The Pt-Ba Interaction in Lean NOx Trap Systems

Nova, Isabella; Castoldi, L.; Lietti, Luca; Tronconi, Enrico; Forzatti, Pio; Prinetto, F.; Ghiotti, G.

doi:10.4271/2005-01-1085

Cited by 77 publications

(178 citation statements)

References 19 publications

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“…In addition, no evident intermediate species such as nitrites were observed during the entire storage process. However, the formation of nitrites has been widely reported on Pt/Ba/Al 2 O 3 catalysts and has been considered an important pathway for NO x adsorption [32][33][34]. Urakawa et al [35] also detected nitrites formation at the location of 1204 cm −1 on the surface of Pt/Ba/CeO 2 by time-resolved DRIFTS.…”

Section: Characterization Resultsmentioning

confidence: 96%

Effects of temperature and reductant type on the process of NOx storage reduction over Pt/Ba/CeO2 catalysts

Wang

2011

Applied Catalysis B: Environmental

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a b s t r a c tThe influences of temperature and reductant type on NO x storage and reduction behavior were studied by transient lean/rich cycles and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) experiments over Pt/Ba/CeO 2 catalysts. It is found that the reducing ability of H 2 is more predominant than that of CO and C 3 H 6 especially at low temperatures. DRIFTS results showed that NO x can be stored as nitrates on both Ba and Ce sites by replacing carbonates species during the lean phase. During the rich phase, however, H 2 regenerated Ba storage sites more effectively than did CO and C 3 H 6 , and Ba(NO 3 ) 2 could be easier reduced than Ce(NO 3 ) 4 . The relatively low reduction performance of CO was attributed to Pt sites being poisoned by CO, which affected low temperature performance, and by carbonates formation, which affected high temperature conversions. The least reactivity of C 3 H 6 was due to its lowest activation ability by the catalysts. Furthermore, water addition had a positive effect on CO reduction ability at 200• C but little influence at elevated temperatures. It was assumed that H 2 O improved the low temperature NO x reduction process by alleviating CO poisoning of Pt.

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Section: Characterization Resultsmentioning

confidence: 96%

Effects of temperature and reductant type on the process of NOx storage reduction over Pt/Ba/CeO2 catalysts

Wang

2011

Applied Catalysis B: Environmental

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“…Once the trap is saturated a pulse of hydrocarbons over the material reacts to release NO, regenerate the BaO sorbent material and reduce the NO to N 2 [4][5][6][7][8][9][10]. The first step in this cycle is the oxidation of NO (over Pt) to form NO 2 [11,12].…”

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confidence: 99%

The effect of C(s) on the trapping of NOx onto Pt/Ba/Al2O3 catalysts

Sullivan¹,

Dulgheru²

2010

Applied Catalysis B: Environmental

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“…[7][8][9] Detailed kinetic interpretations have also been rendered equivocal by the complete NO conversion levels that prevailed throughout these studies. [7][8][9] Here, we provide kinetic and isotopic evidence for the identity and relevance of elementary steps involved in NO oxidation on Pt clusters under conditions of strict kinetic control. We show that oxygen isotopic exchange requires kinetically relevant steps identical to those involved in NO oxidation, confirming that these processes reflect the dynamics of O 2 reaction with surface vacancies and the thermodynamics of oxygen binding.…”

Section: Introductionmentioning

confidence: 99%

“…These studies have claimed that atomic contact among Pt and BaO species is required for efficient NO 2 removal. [7][8][9] These conclusions relied on data from materials for which the structure of Pt clusters and of BaO adsorption sites changed concurrently with their proximity. [7][8][9] Detailed kinetic interpretations have also been rendered equivocal by the complete NO conversion levels that prevailed throughout these studies.…”

Section: Introductionmentioning

confidence: 99%

“…[7][8][9] These conclusions relied on data from materials for which the structure of Pt clusters and of BaO adsorption sites changed concurrently with their proximity. [7][8][9] Detailed kinetic interpretations have also been rendered equivocal by the complete NO conversion levels that prevailed throughout these studies. [7][8][9] Here, we provide kinetic and isotopic evidence for the identity and relevance of elementary steps involved in NO oxidation on Pt clusters under conditions of strict kinetic control.…”

Section: Introductionmentioning

confidence: 99%

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NO Oxidation Catalysis on Pt Clusters: Elementary Steps, Structural Requirements, and Synergistic Effects of NO₂Adsorption Sites

2009

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Kinetic and isotopic methods show that NO oxidation on supported Pt clusters involves kinetically relevant reaction of O 2 with vacancy sites on surfaces nearly saturated with oxygen adatoms (O*). The oxygen chemical potential at Pt surfaces that determines the O* coverage is rigorously described by an O 2 virtual pressure and determined by the thermodynamics of NO 2 -NO interconversion reactions. NO oxidation and oxygen isotopic exchange processes are described by the same rate constant, consistent with similar kinetically relevant O 2 dissociation steps for both reactions. NO oxidation, NO 2 decomposition, andO 2 exchange rates increased markedly with increasing Pt cluster size (1-8 nm); these clusters remain metallic at all O 2 virtual pressures prevalent during NO oxidation. These effects of cluster size reflect the higher vacancy concentrations and more facile oxygen desorption on larger Pt clusters, which bind oxygen adatoms weaker than more coordinatively unsaturated surface Pt atoms on smaller clusters. These trends are similar to those found for methane and dimethyl ether combustion on Pt and Pd catalysts, which also require vacancy sites on O*-saturated cluster surfaces in their respective kinetically relevant steps. Inhibition of NO oxidation by NO 2 persists to undetectable NO 2 concentrations; thus, NO oxidation turnover rates increase significantly when NO 2 adsorption sites present on BaCO 3 /Al 2 O 3 are placed within diffusion distances of Pt clusters. NO oxidation rates on intrapellet catalyst-adsorbent mixtures are described accurately by a simple reaction-adsorption model in which NO 2 adsorbs via displacement of CO 2 on BaCO 3 surfaces.

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The Pt-Ba Interaction in Lean NOx Trap Systems

Cited by 77 publications

References 19 publications

Effects of temperature and reductant type on the process of NOx storage reduction over Pt/Ba/CeO2 catalysts

Effects of temperature and reductant type on the process of NOx storage reduction over Pt/Ba/CeO2 catalysts

The effect of C(s) on the trapping of NOx onto Pt/Ba/Al2O3 catalysts

NO Oxidation Catalysis on Pt Clusters: Elementary Steps, Structural Requirements, and Synergistic Effects of NO₂Adsorption Sites

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The Pt-Ba Interaction in Lean NOx Trap Systems

Cited by 77 publications

References 19 publications

Effects of temperature and reductant type on the process of NOx storage reduction over Pt/Ba/CeO2 catalysts

Effects of temperature and reductant type on the process of NOx storage reduction over Pt/Ba/CeO2 catalysts

The effect of C(s) on the trapping of NOx onto Pt/Ba/Al2O3 catalysts

NO Oxidation Catalysis on Pt Clusters: Elementary Steps, Structural Requirements, and Synergistic Effects of NO2Adsorption Sites

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NO Oxidation Catalysis on Pt Clusters: Elementary Steps, Structural Requirements, and Synergistic Effects of NO₂Adsorption Sites