Study On Modification Of MnO_x/MWCNTs Catalyst For Low Temperature SCR

NOxpollution has become a serious environment problem recently. Selective catalyticreduction (SCR) of NOxwith NH3is one of the most effective flue gas DeNOx technologiesfor stationary sources and is the most extensively applied at home and abroad. However, thedevice of commercial catalyst is usually arranged in a circumstance with high concentrationof dust and sulfur dioxide as it is active only in a high temperature window of290–400℃.The catalyst is susceptible to be deactivated by high concentration of SO2and dust. So it hasgreat importance to develop low-temperature SCR technology and catalyst with a temperaturewindow below200℃.MnOx/MWCNTs catalyst has a good activity in low-temperature SCR. Activecomponent and the structure and surface properties of MWCNTs have great importance in theperformance of catalyst. Catalyst with iron doping usually has a wide temperature windowand nice sulfur resistant properties. Plasma technology is a superior method for surfacemodification and nitrogen containing groups can well regulate surface alkaline for materials.In this paper, multi-walled carbon nanotubes(MWCNTs) were modified by NH3plasma firstand MnOx/MWCNTs catalyst with pristine and modified MWCNTs were prepared for lowtemperature SCR. Besides, Iron was doped into the active part to achieve a better performancein low temperature denitrification.In the aspect of carrier modification, first, MWCNTs with diameters of60-100nm weremodified by low-temperature plasma produced by dielectric barrier discharge in NH3flow.Structures of the pristine and plasma modified MWCNTs were characterized by SEM, BET,Raman, FT-IR and XPS. Results showed that a little decrease in specific surface area and porevolume was produced by NH3plasma. The degree of reduction was affected by modificationtime and power In addition, a certain content of nitrogen containing groups were produced bythe modification on the surface. The nitrogen content of6.11at.%was got when themodification power was20w and time60min.Second, several kinds of MnOx/MWCNTs catalyst with pristine and modified MWCNTswere prepared for low temperature SCR. Structures of the pristine and plasma modifiedMWCNTs and the catalyst were characterized by SEM, BET, Raman, FT-IR and NO-TPD.The modification of MnOx/MWCNTs catalyst could somewhat improve the catalystactivation. Catalyst modified by20w,30min has the best activity in low-temperature SCR.Data showed that the improvement of NO conversion could be attributed to the increase ofsurface defects and adsorption of NO on the MnOx/MWCNTs catalyst. Besides, the effects of different MnOxprecursors on properties of SCR were also studied. The precursor manganeseacetate has got a better activity in low-temperature with a higher proportion of Mn4+.As for the active part, iron oxide was doped in as a part of active component. The effectsof Fe doping amount, calcination temperature, and the loading method on selective catalyticreduction (SCR) of NO with NH3were investigated. Catalysts were characterized by BET,XRD, Raman, H2-TPR and XPS to investigate the internal relationship between catalyticactivity and its physical and chemical properties. The results revealed that activity of catalystsincreased first and then decreased with the addition of Fe and the optimal additive molar ratiowas Fe/(Fe+Mn)=0.5. The best calcinations temperature was400℃. The performance wassimilar when catalysts were prepared by the equal volume impregnation and coprecipitationmethod High Mn3O4phase content was obtained by the preparation method of equivalent-volume impregnation could enhance the SCR activity of catalysts. Highly dispersed of MnOxwhich prepared by the method of coprecipitation was one of the reason to reach a better SCRactivity. XRD, Raman and XPS results showed that the doping of Fe had an interaction withMnOx and promoted the formation of a part of Mn3O4on the surface of catalysts and thenpromoted the low-temperature SCR.