Role of C-Defective Sites in CO Adsorption over ε-Fe2C and η-Fe2C Fischer-Tropsch Catalysts.

Herein, we report the crucial importance of C-defective sites on the CO adsorption over e -Fe 2 C and η-Fe 2 C Fischer-Tropsch catalysts via systematic DFT calculations. The simulated XRD and Wulff construction show the significant differences in their equilibrium shapes and most exposed surfaces. It is observed that the e -Fe 2 C exposes a high proportion (89%) of facets (1 2 ( _ ) 1) with similar structure to that of η-Fe 2 C (011) which has been proved to be the active surface of CO activation. Several most exposed facets of e-Fe 2 C and η-Fe 2 C were subsequently selected to investigate the CO adsorption, and a linear relationship between the CO adsorption energies and the vibration frequencies of C-O bond was observed. CO adsorption energies on perfect and C-defective Fe 2 C surfaces were comparatively studied, and the CO adsorption on C-defective surfaces are found to be much more stable. Further Bader charge and PDOS analysis showed that the promotional effects of C-defective sites on CO adsorption can be ascribed to the electron-rich involved Fe atoms with higher abilities to donate electrons to CO molecules.