Catalysis Letters

, Volume 11, Issue 1, pp 19–31

Microstructure of the activated industrial ammonia synthesis catalyst

Authors

  • W. Mahdi
    • Fritz Haber Institut der Max-Planck Gesellschaft
  • J. Schütze
    • Fritz Haber Institut der Max-Planck Gesellschaft
  • G. Weinberg
    • Fritz Haber Institut der Max-Planck Gesellschaft
  • R. Schoonmaker
    • Fritz Haber Institut der Max-Planck Gesellschaft
  • R. Schlögl
    • Fritz Haber Institut der Max-Planck Gesellschaft
    • Institut für Anorganische Chemie der Universität Niederurseler Hang
  • G. Ertl
    • Fritz Haber Institut der Max-Planck Gesellschaft
Article

DOI: 10.1007/BF00866897

Cite this article as:
Mahdi, W., Schütze, J., Weinberg, G. et al. Catal Lett (1991) 11: 19. doi:10.1007/BF00866897
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Abstract

Industrial doubly-promoted iron catalysts and model systems of singly-promoted K- and Al-iron catalysts were characterised by their catalytic performance at 1 bar pressure. The relevance of bulk nitrogen for catalytic performance is shown. The catalysts were also activated in an in-situ reaction chamber of a He-ion scattering spectrometer (ISS) and their top atomic layer elemental composition was determined after they had reached similar performance as in the microreactor tests. The bulk microstructure of these samples was investigated by high resolution transmission electron microscopy (TEM) and microdiffraction.

All evidence indicates that small highly crystalline α-Fe platelets act as active phase. Their surfaces are covered to a large extent by promotor compounds which are partly present as poorly crystalline aggregates with iron oxide leaving only a small fraction of elemental iron directly exposed to the gas phase. The intimate contact between iron crystals and promoters particles prevents recrystallisation and is the key to the understanding of the structural stability of the catalyst system.

Keywords

Ammonia synthesisiron catalystsurface characterizationpromoter effectsnitridesion scattering spectroscopyXPSHRTEM
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Copyright information

© J.C. Baltzer A.G. Scientific Publishing Company 1991