Effect of manganese on an iron-based Fischer–Tropsch synthesis catalyst prepared from ferrous sulfate

The effects of manganese on the textural properties, bulk and surface phase compositions, reduction/carburization behaviors and surface basicity of an Fe–Mn–K/SiO2 catalyst prepared from ferrous sulfate were investigated by N2 physisorption, Mössbauer spectroscopy, X-ray photoelectron spectroscopy (XPS), H2 (or CO) temperature-programmed reduction (TPR) and CO2 temperature-programmed desorption (TPD). The Fischer–Tropsch synthesis (FTS) performance of the catalysts with different contents of manganese was studied in a slurry-phase continuously stirred tank reactor. The characterization results suggested that the added manganese suppressed the crystal growth of hematite and the catalyst reduction from FeO to Fe in H2. An appropriate amount of manganese improved the FTS activity, increased the surface basicity and enhanced the carburization of the catalyst. However, the excessive addition of manganese retarded the catalyst carburization in CO and syngas due to the high enrichment of manganese on the catalyst surface. At the same time, the addition of manganese suppressed the formation of CH4 and shifted the selectivity to heavy hydrocarbons (C12+).