Preparation Of Co₃O₄ Constructed In Situ By Plant Vessels For Element Mercury Removal

Mercury,which causes great harm to the ecosystem,is a kind of pollutant that circulates,accumulates and transports around the world due to its strong stability and bioaccumulation.Coal fired flue gas from thermal power plants is the main anthropogenic mercury emission source,especially Hg⁰,which is easy to volatilize and has low water solubility.The catalytic oxidation method is a very feasible method to remove mercury from coal-fired flue gas because it can oxidize Hg⁰ to Hg²⁺and then remove it with existing mercury removal equipment.Transition metal oxides are often used as catalysts for mercury oxide since their excellent oxidation ability and regeneration performance.Co₃O₄ based catalysts have strong redox and electron transfer capabilities due to its unique redox electron pairs.The irregular pores of traditional catalysts result in large mass transfer resistance and poor dispersion of active components in mercury removal reaction,which limits the improvement of catalyst performance.Given this,the wood with natural three-dimensional interconnected pores as the substrate was selected the substrate to prepare catalysts with regular pores,and the Hg⁰performance was studied for different catalystsFour kinds of fast-growing wood（Cedarwood,Poplar,Locust and Mulberry）with different duct channels were selected to determine the optimal substrate.SEM results showed that Locust and Mulberry were composed of macropores and dense pores,while Cedarwood and Poplar were square pores.The pore size of Cedarwood was more regular and orderly,which was conducive to reducing the mass transfer resistance.By controlling the relevant variables,different catalysts with the same loading were prepared by impregnation method.BET results showed that the catalyst（Co₃O₄-C）supported by Cedarwood had the highest specific surface area and porosity.XRD results showed that the active components of Co₃O₄-C were well dispersed.In the performance test,when the volume and mass space velocity are consistent,Co₃O₄-C can achieve 90%Hg⁰ removal efficiency at 200 ℃.Co₃O₄-C had a certain stability and Hg⁰ oxidation efficiency almost remained at 90%for 20 h.Based on the screening of the optimal vector,Co₃O₄ nanoparticles were synthesized in situ in the pores of Cedarwood by hydrothermal method.The effects of synthetic conditions of hydrothermal temperature and NH₄F concentration on catalyst morphology and catalytic performance were investigated.The results show that the increase of hydrothermal reaction temperature makes Co₃O₄ nanoparticles form a whole shell,and the increase of NH₄F concentration makes Co₃O₄ nanoparticles grow radially.When the hydrothermal reaction temperature is 90 ℃ and the addition amount of NH₄F is 0.05 M,the catalyst(T₉₀C_0.05)has the most uniform particle morphology,larger specific surface area and porosity,and the highest proportion of chemically adsorbed oxygen.Thanks to this,T₉₀C_0.05 can achieve 98%Hg⁰removal efficiency at the test temperature of 200 ℃.In order to solve the problem of poor thermal stability of carbon catalyst,Co₃O₄ catalyst with ordered channels and high thermal stability was prepared by using Cedarwood channels as sacrificial templates.The effects of pore morphology and structure on the activity of the catalyst were studied.The structure and morphology of Co₃O₄ channels are different due to different concentrations of precursor solution.When the mass fraction of precursor solution is 20%,the catalyst（20%-Co）has the most fluffy structure with appropriate thickness and the largest specific surface area.It can achieve more than 90%Hg⁰ removal performance at the test temperature of 200-350 ℃.and can be maintained for more than 70 h,with thermal stability.The catalyst has excellent thermal stability and Hg⁰ removal efficiency was maintained at 95% for 70 h.