Structure and Fischer-Tropsch performance of iron-manganese catalyst incorporated with SiO2

A systematic study has been carried out to investigate the impacts of SiO2 content, incorporation manner of SiO2 and drying process on the physico-chemical and catalytic performances of a precipitated iron-manganese catalyst for Fischer-Tropsch synthesis (FTS) in a fixed bed reactor (H2/CO = 2.0, T = 265 °C, P = 2.5 MPa and GHSV = 1000 h−1). Characterization technologies of N2 physisorption, X-ray diffraction (XRD), Mössbauer effect spectroscopy (MES), temperature-programmed reduction (TPR) and scanning electron microscopy (SEM) were used to study the textural properties, bulk phase composition, reduction behavior and morphologies of the catalysts, and the SiO2 framework in the catalysts. The results of characterization showed that the incorporation of SiO2 leads to the increase in surface area. The catalyst with incorporated with precipitated SiO2 has the highest surface area and exhibits a stronger interaction between iron and SiO2 matrix than the interaction with binder SiO2. The strong Fe-SiO2 interaction restrains the reduction in H2 and the carburization in syngas of the catalysts. The addition of both binder and precipitated SiO2 greatly influences the activity and selectivity of FTS, and obviously improves its stability. For the FTS reaction tests, it was found that the catalyst activity is decreased with the increase of the amount of SiO2 incorporated. For the catalysts incorporated with the same levels of SiO2, the spray-dried catalyst has lower activity than the normal dried one. In addition, the catalyst incorporated with precipitated SiO2 has higher activity than that with binder SiO2. The FTS stability of the catalysts is improved with the incorporation of SiO2. The selectivity to gaseous hydrocarbons (C1-C4) and olefins decreases with the increase of SiO2 content. The spray-dried catalysts incorporated with either precipitated SiO2 or binder SiO2 produce more gaseous hydrocarbons and fewer olefins, while the normal-dried process and the addition of binder SiO2 cause a great increase in selectivity to light hydrocarbons. The selectivity to oxygenates in product decreases with the increase of SiO2 content in the catalyst. For the catalysts incorporated with binder SiO2, the spray-dried catalyst (SPUW) produces more oxygenates than the normal dried catalyst (FMSC), whereas the spray-dried catalyst incorporated with precipitated SiO2 (FSCP) produces the least oxygenates among all catalysts.