Influence Of Ions Dopinig On Low Temperature Denitrtion Activity Of Mn-based Catalysts

Excessive nitrogen oxides（NO_x）in the atmosphere can directly cause people to suffer from respiratory diseases,and also cause problems such as photochemical smog,ozone hole,acid rain,PM2.5 and so on.Industrial flue gas emissions are one of the main sources of NO_x in China.Ammonia-selective catalytic reduction（NH₃-SCR）technology can effectively reduce the emission of industrial NO_x,but the vanadium-based catalysts is susceptible to SO₂,water vapor（H2O）,alkaline（earth）metals in the flue gas poisoning.Considering the actual working conditions,demand and economic benefits,it is best to place the denitration facilities after desulfurization and dust removal.However,the activity of vanadium catalyst decreases with the decrease of flue gas temperature when the denitration facilities moved.What’s more,vanadium species are biologically toxic.This makes the research and development of non-vanadium group denitration catalyst have important practical significance.In addition,some low-temperature industrial flue gas denitration has gradually received attention,such as the steel industry.Therefore,the development of green and efficient low-temperature NH₃-SCR catalysts is urgent.Mn-based catalysts have become important research objects due to their excellent denitration activity at low temperature.However,the low-temperature denitration activity and anti-poisoning performance of Mn-based catalysts need to be further improved.In order to improve the low-temperature denitration activity and anti-poisoning performance of Mn-based catalysts,it is necessary to explore the effect of doping on the denitration performance of Mn-based catalysts.In this study,the structural properties and physicochemical properties of Mn-based catalysts were changed by doping rare earth(Ce⁴⁺,Nd³⁺,Sm³⁺)Mn O_x catalysts and transition metal(Fe³⁺,Co³⁺,Ni²⁺)doping Mn Ce O_x/GR catalysts,thereby improving the low-temperature denitration activity and anti-poisoning properties.In addition,various characterization methods were used to analyze the reaction mechanism.The main research results include the following:（1）Ce⁴⁺,Nd³⁺,Sm³⁺were doped on Mn O_x catalyst by reverse co-precipitation method,and Mn Ce O_x,Mn Nd O_x,Mn Sm O_x and Mn O_x catalysts were synthesized.The research results show that the doping of rare earth metal ions can effectively improve the denitration activity of Mn O_x catalysts.Among them,Ce-doped Mn O_x catalyst can significantly improve its low-temperature denitration activity and H₂O+SO₂ resistance,indicating that Ce⁴⁺is the best dopant ion among these rare earth metal.The main reasons are as follows:（a）Ce⁴⁺doping significantly enhances the low-temperature reducibility and surface acidity of Mn O_x catalysts;（b）Ce⁴⁺doping promotes the adsorption and activation of NH₃ in the reaction gas,thereby promoting the NH₃-SCR reaction.（c）.Ce⁴⁺doping makes（NH₄）₂SO₄ or NH₄HSO₄ preferentially react with Ce⁴⁺,thereby protecting the active site and enhancing the anti-poisoning performance.（2）Introduce transition metal Fe³⁺,Co³⁺,Ni²⁺to improve the physicochemical properties of the catalyst,and at the same time load the catalyst on graphene to promote the dispersion of each component,in order to improve its reducing ability,surface acidity and structural properties.The results show that Co³⁺doping can enhance the low-temperature denitration activity and N₂ selectivity of Mn Ce O_x catalysts.The main reasons are as follows:（a）.Co³⁺doping enhances the acid strength of the Mn Ce O_x/GR catalyst and enhances the adsorption of NH₃.（b）.Co³⁺promotes the electronic interaction between Mn⁴⁺and Ce³⁺,which promotes the NH₃-SCR reaction.