Low Temperature NH₃-SCR Performance Modification Of Vanadium Titanium Catalyst ?V₂O₅-WO₃/TiO₂?

Selective catalytic reduction with NH₃?NH₃-SCR?was the most mature NO_x removal technology in industrial application,and the core of this technology was the catalyst.Commercial catalyst V₂O₅-WO₃/TiO₂?V-W/Ti?had high denitration performance in 300-400?and was widely used at present.But,the temperature of flue gas emited from a large number of non-electric industries?cement,kiln,coking,petrochemical,etc.?was almost low?<300??during the recent years,it was difficult to directly use the current medium and high temperature SCR denitrification technology.Based on the above situations,it is necessary to develop new low-temperature SCR denitrification catalyst with higher denitrification activity and lower reaction temperature.At first,this paper adopts the traditional impregnation method,the transition metal?Fe,Cu,Mn?and rare earth metals?Ce,La?were loaded on the V-W/Ti catalysts to modify the SCR performance at the low temperature.And results showed:that V-W/Ti catalysts modified with Mn exhibited the best catalytic performance.Then the modified catalyst Mn9-V-W/Ti was prepared by dipping method,coprecipitation method and in-situ growth method,and the influence of different preparation methods on the denitrification activity of the catalyst was investigated.The resulted show Compared with V-W/Ti catalysts,the denitrification activity of catalyst modified by in situ growth method was improved by about 90%(10500 h^-1gas hourly space velocity and 100?reaction temperature),and the denitrification activity has maintained about 100%from 100?to 280?and it was the best modification method to improve the low temperature SCR denitrification performance of V-W/Ti catalyst.Through characterization analysis,it was found that there was no sintering phenomenon on the surface of the catalyst prepared by in-situ growth method,the active component Mn had higher dispersion performance,and the size of catalyst particles was small and relatively uniform,which was mainly attributed to the in-situ reaction at room temperature.Moreover,MnOx generated in this way mostly exists on the catalyst in the form of Mn⁴⁺,which enhanced the redox performance and surface acidity of the catalyst.Therefore,the catalyst prepared by in-situ growth method can show excellent low temperature denitrification activity.In-situ growth method was more advantageous than the other two traditional methods.In order to further improve this method,the systematic study of the influence of preparation parameters?ratio of the reaction of KMnO₄ and Mn?NO₃?₂,the content of Mn,?and working conditions?gas hourly space velocity?GHSV?,long-term test,sulfur resistance etc.?on the low-temperature SCR denitrification performance of Mnx-V-W/Ti-S catalyst.The relationship between preparation conditions and the structure characteristics of the catalysts was thoroughly investigated,and discussion of the structure-activity relationship between the catalyst structure characteristics and denitrification performance.The results showed that the catalyst prepared with reactant ratio KMnO₄:Mn?NO₃?₂=2:3 and Mn load of 9 wt%had the best denitration activity.The catalyst prepared under this condition had the maximum specific surface area and enables the dispersion of active components on the catalyst surface.Because the catalyst was susceptible to the toxicity of SO₂ in practical application,we also investigated the influence of different sulfur concentrations at different temperatures on the denitrification performance of Mn9-V-W/Ti-S catalyst SCR.The long-term test results showed that Mn9-V-W/Ti catalyst was more susceptible to SO₂ at low temperature and the denitration activity dropped to 40%from 100%beginning under 160?,10 ppmSO₂.Moreover,the higher the SO₂concentration,the greater the influence on the catalyst.In order to improve the sulfur resistance of the catalyst,we also explored whether the sulfur resistance of the catalyst could be improved by other active element doping,it was found that the appropriate Ce doping could improve the sulfur resistance of Mn9-V-W/Ti catalyst to some extent.