AVS 50th International Symposium
    Surface Science Thursday Sessions
       Session SS2-ThM

Invited Paper SS2-ThM5
STM Observation of Model Catalysts in Action: from Vacuum to High Pressures

Thursday, November 6, 2003, 9:40 am, Room 327

Session: Catalysis III: High vs. Low Pressures
Presenter: J.W.M. Frenken, Leiden University, The Netherlands
Authors: J.W.M. Frenken, Leiden University, The Netherlands
B.L.M. Hendriksen, Leiden University, The Netherlands
M. Ackermann, Leiden University, The Netherlands
S. Bobaru, Leiden University, The Netherlands
Correspondent: Click to Email
Surface-science research in the field of catalysis is plagued by the presence of a large disparity between the gas pressures acceptable in most surface-sensitive instruments and the pressures used in practical catalysis. This so-called 'pressure gap' can easily be as large as ten orders of magnitude. One may expect that there are several phenomena that behave non-linearly over this enormous pressure range, which makes it difficult, and in some cases even impossible to simply extrapolate the results of low-pressure experiments to the high-pressure reality of catalysis. In order to bridge the pressure gap, we have recently constructed a special-purpose STM, which is integrated with a tiny flow reactor cell. Only the tip of the STM is inside the reactor. With this new instrument, we have obtained a first atomic-scale look at 'live' (model) catalysts, while they were active under semi-realistic conditions, namely high pressures and elevated temperatures. Simultaneously with the STM-observation, the instrument can analyze the composition of the gas leaving the reactor. Results will be shown for CO-oxidation on Pt(110), Pt(111), and Pd(001). These results reveal a new reaction mechanism, the so-called 'Mars-van-Krevelen'-mechanism, which is only active at high pressures. On each of these surfaces, the surface structure and the chemical reactivity are observed to switch simultaneously at a specific pressure ratio between O@sub2@ and CO. In each case, the most active structure is identified as a thin surface oxide, which takes part in the reaction with CO. @FootnoteText@ @footnote 1@ B.L.M. Hendriksen and J.W.M. Frenken, Phys.Rev. Lett. 89 (2002) 046101.@footnote 2@ STM movies of cataysts in action can be viewed on our website: http://www.physics.leidenuniv.nl/sections/cm/ip.