Fischer–Tropsch on Iron with H2/CO and H2/CO2 as Synthesis Gases: The Episodes of Formation of the Fischer–Tropsch Regime and Construction of the Catalyst

Abstract

Fischer–Tropsch synthesis experiments have been performed with reduced precipitated Fe-Al-Cu-K2O catalysts, using a H2/CO and a H2/CO2 synthesis gas. Samples of the reaction products and of the catalyst were taken at distinct run lengths. The product samples were analyzed in detail and from their composition the kinetic data of elemental reaction steps (growth, branching, desorption as olefin or paraffin) calculated, applying the extended model of “nontrivial surface polymerization”. The catalyst samples were characterized by BET, XRD, Mössbauer spectroscopy, XPS and TPD in hydrogen and thus specifically phase changes of e.g. alpha iron, iron oxides, and iron carbides observed. It has been measured how the product composition changed with time, up to the steady state of synthesis. Several episodes with their own kinetic regimes were identified. These were then correlated with compositional and structural changes of the catalyst. This is addressed as “construction of the true iron Fischer–Tropsch catalyst”.