An Energy Descriptor To Quantify Methane Selectivity in Fischer−Tropsch Synthesis: A Density Functional Theory Study

Selectivity is a fundamental issue in heterogeneous catalysis. In this study, the CH 4 selectivity in Fischer−Tropsch synthesis is chosen to be investigated: CH 4 selectivity on Rh, Co, Ru, Fe, and Re surfaces is computed by first-principles methods. In conjunction with kinetic analyses, we are able to derive the effective barrier difference between methane formation and chain growth (Δ E eff ) to quantify the CH 4 selectivity. By using this energy descriptor, the ranking of methane selectivity predicted from density functional theory (DFT) calculations is consistent with experimental work. Moreover, a linear correlation between Δ E eff and the chemisorption energy of C + 4H (Δ H ) is found. This fundamental finding possesses the following significance: (i) it shows that the selectivity, which appears to have kinetic characteristics, is largely determined by thermodynamic properties; and (ii) it suggests that an increase of the binding strength of C + 4H will suppress methane selectivity.