Publication Date:
2011-04-08
Description:
Exhaust gas aftertreatment systems, which reduce nitrogen oxide emissions of heavy-duty diesel engines, commonly use a selective catalytic reduction (SCR) catalyst. Currently, emissions are controlled by evaluating NO x or NH 3 in the gas phase downstream the catalyst and calculating the NH 3 loading via a chemical storage model. Here, a microwave-cavity perturbation method is proposed in which electromagnetic waves are excited by probe feeds and the reflected signals are measured. At distinct resonance frequencies, the reflection coefficient shows a pronounced minimum. These resonance frequencies depend almost linearly on the NH 3 loading of a zeolite-based SCR catalyst. Since the NH 3 loading-dependent electrical properties of the catalyst material itself are measured, the amount of stored ammonia can be determined directly and in situ. The cross-sensitivity towards water can be reduced almost completely by selecting an appropriate frequency range. A novel approach to measure the ammonia loading of zeolite-based SCR catalysts directly and in operation is presented. In this microwave-cavity perturbation method electromagnetic waves are excited by probe feeds and the reflected signals are measured. Compared to typical gas sensors, the resonance frequency system does not analyze the gas phase but gives direct information on the catalytic material itself.
Print ISSN:
0930-7516
Electronic ISSN:
1521-4125
Topics:
Chemistry and Pharmacology
,
Process Engineering, Biotechnology, Nutrition Technology
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