Manganese Promoter Hinders Carbon Permeation on Iron-Based Catalyst Surfaces: A First-Principles Study

• • DFT calculations reveal that manganese addition increases the thermodynamic barrier for carbon permeation into Fe-Mn alloy surfaces compared to pure iron, as evidenced by less favorable energetics for subsurface carbon occupancy. • • Minima-hopping structural searches confirm that within the considered carbon coverage range, no surface reconstructions leading to iron carbide phases occur, indicating that early carburization stages do not spontaneously form active carbide surfaces. • • Electronic structure analysis shows that carbon deposition modulates the d-band centers of metal surfaces, but manganese suppresses the shift toward values characteristic of bulk iron carbides, explaining the hindered carburization. • • The study provides atomic-scale mechanistic insight into the role of manganese as a promoter, which is critical for optimizing Fe-Mn catalysts in industrial FTS processes where product selectivity and catalyst stability are paramount.