Abstract
Ammonia decomposition on Ir(100) has been studied over the pressure range from ultrahigh vacuum to 1.5 Torr and at temperatures ranging from 200 to 800 K. The kinetics of the ammonia decomposition reaction was monitored by total pressure change. The apparent activation energy obtained in this study (84 kJ/mol) is in excellent agreement with our previous studies using supported Ir catalysts (Ir/Al2O3 82 kJ/mol). Partial pressure dependence studies of the reaction rate yielded a positive order (0.9±0.1) with respect to ammonia and negative order (−0.7 ±0.1) with respect to hydrogen. Temperature-programmed desorption data from clean and hydrogen co-adsorbed Ir(100) surfaces indicate that ammonia undergoes facile decomposition on both these surfaces. Recombinative desorption of N2 is the rate-determining step with a desorption activation energy of ∼63 kJ/mol. Co-adsorption data also indicate that the observed negative order with respect to hydrogen pressure is due to enhancement of the reverse reaction (NH x + H → NH x+1, x=0–2) in the presence of excess H atoms on the surface.
Similar content being viewed by others
References
J.R. Rostrup-Nielsen, in: Catalytic Steam Reforming, Science and Engineering, Vol. 5, eds. J.R. Anderson and M. Boudart Springer, Berlin, (1984).
J.N. Armor, Appl. Catal. 176 (1999) 159.
T.V. Choudhary and D.W. Goodman, Catal. Lett. 59 (1999) 93.
T.V. Choudhary and D.W. Goodman, J. Catal. 192 (2000) 316.
T.V. Choudhary, C. Sivadinarayana, C. Chusuei, A. Klinghoffer and D.W. Goodman, J. Catal. 199 (2001) 9.
T.V. Choudhary, C. Sivadinarayana, A. Klinghoffer and D.W. Goodman, Stud. Surf. Sci. Catal., in press.
R. Metkemeijer and P. Achard, Int. J. Hydrogen Energy 19 (1994) 535; J. Power Sources 49 (1994) 271.
R. Metkemeijer and P. Achard, J. Power Sources 49 (1994) 271.
M. Asscher and Z. Rosenzweig, Surf. Sci. 225 (1990) 249.
Y.K. Sun, Y. Q. Wang, C.B. Mullin and W.H. Weinberg, Langmuir 7 (1991) 1689; W. Tsai and W. H. Weinberg, J. Phys. Chem. 91 (1987) 5302; C. Egawa, T. Nishida, S. Naito and K. Tamaru, J. Chem. Soc. Faraday Trans. 80 (1984) 1595; J.M. Bradeley, A. Hopkinson and D.A. King, Surf. Sci. 371 (1997) 255.
W. Tsai, J.J. Vajo and W.H. Weinberg, J. Phys. Chem. 89 (1985) 4926; J.J. Vajo,W. Tsai andW.H.Weinberg, J. Phys. Chem. 90 (1986) 6531; 89 (1985) 3243; D.G. Loffler and L.D. Schmidt, Surf. Sci. 59 (1976) 195.
C. Egawa, S. Naito and K. Tamaru, Surf. Sci. 131 (1983) 49; M. Grossman and D.G. Loffler, J. Catal. 80 (1983) 188; A.P.C. Reed and R.M. Lambert, J. Phys. Chem. 88 (1983) 1955.
I.C. Bassignana, K. Wagemann, J. Kuppers and G. Ertl, Surf. Sci. 175 (1986) 22; M. Huttinger and J. Kuppers, Surf. Sci. 130 (1983) L277; D. Chrysostomou, J. Flowers and F. Zaera, Surf. Sci. 439 (1999) 34.
G. Papapolymerou and V. Bontozoglou, J. Mol. Catal. A 120 (1997) 165.
R.W. McCabe, J. Catal. 79 (1983) 445.
E. Schmidt, Hydrazine and its Derivatives, Preparation, Properties, Applications (Wiley, New York, 1984).
T.V. Choudhary and D.W. Goodman, J. Mol. Catal. 163 (2000) 9.
C. Xu, W.S. Oh, D.Y. Kim and D.W. Goodman, J. Vac. Sci. Technol. A 15 (1997) 1261.
T.V. Choudhary, C. Sivadinarayana and D.W. Gooodman, Catal. Lett. 72 (2001) 197.
M. Grossman and D.G. Loffler, React. Kinet. Catal. Lett. 33 (1987) 87.
A.K. Santra, B.K. Min, C.-W. Yi, T.V. Choudhary and D.W. Goodman, in preparation.
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Choudhary, T., Santra, A., Sivadinarayana, C. et al. Ammonia Decomposition on Ir(100): From Ultrahigh Vacuum to Elevated Pressures. Catalysis Letters 77, 1–5 (2001). https://doi.org/10.1023/A:1012754319273
Issue Date:
DOI: https://doi.org/10.1023/A:1012754319273