Research On The Denitration Performance And Mechanism Of Composited Mn-Ce-V-WO_x/TiO₂ Catalysts

As one of the major air pollutants,NO_x brings serious harm to our living environment.For now,the selective catalytic reduction?SCR?technology is more suitable for application and popularization among numerous denitration technologies due to its easy process and low reaction condition.Catalysts are the core of SCR,but are easily poisoned by the bad SCR reaction conditions,and lose activity.Therefore,SCR system is urged to be improved by the catalyst with high activity at low temperature,which is hoped with high resistance of H₂O and SO₂.In this study,a series of catalysts with different ratios of active substances/TiO₂ were prepared by the wet impregnation method,which are based on the V₂O₅-WO₃/TiO₂ catalyst with the addition of Mn and Ce.The catalyst with the ratio of active substance/support at 0.2exhibits the best denitration activity.There is the optimal ratio between active substances and support,which makes the catalyst show the best denitration activity.The results of XRD,BET,TEM and HRTEM indicate that active substances are highly dispersed on the carrier surface when the ratio is 0.1.When the ratio increases to 0.6,large amount of active substances gather into crystal,which makes the catalyst particles 4 times bigger than the support and specific surface area rapid decrease.The 100 h stability test indicates that the activity maintains about 95.3%.And the catalyst shows great resistance of H₂O and SO₂.The H₂-TPR results reveal that the oxides in the catalyst are more than physically mix and the interaction among them construct the catalyst,which contribute to the high performance.The in situ FTIR results indicate that there are NH₃ and NO adsorbed on catalyst surface even when the temperature got to 400°C and SO₂ is only adsorbed on the specific sites.The XPS analysis demonstates that valence states of V are easy to transform,W shows strong stability,Mn is similar with Ce,but the valence states of Mn and Ce reveal inversely change with the increase of active substances.After 100 h test,a little amount of low valence states of V and W transform to the high valence states,and Mn and Ce show inverse change.To sum up,the mechanism was proposed in the end,which contain two aspects:the adsorption,transformation and desorption reaction of the reactant gas and the electron transport.