Preparation And Application Of SCR Denitration Catalyst At Low Temperature

With the rapid development of economic and persistent consumption of energy,an increasing number of oxynitride（NO_X）has resulted in serious impact on environment and human health.At the present stage,the selective catalytic reduction（SCR）technology is the most effective way to remove NOx.The low-temperature SCR technology has attached more and more attention for its superiority,including low running cost and saving energy.Catalyst is the core and key factor of denitration technology,which directly impacts on the effect of NOx removal.V₂O₅-WO₃（Mo O₃）/TiO₂is one of the widely used catalyst in SCR technology.But it’s not suitable for its application in the low-temperature SCR,because it has optimum denitrification effect only in high temperature range of300～400℃.Recently,the manganese oxide-based catalysts have arousd widespread concerns,due to its excellent catalytic activity at low temperature in SCR technology.In this dissertation,the manganese composite metal oxides catalysts were studied as study object.Firstly,manganese nitrate/iron nitrate and manganese acetate/iron nitrate were respectively used as precursor of active components,nanoscaleγ-Al₂O₃ was used as support.The different Mn-Fe/γ-Al₂O₃catalysts were prepared by coprecipitation or impregnation method and their denitration performance were also studied.The results showed that NO conversion could reach more than 96%when manganese nitrate was used as precursor by coprecipitation method at 200℃.The optimum conditions to metal loading were molar ratio of Mn/Fe 4:1,space velocity 16000 h^-1,oxygen content 20 wt%,and mole ratio of NH₃/NO 1.2.Mn-Fe oxides were respectively supported on TiO₂,ZSM-5 and active carbon to prepare different supported catalysts,and then the denitration performance was examined.Within the scope of the reaction temperature,it was found that Mn-Fe/TiO₂and Mn-Fe/γ-Al₂O₃had relatively higher low-temperature SCR activity than Mn-Fe/ZSM-5.The Mn-Fe/AC had the worst low-temperature SCR acivity compared with others.In addition,Mn-Fe/TiO₂catalyst was modified by matal-doping.It was found that Ce-doped Mn-Fe/TiO₂catalyst had greatly enhanced its low-temperature SCR activity.The NO conversion could reach higher than 80%when reaction temperature was 80℃.For the Ce doping,the Mn-Fe-Ce/TiO₂ catalyst had a higher stability and poisoning resistance of H₂O and SO₂.The repeatability of deactivated Mn-Fe-Ce/TiO₂ catalyst was studied,which exhibited well stability by ultrasonic washing.The results showed that the catalytic activity could remain at about 70%after regeneration for six times.The catalysts were characterized by XRD and BET techniques.The results showed that the active components of Mn-Fe/γ-Al₂O₃and Mn-Fe-Ce/TiO₂ had low crystallinity and good dispersibility on the surface of support in amorphous structure except that the diffraction peak of Mn₂O₃ and Fe₃O₄ on the carrier TiO₂ was detected for Mn-Fe/TiO₂catalyst.Mn-Fe/γ-Al₂O₃ catalysts had abundant mesoporous structure.The specific surface area and pore volume of Mn-Fe/γ-Al₂O₃is higher than Mn-Fe/TiO₂.The Ce doping also increased the specific surface area and pore volume of Mn-Fe/TiO₂catalyst,which could improve catalyst activity in the catalyst.