Study On The SCR NO_x Removal Performance Of Doped Siderite Catalyst For Diesel Engine Exhaust

With the increase of diesel vehicles,the problem of NO_x emission from diesel engines has become increasingly prominent.SCR technology has high removal efficiency of NO_x,which is one of the most potential post-treatment technologies for diesel engine NO_x.The core of this technology lies in efficient catalysts.The V₂O₅/TiO₂ is the common commercial SCR de-NO_x catalyst with high NO_x removal efficiency.However,its active temperature window is narrow,and vanadium is toxic,so that it is not suitable for diesel engine exhaust NO_x removal.Therefore,the development of catalysts with wide active temperature window,low price and safety and non-toxicity has been a research hotspot in diesel engine exhaust SCR de-NO_x technology.In this study,therefore,a series of Siderite SCR de-NO_x catalysts modified by Ce doping,Mn doping,W doping,Ce/W doping and Mn/W doping were prepared by mixing stirring method.The effects of doping were studied.The features of catalysts,such as elemental composition,pore structure,crystalline form and surface acidity of siderite catalysts,were analyzed by XRF,BET,XRD and NH₃-TPD.The main results are as follows:?1?The temperature of calcination has a certain effect on the SCR de-NO_x activity of siderite catalyst.The temperature window of de-NO_x activity of calcined siderite at 500?is the widest,which is 240³30?.The main component of calcined siderite is Fe₂O₃ and the second component is MnO,and the specific surface area is large,which can provide more active sites.The catalytic activity of iron oxides and manganese oxides and the interaction between Fe and Mn elements are the main reasons for its high SCR de-NO_x efficiency.?2?Ce doping can improve the catalytic activity at low temperature,but inhibit the activity at high temperature.When Ce doping content is 3%,the maximum active temperature window is 180³30?.Doping W can obviously improve the catalytic de-NO_x activity at high temperature,but it can inhibit the activity at low temperature.W_0.03-siderite has the best catalytic effect,the active temperature window is 240³90?.Mn doping can significantly improve the catalytic activity at low temperature,and almost has no effect on the activity of catalyst at high temperature.Mn_0.03-siderite has the best catalytic effect,and the de-NO_x efficiency reaches more than 90%in 180³30?.Characterization analysis shows that Ce doping,Mn doping and W doping are beneficial to increase the specific surface area of the catalyst,inhibit the surface crystallization of the catalyst,enhance the acidity of the surface adsorption center,and facilitate the catalytic reaction.?3?The effect of doping of Ce/W and Mn/W on the de-NO_x performance of siderite catalyst is studied.It is found that the temperature window of siderite catalyst doped with 1%Ce3%W is 180³60?.Furthermore,the the temperature window of siderite catalyst doped with 1%Mn3%W is given 200³90?,which is very close to the exhaust temperature range of diesel engine 200⁴00?.Therefore,it is suitable for SCR de-NO_x of diesel engine exhaust.The effects of ammonia-nitrogen ratio,oxygen concentration and space velocity on the de-NO_x efficiency of Mn_0.01W_0.03-siderite catalyst are studied.It is found that the catalytic performance is the best when ammonia-nitrogen ratio is 1.0¹.1,oxygen concentration is 3%and space velocity is 30000h^-1.