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

Paper SS2-TuM7
In-situ Investigation of the Catalytic Reaction 2 H@sub 2@ + O @sub 2@ @>=@ 2 H@sub 2@O on Pt(111) with Second Harmonic Generation

Tuesday, November 3, 1998, 10:20 am, Room 309

Session: Noble Metal Catalysis
Presenter: F. Gudmundson, Chalmers University of Technology, Sweden
Authors: F. Gudmundson, Chalmers University of Technology, Sweden
F. Eisert, University of Heidelberg, Germany
A. Rosén, Chalmers University of Technology, Sweden
Correspondent: Click to Email
Most knowledge about catalytic reactions is obtained by the use of surface analytical tools, which are restricted to ultrahigh vacuum conditions. The extrapolation to real reaction conditions at ambient pressure however is connected with a relatively high uncertainty. Nonlinear optical techniques like Second Harmonic Generation (SHG) combine the capability of in-situ investigations with an inherent surface sensitivity. We present in-situ SHG investigations of the catalytic reaction 2 H@sub 2@ + O @sub 2@ @>=@ 2 H@sub 2@ O on Pt(111) in the pressure range between 200 mtorr and 10 torr at a catalyst temperature of T=700 K. With SHG the oxygen coverage is determined as function of the hydrogen partial pressure. In the pressure range investigated, the gas flow changes from molecular flow to laminar flow. This transition has a profound influence on the experimental observed oxygen coverages. However, using a kinetic reaction model of the hydrogen oxidation developed by Hellsing, Kasemo and Zhdanov the experimental results can readily be interpreted, if the transition of the gas flow conditions from molecular to laminar flow is taken into account.