洁净煤技术

2020, v.26;No.130(06) 203-209

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α-Fe_2O_3表面SO_2吸附及SO_3催化生成的密度泛函分析
DFT study on the adsorption of SO_2 and catalytic formation of SO_3 on the α-Fe_2O_3 surface

王永兵;戴高峰;单志亮;王学斌;尤红军;谭厚章;
WANG Yongbing;DAI Gaofeng;SHAN Zhiliang;WANG Xuebin;YOU Hongjun;TAN Houzhang;Xinjiang Uygur Autonomous Region Special Equipment Inspection and Research Institute;School of Energy and Power Engineering,Xi'an Jiaotong University;

摘要(Abstract):

燃煤电厂排放了大量SO_2和少量SO_3,SO_3的产生不仅危害环境,且不利于电厂的安全运行,飞灰和锅炉壁面中的Fe_2O_3对SO_3生成有显著催化作用,而目前对Fe_2O_3催化生成SO_3的路径研究和机理揭示还不够深入。建立了α-Fe_2O_3(001)表面,利用密度泛函分析方法,对SO_2和O_2在α-Fe_2O_3(001)表面的吸附方式进行研究,得到SO_2的稳定吸附构型和O_2在Fe_2O_3表面的解离方式,利用过渡态搜索方法研究了α-Fe_2O_3表面催化生成SO_3的反应路径和反应能垒,并对比了气相反应生成SO_3的反应能垒。结果表明,SO_2最稳定的吸附方式是SO_2中的O原子和S原子吸附在α-Fe_2O_3晶体上的Fe原子上方,S原子不易在α-Fe_2O_3表面的晶格氧上方吸附;O_2在α-Fe_2O_3表面的吸附能大于SO_2的最大吸附能,表明O_2更易在α-Fe_2O_3表面吸附;O_2极易在表面有氧空位的Fe_2O_3晶体上发生解离并生成O原子,说明有氧空位存在的α-Fe_2O_3更易促进O_2的解离和表面吸附氧的产生。SO_3生成的L-H机理为气相中的SO_2和O原子先在α-Fe_2O_3表面吸附,再结合生成SO_3,该过程的反应能垒为231.65 k J/mol;E-R机理为气相中的SO_2与α-Fe_2O_3的表面吸附氧发生反应生成SO_3,其反应能垒为24.82 k J/mol,小于L-H机理的反应能垒,也远小于气相反应中SO_3生成的反应能垒。证实Fe_2O_3对SO_3的生成具有显著的催化作用,且E-R机理为主导的反应机理,氧空位的存在促进了O_2在α-Fe_2O_3表面的解离,且表面吸附氧在催化过程中起关键作用。
A large amount of SO_2 and a small amount of SO_3 are emitted from coal-fired power plants.The generation of SO_3 is not only harmful to the environment,but also dangerous to the safe operation of the power plant.Current studies show that Fe_2O_3 contained in the fly ash and the boiler wall have a significant catalytic effect on the SO_3formation.However,the research on the path and mechanism of SO_3catalytic formation by Fe_2O_3 is not deep enough.In this paper,theα-Fe_2O_3(001) surface was established firstly,and the adsorption configuration of SO_2and O_2onα-Fe_2O_3(001) surface was studied by density functional theory(DFT).The stable adsorption configuration of SO_2 and the dissociation pathway of O_2on Fe_2O_3(001) surface were obtained.The reaction path and energy barrier of catalytic formation of SO_3 onα-Fe_2O_3 surface were studied by using transition state search method.Then the energy barrier of catalytic formation of SO_3 in gas phase reaction were compared.The results show that the most stable adsorption configuration of SO_2 is that O and S atom in SO_2 are adsorbed above Fe atoms onα-Fe_2O_3,while S atom is not easy to be adsorbed above lattice oxygen ofα-Fe_2O_3 crystal.The adsorption energy of O_2 onα-Fe_2O_3 surface is greater than the maximum adsorption energy of SO_2,which means that O_2 is more easily adsorbed onα-Fe_2O_3 surface.In addition,O_2 is easy to dissociate and form O atom on the defect Fe_2O_3 surface with oxygen vacancy,which indicates thatα-Fe_2O_3 with oxygen vacancy is easier to promote the dissociation of O_2 and the generation of adsorbed oxygen on the surface.The L-H mechanism of SO_3 formation is that SO_2 and O atoms in the gas phase are adsorbed firstly on theα-Fe_2O_3 surface,and then combine to form SO_3,and the reaction energy barrier is 231.65 kJ/mol.The E-R mechanism is that SO_2in the gas phase reacts with adsorbed oxygen onα-Fe_2O_3surface to form SO_3while the reaction energy barrier is 24.82 k J/mol,which is less than that of L-H mechanism and far less than that of SO_3formation in gas phase reaction.The above results confirm that Fe_2O_3has a significant catalytic effect on the formation of SO_3,and the E-R mechanism is the dominant reaction mechanism.The existence of oxygen vacancy promotes the dissociation of O_2on the surface ofα-Fe_2O_3,and the surface adsorbed oxygen plays an important role in the catalytic process.

关键词(KeyWords): Fe_2O_3;SO_2吸附;SO_3;密度泛函;催化
Fe_2O_3;SO_2 adsorption;SO_3;density functional theory;catalytic reaction

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基金项目(Foundation): 新疆维吾尔族自治区自然科学基金面上资助项目(2017D01A69);; 新疆维吾尔族自治区自然科学基金青年基金资助项目(2017D01B41)

作者(Author): 王永兵;戴高峰;单志亮;王学斌;尤红军;谭厚章;
WANG Yongbing;DAI Gaofeng;SHAN Zhiliang;WANG Xuebin;YOU Hongjun;TAN Houzhang;Xinjiang Uygur Autonomous Region Special Equipment Inspection and Research Institute;School of Energy and Power Engineering,Xi'an Jiaotong University;

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DOI: 10.13226/j.issn.1006-6772.19122101

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