Monitoring of Electrochemical Processes in Catalysts by Microwave Methods
Many electrochemical reactions occur at high temperatures and inside bulk materials. Because of the difficulties associated with a direct observation of the reaction, one often resorts to indirect measurement strategies. An example is the three-way catalyst (TWC) in the exhaust pipe of a gasoline engine which stores oxygen when it is abundant in the exhaust gas and releases it later to oxidize noxious gas components such as CO in oxygen-deficient (“lean”) exhaust gases. Currently, the oxygen loading of the TWC is derived indirectly from the output signals of two lambda probes, one upstream and the other downstream of the catalyst, which monitor the air-to-fuel ratio λ in the exhaust gas. We have investigated a microwave cavity perturbation approach towards the direct measurement of the catalyst state. It will be shown that the uptake or release of oxygen in the catalyst is observable in situ via the S-parameters of a cavity resonator.
KeywordsCavity Resonator Exhaust Pipe Perfect Electric Conductor Transverse Magnetic Mode Transverse Electric Mode
This work was supported by the German Research Foundation (DFG), grants number Fi 956/3–1 and Mo 1060/6–1. The authors are indebted to Drs. Ulrich Göbel, Jürgen Gieshoff, and Martin Rösch from Umicore, Hanau, Germany who provided TWC samples.
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