SIMULTANEOUS EFFECT OF PHASE-COMPOSITION AND WATER-VAPOR ON THE REDUCTION OF IRON CATALYST FOR AMMONIA-SYNTHESIS

Water vapour causes a dramatic decrease in the reduction rate of an iron catalyst for ammonia synthesis and also effects the topochemistry of the reduction. Core-and-shell behaviour and reduction of an internal type have been observed in dry and wet atmospheres, respectively. Magnetite is the main component of the catalyst. Some industrial catalysts, e. g. Topso phi e KM I, also contain a small amount (ca. 10 percent) of wustite. A sample of singly aluminium-promoted catalyst was divided into two parts; one part was oxidized to magnetite and the other was reduced to wustite. It has been shown that the reduction of the magnetite sample was completely retarded by 10,000 ppm of water vapour, whereas that of the wustite was only slightly affected. The results indicate that the retardation effect of water vapour is due to the magnetite phase promoted with aluminium. This result, supported by already published porosimetric and Mossbauer data and microscopic observations, explain the topochemistry of reduction of the iron catalyst in dry and wet atmospheres.