Effect of magnesium promoter on iron-based catalyst for Fischer–Tropsch synthesis

A series of precipitated Fe/Cu/K/SiO2 Fischer–Tropsch synthesis (FTS) catalysts incorporated with the magnesium promoter were prepared by the combination of coprecipitation and spray-drying technology. The catalysts were characterized by using N2 physisorption, H2 or CO temperature-programmed reduction (TPR), X-ray diffraction (XRD), and Mössbauer spectroscopy (MES) methods. The results show that the addition of the magnesium promoter increases the BET surface area of the catalyst, and leads to the formation of the relatively smaller crystallite size of α-Fe2O3 in the catalysts, facilitating the reduction and carburization. The extent of carburization increases with the increase of the magnesium content, and passes through a maximum at an Mg/Fe weight ratio of 0.07. The FTS performance of the catalyst were tested in a fixed bed reactor under the conditions of 250 °C, 2.0 MPa and 2000 h−1 for 230 h on stream with syngas (molar ratio, H2/CO = 2) used as feed gas. The results indicate that an appropriate amount of magnesium can improve the activity and stability of the catalysts, enhance the selectivity to C5C11 and increase the space time yield of C5+ hydrocarbon. The magnesium promoter can also slightly inhibit the activity of WGS, resulting in the decline of CO2 selectivity and increase of the carbon utilization. However, excessive addition of the magnesium promoter will lead to a rapid deactivation of the catalyst. The optimal catalyst with Mg/Fe = 0.07 (M-3) has high activity and good stability, and keeps the selectivities of effective hydrocarbons (C2C4 + C5+) and CH4 at about 83% and 8%, respectively, during the entire run period.

A series of precipitated Fe/Cu/K/SiO2 catalysts incorporated with the magnesium promoter were prepared by the combination of coprecipitation and spray-drying technology. The addition of the magnesium promoter increases the BET surface area of the catalyst, and facilitates the reduction and carburization, resulting in improved activity and stability for Fischer–Tropsch synthesis. Figure optionsDownload as PowerPoint slide