SCR DeNO_x Performance And Ca Poisoning Resistance Of Copper-Based Catalyst At Medium/Low Temperature

Nitrogen oxide is one of the main pollutants in the atmosphere,and it is also an important cause for the environmental problems such as photochemical smog,acid rain and haze.Currently,selective catalytic reduction（SCR）is the most widely used technologies for the removal of nitrogen oxides（DeNO_x）.There are some disadvantages of the commercial vanadium-based catalysts,e.g.the low activity at a low temperature,poor resistance to water and sulfur,poor resistance to alkali/alkali earth,and the toxicity of vanadium species.It is necessary to develop a SCR catalyst possessing a high activity at low temperature,a high stability and environmental benignity.In this study,a series of copper-based catalysts were prepared by using HZSM-5 as the support.The effects of different loading amount of Cu and Ca on the Cu/ZSM-5 catalyst were investigated.The influence of Zr doping on the catalytic activity of Ca/Cu/ZSM-5 catalyst was examined.Furthermore,the catalytic performance and reaction mechanism of MnCo/Cu-ZSM-5 catalyst prepared by impregnation method with Cu-ZSM-5 catalyst as carrier were also studied.The main results are as follows:（1）The effects of Cu loading and Ca loading on the catalytic performance of catalystA series of Cu/ZSM-5 catalysts for DeNO_x were prepared by impregnation method.When the loading amount of Cu was 4 wt%,a maximum in catalytic activity was obtained.A strong poisoning effect of Ca impregnation on Cu/ZSM-5 catalyst was observed for the NH₃-SCR.The Ca impregnation decreases the specific surface area of Cu/ZSM-5 catalyst,the amount of surface acid sites,the reducibility of CuO,the dispersion of Cu and the concentration of Cu atom on the surface of catalyst.In addition,the Ca loading also affects the form of copper species on the surface of catalyst.With the increase in Ca loading,the ratio of CuO crystallites to isolated Cu²⁺decreased gradually.The co-effects of these factors decrease the activity of Cu/ZSM-5 catalyst in NH₃-SCR reaction.（2）The influence of Zr doping on Ca/Cu/ZSM-5 catalyst performanceWith the addition of Zr,an enhanced Ca poisoning resistance of Cu/ZSM-5 catalyst for the SCR of NO was obtained.The highest catalytic activity was observed over the catalyst with the Zr amount of 0.10 wt%.After the addition of Zr,there is no significant change in the acidity of Ca/Cu/ZSM-5 catalyst,but the surface area of copper(S_Cu)on the catalyst increases.The interaction between CuO and CaO was depressed,and the reducibility of copper species was enhanced.These two changes contribute to the increase in the catalytic activity.（3）Study on the catalytic performance and reaction mechanism of MnCo/Cu-Z catalystsFirst,Cu-ZSM-5 catalyst（Cu-Z）was prepared by an ion exchange method,and then a series of MnCo/Cu-Z catalysts were prepared by the impregnation of Mn and Co.The MnCo/Cu-Z catalyst with a Mn/Co of 1/2 exhibited the highest catalytic activity at low temperature.The conversion of NO_x reaches 93%at 150^oC.The impregnation of Mn and Co on Cu-ZSM-5 catalyst gives rise to an increase in the conversion of NO to NO₂ at low temperature.Moreover,the reduction of catalyst,the concentration of metal atoms and the amount of chemically adsorbed oxygen increase after impregnating Mn and Co,which is beneficial to the enhancement of the catalytic activity at low temperature.Two reaction paths（E-R and L-H mechanisms）were found on the surface of Mn₁Co₂/Cu-ZSM-5 catalyst for the SCR DeNO_x by the in situ DRIFT measurement.