Abstract: A series of SiO2-incorporated precipitated Fe-Si-Cu-K (100Fe∶xSi∶3.0Cu∶2.0K, x=0, 2.8, 6.4, 8.2, atomic ratio) catalysts were prepared using the co-precipitation method for the Fischer-Tropsch synthesis (FTS). The in-situX-raydiffraction (XRD) and N2 physisorption were used to characterize the catalysts. The catalytic properties for FTS were tested in a fixed-bed reactor under pressure of 1.0 MPa and temperature of 543 K. The SiO2 incorporation increased the surface area and decreased the pore size of the precipitated iron catalysts, and the transition of different iron oxide and iron carbide phases (Fe2O3, Fe3O4, Fe3C, Fe5C2, and Fe7C3) was detected by in-situ XRD during the catalyst reduction in CO and FTS reaction in syngas (H2/CO molar ratio=0.7). The activity of the catalyst without SiO2 increased sharply with time on stream during the FTS process, which was accompanied by the transition of Fe5C2 to Fe7C3. The catalyst without SiO2 deactivated rapidly when the highest CO conversion was achieved, whereas a persistent increase in the activity of catalysts with SiO2 was achieved with time on stream. These indicate that SiO2 can stabilize the activity of the precipitated iron catalyst. The observed effects of SiO2 on the catalytic performance of precipitated iron catalysts can be explained by the fact that SiO2 can improve the dispersity of iron oxides and iron carbides in the catalyst and restrain the conversion of different iron carbide phases during the catalyst reduction and FTS reaction.

Key words: Fischer-Tropsch synthesis, precipitated iron-based catalyst, silica, iron carbide, in-situX-raydiffraction