θ-Fe3C dominated Fe@C core–shell catalysts for Fischer-Tropsch synthesis: Roles of θ-Fe3C and carbon shell

Abstract

θ-Fe3C formation is usually considered as a deactivation factor in Fischer-Tropsch synthesis (FTS). Herein, θ-Fe3C dominated Fe@C core–shell catalysts were fabricated by pyrolysis of MIL-101(Fe) in ethyne for studying the roles of θ-Fe3C and carbon shell in FTS. In the evolution of MIL-101(Fe) into Fe@C catalysts, ethyne decomposition promotes the formation of θ-Fe3C and carbon shells around nanoparticles. By modulating the pyrolysis temperature, θ-Fe3C and/or α-Fe nanoparticles coated with different carbon shells (amorphous carbon, graphene or graphite shells) are acquired. By exploring the relationship between phase composition, structure of catalysts and FTS performance, it is found that θ-Fe3C is confirmed to be FTS active, which exhibits superior CC chain growth ability, i.e., higher C5+ selectivity and lower CH4 selectivity. Meanwhile, graphene shell inhibits iron nanoparticles aggregation and stabilizes the catalysts.