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
Article

Abstract

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.

Keywords

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

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

References

  1. [1]
    J.R. Jennings, ed.,Catalytic Ammonia Synthesis, 1st Ed. (Plenum Press, New York, 1991).Google Scholar
  2. [2]
    M. Boudart and G. Djéga-Mariadassou,Kinetics of Heterogeneous Catalytic Reactions, 1st Ed. (Princeton Univ. Press, Princeton, 1984).Google Scholar
  3. [3]
    R. Schlögl, R.C. Schoonmaker, M. Muhler and G. Ertl, Catal. Lett. 1 (1988) 237.Google Scholar
  4. [4]
    F. Bozso, G. Ertl, M. Grunze and M. Weiss, J. Catal. 49 (1977) 18.Google Scholar
  5. [5]
    F. Bozso, G. Ertl and M. Weiss, J. Catal. 50 (1977) 519.Google Scholar
  6. [6]
    G. Ertl, S. Lee and M. Weiss, Surf. Sci. 114 (1982) 515.Google Scholar
  7. [7]
    G. Ertl, S. Lee and M. Weiss, Surf. Sci. 114 (1982) 527.Google Scholar
  8. [8]
    M. Bowker, I. Parker and K.C. Waugh, Appl. Catal. 14 (1985) 101.Google Scholar
  9. [9]
    M. Bowker, I. Parker and K.C. Waugh, Surf. Sci. 197 (1988) L223.Google Scholar
  10. [10]
    I. Parker, K.C. Waugh and M. Bowker, J. Catal. 114 (1988) 457.Google Scholar
  11. [11]
    M. Bowker, Catal. Today 12 (1992) 153.Google Scholar
  12. [12]
    C.T. Rettner and H. Stein, Phys. Rev. Lett. 59 (1987) 2768.Google Scholar
  13. [13]
    C.T. Rettner and H. Stein, J. Chem. Phys. 87 (1987) 770.Google Scholar
  14. [14]
    H.D. Vandervell and K.C. Waugh, Chem. Phys. Lett. 171 (1990) 462.Google Scholar
  15. [15]
    M. Muhler, L.P. Nielsen and B. Fastrup, Chem. Phys. Lett. 181 (1991) 380.Google Scholar
  16. [16]
    K.C. Waugh, D. Butler and B.E. Hayden, Catal. Lett. 24 (1994) 197.Google Scholar
  17. [17]
    M. Muhler, L.P. Nielsen, E. Törnqvist, B.S. Clausen and H. Topsøe, Catal. Lett. 14 (1992) 241.Google Scholar
  18. [18]
    P. Stoltze and J.K. Nørskov, Phys. Rev. Lett. 55 (1985) 2502.Google Scholar
  19. [19]
    P. Stoltze and J.K. Nørskov, Surf. Sci. 197 (1988) L230.Google Scholar
  20. [20]
    P. Stoltze, Phys. Scripta 36 (1987) 824.Google Scholar
  21. [21]
    J.A. Dumesic and A.A. Trevino, J. Catal. 116 (1989) 119.Google Scholar
  22. [22]
    R. Imbihl, R.J. Behm, G. Ertl and W. Moritz, Surf. Sci. 123 (1982) 129.Google Scholar
  23. [23]
    J. Scholten, P. Zwietering, J. Konvalinka and J. de Boer, Trans. Faraday Soc. 55 (1959) 2166.Google Scholar
  24. [24]
    B. Fastrup, M. Muhler, H.N. Nielsen and L.P. Nielsen, J. Catal. 142 (1993) 135.Google Scholar
  25. [25]
    B. Fastrup and H.N. Nielsen, Catal. Lett. 14 (1992) 233.Google Scholar
  26. [26]
    T.Z. Srnak, J.A. Dumesic, B.S. Clausen, E. Törnqvist and N.-Y. Topsøe, J. Catal. 135 (1992) 246.Google Scholar
  27. [27]
    A. Nielsen, J. Kjaer and B. Hansen, J. Catal. 3 (1964) 68.Google Scholar
  28. [28]
    J.A. Dumesic, D.F. Rudd, L.M. Aparicio, J.E. Rekoske and A.A. Trevino,The Microkinetics of Heterogeneous Catalysis, ACS professional reference book (Am. Chem. Soc., Washington, 1993).Google Scholar
  29. [29]
    H.J. Grabke, Z. Phys. Chem. NF 100 (1976) 185.Google Scholar
  30. [30]
    W. Mahdi, J. Schütze, G. Weinberg, R.C. Schoonmaker, R. Schlögl and G. Ertl, Catal. Lett. 11 (1991) 19.Google Scholar
  31. [31]
    J. Scholten and P. Zwietering, Trans. Faraday Soc. 53 (1957) 1363.Google Scholar
  32. [32]
    Z. Paal, G. Ertl and S.B. Lee, Appl. Surf. Sci. 8 (1981) 231.Google Scholar
  33. [33]
    M. Muhler, F. Rosowski, B. Fastrup and G. Ertl, to be published.Google Scholar
  34. [34]
    Y. Amenomiya and G. Plezier, J. Catal. 28 (1973) 442.Google Scholar

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

Personalised recommendations