Limits...
Dosimeter-type NOx sensing properties of KMnO4 and its electrical conductivity during temperature programmed desorption.

Groß A, Kremling M, Marr I, Kubinski DJ, Visser JH, Tuller HL, Moos R - Sensors (Basel) (2013)

Bottom Line: An impedimetric NOx dosimeter based on the NOx sorption material KMnO4 is proposed.With this dosimeter, low levels of NO and NO2 exposure can be detected electrically as instantaneous values at 380 °C by progressive NOx accumulation in the KMnO4 based sensitive layer.The linear NOx sensing characteristics are recovered periodically by heating to 650 °C or switching to rich atmospheres.

View Article: PubMed Central - PubMed

Affiliation: Zentrum für Energietechnik, Bayreuth Engine Research Center (BERC), Department of Functional Materials, University of Bayreuth, 95440 Bayreuth, Germany. andrea.gross@uni-bayreuth.de

ABSTRACT
An impedimetric NOx dosimeter based on the NOx sorption material KMnO4 is proposed. In addition to its application as a low level NOx dosimeter, KMnO4 shows potential as a precious metal free lean NOx trap material (LNT) for NOx 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 NOx accumulation in the KMnO4 based sensitive layer. The linear NOx sensing characteristics are recovered periodically by heating to 650 °C or switching to rich atmospheres. Further insight into the NOx 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 NOx loading amount increases proportionally to the NOx exposure time at sorption temperature. The cumulated NOx exposure, as well as the corresponding NOx loading state, can be detected linearly by electrical means in two modes: (1) time-continuously during the sorption interval including NOx concentration information from the signal derivative or (2) during the short-term thermal NOx release.

No MeSH data available.


Related in: MedlinePlus

NOx sensing properties at 380 °C (10% O2, 50% N2/H2O, 5% CO2 in N2): (a) stepwise increase of sensor response ΔRrel (Equation (3)) during cyclic exposure to NO or NO2, (b) resulting linear ΔRrelvs. ANOx,in characteristic line.
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC3673092&req=5

f5-sensors-13-04428: NOx sensing properties at 380 °C (10% O2, 50% N2/H2O, 5% CO2 in N2): (a) stepwise increase of sensor response ΔRrel (Equation (3)) during cyclic exposure to NO or NO2, (b) resulting linear ΔRrelvs. ANOx,in characteristic line.

Mentions: The presence of NOx was found to decrease the resistivity of KMnO4/La-Al2O3, with the electrical response continuing to satisfy the R‖C equivalent circuit (not shown). The temporal dependence of R on NOx at 380 °C was studied by exposing the sample to pulses of NO and NO2 for periods of tNOx,in = 100 s with concentrations ranging up to 16 ppm. The pulse heights in terms of cNO,in and cNO2,in, together with the resulting sensor response, are displayed in Figure 5(a). The sensor response ΔRrel (Equation (3)) increases stepwise in the presence of NO and NO2 without any recovery at 0 ppm NOx. The slope of ΔRrelvs. t increases with cNOx,in. The characteristic line in Figure 5(b) is extracted from the measured data points and the course of the NOx concentration according to Figure 4. ΔRrel correlates almost linearly with the cumulated NOx exposure ANOx,in, independent of the NOx species, up to at least 40% signal change with a NOx sensitivity of 4.8%/1,000 ppm·s. The specimen thus provides comparable sensitivity to both NO and NO2. Small deviations of the NO2 related data points from linearity at the initial stage of exposure may originate from NO2 adsorption on the inner surface of the feed lines. The sensing characteristics and in particularly the sensitivity of NOx dosimeter with a comparable sensitive material were found to be dependent on the temperature as well as on the thickness of the sensitive layer [6,16].


Dosimeter-type NOx sensing properties of KMnO4 and its electrical conductivity during temperature programmed desorption.

Groß A, Kremling M, Marr I, Kubinski DJ, Visser JH, Tuller HL, Moos R - Sensors (Basel) (2013)

NOx sensing properties at 380 °C (10% O2, 50% N2/H2O, 5% CO2 in N2): (a) stepwise increase of sensor response ΔRrel (Equation (3)) during cyclic exposure to NO or NO2, (b) resulting linear ΔRrelvs. ANOx,in characteristic line.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3673092&req=5

f5-sensors-13-04428: NOx sensing properties at 380 °C (10% O2, 50% N2/H2O, 5% CO2 in N2): (a) stepwise increase of sensor response ΔRrel (Equation (3)) during cyclic exposure to NO or NO2, (b) resulting linear ΔRrelvs. ANOx,in characteristic line.
Mentions: The presence of NOx was found to decrease the resistivity of KMnO4/La-Al2O3, with the electrical response continuing to satisfy the R‖C equivalent circuit (not shown). The temporal dependence of R on NOx at 380 °C was studied by exposing the sample to pulses of NO and NO2 for periods of tNOx,in = 100 s with concentrations ranging up to 16 ppm. The pulse heights in terms of cNO,in and cNO2,in, together with the resulting sensor response, are displayed in Figure 5(a). The sensor response ΔRrel (Equation (3)) increases stepwise in the presence of NO and NO2 without any recovery at 0 ppm NOx. The slope of ΔRrelvs. t increases with cNOx,in. The characteristic line in Figure 5(b) is extracted from the measured data points and the course of the NOx concentration according to Figure 4. ΔRrel correlates almost linearly with the cumulated NOx exposure ANOx,in, independent of the NOx species, up to at least 40% signal change with a NOx sensitivity of 4.8%/1,000 ppm·s. The specimen thus provides comparable sensitivity to both NO and NO2. Small deviations of the NO2 related data points from linearity at the initial stage of exposure may originate from NO2 adsorption on the inner surface of the feed lines. The sensing characteristics and in particularly the sensitivity of NOx dosimeter with a comparable sensitive material were found to be dependent on the temperature as well as on the thickness of the sensitive layer [6,16].

Bottom Line: An impedimetric NOx dosimeter based on the NOx sorption material KMnO4 is proposed.With this dosimeter, low levels of NO and NO2 exposure can be detected electrically as instantaneous values at 380 °C by progressive NOx accumulation in the KMnO4 based sensitive layer.The linear NOx sensing characteristics are recovered periodically by heating to 650 °C or switching to rich atmospheres.

View Article: PubMed Central - PubMed

Affiliation: Zentrum für Energietechnik, Bayreuth Engine Research Center (BERC), Department of Functional Materials, University of Bayreuth, 95440 Bayreuth, Germany. andrea.gross@uni-bayreuth.de

ABSTRACT
An impedimetric NOx dosimeter based on the NOx sorption material KMnO4 is proposed. In addition to its application as a low level NOx dosimeter, KMnO4 shows potential as a precious metal free lean NOx trap material (LNT) for NOx 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 NOx accumulation in the KMnO4 based sensitive layer. The linear NOx sensing characteristics are recovered periodically by heating to 650 °C or switching to rich atmospheres. Further insight into the NOx 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 NOx loading amount increases proportionally to the NOx exposure time at sorption temperature. The cumulated NOx exposure, as well as the corresponding NOx loading state, can be detected linearly by electrical means in two modes: (1) time-continuously during the sorption interval including NOx concentration information from the signal derivative or (2) during the short-term thermal NOx release.

No MeSH data available.


Related in: MedlinePlus