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Site blocking and CO/sulfur site exchange processes on stepped Pt surfaces
R Streber1, C Papp, M P A Lorenz
1Lehrstuhl für Physikalische Chemie II, Universität Erlangen-Nürnberg, Egerlandstraße 3, D-91054 Erlangen, Germany.
Summary
Preadsorbed sulfur passivates step sites on platinum surfaces, hindering carbon monoxide (CO) adsorption. Heating induces CO/sulfur site exchange, with different transition temperatures for Pt(355) and Pt(322) surfaces.
Area of Science:
- Surface Science
- Heterogeneous Catalysis
- Materials Science
Background:
- Understanding the interaction of adsorbates with metal surfaces is crucial for catalysis.
- Sulfur is a common catalyst poison that can modify surface reactivity.
- Platinum surfaces are widely used in catalytic applications.
Purpose of the Study:
- To investigate the influence of preadsorbed sulfur on carbon monoxide (CO) adsorption on Pt(355) and Pt(322) surfaces.
- To determine the effect of sulfur precoverage on CO adsorption sites and kinetics.
- To compare the behavior of two platinum surfaces with different step orientations.
Main Methods:
- In situ X-ray photoelectron spectroscopy (XPS) was used to monitor C 1s and S 2p core levels.
- Systematic variation of sulfur precoverages (0.02–0.30 ML) was employed.
- Experiments were conducted at different temperatures (130–245 K).
Main Results:
- Sulfur preferentially adsorbs at step sites on both Pt(355) and Pt(322) surfaces, passivating them for CO adsorption at low temperatures.
- Lower sulfur precoverage is required for passivation on Pt(322) due to S-induced double-step formation.
- Upon heating, irreversible CO/S site exchange occurs, with significantly different transition temperatures (165 K for Pt(355), 245 K for Pt(322)) at low sulfur coverages.
- The transition temperature behavior changes with increasing sulfur coverage, indicating modified surface kinetics.
Conclusions:
- Sulfur acts as a kinetic passivator of step sites on platinum surfaces at low temperatures.
- The step orientation and structure significantly influence the sulfur-CO interaction and CO/S site exchange kinetics.
- Heating lifts the kinetic passivation, allowing CO to occupy step sites via irreversible site exchange, with activation barriers dependent on surface structure and sulfur coverage.
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