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Ammonia storage studies on H-ZSM-5 zeolites by microwave cavity perturbation: correlation of dielectric properties with ammonia storage

Title data

Dietrich, Markus ; Rauch, Dieter ; Simon, Ulrich ; Porch, Adrian ; Moos, Ralf:
Ammonia storage studies on H-ZSM-5 zeolites by microwave cavity perturbation: correlation of dielectric properties with ammonia storage.
In: Journal of Sensors and Sensor Systems. Vol. 4 (2015) Issue 2 . - pp. 263-269.
ISSN 2194-878X

Official URL: Volltext

Project information

Project title:
Project's official title
Project's id
No information
Mo 1060/19-1

Project financing: Deutsche Forschungsgemeinschaft

Abstract in another language

To meet today's emission standards, the ammonia-based selective catalytic reduction (SCR) has become the major NOx control strategy for light and heavy diesel engines. Before NOx reduction can proceed, adsorption of ammonia on the acidic sites of the catalyst is necessary. For improvements in efficiency and control of the exhaust gas aftertreatment, a better understanding of the ammonia storage on the acidic sites of zeolite-based SCR catalysts is needed. Thereby, the correlation of dielectric properties of the catalyst material itself with the ammonia storage is a promising approach. Recently, a laboratory setup using microwave cavity perturbation to measure the dielectric properties of catalyst material has been described. This study shows the first experimental data on zeolite-based SCR materials in their H-form. The SCR powder samples are monitored by microwave cavity perturbation while storing and depleting ammonia, both with and without admixed NOx at different temperatures. Its complex dielectric permittivity is found to correlate closely with the stored mass of ammonia. The influence of the temperature and the Si / Al ratio of the zeolite to the ammonia storage behavior are also examined. These measurements disclose different temperature dependencies and differing sensitivities to ammonia storage for both real and imaginary parts of the complex permittivity. The apparent constant sensitivity of the real part can be related to the polarity of the adsorbed ammonia molecules, whereas the imaginary part depends on the Si / Al ratio and is related to the conductivity mechanisms of the zeolite material by proton hopping. It provides information about the zeolite structure and the number of (and the distance between) acidic storage sites, in addition to the stored ammonia mass.
The effect of stored ammonia on the complex dielectric permittivity of H-ZSM-5 zeolites with varying storage site density was observed between 200 and 300 °C under reaction conditions by microwave cavity perturbation. Polarization and dielectric losses were differently affected. The sensitivity of the polarization to stored ammonia is almost independent, the sensitivity of the dielectric losses strongly dependent on the storage site density. The results can be explained by proton hopping.

Further data

Item Type: Article in a journal
Refereed: Yes
Institutions of the University: Faculties > Faculty of Engineering Science
Faculties > Faculty of Engineering Science > Chair Functional Materials > Chair Functional Materials - Univ.-Prof. Dr.-Ing. Ralf Moos
Research Institutions > Research Units > ZET - Zentrum für Energietechnik
Research Institutions > Research Units > BERC - Bayreuth Engine Research Center
Faculties > Faculty of Engineering Science > Chair Functional Materials
Research Institutions
Research Institutions > Research Units
Profile Fields > Advanced Fields > Advanced Materials
Research Institutions > Research Centres > Bayreuth Center for Material Science and Engineering - BayMAT
Profile Fields
Profile Fields > Advanced Fields
Research Institutions > Research Centres
Result of work at the UBT: Yes
DDC Subjects: 600 Technology, medicine, applied sciences > 620 Engineering
Date Deposited: 21 Sep 2015 12:59
Last Modified: 18 Apr 2016 07:27