Alumina-supported iron oxide nanoparticles as Fischer-Tropsch catalysts: Effect of particle size of iron oxide

The Fischer-Tropsch synthesis of unpromoted and nano-sized iron oxide supported on δ-Al₂O₃ was investigated using a fixed-bed reactor. The catalysts prepared from pre-synthesized iron oxide with varying particle size (2-12 nm) showed much higher catalytic activities than the one prepared by using conventional impregnation method. The best results for CO conversion were obtained when the catalyst had Fe particle size of 6.1 nm. With an increase in particle size, the reduction degree and C₅+ selectivity was increased, whereas CH₄ selectivity and the uptake of adsorbed CO were decreased. Turnover frequency (TOF) at 300 °C was increased from 0.02 to 0.16 s^-1 when d(Fe⁰) was increased from 2.4 to 6.2 nm, and then it remains almost constant up to a particle size of 11.5 nm. Particle sizes of prepared iron oxide were analyzed by XRD and TEM, and the reduction behaviors of Fe/Al₂O₃ catalysts were studied by H₂-TPR. The effective iron size, metal dispersion and reduction degree of Fe/Al₂O₃ catalysts were measured by CO chemisorption and O₂ titration.