCl atmosphere. Compared with the effects of HCl on the Hg0 oxidation activity, the similar results were obtained for effects of NO on the performance Hg0 oxidation. NO could facilitate the Hg0 oxidation activity, especially in the presence of O2. In N2+SO2 atmosphere, SO2 inhibited Hg0 oxidation. In N2+O2+SO2 atmosphere, SO2 promoted Hg0 oxidation probably due to the generation of SO3. Water vapor inhibited Hg0 oxidation, because it diminished the HCl and Hg0 adsorption. The characterization of the CZM0.3 indicated that the higher activity of the catalyst was most likely attributed to the presence of more oxygen vacancies, enhanced Mn4+/(Mn4++Mn3+) ratio and more surface adsorbed oxygen on the catalyst surface.