Microstructured Al-fiber@meso-Al₂O₃@Fe-Mn-K Fischer-Tropsch catalyst for lower olefins

A thin-sheet Al-fiber@meso-Al₂O₃@Fe-Mn-K catalyst is developed for the mass/heat-transfer limited Fischer-Tropsch synthesis to lower olefins (FTO), delivering a high iron time yield of 206.9 μmol_CO s^-1 at 90% CO conversion with 40% selectivity to C₂-C₄ olefins under optimal reaction conditions (350°C, 4.0 MPa, 10,000 mL/(g·h)). A microfibrous structure consisting of 10 vol % 60-μm Al-fiber and 90 vol % voidage undergoes a steam-only-oxidation and calcination to create 0.6 μm mesoporous γ-Al₂O₃ shell along with the Al-fiber core. Active components of Fe and Mn as well as additives (K, Mg, or Zr) are then placed into the pore surface of γ-Al₂O₃ shell of the Al-fiber@meso-Al₂O₃ composite by incipient wetness impregnation method. Neither Mg-modified nor Zr-modified structured catalyst yields better FTO results than K-modified one, because of their lower reducibility, poorer carbonization property, and fewer basicity. The favorable heat/mass-transfer characteristics of this new approach are also discussed.