CO Adsorption and Activation of η-Fe₂C Fischer–Tropsch Catalyst

Herein, spin-polarized density functional theory calculations are performed to investigate CO adsorption and activation on both perfect and defective η-Fe2C surfaces. The equilibrium shape of the η-Fe2C crystallite is first predicted by Wulff construction based on the surface energies of the experimentally observed crystal facets. The thermodynamically stable η-Fe2C (011) surface is observed to have the largest percentage followed by the (110), (211), and (121) surfaces. The H-assisted CO dissociation via the HCO* intermediate is suggested as the preferred CO activation pathway on these four mostly exposed η-Fe2C surfaces, while the direct CO dissociation is the preferred CO activation pathway on the corresponding four defective η-Fe2C surfaces because the presence of the carbon vacancy leads to less electrons donated to the absorbed CO by the surface Fe atoms based on Bader charge analysis. The insights reported here could shed new light on the rational design and manipulation of η-Fe2C Fischer–Tropsch catalysts.