Enhancing CO Activity and Reducing CH4 Formation of Fe3C by Graphene Oxide during Syngas Conversion

Abstract

The Fischer−Tropsch synthesis (FTS), the key industrial process for the transformation of syngas into valuable chemicals and clean fuels, benefits from advanced catalyst design. Iron carbide nanoparticles (Fe3C) and their graphene oxide-derived counterpart (Fe3C/Graphene) were successfully synthesized. Fe3C/Graphene exhibits a large specific surface area, high pore volume, and abundant surface defective sites provided by the reduced graphene oxide support. Together with the stabilized Fe3C active phase, these features promote CO activation and C−C coupling, leading to enhanced CO conversion, higher C5+ selectivity, and suppressed CH4 formation comparedwith Fe3C. Density functional theory calculations reveal that the improved CO activation on Fe3C/Graphene originates from reduced electron transfer and weakened Fe−C and C−O bonds. For Fe3C, the rate-determining step is CO* + H* → CHO*, whereas for Fe3C/Graphene, the rate-determining step is CHO* → CH* + O*. It also reveals that Fe3C/Graphene accelerates this step, corroborating the enhanced CO activation observed experimentally. Furthermore, the simulations confirm that defective graphene significantly raises the effective barrier for methanation, perfectly rationalizing the suppressed CH4 formation. These findings demonstrate that the introduction of graphene oxide is a effective strategy for tailoring the catalytic performance of Fe-based FTS catalysts.