Effective Model for Prediction of N2O and NH3 Formation During the Regeneration of NO x Storage Catalyst

Kočí, Petr; Bártová, Šárka; Mráček, David; Marek, M.; Choi, Jae‐Soon; Kim, Miyoung; Pihl, Josh A.; Partridge, William P.

doi:10.1007/s11244-013-9939-y

Cited by 26 publications

(24 citation statements)

References 7 publications

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“…At variance, N 2 O is a highly undesired by-product in view of its very high global warming potential (nearly 300 times that of CO 2 ). Over fully formulated catalysts, it has been shown that N 2 O formation is apparent both upon switch from lean to rich mode but also during the alternation from rich to lean regime [3][4][5][6][7][8]. It has been suggested that N 2 O formation at the lean to rich transition occurs at the regeneration front, upon reduction of the stored NO x over not fully reduced Platinum-Group-Metal (PGM) sites.…”

Section: Introductionmentioning

confidence: 99%

“…It has been suggested that N 2 O formation at the lean to rich transition occurs at the regeneration front, upon reduction of the stored NO x over not fully reduced Platinum-Group-Metal (PGM) sites. On the other hand, N 2 O formation upon the rich to lean transition originates from reaction between residual surface NO x with reductive species (like NCO, CO or NH 3 ) in an adsorbed state [3,4,7]. This N 2 O peak can be reduced if a neutral or slightly lean phase is inserted between the rich and the lean phase, since a more complete regeneration of the catalyst can be attained [9].…”

Section: Introductionmentioning

confidence: 99%

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Study of N2O Formation over Rh- and Pt-Based LNT Catalysts

et al. 2016

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Abstract:In this paper, mechanistic aspects involved in the formation of N 2 O over Pt-BaO/Al 2 O 3 and Rh-BaO/Al 2 O 3 model NO x Storage-Reduction (NSR) catalysts are discussed. The reactivity of both gas-phase NO and stored nitrates was investigated by using H 2 and NH 3 as reductants. It was found that N 2 O formation involves the presence of gas-phase NO, since no N 2 O is observed upon the reduction of nitrates stored over both Pt-and Rh-BaO/Al 2 O 3 catalyst samples. In particular, N 2 O formation involves the coupling of undissociated NO molecules with N-adspecies formed upon NO dissociation onto reduced Platinum-Group-Metal (PGM) sites. Accordingly, N 2 O formation is observed at low temperatures, when PGM sites start to be reduced, and disappears at high temperatures where PGM sites are fully reduced and complete NO dissociation takes place. Besides, N 2 O formation is observed at lower temperatures with H 2 than with NH 3 in view of the higher reactivity of hydrogen in the reduction of the PGM sites and onto Pt-containing catalyst due to the higher reducibility of Pt vs. Rh.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Study of N2O Formation over Rh- and Pt-Based LNT Catalysts

et al. 2016

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“…During and after catalyst regeneration, N 2 and N 2 O products are formed concurrently in two peaks. While the primary peaks are associated with rich pulse inception and appear at the catalyst outlet during regeneration, the secondary peaks can be observed immediately after the rich pulse as a result of subsequent reactions [6][7][8][9][10][11][12][13]. The secondary peak diminishes with a longer and more complete regeneration that does not leave enough residual NO x and reduction intermediates on the catalyst surface [14].…”

Section: Introductionmentioning

confidence: 99%

“…As the reduction front travels along the monolith channel during the rich phase, the reductants can react with the stored NO x , either at the leading edge of the reduction front over incompletely reduced PGM sites, which typically leads to N 2 O formation, or behind the front in the fully reduced part of the catalyst resulting in N 2 and NH 3 production. After switching back to lean conditions, the adsorbed reductants and reduction intermediates can further react with the residual NO x remaining on the surface due to an incomplete regeneration and form additional N-products [11,14]. These secondary products can significantly contribute to the overall N 2 and N 2 O yield [6,7].…”

Section: Introductionmentioning

confidence: 99%

“…Although up to 50% of the total N 2 O product can originate from the secondary peak [6], no suggestions have yet been published for specifically addressing this issue. Our previous research [6,9,11,14] enabled better understanding of the general principle of NO x reduction selectivity depending on the actual oxidation state of PGM sites. Particularly, we have shown that N 2 O formation is minimized over well reduced PGM sites, regardless of the specific reductant used [11].…”

