Adsorption and activation of CO on perfect and defective h-Fe7C3 surfaces for Fischer-Tropsch synthesis

Abstract

As a structure-sensitive reaction, one important issue in Fischer–Tropsch synthesis (FTS) reaction is to clarify the relationship between the iron catalyst composition and its effects on activity and selectivity. In this work, the adsorption and activation of CO on both perfect and defective h-Fe7C3 surfaces were investigated theoretically. The results indicate that the direct CO dissociation pathway is preferred with the effective energy barriers less than 1.50 eV on both perfect (101) and (11¯1) surfaces, which play a dominant role in FTS reaction. Instead, the effective energy barriers of the preferred HCO pathway on the perfect (11¯1¯) and (11¯0) surfaces are higher than 2.40 eV. When defects occur on the surfaces, CO is inclined to adsorb on resemble B5 site and direct CO bond dissociation with barriers around 0.8 eV is more favorable than hydrogenation routes for all the four defective surfaces. Thus it can be concluded that the presence of B5-like site can facilitate to form a multiple coordinated state and lead to a stretched CO bond. Specifically, we have theoretically revealed that on B5-like site, the stronger interaction between CO and h-Fe7C3 surface with more electrons transformation, the higher activation of CO bond facilitated to CO direct dissociation.