In situ Mossbauer and EXAFS investigations have shown that the reduction of iron in the monometallic Fe/SiO2 catalyst is only partial, the reduction being mostly to a ferrous silicate phase. In the bimetallic Fe-Ru/SiO2 catalysts, the proportion of the FeRu alloy formed on reduction increases markedly with the increase in Ru content; clearly, Ru significantly enhances the reduction of iron on SiO2. In the Ru-rich compositions (Ru/Fe 1.0), most of the iron is present in the alloy phase and there is no segregation of α-Fe. A comparative study of the different supports has shown that γ-Al2O3 and SiO2 interact with iron strongly at low reduction temperatures while the TiO2 support interacts at higher temperatures. The presence of traces of Fe3+ often found in reduced Fe-Ru catalysts is shown to arise from the oxidation of fine segregated iron particles on the support.