Study Of Denitrification And Demercuration By MnO₂@TiO₂ Catalysts

China is the currently the country with the largest amount of coal production and demand in the world.The coal-fired flue gas is one of the primary sources of air pollutants,especially NO_x and Hg⁰ have received extensive attention as two atmospheric contaminants emitted from coal-fired boilers.NO_x emissions can cause photochemical smog,acid rain and other environmental problems,Hg⁰ is a global pollutant with toxicity,bio-accumulation and volatility,both of them can result in lots of environmental and health risks.It has been proven that a lot of commercial catalysts used in selective catalytic reduction?SCR?are favorable for the oxidation of Hg⁰ along with NO removal process.Accordingly,based on the situation of our country and existing pollution control devices in coal-fired power plants,it is the most economical way to use currently available pollution control devices such as SCR to remove Hg⁰ from the flue gas.However,the conventional supported SCR catalysts are prone to SO₂poisoning at low temperature.In this dissertation,a series of MnO₂@TiO₂ catalysts are prepared by constructing a core-shell structure.MnO₂ with high low temperature activity is used as the core,and TiO₂ is the shell with high sulfur resistance.A series of MnO₂@TiO₂catalysts are prepared by adjusting the amount of precursor.The denitration test of MnO₂@TiO₂ catalyst and the resistance performance test of SO₂ and H₂O are carried out in a fixed bed.The best catalyst MnO₂@TiO₂ is used for the study of mercury removal and synergistic denitrification and mercury removal.The effect of SO₂ on the performance is mainly investigated.Firstly,the core-shell structure MnO₂@TiO₂ catalyst is prepared by two-step method,and TEM found that it has obvious core-shell boundary.The removal efficiency of NO and the resistance to SO₂ and H₂O poisoning over MnO₂ and MnO₂@TiO₂?x:y?catalysts are compared.The results show that the TiO₂ shell enhance the high temperature activity and sulfur and water resistance of the catalyst,and with the increase of the amount of TiO₂,the higher the NO removal efficiency and sulfur and water resistance in the middle and high temperature range.However,excessive TiO₂ will result in poor activity at low temperature.The NO conversion efficiency of MnO₂@TiO₂ remained above 78%within the temperature range of 225-350?.In view of the MnO₂@TiO₂?1:2?catalyst with the best relative denitrification activity in the upper part,mercury removal performance and SO₂ toxicity resistance is further explored.The results show that MnO₂@TiO₂?1:2?has high mercury removal performance and SO₂toxicity resistance.The removal efficiency of Hg⁰ is about 45%for 130 min pure N₂ flue gas component and it is about 25%for 75 min N₂+100 ppm SO₂ flue gas component.TGA result shows that MnSO₄ accumulated on the surface of MnO₂@TiO₂?1:2?is low,so its SO₂ toxicity resistance is high.Finally,the synergistic denitrification and mercury removal performance and the effects of various flue gas components NSR,O₂,H₂O and SO₂ on the synergistic denitrification and mercury removal on MnO₂@TiO₂?1:2?catalyst are investigated.The results show that the NO conversion efficiency and Hg⁰ oxidation efficiency of MnO₂@TiO₂?1:2?in SCR+Hg⁰atmosphere are lower than those of simulated flue gas alone.NH₃ inhibits the mercury removal efficiency of the catalyst and promotes the denitration efficiency;O₂ can enhance the catalytic activity of MnO₂@TiO₂?1:2?for simultaneous Hg⁰ oxidation and NO conversion;While,H₂O and SO₂ show prohibitive effects on the simultaneous Hg⁰ oxidation and NO conversion.