Coarsening of Pt Particles in a Model NO<sub>x</sub>Trap

Graham, George W.; Jen, Hung-Wen; Wang, Chun; Sun, Hu; Pan, Xiaoqing; McCabe, Robert W.

doi:10.1023/b:catl.0000017065.47758.34

Cited by 52 publications

(29 citation statements)

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“…1 that are characteristic of crystalline BaAl 2 O 4 (PDF 82-2001). Although both samples contains several peaks arising from BaAl 2 O 4 , its average crystallite size, based on a peak-width analysis using the Scherrer equation, of the reduced sample is 95 nm, while that of the oxidized one is 55 nm, consistent with previous conclusions [7] that reducing treatments are much more effective than oxidizing ones in the formation of BaAl 2 O 4 . In addition to the new BaAl 2 O 4 phase, the XRD patterns of the high temperature treated samples (Fig.…”

Section: Effect Of Oxidizing or Reducing Conditions Duringsupporting

confidence: 89%

“…Therefore, a high temperatures de-sulfation process to convert BaSO 4 back into BaO or BaCO 3 is required for regeneration of the catalyst. During this de-sulfation process, several effects of thermal aging, such as Pt sintering, loss of Al 2 O 3 surface area, and formation a of less-reactive BaAl 2 O 4 phase, have been reported on this class of LNT catalysts [6,7]. Pt sintering is detrimental because it reduces the interaction between the Pt and Ba phases, with such an interaction likely important for efficient operation during the lean cycle for the transfer of NO 2 , formed over Pt sites, to vicinal barium sites for storage [8].…”

Section: Introductionmentioning

confidence: 99%

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Promotional Effects of H2O Treatment on NO x Storage Over Fresh and Thermally Aged Pt–BaO/Al2O3 Lean NO x Trap Catalysts

et al. 2008

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A simple liquid water treatment applied to fresh and thermally aged Pt(2 wt%)-BaO(20 wt%)/Al 2 O 3 lean NO x trap catalysts at room temperature induces morphological and structural changes in the barium species as followed by XRD and TEM analysis. During the water treatment, liquid water sufficient to fill the catalyst pore volume is brought into contact with the samples. It was found that irrespective of the original barium chemical state (highly dispersed BaO or crystalline BaAl 2 O 4 ), exposing the sample to this liquid water treatment promotes the formation of BaCO 3 crystallites (about 15-25 nm of its size) without changing the Pt particle size. Such transformations of the barium species are found to significantly promote NO x uptake from 250 to 450°C. The increase in the NO x uptake for the water-treated samples can be attributed to an enhanced Pt-Ba interaction through the redistribution of barium species. These results provide useful information for the regeneration of aged lean NO x trap catalysts since water is plentiful in the exhaust of diesel or lean-burn engines.

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Section: Effect Of Oxidizing or Reducing Conditions Duringsupporting

confidence: 89%

Section: Introductionmentioning

confidence: 99%

Promotional Effects of H2O Treatment on NO x Storage Over Fresh and Thermally Aged Pt–BaO/Al2O3 Lean NO x Trap Catalysts

et al. 2008

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“…Pt is generally regarded as one of the best catalysts for NO oxidation, but supported Pt catalysts tend to lose Pt surface area rapidly under high-temperature lean conditions due to Pt-particle coarsening [4]. Alloying Pt with metals such as Pd or Rh has been proposed as a possible means of retarding such coarsening [5], but few systematic studies of alloying on the dispersion stability of supported catalysts have been performed [6].…”

Section: Introductionmentioning

confidence: 99%

Effect of alloy composition on dispersion stability and catalytic activity for NO oxidation over alumina-supported Pt–Pd catalysts

et al. 2007

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Applying a synthesis procedure that promotes alloy formation, highly-dispersed alumina-supported Pt-Pd catalysts spanning the Pt-rich half of the composition range were prepared, aged under oxygen-rich hydrothermal conditions, and characterized by CO chemisorption, XRD, and TEM. Anomalously large particles, typical of pure Pt catalysts treated under such conditions, were not found in any of the Pd-containing catalysts, and the extent of particle coarsening due to aging was found to decrease with increasing Pd content. Alloying appears to have little effect on the NO oxidation turn-over frequency, which increases with decreasing dispersion.