Section: Introductionmentioning

confidence: 99%

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New operation strategy for driving the selectivity of NO reduction to N2, NH3 or N2O during lean/rich cycling of a lean NO trap catalyst

Mráček

Kočí

Choi

et al. 2016

Applied Catalysis B: Environmental

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a b s t r a c tPeriodical regeneration of NO x storage catalyst (also known as lean NO x trap) by short rich pulses of CO, H 2 and hydrocarbons is necessary for the reduction of nitrogen oxides adsorbed on the catalyst surface. Ideally, the stored NO x is converted into N 2 , but N 2 O and NH 3 by-products can be formed as well, particularly at low-intermediate temperatures. The N 2 and N 2 O products are formed concurrently in two peaks. The primary peaks appear immediately after the rich-phase inception, and tail off with the breakthrough of the reductant front accompanied by NH 3 product. The secondary N 2 and N 2 O peaks then appear at the rich-to-lean transition as a result of reactions between surface-deposited reductants/intermediates (CO, HC, NH 3 , NCO) and residual stored NO x under increasingly lean conditions. Based on these mechanistic insights, we propose and demonstrate a novel strategy for driving the selectivity of the secondary peaks towards desired products. It is based on a transition phase of neutral or slightly lean (nearly stoichiometric) character inserted between the rich and the fully lean phase. This strategy allows more complete regeneration of the catalyst with higher N 2 yield and without the undesired formation of a secondary N 2 O peak. Furthermore, NH 3 can be formed during this slightly lean transition phase without any CO or hydrocarbons breakthrough. Such ammonia formation is desirable in the exhaust gas aftertreatment systems combining LNT with passive SCR technology.

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Comparison of different kinetic models for NO_X storage on a lean NO_X trap

2014

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The kinetics of NOX storage on a lean NOX trap (LNT) were studied using NOX breakthrough curves measured with a laboratory reactor. A much wider range of temperatures (125–450°C) was used than in most studies to facilitate discrimination between potential models. The breakthrough curves were run until the LNT was saturated to (i) enable NO oxidation to NO2 to be studied in the absence of NOX storage, (ii) to enable the effective NOX capacity as a function of temperature to be determined, and (iii) to provide a more demanding test for potential models. Breakthrough curves for 125 and 450°C were very similar, while curves at intermediate temperatures initially followed that for 125°C before breaking away from this curve at a point that became earlier with increasing temperature. Thus, the breakthrough curves have a temperature independent initial portion, followed by a temperature dependant portion. This was explained by there being two types of site: fast sites and slow sites. Fast sites are responsible for the initial part of the curve; both the rate of storage on these sites and the available capacity are independent of temperature. The rate of storage on slow sites, on the other hand, is temperature dependant, as is the available storage capacity. Slow sites are more abundant than fast sites. The performance of three NOX storage models for these sites was compared. The amount of NOX stored as a function of temperature was bell‐shaped. The models naturally predicted that storage was limited by kinetics at lower temperatures and nitrate stability at higher temperatures.

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Effective Model for Prediction of N2O and NH3 Formation During the Regeneration of NO x Storage Catalyst

Cited by 26 publications

References 7 publications

Study of N2O Formation over Rh- and Pt-Based LNT Catalysts

Study of N2O Formation over Rh- and Pt-Based LNT Catalysts

New operation strategy for driving the selectivity of NO reduction to N2, NH3 or N2O during lean/rich cycling of a lean NO trap catalyst

Comparison of different kinetic models for NO_X storage on a lean NO_X trap

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Effective Model for Prediction of N2O and NH3 Formation During the Regeneration of NO x Storage Catalyst

Cited by 26 publications

References 7 publications

Study of N2O Formation over Rh- and Pt-Based LNT Catalysts

Study of N2O Formation over Rh- and Pt-Based LNT Catalysts

New operation strategy for driving the selectivity of NO reduction to N2, NH3 or N2O during lean/rich cycling of a lean NO trap catalyst

Comparison of different kinetic models for NOX storage on a lean NOX trap

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Comparison of different kinetic models for NO_X storage on a lean NO_X trap