Catalysis Letters

, Volume 24, Issue 3–4, pp 317–331 | Cite as

The dissociative adsorption of N2 on a multiply promoted iron catalyst used for ammonia synthesis: a temperature-programmed desorption study

  • M. Muhler
  • F. Rosowski
  • G. Ertl


The temperature-programmed desorption (TPD) of N2 from a multiply promoted iron catalyst used for ammonia synthesis has been studied in a microreactor system at atmospheric pressure. From TPD experiments with various heating rates a preexponential factorA = 2 × 109 molecules/site s and an activation energyE = 146 kJ/mol was derived assuming second-order desorption. The observed dependence of the TPD peak shapes on the heating rates indicated the influence of readsorption of N2 in agreement with the results obtained for various initial coverages. Simulating the N2 TPD curves using the model by Stoltze and Nørskov revealed that the calculated TPD curves were not influenced by the molecular precursor to desorption. However, the calculated rate of readsorption was found to be overestimated at high coverage compared with the experimental results. A coverage-dependent net activation energy for dissociative chemisorption (E*) was introduced as the simplest assumption rendering the dissociative chemisorption of N2 activated at high coverage. The best fit of the experimental data yieldedE* = (−15+30θ) kJ/mol using only a single type of atomic nitrogen species. These findings are in satisfactory agreement with the parameters underlying the Stoltze-Nørskov model for the kinetics of ammonia synthesis as well as with the data reported for Fe(111) single crystal surfaces.


Nitrogen adsorption N2 TPD iron-based catalyst ammonia synthesis microkinetic analysis 


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Copyright information

© J.C. Baltzer AG, Science Publishers 1994

Authors and Affiliations

  • M. Muhler
    • 1
  • F. Rosowski
    • 1
  • G. Ertl
    • 1
  1. 1.Fritz-Haber-Institut der Max-Planck-GesellschaftBerlinGermany

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