Research On Oxidation Behavior And Resistance To Sulfur Characteristics Over CuCl₂ Modified Deactivated SCR Catalyst For Simultaneous Removal Of NO And Hg⁰

In recent years,more and more attentions have been focused on the problem of air pollution.Thus,the emission standards of Hg in coal-fired flue gas have been continuously improved.SCR is the largest flue gas denitration technology applied in coal-fired power plants currently.As the most important part of SCR,the activity of catalyst will gradually decrease due to the complex operating conditions.The catalyst needs to be replaced every 3 to 5 years,which results in a large number of waste SCR catalysts.The waste SCR catalysts will cause environmental problems and waste of resources.The researches shows that the regeneration can not only effectively restore the activity of waste SCR catalyst but also recycle resource and reduce expenses of the equipment.What’s more,that mercury emissions from coal-fired power plants may cause threats to human health has also attracted more and more attention.Many countries have promulgated national standards for Hg emission control.Using SCR technology for the simultaneous removal of Hg⁰ and NO is considered as an economic feasible research direction.However,oxidation of Hg⁰ on catalyst is greatly affected by the HCl content in the simulated flue gas while the chlorine content of coal in China is generally low.Therefore,developing news catalysts that can efficiently oxidate Hg⁰ in a low-chlorine or chlorine-free environment will become the future direction of SCR technology.By modifying the deactivated SCR catalyst with transition metals,removal of NO and Hg⁰ in simulated flue gas can be realized by SCR equipment.Reusing deactivated catalysts,prolonging the service life of catalysts and reducing the expenses can be realized through regeneration and modification of deactivated SCR catalyst.At the same time,there is no need to build a new device for control mercury pollution,which saves space and construction costs.Therefore,the unity of environmental and economic benefits can be reached.In this study,CuCl₂/RSC was prepared after the deactivated SCR catalyst was treated with regeneration and modification for simultaneous removal of Hg⁰ and NO.At firstly,the influences of regeneration on the performance of deactivated catalysts was studied.The factors lead to deactivation of and regeneration effects of deactivated SCR catalyst were analyzed by means of XPS,BET and XRD.Secondly,the influences of different flue gas constituents such as O₂,NO and NH₃ on mercury removal efficiency over CuCl₂/RSC are also studied.Several kinds of characterization methods are used to analyze the mechanism of mercury removal reaction over CuCl₂/RSC.Lastly,in order to solve the problem that SO₂ will greatly degrade performance of catalyst,resistance to sulfur characteristics of 7%CuCl₂/RSC was studied after it was exposed to SO₂.The reasons for the improvement of sulfur resistance of 7%CuCl₂/RSC are studied by several characterization methods.The experimental results show that alkali poisoning and SO₂ poisoning are the main factors that leading to the deactivation of commercial catalysts.After washing by diluted H₂SO₄,the content of alkali and sulfur on the catalyst surface decrease significantly.The denitrification performance of regenerated catalyst can reach up to83.1%while the mercury removal performance of regenerated catalyst is also slightly improved,indicating that washing by diluted H₂SO₄ has good effects on regeneration of deactivated catalyst.What’s more,the deactivated catalyst has good renewable performance.After regeneration and modification,simultaneous removal of Hg⁰ and NO from simulated flue gas over catalyst is significantly improved.V and Cu have a synergy effect in oxidation of Hg⁰.The results show that when the CuCl₂ loading is7%and the temperature is 300 degrees Celsius,the performance of CuCl₂/RSC for simultaneous removal of NO and Hg⁰ is best.At this point,7%CuCl₂/RSC exhibited simultaneous catalytic oxidation of Hg⁰（around 80.4%）and NO（around 78.3%）.In addition,when the temperature is 250 to 350 degrees Celsius,both denitration efficiencies and mercury removal efficiency can keep above 70%.Both O₂ and NO are beneficial for mercury removal while O₂ plays a greater influence in mercury removal over 7%CuCl₂/RSC.NH₃ will compete with Hg⁰ for active sites,which leds to the decrease of mercury removal efficiency.The characterization showed that CuCl₂ on the surface of 7%CuCl₂/RSC is highly dispersive.After the mercury removal,some of high valence state Cu and V were reduced.The mercury removal over 7%CuCl₂/RSC under the chloride-free condition occurs via a Mars-Maessen mechanism.After exposed to SO₂,denitrification efficiencies of 7%CuCl₂/RSC increased slightly while the mercury removal efficiency of 7%CuCl₂/RSC decreased slightly.We can also find that sulfur resistance of catalyst is excellent.From the results of XRD,BET,TG,XPS,NH₃-TPD,we can know that part of the CuCl₂ in the catalyst was transformed into Cu SO₄ after 7%CuCl₂/RSC was exposed to SO₂ while both of CuCl₂ and Cu SO₄ were highly dispersive on the surface of 7%CuCl₂/RSC.And the catalyst showed stronger acidity after exposed to SO₂,which is benefit for simultaneous removal of NO and Hg⁰.In addition,that CuCl₂ is more easily to react with SO₂ improves the sulfur resistance of the catalyst.