Dynamics of N2 and N2O peaks during and after the regeneration of lean NOx trap

David Mráček; Petr Kočí; Miloš Marek; Jae Soon Choi; Josh A. Pihl; William P. Partridge

doi:10.1016/j.apcatb.2014.12.002

Dynamics of N₂ and N₂O peaks during and after the regeneration of lean NO_x trap

David Mráček, Petr Kočí, Miloš Marek, Jae Soon Choi, Josh A. Pihl, William P. Partridge

Research output: Contribution to journal › Article › peer-review

26 Scopus citations

Abstract

The dynamics and selectivity of N₂ and N₂O formation during and after the regeneration of a commercial NO_x storage catalyst containing Pt, Pd, Rh, Ba on Ce/Zr, Mg/Al and Al oxides was studied with high-speed FTIR and SpaciMS analyzers. The lean/rich cycling experiments (60s/5s and 60s/3s) were performed in the temperature range 200-400°C, using H₂, CO, and C₃H₆ individually for the reduction of adsorbed NO_x. Isotopically labeled ¹⁵NO was employed in combination with Ar carrier gas in order to quantify the N₂ product by mass spectrometry. N₂ and N₂O products were formed concurrently. The primary peaks appeared immediately after the rich-phase inception, and tailed off with breakthrough of the reductant front (accompanied by NH₃ product). Secondary N₂ and N₂O peaks appeared at the rich-to-lean transition as a result of reactions between surface-deposited reductants/intermediates (CO, HC, NH₃, -NCO) and residual stored NO_x. At 200-300°C, up to 30% of N₂ and 50% of N₂O products originated from the secondary peaks. The N₂O/N₂ selectivity ratio as well as the magnitude of secondary peaks decreased with temperature and duration of the rich phase. Among the three reductants, propene generated secondary N₂ peak up to the highest temperature. The primary N₂ peak exhibited a broadened shoulder aligned with movement of reduction front from the zone where both NO_x and oxygen were stored to the NO_x-free zone where only oxygen storage capacity was saturated. N₂ formed in the NO_x-free zone originated from reaction of NH₃ with stored oxygen, while N₂O formation in this zone was very low.

Original language	English
Pages (from-to)	509-517
Number of pages	9
Journal	Applied Catalysis B: Environmental
Volume	166-167
DOIs	https://doi.org/10.1016/j.apcatb.2014.12.002
State	Published - May 1 2015

Funding

This work has been financially supported by the Czech Ministry of Education (Project LH 12086 ) and the US Department of Energy (DOE) Vehicle Technologies Office (program managers: Gurpreet Singh, Ken Howden and Leo Breton). The co-authors would like to thank Dr. Mi-Young Kim of the ORNL Fuels, Engines and Emissions Research Center for her contributions to the experimental catalyst work. Notice: This manuscript has been authored by UT-Battelle, LLC under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan ( http://energy.gov/downloads/doe-public-access-plan ).

Funders	Funder number
U.S. Department of Energy
Ministerstvo Školství, Mládeže a Tělovýchovy	LH 12086

Keywords

Exhaust gas aftertreatment
N formation
NO formation
NO reduction
NO storage catalyst

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10.1016/j.apcatb.2014.12.002

Cite this

@article{aadc12881699494c87840f21afcd17dc,

title = "Dynamics of N2 and N2O peaks during and after the regeneration of lean NOx trap",

abstract = "The dynamics and selectivity of N2 and N2O formation during and after the regeneration of a commercial NOx storage catalyst containing Pt, Pd, Rh, Ba on Ce/Zr, Mg/Al and Al oxides was studied with high-speed FTIR and SpaciMS analyzers. The lean/rich cycling experiments (60s/5s and 60s/3s) were performed in the temperature range 200-400°C, using H2, CO, and C3H6 individually for the reduction of adsorbed NOx. Isotopically labeled 15NO was employed in combination with Ar carrier gas in order to quantify the N2 product by mass spectrometry. N2 and N2O products were formed concurrently. The primary peaks appeared immediately after the rich-phase inception, and tailed off with breakthrough of the reductant front (accompanied by NH3 product). Secondary N2 and N2O peaks appeared at the rich-to-lean transition as a result of reactions between surface-deposited reductants/intermediates (CO, HC, NH3, -NCO) and residual stored NOx. At 200-300°C, up to 30% of N2 and 50% of N2O products originated from the secondary peaks. The N2O/N2 selectivity ratio as well as the magnitude of secondary peaks decreased with temperature and duration of the rich phase. Among the three reductants, propene generated secondary N2 peak up to the highest temperature. The primary N2 peak exhibited a broadened shoulder aligned with movement of reduction front from the zone where both NOx and oxygen were stored to the NOx-free zone where only oxygen storage capacity was saturated. N2 formed in the NOx-free zone originated from reaction of NH3 with stored oxygen, while N2O formation in this zone was very low.",

