N-doped ordered mesoporous carbon (N-OMC) confined Fe3O4-FeCx heterojunction for efficient conversion of CO2 to light olefins

Abstract

Converting CO2 into light olefins is full of challenges and opportunities, which was limited by poor activity catalysts. Herein, Fe3O4-FeCx heterojunction active site confined in N-doped graphene shell was synthesized on the surface of N-OMC. Alkali metal and N atom was used for modifying the surface electron density, which could suppress the excessive hydrogenation of CHx and improve the adsorption of CO2, thus increasing the yield of light olefins. The 0.8Fe-0.1K@N-OMC showed CO2 conversion of 54.5%, C2=–C4= selectivity of 65.63%, and a stability of 100 h (3.0 MPa, 320 °C, and GHSV = 4800 mL/gcat/h). The reaction mechanism was investigated using various characterization techniques, which demonstrates that the excellent catalytic active was originated from Fe3O4-FeCx heterojunction. The CO was first produced by the RWGS reaction catalyzed by Fe3O4, and then converted to light olefins on the neighboring FeCx active site by FTs reaction. Confinement effect of N-doped graphene shell inhibits the reoxidation and agglomeration of heterojunction active components, which boosts the catalyst' stability. This work proposes a simple and feasible synthesis strategy to construct Fe3O4-FeCx heterojunction catalysts, which provides insights into catalysts design and the reaction mechanism of CO2 conversion to light olefins.