Mechanism And Deactivation Analysis On Selective Catalytic Reduction DeNO_x Catalyst

With the development of economy, the widespread use of fossil fuels such as oil and coal makes the environment an increasingly serious problem, which caused extensive concern of all countries in the world. The emission of nitrogen oxides (NOx) are the major originations of acid pollution. The main source of NOx is the fossil fuels combustion in power plants.SCR (Selective Catalytic Reduction) was most widely used and had the best catalytic performance. At present, the cost of the catalyst achieve about half initial investment of of the SCR system, catalyst is not only related to the catalytic efficiencies, and the life of the catalyst is very important to decrease the cost of the operation of the SCR system.Based on the independent development of V2O5-WO3-MoO3/TiO2catalyst as the research object, This article study the mechanism of SCR reaction and The ability of resistance to alkali metal poisoning.1.The adsorption of NO and NH3on different sites of vanadia-based catalysts has been studied with the density functional theory to investigate the mechanism of the SCR reaction using the cluster of V2O9H8. The calculated results indicate that H atom easily react with the surface of the cluster of V2O9H8to form the Br(?)nsted sites. NO scarcely interacts with the surface of V2O5and ammonia adsorption takes place on both the Lewis and Br(?)nsted sites of V2O5, whereas the adsorption on the Br(?)nsted sites is found to be more favorable energetically. NH3can react with the OH on the01site easily, which shows01plays an important role in SCR reaction. The calculated results support the Eley-Rideal type mechanism.2. The SCR catalysts were produced with V2O5, WO3, MoO3and anatase type TiO2. The catalytic efficiencies of catalysts were tested with the SO2to study the effects of the SO2content on NOx reduction efficiency. The structural and physico-chemical properties were analyzed with BET and (Fourier transform infrared spectroscopy) FT-IR.Experient results shows that SO2will inhibit the activity of the SCR, but the affect was small,which reveals that the catalysts was tolerant to the S02;A low concentration of SO2has little effect on the catalytic efficiencies of catalysts but the excessive concentrations can inhibit the activity of the SCR heavily;The deactivation is caused by deposition of sulfate salts on the catalyst surface in the presence of SO2,reducing the surface area and blocking the pores of the catalyst.3. The ability of resistance to alkali metal poisoning was studied by the addition of alkali metal salt (KC1, NaCl) on V2O5-WO3-MoO3/TiO2catalyst. The structural and physico-chemical properties were investigated from the microstructure to analyze the effect of alkali matal. The effect of NH3adsorption capacity of catalyst by alkali metal impregnated were investigated by NH3-TPD measurements and the mechanism of the poison of the catalyst by alkali matal has been studied with the density functional theory. The results indicated that the catalytic activity is decreased by adding alkali metals; potassium is more poisonous than sodium. It was found from NH3-TPD experiments that strongly basic elements like K or Na drastically affect the acidity of the catalysts. The DFT calculations have shown that the doping of alkali atom will cause the great change of the surface electronic property. Each alkali atom will influence four active sites, resulting in the decrease of the acid formability and reducibility of the catalyst surface.