| Coal-fired power plants have become one of the leading anthropogenic emission sources and produce various air pollutants.Among,elemental mercury(HgO)and nitrogen oxides(NOx)are central environmental issues,which have drawn great attention recently.Due to the volatility,persistence,and bioaccumulation of mercury in the environment,it is a major air toxic contaminant.Meanwhile,NOx(NO,NO2 and N2O)generate plenty of problems,including photochemical smog,acid rain and greenhouse effects.Hence,mercury and NOx emission need to be synthetically and strictly constrained.The paper introduces the sources,harm and character of mercury and NOx,as well as mercury and nitrogen oxides control technologies in the coal-fired flue gas.In addition,it discusses the experimental study in both mercury and nitrogen oxides control technologies;SCR catalyst applied to the removal technologies and mechanism of mercury and NOx was described respectively.The research proposed the ZrO2-modified SCR catalyst on Hg0 removal and SCR reaction,and prepared the TiO2-ZrO2 composite metal oxides and active components were impregnated on the carrier.The modified SCR catalyst could enhance simultaneous removal efficiency of Hg0 and NO in the coal-fired flue gas.This study discussed the ZrO2 modified support on CuO-CeO2/TiO2 catalysts prepared by co-precipitation method for Hg0 and NO removal in the coal-fired flue gas.The different addition amounts of ZrO2 on CuO-CeO2/TiO2 catalyst were investigated to research the simultaneous removal of Hg0 and NO at 100-350?.Effects of simultaneous removal of Hg0 and NO with the changes of reaction conditions(Hg0?NH3/NO?GHSV?SO2 and H2O)of individual Hg0 and NO removal were investigated.The physicochemical characteristics and structure properties of catalysts with ZrO2 additive were observed and characterized using the essential characterizations including BET,XRD,SEM,XPS,H2-TPR and FTIR.Results indicated that Zr doping was beneficial to removal efficiency of Hg0 and NO and the CuCe/TiZr0.15 catalyst exhibited the superior Hg0 removal efficiency(72.7%)and prominent NO conversion(83.3%).Hg0 as the necessary component for the simultaneous removal of Hg0 and NO,slightly restrained the NO conversion.Except for the effect of the separate NH3 and NO on Hg0 removal,significant effect of the increased NH3/NO ratio on Hg0 removal and NO conversion were detected.6%O2 for CuCe/TiZr0.15 could be sufficient for Hg0 and NO removal.Appropriate GHSV could provide much more contact time for catalysts exposed into reactant gases and had prominent effect on Hgo and NO removal.With the existence of SO2 and H2O,the slightly prohibitive effect on Hg0 and NO removal was displayed.SO2 might possess the effects of SO2 on CuCe/TiZr0.15 for Hg0 removal might be associated with the SO2 concentration level,and the existence of SO2 inhibited the activity of NO removal.The available active sites for mercury adsorption were occupied by H2O,which probably led to the decrease of Hg0 removal efficiency.Meanwhile,the addition of H2O caused an obvious decline of NO conversion,which might be related to the competitive adsorption between H2O and NH3/NOx.The characterizations analysis revealed that the introduction of Zr benefited great surface area,produced titanium-zirconium composite oxide,weakened crystallinity of TiO2 and then improved the dispersion of metal oxide species.The small particles of catalyst presented the uniform distribution on catalyst surface.The ZrO2 modified support on CuO-CeO2/TiO2 resulted in strong redox ability,great mobility of surface oxygen and growing total amount of chemisorbed oxygen and lattice oxygen,which favorably impacted on Hg0 and NO removal.More stable Lewis acid sites to form coordinated NH3 were generated due to ZrO2 additive.The synergetic effect through redox equilibrium of Ce3+ +Cu2+?? Ce4+Cu+ contributed to Hg0 removal and NO conversion.In addition,the simultaneous removal of Hg0 and NO on CuCe/TiZr0.15 in terms of detailed mechanism was discussed. |
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