Synthesis Of The Modified Mn-based Catalysts And Its NH₃-SCR De-NO_x Reaction Performance

With the acceleration of China’s industrialization process,air pollution is one of the important environmental problems currently facing,and the sources are mainly from fixed pollution（thermal power,cement,steel,coking and other industries）and mobile pollution（motor vehicles,ships,aircraft,et al.）.Flue gas denitration technology refers to a technology that has generated NO_xreduction into N₂harmless component.Selective catalytic reduction（SCR）is the most effective way among all flue gas denitration control technologies.Large-scale commercial application of NH₃-SCR denitrification catalyst V-based catalyst can effectively remove NO_xfrom the exhaust gas from coal-fired power plants and motor vehicles to a certain extent.But the temperature window is mainly concentrated in 300-400℃,only applicable to medium-temperature flue gas,and has biological toxicity.When the industrial kilns such as coal-fired power plants run under low load,the catalysts have higher low temperature activity requirements.Current NH₃-SCR commercial catalysts cannot meet the requirements of ultra-low emissions.Therefore,it is particularly urgent and important to develop non-vanadium based catalysts with excellent low temperature activity and wide operating temperature window in view of the low low-temperature activity and narrow operating temperature window of denitration catalyst.Therefore,it is particularly urgent and important to develop non-vanadium based catalysts with excellent low-temperature activity and wide operating temperature window in view of the low low-temperature activity and narrow operating temperature window of denitration catalyst.In this paper,Mn-Ni-Zr/TiO₂catalyst and Mn-W-Ce/TiO₂catalyst were designed and synthesized by NH₃-SCR technology to process NO.The structure of the catalyst was characterized by XRD,BET,TPR,UV-Vis,TG-DTA,XPS and SEM.The specific research contents are as follows:（1）In this paper,Mn-Ni-Zr/TiO₂catalyst was prepared by citric acid assisted impregnation method by optimizing the active components,additives and loading capacity.The denitrification activity of the catalyst in NH₃-SCR was studied first,and then its characterization was analyzed.The results showed that 20%Mn-3%Ni-1%Zr/TiO₂-0.7catalyst has the best denitrification activity.The conversion rate is 89.47%at 100℃,the highest NO conversion temperature is T_top=150℃,the highest NO conversion rate is97.89%,and the operating temperature window is T₈₀=93-307℃.XRD results showed that the Niand Zr additives significantly reduce the grain size of the catalyst,increase the specific surface area,and improve the dispersity of the active component and the promoter.BET results showed that specific surface area was not the most important factor affecting reactivity.H₂-TPR results showed that Niand Zr additives can improve the redox performance of the catalyst and effectively broaden the operating temperature window.TG results showed that Mn O₂was an effective active component in Mn-based catalyst.UV-Vis results showed that Mn species with high valence may exist in the defective sites of the carrier or in the calcined carrier skeleton,and the active components had a high dispersity.XPS results showed that Mn⁴⁺was the main reason for the higher activity of the catalyst,and higher surface chemisorbed oxygen species could also promote the“fast SCR”reaction and low temperature SCR reaction.SEM results showed that the doping of Niand Zr can reduce the grain size of the catalyst and make the crystal particles evenly dispersed on the TiO₂support.（2）Based on the above recipe,our Mn load is 20%,which is relatively high,and not conducive to the cost control.Therefore,we take 10%Mn as the active component and optimize the active component,auxiliary agent and load by citric acid assisted impregnation method to prepare Mn-W-Ce/TiO₂catalyst.The reactivity of the catalyst in NH₃-SCR was studied and its characterization was analyzed.The results showed that10%Mn-2%W-1%Ce/TiO₂catalyst had the best reverse denitrification activity.The NO conversion rate reached 38.12%at 100℃,the highest NO conversion temperature is T_top=250℃,the highest NO conversion rate is 92.69%,and the active operating temperature window is T₈₀=148-318℃.XRD results showed that Mn,W and Ce species in the catalyst are amorphous,and the doping of W and Ce significantly reduces the grain size of the catalyst,thus increasing the specific surface area of the catalyst,improving the dispersity of the active component and the promoter.BET results show that the specific surface area of the catalyst is one of the factors affecting the catalytic activity.TG results showed that Mn O₂was an effective active component in Mn catalyst.UV-Vis results showed that Mn species with high valence may exist in the defective sites of the carrier or in the calcined carrier skeleton,and the active components had a high dispersity.XPS results showed that the surface chemisorption of oxygen and Mn⁴⁺on the surface of W and Ce modified Mn-W-Ce/TiO₂catalyst promoted the oxidation of NO to NO₂.And promoted the“fast SCR”reaction and low temperature SCR reaction.SEM results showed that the crystal size of catalyst modified with W and Ce additives decreased significantly,and the crystal particles were evenly dispersed in TiO₂support.（3）Based on the activity of（2）,it was found that the activity of the catalyst was lower than 20%loading when the load of Mn decreased to 10%.Therefore,Mn-W-Ce/TiO₂-CP catalyst was synthesized by different preparation methods coprecipitation method.Then the reaction activity of the catalyst in NH₃-SCR was studied,and its characterization was analyzed.The results showed that the NO conversion rate of Mn-W-Ce/TiO₂-CP catalyst reached 71.21%at 100℃,the reaction temperature is T_top=250℃,the highest NO conversion rate is 95.2%,and the active operating temperature window is T₈₀=128-323℃.XRD results showed that Mn,W and Ce in the catalyst prepared by coprecipitation were amorphous and highly dispersed in the carrier,which significantly reduced the grain size of the catalyst,increased the specific surface area of the catalyst,and improved the dispersity of the active components and additives.BET results show that the specific surface area of the catalyst is one of the factors affecting the catalytic activity.TG results showed that Mn O₂was an effective active component in Mn catalyst.UV-Vis results showed that Mn species with high valence may exist in the defective sites of the carrier or in the calcined carrier skeleton,and the active components had a high dispersity.XPS results showed that the coprecipitation method can effectively reduce the catalyst grain size and make the catalyst crystal particles evenly dispersed on the surface.SEM results showed that the crystal size of the catalyst prepared by coprecipitation method decreased significantly,and the crystal particles were evenly dispersed in the TiO₂carrier.