Catalyst State Observation via the Perturbation of a Microwave Cavity Resonator

Fischerauer, Gerhard; Spörl, Matthias; Gollwitzer, A.; Wedemann, Marion; Moos, Ralf

doi:10.1515/freq.2008.62.7-8.180

Cited by 44 publications

(30 citation statements)

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“…A typical S11-spectrum around a resonance mode is shown in Figure 1b. Further details on the microwave cavity perturbation method applied in the automotive exhaust can be found in [15,18,19]. Prior investigations with this method on the state observation of three-way catalysts with the size of ∅ 4.66″ × 6″ (∅ 11.84 cm × 15.24 cm; full size as it is installed in the exhaust pipe) [11,12,20] and ∅ 1″ × 3″ (∅ 2.54 cm × 7.62 cm; typical lab sample) [6,8] have shown that there is a good correlation between the resonance parameter "resonance frequency" and the catalysts' oxidation states.…”

Section: Introductionmentioning

confidence: 99%

In operando Detection of Three-Way Catalyst Aging by a Microwave-Based Method: Initial Studies

2015

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Initial studies on aging detection of three way catalysts with a microwave cavity perturbation method were conducted. Two physico-chemical effects correlate with the aging state. At high temperatures, the resonance frequencies for oxidized catalysts (λ = 1.02) are not influenced by aging, but are significantly affected by aging in the reduced case (λ = 0.98). The catalyst aging state can therefore potentially be inferred from the resonance frequency differences between reduced and oxidized states or from the resonance frequency amplitudes during lambda oscillations. Secondly, adsorbed water at low temperatures strongly affects the resonance frequencies. Light-off experiment studies showed that the resonance frequency depends on the aging state at temperatures below the oxygen storage light-off. These differences were attributed to different water sorption capabilities of differently aged samples due to a surface area decrease with proceeding aging. In addition to the aging state, the water content in the feed gas and the temperature affect the amount of adsorbed water, leading to different integral electrical material properties of the catalyst and changing the resonance properties of the catalyst-filled canning. The classical aging-related properties of the catalyst (oxygen storage capacity, oxygen storage light-off, surface area), agreed very well with data obtained by the microwave-based method. OPEN ACCESSAppl. Sci. 2015, 5 175

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Section: Introductionmentioning

confidence: 99%

In operando Detection of Three-Way Catalyst Aging by a Microwave-Based Method: Initial Studies

2015

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“…18,19 It was even shown that the state of automobile three-way-catalysts under lean and rich synthetic exhaust gas, respectively, can be monitored qualitatively by using the catalyst housing as microwave resonator and determining its resonance characteristics in situ. 20,21 However, to the best of our knowledge MCPT has not been used to quantitatively determine the complex permittivity and conductivity of catalysts under working conditions, i.e. in a reactor at elevated temperatures in a reaction gas mixture while monitoring the catalytic performance.…”

Section: Introductionmentioning

confidence: 99%

The microwave cavity perturbation technique for contact-free and in situ electrical conductivity measurements in catalysis and materials science

Eichelbaum

Stößer

Karpov

et al. 2012

Phys. Chem. Chem. Phys.

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We have developed a noncontact method to probe the electrical conductivity and complex permittivity of single and polycrystalline samples in a flow-through reactor in the temperature range of 20-500 1C and in various gas atmospheres. The method is based on the microwave cavity perturbation technique and allows the simultaneous measurement of microwave conductivity, permittivity and of the catalytic performance of heterogeneous catalysts without any need for contacting the sample with electrodes. The sensitivity of the method towards changes in bulk properties was proven by the investigation of characteristic first-order phase transitions of the ionic conductor rubidium nitrate in the temperature range between 20 and 320 1C, and by studying the temperature dependence of the complex permittivity and conductivity of a niobium(V)-doped vanadium-phosphorous-oxide catalyst for the selective oxidation of n-butane to maleic anhydride. Simultaneously, the catalytic performance was probed by on line GC analysis of evolving product gases making the technique a real in situ method enabling the noninvasive investigation of electronic structure-function relationships.

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“…Further details of the measurement technique can be found in the literature (Fischerauer et al, 2008(Fischerauer et al, , 2010a. Microwave concepts such as electromagnetic waveguides, cavity resonators, and S-parameters are treated in many standard texts (Harrington, 1961).…”

Section: Principlementioning

confidence: 99%

Automotive Catalyst State Diagnosis Using Microwaves

Moos

Fischerauer

2014

Oil Gas Sci. Technol. – Rev. IFP Energies nouvelles

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-The state of catalysts plays a key role in automotive exhaust gas aftertreatment. The soot or ash loading of Diesel particulate filters, the oxygen loading degree in three-way catalysts, the amount of stored ammonia in SCR catalysts, or the NO x loading degree in NO x storage catalysts are important parameters that are today determined indirectly and in a model-based manner with gas sensors installed upstream and/or downstream of the catalysts. This contribution gives an overview on a novel approach to determine the catalyst state directly by a microwave-based technique. The method exploits the fact that the catalyst housing acts as a microwave cavity resonator. As "sensing" elements, one or two simple antennas are mounted inside the catalyst canning. The electrical properties of the catalyst device (ceramic honeycomb plus coating and storage material) can be measured. Preferably, the resonance characteristics, e.g., the resonance frequencies, of selected cavity modes are observed. The information on the catalyst interior obtained in such a contactless manner is very well correlated with the catalyst state as will be demonstrated for different exhaust gas aftertreatment systems.Re´sume´-Diagnostic de l'e´tat de catalyseurs d'automobiles a`l'aide de micro-ondes -L'e´tat des catalyseurs joue un roˆle essentiel dans le post-traitement des gaz d'e´chappement automobiles. Le chargement en suie ou en cendres des filtres Diesel a`particules, la teneur en oxyge`ne dans les catalyseurs trois voies, la quantite´d'ammoniac stocke´e dans les catalyseurs SCR ou le niveau de chargement en NO x dans les catalyseurs de stockage de NO x sont des parame`tres importants de´termine´s aujourd'hui de manie`re indirecte et sur la base de mode`les avec des capteurs de gaz se trouvant en amont et/ou en aval des catalyseurs. Cette contribution pre´sente une nouvelle approche permettant de de´terminer l'e´tat du catalyseur, directement en utilisant une technique a`micro-ondes. La me´thode exploite le fait que le boıˆtier du catalyseur agit comme cavite´re´sonnante de micro-ondes. En tant qu'e´le´ments de de´tection, une ou deux antennes simples sont installe´es a`l'inte´rieur du conditionnement du catalyseur. Les proprie´te´s e´lectriques du dispositif catalytique (nid d'abeille en ce´ramique plus reveˆtement et mate´riau de stockage) peuvent eˆtre mesure´es. De pre´fe´rence, les caracte´ristiques de re´sonnance, par exemple les fre´quences de re´sonnance, des modes de cavite´se´lectionne´s, sont observe´es. Les donne´es obtenues de cette manie`re sans contact, sont tre`s bien corre´le´es avec l'e´tat du catalyseur, tel que cela sera de´montre´pour diffe´rents syste`mes de post-traitement des gaz d'e´chappement.

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Catalyst State Observation via the Perturbation of a Microwave Cavity Resonator

Cited by 44 publications

References 1 publication

In operando Detection of Three-Way Catalyst Aging by a Microwave-Based Method: Initial Studies

In operando Detection of Three-Way Catalyst Aging by a Microwave-Based Method: Initial Studies

The microwave cavity perturbation technique for contact-free and in situ electrical conductivity measurements in catalysis and materials science

Automotive Catalyst State Diagnosis Using Microwaves

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