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This study displays the results obtained with a planar, impedance-metric sensor having a NiCr 2 O 4 -SE and a specially manufactured FSZ electrolyte. The sensing characteristics to NO and to O 2 /NO-gas mixtures were analyzed at temperatures up to 700 °C. The cross-selectivity to other flue-gases was tested. As a new capable type of sensing parameter the total impedance was applied.

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Dedicated to Prof. Wolfgang Bunk on the occasion of his 80th birthdayUpcoming emission regulations order highly effective NO x -reduction systems in lean-burn engines requiring new catalytic materials and integrated control of the reduction process. Thus, new approaches for NO x -reduction and its monitoring over an OnBoard-Diagnostic (OBD) system are suggested throughout the globe. A promising attempt is the development of a catalytic system having an integrated NO x -sensor, based on selective catalytic reduction process and impedance sensors. The study displays the results achieved both with a perovskite type of self-regenerative catalyst functioning by H 2 -reductant and with impedance NO x -sensors. The catalysts were tested at the temperature range of 150 C to 360 C yielding NO x conversion rates of 92 % with high selectivity to N 2 .

The nature of the NOx species produced during the adsorption of NO at room temperature and during its coadsorption with oxygen on LaMnAl 11O19 sample with magnetoplumbite structure obtained by a sol-gel process has been investigated by means of in situ FT-IR spectroscopy. The adsorption of NO leads to formation of anionic nitrosyls and/or cis-hyponitrite ions and reveals the presence of coordinatively unsaturated Mn3+ ions. Upon NO/O2 adsorption at room temperature various nitro-nitrato structures are observed. The nitro-nitrato species produced with the participation of electrophilic oxygen species decompose at 350 °C directly to N2 and O2. No NO decomposition is observed in absence of molecular oxygen. The adsorbed nitro-nitrato species are inert towards the interaction with methane and block the active sites (Mn 3+ ions) for its oxidation. Noticeable oxidation of the methane on the NOx - precovered sample is observed at temperatures higher than 350 °C due to the liberation of the active sites as a result of decomposition of the surface nitro-nitrato species. Mechanism explaining the promoting effect of the molecular oxygen in the NO decomposition is proposed. © 2005 Elsevier B.V. All rights reserved