AVS 51st International Symposium
    Surface Science Tuesday Sessions
       Session SS-TuP

Paper SS-TuP50
Investigation of OH Desorption Energies and Reaction Paths within the H2/O2 Reaction on a Pd Catalyst using Kinetic Modelling and Laser-induced Fluorescence

Tuesday, November 16, 2004, 4:00 pm, Room Exhibit Hall B

Session: Poster Session
Presenter: P. Bjornbom, Royal Institute of Technology, Sweden
Authors: J.C.G. Andrae, Royal Institute of Technology, Sweden
A. Johansson, Goteborg University and Chalmers, Sweden
P. Bjornbom, Royal Institute of Technology, Sweden
A. Rosen, Goteborg University and Chalmers, Sweden
Correspondent: Click to Email
A kinetic model for the H@sub 2@/O@sub 2@ reaction on a polycrystalline palladium catalyst has been constructed from experimental data. The aim was to obtain a deeper understand of the coverage-dependent OH desorption energy. The CHEMKIN software package was used in the modelling and each adsorbed oxygen atom was set to cover four Pd surface sites. The yield of OH and the water production were measured with laser-induced fluorescence (LIF) and microcalorimetry as a function of the relative hydrogen concentration, @alpha@@sub H2@. The temperature of the catalyst was 1300 K, the total pressure was 13 Pa and the flow was set to 100 SCCM. In fitting the model to the experimental data, the OH desorption energy E@super d@@sub OH@ was found to have a first-order coverage dependence according to: E@super d@@sub OH@ (@theta@)= E@super d@@sub OH@(0)-B@theta@, where @theta@ is the total coverage and B is a constant set to 92 kJ/mol. The desorption energy at zero coverage E@super d@@sub OH@(0) was determined to be 226 kJ/mol. The model could qualitatively and quantitatively reproduce the OH apparent desorption energy as a function of @alpha@@sub H2@ therefore it is believed that the coverage could be predicted by the model. It was found that the coverage on the Pd surface is in principle dominated by oxygen for all @alpha@@sub H2@. The values for E@super d@@sub OH@ (@theta@) were calculated as a function of @alpha@@sub H2@. Results of sensitivity analysis and rate of production calculations using this model imply that the main water-forming reaction on Pd at 1300 K is the hydrogen addition reaction H+OH ->H@sub 2@O.