The NO x reduction mechanism by H2 under near isothermal conditions over Pt–Ba/Al2O3 Lean NO x Trap systems

Castoldi, L.; Nova, Isabella; Lietti, Luca; Tronconi, Enrico; Forzatti, Pio

doi:10.1007/s11244-007-0176-0

Cited by 9 publications

(11 citation statements)

References 15 publications

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“…8, it can be concluded that first the consumption of the NO from the gas phase occurs and later reduction of surface nitrites/nitrates with ammonia. As was found previously, Pt must be involved in the reaction, because the reduction of stored nitrates/nitrites by NH 3 is not effective over Pt-free samples [54,60]. Moreover, this current study shows that when ammonia is a limiting agent, nitrates/nitrites remain on the catalyst surface unreacted, and at temperatures higher than 623 K decompose.…”

Section: Tpsr Over Catalyst With Preformed Nitrites/ Nitratessupporting

confidence: 57%

“…It has been reported that Ba addition to supported Pt catalysts results in an increase in NO x reduction activity in the absence of O 2 [19,52,53]. It was suggested that according to reactions (4)- (6), the presence of the alkaline or alkaline-earth metal ion weakens the N-O bond [54]. This will favor dissociation and subsequent reduction.…”

Section: Nh 3 Versus H 2 Reduction Of Nitrites/nitratesmentioning

confidence: 99%

“…The mechanism N 2 O formation describes the recombination of N-species on reduced Pt particles. Previous studies showed that the recombination of N ad-species gives N 2 as a product and recombination of N and NO ad-species leads to N 2 O formation according to reactions (6)- (8) [54,58,59].…”

Section: Tpsr Over a Catalyst Without Preformed Nitrites/nitratesmentioning

confidence: 99%

“…Moreover it was shown that the addition of Ba, especially its presence in close proximity to Pt, also increases the selectivity of the reaction to N 2 . This enhanced selectivity was associated with the increase in the NO dissociation rate, which decreases the formation of N 2 O according to reaction (8) [54].…”

Section: Tpsr Over a Catalyst Without Preformed Nitrites/nitratesmentioning

confidence: 99%

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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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Section: Tpsr Over Catalyst With Preformed Nitrites/ Nitratessupporting

confidence: 57%

Section: Nh 3 Versus H 2 Reduction Of Nitrites/nitratesmentioning

confidence: 99%

Section: Tpsr Over a Catalyst Without Preformed Nitrites/nitratesmentioning

confidence: 99%

Section: Tpsr Over a Catalyst Without Preformed Nitrites/nitratesmentioning

confidence: 99%

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

et al. 2018

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“…More recently, the regeneration of model Pt-Ba/Al 2 O 3 Lean NOx Trap systems was also investigated. 18,[25][26][27][28][29][30] In this review the results obtained in our studies of the reduction phase will be reported, along with new data recently collected which better explain the chemistry involved in the reduction by H 2 of the stored NO x . NO (1000 ppm) was admitted to the reactor at t ¼ 0 s under He + O 2 (3% v/v) flow; after 100 s NO breakthrough was observed, while NO 2 evolution was seen starting from 200 s. Both the NO and NO 2 outlet concentrations increased with time until the NO feed flow was switched off (t ¼ 600 s).…”

Section: A Introductionmentioning

confidence: 99%