Removal of elemental mercury from simulated flue gas over MnOx/TiO2 adsorbent: The synergistic effect of anatase and brookite TiO2

MnOx on TiO2 support with different mixed crystal phases (anatase/brookite (A/B), rutile/brookite (R/B) and anatase/rutile (A/R)) were prepared for the removal of Hg0. The effect of TiO2 crystal phase on Hg0 removal performance was investigated. MnOx/TiO2-A/B showed optimal Hg0 removal activity. Due to the strong metal oxide-support interaction between MnOx and TiO2-A/B, MnOx/TiO2-A/B possessed abundant defect oxygen and Mn4+ species which were beneficial to the oxidation of Hg0, resulting in high Hg0 removal activity. Furthermore, there were significant differences in the interaction strength between MnOx and TiO2 prepared by different methods (solvent mixing and calcination method (SMC) and sol-gel method (SG)). Compared to MnOx/TiO2-A/B (SMC), MnOx/TiO2-A/B (SG) exhibited excellent redox property due to its smaller particle size and better contact between anatase phase and brookite phase. The characterization results indicated that the stronger interaction between MnOx and TiO2-A/B (SG) induced the formation of more Mn4+ species over the adsorbent. On the other hand, the effects of common flue gas components on the Hg0 removal performance were also studied. There was competitive adsorption between H2O and Hg0 over adsorbent, which slightly inhibited the removal of Hg0. As a common acidic gas, SO2 was easily adsorbed onto the alkaline site (Mn site) and consumed the active species, thus deteriorating its capability for Hg0 removal.