A New Insight into CO + H2 Reactions on Reduced or Oxidized Supported Iron

The CO + H 2 reaction carried out at 250°C on the silica supported preoxidi-zed iron (10 % Fe) aerogel catalyst shows a particularly high activity and stability with time on stream of the Fischer-Tropsch (F.-T.) type. The spent catalyst is found uncarburized and in the oxidized state (Fe 3 O 4 ) and it contains only a small amount of inactive carbon deposit. The mechanism of the F.-T. reaction, assuming the dissociation of CO, would be of a redox type implying Fe 2 O 3 and Fe 3 O 4. If the same catalyst is prereduced to metallic iron it deactivates with time on stream and the spent catalyst contains iron carbides and inactive carbon deposit. Its peak activity is also much smaller than that of the preoxidized catalyst. The disproportionate of CO at 250°C leaves carbon on the two types of catalysts which may be hydrogenated at 250°C into CH, on the prereduced catalyst (active C)but only above 380°C on the preoxidized catalyst (inactive carbon). It is inferred that the active carbon deposited during CO+H 2 reaction on preoxidized catalyst, which accounts for its high activity, is easily transformed into inactive carbon during disproportionate of CO in the absence of H 2.