Mechanistic investigation on the Hg0 elimination ability of MnOx–CeOx nanorod adsorbents: effects of Mn/Ce molar ratio

Abstract

Mercury pollution is created by coal combustion processes in multi-component systems. Adsorbent injection was identified as a potential strategy for capturing Hg⁰ from waste gases, with adsorbents serving as the primary component. The hydrothermal approach was used to synthesize a series of MnO_x–CeO_x nanorod adsorbents with varying Mn/Ce molar ratios to maximize the Hg⁰ capture capabilities. Virgin CeO_x had weak Hg⁰ elimination activity; <8% Hg⁰ removal efficiency was obtained from 150 °C to 250 °C. With the addition of MnO_x, the amount of surface acid sites and the relative concentration of Mn⁴⁺ increased. This ensured the sufficient adsorption and oxidation of Hg⁰ while overcoming the limitations of restricted adsorbate-adsorbent interactions caused by the lower surface area, endowing MnO_x–CeO_x with increased Hg⁰ removal capacity. When the molar ratio of Mn/Ce reached 6/4, the adsorbent’s Hg⁰ removal efficiency remained over 92% at 150 °C and 200 °C. As the molar ratio of Mn/Ce grew, the adsorbent’s Hg⁰ elimination capacity declined due to decreased surface area, weakened acidity, and decreased activity of Mn⁴⁺; <75% Hg⁰ removal efficiency was reached between 150 °C and 250 °C for virgin MnO_x. Throughout the overall Hg⁰ elimination reactions, Mn⁴⁺ and O_α were in charge of oxidizing Hg⁰ 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 MnO_x–CeO_x nanorod adsorbent is required.

Graphical abstract