Mechanistic Aspects of N2O Formation Over Pt-Based Lean NOx Trap Catalysts

Kubiak, Lukasz Maciej; Righini, Laura; Castoldi, L.; Matarrese, Roberto; Forzatti, Pio; Lietti, Luca; Daturi, Marco

doi:10.1007/s11244-016-0577-z

Cited by 9 publications

(12 citation statements)

References 18 publications

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“…At higher temperature, above 250˝C, nitrites are transformed into nitrates, in line with previous results [10].…”

Section: No-temperature Programmed Reaction (No-tpr)supporting

confidence: 92%

“…It may also increase the reactivity of the PGM sites in the NO dissociative chemisorption, as suggested in the literature [10,12]. In fact, experiments carried out over a Ba-free sample showed a much lower N 2 O formation if compared to the Ba-containing catalysts [14].…”

Section: Pathways For N 2 O Formationmentioning

confidence: 92%

“…Notably, due to the low reductant concentration, experiments were carried out under nearly isothermal conditions, i.e., in the absence of significant temperature effects during the experiments. Further details concerning apparatuses and procedures can be found in [10,15].…”

Section: Methodsmentioning

confidence: 99%

“…In order to provide further insights on the pathway involved in N 2 O formation, a fundamental study was carried out on a model Pt-BaO/Al 2 O 3 catalyst under simplified and controlled reaction conditions [10]. Accordingly the reactivity of gaseous NO alone and in the presence of various reducing agents like H 2 , NH 3 , and CO was analyzed by micro-reactor transient reactivity experiments and operando Fourier transform infrared (FT-IR) spectroscopy, to provide a complementary overview on the pathway of N 2 O evolution.…”

Section: Introductionmentioning

confidence: 99%

“…Accordingly the reactivity of gaseous NO alone and in the presence of various reducing agents like H 2 , NH 3 , and CO was analyzed by micro-reactor transient reactivity experiments and operando Fourier transform infrared (FT-IR) spectroscopy, to provide a complementary overview on the pathway of N 2 O evolution. It has been shown that N 2 O is formed from gaseous NO provided that a proper oxidation degree of the Pt sites is attained [10]. Accordingly the N 2 O evolution was observed only in a narrow temperature range corresponding to the PtO to Pt transformation, determined by the reactivity of the reducing agents (H 2 > NH 3 > CO).…”

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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“…At higher temperature, above 250˝C, nitrites are transformed into nitrates, in line with previous results [10].…”

Section: No-temperature Programmed Reaction (No-tpr)supporting

confidence: 92%

Section: Pathways For N 2 O Formationmentioning

confidence: 92%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

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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Mechanistic Aspect of N2O Formation Over Pt–Ba/γ-Al2O3 Catalysts

et al. 2018

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NO X reduction in lean-burn gasoline or diesel engines is challenging in the oxidizing environment, and depending on the after-treatment technology, can lead to by-product, such as N 2 O or ammonia, formation. The current study focuses on possible N 2 O formation pathways over NO x storage/reduction (NSR) catalysts. More specifically, NH 3 reactivity with catalyst surface species was investigated over a model Pt-Ba/γ-Al 2 O 3 (1/20/100, w/w) NSR catalyst with and without NO x species stored (nitrites and nitrates). The NH 3 originates from reduction of NO x in the regeneration phase. With NH 3 , two overall reactions can lead to N 2 or N 2 O formation, namely 3NO + 2NH 3 → 5/2 N 2 + 3H 2 O and 4NO + NH 3 → 5/2 N 2 O + 3/2H 2 O. These two are considered for catalyzed reaction between the entering NO and NH 3. Surface nitrite and nitrate reduction reactions leading to N 2 or N 2 O were also evaluated, all as a function of temperature and relative amount of NH 3 in the gas phase. N 2 O was formed in the lower temperature range, and was more significant with lower NH 3 concentrations. At higher temperatures, above 423 K, for NH 3 concentrations higher than stoichiometric, only N 2 was produced. In comparing the results from the samples with preformed nitrites/nitrates on the surface to those without, it is apparent that NH 3 first reacts with gas-phase NO and then with pre-stored surface NO x species. Moreover, the reduction of surface nitrites/nitrates is complete only for high NH 3 /NO ratios, and when NH 3 is the limiting reactant, they remain on the catalyst surface unreacted until temperatures higher than 623 K, where they decompose. In general, for all performed experiments, N 2 O was the dominant product at low temperature, when NO and NH 3 conversions are low. At higher temperature, with increasing NO and NH 3 conversions, N 2 selectivity increases.

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