CuO-CeO2/TiO2 (CuCeTi) catalyst synthesized by a sol-gel method was employed to investigate mercury conversion under a selective catalytic reduction (SCR) atmosphere (NO, NH3 plus O2). Neither NO nor NH3 individually exhibited an inhibitive effect on elemental mercury (Hg(0)) conversion in the presence of O2. However, Hg(0) conversion over the CuCeTi catalyst was greatly inhibited under SCR atmosphere. Systematic experiments were designed to investigate the inconsistency and explore the in-depth mechanisms. The results show that the copresence of NO and NH3 induced reduction of oxidized mercury (Hg(2+), HgO in this study), which offset the effect of catalytic Hg(0) oxidation, and hence resulted in deactivation of Hg(0) conversion. High NO and NH3 concentrations with a NO/NH3 ratio of 1.0 facilitated Hg(2+) reduction and therefore lowered Hg(0) conversion. Hg(2+) reduction over the CuCeTi catalyst was proposed to follow two possible mechanisms: (1) direct reaction, in which NO and NH3 react directly with HgO to form N2 and Hg(0); (2) indirect reaction, in which the SCR reaction consumed active surface oxygen on the CuCeTi catalyst, and reduced species on the CuCeTi catalyst surface such as Cu2O and Ce2O3 robbed oxygen from adjacent HgO. Different from the conventionally considered mechanisms, that is, competitive adsorption responsible for deactivation of Hg(0) conversion, this study reveals that oxidized mercury can transform into Hg(0) under SCR atmosphere. Such knowledge is of fundamental importance in developing efficient and economical mercury control technologies for coal-fired power plants.

CuO-CeO 2 /TiO 2 (CuCeTi) catalyst prepared by a sol-gel method was employed for the first time to simultaneously reduce nitrogen monoxide (NO) and oxidize elemental mercury (Hg 0 ) in the presence of ammonia (NH 3 ) at low flue gas temperatures. The combination of copper oxides and cerium oxides yielded apparent synergy for NO reduction and Hg 0 oxidation. Over 90% of NO reduction and over 80% of Hg 0 oxidation were simultaneously obtained on the CuCeTi catalyst at 200°C to 250°C under simulated coal combustion flue gas with a gas hourly space velocity (GHSV) of 54 000 h −1 which is more than 10 times higher than the actual GHSV in selective catalytic reduction (SCR) reactors. The well-dispersed active species and abundant chemisorbed surface oxygen on the CuCeTi catalyst were responsible for its excellent catalytic performance. Neither Hg 0 vapor in flue gas nor HgO loaded on the catalyst surface inhibited NO reduction by NH 3 at 200°C. In the absence of gas phase oxygen (O 2 ), NH 3 consumed surface oxygen and hence resulted in the deactivation of Hg 0 oxidation. In the presence of O 2 , neither NO nor NH 3 individually exhibited an inhibition on Hg 0 oxidation. However, Hg 0 oxidation over the CuCeTi catalyst was inhibited by the co-presence of NO and HH 3 . Fortunately, this inhibitive effect was entirely scavenged when a lower GHSV was adopted. This study reveals the feasibility of simultaneously reducing NO and oxidizing Hg 0 at low flue gas temperatures. Such knowledge is of fundamental importance in developing efficient, practical and economical NO and Hg 0 control technologies for coal-fired power plants.Catal. Sci. Technol. This journal is

Synergy for low temperature Hg 0 oxidation under selective catalytic reduction (SCR) atmosphere was achieved when copper oxides and cerium oxides were combined in a CuO-CeO 2 /TiO 2 (CuCeTi) catalyst. Hg 0 oxidation efficiency as high as 99.0% was observed on the CuCeTi catalyst at 200 °C, even the gas hourly space velocity was extremely high. To analyze the synergistic effect, comparisons of catalyst performance in the presence of different SCR reaction gases were systematically conducted over CuO/TiO 2 (CuTi), CeO 2 /TiO 2 (CeTi) and CuCeTi catalysts prepared by sol-gel method. The interactions between copper oxides and cerium oxides in CuCeTi catalyst yielded more surface chemisorbed oxygen, and facilitated the conversion of gas-phase O 2 to surface oxygen, which are favorable for Hg 0 oxidation. Copper oxides in the combination interacted with NO forming more chemisorbed oxygen for Hg 0 oxidation in the absence of gas-phase O 2. Cerium oxides in the combination promoted Hg 0 oxidation through enhancing the transformations of NO to NO 2. In the absence of NO, NH 3 exhibited no inhibitive effect on Hg 0 oxidation, because enough Lewis acid sites due to the combination of copper oxides and cerium oxides scavenged the competitive adsorption between NH 3 and Hg 0. In the presence of NO, although NH 3 lowered Hg 0 oxidation rate through inducing reduction of oxidized mercury, complete recovery of Hg 0 oxidation activity over the CuCeTi catalyst was quickly achieved after cutting off NH 3. This study revealed the synergistic effect of the combination of copper oxides and cerium oxides on Hg 0 oxidation, and explored the involved mechanisms. Such knowledge would help obtaining maximum Hg 0 oxidation co-benefit from SCR units in coal-fired power plants.

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