Preparation And Experimental Study Of SCR Catalyst For Wide Temperature Denitrification And Catalytic Oxidation Of Elemental Mercury

While ensuring social development,coal-fired power plants also aggravate the problem of environmental pollution caused by coal-fired flue gas.Among them,nitrogen oxides（NO_x）and mercury（Hg）have been widely concerned by countries around the world.With the development of coal-fired power plants,the emission standards for flue gas from coal-fired power plants have become more stringent.Selective catalytic reduction（SCR）is one of the most effective flue gas denitrification technologies at present,and it can synergistically catalyze and oxidize the elemental mercury while denitrifying.At present,commercial SCR catalyst only has excellent denitration activity at high temperature（350～450℃）,under the conditions of reduced load operation or startup and shutdown of the unit,the flue gas temperature is low,and the catalyst denitration activity is poor,which makes it difficult to meet the ultra-low emission requirements of coal-fired power plants,the mercury removal efficiency of commercial SCR catalysts is seriously affected by flue gas components and other conditions,especially on the content of HCl in flue gas.Therefore,it is of great significance to develop catalysts that can achieve high-efficiency denitrification and synergistic catalytic oxidation of elemental mercury under the actual flue gas conditions of coal-fired power plants.In this study,a series of manganese-doped V-W/Ti catalysts（Mn-V-W/Ti）were prepared,and denitrification efficiency and mercury removal efficiency of Mn-V-W/Ti catalysts under different preparation conditions were tested in the temperature range of200-450°C.The effect of flue gas components such as NH₃,O₂,H₂O,SO₂ and HCl on the performance of the catalyst was investigated respectively.It was found that the drying temperature had a great influence on the performance of the catalyst prepared by the sol-gel method,and drying at low temperature was more conducive to improving the catalytic oxidation activity of the catalyst.Under the flue gas condition of the front（rear）SCR catalyst,the catalyst achieved denitration efficiency of 81.39%（87.49%）and catalytic oxidation efficiency of elemental mercury of 63.39%（78.08%）at 250°C,respectively.The denitration efficiency increased with the increase of temperature.However,the efficiency of catalytic oxidation of elemental mercury decreased slightly at about 400°C.The catalysts were characterized by X-ray diffraction（XRD）,X-ray photoelectron spectroscopy（XPS）,specific surface area（BET）,scanning electron microscopy（SEM）and H₂-temperature programmed reduction（H₂-TPR）.The results showed that the specific surface area,pore volume and pore size of the Mn-V-W/Ti catalyst with manganese were slightly decreased.With the increase of the drying temperature,the specific surface area,pore volume and pore size of the catalyst first decreased and then increased,the Ti O₂ on the catalyst surface was transformed from anatase crystal to rutile crystal,and the proportion of chemically adsorbed oxygen on the catalyst surface significantly reduced,the proportion of high-valent manganese decreased,and the low-temperature reduction peak of the catalyst gradually disappeared,which resulted in a decrease of the catalytic oxidation activity of the catalyst.The catalyst dried at 20℃formed spherical structures with a diameter of 1000-2000nm and a smooth surface,while the catalyst dried at 80℃showed obvious agglomeration on the surface.The element content on the catalyst surface was basically unchanged before and after the introduction of water vapor.After the introduction of SO₂,metal sulfate and ammonium sulfate were formed on the catalyst surface,which partially covered the active sites on the catalyst surface.