Study on an iron–manganese Fischer–Tropsch synthesis catalyst prepared from ferrous sulfate

A systematic study was undertaken to investigate the effects of the initial oxidation degree of iron on the bulk phase composition and reduction/carburization behaviors of a Fe–Mn–K/SiO₂ catalyst prepared from ferrous sulfate. The catalyst samples were characterized by powder X-ray diffraction (XRD), Mössbauer spectroscopy, X-ray photoelectron spectroscopy (XPS) and H₂ (or CO) temperature-programmed reduction (TPR). The Fischer–Tropsch synthesis (FTS) performance of the catalysts was studied in a slurry-phase continuously stirred tank reactor (CSTR). The characterization results indicated that the fresh catalysts are mainly composed of α-Fe₂O₃ and Fe₃O₄, and the crystallite size of iron oxides is decreased with the increase of the initial oxidation degree of iron. The catalyst with high content of α-Fe₂O₃ in its as-prepared state has high content of iron carbides after being reduced in syngas. However, the catalyst with high content of Fe₃O₄ in its as-prepared state cannot be easily carburized in CO and syngas. FTS reaction study indicates that Fe-05 (Fe³⁺/Fe_total = 1.0) has the highest CO conversion, whereas Fe-03 (Fe³⁺/Fe_total = 0.55) has the lowest activity. The catalyst with high CO conversion has a high selectivity to gaseous hydrocarbons (C₁–C₄) and low selectivity to heavy hydrocarbons (C₅₊).