Chain growth mechanism of Fischer–Tropsch synthesis on Fe 5C 2(0 0 1)

Abstract

The chain growth mechanisms of Fischer–Tropsch synthesis on Fe 5C 2(0 0 1) were investigated at the levels of density functional theory. On the H 2 and CO co-adsorbed surface, the formation of CH and CCO is the most favored initial steps. The subsequent steps of CCO coupling with C into CCCO and CCO hydrogenation into CCH 2 and CHCH are competitive. Furthermore, CCH from CCH 2 and CHCH dehydrogenation can couple with C to form CCCH. Since chain initiation from CO insertion obeys insertion mechanism, and chain propagation from CCH coupling obeys carbide mechanism, both mechanisms are operative and co-operative in Fischer–Tropsch synthesis. The carburized active surfaces can be regenerated and maintained by CO adsorption on the vacancy site, followed by hydrogenation into surface formyl (CHO) and successive dissociation into surface CH and O. In addition surface O can be hydrogenated into surface OH, and H 2O formation from surface OH disproponation is energetically more favored than surface OH hydrogenation.