Study On The Mechanism Of Mercury Removal Based On CeO₂

There are three forms of mercury in flue gas : elemental mercury?Hg0?,oxidized mercury?Hg2+?and particulate mercury?Hgp?.Among them,elemental mercury is extremely difficult to be removed.At present,the removal of elemental mercury mainly includes two kinds of methods,adsorption method and oxidation method.However,the detailed reaction mechanism remains undetermined.Therefore,exploring the mechanism of elemental mercury removal effectively is the key to solve the problem of mercury pollution.In this study,the method of density functional theory is used to study the mechanism of mercury removal from CeO₂?110?surface.Firstly,the adsorption mechanism of mercury and HCl on CeO₂?110?surface was explored.The results show that the elemental mercury is the physical adsorption on CeO₂?110?surface,the most stable adsorption site is the hollow site in the subsurface layer.HCl in CeO₂?110?surface is chemical adsorption,the whole molecule is in a state of dissociation.Hg oxidation prefers the pathway of HgCl₂ directly formed through the reaction with the adsorbed Cl.The entire reaction occurs via the E–R mechanism.Secondly,it was discussed how SO₂ and H₂O affect the adsorption of mercury on CeO₂?110?surface.The results show that the adsorption of SO₂ and H₂O on CeO₂?110?surface is chemical adsorption.Among them,SO₂ combine with surface lattice oxygen,and forms SO32-.H₂O exists in the dissociated form on the CeO₂?110?surface.The adsorption of SO₂ and H₂O on the catalyst surface has a detrimental effort for the adsorption of mercury on CeO₂?110?surface.By calculating the Gibbs free energy,it can be found that the inhibitory effect of SO₂ on the catalyst surface is more serious than that of H₂O.Neglecting the zero point vibration energy,the adsorption equilibrium temperatures of SO₂ and H₂O on the catalyst surface are 750 K and 500 K,respectively.Finally,the effect of doping on the adsorption of CeO₂?110?surface was explored.The results show that the four elements of Ti,Zr,Hf and Si all can enhance the adsorption energy of elemental mercury?Hg0?on CeO₂?110?surface,and the doping effect of Ti and Si are better.In addition,the effect of other components in the flue gas on the Ti doped CeO₂?110?surface is explored.A new mechanism for the oxidation of Hg through O₂ on Ti doped CeO₂?110?surface was proposed.