Modification And Molding Of Siderite Catalysts For SCR Of NO_x With NH₃

It is known that the control of NO_X is a difficult and important task in environmental governance which has become a top priority in today’s social work.Selective Catalytic Reduction（SCR）is the most widely accepted and applied flue gas denitrification technology in the world.The catalyst is the kernel of the technology.Currently,the most common catalyst in engineering is V₂O₅-WO₃/TiO₂ catalyst.However,there are still some problems to solve.Firstly,the active window temperature of V₂O₅-WO₃/TiO₂ catalyst is so high that the arrangement of high temperature and high dust could poison the catalysts to lose their activities.Moreover the main active components of the expensive catalysts,vanadium and their compounds,belong to toxic substances.Consequently,developing an environmentfriendly commercial catalyst,which performs high efficiency at low reaction temperature,is a hot topic in the field of denitration in recent years.Siderite powder was used as the research object in this study.A series of modified and pressure molded siderite catalysts doping with Mn,Ce,codoping with Mn and Ce are prepared to study the denitrification activity change regulation of these catalysts at middle and low temperature.The results are used to simulate the denitrification property of full-scale honeycomb shaped catalysts.After that,a series of honeycomb shaped siderite catalyst are prepared with mixed materials,doping with Mn,changing calcination temperature and using different precursors to study the influence of different preparation processes on the denitrification efficiency of honeycomb catalyst at medium and low temperature.In addition,the properties of pressure molded siderite catalysts and honeycomb shaped siderite catalyst including surface properties,crystal structure,surface acidity are characterized by BET,XRD and NH₃-TPD.The main conclusions are as follows:For the pressure molded siderite catalysts,the low temperature denitrification efficiency of catalysts increase significantly with the increase of Mn doping amount.The characterization analysis shows that the doping of Mn can effectively improve the specific surface area and reduce the crystallinity of catalysts,however,it has little effect on catalysts’ surface acidity.The sulphur resistance of the siderite catalyst at different reaction temperatures is different,and the degree of poisoning at the reaction temperature of 270℃ is less than the degree of poisoning at the reaction temperature of 210℃.The increase of catalysts’ denitrification efficiency is limited dy doping with Ce and the best effect of Ce doping is 1%.The doping of Ce can slightly improve the specific surface area,active substances dispersion and the surface acidity.In the study of the pressure molded siderite catalyst codoping with Mn and Ce,we find the catalyst activity is best while the doping amount of Mn is 3% and the doping amount of Ce is 1%.The catalyst prepared by this mixture has the maximum specific surface area,the lowest crystallinity and the strongest surface acidity.Meanwhile,the synergistic reaction of Mn and Ce has beneficial effects on catalyst activity.The denitration efficiency of honeycomb shaped catalysts is not affected by calcination temperature which is within the range of 450⁵50 C.On the one hand,organic decomposition and water evaporation generate bubbles to increase catalysts’ specific surface area;on the other hand,calcination will crystallize catalysts’ substance.According to the analysis results of BET and XRD,the change of catalysts’ activity could be affected by these two factors.Doping Mn can effectively improve the low temperature activity of honeycomb shaped siderite denitration catalyst due to TiO₂ providing large specific surface to hold manganese oxide.The modification of doped Mn is beneficial to increase the specific surface area,decrease the crystallinity and increase the surface acidity of the catalyst.Honeycomb shaped and modified siderite catalysts prepared by different precursor show different catalytic activity.The honeycomb shaped catalyst with manganese nitrate as precursor has better performance in denitrification.The reason may be that manganous nitrate has higher solubility and easier pyrolysis for manganese oxide than manganous acetate.The honeycomb shaped modified siderite catalyst with manganese nitrate as precursor has larger specific surface area,lower crystallinity and stronger surface acidity.This is in accordance with the mechanism of improving the catalytic activity.The denitrification activity of honeycomb shaped and modified siderite catalyst is mainly affected by the temperature of flue gas inlet and outlet.The reason mainly is the decomposition of ammonium sulfate at higher temperature can reduce the toxic effect of SO₂ on the catalyst.