The influence of morphologies on the physicochemical properties and Fischer-Tropsch synthesis performance of iron catalysts

Abstract

Research on Fe-based catalysts for Fischer–Tropsch synthesis (FTS) has attracted significant attention. Various morphologies of Fe usually expose different crystal planes, affecting the reduction, carburization, and reaction behaviors in FTS. In this study, six different morphologies of Fe₂O₃ catalysts, which include spindle, spheres, long-hexagonal columns, cubes, short-hexagonal columns, and flower-like were prepared. The impact of morphology on phase structural transformations, reduction behaviors, H₂ and CO adsorption, and FTS performance was investigated using a suite of characterization techniques, including XRD, SEM, TEM, in situ XRD, H₂-TPR, H₂-TPD, CO-TPD, and DFT. The results indicate that the six catalysts have regular morphologies, clear lattice fringes, and high crystallinity. The spindle catalyst is more easily reduced and exhibits better adsorption for CO and H₂, while the cubic catalyst is more difficult to reduce and shows weaker adsorption for CO and H₂. DFT experiments suggest that CO readily dissociates on the (125) crystal plane of the spindle catalyst to form CO* (-0.77 eV), whereas on the (024) crystal plane of the cube catalyst, it dissociates into C* and O* (1.65 eV). The FTS catalytic performance is consistent with the characterization, with the spindle-shaped catalyst showing an activity of 95.35 %, and an activity of 20.29 % on cubic catalyst.