Study Of Element Mercury Removal Efficiency Over Ce Modified Zr-MnO_x In Sulfur-Containing Flue Gas

The transition metal oxide catalyst has a great potential application in mercury removal from flue gas.However,it’s mercury removal efficiency can be easily affected by the flue gas conditions,especially SO₂.At present,the mechanism for the influence of SO₂ in mercury removal over catalysts has not been well concluded.Therefore,it is necessary to study the mechanism of SO₂ in the process of mercury removal for developinghigh efficiencytransition metal oxides catalyst for mercury removal.In this paper,Ce modified Zr-Mn was prepared by co-precipitation and impregnation method.And it’sHg⁰adsorption efficiency and Hg⁰ oxidation efficiency has been invetstigated.Furthermore,the infulence mechanism of SO₂ on Ce0.1-Zr-Mnin Hg⁰ adsorption process and Hg⁰ oxidation process were carefly studied,seperatly.The physical and chemical properties of the catalysts were characterized by XRD,BET,H₂-TPR,XPS,TGA and the influence mechanism of SO₂ on the adsorption process of Hg⁰ and the catalytic oxidation process of Hg⁰ was illustrated.The results showed that:With Ce modification,the Hg⁰ adsorption capacity and the Hg⁰ catalytic oxidation efficiency of the catalysts have been improved greatly,especially Ce0.1-Zr-Mn.It’s Hg⁰ adsorption efficiency keptat more than 90% in the initial 40 hours and gradually decreased to about 30% after nearly 95 hours and the adsorption capacity of Ce0.1-Zr-Mn was 1.22×10-1 mg;Ce0.05-Zr-Mn and Ce0.1-Zr-Mn showed excellent activity for Hg⁰ oxidation,the Hg⁰ catalytic oxidation efficiency was maintained at above 90%around100-250℃;the characterization results showed that with the Ce modificated,the BET surface area inceased,the crystallinity ofactive components on the catalyst surface reduced and the reduction temperature of the catalyst shifted to lower temperature.Therefore,after Ce modificated,the catalyst redox activity was improved.For the influence mechanism of SO₂,the experimental results and the characterization results showed that: in the Hg⁰ adsorption process,SO₂ could posion the adsorption sites of Ce0.1-Zr-Mnto form Mn-SO42-,and thus,Ce0.1-Zr-Mn lost Hg⁰ adsorption activity;in the Hg⁰ catalytic oxidation process,when all the active sites of Ce0.1-Zr-Mn transformed to Mn-SO42-,the Hg⁰ catalytic oxidation on the surface of Ce0.1-Zr-Mn obeyed the Eley-Rideal mechanism,and SO₂ first adsorbed on Ce0.1-Zr-Mn surface,then reacted with the gas phase to form SO3,and the SO3 acted as new active sites to react with Hg⁰ and O₂ to form HgSO4,thus completed the Hg⁰ catalytic oxidation.In this research,the influence mechanism of SO₂ on Hg⁰ adsorption process and Hg⁰ catalytic oxidation process over Ce0.1-Zr-Mn were studied carefully.The results provide a theoretical basis for the development of high efficiencytransition metal oxides catalysts for the removal of mercury from flue gas.