First principle study of chain termination reactions during Fischer-Tropsch Synthesis on χ-Fe5C2(010)

Abstract

Elementary steps for the chain termination reactions in the carbide mechanism of Fischer-Tropsch Synthesis (FTS) were studied on χ-Fe5C2(010), which is commonly accepted as an active phase for Fischer-Tropsch Synthesis (FTS). Rate coefficients for the n-alkyl hydrogenation and n-alkyl dehydrogenation were calculated as function of the chain length using spin-polarized density functional theory calculations with the vdW-DF2 functional. The kinetic parameters are independent of the hydrocarbon chain length from a chain length of three carbon atoms onwards for n-alkyl hydrogenation and for n-alkyl β-dehydrogenation. For small n-alkyl species the chain length dependence is the result of structural differences of the transition states and differences in bond strength of reactants and products. The dehydrogenation of n-alkyls leads to 1-alkenes that are strongly adsorbed to the catalyst surface.