Research On The Influences Of Preparation Optimization And Fluoride Doping Modification On Denitration Performance Of V₂O₅-WO₃/TiO₂ Catalyst

Although the current research on selective catalytic reduction(SCR)denitration technology of flue gas is becoming increasingly mature both at home and abroad,the cost of catalyst still occupies a large proportion in the entire SCR denitration system.Besides,in the actual application process,the influence of dust collector and desulfurization system on the SCR denitration system layout should be taken into account.In the practical application of SCR denitration system,therefore,the research on SCR denitration catalyst remains the current focus.While the preparation technology of NH3-SCR denitration catalyst was optimized,this study combined the particularity of low-load operation conditions of China's coal-fired thermal power units for the purpose of developing NH3-SCR denitration catalysts with high denitration activity and strong resistance to sulfur and water intoxication.Besides,V2O5-WO3/T1O2 catalyst was investigated from the two perspectives of preparation optimization and catalyst modification,so as to improve the low temperature denitration performance as well as resistance to sulfur and water intoxication.The main contents of the study are as follows:(1)Based on the previous research in the laboratory,the calcining temperature was controlled at 500 ?,and the calcining time was controlled at 5 h,4 h and 3 h respectively;three groups of V2O5-WO3/TiO2 catalysts were prepared by ultrasonic impregnation,co-precipitation methods and Sol-gel method.And their denitration performance was compared so as to investigate the influence of calcining time on the denitration performance of the catalysts.The results show that the duration of calcining time did not change the crystal structure of the carrier TiO2,but it affected the crystallinity of the catalysts.Among them,the size of crystal particles and the distribution of active components of catalyst with calcining time of 5 h were more uniform.Meanwhile,in almost the whole process of activity test,catalysts with calcining time of 5 h showed better denitration activity and stability than those prepared with calcining time of 4 h and 3 h.(2)A series of V2O5-WO3/TiO2 denitration catalysts were prepared by three-factor mixed-level orthogonal experiment,and their denitration performance were compared.Besides,the effects of different preparation methods(ultrasonic impregnation;co-precipitation;Sol-gel method),different V precursors(NH4VO3;VO(acac)2)and different addition methods of W(W as addition agent;W as both carrier and addition agent)on the denitration performance of the catalysts were investigated,and the physical and chemical properties of the catalysts were analyzed.The results show that the V2O5-WO3/TiO2 catalyst prepared by ultrasonic impregnation and co-precipitation had larger specific surface area and pore volume,which is more favorable to the adsorption and diffusion of gases on the surface and inside part of the catalyst;VO(acac)2 as V precursor,enhanced the interaction between the active component V and the carrier TiO2,and increased the dispersion between the active component and the carrier.The V2O5-WO3/TiO2 catalyst prepared by using VO(acac)2 as the V precursor and W as both carrier and addition agent has better denitration performance.It showed good resistance to sulfur and water intoxication in the temperature range above 300 ?.Besides,it exhibited good denitration stability and the stability of resistance to sulfur and water intoxication at a continuous 96 h stability test at 350 ?.(3)This study aims to develop a medium and low temperature NH3-SCR denitration catalyst with low activation temperature,high denitration activity as well as strong resistance to sulfur and water intoxication,so carries out fluorine doping modification on V2O5-WO3/TiO2 catalyst.The effects of different V precursors(NH4VO3,VO(acac)2),different F sources(HsF6N2Ti,NH4F)and different preparation methods for F doping carriers(F-TiO2 carrier prepared by Sol-gel method,F-TiO2 carrier prepared by ultrasonic impregnation,F-WO3/TiO2 carrier prepared by ultrasonic impregnation)on the denitration performance of catalysts was investigated by three-factor mixed-level orthogonal experiment.Meanwhile,the resistance to sulfur and water intoxication of catalysts was explored.At the same time,the physical and chemical properties of catalysts were analyzed.The results show that fluorine doping increased the amount of chemically adsorbed oxygen on the catalyst surface and promoted the formation of reduced V species and reduced W species.F-WO3/TiO2 carrier prepared by ultrasonic impregnation is helpful to promote the binding of NH3 and V=O on Lewis acid sites.groups on the catalyst surface.Among them,F-doped V2O5-WO3/TiO2 catalyst prepared by taking NH4F as the F source,with F-WO3/TiO2 carrier prepared by ultrasonic impregnation,and taking VO(acac)2 as the V precursor,showed the best denitration performance at medium and low temperature;its denitration activity could be maintained above 90%within the reaction temperature range of 150-300 ?;it showed strong denitration stability and good stability of resistance to sulfur and water intoxication in the stability test of 200 ?and 250?.