Superior activity of MnOx-CeO2/TiO2 catalyst for catalytic oxidation of elemental mercury at low flue gas temperatures

TiO2 supported Mn-Ce mixed oxides (Mn-Ce/Ti) synthesized by an ultrasound-assisted impregnation method were employed to oxidize elemental mercury (Hg-0) at low temperatures in simulated low-rank (sub-bituminous and lignite) coal combustion flue gas and corresponding selective catalytic reduction (SCR) flue gas. The catalysts were characterized by BET surface area analysis. X-ray diffraction (XRD) measurement and X-ray photoelectron spectroscopy (XPS) analysis. The combination of MnOx and CeO2 resulted in significant synergy for Hg-0 oxidation. The Mn-Ce/Ti catalyst was highly active for Hg-0 oxidation at low temperatures (150-250 degrees C) under both simulated flue gas and SCR flue gas. The dominance of Mn4+ and the presence of Ce3+ on the Mn-Ce/Ti catalyst were responsible for its excellent catalytic performance. Hg-0 oxidation on the Mn-Ce/Ti catalyst likely followed the Langmuir-Hinshelwood mechanism, where reactive species on catalyst surface react with adjacently adsorbed Hg-0 to form Hg2+. NH3 consumed the surface oxygen and limited the adsorption of Hg-0, hence inhibiting Hg-0 oxidation over Mn-Ce/Ti catalyst. However, once NH3 was cut off, the inhibited mercury oxidation activity could be completely recovered in the presence of O-2. This study revealed the possibility of simultaneously oxidizing Hg-0 and reducing NOx at low flue gas temperatures. Such knowledge is of fundamental importance in developing effective and economical mercury and NOx control technologies for coal-fired power plants. (C) 2011 Elsevier B.V. All rights reserved.