Crystal Facet Dependence for the Selectivity of C₂ Species over Co₂C Catalysts in the Fischer–Tropsch Synthesis

The effect of Co 2 C crystal facets on the selectivity of C 2 species (C 2 oxygenates and hydrocarbons) in Fischer–Tropsch synthesis (FTS) reaction was investigated using density functional theory calculations, and the selectivity comparisons among five exposed Co-termination (101), (011), (010), (110), and (111) crystal facets are examined to shed light on the essential relationship between FTS selectivity and the structure of Co 2 C crystal facets. The results show that the C–C bond of C 2 species prefers to be formed instead of C 1 species CH 4 over Co 2 C catalysts in the FTS reaction, and the selectivity of C 2 species and the dominant existence form of key CH x intermediates are sensitive to the crystal facet of Co 2 C catalysts, which are closely associated with Co 2 C crystal facet’s electronic and structural properties. The electronic and structural properties of different Co 2 C crystal facets show that the high selectivity of C 2 oxygenates over the (011) and (111) facets are attributed to the upshift of their surface d-band centers, as well as the presence of the step B 5 -type active unit with five Co atoms consisted of much denser surface active sites. However, both (101) and (010) facets exhibit high selectivity toward C 2 hydrocarbons, and the (110) facet presents high selectivity toward the formation of CH 4 . Thus, regulating the exposed crystal facets of Co 2 C catalyst can control the selectivity of desirable C 2 species. This work provides evidence at a molecular level to support that the sensitivity of Co 2 C crystal facet is a cause to affect the selectivity of desired products in the FTS reaction.