Oxygen chemisorption on flat and stepped Pt surfaces probed by an alignment-controlled O2 beam
- Mitsunori Kurahashi (National Institutes for Materials Science, Tsukuba, Japan)
- Tuesday 31 March 2020
- Hotel NH Noordwijk Conference Centre Leeuwenhorst
National Institutes for Materials Science, 1-2-1 Sengen Tsukuba Ibaraki 305-0047, Japan
O2 chemisorption on Pt surfaces has been a subject of numerous studies due to its relevance to technologically important catalytic processes such as car exhaust gas purification and oxygen reduction reaction on fuel cell electrodes. Since O2 is a linear diatomic molecule, the alignment of the O2 axis relative to the surface local structure is a key to understand the elementary processes of O2 chemisorption. Such stereochemistry in O2-surface interaction has been investigated by theoretical simulations, but there have been little experimental evidences for it. We have developed a single spin-rotational state-selected [(J,M)=(2,2)] O2 (3Σg-) beam, for which both the molecular alignment and spin orientation are well defined, using the magnetic deflection technique. Since the O2 axis is distributed mainly perpendicular to the local magnetic field (H) in this state, three non-equivalent geometries illustrated in the figure can be realized by controlling the H direction at the sample. Comparison of the reaction probabilities measured at these geometries enables us to clarify the alignment effect in O2 chemisorption in details.
In this talk, after a brief introduction of this method, its application to the study of O2 chemisorption on flat and stepped Pt surfaces will be presented. We will show that, on flat Pt(111), the O2 chemisorption probability  and CO oxidation rate are much higher in case that O2 impinges with its axis parallel to the surface, reflecting the strong alignment dependence in chemisorption barrier. On stepped Pt(553) and (533) surfaces, O2 parallel to the step is more reactive while the alignment effect depends on the local structure of the step [4,5].
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