Unravelling the metal–support interactions in χ-Fe5C2/MgO catalysts for olefin synthesis directly from syngas

Abstract

We reported a χ-Fe₅C₂/MgO catalyst for olefin synthesis directly from syngas (STO), showing high selectivity to C₂–C₄ olefins and catalytic stability. With characterization of the morphology, electronic structures, and adsorption/desorption properties using in/ex situ techniques (XPS, TEM, XRD, MES, PHTA and TPD), we revealed that MgO could act not only as a structural promoter to disperse the active iron phase and prevent particle agglomeration during the reaction, but also as an electronic modifier to transfer electrons to iron. In particular, by combination of spectroscopy and theory calculations, we have proved that the close intimacy between χ-Fe₅C₂ and MgO (∼0.3 electrons transfer from MgO to χ-Fe₅C₂) enhanced CO dissociative adsorption whilst weakening the secondary hydrogenation of olefins, leading to the enhancement of selectivity. The dual roles of MgO in χ-Fe₅C₂/MgO may shed light upon rational design of practical STO catalysts by taking advantage of the exceptional strong metal–support interactions (SMSIs).