Role of flue gas components in mercury oxidation over TiO2 supported MnOx-CeO2 mixed-oxide at low temperature

Abstract

MnOx-CeO2 mixed-oxide supported on TiO2 (Mn-Ce/Ti) was synthesized by an ultrasound-assisted impregnation method and employed to oxidize elemental mercury (Hg0) at 200°C in simulated coal combustion flue gas. Over 90% of Hg0 oxidation was achieved on the Mn-Ce/Ti catalyst at 200°C under simulated flue gas representing those from burning low-rank coals with a high gas hourly space velocity of 60,000h−1. Gas-phase O2 regenerated the lattice oxygen and replenished the chemisorbed oxygen, which facilitated Hg0 oxidation. HCl was the most effective flue gas component responsible for Hg0 oxidation. 10ppm HCl plus 4% O2 resulted in 100% Hg0 oxidation under the experimental conditions. SO2 competed with Hg0 for active sites, thus deactivating the catalyst's capability in oxidizing Hg0. NO covered the active sites and consumed surface oxygen active for Hg0 oxidation, hence limiting Hg0 oxidation. Water vapor showed prohibitive effect on Hg0 oxidation due to its competition with HCl and Hg0 for active adsorption sites. This study provides information about the promotional or inhibitory effects of individual flue gas components on Hg0 oxidation over a highly effective Mn-Ce/Ti catalyst. Such knowledge is of fundamental importance for industrial applications of the Mn-Ce/Ti catalyst in coal-fired power plants.