Interactions of nitrogen and hydrogen on iron surfaces

G. Ertl, M. Huber, S. B. Lee, Z. Paál, M. Weiss

Research output: Contribution to journalArticle

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Abstract

Interactions between nitrogen and hydrogen on single and polycrystalline Fe surfaces were studied by thermal desorption and Auger spectroscopy under UHV conditions and by applying total pressures up to about 1 atm. Molecularly adsorbed nitrogen, N2,ad, is displaced from the surface by admission of hydrogen. Adsorbed hydrogen in turn inhibits adsorption of molecular nitrogen and as a consequence lowers the rate of dissociative nitrogen adsorption (which proceeds through N2,ad). Ammonia synthesis is therefore most favourably run under conditions where the stationary Had-concentration is not too high, which will usually be fulfilled at the rather high reaction temperatures (≳ 700 K), even if the H2 pressure is high. Adsorbed atomic nitrogen, Ns, on the other hand, blocks the sites for hydrogen adsorption, so that also the stationary Ns-concentration should not be too high. That this latter condition will be fulfilled with a stoichiometric N2+H2 mixture at T≳580K (as long as NH3 decomposition plays no important role) was demonstrated by means of high pressure studies in which the stationary Ns-concentration was determined after evacuation. These measurements showed unequivocally that under the stated conditions dissociative nitrogen adsorption is the rate-limiting step of ammonia synthesis. Complications arise from bulk dissolution and surface segregation of atomic nitrogen which processes are affected by the presence of hydrogen.

Original languageEnglish
Pages (from-to)373-386
Number of pages14
JournalApplications of Surface Science
Volume8
Issue number4
DOIs
Publication statusPublished - 1981

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Hydrogen
Nitrogen
Iron
Adsorption
Ammonia
Surface segregation
Thermal desorption
Dissolution
Spectroscopy
Decomposition
Temperature

ASJC Scopus subject areas

  • Engineering(all)

Cite this

Interactions of nitrogen and hydrogen on iron surfaces. / Ertl, G.; Huber, M.; Lee, S. B.; Paál, Z.; Weiss, M.

In: Applications of Surface Science, Vol. 8, No. 4, 1981, p. 373-386.

Research output: Contribution to journalArticle

Ertl, G. ; Huber, M. ; Lee, S. B. ; Paál, Z. ; Weiss, M. / Interactions of nitrogen and hydrogen on iron surfaces. In: Applications of Surface Science. 1981 ; Vol. 8, No. 4. pp. 373-386.
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