Phase transformation and textural properties of an unpromoted iron Fischer–Tropsch catalyst

The phase transformations and textural properties were systematically investigated over an unpromoted iron Fischer–Tropsch synthesis (FTS) catalyst prepared from ferrous sulfate with different Fe3+/Fetotal ratios at different preparation stages (precipitation, dryness and calcination). The catalyst samples were characterized by X-ray diffraction (XRD), Mössbauer spectroscopy and N2 physisorption. The characterization studies show that after precipitation the samples are composed of α-FeOOH, Fe3O4 and α-Fe2O3. The content of Fe3O4 increases with the increase of Fe3+/Fetotal ratio (Rm) and reaches the maximum content at the Rm of 0.72. There is not a significant phase transformation during the dryness of the catalyst samples. After being calcined at 500 °C for 5 h, α-FeOOH and Fe3O4 existed in the catalyst samples are transformed into α-Fe2O3. The characterization results from N2 physisorption show that when the Rm of sample is 0.72, the BET surface area and pore volume have the maximum values (26 m2/g, 0.21 cm3/g) after the samples being calcined at 500 °C.