| NOx which seriously affects people's normal life will destroy the ozone layer and result in greenhouse effect.Compared with other deNOx catalysts,V2O5-WO3/TiO2 catalysts are widely used in commercialization because they have good activity at medium and high temperature(optimum reaction temperature between 300? and 500?)and good anti-sulfur performance.But this type of catalyst needs further optimize because they have low activity at low temperature.It is found that different V4+(3+)/V5+ ratios on the surface of deNOx catalysts are related to the rate of deNOx.The difference of V4+(3+)/V5+ ratio affects the type and content of the acid sites on the catalyst,which lead to the denitrification activity.V2O5-WO3/TiO2 catalyst was prepared by impregnation method through changing the aging time of precursor solution and the content of the active component and used TiO2 as carrier.The experimental results from XRD,BET,H2-TPR,NH3-TPD showed that the aging time just had little influence on the specific surface area of the catalyst and had no effect on the state of V2O5 which was highly dispersed on the carrier TiO2,only the anatase TiO2 on the surface of catalyst.We discovered that the ammonia adsorption capacity and B/L value of the catalyst surface showed a trend of firstly increased and then decreased when increased of the aging time.When the aging time was 8 h,we found that the lowest reduction temperature of the catalyst was 502?,and the maximum of ammonia adsorption capacity,the value of B/L and the ratio of V4+(3+)/V5+ respectively was 1.97 ×10-8 mol,0.53 and 1.28,and the denitration activity of the catalyst reached a highest level(85%)at a reaction temperature of 400?.For V2O5-WO3/TiO2 catalyst prepared by different loading amount of V,the V2O5 diffraction peak and the diffraction peak of anatase TiO2 were observed and the specific surface area of catalyst decreased rapidly when the V loading reached 11%,this indicates that the formation of the crystal phase of catalyst resulting in a decrease in specific surface area.With the increase of the loading content of V,the state of the vanadium species on the catalyst surface changed from the isolated state to aggregation state and finally to the crystalline phase,and the reduction temperature became higher and higher,the adsorption amount of ammonia and the value of B/L on the surface of the catalyst firstly increased and then decreased,and they reached the maximum at the loading content of 9%,at this time,the adsorption capacity of ammonia was 2.49×10-8 mol,the value of B/L was 0.56,the ratio of(V4++V3+)/V5+ reached the maximum of 2.56 and the denitration activity of the catalyst was the best(84%)at a reaction temperature of 400?.The adsorption of NH3 and NO on the surface of the catalyst showed that NH4+ which formed by NH3 adsorbing on the acidic sites of the surface of the catalyst played a key role during the SCR reaction.NO adsorbed on the surface of the catalyst to form nitrites and nitrates and the activity of mono-dentate nitrate was the highest.The presence of O2 activated the B acidic sites on the surface of the catalyst,which made NO more quickly form nitrate species on the catalyst surface.There were E-R mechanism and L-H mechanism on the surface of V2O5-WO3/TiO2 catalyst,and the reaction of NH4+ at B acidic sites is the main reaction. |
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