Morphological effect of MnO2 promoter on iron-based Fischer-Tropsch synthesis catalysts

In this work, flower-like spherical, sea urchin-like and tubular MnO2 are prepared via hydrothermal synthesis and used as promoters of iron-based Fischer-Tropsch synthesis (FTS) catalysts to investigate their morphological effects. It is found that the different morphology of MnO2 exhibits observably distinct promotion functions on iron-based FTS catalysts. Tubular MnO2 contains moderate amount of surface oxygen vacancies accompany with weak Fe-Mn electronical interaction, as a result, tubular MnO2 promotes the formation of long-chain hydrocarbon and olefins, and restrains the generation of CH4. Flower-like spherical MnO2 presents negative roles in the CO conversion and formation of long-chain hydrocarbon, due to its insufficient oxygen vacancies and moderate Fe-Mn electronical interaction. With the most abundance of oxygen vacancies and strongest Fe-Mn interaction, sea urchin-like MnO2 modified catalysts exhibits the highest initial CO conversion, but deactivates rapidly. Besides, the sea urchin-like MnO2 enhances the formation of long-chain paraffins. This work presents new insights of the promotion roles of Mn additive, which is beneficial for the rational design of efficient iron-based FTS catalysts.