A DFT Study Of Surface Properties And Methane Adsorption Mechanism Of Perovskite-type LaCoO₃

Due to the low concentration of methane in the Ventilation Air Methane,it cannot be used directly,so it is directly discharged into the air by most coal mines.As a kind of greenhouse gas,methane has a greenhouse effect and damage to the ozone layer much higher than that of carbon dioxide.The methane in the wind is directly discharged into the air,which will not only waste resources,but also bring irreversible damage to the environment.At present,the most economical and effective way to solve this problem is to carry out catalytic combustion.Catalytic combustion has the advantages of low starting temperature,low concentration operation,and no pollution of products.Therefore,the study of catalytic combustion has double significance for the development of resources and the environment.Catalysts used for the catalytic combustion of methane can be divided into noble metal catalysts and non-noble metal catalysts according to their active components.Generally speaking,non-noble metal catalysts have broad development space because of their low price,easy availability of raw materials and strong thermal stability.A large number of studies have shown that in non-noble metal catalysts,perovskite oxide catalyst has a good catalytic performance,its superior catalytic performance mainly comes from its unique structure.If we can understand the relationship between the structure and properties of perovskite oxides from a microscopic perspective,it will have great guiding significance for the design and development of methane catalysts,and provide new solutions for the treatment and utilization of methane in the ventilation air methane.（1）The bulk phase structure of perovskite oxide catalyst（LaCoO₃）was established in this paper,and its structure was optimized by selecting appropriate parameters.Its band structure and state density of each element were analyzed.The results show that the 3d orbital electrons of Coaffect the catalytic activity of the catalyst.The formation of O defect can improve the electronic activity of Coelement and the catalytic activity of catalyst.The stability of LaCoO₃ catalyst mainly comes from CoO₆ octahedron.The interaction between Laand O is smaller than that between Coand O,so Lais easy to be doped.（2）There have been many experimental studies on the catalytic application of perovskite in methane combustion,but relatively few theoretical studies,and its catalytic mechanism is not completely clear at present.As the catalytic reaction is mainly carried out on the surface of the catalyst,the（001）surface is the most stable section of LaCoO₃.Therefore,we select the section of LaCoO₃ along the direction of（001）to form two end surfaces,LaO-terminated and CoO₂-terminated surface respectively.These two kinds of terminated surfaces model are established and the structures are optimized.The results show that the stability of CoO₂-terminated surface is higher than LaO-terminated surface,and relaxation phenomenon occurs on the two optimized surfaces.By observing the relaxation results,it can be found that the relaxation of Coatom is smaller than that of Laatom on both LaO-terminated surface and CoO₂-terminated surface,the stability of CoO₆ octahedron is proved again.（3）Adsorption is an important step in catalytic combustion.In this paper,the adsorption behavior of CH₄ and O₂ molecules on LaCoO₃（001）surface is studied by using density functional theory and VASP package.There are three possible adsorption configurations of CH₄ molecule,which are the top position of Coatom on the surface,the bridge position of Laatom and the bridge position of O atom;There are two kinds of O₂ molecules:the top position of Coatom and the bridge position of Laatom.By comparing the adsorption energy of different adsorption configurations,find out the most stable adsorption configuration,analyze its charge,explore the relationship between adsorption energy and charge transfer,and explore the reason why LaCoO₃（001）has strong adsorption on methane by analyzing the density of states of the most stable adsorption configuration of methane.The results show that the best adsorption site of methane on LaCoO₃（001）surface is the top position of CO,and oxygen also tends to be adsorbed at this position;When the adsorbed molecules are on the same surface,the greater the adsorption energy,the more Bader charge transfer.According to the density of states analysis of CH₄ molecule adsorbed on LaCoO₃（001）surface,the d-orbital electrons of CO determine the adsorption capacity of LaCoO₃（001）to CH₄.The more active the electrons are,the stronger the catalytic activity of the catalyst is.