High Pressure Desorption of K+ from Iron Ammonia Catalyst – Migration of the Promoter Towards Fe Active Planes

The thermal desorption of potassium ions from industrial iron catalysts was studied in situ in the wide pressure range of 10−8–10 bar of Ar, N2 and synthesis gas mixture of N2:3H2. While high activation energy of 284 ± 1 kJ/mol, for K+ was determined for the catalyst precursor, in the reaction conditions it drops down to 231 ± 5 kJ/mol, corresponding well to that found for iron single crystals in UHV studies. The results are rationalized in terms of potassium migration from oxide storage phases towards the iron facets developed during the catalyst activation.