Investigating the CO activation mechanism on hcp-Fe7C3 (211) via density functional theory

Abstract

The Fischer-Tropsch to Olefins (FTO) process over iron catalysts has attracted interests of academia due to its promising catalytic performance. Several iron carbides phases have been discovered in the spent iron catalysts. Recently, the hcp-Fe7C3 phase was reported to be active in the FTO process. Hence, to figure out how the hcp-Fe7C3 works in the FTO process, DFT calculations were performed to investigate the CO activation mechanism first. It was found that the top site and 4-fold site are the major adsorption sites for CO. The surface carbon is able to be the CO activation site by CO insertion dissociation pathway. The effective barrier energy of the preferred CO insertion dissociation pathway is 1.48 eV. The CO could also be activated on the top site through H-assist CO dissociation pathway or the 4-fold site through direct CO dissociation pathway with the effective barrier energy of 1.30 eV and 1.18 eV, respectively. Compared the effective barrier energy of CO activation mechanism on the hcp-Fe7C3 (211) with those on other iron carbides, the hcp-Fe7C3 (211) is thought to be high active on the CO activation process under the FTO condition.