Study of an iron-manganese Fischer–Tropsch synthesis catalyst promoted with copper

The metal–silica interaction and catalytic behavior of Cu-promoted Fe–Mn–K/SiO2 catalysts were investigated by temperature-programmed reduction/desorption (TPR/TPD), differential thermogravimetric analysis, in situ diffuse reflectance infrared Fourier transform analysis, and Mössbauer spectroscopy. The Fischer–Tropsch synthesis (FTS) performance of the catalysts with or without copper was studied in a slurry-phase continuously stirred tank reactor. The characterization results indicate that several kinds of metal oxide–silica interactions are present on Fe–Mn–K/SiO2 catalysts with or without copper, which include iron–silica, copper–silica, and potassium–silica interactions. In addition to the well-known effect of Cu promoter on easing the reduction of iron-based FTS catalysts, it is found that Cu promoter can increase the rate of carburization, but does not vary the extent of carburization during the steady-state FTS reaction. The basicity of the Cu and K co-promoted catalyst is greatly enhanced, as demonstrated by CO2-TPD results. In the FTS reaction, Cu improves the rate of catalyst activation and shortens the induction period, whereas the addition of Cu has no apparent influence on the steady-state activity of the catalyst. Promotion of Cu strongly affects hydrocarbon selectivity. The product distribution shifts to heavy hydrocarbons, and the olefin/paraffin ratio is enhanced on the catalyst due to the indirect enhancement of surface basicity by the copper promotion effect.