Monitoring the Ammonia Loading of Zeolite‐Based Ammonia SCR Catalysts by a Microwave Method

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.

[1]  O. Kröcher,et al.  Chapter 9 Aspects of catalyst development for mobile urea-SCR systems — From Vanadia-Titania catalysts to metal-exchanged zeolites , 2007 .

[2]  Ralf Moos,et al.  Electrical In Situ Characterization of Three-Way Catalyst Coatings , 2009 .

[3]  Ralf Moos,et al.  Effects of H2O, CO2, CO, and flow rates on the RF-based monitoring of three-way catalysts , 2011 .

[4]  E. Tronconi,et al.  Reactivity of NO/NO2–NH3 SCR system for diesel exhaust aftertreatment: Identification of the reaction network as a function of temperature and NO2 feed content , 2007 .

[5]  Ulrich Simon,et al.  Characteristics of Proton Hopping in Zeolite H‐ZSM5 , 2000 .

[6]  Gunter Hagen,et al.  Combination of Wirebound and Microwave Measurements for In Situ Characterization of Automotive Three-Way Catalysts , 2011, IEEE Sensors Journal.

[7]  Ralf Moos,et al.  Sensing the soot load in automotive diesel particulate filters by microwave methods , 2010 .

[8]  Ralf Moos,et al.  Catalyst State Observation via the Perturbation of a Microwave Cavity Resonator , 2008 .

[9]  Ralf Moos,et al.  Mikrowellengestützte Aufklärung elektrochemischer Vorgänge in Katalysatoren und verwandten Systemen , 2010 .

[10]  Ralf Moos,et al.  Catalysts as Sensors—A Promising Novel Approach in Automotive Exhaust Gas Aftertreatment , 2010, Sensors.

[11]  M. Kleemann,et al.  Investigation of the ammonia adsorption on monolithic SCR catalysts by transient response analysis , 2000 .

[12]  Maximilian Fleischer,et al.  Selective Mixed Potential Ammonia Exhaust Gas Sensor , 2009 .

[13]  Lothar Mussmann,et al.  Investigation of the selective catalytic reduction of NO by NH3 on Fe-ZSM5 monolith catalysts , 2006 .

[14]  Martin Elsener,et al.  Chemical deactivation of V2O5/WO3–TiO2 SCR catalysts by additives and impurities from fuels, lubrication oils, and urea solution: I. Catalytic studies , 2008 .

[15]  Carsten Plog,et al.  The effect of NH3 on the ionic conductivity of dehydrated zeolites Na beta and H beta , 1998 .

[16]  D. Kubinski,et al.  Sensor and method for determining the ammonia loading of a zeolite SCR catalyst , 2008 .

[17]  E. Tronconi,et al.  NH3–NO/NO2 chemistry over V-based catalysts and its role in the mechanism of the Fast SCR reaction , 2006 .

[18]  Ralf Moos,et al.  Direct Catalyst Monitoring by Electrical Means: An Overview on Promising Novel Principles , 2009 .

[19]  M. Elsener,et al.  Urea-SCR: a promising technique to reduce NOx emissions from automotive diesel engines , 2000 .

[20]  Ralf Moos,et al.  Development and working principle of an ammonia gas sensor based on a refined model for solvate supported proton transport in zeolites , 2003 .

[21]  Guido Busca,et al.  Chemical and mechanistic aspects of the selective catalytic reduction of NOx by ammonia over oxide catalysts: A review , 1998 .