Mechanistic investigation on the Hg⁰ elimination ability of MnO_x-CeO_x nanorod adsorbents: effects of Mn/Ce molar ratio

Mercury pollution is created by coal combustion processes in multi-component systems. Adsorbent injection was identified as a potential strategy for capturing Hg-0 from waste gases, with adsorbents serving as the primary component. The hydrothermal approach was used to synthesize a series of MnOx-CeOx nanorod adsorbents with varying Mn/Ce molar ratios to maximize the Hg-0 capture capabilities. Virgin CeOx had weak Hg-0 elimination activity; <8% Hg-0 removal efficiency was obtained from 150 degrees C to 250 degrees C. With the addition of MnOx, the amount of surface acid sites and the relative concentration of Mn4+ increased. This ensured the sufficient adsorption and oxidation of Hg-0 while overcoming the limitations of restricted adsorbate-adsorbent interactions caused by the lower surface area, endowing MnOx-CeOx with increased Hg-0 removal capacity. When the molar ratio of Mn/Ce reached 6/4, the adsorbent's Hg-0 removal efficiency remained over 92% at 150 degrees C and 200 degrees C. As the molar ratio of Mn/Ce grew, the adsorbent's Hg-0 elimination capacity declined due to decreased surface area, weakened acidity, and decreased activity of Mn4+; <75% Hg-0 removal efficiency was reached between 150 degrees C and 250 degrees C for virgin MnOx. Throughout the overall Hg-0 elimination reactions, Mn4+ and O-alpha were in charge of oxidizing Hg-0 to HgO, with Ce4+ acting as a promoter to aid in the regeneration of Mn4+. Because of its limited adaptability to flue gas components, further optimization of the MnOx-CeOx nanorod adsorbent is required.