Carbon monoxide oxidation at the interface of a direct barrier discharge and a thin layer of Yttria-stabilized Zirconia : characterization of discharge properties and determination of reaction rates
This thesis investigates the carbon monoxide oxidation at the interface between a Direct Barrier Discharge (DBD) and a thin layer of Yttria-stabilized Zirconia (YSZ), which is an oxygen ion conductor. The thin film is deposited on a dielectric consisting of fused silica. The aim of this work was to investigate the reaction rates of the carbon monoxide oxidation according to the new concept of heterogeneous plasma catalysis with an oxygen ion conducting catalyst. In this work the uncoated fused silica dielectrics were used as reference system and compared with coated dielectrics with a thin YSZ film. The temperature dependent behavior of this system and the discharge itself was monitored as there should be differences according to the thermally activated electrode kinetics and oxygen transport processes in the bulk. A second aspect of the investigations was the frequency dependent behavior of the discharge and the influence of the discharge frequency on the catalytic rate enhancement.The different discharge setups were investigated according to the distribution of the ionic and excited species with Optical Emission Spectroscopy (OES). Theses results were compared with data obtained by Quadrupol Mass Spectroscopy (QMS). Additionally plasma ignition voltages according to the different discharge compositions at room and elevated temperatures were measured.The QMS signal intensities were used to compare carbon dioxide reaction rates of the reference and the YSZ coated discharge setups. The obtained data was used to discuss possible kinetic models.The OES investigations showed that the discharge is strongly influenced by the carbon monoxide gas. The dominant lines recorded are related to CO+ ions, only at very low CO partial pressures lines of Ar+ occur. Only rarely and with decreasing intensity at higher oxygen partial pressures oxygen emission lines can be found. This might be a clue to increased concentrations of negatively charged oxygen ions.With all performed observations it can be concluded that the thin film deposition of a YSZ layer on a fused silica dielectric enhances the reaction rate of the carbon monoxide oxidation due to a discharge YSZ surface interaction or to a YSZ surface restructuring, which takes especially place at room temperature conditions. Possible kinetic models were proposed.
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