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Sensors 2015, 15(11), 28915-28941; doi:10.3390/s151128915

Correlating the Integral Sensing Properties of Zeolites with Molecular Processes by Combining Broadband Impedance and DRIFT Spectroscopy—A New Approach for Bridging the Scales

1
Institute of Inorganic Chemistry (IAC) and Center for Automotive Catalytic Systems Aachen (ACA), RWTH Aachen University, Landoltweg 1, 52074 Aachen, Germany
2
Department of Functional Materials, Bayreuth Engine Research Center (BERC) and Zentrum für Energietechnik (ZET), University of Bayreuth, Universitätsstraße 30, 95440 Bayreuth, Germany
*
Authors to whom correspondence should be addressed.
Academic Editor: Michael Tiemann
Received: 6 October 2015 / Revised: 2 November 2015 / Accepted: 5 November 2015 / Published: 13 November 2015
(This article belongs to the Special Issue Gas Sensors—Designs and Applications)
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Abstract

Zeolites have been found to be promising sensor materials for a variety of gas molecules such as NH3, NOx, hydrocarbons, etc. The sensing effect results from the interaction of the adsorbed gas molecules with mobile cations, which are non-covalently bound to the zeolite lattice. The mobility of the cations can be accessed by electrical low-frequency (LF; mHz to MHz) and high-frequency (HF; GHz) impedance measurements. Recent developments allow in situ monitoring of catalytic reactions on proton-conducting zeolites used as catalysts. The combination of such in situ impedance measurements with diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), which was applied to monitor the selective catalytic reduction of nitrogen oxides (DeNOx-SCR), not only improves our understanding of the sensing properties of zeolite catalysts from integral electric signal to molecular processes, but also bridges the length scales being studied, from centimeters to nanometers. In this work, recent developments of zeolite-based, impedimetric sensors for automotive exhaust gases, in particular NH3, are summarized. The electrical response to NH3 obtained from LF impedance measurements will be compared with that from HF impedance measurements, and correlated with the infrared spectroscopic characteristics obtained from the DRIFTS studies of molecules involved in the catalytic conversion. The future perspectives, which arise from the combination of these methods, will be discussed. View Full-Text
Keywords: impedance spectroscopy; microwave cavity perturbation; DRIFTS; ZSM-5 zeolite; gas sensing; ammonia; DeNOx-SCR; proton motion; polarization; in situ impedance spectroscopy; microwave cavity perturbation; DRIFTS; ZSM-5 zeolite; gas sensing; ammonia; DeNOx-SCR; proton motion; polarization; in situ
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Chen, P.; Schönebaum, S.; Simons, T.; Rauch, D.; Dietrich, M.; Moos, R.; Simon, U. Correlating the Integral Sensing Properties of Zeolites with Molecular Processes by Combining Broadband Impedance and DRIFT Spectroscopy—A New Approach for Bridging the Scales. Sensors 2015, 15, 28915-28941.

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