Unusual Effect of Support Carbonization on the Structure and Performance of Fe/Mgal2o4 Fischer–Tropsch Catalyst

Abstract

Carbonization of MgAl2O4 spinel via glucose treatment is applied for preparation of spinel‐supported iron Fischer–Tropsch synthesis (FTS) catalysts. The catalysts are characterized by low‐temperature adsorption of N2, transmission electron microscopy (TEM), Mössbauer spectroscopy, in situ magnitometry, and are tested in high‐temperature FTS conditions. Surface carbonization leads to magnetite formation in the course of catalyst calcining, likely due to reductive function of surface carbon. In contrast, hematite is formed if iron precursor is deposited on pristine spinel. Support carbonization facilitates iron precursor reduction into carbide during catalyst activation step in synthesis gas flow and gives rise to highly dispersed iron nanopartilcles. Comparison of sequential and co‐impregnation approaches for support carbonization reveal that the first is preferable in terms of Hägg carbide formation during catalyst activation. Specific activity of the catalysts in high‐temperature FTS is approximately doubled due to the support carbonization. The carbonization also boosts C5+ selectivity and olefin percentage in the product hydrocarbons, while methane formation is suppressed. Adding potassium to catalyst formulation suppresses iron carbide oxidation and Fe3O4 formation, and promotes conversion of χ‐Fe5C2 into θ‐Fe7C3 in FTS conditions.