Mechanistic aspects of the release and the reduction of NO  stored on Pt–Ba/Al2O3

Castoldi, L.; Righini, Laura; Matarrese, Roberto; Lietti, Luca; Forzatti, Pio

doi:10.1016/j.jcat.2015.02.005

Cited by 25 publications

(16 citation statements)

References 31 publications

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“…The reduction process is initiated by the reduction of the PGM sites by the reductant, which precedes the NO release. The observation that no N 2 O is formed in this case may be explained by considering that the rate determining step in the reduction of the stored NO x is the NO release step [16]; once NO is released, it is readily converted to the reduction products. Accordingly the gas-phase concentration of NO is small and this prevents N 2 O formation.…”

Section: Pathways For N 2 O Formationmentioning

confidence: 91%

“…Notably, the intermediacy of species like ammonium nitrate in N 2 O formation is apparently ruled out since no N 2 O was observed in the NH 3 /nitrate reaction over both Pt-and Rh-based catalytic materials. It has been suggested that the reduction of the stored NO x species is involved in the release of NO from the stored NO x as first step, followed by the reduction of the released NO over the PGM sites [16][17][18][19]. The reduction process is initiated by the reduction of the PGM sites by the reductant, which precedes the NO release.…”

Section: Pathways For N 2 O Formationmentioning

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: Pathways For N 2 O Formationmentioning

confidence: 91%

Section: Pathways For N 2 O Formationmentioning

confidence: 99%

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

et al. 2016

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“…El dióxido de carbono producido es resultado de la combustión directa del carbón, que va acompañado de una ligera formación de agua consecuencia del bajo contenido en H de la carbonilla. El mecanismo de combustión de carbonilla está basado en la interacción de la molécula de oxígeno quimisorbida en un centro activado de carbón a alta temperatura, con formación de especies superficiales -CO que se liberan en forma de CO o CO 2 que, tal y como han mostrado otros autores [18,24] es el proceso generalmente aceptado por el que se produce la eliminación no catalítica de la carbonilla, y depende del carácter oxidante de la corriente, que en este caso es suficientemente alto para que no se detecte CO a la salida y el CO 2 sea el único producto de reacción. Para el caso de la eliminación de carbonilla en contacto con el catalizador Pt-K, la reducción del intervalo de temperatura en el que se produce y la ocurrencia de una serie de procesos secuenciales son confirmadas en base al perfil de los productos detectados.…”

Section: Resultados Y Discusiónunclassified

Eliminación de carbonilla en gases de escape con catalizadores DeNOx. Determinación de parámetros cinéticos

Cortés‐Reyes¹,

Herrera²,

Larrubia³

et al. 2019

rev.ion

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Los catalizadores DeNOx se emplean en la eliminación de los óxidos de nitrógeno en vehículos diésel y, también, puede que entren en contacto con carbonilla o incluso sean utilizados como sistemas de reducción de NOx y soot simultáneamente (DPNR-Diesel Particulate NOx Reduction). Por ello, es importante profundizar en el mecanismo de interacción entre el Soot y el catalizador. Se ha utilizado un Soot Printex U modelo y un catalizador Pt-K/Al2O3, con el potasio en forma de óxido e hidroxicarbonato hidratado. Se ha estudiado mediante TG-MS el proceso de eliminación en diferentes atmósferas oxidantes. Los procesos han sido desacoplados mediante el establecimiento de la función de distribución de energía de activación. En ausencia de catalizador, se produce la combustión del carbonilla con el oxígeno molecular en fase gas a temperaturas alrededor de los 1100 K. En presencia de NO, la reducción tiene lugar a menor temperatura debido a su carácter más oxidante y a las especies de óxidos de nitrógeno retenidas y en fase gas. Si la carbonilla se encuentra en contacto con el catalizador Pt-K/Al2O3, los centros Pt-OH-K son los responsables de la eliminación vía gasificación a 780 K con una energía de activación alrededor de 85 kJ mol-1

