Skip to main content

Thank you for visiting You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

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.

This is a preview of subscription content, access via your institution

Relevant articles

Open Access articles citing this article.

Access options

Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

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

    Article  ADS  Google Scholar 

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

    Article  ADS  CAS  Google Scholar 

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

    CAS  Google Scholar 

  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)

    Article  CAS  Google Scholar 

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

    Google Scholar 

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

    Google Scholar 

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

    Article  ADS  CAS  Google Scholar 

  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)

    Article  ADS  CAS  Google Scholar 

  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)

    Article  ADS  CAS  Google Scholar 

  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)

    Article  ADS  Google Scholar 

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

Download references


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

Author information

Authors and Affiliations


Corresponding author

Correspondence to M. Salmeron.

Ethics declarations

Competing interests

The authors declare that they have no competing financial interests.

Supplementary information


Supplementary Movie: Hydrogen vacancy diffusion, 180 seconds. In this movie, vacancies appear as bright spots surrounded by dark rings, while the periodic background represents the 1×1 H adlayer. (MPG 552 kb)

Rights and permissions

Reprints and Permissions

About this article

Cite this article

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).

Download citation

  • Received:

  • Accepted:

  • Issue Date:

  • DOI:

This article is cited by


By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.


Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing