Microstructure of the activated industrial ammonia synthesis catalyst
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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.
KeywordsAmmonia synthesis iron catalyst surface characterization promoter effects nitrides ion scattering spectroscopy XPS HRTEM
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- R. Schlögl, R.C. Schoonmaker, M. Muhler and G. Ertl, Catal. Lett. 1 (1988) 237.Google Scholar
- P. Stoltze, Physica Scripta 36 (1987) 824.Google Scholar
- H.D. Vandervell and K.C. Waugh, Chem. Phys. Lett. 171 (1990) 426.Google Scholar
- G. Ertl, J. Vac. Sci. A1 (1983) 1247.Google Scholar
- R. Schlögl, in:Science and Technology of Ammonia Synthesis, ed. J.R. Jennings (Plenum, 1991) in press.Google Scholar
- D.C. Silverman and M. Boudart, J. Catal. 77 (1982) 208.Google Scholar
- T. Rayment, R. Schlögl, J.M. Thomas and G. Ertl, Nature 315 (1985) 311.Google Scholar
- A. Baiker, R. Schlögl, F. Armbruster and H.J. Güntherodt, J. Catal. 107 (1987) 221.Google Scholar
- A. Baranski, A. Reizer, A. Kotarba and E. Pyrczak, Appl. Catal. 19 (1985) 417.Google Scholar
- G. Ertl, M. Huber and M. Thiele, Z. Naturforsch. 34a (1979) 30.Google Scholar
- M. Grunze, M. Golze, J. Fuhler, M. Neumann and E. Schwartz, Proc. 8th ICC, Vol. 4 (1985) 133.Google Scholar
- G. Ertl, D. Prigge, R. Schlögl and M. Weiss, J. Catal. 79 (1983) 359.Google Scholar
- D.R. Strongin, S.R. Bare and G.A. Somorjai, J. Catal. 103 (1987) 289.Google Scholar
- A. Nielsen,An Investigation on Promoted Iron Catalysts for the Synthesis of Ammonia, 3rd ed. (Gjellerup, 1968).Google Scholar