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“…The mechanism for NO isotopic exchange has been already reported in previous work [10] and here resumed for sake of clarity. Upon interaction of unlabeled nitrates species stored at a Ba site with a neighboring metallic site (Pt and/or Rh), unlabeled NO is released in the gas phase and a free BaO site is formed; in the meantime oxygen is left at metal site, leading to oxygen adsorbed on it and/or to oxidized metal site.…”

Section: No (3)mentioning

confidence: 98%

“…O and then in the activation of stored NOx by metal reduced centers, that seems to represent the rate determining step of the reduction of stored NOx [10]. In the presence of efficient reductants like H2 (and NH3), it is likely that NO formed upon the activation of stored NOx does not desorb from the metal sites, but is readily decomposed to N-and O-adatoms over them.…”

Section: Tpsr Of Nitrates -mentioning

confidence: 99%

Al2O3-supported Pt/Rh catalysts for NOx removal under lean conditions

Castoldi

Matarrese

Daturi

et al. 2019

Applied Catalysis A: General

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In this work the reactivity of Pt-Rh NOx storage-reduction (NSR) catalysts in the reduction of NOx under lean conditions is investigated. It is found that significant amounts of NOx are stored on both Rh-and Pt-based samples at all the investigated temperatures (in the range 150-350¿°C). Mostly chelating nitrites are adsorbed at the lowest investigated temperature (150¿°C), while nitrates (both bidentate and ionic) at higher temperatures. However, at all temperatures nitrites prevail at the beginning of the storage phase, while nitrates represent the most abundant adsorbed species after prolonged contact. Pt-containing catalysts (either monometallic Pt or bimetallic Pt/Rh) show higher NOx storage capacity than the Rh monometallic sample, possibly due to the higher dispersion of Pt vs. Rh and/or to the higher oxidizing capability of Pt vs. Rh.The stored NOx species show relevant thermal stability, and decompose to NOx and O2 upon heating.In particular, nitrites disproportionate to gaseous NO and nitrates; these latter then decompose to NOx and O2. On the Rh-Ba/Al2O3 catalyst the disproportionation reaction is observed with a higher temperature onset if compared to the Pt-based samples. The analysis of the reactivity of the stored NOx species (probed by isotopic labeling experiments and reduction with H2 and NH3) showed the lower reactivity of the Rh-Ba/Al2O3 sample; however Rh shows activity in the ammonia decomposition reaction to N2 and H2, unlike Pt. The lower reactivity of the Rh-Ba/Al2O3 sample is also pointed out by experiments under cyclic lean-rich conditions. However, the presence of Rh increases the reactivity of the catalyst in the steam reforming of hydrocarbons, especially at high temperature, and accordingly the reactivity of the bimetallic Pt/Rh sample at high temperatures is higher than that of the Pt and Rh monometallic catalysts.High resolution transmission electron microscopy (HRTEM) was carried out using a JEOL 2010F electron microscope equipped with a field emission source at an accelerating voltage of 200 kV.Samples were deposited on holey Cu grids. The point-to-point resolution achieved was 0.19 nm and the resolution between lines was 0.14 nm. X-ray photoelectron spectroscopy (XPS) was performed on a SPECS system equipped with an Al anode XR50 source operating at 150 mW and a Phoibos MCD-9 detector. The pass energy of the hemispherical analyzer was set at 25 eV and the energy step was set at 0.1 eV. The pressure in the analysis chamber was kept below 10−7 Pa. The area analysed was about 2 mm × 2 mm. Data processing was performed with the CasaXPS program (Casa Software Ltd., UK).The interaction of NO/O2 with the catalytic surface has been investigated by IR spectroscopy and temperature-programmed desorption.NO/O2 mixture (1000 ppm NO + 3% O2 in He) has been fed to the IR reactor for the analysis of the surface species. It consists in a "Sandwich" IR cell containing the catalyst (15 mg) in form of selfsupported wafer; the gases leaving the cell were analyzed by mass spectrometer (ThermoStar TM...

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Mechanistic aspects of the release and the reduction of NO stored on Pt–Ba/Al2O3

Cited by 25 publications

References 31 publications

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

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

Eliminación de carbonilla en gases de escape con catalizadores DeNOx. Determinación de parámetros cinéticos

Al2O3-supported Pt/Rh catalysts for NOx removal under lean conditions

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