Effect of graphitic carbon modification on the catalytic performance of Fe@SiO2-GC catalysts for forming lower olefins via Fischer-Tropsch synthesis

Abstract

Mesoporous silica-encapsulated iron materials contribute to the suppression of self-aggregation and thereby enhances the Fischer-Tropsch synthesis activity. However, constructing Fe-based supported catalysts with high activity and selectivity in the Fischer-Tropsch synthesis to lower olefins (FTO) by a conventional mesoporous silica support has been proven challenging due to its low hydrothermal stability and low reducibility. Herein, we developed a core-shell Fe@SiO₂-GC structure with an optimized interface of the catalyst by introducing graphitic carbon (GC) that weakened the Fe-SiO₂ interaction. Transmission electron microscopy and nitrogen adsorption-desorption characterization proved GC-modified catalysts had well-defined core-shell structures. The Fe@SiO₂-GC-2 containing the optimal GC content had the largest surface area and pore volume, and outperformed Fe₂O₃@SiO₂ in terms of CO conversion (60.1%) and C₂-C₄ olefin selectivity (40.7%) within 100 h. The significant improvement of FTO performance was attributed to the rigid porous framework of GC, which allowed free access of syngas and inhibited mesoporous channel collapse during FTO, so the catalytic activity and stability were improved by the synergism between higher Fe dispersion and reducibility. Moreover, the narrow well-defined mesoporous channel also exerted a modest spatial restriction effect, which inhibited the formation of long-chain hydrocarbon and tailored the product distribution toward lower distillate, thus improving the selectivity toward C₂-C₄.

Keywords: Core-shell; Fe@SiO(2)-GC; Fischer-Tropsch synthesis; Graphitic carbon; Reducibility.