Manganese promoter hinders carbon permeation on iron-based catalyst surfaces:A first-principles studyOA

Fe-Mn catalysts have garnered considerable attention for industrial applications in the Fischer-Tropsch synthesis(FTS)process.Carbon adsorption and permeation on catalyst surfaces constitute critical elementary steps in the in situ formation of active phases in iron-based FTS catalysts.Herein,density functional theory(DFT)calculations are employed to systematically investigate the atomistic structures,thermodynamic stabilities,and electronic properties of carbon-deposited Fe-Mn alloy surfaces at the early stage of carburization.These Fe-Mn alloy surfaces show distinct thermodynamic sensitivity to carbon atoms adsorbed on the surface and permeating into the interstitial sites.By combining DFT with minima-hopping structural searches,we demonstrate that the initial stage of carbon permeation cannot trigger the reconstruction of surface regions to form surface iron carbide phases.The addition of manganese thermodynamically hinders the carbon permeation process.Although deposited C atoms modulate the electronic structure of metals,the presence of manganese retards the shift of d-band centers of metals to those of the bulk iron carbide phases.Our study provides an atomic-scale insight into the in situ evolution of Fe-Mn catalyst surfaces during the carbon deposition process and indicates that the manganese promoter has a noticeable effect on carbon permeation.