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Recently, it has been shown that the degree of loading of several types of automotive exhaust aftertreatment devices can be directly monitored in situ and in a contactless way by a microwave-based method. The goal of this study was to clarify whether this method can also be applied to NOx storage and reduction catalysts (lean NOx traps) in order to obtain further knowledge about the reactions occurring in the catalyst and to compare the results with those obtained by wirebound NOx loading sensors. It is shown that both methods are able to detect the different catalyst loading states. However, the sensitivity of the microwave-based method turned out to be small compared to that previously observed for other exhaust aftertreatment devices. This may limit the practical applicability of the microwave-based NOx loading detection in lean NOx traps.

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Very often, high-temperature operated gas sensors are cross-sensitive to oxygen and/or they cannot be operated in oxygen-deficient (rich) atmospheres. For instance, some metal oxides like Ga2O3 or doped SrTiO3 are excellent materials for conductometric hydrocarbon detection in the rough atmosphere of automotive exhausts, but have to be operated preferably at a constant oxygen concentration. We propose a modular sensor platform that combines a conductometric two-sensor-setup with an electrochemical pumping cell made of YSZ to establish a constant oxygen concentration in the ambient of the conductometric sensor film. In this paper, the platform is introduced, the two-sensor-setup is integrated into this new design, and sensing performance is characterized. Such a platform can be used for other sensor principles as well.

The novel integrating NO x gas sensor concept provides the opportunity to detect very low NO x levels, as they appear for instance downstream of automotive catalytic converters, with a high sensitivity and accuracy. Unlike common gas sensors, the integrating NO x sensor detects the amount of NO x during the measurement period instead of the actual NO x concentration. The integrating sensing concept is realized by using a lean NO x trap material as sensitive layer, accumulating a constant fraction of the upcoming exhaust NO x molecules in the sensitive layer. The chemical storage of NO x in the form of nitrates goes along with a change in the electrical properties of the lean NO x trap material serving as sensor signal. In this contribution, the details of the integrating sensing concept are explained and the benefits of this novel gas sensing method are pointed out. The measurement data demonstrate the integrating properties of the NO x sensor. In addition, the issues of varying NO x concentrations and sensitivities to both NO and NO 2 are addressed.

Das integrierende (akkumulierende) Messprinzip ist ein sehr vielversprechendes Verfahren, mit dem selektiv kleinste Mengen an Analyt mit einer hohen Genauigkeit detektiert werden können. Dabei wird die Änderung der elektrischen Eigenschaften eines Speichermaterials infolge der Sorption des Analyten gemessen. In bisherigen Arbeiten zum integrierenden NO x -Sensor wurde das Hauptaugenmerk auf die integrierenden Eigenschaften bezüglich der Konzentration gelegt. Mit diesem ersten Design war es nur möglich, unabhängig von der Gasgeschwindigkeit zu messen. Mit dem vorgestellten neuen Sensordesign kann nun abhängig von Analytkonzentration und Volumenstrom die tatsächliche geflossene Menge einer Gasspezies selektiv detektiert werden. Bild 1 a) Sensordesign zur Integration der KonzentrationDas integrierende Messverfahren bietet eine Reihe an Vorteilen gegenüber herkömmlichen Gassensoren. Zum Einen können selbst kleinste Mengen an Analytgas in der sensitiven Schicht gespeichert werden und somit zur Signaländerung beitragen. Indem man die zeitliche Ableitung des Signals bei konstanter

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