keywords = "Exhaust gas aftertreatment, N formation, NO formation, NO reduction, NO storage catalyst",

author = "David Mr{\'a}{\v c}ek and Petr Ko{\v c}{\'i} and Milo{\v s} Marek and Choi, {Jae Soon} and Pihl, {Josh A.} and Partridge, {William P.}",

note = "Publisher Copyright: {\textcopyright} 2014 Elsevier B.V.",

year = "2015",

month = may,

day = "1",

doi = "10.1016/j.apcatb.2014.12.002",

language = "English",

volume = "166-167",

pages = "509--517",

journal = "Applied Catalysis B: Environmental",

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TY - JOUR

T1 - Dynamics of N2 and N2O peaks during and after the regeneration of lean NOx trap

AU - Mráček, David

AU - Kočí, Petr

AU - Marek, Miloš

AU - Choi, Jae Soon

AU - Pihl, Josh A.

AU - Partridge, William P.

PY - 2015/5/1

Y1 - 2015/5/1

N2 - The dynamics and selectivity of N2 and N2O formation during and after the regeneration of a commercial NOx storage catalyst containing Pt, Pd, Rh, Ba on Ce/Zr, Mg/Al and Al oxides was studied with high-speed FTIR and SpaciMS analyzers. The lean/rich cycling experiments (60s/5s and 60s/3s) were performed in the temperature range 200-400°C, using H2, CO, and C3H6 individually for the reduction of adsorbed NOx. Isotopically labeled 15NO was employed in combination with Ar carrier gas in order to quantify the N2 product by mass spectrometry. N2 and N2O products were formed concurrently. The primary peaks appeared immediately after the rich-phase inception, and tailed off with breakthrough of the reductant front (accompanied by NH3 product). Secondary N2 and N2O peaks appeared at the rich-to-lean transition as a result of reactions between surface-deposited reductants/intermediates (CO, HC, NH3, -NCO) and residual stored NOx. At 200-300°C, up to 30% of N2 and 50% of N2O products originated from the secondary peaks. The N2O/N2 selectivity ratio as well as the magnitude of secondary peaks decreased with temperature and duration of the rich phase. Among the three reductants, propene generated secondary N2 peak up to the highest temperature. The primary N2 peak exhibited a broadened shoulder aligned with movement of reduction front from the zone where both NOx and oxygen were stored to the NOx-free zone where only oxygen storage capacity was saturated. N2 formed in the NOx-free zone originated from reaction of NH3 with stored oxygen, while N2O formation in this zone was very low.

AB - The dynamics and selectivity of N2 and N2O formation during and after the regeneration of a commercial NOx storage catalyst containing Pt, Pd, Rh, Ba on Ce/Zr, Mg/Al and Al oxides was studied with high-speed FTIR and SpaciMS analyzers. The lean/rich cycling experiments (60s/5s and 60s/3s) were performed in the temperature range 200-400°C, using H2, CO, and C3H6 individually for the reduction of adsorbed NOx. Isotopically labeled 15NO was employed in combination with Ar carrier gas in order to quantify the N2 product by mass spectrometry. N2 and N2O products were formed concurrently. The primary peaks appeared immediately after the rich-phase inception, and tailed off with breakthrough of the reductant front (accompanied by NH3 product). Secondary N2 and N2O peaks appeared at the rich-to-lean transition as a result of reactions between surface-deposited reductants/intermediates (CO, HC, NH3, -NCO) and residual stored NOx. At 200-300°C, up to 30% of N2 and 50% of N2O products originated from the secondary peaks. The N2O/N2 selectivity ratio as well as the magnitude of secondary peaks decreased with temperature and duration of the rich phase. Among the three reductants, propene generated secondary N2 peak up to the highest temperature. The primary N2 peak exhibited a broadened shoulder aligned with movement of reduction front from the zone where both NOx and oxygen were stored to the NOx-free zone where only oxygen storage capacity was saturated. N2 formed in the NOx-free zone originated from reaction of NH3 with stored oxygen, while N2O formation in this zone was very low.

KW - Exhaust gas aftertreatment

KW - N formation

KW - NO formation

KW - NO reduction

KW - NO storage catalyst

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U2 - 10.1016/j.apcatb.2014.12.002

DO - 10.1016/j.apcatb.2014.12.002

M3 - Article

AN - SCOPUS:84919884486

SN - 0926-3373

VL - 166-167

SP - 509

EP - 517

JO - Applied Catalysis B: Environmental

JF - Applied Catalysis B: Environmental

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