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Advanced Catalyst Solutions for Hydrocarbon Emissions Control During Rich Operation of Lean NOx Trap Systems
ISSN: 0148-7191, e-ISSN: 2688-3627
Published April 20, 2009 by SAE International in United States
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The operation of NOx Adsorber catalysts (NAC), also often referred to as Lean NOx Trap catalysts or NOx Storage-reduction catalysts, entails frequent periodic NOx regeneration events. These are accomplished by creating a net reducing, fuel-rich environment in the exhaust. The reduction of hydrocarbon emissions which occur during such fuel-rich events is challenging, due to the oxygen-deficient environment. In order to overcome this limitation, two possibilities exist: (i) oxygen can be stored during lean phase, to be used for hydrocarbon slip oxidation in the subsequent rich phase, or (ii) unreacted hydrocarbons can be trapped during the rich phase and oxidized during the following lean phase. In this work, two groups of catalytic solutions were developed and evaluated for hydrocarbon emission control based on these approaches: an Oxygen Storage Compound (OSC) based catalyst and zeolite-based hydrocarbon trap catalyst.
The experimental evaluation of these two approaches included several stages. The initial concept demonstration was focused on comparing powder samples against a reference oxidation catalyst, using a simplified laboratory screening protocol. Following that, a series of monolith-coated samples with various levels of precious metal loading were studied in-depth using a set of cyclic and steady-state bench-reactor performance tests. These tests were targeted at characterizing the hydrocarbon slip reduction performance, as well as understanding the details of their behavior, in order to guide their potential practical application. Finally, the developed catalyst solutions were tested on engine, including a more detailed study of the precious metal loading level impact on the hydrocarbon slip control.
Both the OSC-based and zeolite-based catalyst formulations demonstrated excellent rich hydrocarbon slip control performance. The OSC-based catalysts performed better at higher temperatures, due to increased dynamic availability of stored oxygen; on the other hand, zeolite-based catalysts performance was less dependent on the temperature, due to efficient hydrocarbon trapping. The resulting understanding enabled the development of advanced hydrocarbon slip control system with reduced precious metal loading.
CitationSzailer, T., Currier, N., Yezerets, A., Stroia, B. et al., "Advanced Catalyst Solutions for Hydrocarbon Emissions Control During Rich Operation of Lean NOx Trap Systems," SAE Technical Paper 2009-01-0282, 2009, https://doi.org/10.4271/2009-01-0282.
- Yu R. C. et al “Development of Diesel Exhaust Aftertreatment System for Tier II Emissions,” SAE Paper 2002-01-1867 2002
- Stroia B. J. et al “Critical Performance and Durability Parameters of an Integrated Aftertreatment System used to Meet 2007 Tier II Emission Standards” SAE Paper 2008-01-0769 2008
- Kanazawa, Takaaki “Development of hydrocarbon adsorbents, oxygen storage materials for three-way catalysts and NOx storage-reduction catalyst” Catalysis Today 96 171 177 2004
- Li, H.-X. et al “Application of zeolites as hydrocarbon traps in automotive emission controls” Studies in Surface Science and Catalysis 158 B 1375 1382 2005
- Onodera Hitoshi et al “Development of a Diesel Emission Catalyst System for Meeting US SULEV Standards” SAE Paper 2008-01-0449 2008
- Bedrane Sumeya et al “Towards the comprehension of oxygen storage processes on model three-way catalysts” Catalysis Today 73 233 238 2002
- Han Manbae et al “Method and detailed analysis of individual hydrocarbon species from diesel combustion modes and diesel oxidation catalyst” Proceedings of the ASME Internal Combustion Engine Division 2007 Fall Technical Conference, ICEF2007-1632 2007