Structural changes in a 2 wt.-% Fe/SiO2 catalyst on the addition of rhenium and/or potassium were investigated. X-ray fluorescence, X-ray photoelectron and Mössbauer spectroscopy and temperature-programmed reduction (TPR) were applied to study the interaction between FeRe, FeK, ReK and FeReK samples. In the FeRe catalysts the reduction of the iron is limited, probably because an irreducible rhenium oxide interphase is formed and thereby during the reduction in hydrogen small iron particles are stabilized. Addition of potassium results in a 150 K shift to higher temperature in the TPR peak position and the total amount of hydrogen consumed is increased. Potassium interacts with rhenium and with iron and the initial dispersion of the catalyst is very effectively stabilized during reduction. This stabilization is probably due to the barrier built up by potassium, by which surface migration of iron and rhenium is diminished. A model has been constructed by means of which the chemical states and the morphology of the catalyst during different treatments can be interpreted.
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