AVS 45th International Symposium
    Surface Science Division Tuesday Sessions
       Session SS2-TuM

Paper SS2-TuM5
Ab Initio Density-Functional Theory Study of CO Oxidation Over Ru(0001)

Tuesday, November 3, 1998, 9:40 am, Room 309

Session: Noble Metal Catalysis
Presenter: C. Stampfl, Fritz-Haber-Institut der MPG, Germany
Authors: C. Stampfl, Fritz-Haber-Institut der MPG, Germany
M. Scheffler, Fritz-Haber-Institut der MPG, Germany
Correspondent: Click to Email
Under "Realistic conditions'' the rate of oxidizing catalytic reactions is very much higher at ruthenium than at any other transition metal, and the dependence on the oxygen partial pressure is qualitatively different.@footnote 1@ Yet, under ultra high vacuum (UHV) conditions Ru is by far the worst catalyst, and the question was frequently raised concerning the relevance of Surface Science studies for real catalysis. Using density-functional theory we show in this contribution that the above noted "pressure gap'' phenomenon is only apparent. Thus, if understood, it can be circumvented. In particular, we investigate both a scattering reaction of CO at the O-covered surface [Eley-Rideal mechanism (E-R)]@footnote 2@ and the Langmuir-Hinshelwood (L-H) reaction. In each case the transition state corresponds to a bent CO@sub 2@-complex with an associated bond angle of 131° (E-R) and 125° (L-H). The metastability of a carbonate species is also identified which could act as an intermediory species for CO@sub 2@ production. We attribute the enhanced CO@sub 2@ formation rate at elevated gas pressures (and high coverage) to be due to the notably weaker O-Ru bond strength compared to that at lower O-coverages as are present under UHV conditions. In this respect we also report results investigating the affect of subsurface oxygen on the energetics of the reaction. Subsurface O has been proposed to be responsible for the very recently reported CO@sub 2@ reaction rates@footnote 3@ that are two orders of magnitude higher than those measured in Ref. 1. @FootnoteText@ @footnote 1@C. H. F. Peden and D. W. Goodman, J. Phys. Chem. 90, 1360 (1986). @footnote 2@C. Stampfl and M. Scheffler, Phys. Rev. Lett. 78, 1500 (1997). @footnote 3@A. Böttcher, H. Niehus, S. Schwegmann, H. Over, and G. Ertl, J. Phys. Chem. 101, 11185 (1997).