The nature of the potassium compound acting as a promoter in iron-alumina catalysts for ammonia synthesis

J.G. van Ommen, W.J. Bolink, J. Prasad, P. Mars

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Abstract

The chemical form of the potassium promoter on an iron-alumina catalyst during ammonia synthesis has been studied by two methods, viz, (i) the measurement of the equilibrium constant of the process KNH2 + H2 KH + NH3, and (ii) chemical analysis of the used catalyst. The equilibrium constant measurements gave K723 = (12.9 ± 0.5) × 10−3, ΔHf2980(KNH2) = −119 ± 3 kJ mol−1 and S2980(KNH2) = 109 ± 4 J mol−1 K−1. The chemical analysis showed that no KNH2 is present on the catalyst during synthesis. From these results and with the aid of thermodynamic considerations it is concluded that KNH2, K and K2O are not stable compounds under conditions of ammonia synthesis. X-Ray diffraction showed that part of the potassium reacts with Al2O3, probably leaving part of the potassium in the form of KOH which is quite stable under ammonia synthesis conditions.
Original languageUndefined
Pages (from-to)120-127
JournalJournal of catalysis
Volume38
Issue number1-3
DOIs
Publication statusPublished - 1975

Keywords

  • IR-68334

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