Effects Of Tungsten (molybdenum) Modification On W_a(Mo_a)CeO_x Catalyzed Ammonia-selective Reduction Of NO_x

Nitrogen oxide(NO_x),as one of the main atmospheric pollutants,has brought many dangers to people's living environment and physical condition.Therefore,how to efficiently remove NO_x is a global environmental issue that needs to be faced with.NH₃-SCR is the most effective NO_x removal technology at present.Commercial V₂O₅-WO₃(Mo O₃)/Ti O₂ catalysts used in large power plants have some shortcomings,such as narrow active temperature window in the middle temperature region,high biological toxicity of V₂O₅,poor selectivity of N₂ at high temperature,poor SO₂resistance,etc.Traditional commercial catalysts can not meet the demand of flue gas denitrification at lower emission temperature.Therefore,CeO₂ was selected as the main materials of SCR catalyst in this paper,and the acidity of CeO₂-based catalysts was adjusted by doping Mo O₃ and WO₃ so as to improve the low temperature SCR catalytic performance.In addition,the effects of Mo O₃ and WO₃ modification on the structure and performance of the Mo_aCeO_x and W_aCeO_x catalysts were investigated by XRD,Raman,H₂-TPR,O₂-TPD,NH₃-TPD,SO₂-TPD,XPS and In-situ DRIFTS,respectively.Firstly,a series of Mo_aCeO_x(a=0.1,0.2,0.3 and 0.4)composite oxides catalysts were prepared by co-precipitation method.The effects of Mo O₃ doping amounts,GHSV,H₂O and SO₂ on the denitrification performance of the Mo_aCeO_x catalysts were investigated.The results showed that the activity of Mo_aCeO_x catalysts could be significantly improved by doping appropriate amount of Mo O₃.Mo_0.3CeO_x catalyst showed 100%NO conversion and excellent N₂ selectivity in the temperature range of160-425?at 40,000 h^-1.Even at high GHSV(100,000 h^-1),the Mo_0.3CeO_x catalyst still maintainsed more than 90%denitration activity in the range of 200-400?.Moreover,it exhibited excellent H₂O and SO₂ resistance,and good activity stability.In addition,the influences of different Mo O₃ doping amount on the specific surface area,acidity,redox capacity and other physical and chemical properties of the Mo_aCeO_x catalysts were analyzed through many characterizations.The reaction path was investigated by kinetic test over the Mo_0.3CeO_x catalyst.A series of W_aCeO_x(a=0.06,0.12,0.18 and 0.24)binary mixed bimetallic oxides catalysts were synthesized by simple co-precipidation method.The effect of WO₃modification on NO removal ability of W_aCeO_x catalyst NH₃-SCR was investigated.Among them,the W_0.18CeO_x catalyst exhibited the best SCR performance at low temperature(150-490?,100%),and excellent H₂O resistance.NO can be completely converted within the temperature window of 190-490?when 5%water vapor was added into the flue gas.In addition,the W_0.18CeO_x catalyst also showed excellent hydrothermal stability,SO₂ tolerance and activity stability.Furthermore,many analysis and detection techniques have confirmed that the catalyst showed excellent denitrification activity due to the synergistic effect of the addition of WO₃,which significantly enhanced the surface acidity of the catalyst and the original soft oxidation reduction performance of CeO₂.In-situ DRIFTS tests were conducted to investigate the reason why W_0.18CeO_x catalyst had excellent water and sulfur resistance.