Study On Mechanism Of Alkaline Earth Metal Poisoning For Medium Temperature Commercial SCR Catalyst

Selective Catalytic Reduction（SCR）was widely used in coal-fired power plants because of its high activity and high denitration efficiency.The catalyst was the core of the whole SCR denitration technology.And its denitration performance was easily reduced by the influence of various alkaline earth metal components in the fly ash.The effects different toxic components on the catalyst were also different.Therefore,the performance of denitration catalyst under different flue gas components was studied and the poisoning law and poisoning mechanism of the catalyst were studied.It was of great significance to ensure the stable operation of the catalyst and to develop anti-poisoning catalysts in the future.In this paper,the medium temperature commercial V₂O₅-MoO₃/TiO₂ catalyst was studied.First,the catalyst CaO poisoning was simulated by dry or wet mixing.Based on the denitrification activity test.The catalysts were characterized by BET,XRD,XPS,NH3-TPD and H2-TPR to investigate the changes of physical and chemical properties before and after catalyst poisoning.It indicated different poisoning methods had different effects on catalyst poisoning.The effect of wet mixing CaO poisoning on catalyst denitrification efficiency was greater than dry mixing.At 300^oC,3%Dry mixing-CaO（83.56%）>3%Wet mixing-CaO（70.79%）.And the inhibition increased with the increase of loading.The CaO poisoning led to a decrease in the specific surface area and pore volume of the catalyst.What’s more,the active component V⁵⁺/V and the chemisorbed oxygen content decreased.TPD and TPR showed that CaO incorporation reduceds the amount of acid on the catalyst resulting in a decrease in the adsorption capacity of NH3.At the same time,the reactivity of the reduction site was lowered.Combined with the In Situ DRIFTS characterization,it was concluded that the catalyst CaO poisoning was mainly achieved by affecting the Br?nsted acid sites on the catalyst surface.Compared the difference in performance after dry and wet mixed poisoning,it illustrated that the wet mixing method poisoning due to immersion and high temperature calcination,the CaO fluidity was enhanced to penetrate into the catalyst and the crystallization of TiO₂ on the surface was enhanced.As the result the catalyst deactivation wasaggravation.Secondly,the effect of Mg O deposition on the catalytic activity of medium temperature V₂O₅-MoO₃/TiO₂ was investigated,and its effect on the physicochemical properties of the catalyst was analyzed by correlation characterization.The results showedthat Mg O deposition had an inhibitory effect on the denitrification activity of the catalyst.The results showed that Mg O deposition had an inhibitory effect on the denitrification activity of the catalyst.Dry mixing-Mg O has little effect on the valence and content of the surface active component of the catalyst.However,Mg O caused the adsorption of NH3 on the surface of the catalyst was weakened.The reduction activity was reduced.Wet mixing also increased the inactivation of Mg O poisoning.In Situ DRIFTS studies had shown that the mechanism of Mg O poisoning was the same as that of CaO.Finally,the performance of the catalyst after CaO and Mg O poisoning was compared.The results showed that the effect of CaO was stronger than that of Mg O,and the degree of alkaline earth metal poisoning was related to the alkalinity of alkaline earth metals.