The Experimental Study On Simultaneous Hg⁰ Oxidation And NO Reduction Using The Modified Ce/TiO₂ Catalysts

China is one of the major states of coal production and consumption,and coal plays an important role in China's energy structure.The heavy metal mercury released by coal combustion has volatility and bio-accumulation,and nitrogen oxides of the fuel gas can react with hydrocarbons creating photochemical smog,which seriously harm to the ecological environment and human health.China has introduced relevant laws and regulations for this to strictly limit the emission of mercury and NO in coal-fired power plants.Therefore it is urgent to study the efficient and economical simultaneous technology of de-mercury and denitrification.In this paper,the two main kinds of technologies of flue gas pollution control were first introduced,which was the traditional process and the integration process,respectively.The traditional technology is the flue gas pollutants are removed separately,and many coal-fired power plants adopt the series form of“the selective catalytic reduction of NO?SCR?+activated carbon injection?ACI?+wet flue gas desulfurization?WFGD?”to purify the flue gas,which is the most widely used flue gas removal method due to its mature.However,the system of traditional process was complex,investment cost is high,the matching degree between each other is poor,and it is uneasy to manage.The integration technology of flue gas control is simultaneously removing two or more pollutants in the same pollutant control equipment,which can effectively avoid the disadvantages of traditional technology,cut the cost of investment and simplify the system,thus it causes extensive domestic and foreign research.In recent years,a large number of low-temperature SCR catalysts have been studied for the Hg⁰ catalytic oxidation.However,the efficiency of traditional SCR catalyst is not high due to the composition of flue gas and other factors.Therefore,it is of practical significance to study the efficient SCR catalysts for simultaneous Hg⁰ oxidation and NO reduction,which will be a good solution for mercury and NO pollution control in coal-fired power plants.This paper used four transition metals of Mo,Nb and Sb and Sm to modify Ce/TiO₂catalyst,and took TiO₂ and Ce/TiO₂ catalysts as control groups to explore the modified Ce/TiO₂ catalytic performance of Hg⁰ oxidation and NO reduction.The activity changes of the modified catalysts with temperature were investigated,and the effects of NO,O₂,NH₃ and SO₂ on the Hg⁰ catalytic oxidation were also studied,respectively.In addition,the low temperature N₂ adsorption-desorption?BET?,X-ray diffraction?XRD?,H₂temperature-programmed reduction?H2-TPR?,and X-ray photoelectron spectroscopy?XPS?were used to characterize the catalysts.The results showed that the doping of the four transition metals could improve the activity of Ce/TiO₂ catalyst.Compared with the other modified catalysts,Ce-Mo/TiO₂ catalyst showed better catalytic activity of NO reduction and Hg⁰ oxidation.And in the range of the test temperature,the biggest Hg⁰oxidation and NO reduction efficiency could reach 97%.NH₃ and SO₂ had different inhibition on the activity of catalysts,and with the increase of NH₃ concentration,the NH₃ inhibition on the catalytic activity was enhanced.Compared with the other three modified catalysts,NH₃ had a relative weak inhibition on the activity of the Ce-Sb/TiO₂catalyst.When 5%O₂ was added,the introduced O₂ supplemented the consumed surface active oxygen by NH₃,and improved the mercury oxidation activity.And Ce-Mo/TiO₂catalyst exhibited better resistance to sulfur poisoning.For Ce-Sb/TiO₂ catalyst,at low NO concentration the competition between NO molecules and mercury for the surface active sites possessed the dominance.When NO concentration was high,abundant NO₂could promote the Hg⁰ oxidation.According to the BET and XRD results,for the transition metals of Mo?Nb and Sb modified Ce/TiO₂ catalysts,specific surface area was not the main factor affecting the activity of catalyst.The doping of transition metal changed the surface structure of the catalyst,and decreased the crystallinity,which was beneficial to increase the number of surface defects and oxygen vacancies.XPS result showed that the adding of transition metals could improve the proportion of Ce³⁺and chemisorbed oxygen,and the flexibility of oxygen is enhanced,which is beneficial to improve the Hg⁰ oxidation and NO reduction.