The SCR De-NO_x Activity And Sulfur And Water Resistance Of Modified Siderite Catalyst

NO_x is one of the main air pollutants and Selective Catalytic Reduction（SCR）is an effective method to remove NO_x in the flue gas.Catalysts are the kernel of SCR de-NO_x technology.The V₂O₅/TiO₂ series catalyst is a common commercial SCR de-NO_x catalyst which has high catalytic activity.However,there are also some disadvantages,such as high price,high active temperature window,and heavy metal vanadium is a toxic substance.Therefore,the development of a new type of SCR de-NO_x catalyst with low temperature de-NO_x activity,high efficiency,low price and no toxicity has become a research hotspot in the field of flue gas de-NO_x in recent years.In this study,the siderite was used as the research object,and the siderite de-NO_x catalyst modified by Ce doping,Zr doping and Ce-Zr co-doping was prepared by mixing and stirring method.The experimental researches of de-NO_x activity and sulfur and water resistance of catalysts were carried out.The effects of Ce and Zr doping on the de-NO_x activity and sulfur and water resistance of the catalyst were studied.The characteristics of the catalyst,such as elemental composition,surface structure,crystal form and surface acidity were determined by XRF,BET,XRD,NH₃-TPD,TG and other experimental means.The main research results are as follows:（1）The doping of Ce and Zr can greatly improve the low-temperature SCR de-NO_x activity of the catalyst.3%Ce+3%Zr-doped siderite catalyst has the highest de-NO_x activity,the catalytic de-NO_x efficiency is above 92%in the temperature range of 180-330℃.The results obtained by BET,XRD and NH₃-TPD showed that the doping of Ce and Zr can increase the specific surface area of the catalyst,decrease the crystallinity,and enhance the surface acidity,so that the catalyst has better de-NO_x performance.（2）Parameters such as space velocity,oxygen content and ammonia-nitrogen ratio have certain influences on the de-NO_x performance of modified siderite catalyst.The SCR de-NO_x efficiency of modified siderite catalyst is decreased with the increase of space velocity.The optimum O₂ concentration is 3%and the optimum ammonia-nitrogen ratio is 1.（3）The doping of Ce and Zr can inhibit the sulfation of the active component,reduce the thermal stability of the ammonium sulfate and promote the decomposition of ammonium sulfate.It can also increase the specific surface area of the carrier,improve the oxygen storage performance of the catalyst surface,and slow down the inhibition of H₂O on the de-NO_x activity.Therefore,after doping of Ce and Zr,the siderite catalyst has better sulfur and water resistance.Ce_0.03/Zr_0.03-siderite catalyst has excellent sulfur and water resistance,the de-NO_x efficiency is still more than 87%after introducing 5%H₂O and 100ppm SO₂ for 8h at 210℃.（4）The higher concentration of H₂O and SO₂,the faster deposition rate of ammonium sulfate on the catalyst surface,and the more obvious loss of de-NO_x activity.However,the higher reaction temperature,the more ammonium sulfate decomposed,the less H₂O adsorbed on the catalyst surface,the catalyst has better sulfur and water resistance at high temperature.