The Morphology Control Of Co-Ce-based Catalysts For Element Mercury Removal

Mercury is a highly toxic atmospheric pollutant that can cause long-term harm to the environment.Coal combustion is the largest source of mercury emissions,so the most important thing to reduce mercury emissions is to reduce the mercury content in coal-fired flue gas.The catalytic oxidation method,which can convert elemental mercury into water-soluble oxidation state Hg²⁺,is a very potential technique for the Hg⁰ removal from flue gas.The transition metal oxides are wide-used catalysts for Hg⁰ oxidation due to their good redox properties.However,the catalysts prepared by traditional method have relatively poorer structure and fewer active sites,which affect the mass transfer and adsorption of reaction gas and limit the Hg⁰ oxidation efficiency of catalysts.In this paper,we try to solve the problems of existing Hg⁰ removal catalysts by regulating the morphology of them.Firstly,the properties of catalyst were improved by controlling its pore structure.Its Hg⁰ removal activity and the effects of flue gas components were studied.On this basis,we investigated the interaction between Ce and Co.The way and mechanism of the interaction are explored.Secondly,the number of surface active sites of catalyst was increased by modulating its exposed crystal surface.The properties and Hg⁰ removal performance was analyzed by activity test and characterization.The Ce-Co catalysts were prepared by template method and co-precipitation method?respectively denoted as Ce-Co-T and Ce-Co-C?.Characterization results show that compared with Ce-Co-C,the Ce-Co-T has larger specific surface area,more uniform pore size and particle size,more favorable metal component dispersion,more surface active oxygen and better redox capacity,so it has a better Hg⁰ oxidation activity.Moreover,its activity and structure is stable after 3000 min of test with the space velocity of 180,000 h^-1.The components of flue gas,including NO,O₂,HCl,H₂O and SO₂,will affect the activity of catalyst.O₂ can supplement the oxygen consumption of catalysts,which is one of the key factors for the catalytic Hg⁰ removal.NO and HCl can form the active sites on the catalysts to improve the Hg⁰ oxidation efficiency.SO₂ and H₂O have the competitive adsorption with Hg⁰and will form sulfate,which inhibit the efficiency of catalysts.The effects of different Ce/Co ratio on the catalysts were studied.We found that the interaction between Ce and Co leads to lattice distortion,which decreases the structure order and specific surface area of catalyst,but the lattice distortion can increase the number of surface active O.Due to the high Ce content in the Ce₃-Co₁ and Ce₆-Co₁ catalysts,the CeO₂sintering reduced the order and specific surface area of catalysts.The number of active O was also decreased.Therefore,the Ce₁-Co₃ catalyst with moderate lattice distortion and high CeO₂dispersion has the best properties and activity.The Hg⁰ oxidation efficiency of Co₃O₄ nanorods is much larger than Co₃O₄nanoparticles',which is over 90%in 100-300oC and the highest efficiency is 98%.The difference of crystallinity,structure and total redox ability of the two catalysts are not significant.The main reason for its active difference is that the Co₃O₄ nanorods exposed more?220?crystal surface,so it has more surface chemical adsorption O.