scholarly journals E6.2 - Correlation of Ammonia Storage and Dielectric Properties of SCR Catalyst Materials by Microwave Cavity Perturbation

2015 ◽  
Author(s):  
M. Dietrich ◽  
D. Rauch ◽  
R. Moos ◽  
U. Simon ◽  
A. Porch
Keyword(s):  
Dielectric Properties ◽  
Microwave Cavity ◽  
Scr Catalyst ◽  
Ammonia Storage ◽  
Cavity Perturbation ◽  
Microwave Cavity Perturbation

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

2015 ◽  
Vol 4 (2) ◽  
pp. 263-269 ◽  
Author(s):  
M. Dietrich ◽  
D. Rauch ◽  
U. Simon ◽  
A. Porch ◽  
R. Moos
Keyword(s):  
Dielectric Properties ◽  
Catalytic Reduction ◽  
Nox Reduction ◽  
Microwave Cavity ◽  
Laboratory Setup ◽  
Scr Catalysts ◽  
Ammonia Storage ◽  
Cavity Perturbation ◽  
Acidic Sites ◽  
Microwave Cavity Perturbation

Abstract. 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.

scholarly journals Determination of the Dielectric Properties of Storage Materials for Exhaust Gas Aftertreatment Using the Microwave Cavity Perturbation Method

Sensors ◽  
2020 ◽  
Vol 20 (21) ◽  
pp. 6024
Author(s):  
Carsten Steiner ◽  
Stefanie Walter ◽  
Vladimir Malashchuk ◽  
Gunter Hagen ◽  
Iurii Kogut ◽  
...  
Keyword(s):  
Dielectric Properties ◽  
Perturbation Method ◽  
Microwave Cavity ◽  
Powder Materials ◽  
Exhaust Gas ◽  
Storage Materials ◽  
Exhaust Gas Aftertreatment ◽  
Cavity Perturbation ◽  
Powder Samples ◽  
Microwave Cavity Perturbation

Recently, a laboratory setup for microwave-based characterization of powder samples at elevated temperatures and different gas atmospheres was presented. The setup is particularly interesting for operando investigations on typical materials for exhaust gas aftertreatment. By using the microwave cavity perturbation method, where the powder is placed inside a cavity resonator, the change of the resonant properties provides information about changes in the dielectric properties of the sample. However, determining the exact complex permittivity of the powder samples is not simple. Up to now, a simplified microwave cavity perturbation theory had been applied to estimate the bulk properties of the powders. In this study, an extended approach is presented which allows to determine the dielectric properties of the powder materials more correctly. It accounts for the electric field distribution in the resonator, the depolarization of the sample and the effect of the powder filling. The individual method combines findings from simulations and recognized analytical approaches and can be used for investigations on a wide range of materials and sample geometries. This work provides a more accurate evaluation of the dielectric powder properties and has the potential to enhance the understanding of the microwave behavior of storage materials for exhaust gas aftertreatment, especially with regard to the application of microwave-based catalyst state diagnosis.

Microwave cavity perturbation technique: Part I: Principles

1993 ◽  
Vol 14 (12) ◽  
pp. 2423-2457 ◽  
Author(s):  
Olivier Klein ◽  
Steve Donovan ◽  
Martin Dressel ◽  
George Grüner
Keyword(s):  
Perturbation Technique ◽  
Microwave Cavity ◽  
Cavity Perturbation ◽  
Microwave Cavity Perturbation
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