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Monitoring the Ammonia Loading of Zeolite‐Based Ammonia SCR Catalysts by a Microwave Method
Author(s) -
Reiß S.,
Schönauer D.,
Hagen G.,
Fischerauer G.,
Moos R.
Publication year - 2011
Publication title -
chemical engineering and technology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.403
H-Index - 81
eISSN - 1521-4125
pISSN - 0930-7516
DOI - 10.1002/ceat.201000546
Subject(s) - catalysis , selective catalytic reduction , zeolite , ammonia , microwave , exhaust gas , nitrogen oxide , nox , chemistry , diesel exhaust , analytical chemistry (journal) , diesel fuel , inorganic chemistry , materials science , chemical engineering , environmental chemistry , organic chemistry , combustion , physics , quantum mechanics , engineering
Abstract 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.