Catalytic oxidation of Hg0 by MnOx–CeO2/γ-Al2O3 catalyst at low temperatures

• It is the first time of using MnOx–CeO2/γ-Al2O3 catalysts on Hg0 oxidation.
• This study showed a potential for SCR and Hg0 oxidation in a single-step process.
• We investigated the impacts of acid gases on Hg0 oxidation.
• More information on Hg0 oxidation mechanism over SCR catalysts was revealed.

MnOx–CeO2/γ-Al2O3 (MnCe) selective catalytic reduction (SCR) catalysts prepared by sol–gel method were employed for low-temperature Hg0 oxidation on a fixed-bed experimental setup. BET, XRD and XPS were used to characterize the catalysts. MnCe catalysts exhibited high Hg0 oxidation activity at low temperatures (100–250 °C) under the simulated flue gas (O2, CO2, NO, SO2, HCl, H2O and balanced with N2). Only a small decrease in mercury oxidation was observed in the presence of 1200 ppm SO2, which proved that the addition of Ce helped resist SO2 poisoning. An enhancing effect of NO was observed due to the formation of multi-activity NOx species. The presence of HCl alone had excellent Hg0 oxidation ability, while 10 ppm HCl plus 5% O2 further increased Hg0 oxidation efficiency to 100%. Hg0 oxidation on the MnCe catalyst surface followed the Langmiur–Hinshelwood mechanism, where reactions took place between the adsorbed active species and adsorbed Hg0 to form Hg2+. NH3 competed with Hg0 for active sites on the catalyst surface, hence inhibiting Hg0 oxidation. This study shows the feasibility of a single-step process integrating low-temperature SCR and Hg0 oxidation from the coal combustion flue gas.