The role of nano-sized iron particles in slurry phase Fischer-Tropsch synthesis

The slurry phase Fischer-Tropsch (F-T) activity of three α-Fe ₂O₃-based materials, two unsupported nano-sized, NANOCAT (3 nm) and BASF (20-80 nm), and a supported micron-sized (32.5μm) UCI, are compared with respect to total hydrocarbon production from synthesis gas (H ₂/CO∼2/1) at 513 K. Low temperature Mössbauer spectra of the quenched slurry samples after 120 h on-line show that all three catalysts are essentially a mixture of oxide and carbide phases with magnetite (Fe ₃O₄) being the dominant phase. TEM images of the quenched samples reveal unexpected particle characteristics. While both unsupported nano-sized materials essentially avoid expected agglomeration, the micron-sized UCI transforms into nano-sized material. These results suggest a crucial role of nano Fe during F-T synthesis.