Study On Modification Of V₂O₅/TiO₂Catalyst In SCR Flue Gas Denitrification

Selective catalytic reduction has high denitration efficiency which has been applied to coal-fired power plants. Catalyst is the key of this technology. The most widely used SCR catalyst is V2O5/TiO2catalyst series, but its high temperature window leads to the poison of catalyst due to dust and SO2. So, low temperature modification of V2O5/TiO2catalyst becomes a research hotspot at home and abroad.The research of low temperature modification on V2O5/TiO2catalyst mainly includes optimizing preparation technology and adding suitable promoter in this work. The characteristic of microwave radiation is volume heating, which can be used in catalyst preparation technology. The microwave dying can improve the pore structure and the degree of dispersion of active constituent on the supporter. Adding transition metal can improve the activity of V2O5/TiO2catalyst at low temperature. The crystalline phase and microstructure of the catalysts were studied by XRD and SEM.Firstly, the microwave drying technology was introduced into the catalyst preparation. The effects of microwave drying on catalytic activity and structural performance, and the optimum microwave operation parameters were studied. Experimental results showed that microwave drying could improve SCR activity of V2O5/TiO2catalyst greatly(the NO reduction is from50.4%to83.6%at250℃). The optimum microwave parameters were that power was210W and time was20min. The characterization results showed that microwave dying could improve the pore structure and degree of dispersion of active constituent on the supporter, the particle size became smaller and distributed more uniformly.Secondly, the effects of Mn、Ce、Fe and W promoters on V2O5/TiO2catalyst dentration activity were studied. The results showed that, Mn and Ce promoters both could improve catalyst activity, but Fe and W promoter could not. After selecting,3V5Mn5Ce/TiO2-W exhibited the highest denitration efficiency, which reached to93.9%at220℃. The characterization results showed that TiO2was mainly anatase, vanadium and manganese oxides were all nonstoichiometric compound on the supporter, adding Ce promoter and mircrowave drying could both increased catalyst surface area.Thirdly, the effects on denitration activity of3V5Mn5Ce/TiO2-Wby calcination temperature, reaction temperature, NH3/NO mol ratio, space velocity and oxygen content ratio were studied, which provided basic data for catalyst industrial application. The results showed that lower calcination temperature (400℃) was beneficial to SCR reaction, active components would be crystallized or sintered if calcination temperature was too high. Increasing reaction temperature, NH3/NO mol ratio, oxygen content ratio and decreasing space velocity could improve NO reduction. Repeated experiments showed that NO reduction of3V5Mn5Ce/TiO2-W kept over90%at220℃, so this catalyst had good stability. Transient response experiments showed that reactions on this catalyst followed Eley-Rideal mechanism.At last, kinetics of SCR reaction on V-Mn-Ce/TiO2-W was studied. The results showed that SCR reaction on V-Mn-Ce/TiO2-W was first-order reaction, reaction rate constant was5.11L/(g·min) and activation energy was50.94kJ/mol. The activation energy was lowered obviously compared with traditional V2O5/TiO2catalyst.