NH3 inhibits mercury oxidation over low-temperature MnOx/TiO2 SCR catalyst

Manganese oxide/titanium dioxide (MnO x /TiO 2 , or MnTi) catalyst prepared by an ultrasound-assisted impregnation method was employed for simultaneous nitrogen oxide (NO) reduction and elemental mercury (Hg 0 ) oxidation under a simulated selective catalytic reduction (SCR) atmosphere. An NO reduction rate of 83% and Hg 0 oxidation rate of 96% were simultaneously achieved at a relatively low temperature of 200 °C. Ammonia (NH 3 ) as a reducing agent in the NO-SCR process was systematically investigated for its effect on Hg 0 oxidation. The results showed that NH 3 inhibited Hg 0 oxidation over the low-temperature MnTi catalysis process. In the presence of NH 3 , competitive adsorption between NH 3 and Hg 0 on the MnTi catalyst was partly responsible for the weakening Hg 0 oxidation. NH 3 consumed surface oxygen (O 2 ) on the MnTi catalyst, which also resulted in lower Hg 0 oxidation rate, especially in the absence of gas phase O 2 in the flue gas . More importantly, oxidized mercury was reduced by NH 3 to form Hg 0 with the aid of NO, i.e., the combined presence of NO and NH 3 induced the reduction of oxidized mercury, and hence partially offset Hg 0 oxidation. The effects of individual SCR gases, such as O 2 , NO, and the combinations, on Hg 0 oxidation were also elaborated.