| Mercury and SO3 are important pollutants in coal-fired flue gas of power plant,excessive emissions of them will seriously threaten environmental and ecological safety.CeO2 is non-toxic,low in price and large in lattice oxygen storage.It can not only remove mercury,but also has superior desulfurization performance.The study of the co-removal mechanism of Hg0 and SO3 by CeO2 catalyst is important can provide a theoretical basis for improving the performance of cerium-based catalysts for desulfurization and mercury removal.In the study,the density functional theory(DFT)was used for theoretical research.Firstly,we build the CeO2(110)surface model to study the co-removal mechanism of Hg0 and SO3 by CeO2 catalyst and the oxidation mechanism of Hg0 under HCl and O2 atmosphere.Next,the Cu/Mn doping CeO2(110)surface model was built to study the effect of Cu and Mn doping on Hg0 adsorption.Moreover,the Cu/CeO2 and Mn/CeO2 catalysts were prepared by the impregnation method and the adsorption efficiency of Hg0 were tested to verify the correctness of the theoretical results.The main conclusions are as follows:DFT calculations shown that Hg0 is physically adsorbed on the surface of CeO2(110),and chemically adsorbed on the surfaces of Cu-CeO2(110)and Mn-CeO2(110).Cu/Mn doping can promote the adsorption of Hg0,and the doping of Cu/Mn in the first layer can promote the adsorption of Hg0 better than that in the second layer.The experimental results shown that the adsorption efficiency of CeO2,Cu/CeO2 and Mn/CeO2 catalyst for Hg0 are 3%,42%and 32%,respectively,Cu/Mn doping can promote the adsorption of Hg0 by CeO2.It is consistent with the DFT calculation result.When SO3 is adsorbed on CeO2(110),Cu-CeO2(110)and Mn-CeO2(110)surfaces,it will interact with surface lattice O to generate SO42-.The adsorption energy of SO3 on this three surfaces is greater than that of Hg0.SO3 could occupy the active sites prior and competes with Hg0 when SO3 and Hg0 coadsorbed on the three surfaces.SO3 preadsorbed on the CeO2(110)surface will decrease the electronegativity of surface O atoms,directly causing a negative effect on Hg0 adsorption.Therefore,the presence of SO3 will inhibit the adsorption of Hg0 on the surfaces.The generation of HgO on CeO2(110)by Hg and O atoms is an exothermic process.However,due to the high energy barrier of 149.53 kJ/mol,it is difficult to oxidize Hg0 to HgO in a pure O2 atmosphere.Two HCl molecules directly oxidize Hg0 to HgCl2,and the energy barrier of 30.05 kJ/mol in this process is low,which is much lower than the heat released by the dissociation of two HCl molecules on CeO2(110).Thus,HCl can effectively oxidize Hg0 to HgCl2. |
