Dosimeter-Type NOx Sensing Properties of KMnO4 and Its Electrical Conductivity during Temperature Programmed Desorption.

An impedimetric NO_x dosimeter based on the NO_x sorption material KMnO₄ is proposed. In addition to its application as a low level NO_x dosimeter, KMnO₄ shows potential as a precious metal free lean NO_x trap material (LNT) for NO_x storage catalysts (NSC) enabling electrical in-situ diagnostics. With this dosimeter, low levels of NO and NO₂ exposure can be detected electrically as instantaneous values at 380°C by progressive NO_x accumulation in the KMnO₄ based sensitive layer. The linear NO_x sensing characteristicsare recovered periodically by heating to 650°C or switching to rich atmospheres. Further insight into the NO_x sorption-dependent conductivity of the KMnO₄-based material is obtained by the novel eTPD method that combines electrical characterization with classical temperature programmed desorption (TPD). The NO_x loading amount increases proportionally to the NO_x exposure time at sorption temperature. The cumulated NO_x exposure, as well as the corresponding NO_x loading state, can be detected linearly by electrical means in two modes: (1) time-continuously during the sorption interval including NO_x concentration information from the signal derivative or (2) during the short-term thermal NO_x release. [ABSTRACT FROM AUTHOR]