title: Correlating the Integral Sensing Properties of Zeolites with Molecular Processes by Combining Broadband Impedance and DRIFT Spectroscopy--A New Approach for Bridging the Scales.
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.
authors.affiliation: Institute of Inorganic Chemistry (IAC) and Center for Automotive Catalytic Systems Aachen (ACA), RWTH Aachen University, Landoltweg 1, 52074 Aachen, Germany. peirong.chen@ac.rwth-aachen.de.
authors.forename: Peirong
authors.initials: P
authors.lastname: Chen
authors.affiliation: Institute of Inorganic Chemistry (IAC) and Center for Automotive Catalytic Systems Aachen (ACA), RWTH Aachen University, Landoltweg 1, 52074 Aachen, Germany. simon.schoenebaum@ac.rwth-aachen.de.
authors.forename: Simon
authors.initials: S
authors.lastname: Schönebaum
authors.affiliation: Institute of Inorganic Chemistry (IAC) and Center for Automotive Catalytic Systems Aachen (ACA), RWTH Aachen University, Landoltweg 1, 52074 Aachen, Germany. thomas.simons@rwth-aachen.de.
authors.forename: Thomas
authors.initials: T
authors.lastname: Simons
authors.affiliation: Department of Functional Materials, Bayreuth Engine Research Center (BERC) and Zentrum für Energietechnik (ZET), University of Bayreuth, Universitätsstraße 30, 95440 Bayreuth, Germany. Functional.Materials@uni-bayreuth.de.
authors.forename: Dieter
authors.initials: D
authors.lastname: Rauch
authors.affiliation: Department of Functional Materials, Bayreuth Engine Research Center (BERC) and Zentrum für Energietechnik (ZET), University of Bayreuth, Universitätsstraße 30, 95440 Bayreuth, Germany. Functional.Materials@uni-bayreuth.de.
authors.forename: Markus
authors.initials: M
authors.lastname: Dietrich
authors.affiliation: Department of Functional Materials, Bayreuth Engine Research Center (BERC) and Zentrum für Energietechnik (ZET), University of Bayreuth, Universitätsstraße 30, 95440 Bayreuth, Germany. Functional.Materials@uni-bayreuth.de.
authors.forename: Ralf
authors.initials: R
authors.lastname: Moos
authors.affiliation: Institute of Inorganic Chemistry (IAC) and Center for Automotive Catalytic Systems Aachen (ACA), RWTH Aachen University, Landoltweg 1, 52074 Aachen, Germany. ulrich.simon@ac.rwth-aachen.de.
authors.forename: Ulrich
authors.initials: U
authors.lastname: Simon
keywords: DRIFTS; DeNOx-SCR; ZSM-5 zeolite; ammonia; gas sensing; impedance spectroscopy; in situ; microwave cavity perturbation; polarization; proton motion