石墨烯限域调控Fe原子的电子性质和CO活化机理OA

Using the density functional theory(DFT),the comprehensive and in-depth exploration was conducted into the structure,electronic properties,CO adsorption and activation performance of Fe atoms modulated by graphene confinement to reveal the influence of different coordination environment of Fe active centers on Fischer-Tropsch(FT)performance.The binding energies of Fe-doped single-atom defect graphene(FeC@graphene)and Fe-doped di-atom defect graphene are-7.49 and-6.50 eV,respectively,which indicates that FeC@graphene structure exhibits greater stability compared to the Fe2C@graphene.The density of states(DOS)of FeC@graphene exhibits the more significant left-shift compared to that of Fe2C@graphene,with values of 1.5 and 0.8 eV,respectively.The greater left-shift indicates that the FeC@graphene structure possesses lower energy,and the higher stability.The adsorption energies of CO on FeC@graphene and Fe2C@graphene are-1.43 and-1.69 eV,respectively,which reflects that CO adsorption on Fe2C@graphene is more stable than that of FeC@graphene.The d band center values of FeC@graphene and Fe2C@graphene are-1.26 and-0.83 eV,respectively,while their energy band gaps are 0.45 and 0.01 eV,respectively.The closer the d-band center is to the Fermi level,and the smaller the band gap,which is more conducive to the adsorption of species.Thus,compared with FeC@graphene,CO has a higher propensity to be adsorbed onto Fe2C@graphene.The band gap of Fe2C@graphene-CO increases by 0.25 eV,while FeC@graphene decreases by 0.04 eV;the antibonding component of FeC@graphene-CO is more than that of Fe2C@graphene-CO,and the integrated crystal orbital Hamilton population(ICOHP)values are-1.99 and-2.50 eV.These suggest that the interaction between Fe2C@graphene and CO is stronger,while strong interaction is unfavorable for CO activation.On the FeC@graphene and Fe2C@graphene,the most favorable pathway for CO activation follows the sequence:CO* →CHO* → CH*+O*,with an effective energy barrier of 2.53 and 3.50 eV,respectively.It is easier for CO activation on FeC@graphene.Therefore,the three-coordination structure of the active center Fe is more stable and beneficial for enhancing FTS activity.