Storage and Reduction of NO x Over LNT Catalysts

Forzatti, Pio; Lietti, Luca; Castoldi, L.

doi:10.1007/s10562-014-1343-0

Cited by 19 publications

(22 citation statements)

References 113 publications

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“…In such a case O-adatoms formed upon NO decomposition are scavenged by NO itself leading to the formation of nitrite species so that the formation of N 2 O occurs according to the stoichiometry of the NO disproportionation reaction Equation (1).…”

Section: Discussionmentioning

confidence: 99%

“…In this respect, NO itself acts as a weak reductant, being able to scavenge O-adatoms and resulting in the formation of nitrite species adsorbed over the storage component (Ba). The overall stoichiometry of the process is then well described by following NO disproportion reaction Equation (1).…”

Section: Pathways For N 2 O Formationmentioning

confidence: 99%

“…The removal of NO x under lean conditions according to the NO x Storage-Reduction (NSR) technique is a viable approach for both diesel and lean gasoline fueled engines [1]. In this process NO x conversion is based on a cyclic engine operation alternating between fuel lean and rich conditions: NO x (NO+NO 2 ) are adsorbed on the catalyst surface during lean operations, while the surface of the trap is regenerated under the fuel rich environment.…”

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: Discussionmentioning

confidence: 99%

Section: Pathways For N 2 O Formationmentioning

confidence: 99%

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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“…In fact, legislations are becoming stricter regarding the emission levels permitted, especially for nitrogen oxides (NOx) and particulate matter (soot) [2][3][4]. Therefore, new strategies were and are being developed, in order to achieve the abatement of these pollutants [5][6][7][8][9][10].…”

Section: Introductionmentioning

confidence: 99%

Study of Ce/Pr ratio in ceria-praseodymia catalysts for soot combustion under different atmospheres

Guillén-Hurtado¹,

Giménez-Mañogil²,

Martínez-Munuera³

et al. 2020

Applied Catalysis A: General

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The effect of Ce/Pr ratio on ceria-praseodymia on structural and surface properties is studied. The catalytic activity towards soot combustion under NOx/O2 and O2/N2 atmospheres is also evaluated, together with the NO oxidation activity to NO2. CexPr1-xO2-δ compositions (x = 0.8, 0.5 and 0.2) have been prepared along with ceria and praseodymia. Catalysts were prepared by coprecipitation. The Ce0.5Pr0.5O2-δ composition, was also prepared by nitrate calcination. Ceriapraseodymia mixed oxides yield reduction profiles shifted to lower temperatures, higher NO oxidation activities to NO2 and improved catalytic activities for soot combustion with respect to pure ceria. Ce0.5Pr0.5O2-δ was the most active one. Under NOx/O2, it has greater soot combustion activity if it is prepared by nitrate calcination. However, under O2/N2, the co-precipitation method is more favorable because of the better dopant insertion achieved in the ceria lattice, which seems to lead better oxygen mobility on the surface and in the bulk oxide.

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“…In contrast, NSR technology, also referred to as lean NOx trap (LNT) technology, involves cyclic operation comprising a sequential lean phase (typically 30-90 s) and much shorter rich phase (3-10 s). LNT catalyst contains noble metals (e.g., Pt, Rh) and NOx storage materials (e.g., K 2 O, BaO) supported on high surface area γ-Al 2 O 3 [4,5,6]. Ceria (CeO 2 ) is often added to the LNT catalyst as a promotor.…”

Section: Commercial Lean Nox Abatement Technologies Include Selectivementioning

confidence: 99%

Rapid propylene pulsing for enhanced low temperature NO conversion on combined LNT-SCR catalysts

Zheng

Wang

et al. 2016

Catalysis Today

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Lean reduction of NOx (NO + NO 2) was conducted over combined LNT-SCR dual-layer and zoned monolithic catalysts using rapid propylene periodic pulsing into a lean feed. We investigated the effects of cycling frequency, reaction exotherm, hydrocarbon (HC) intermediates, top-layer material, LNT ceria content and catalyst configuration on the performance of dual-layer catalysts under fast propylene pulsing. High frequency propylene injection expands the operating temperature window of a conventional NOx storage and reduction (NSR) system in both low and high-temperature regions. The combination of rapid propylene pulsing and the dual-layer catalyst architecture achieves a low-temperature NOx conversion of up to 80% at a feed temperature of ca. 200 °C and relevant space velocities (~ 70k h −1). The working mechanisms of rapid propylene pulsing on both LNT and LNT-SCR catalysts are discussed. Fast cycling facilitates the generation of partially oxidized hydrocarbon intermediates over the LNT that can then either directly react with NOx or act as oxygen scavenger to maintain Pt in a reduced state for direct NO decomposition. The SCR top-layer traps partially oxygenated species that desorb from the LNT layer, enabling further production of N 2 through a LNT-assisted HC-SCR pathway. Optimization of ceria content, top-layer material and catalyst configuration like SCR and PGM zoning can improve system performance at lower cost.

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Storage and Reduction of NO x Over LNT Catalysts

Cited by 19 publications

References 113 publications

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

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

Study of Ce/Pr ratio in ceria-praseodymia catalysts for soot combustion under different atmospheres

Rapid propylene pulsing for enhanced low temperature NO conversion on combined LNT-SCR catalysts

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