Structure and Fischer–Tropsch performance of iron–manganese catalyst incorporated with SiO 2

Abstract

A systematic study has been carried out to investigate the impacts of SiO 2 content, incorporation manner of SiO 2 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 (H 2/CO = 2.0, T = 265 °C, P = 2.5 MPa and GHSV = 1000 h −1). Characterization technologies of N 2 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 SiO 2 framework in the catalysts. The results of characterization showed that the incorporation of SiO 2 leads to the increase in surface area. The catalyst with incorporated with precipitated SiO 2 has the highest surface area and exhibits a stronger interaction between iron and SiO 2 matrix than the interaction with binder SiO 2. The strong Fe–SiO 2 interaction restrains the reduction in H 2 and the carburization in syngas of the catalysts. The addition of both binder and precipitated SiO 2 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 SiO 2 incorporated. For the catalysts incorporated with the same levels of SiO 2, the spray-dried catalyst has lower activity than the normal dried one. In addition, the catalyst incorporated with precipitated SiO 2 has higher activity than that with binder SiO 2. The FTS stability of the catalysts is improved with the incorporation of SiO 2. The selectivity to gaseous hydrocarbons (C 1–C 4) and olefins decreases with the increase of SiO 2 content. The spray-dried catalysts incorporated with either precipitated SiO 2 or binder SiO 2 produce more gaseous hydrocarbons and fewer olefins, while the normal-dried process and the addition of binder SiO 2 cause a great increase in selectivity to light hydrocarbons. The selectivity to oxygenates in product decreases with the increase of SiO 2 content in the catalyst. For the catalysts incorporated with binder SiO 2, the spray-dried catalyst (SPUW) produces more oxygenates than the normal dried catalyst (FMSC), whereas the spray-dried catalyst incorporated with precipitated SiO 2 (FSCP) produces the least oxygenates among all catalysts.