Fischer-Tropsch synthesis to light olefins over iron-based catalysts supported on KMnO4 modified activated carbon by a facile method

Fischer-Tropsch synthesis to light olefins (FTO) using biomass-derived syngas is an economical and renewable way to produce olefins. By using KMnO4 as precursor, a number of low cost iron based catalysts was produced and their FTO performances were tested. Firstly, a series of KMnO4 solutions with different concentrations were used to pretreat activated carbon (AC). Support was coated uniformly by K-doped bimessite MnO2 and substantial amount of surface oxygen-containing groups and defects were obtained simultaneously. Then, iron catalysts loaded on KMnO4 modified AC support was prepared by incipient wetness impregnation method. Characterization of the catalyst showed that alpha-Fe2O3 nanoparticles were uniformly loaded on the surface of KMnO4 treated AC. The valent of manganese (IV) was then transformed into Mn (II) and Mn (III) with AC served as a reducing agent. The redox reaction during preparation leads to a lower Mn chemical valence, which makes it easier to further reduction. More defects on support after calcination procedure were also observed due to the enrichment of oxygen-containing groups, which was helpful in anchoring alpha-Fe2O3 particles and decreasing its average particle size. High-content manganese played not only as a structural promoter to anchor Fe2O3 nanoparticles, but also a H-2 adsorption competitor that decreased H-2/CO ratio over active sites to reduce the possibility of further hydrogenation of olefins. The KMnO4 modified iron catalysts exhibited high CO conversion and olefins selectivity (similar to 40%) due to the improved distribution of iron and the auxiliary functions of Mn. Residual potassium is also in favor of the formation of iron carbides to increase CO conversion.