An Experimental Study On Mn-Fe-based Catalysts For Low-temperature Catalytic Reduction Of NO

NOx is one of the major primary pollutants in the atmosphere,and is one kind of important precursors causing acid rain and smog air pollution.It causes serious damage to the ecological environment and human health.The article describes the source,formation mechanism and control status of nitrogen oxides,and summarizes the current common nitrogen oxide emission reduction technologies.The most widely used denitrification technology is NH₃ selective catalytic reduction?NH₃-SCR?,it has an efficient temperature window of about 350°C for Ti-based and V-based catalysts.According,the traditional NH₃-SCR technology cannot meet the need of flue gas denitrification in non-power industries.In order to seek a suitable flue gas denitrification technology for non-power industry,it is of great significance to study the high-efficient SCR catalyst under low temperature.Firstly,a series of Mn/?-Al₂O₃ and Mn-Fe/?-Al₂O₃ catalysts with?-Al₂O₃ as the support and MnOx,FeOx as the active component were prepared by wet impregnation method.The influence of different active component loaded on the catalytic on reduction NO performance was investigated.The experimental results show that NO conversion rate increases with the increase of temperature within a certain temperature range.The SCR activity of the catalyst is the best among all Mn/?-Al₂O₃ series catalysts when the Mn loaded amount is 1.2 mmol/g-support.It was found that the SCR activity of Mn/?-Al₂O₃ catalysts was obviously improved after iron-doped.When the Mn loaded amount is 1.2 mmol/g-support and Fe loaded amount is 0.04 mmol/g-support,Mn-Fe-2/?-Al₂O₃ catalyst had the best SCR activity.The efficiency of denitrification can be reached to 93%under the condition of 400mg/m³ NO,250mg/m³ NH₃,6%O₂,the rest of nitrogen and the gas temperature is 150?,the air velocity is 6000h^-1.Repeated experiments showed that Mn-Fe-2/?-Al₂O₃ catalyst had relatively stable denitrification performance.On this basis,the toxic effect of H₂O and SO₂ content in the flue gas on the catalyst is discussed.It is found that the toxic effect of H₂O on the catalyst is weak and reversible,and the toxic effect of SO₂ on the catalyst is obvious and irreversible.The addition of Fe can improve the water and sulfur resistance of the catalyst.In the presence of 250mg/m³SO₂,the conversion rate of NO can be maintained at over 86%.Then the catalysts were characterized by SEM,XRD,BET and XPS,and the reaction mechanism was studied.According to the analysis of SEM and XRD,it is found that when the load of Mn is 1.2 mmol/g-support,the crystal of spherical ?-MnO₂ is formed on the surface of the?-Al₂O₃,which is the most favorable for the reaction of SCR.When the load of Mn is changed,the crystal form changes correspondingly,which leads to the decrease of the denitrification efficiency of the catalyst.The addition of Fe can improve the dispersion of active components and also affect the crystal form.When the addition amount of Fe is 0.04mmol/g-support,the spheroidal?-MnO₂ crystallization is still formed on the surface of?-Al₂O₃,but the dispersion degree is greatly improved,and the SCR activity of the catalyst is further improved.The BET characterization analysis shows that the specific surface area and pore structure of the catalysts with different active components are different,and the specific surface area and pore size of Mn-Fe-2/?-Al₂O₃catalyst are not the biggest but the SCR activity is the best.Therefore,the specific surface area and pore structure are not the decisive factors for the efficiency of denitrification.The reaction mechanism combined with the characterization analysis:the Mn metal oxide loaded on the surface of the?-Al₂O₃ is the active center of the catalyst.Although the specific surface area of the spheroidal?-MnO₂ is slightly lower than the rod like?-MnO₂crystallization,the lattice oxygen flow on the spherical crystal is good,so the catalytic activity is better than the rod like crystallization.When Fe was added,the dispersity of Mn species on the catalyst surface increased,and the dispersion and catalytic activity of active components were closely related.In addition,the chemical oxygen adsorption of catalysts increased significantly after the addition of Fe,and played an important role in enhancing the catalytic activity.In order to lay a foundation for further industrial application,we have prepared honeycomb monolithic Mn-Fe based catalysts and carried out related researches.Under the same experimental conditions with the activity test of granular catalyst,more than83%denitration efficiency can be achieved.The reasons for the low efficiency of the denitration are the less active load and the uneven dispersion of monolithic catalysts.This research will promote the development of flue gas low temperature denitrification technology in non electric power industry.