Effect of Preparation Conditions on Precipitated Iron-Based Catalysts for High-Temperature Fischer–Tropsch Synthesis of Light Olefins

A series of catalysts prepared by precipitation method were used to investigate the effects of preparation conditions on iron-based catalysts for high-temperature Fischer–Tropsch synthesis (HTFT) of light olefins. In this study, we varied the titration methods (forward precipitation, concurrent precipitation, and reverse precipitation), iron precursors [Fe(NO₃)₃, Fe₂(SO₄)₃, and FeCl₃], precipitants (ammonium carbonate, sodium carbonate, ammonia solution, sodium hydroxide, and potassium hydroxide), precipitation pH values (pH = 6.0, 7.0, 8.0, and 9.0), precipitation temperature (temperature = 25 °C, 45 °C, 65 °C, 75 °C, and 85 °C) and incorporation manners of Mn promoter (precipitation and incipient wetness impregnation method). It was demonstrated that different preparation conditions affect the BET specific surface area, pore structure, the morphology and dispersion of the catalyst, grain size, reduction ability, and CO adsorption ability of the catalyst, which in turn affect the activity of the catalyst and the production of light olefins during the HTFT. The results showed that the iron-based catalysts with the optimum catalytic performance and production of light olefins were prepared under the following conditions: ammonium carbonate as the precipitant and ferric trichloride as the iron precursor by concurrent precipitation method at pH 8.0 and 65 °C, followed by the introduction of Mn promoter by precipitation method. Catalysts were characterized by Ar adsorption–desorption, X-ray diffraction (XRD), scanning electron microscopy (SEM), H₂ temperature-programmed reduction (H₂-TPR), and CO-temperature-programmed desorption (CO-TPD).