DFT Study Of Oxidative Coupling Of Methane On O Atom Regulated RuO₂（110） And Methane Dissociation Reaction On Au₃Ni（111） Alloy Catalyst

Methane（CH₄）is the main component of biogas,natural gas,coal-bed methane,shale gas and natural gas hydrate.CH₄ can be directly converted into value-added products through a variety of methods,which is a kind of cheap and readily available carbon source.However,the activation of CH₄ in industry requires high temperature conditions,under which it is easy to cause excessive oxidation to generate CO or CO₂.Therefore,it is of great significance to develop catalysts that can activate methane at low temperature and have high activation performance and selectivity to C₂ products.In this paper,RuO₂（110）,O-RuO₂（110）and Au₃Y（111）（Y=Ni,Ag,Cu）model catalysts are constructed.Through density functional theory method studied the dissociation of CH₄ on RuO₂（110）and O-RuO₂（110）catalyst surfaces and the coupling reaction of intermediates on RuO₂（110）catalyst surface.Meanwhile,the key steps of CH₄ activation on the surface of Au₃Ni（111）alloy catalyst and the stable structure of CH₃ and H atoms on the catalyst surface are theoretically studied.Theoretical calculation results show that RuO₂（110）catalyst has a high ability to activate CH₄,and the special arrangement of its surface atoms plays a key role in the adsorption and activation process of CH₄ molecules.CH₄ dissociates on pure RuO₂（110）catalyst to generate various C species（CH_x,x=0-3）,and when C species are adsorbed on the surface of the catalyst,there is a certain difference in the stability of the structure.Among them,the CH₂ intermediate is easily coupled to generate ethylene（C₂H₄）.However,under practical conditions,the catalytic reaction is difficult to carry out under ultra-high vacuum conditions.Therefore,the O₂ in the environment is likely to have an effect on the active center structure of the catalyst.Under non-vacuum conditions,Ru atoms on RuO₂（110）catalysts have a strong ability to activate O₂,and O₂ easily generated to top O atoms(O_ot).The results of electronic structure analysis show that the RuO₂（110）and O-RuO₂（110）have obvious differences,which are made by the existence of O_ot atoms.Although the CH₄adsorption energies on different catalyst surfaces are not significantly affected,the coupling reactions between C species are greatly affected.Coupling between C species on the surface of O-RuO₂（110）catalyst is difficult,and it is easier to form carbon deposits.That means O₂ has great selectivity for RuO₂（110）catalyzed methane oxidation coupling reaction Impact.The Au₃Y（111）（Y=Ni,Ag,Cu）alloy catalysts that can exist stably are not easily affected by O₂.Therefore,a theoretical study on the surface CH₄ activation of Au₃Y alloy catalyst is carried out in this paper.The calculation results show that CH₄dissociates on the Ni atoms on the surface of Au₃Ni（111）alloy catalyst at low temperature.The generated CH₃ can easily migrate from Ni atoms to adjacent Au atoms on the surface of Au₃Ni（111）.Therefore,the active centers on Au₃Ni（111）are not easily occupied,and the catalyst is not easily deactivated.Changes in the structure of the active center of the catalyst will directly affect the activation degree of CH₄dissociation and the selectivity of the C species intermediate coupling reaction.It provides a new idea for the selection of relatively simple and stable CH₄ coupling reaction catalysts.