Research On The SCR Denitration Performance And Dynamics Of V-W-Mn-Ce/TiO₂ Catalyst

NOx is one of the main gases in the atmospheric pollutants. It can be harmful to the human health and ecosystem. The SCR technology is an efficient technique for abating NOx.It is a hotspot to improve the low temperature activity of the catalyst in the research. The reaction activation energy can determine the difficulty which a reaction occurs, so the De-NOx activity at low temperatures and reaction dynamics of the V-W-Mn-Ce/TiO2 catalyst are researched.V-W-Mn-Ce/TiO2 catalyst was prepared by the impregnation method. The catalyst activities were compared in different roasting temperatures, space velocity and ratios between active component and support. Finally the optimal experimental conditions were obtained: the roasting temperature is 500?, the space velocity is 20000h-1 and the ratio between active component and support is 0.2. The V-W-Mn-Ce/TiO2 catalyst activity is higher than Mn-V-W/TiO2 catalyst? Ce-V-W/TiO2 catalyst? V-W/TiO2 catalyst and Mn-Ce/TiO2 catalyst at different temperatures, especially at low temperatures.The results of XRD and BET show that the TiO2 diffraction peaks are anatase-type. The active component of V-W-Mn-Ce/TiO2 catalyst only gathered together and they didn't form crystals. The appearance of crystals can lead to the lower surface area. The XPS result indicates that the catalyst showed an excellent activity with the high ratio of V4+/V5+ when the ratio was below 1, ratio is too large or too small would reduce the denitration activity. It will be more conducive to the oxidation and reduction reaction when the high-low valence of W,Ce in a similar content. The ratio of (Mn4++Mn3+)/Mn2+ in V-W-Mn-Ce/TiO2 catalyst is 13.29 and it is higher than Mn-Ce/TiO2 catalyst and Mn-V-W/TiO2 catalyst. Mn4+ and Mn3+ can improve the catalyst De-NOx activity at low temperatures. H2-TPR and H2-TPR peak-differentation-imitating analysis reveal that the oxides in the catalyst are more than physically mix and interact with each other, which can contribute to the redox performance together.NH3-TPD and NO-TPD results reveal that the V-W-Mn-Ce/TiO2 catalyst can absorb not only large quantities of NH3, but also a portion of NO. The in situ FTIR results show V and W mainly provide Bronsted acidic sites and they play a major role at high temperatures. The Lewis acidic is stronger in the Mn catalyst and it works at low temperatures and the Lewis acidic is stronger in V-W-Mn-Ce/TiO2 catalyst. The catalyst life test indicates that the catalyst has excellent stability at different temperatures in 100h. Although some fluctuations occurred,the activity remained above 80 percent. It reveals that the catalyst has a long service life.Resistance of SO2 result shows the catalyst activity would decrease when SO2 was bubbled into gas. This is because the formation of sulfate is attached to the catalyst surface. It will reduce NO adsorption capacity and adsorbed ammonia activity. The activity of the catalyst was gradually restored by closing the SO2 gas at 350? and the activity did not resume at lower temperature.The results of gas adsorption-desorption and transient-response reaction reveal that there are plenty of NH3 adsorption sites on the catalyst surface. Lewis acidic plays a major role. At the same time, it can also absorb a certain amount of NO, but the adsorption capacity is far less than that of NH3. These indicate that both E-R mechanism and L-H mechanism exists in V-W-Mn-Ce/TiO2 catalyst. The reaction activation energy is 50.17kJ/mol and it is less than traditional catalysts.