Theoretical Study of CO Adsorption and Activation on Orthorhombic Fe7C3(001) Surfaces for Fischer-Tropsch Synthesis Using Density Functional Theory Calculations

Fischer-Tropsch synthesis (FTS), which converts CO and H-2 into useful hydrocarbon products, has attracted considerable attention as an efficient method to replace crude oil resources. Fe-based catalysts are mainly used in industrial FTS, and Fe7C3 is a common carbide phase in the FTS reaction. However, the intrinsic catalytic properties of Fe7C3 are theoretically unknown. Therefore, as a first attempt to understand the FTS reaction on Fe7C3, direct CO* dissociation on orthorhombic Fe7C3(001) (o-Fe7C3(001)) surfaces was studied using density functional theory (DFT) calculations. The surface energies of 14 terminations of o-Fe7C3(001) were first compared, and the results showed that (001)(0.20) was the most thermodynamically stable termination. Furthermore, to understand the effect of the surface C atom coverage on CO* activation, C-O bond dissociation was performed on the o-Fe7C3(001)(0.85), (001)(0.13), (001)(0.20), (001)(0.09), and (001)(0.99) surfaces, where the surface C atom coverages were 0.00, 0.17, 0.33, 0.33, and 0.60, respectively. The results showed that the CO* activation linearly decreased as the surface C atom coverage increased. Therefore, it can be concluded that the thermodynamic and kinetic selectivity toward direct CO* dissociation increased when the o-Fe7C3(001) surface had more C* vacancies.

Automated summary

The study showed that the activation of CO* decreased linearly as the surface C atom coverage increased on the o-Fe7C3(001) surface, leading to an increase in thermodynamic and kinetic selectivity towards direct CO* dissociation.