Fischer–Tropsch Synthesis: Influence of Pore Size on Silica-Supported Iron Catalysts

The Fischer–Tropsch (FT) synthesis is a promising technology to convert carbon-containing feedstocks into clean fuels and high-value chemicals. Due to the high specific surface area, tunable pore structure, and moderate metal–support interactions, silica is widely used in Fischer–Tropsch synthesis catalysts. Herein, silica-supported iron catalysts with pore sizes of 6.2–44.3 nm were prepared via impregnation to investigate the effect of support pore size on FT performance. Mesoporous SiO 2 supports with tunable pore diameters were synthesized by a sol–gel pore-enlargement technique. Results show that inappropriate iron impregnation damages the SiO 2 support’s porous structure, especially for high-specific-surface-area samples. Both metal–support interactions and SiO 2 pore size critically regulate the iron catalyst’s performance. A larger SiO 2 surface area favors Fe–O–Si interfacial bond formation, while pore size variation negligibly affects the surface oxygen chemical environment. Notably, the cost-effective large-pore catalyst exhibits excellent FT performance: 52.2% CO conversion at 270 °C, 3.00 MPa, and a gas hourly space velocity of 3.6 L·g cat –1 ·h –1, with 144 h long-term stability. It also achieves a high C 2–4 olefin/paraffin ratio of over 3.10 and suppresses the CO 2 selectivity to as low as 3.66%, significantly lower than conventional iron-based catalysts. The enhanced activity and selectivity are attributed to the silica support’s optimized pore structure, which improves mass transfer and modulates the iron active sites’ surface catalytic properties.