Study On Preparation And Forming Properties Of SCR Denitration Catalysts By Sintering Dust

Nitrogen oxide?NO_x?is an important air pollutant.In recent years,the NO_x emission standard has been further improved,which makes many coal-fired enterprises face enormous emission pressure.NH₃-SCR technology is one of the most effective methods for NO_x removing.However,vanadium based catalyst as the core component of SCR system remains a high production cost.In addition,V₂O₅ will endanger human health,which limits its application in many fields.Therefore,it is of great significance to develop a green and inexpensive SCR catalyst with independent intellectual property rights.In this paper,the preparation and application of iron-based SCR catalyst from steel-making solid waste“sintering dust”have been studied systematically.Firstly,a series of SCR catalysts with Fe₂O₃ as the active component were prepared by sintering dust.The effects of physicochemical properties of sintering dust and its pretreated-modified process on the performance of sintering dust catalysts were investigated by XRF,XRD,TG,BET and SCR performance test.The results indicate that the sintering dust contains more than 45 wt%Fe₂O₃,which is a feasible material for SCR catalysts.However,the raw sintering dust almost has no SCR activity due to the high content of alkali and alkaline earth metal elements?K,Na,Ca?.HNO₃ treatment cannot only remove the KCl and carbonate impurities,dredge the pore structure and alleviate the alkali poisoning of catalyst,but also stimulate the activity of Fe₂O₃,so as to improve its catalytic activity effectively.MnO_x modification can significantly improve the low-temperature activity of the sintering dust catalysts,which obtained a best SCR performance with a 10 wt%MnO_x loading.The NO conversion rate could reache 75% at 240?.Secondly,the Fe₂O₃ was successfully converted into Fe?OH?SO₄ by a washing-acidification-impurity process,and then a series of supported SCR catalysts were obtained by loading the Fe?OH?SO₄ on different supports with Fe₂?SO₄?₃ as the active component.With the help of SEM,XPS and DRIFTS measurement,the performance improvement and reaction mechanism of Fe₂?SO₄?₃ catalyst were systematically analyzed.The results indicate that the Fe₂O₃ conversion could reach99.8%at 110?-10 h,expressing a high utilization of sintered dust.TiO₂ can make a stronger electronic interaction with the active component,and provide a larger specific surface area and more surfaces active oxygen for the catalyst.Therefore,the Fe₂?SO₄?₃/TiO₂ catalyst exhibits an excellent SCR performance.The NO conversion could over 80%between 280-400?and reaches 95% at 340?.Moreover,the surface catalytic reaction mainly follows the L-H mechanism.The NH₃ is mainly adsorbed by Bronsted acid site on the catalyst surface,while NO is adsorbed in the form of nitrate,nitrite and nitroso-acyl substances,and then they react with each other to form N2 and H2O.Finally,the monolithic honeycomb catalyst was prepared by extrusion method with 0.4Fe₂?SO₄?₃/TiO₂ as the matrix.The optimum extrusion process and industrial application conditions of the honeycomb catalyst were systematically studied.The results show that the gas release rate in the green body can be controlled by a sectional calcination method so as to improve the compressive strength of the honeycomb catalyst.Increasing the content of silica sol can significantly improve the compressive strength of the catalyst.However,the catalytic activity could also be reduced at the low-temperature range.When the silica sol content is 40 wt%,the compressive strength of the catalyst can reach 5.51 MPa,and the NO conversion exceed 80%at 300-400?.These results have met and exceeded the requirements of national standards.The optimum operating conditions of this honeycomb catalyst are as follows:space velocity is 3000 h^-1,ammonia-nitrogen ratio is 1.1 and oxygen concentration is 3 vol%.The NO conversion is maintained at 90%within 12 hours under 320?,which indicate a good thermal stability.In addition,SO₂ only has a little and reversible effect on the SCR performance of the catalyst.In summary,the iron-based honeycomb SCR catalyst prepared in this paper has the advantages of high strength,good thermal stability,high efficiency,environmental friendliness and low cost.It is a new type of SCR denitrification catalyst with a certain practical application value.