Research On The Mechanism Of Composition Of Fly Ash On Mn/TiO₂ Denitration Catalyst Performance

NOx is one of the main sources of pollution in the atmosphere.It not only causes a series of problems destroying the ecological environment such as acid rain, photochemical smog etc,but also seriously harmful to our body health.As a result,how to effectively reduce emissions of NOx has become a hot topic that everyone concerned.The technology of SCR is one of the most effective control measures for flue gas to denitrate because of the high denitration efficiency and mature technology.And it has been widely used. The poison resistance of catalyst has been a focus in the research of SCR technology as the core of denitration technology.The service life of the catalyst relates to the feasibility and economical efficiency of SCR technology.The main reason for catalyst deactivation is poisoning of the catalyst.Consequently,the study of catalyst poisoning has become a important topic.There are many causes of catalyst poisoning.The various components of flue gas is the main factor that cause catalyst poisoning,mainly including alkali, alkaline earth metal, heavy metal, hydrogen chloride, sulfur dioxide, and phosphorus, etc. The problem of poisoning has been lacking of systematic research in the use process of catalyst.In order to solve this problem, we carried on the systematic study of the catalyst poisoning in this passage,based on the poisoning mechanism of Alkali, alkaline earth metal, heavy metal, hydrogen chloride, sulfur dioxide, and halogen elements,etc in Mn/Ti O2 catalyst.We make a series of catalyst through the method of impregnation and sol-gel to do poisoning experiment,and test their activity.We study the performance of the catalyst after poisoning systematically, and analyse the results for the systematically by means of BET, H2-TPR, NH3-TPD, XRD and XPS characterization testing of experimental drugs. And the deposition of alkali metal would lead to the deactivation of Mn/TiO₂ catalyst. In this paper, the poisoning effect of Na and K on Mn/TiO₂ was investigated based on experimental and theoretical study. It was found that K had a stronger poisoning effect than that of Na. The bad performance of K-Mn/TiO₂ may be due to its high crystallinity, weak surface acidity and low concentration of chemisorbed oxygen. The interpretation of the experimental results is supported by DFT calculations. Experimental results indicate that the doping of alkali earth metals would cause the decrease of specific surface area, redox ability, surface acidity, and the concentrations of surface Mn4+ and chemisorbed oxygen, as a result, leading to the deactivation of Mn/TiO₂ catalyst. The different poisoning effects of Ca and Mg on Mn/TiO₂ catalyst are correlated to the four major factors: specific surface area, TiO₂ crystallinity, the reducibility and the atomic concentrations of Mn4+ and chemisorbed oxygen species. Heavy metals have been proven to be of deactivation effect on SCR catalyst It was found that both of Zn and Pb had a poisoning effect on Mn/TiO₂ catalyst and the poisoning effect of Zn was more obvious. The characterization results indicated that the doping of heavy metals on Mn/TiO₂ surface would lead to a great decrease of reducibility and surface acidity. The results of XPS characterization revealed the decrease of Mn4+ atomic concentration and chemisorbed oxygen species caused by the doping of heavy metals. Based on the above mentioned unfavorable properties, the doping of heavy metals would cause a serious deactivation of Mn/Ti O2 catalyst. From the results of DFT calculations, it could be concluded that the doping of heavy metals on Mn/TiO₂ catalyst resulting in a great decrease of NH3 adsorption ability on its surface, which agrees well with the experimental results. The effect of F and Cl on Mn/TiO₂ catalyst for selective catalytic reduction of NO with NH3 was investigated in this study. From the experimental results, we can find that the doping of F or Cl has a deactivation effect on Mn/TiO₂ catalyst. And the poisoning effect of Cl is more serious than that of F. Based on the characterization results of N2 adsorption, X-ray diffraction（XRD）, temperature-programmed reduction（H2-TPR）, temperature-programmed desorption（NH3-TPD） and X-ray photoelectron spectroscopy（XPS）, it can be observed that the doping of F or Cl has great impact on the surface physico-chemical properties of Mn/TiO₂ catalyst. The decrease of BET surface area, the increase of crystallinity, the reduced reducibility and surface acidity, and the decreased surface Mn4+ and chemisorbed oxygen should be responsible for the deactivation of Mn/Ti O2 catalyst by the doping of F or Cl.