Dissociative hydrogen adsorption on palladium requires aggregates of three or more vacancies


During reaction, a catalyst surface usually interacts with a constantly fluctuating mix of reactants, products, ‘spectators’ that do not participate in the reaction, and species that either promote or inhibit the activity of the catalyst. How molecules adsorb and dissociate under such dynamic conditions is often poorly understood. For example, the dissociative adsorption of the diatomic molecule H2—a central step in many industrially important catalytic processes—is generally assumed1 to require at least two adjacent and empty atomic adsorption sites (or vacancies). The creation of active sites for H2 dissociation will thus involve the formation of individual vacancies and their subsequent diffusion and aggregation2,3,4,5,6, with the coupling between these events determining the activity of the catalyst surface. But even though active sites are the central component of most reaction models, the processes controlling their formation, and hence the activity of a catalyst surface, have never been captured experimentally. Here we report scanning tunnelling microscopy observations of the transient formation of active sites for the dissociative adsorption of H2 molecules on a palladium (111) surface. We find, contrary to conventional thinking1, that two-vacancy sites seem inactive, and that aggregates of three or more hydrogen vacancies are required for efficient H2 dissociation.

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Figure 1: STM images of hydrogen atoms on Pd(111).
Figure 2: STM images from a movie showing the formation, separation and annihilation of H-vacancy clusters.
Figure 3: STM images from a movie showing the formation and annihilation of a four-vacancy (4V) cluster.
Figure 4: Lifetimes of three-vacancy clusters.


  1. 1

    Conrad, H., Ertl, G. & Latta, E. E. Adsorption of hydrogen on palladium single crystal surfaces. Surf. Sci. 41, 435–446 (1974)

    ADS  Article  Google Scholar 

  2. 2

    Taylor, H. S. Theory of the catalytic surface. Proc. R. Soc. Lond. A 108, 105–111 (1925)

    ADS  CAS  Article  Google Scholar 

  3. 3

    Boudart, M. Four decades of active centers. Am. Sci. 57, 97–111 (1969)

    CAS  Google Scholar 

  4. 4

    Ponec, V. & Sachtler, W. M. H. The reactions between cyclopentane and deuterium on nickel and nickel-copper alloys. J. Catal. 24, 250–261 (1972)

    CAS  Article  Google Scholar 

  5. 5

    Sinfelt, J. H. Bimetallic Catalysts: Discoveries, Concepts and Applications (Wiley and Sons, New York, 1983)

    Google Scholar 

  6. 6

    Somorjai, G. A. Introduction to Surface Chemistry and Catalysis (Wiley and Sons, New York, 1994)

    Google Scholar 

  7. 7

    Behler, S. et al. A scanning tunneling microscope with continuous flow cryostat sample cooling. Rev. Sci. Instrum. 68, 2479–2485 (1997)

    ADS  CAS  Article  Google Scholar 

  8. 8

    Felter, T. E., Sowa, E. C. & Van Hove, M. A. Location of hydrogen on palladium (111) studied by low-energy electron diffraction. Phys. Rev. B 40, 891–899 (1989)

    ADS  CAS  Article  Google Scholar 

  9. 9

    Paul, J. F. & Sautet, P. Density-functional periodic study of the adsorption of hydrogen on a palladium (111) surface. Phys. Rev. B 53, 8015–8027 (1996)

    ADS  CAS  Article  Google Scholar 

  10. 10

    Lovvik, O. M. & Olsen, R. A. Adsorption energies and ordered structures of hydrogen on Pd(111) from density functional periodic calculations. Phys. Rev. B 58, 10890–10898 (1998)

    ADS  Article  Google Scholar 

  11. 11

    Mitsui, T., Rose, M. K., Fomin, E., Ogletree, D. F. & Salmeron, M. Hydrogen adsorption and diffusion on Pd(111). Surf. Sci. (submitted)

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This work was supported by the Office of Basic Energy Science of the US Department of Energy.

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Correspondence to M. Salmeron.

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Mitsui, T., Rose, M., Fomin, E. et al. Dissociative hydrogen adsorption on palladium requires aggregates of three or more vacancies. Nature 422, 705–707 (2003). https://doi.org/10.1038/nature01557

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