Applied Catalysis B: Environmental 111–112 (2012) 381–388 Contents lists available at SciVerse ScienceDirect Applied Catalysis B: Environmental jo ur n al homepage: www.elsevier.com/locate/apcatb Superior activity of MnO x -CeO 2 /TiO 2 catalyst for catalytic oxidation of elemental mercury at low flue gas temperatures Hailong Li a,b , Chang-Yu Wu b,∗ , Ying Li c , Junying Zhang a a State Key Laboratory of Coal Combustion, Huazhong University of Science and Technology, Wuhan, Hubei 430074, China b Department of Environmental Engineering Sciences, University of Florida, Gainesville, FL 32611, United States c Department of Mechanical Engineering, University of Wisconsin-Milwaukee, Milwaukee, WI 53211, United States a r t i c l e i n f o Article history: Received 21 July 2011 Received in revised form 25 September 2011 Accepted 11 October 2011 Available online 18 October 2011 Keywords: Mercury Manganese oxide Cerium oxide Catalyst Coal combustion a b s t r a c t TiO 2 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 MnO x and CeO 2 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 ◦ C) under both simulated flue gas and SCR flue gas. The dominance of Mn 4+ and the presence of Ce 3+ 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 Hg 2+ . NH 3 consumed the surface oxygen and limited the adsorption of Hg 0 , hence inhibiting Hg 0 oxidation over Mn-Ce/Ti catalyst. However, once NH 3 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 NO x at low flue gas temperatures. Such knowledge is of fundamental importance in developing effective and economical mercury and NO x control technologies for coal-fired power plants. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Emission of mercury (Hg) from anthropogenic sources into the atmosphere has become a major environmental issue that attracts considerable public attention because of the extreme toxicity, per- sistence, and bioaccumulation of methyl mercury transformed from emitted mercury [1]. Coal combustion has been targeted as a major source of anthropogenic mercury emissions in the United States. It is estimated that about one-third of the known anthropogenic mercury emissions in the United States is from coal combustion [2,3]. By April 2010 more than 20 U.S. states had proposed or adopted mercury emission regulations which were more stringent than the Clean Air Mercury Rule (CAMR) to regu- late mercury emissions from coal-fired power plants [4]. The U.S. Environmental Protection Agency (EPA) has also proposed federal mercury and air toxics standards to limit mercury emission from power plants [5]. To meet the demands of these mercury regula- tions, effective control technologies are urgently needed. ∗ Corresponding author. Tel.: +1 352 392 0845; fax: +1 352 392 3076. E-mail address: cywu@ufl.edu (C.-Y. Wu). Activated carbon injection (ACI) is the maximum achievable control technology (MACT) for mercury emission control from coal- fired power plants. Other technologies such as catalytic oxidation plus wet flue gas desulfurization (WFGD) have also been widely investigated. The efficacy of mercury control methods depends largely on the form and species of mercury [6]. Mercury in coal combustion derived flue gas is present in three forms i.e., elemen- tal mercury (Hg 0 ), oxidized mercury (Hg 2+ ) and particulate-bound mercury (Hg p ) [7]. Hg p can be captured by particulate matter (PM) control devices such as electrostatic precipitators (ESP) and fabric filters (FF). Water-soluble Hg 2+ is readily captured in WFGD system [7], and it can also be adsorbed on fly ash and subsequently collected along with fly ash in PM control devices. In contrast, Hg 0 vapor is most likely to escape from existing air pollution control devices (APCDs) because it is highly volatile and nearly insoluble in water [8]. As such, Hg 0 is the dominant mercury species emitted to the atmosphere. For example, Hg 0 accounts for 66–94% of total mercury emitted from coal-fired power plants in China [9], and 67% for coal- fired power plants in Texas [10]. Consequently, catalysts capable of significant conversion (>80%) of Hg 0 to Hg 2+ would have tremen- dous value [11] because Hg 2+ can be removed simultaneously with PM and acid gases in ESP/FF and WFGD, respectively. 0926-3373/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.apcatb.2011.10.021