Microwave Cavity Perturbation as a Tool for Laboratory In Situ Measurement of the Oxidation State of Three Way Catalysts

Three-way catalyst-based automotive exhaust gas aftertreatment is of high importance to meet today’s emission standards. To determine in situ the oxygen loading state of three-way catalysts, a microwave cavity perturbation method is used. In this study, it is investigated whether this measurement setup that had originally been described for full-sized catalysts can be transferred to a lab test bench using cores of 1″ diameter. The initial tests were successful and a high correlation between the oxygen loading degree dependent resonance frequency and the conversion was found. As an application example of the new in situ characterization technique, the steady state degree of oxidation of a three way catalyst was measured as a function of the exhaust stoichiometry. The experimental results are compared with the prediction of a recently published improved kinetic model that takes into account the oxidation of reduced ceria by H2O and CO2. It is shown that the experimental observations agree very well with this improved model. This result provides evidence that under typical operating conditions, the degree of oxidation of the three way catalyst is controlled by equilibrium effects.

[1]  O Deutschmann,et al.  Detailed surface reaction mechanism in a three-way catalyst. , 2001, Faraday discussions.

[2]  Martin Votsmeier,et al.  Overview: Status of the Microwave-Based Automotive Catalyst State Diagnosis , 2013, Topics in Catalysis.

[3]  Ralf Moos,et al.  Mikrowellengestützte Aufklärung elektrochemischer Vorgänge in Katalysatoren und verwandten Systemen , 2010 .

[4]  R. Moos,et al.  Monitoring of Electrochemical Processes in Catalysts by Microwave Methods , 2011 .

[5]  Ralf Moos,et al.  Catalysts as Sensors—A Promising Novel Approach in Automotive Exhaust Gas Aftertreatment , 2010, Sensors.

[6]  Lino Guzzella,et al.  Is oxygen storage in three-way catalysts an equilibrium controlled process? , 2009 .

[7]  Ichiro Matsubara,et al.  Response properties of resistive oxygen sensors using Ce1−xZrxO2 (x = 0.05, 0.10) thick films in propane combustion gas , 2008 .

[8]  Ralf Moos,et al.  Direct Catalyst Monitoring by Electrical Means: An Overview on Promising Novel Principles , 2009 .

[9]  Ralf Moos,et al.  Effects of H2O, CO2, CO, and flow rates on the RF-based monitoring of three-way catalysts , 2011 .

[10]  Gunter Hagen,et al.  Combination of Wirebound and Microwave Measurements for In Situ Characterization of Automotive Three-Way Catalysts , 2011, IEEE Sensors Journal.

[11]  Ralf Moos,et al.  Catalyst State Observation via the Perturbation of a Microwave Cavity Resonator , 2008 .

[12]  T. Jungkunz,et al.  Modellgestützte Bestimmung der komplexen Permittivität heterogener Katalysatoren im instationären Fall , 2012 .

[13]  Gunter Hagen,et al.  TWC: Lambda Control and OBD without Lambda Probe - An Initial Approach , 2008 .