Effect of Hydrothermal Treatment on Precipitated Iron Catalyst for Fischer–Tropsch Synthesis

Abstract

Two series of Fe/Cu/K catalysts were prepared by co-precipitation (CP-xK) and by co-precipitation accompanied with hydrothermal treatment (HY-xK), respectively. The catalysts were investigated by N2 adsorption, X-ray diffraction (XRD), Mossbauer effect spectroscopy (MES), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), H2 temperature-programmed reduction (H2-TPR) and thermogravimetric analysis. N2 adsorption revealed that HY-xK catalysts displayed relatively low surface area, but generated additional macropore. XRD and SEM showed that HY-xK catalysts were well grown crystallite, while the CP-xK catalysts were amorphous. In addition, hydrothermal treatment remarkably influenced the growth orientation of hematite nanocrystals, resulting in the preferential exposure of the (110) plane. HRTEM also indicated that HY-1.32K was dominated by Fe2O3 nanocrystals with (110) plane, and the CP-1.38K primary particle mainly exposed (104) plane. The H2-TPR profiles for the two series of catalysts were similar, though the merged and smooth peak of HY-xK catalysts possibly suggested that the component elements were more uniform. MES and XRD indicated that the catalyst after hydrothermal treatment can be easily reduced into active carbide phases in Fischer–Tropsch synthesis (FTS) reaction. In FTS reaction, the HY-xK catalysts showed higher activity and better stability than the CP-xK catalysts given comparable K content.