First-principles Study On The Adsorption Characteristics Of Metal Doped Graphene For NH₃

Nitrogen oxides produced by coal-fired plants are the main cause of air pollution.China’s 13th Five-Year Plan uses nitrogen oxides as a binding indicator,while NO is the main component of nitrogen oxides,which accounts for more than 90%.In order to save the energy consumption caused by heating flue gas in the current NH₃-SCR technology and save operating costs,many researchers have devoted themselves to the development of new low-temperature NH₃-SCR catalysts.In this paper,using the first-principles,quantum chemical calculation method and density functional theory（DFT）,the six kinds of metal atoms of titanium,chromium,iron,cobalt,nickel and copper are doped in ten kinds of graphene substrates.The adsorption characteristics of NH₃ adsorption on the sixty kinds of structures reveal the influence of different graphene substrates and metal atom types on the adsorption characteristics.The model is composed of six kinds of metal doped in single vacancy（SV） and double vacancy（DV）,a single vacancy with one nitrogen atom decorated（SVN）,a single vacancy with two nitrogen atoms decorated（SVN2）,a single vacancy with three nitrogen atoms decorated（SVN3）,double vacancy with one nitrogen atom decorated（DVN）,double vacancy with two nitrogen atoms decorated（two different forms,referred to as DVN2-13 and DVN2-14,respectively）,double vacancy with three nitrogen atoms decorated（DVN3） and double vacancy with four nitrogen atoms decorated（DVN4）.Sixty structures were analyzed based on the calculated adsorption energy,adsorption structure parameters,Bader charge,charge density difference map and density of states.The results show that:（1）Titanium,chromium,iron,cobalt,nickel and copper,six metal-doped graphene substrates,mainly 3d orbital of metal atoms interact with graphene substrates,metal atoms as electron donors,graphene substrates as the the electron acceptor.Higher the binding energy of and the metal atom doped in the graphene substrate,the more stable the doping is,and the binding energy of the titanium atom doping is the largest.（2）Metal-doped graphene enhances the adsorption capacity of graphene for NH₃,and the N-H bond in the adsorbed NH₃ is activated.The metal atom type and the substrate structure have a significant influence on the adsorption energy.In the sixty structures,the adsorption of NH₃ on the double-vacancy system in the nickel and copper-doped graphene structure is physical adsorption.Ten kinds titanium,chromium and iron atoms of doped graphene substrates exhibited good adsorption capacity for NH₃.（3）In the process of metal-doped graphene system adsorbing NH₃ molecules,both metal atoms and NH₃ molecule act as electron donors,graphene substrates act as electron acceptor.The analysis results of the charge density difference map are consistent with the Bader charge analysis results.Density of states analysis shows that the interaction between the metal atom and the NH₃ molecule does not come from the hybridization between the atoms,mainly the transfer of electrons.The results of this study reveal the influence of metal atom types and substrate differences on the properties of adsorbed NH₃ molecules,and screening the more proper metal doped graphene for the NH₃ adsorption which provides a theoretical basis for better design of low temperature metal doped graphene NH₃-SCR catalysts.