DFT Study On The Conversion Of Methane Catalyzed By A Single Metal Atom On Graphene

Methane is the main component of natural gas,it is widely used in agriculture and industry,and it is one of the most important chemical raw materials in many chemicals.However,its transportation is difficult and its safety is low.Methane is also a greenhouse gas,and the greenhouse effect of methane is 25 times greater than that of carbon dioxide.Compared with methane,methanol has higher safety,and liquid methanol is easier to store and transport.And methanol is a clean energy and an important basic chemical raw material.Therefore,the technology of oxidizing methane to methanol has attracted great attention.We use simulation calculations based on density functional theory to study the conversion of methane to methanol catalyzed by a single metal atom on graphene.In this paper,the conversion of the methane to the methanol product is realized by two steps:(1)Copper-embedded and nitrogen-doped graphene(CuN₄/Gr)undergoes oxidation reaction with ozone,and produces the oxygen-centered radical on CuN₄/Gr that is named as OCuN₄/Gr configuration.(2)Methane is actived and converted into methanol on OCuN₄/Gr.For the above two steps,the specific content is as follows:For the first step,we embed the transition metal Cu into the N-doped graphene structure to form CuN₄/Gr structure,and the stable CuN₄/Gr structure was obtained by optimizing calculation.We calculated that the dissociation energy of copper atom on the CuN₄/Gr structure was 5.490 e V,which confirmed the stability of the CuN₄/Gr structure.In order to convert CH₄ to CH₃OH,it is necessary to provide oxygen supply molecules.After investigation and calculation,O₃ molecules can be adsorbed on Cu atom of CuN₄/Gr,and O atom is further separated from O₃ to form OCuN₄/Gr.We also optimized the free methane structure.These two configurations of OCuN₄/Gr and CH₄ are prepared for the production of methanol.For the second step,CH₄ adsorbs on O atom of OCuN₄/Gr,and the C-H of CH₄ is broken.The energy barrier of the reaction is 0.569 e V.Generally,the C-H bond energy of methane is 4.500 e V.Due to the effect of the catalyst,the energy required to break the C-H bond of methane is greatly reduced.After CH₄ reacts with OCuN₄/Gr,the final structure CH₃OH-CuN₄/Gr is formed.For methanol,the C-H bond activity of this target product is higher than that of methane,and it is susceptible to further oxidation.For the CH₃OH-CuN₄/Gr structure,the weak interaction between CH₃OH and CuN₄/Gr can quickly separate CH₃OH from CH₃OH-CuN₄/Gr and prevent further oxidation of methanol.We calculated that the energy for separating methanol from CH₃OH-CuN₄/Gr is 0.240 e V,which is very small.it prevents further oxidation of methanol.Therefore,copper-embedded and nitrogen-doped graphene(CuN₄/Gr)can effectively catalyze the conversion of methane to methanol.The distribution of this paper is as follows:Chapter 1 points out the research background and current status of the conversion of methane to methanol,the characteristics of graphene materials,the design of single metal atom graphene structure,and the research ideas and processes of this paper.Chapter 2 describes density functional theory,first-principle and its entire evolution process.Chapter 3mainly describes the process of methane to methanol.In order to verify the entire process,differential charge density,bader charge analysis and density of states analysis are performed;Cl-NEB calculation is performed to show structure diagrams and corresponding energy of the reaction process.Chapter 4 summarizes the research work in this paper.The graphene catalytic material we constructed can convert methane to methanol,and reduce the reaction barrier for the conversion of methane to methanol.