Study On The Mechanism Of Mercury Removal And Sulfur Resistance Of Modified MnO_x And CeO_x Based Catalysts

In recent years and for a long time in the future,Coal is the most important power source in China.About 40%of coal consumption is consumed by coal-fired power plants.Coal-fired power plants contain high levels of mercury,which will cause environmental damage and great pollution.Therefore,it is important to remove the mercury contained in the flue gas emitted from coal-fired power plants.At present,solid catalyst research plays a dominant role in mercury removal technology for coal-fired flue gas,but there are not many studies on the influence of SO₂ in flue gas in the study of solid catalysts.In the existing studies considering the influence of SO₂,the research on the mechanism of catalyst mercury removal is not deep enough and comprehensive.In addition to the high mercury content of coal used in power plants in China,the content of sulfur in coal is much higher than the world average.Therefore,it is necessary to accelerate the development of high-quality mercury removal and anti-sulfur catalysts.In this paper,the mechanism of sulfur poisoning of catalysts was studied by suppressing the oxidation of Hg⁰ by Mn-based catalysts by SO₂ and the reverse mercury removal of Hg⁰ by Ce-based catalysts.Through the comparative analysis of mercury removal and sulfur resistance of two types of catalysts,the mercury removal reaction process of two types of catalysts in the presence or absence of SO₂ in flue gas was studied,which revealed the mechanism of mercury removal and sulfur inhibition of the two types of catalysts.on the basis of this,the catalyst with excellent performance was loaded with TiO₂ support and the temperature window was broadened to obtain a catalyst preparation method with excellent mercury removal and sulfur resistance.The specific content and results are as follows:（1）The mechanism of SO₂ inhibition of Mn-based catalysts on Hg⁰ oxidation was investigated.In this paper,a pure MnO_x group and a series of binary modified metal MnO_x based catalysts（MnO_x,Fe-MnO_x,Cu-MnO_x,Cr-MnO_x and Mo-MnO_x）were prepared by coprecipitation method,and the flue gas was simulated on a fixed bed test bench.The conditions for the dehydrogenation and sulfur resistance of various catalysts were investigated.The physicochemical structures of the catalysts before and after the reaction were analyzed by various characterization methods.The adsorption characteristics of Hg⁰ and SO₂ on the surface of MnO_x catalyst and Cr-MnO_x catalyst were investigated by quantum analysis.The results show that the Cr-MnO_x catalyst has the highest Hg⁰ removal efficiency and sulfur resistance performance.（2）The mechanism of SO₂ promoting the oxidation of Hg⁰ by Ce-based catalysts was investigated.Pure CeO₂-based and Ru modified Ru-CeO₂ catalysts were prepared by pyrolysis-impregnation.The physical and chemical structures of the catalysts before and after the reaction were analyzed by various characterization methods.The adsorption characteristics of Hg⁰ and SO₂ on the surface of CeO₂ and Ru-CeO₂ were studied by quantum analysis.（3）Through comparative analysis,the mechanism of the opposite mercury removal and anti-sulfur behavior of manganese-based and ruthenium-based catalysts was clarified,and the Cr-MnO_x catalyst with excellent mercury removal and sulfur resistance was screened out.The results show that the adsorption of Hg⁰ and SO₂ by pure MnO_x catalyst is chemical adsorption,while the adsorption of Hg⁰ by modified Cr-MnO_x catalyst is not weakened,but the adsorption performance of SO₂ is obviously weakened,indicating that Cr-MnO_x after modification the sulfur resistance of the catalyst is significantly enhanced.The adsorption of Hg⁰ by pure CeO₂ catalyst is physical adsorption,the adsorption of SO₂ is chemical adsorption,and the adsorption of modified Ru-CeO₂ catalyst to Hg⁰ is chemical adsorption,but the adsorption performance of SO₂ is not weakened.The Ru-CeO₂ catalyst has enhanced mercury removal performance,but the sulfur resistance has not been enhanced.（4）In order to reduce the application cost of the catalyst,a TiO₂-supported CrO_x-MnO_x-TiO₂ ternary catalyst was prepared.The mercury removal performance and sulfur resistance of catalysts such as CrO_x-MnO_x-TiO₂（CrMnTi）,CrO_x-TiO₂（CrTi）and MnO_x-TiO₂（MnTi）were studied.The physicochemical structures of the catalysts before and after the reaction were analyzed by various characterization methods.Studies have shown that the loading of TiO₂ does not affect the mercury removal and sulfur resistance of the catalyst.（5）In order to broaden the temperature window of the catalyst,combined denitrification and mercury removal.A SnO₂-supported quaternary CrO_x-MnO_x-SnO_x-TiO₂（CrMnSnTi）composite metal oxide catalyst was prepared.Studies have shown that the addition of SnO_x can increase the dispersion of active species,and there are more active sites on the catalyst surface.In addition,the CrMnSnTi quaternary catalyst can significantly expand the temperature window for catalyst mercury removal.In this paper,the mechanism of SO₂ inhibition of MnO_x and the opposite mercury removal and sulfur resistance of CeO₂-based catalysts are revealed.A series of catalysts with high-efficiency mercury removal and sulfur resistance were prepared,which pointed out the development direction for the research and application of mercury removal catalysts.In order to reduce the application cost,the loading of the catalyst the carrier of TiO₂ was carried out.In order to jointly denitrify,the catalyst temperature window has been broadened,which will provide an important theoretical basis and scientific basis for industrial mercury pollution emission control technology,and provide certain technical support for energy saving and emission reduction.