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“…Figure 1 displays XRD spectra of the fresh and thermal aged catalysts. The Pt peak at 2θ = 40°sharpens with aging temperature, indicating that Pt particle sintering increases [13]. Ceria particles only sinter from the 800°C aging, according to the peak at 2θ = 47°.…”

Section: Lean-rich Cycling Conditionsmentioning

confidence: 97%

Diesel Lean NO_x-Trap Thermal Aging and Performance Evolution Characterization

Benramdhane

Millet

Jeudy

et al. 2011

Oil Gas Sci. Technol. – Rev. IFP Energies nouvelles

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Résumé -Caractérisation de l'impact du vieillissement sur l'évolution des performances d'un piège à NO x Diesel -L'étude suivante porte sur l'impact du vieillissement thermique sur la structure et les fonctions d'un piège à NO x . Les essais ont été réalisés sur un banc gaz synthétiques (BGS) et les résultats ont été corrélés à des analyses structurale et chimique du catalyseur. Une étude FTIR Operando a permis de mieux analyser les mécanismes se produisant sur la surface du catalyseur et de mettre en évidence les points les plus critiques. Des échantillons ont été vieillis hydrothermiquement à 900 °C sous un flux oxydant. Les principaux impacts ont été les suivants : la réduction de la surface spécifique, le frittage du Pt qui mène à une diminution de l'efficacité d'oxydation de NO, CO, HC et de la capacité de stockage, la formation de BaAl 2 O 4 est en partie responsable de la perte de capacité de stockage de NO x . D'autres possibilités pour la perte de NSC sont : la transition de la γ-Al 2 O 3 à la δ-Al 2 O 3 et l'évolution de la structure cristalline du baryum qui demande des analyses approfondies. Les études DRX et Operando IR montrent que le vieillissement hydrothermique a un impact assez homogène sur tous les matériaux : la transition de phase de l'alumine et la formation de BaAl 2 O 4 , qui toutes mènent à une diminution partielle de tous les sites de stockage. Abstract -Diesel Lean NO x -Trap Thermal Aging and Performance Evolution CharacterizationThe work described in this paper focuses on the impact of thermal aging on NO x trap structure and functions. They were evaluated on a Synthetic Gas Bench (SGB) and correlated with the analysis of the structural and chemical evolution of the catalyst. A FTIR

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Coarsening of Pt Particles in a Model NO_xTrap

Cited by 52 publications

References 3 publications

Promotional Effects of H2O Treatment on NO x Storage Over Fresh and Thermally Aged Pt–BaO/Al2O3 Lean NO x Trap Catalysts

Promotional Effects of H2O Treatment on NO x Storage Over Fresh and Thermally Aged Pt–BaO/Al2O3 Lean NO x Trap Catalysts

Effect of alloy composition on dispersion stability and catalytic activity for NO oxidation over alumina-supported Pt–Pd catalysts

Diesel Lean NO_x-Trap Thermal Aging and Performance Evolution Characterization

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Coarsening of Pt Particles in a Model NOxTrap

Cited by 52 publications

References 3 publications

Promotional Effects of H2O Treatment on NO x Storage Over Fresh and Thermally Aged Pt–BaO/Al2O3 Lean NO x Trap Catalysts

Promotional Effects of H2O Treatment on NO x Storage Over Fresh and Thermally Aged Pt–BaO/Al2O3 Lean NO x Trap Catalysts

Effect of alloy composition on dispersion stability and catalytic activity for NO oxidation over alumina-supported Pt–Pd catalysts

Diesel Lean NOx-Trap Thermal Aging and Performance Evolution Characterization

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Coarsening of Pt Particles in a Model NO_xTrap

Diesel Lean NO_x-Trap Thermal Aging and Performance Evolution Characterization