Berlin 2008 – scientific programme

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O: Fachverband Oberflächenphysik

O 90: Methods: Scanning Probe Techniques II

O 90.5: Talk

Friday, February 29, 2008, 11:15–11:30, MA 042

Studying the spatial distribution of reactant gases above catalytically active microstructures by means of scanning mass spectrometry — •Matthias Roos, Stefan Kielbassa, Joachim Bansmann, and Rolf Juergen Behm — Institute of Surface Chemisty and Catalysis, Ulm University, D-89069 Ulm, Germany

We present an apparatus for spatially resolving scanning mass spectrometry for measuring the 3D gas composition above planar catalytically active surfaces, which enables us to quantitatively determine local reaction rates, e.g., on individual fields of microstructured model catalysts. A piezo-electrically driven positioning substage allows control of the lateral and vertical positioning of the sample under a stationary capillary probe with micrometer-scale resolution. The diameter of the capillary orifice, connecting the reaction chamber with a differentially pumped quadrupole mass spectrometer, varies from 50 to 150 µm, depending on the used capillary. Measurements can be performed at pressures in the range of 10⁻³ − 10 mbar and temperatures between room temperature and 450^∘C. The CO oxidation reaction on planar Pt microstructures was used as a test reaction for determining the lateral resolution of the setup and the spatial distribution of reactant gases. The CO₂ formation and CO consumption above the microstructures was evaluated as function of lateral displacement and distance between sample and probe to study the effects of gas transport in the regime between sample and probe. Furthermore, the feasibility of determining absolute reaction rates on individual microstructures is demonstrated.