Preparation Of Mn-based Catalyst And Its Catalytic Oxidation Performance Of NO At Medium And Low Temperature

Nitrogen oxides in flue gas are discharged into the atmosphere,which will cause atmospheric environmental pollution problems such as acid rain,ozone layer destruction,photochemical smog and PM2.5 rise.Besides seriously environment pollution,nitrogen oxides discharge can also directly lead to human upper respiratory tract injury and harm.Solution absorption of NOx is a simple and environmentally friendly technology,but the low solubility of NO limits its wide application.In this paper,high-efficiency and low-cost perovskite-type and ferromanganese-oxide-type catalysts for NO oxidation at medium and low temperatures were developed,and the effects of doping different metals and the doping amount of preferred metals on the catalytic performance of the catalysts were investigated.XPS,FTIR,H₂-TPR and O₂-TPD were used to preliminarily explore the mechanism of NO oxidation by Mn-based catalysts.The results are as follows:（1）Preparation and properties of La Co O₃/Mn O₂ catalysts.Three methods of physical blending,adding Mn O₂ to La Co O₃ preparation and adding La Co O₃ to Mn O₂ preparation were adopted respectively.The results showed that the catalytic performance of the catalyst prepared by direct physical blending has no significant improvement.The addition amount of La Co O₃,added during the formation ofγ-Mn O_2,affected the catalytic effect.The highest NO conversion efficiency was 25.7%at 210℃,when the amount ratio of La Co O₃ andγ-Mn O₂ is 3:1.The catalytic effect is higher than that of La Co O₃.When theγ-Mn O₂ was added into precursor of La Co O_3.the effect was greatly reduced.The NO conversion efficiencies of the prepared catalysts were all between 5%and 10%at 210℃.（2）Single-metal modification ofγ-Mn O₂ by Fe,Ce and La.The molar ratio of Mn to single metal is 9:1,and the Fe-modified catalyst has the best catalytic effect,with the NO conversion efficiency of 47%at 210℃.After Fe modification,the surface structure of the catalyst changed from sea urchin shape to spherical shape,the specific surface area increased by 1.5 times,and the catalytic effect was significantly improved.（3）The experiment of optimizing the doping amount of Fe shows that when the molar ratio of Mn to Fe is 8:1,the catalytic oxidation performance of NO is best,and the conversion efficiency of NO can reach 54.7%at 210℃.At this dosage,the crystallization degree of the catalyst is low,amorphous or highly dispersed,and it has the largest chemically adsorbed oxygen and Mn⁴⁺content.（4）Rare earth metal Ce and metal Fe bimetal modifiedγ-Mn O₂.The doping amount of Ce affects the catalytic activity.MFC-8:1:0.5 catalyst has the best catalytic activity,and the NO conversion rate is 66.8%at 210℃.When the doping amount of Ce is too much,the micropore volume and specific surface area of the catalyst decrease.After bimetallic modification,the contents of chemically adsorbed oxygen and Mn⁴⁺in the catalyst are further increased,and the catalytic activity of the catalyst for NO oxidation is improved.（5）No matter theγ-Mn O₂ catalyst synthesized by single metal doping or double metal doping,the decrease of catalyst activity caused by SO₂ can’t be recovered,mainly because SO₂ is easily adsorbed on the catalyst surface,reacts with oxygen and generates sulfate which occupies the active site,resulting in irreversible deactivation of the catalyst.