Direct Catalyst Monitoring by Electrical Means: An Overview on Promising Novel Principles

Moos, Ralf; Wedemann, Marion; Spörl, Matthias; Reiß, Sebastian; Fischerauer, Gerhard

doi:10.1007/s11244-009-9399-6

Cited by 62 publications

(40 citation statements)

References 20 publications

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“…Typical applications are the determination of the oxygen loading of three-way catalytic converters (Moos et al, 2008Beulertz et al, 2013;Reiß et al, 2011a), or the soot loading (Sappok et al, 2010;Feulner et al, 2013) or ash loading (Kulkarni et al, 2013) of fullsized diesel particulate filters. The storage degree of NO in lean NO x traps (Fremerey et al, 2011;Moos et al, 2009) and the NH 3 loading on SCR catalyst devices have also been successfully monitored (Reiß et al, 2011b;Rauch et al, 2014Rauch et al, , 2015 using the cavity perturbation method.…”

Section: Introductionmentioning

confidence: 99%

Ammonia storage studies on H-ZSM-5 zeolites by microwave cavity perturbation: correlation of dielectric properties with ammonia storage

Dietrich

Rauch

Simon

et al. 2015

J. Sens. Sens. Syst.

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Abstract.To meet today's emission standards, the ammonia-based selective catalytic reduction (SCR) has become the major NO x control strategy for light and heavy diesel engines. Before NO x reduction can proceed, adsorption of ammonia on the acidic sites of the catalyst is necessary. For improvements in efficiency and control of the exhaust gas aftertreatment, a better understanding of the ammonia storage on the acidic sites of zeolite-based SCR catalysts is needed. Thereby, the correlation of dielectric properties of the catalyst material itself with the ammonia storage is a promising approach. Recently, a laboratory setup using microwave cavity perturbation to measure the dielectric properties of catalyst material has been described. This study shows the first experimental data on zeolite-based SCR materials in their H-form. The SCR powder samples are monitored by microwave cavity perturbation while storing and depleting ammonia, both with and without admixed NO x at different temperatures. Its complex dielectric permittivity is found to correlate closely with the stored mass of ammonia. The influence of the temperature and the Si / Al ratio of the zeolite to the ammonia storage behavior are also examined. These measurements disclose different temperature dependencies and differing sensitivities to ammonia storage for both real and imaginary parts of the complex permittivity. The apparent constant sensitivity of the real part can be related to the polarity of the adsorbed ammonia molecules, whereas the imaginary part depends on the Si / Al ratio and is related to the conductivity mechanisms of the zeolite material by proton hopping. It provides information about the zeolite structure and the number of (and the distance between) acidic storage sites, in addition to the stored ammonia mass.

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Section: Introductionmentioning

confidence: 99%

Ammonia storage studies on H-ZSM-5 zeolites by microwave cavity perturbation: correlation of dielectric properties with ammonia storage

Dietrich

Rauch

Simon

et al. 2015

J. Sens. Sens. Syst.

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“…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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“…For that purpose, it will also be investigated whether effects like catalyst aging, fouling, and sintering can also be detected by impedance measurements. Initial works in this direction have already been carried out for exhaust gas catalysts [20,21]. …”

Section: Discussionmentioning

confidence: 99%

In situ Monitoring of Coke Deposits during Coking and Regeneration of Solid Catalysts by Electrical Impedance‐based Sensors

2009

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The activity of solid catalysts is often substantially reduced by the formation of coke. The in situ monitoring of the coke load of catalyst particles could therefore be a controlling instrument of high value. Such sensors could be useful to measure the axial coke profile in a fixed bed reactor, both during coke formation and regeneration by coke burn-off. As a contribution to the development of such sensors, single particles of an alumina oxide catalyst were used as a model system. The particles were electrically contacted and characterized by electrical impedance spectroscopy. The coke formation/burn-off and the impedance were simultaneously measured in a magnetic suspension balance. A clear relationship between the coke loading and the respective electrical impedance signal could be observed, both during coke formation and during the regeneration by coke burn-off. Kinetic studies were conducted to verify the influence of mass transfer limitations on the impedance signal.

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Direct Catalyst Monitoring by Electrical Means: An Overview on Promising Novel Principles

Cited by 62 publications

References 20 publications

Ammonia storage studies on H-ZSM-5 zeolites by microwave cavity perturbation: correlation of dielectric properties with ammonia storage

Ammonia storage studies on H-ZSM-5 zeolites by microwave cavity perturbation: correlation of dielectric properties with ammonia storage

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

In situ Monitoring of Coke Deposits during Coking and Regeneration of Solid Catalysts by Electrical Impedance‐based Sensors

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