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Water desorption from an oxygen covered Pt(111) surface: multichannel desorption
G S Karlberg1, G Wahnström, C Clay
1Department of Applied Physics, Chalmers University of Technology, S-41296 Göteborg, Sweden. guka@fy.chalmers.se
The Journal of Chemical Physics
|June 16, 2006
Summary
Water desorption from platinum surfaces is complex, involving multiple pathways and influenced by surface structure. This study reveals intricate kinetics and hydrogen bonding effects on OH/H2O decomposition near 200 K.
Area of Science:
- Surface Science
- Physical Chemistry
- Materials Science
Background:
- Mixed OH/H2O structures form on Pt(111) from O and water reactions.
- These structures decompose near 200 K with water desorption.
- Water desorption kinetics are non-simple, with varying activation barriers.
Purpose of the Study:
- To investigate the complex desorption kinetics of mixed OH/H2O structures on Pt(111).
- To understand the role of hydrogen bonding and surface defects in water desorption.
- To elucidate the multiple desorption pathways and rate-determining steps.
Main Methods:
- First-principles calculations to develop a model potential.
- Monte Carlo simulations of water desorption using the derived potential.
- Analysis of apparent activation barriers dependent on film composition, coverage, and heating rate.
Main Results:
- Water desorption exhibits complex kinetics, not following simple rate laws, with activation barriers ranging from 0.42 to 0.86 eV.
- A complete hydrogen bonding network stabilizes the adsorbate, enhancing decomposition.
- Desorption occurs via multiple pathways including direct, proton-transfer mediated, and OH recombination, with no single rate-determining step.
Conclusions:
- Water desorption is preferential from low-coordination defect or edge sites.
- The complex kinetics are sensitive to temperature, composition, and sample history.
- Understanding these mechanisms is crucial for catalytic processes involving water and oxygen on platinum surfaces.