Evidence for Rh electron-deficient atoms (Rhδ+) as the catalytic species for CO oxidation when supported on Ce0.68Zr0.32O2: A combined N2-FTIR, benzene hydrogenation, and kinetic study

Fontaine, Céline; Krafft, Jean‐Marc; Djéga‐Mariadassou, Gérald; Thomas, Cyril

doi:10.1016/j.jcat.2007.01.005

Cited by 11 publications

(15 citation statements)

References 55 publications

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“…The small but definite electropositive shifts detected for Rh 0 peaks are ascribed to the existence of both Rh 0 and Rh δ+ species, giving evidence to the existence of Rh δ+ /Rh 0 and Ce 4+ /Ce 3+ redox couple [63]. This assignment is in agreement with previous FT-IR result [82,83], which shows the existence of surface electron deficient Rh δ+ species present on CZO support. Like Rh/Al2O3, the Rh 3+ /Rh δ+ ratio in Rh/CZO increased with aging temperature.…”

Section: Catalyst Metal Dispersion (%) Freshsupporting

confidence: 91%

Part I: A Comparative Thermal Aging Study on the Regenerability of Rh/Al2O3 and Rh/CexOy-ZrO2 as Model Catalysts for Automotive Three Way Catalysts

et al. 2015

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The rhodium (Rh) component in automotive three way catalysts (TWC) experiences severe thermal deactivation during fuel shutoff, an engine mode (e.g., at downhill coasting) used for enhancing fuel economy. In a subsequent switch to a slightly fuel rich condition, in situ catalyst regeneration is accomplished by reduction with H2 generated through steam reforming catalyzed by Rh 0 sites. The present work reports the effects of the two processes on the activity and properties of 0.5% Rh/Al2O3 and 0.5% Rh/CexOy-ZrO2 (CZO) as model catalysts for Rh-TWC. A very brief introduction of three way catalysts and system considerations is also given. During simulated fuel shutoff, catalyst deactivation is accelerated with increasing aging temperature from 800 °C to 1050 °C. Rh on a CZO support experiences less deactivation and faster regeneration than Rh on Al2O3. Catalyst characterization techniques including BET surface area, CO chemisorption, TPR, and XPS measurements were applied to examine the roles of metal-support interactions in each catalyst system. For Rh/Al2O3, strong metal-support interactions with the formation of stable rhodium aluminate (Rh(AlO2)y) complex dominates in fuel shutoff, leading to more difficult catalyst regeneration. For Rh/CZO, Rh sites were partially oxidized to Rh2O3 and were relatively easy to be reduced to active Rh 0 during regeneration.

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Section: Catalyst Metal Dispersion (%) Freshsupporting

confidence: 91%

Part I: A Comparative Thermal Aging Study on the Regenerability of Rh/Al2O3 and Rh/CexOy-ZrO2 as Model Catalysts for Automotive Three Way Catalysts

et al. 2015

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“…50 Moreover, Miessner et al reported a direct relation between the IR data and the Rh activity in the CO hydrogenation reaction, but did not compare it to the bridge bonded CO. 17 Finally, the presence of chlorine might have some impact on the Rh catalytic activity, especially at low temperature. 6,34,35,45,62 However, EXAFS, XANES and CO IR data analysis revealed that its impact, if any, is both small and likely to be about the same upon all samples.…”

Section: Resultsmentioning

confidence: 99%

Promotion Effects in the Oxidation of CO over Zeolite-Supported Rh Nanoparticles

et al. 2008

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Rh particles with an average diameter smaller than 1.5 nm have been supported on a series of zeolite Y samples. These zeolite materials contained different monovalent (H + , Na + , K + , Rb + , and Cs + ) and divalent (Mg 2+ , Ca 2+ , Sr 2+ , and Ba 2+ ) cations and were used as model systems to investigate the effect of promoter elements in the oxidation of CO over supported Rh particles in excess of oxygen. Infrared (IR) spectroscopy was carried out to monitor the electronic changes in the local environment of Rh-adsorbed CO. It was found that the bands corresponding to two Rh gem-dicarbonyl species, Rh + (CO) 2 -(O z ) 2 and Rh + (CO) 2 -(O z )(H 2 O), shift to lower wavenumbers with increasing ionic radius/charge ratio of the cation. In addition, the relative intensity of the bridge bonded CO as compared to the total absorbance of Rh-bonded CO species decreases with increasing Lewis acidity, as expressed by the Kamlet-Taft parameter R of the cation. This trend could be directly correlated to the Rh CO oxidation activity, since low temperatures at 50% CO conversion corresponded with catalyst materials with a high contribution of bridge-bonded CO species and hence with small R values. A lower Lewis acidity causes an increased electron density on the framework oxygen atoms and thus an increased electron density on the zeolite-supported Rh particles. Comparable trends have been observed previously on a similar series of cation containing zeolite supported Pt catalyst materials.

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“…[101][102][103][104] With this reaction it is possible to determine the amount of the accessible metallic atoms of low-loaded supported rhodium catalysts. [102,104] A Ni/CeO 2 catalyst exhibited a different behavior from that observed with Al 2 O 3 or SiO 2 supports. The modification of the catalytic properties of Ni/CeO 2 catalysts with reduction pretreatment is correlated to a transformation of the CeO 2 support and to strong interactions between theses species and metal particles.…”

Section: Hydrogenation Of Sunflower Oilmentioning

confidence: 99%

Ceria‐Based Solid Catalysts for Organic Chemistry

Vivier¹,

Duprez²

2010

ChemSusChem

357

244

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Ceria has been the subject of thorough investigations, mainly because of its use as an active component of catalytic converters for the treatment of exhaust gases. However, ceria‐based catalysts have also been developed for different applications in organic chemistry. The redox and acid–base properties of ceria, either alone or in the presence of transition metals, are important parameters that allow to activate complex organic molecules and to selectively orient their transformation. Pure ceria is used in several organic reactions, such as the dehydration of alcohols, the alkylation of aromatic compounds, ketone formation, and aldolization, and in redox reactions. Ceria‐supported metal catalysts allow the hydrogenation of many unsaturated compounds. They can also be used for coupling or ring‐opening reactions. Cerium atoms can be added as dopants to catalytic system or impregnated onto zeolites and mesoporous catalyst materials to improve their performances. This Review demonstrates that the exceptional surface (and sometimes bulk) properties of ceria make cerium‐based catalysts very effective for a broad range of organic reactions.

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Evidence for Rh electron-deficient atoms (Rhδ+) as the catalytic species for CO oxidation when supported on Ce0.68Zr0.32O2: A combined N2-FTIR, benzene hydrogenation, and kinetic study

Cited by 11 publications

References 55 publications

Part I: A Comparative Thermal Aging Study on the Regenerability of Rh/Al2O3 and Rh/CexOy-ZrO2 as Model Catalysts for Automotive Three Way Catalysts

Part I: A Comparative Thermal Aging Study on the Regenerability of Rh/Al2O3 and Rh/CexOy-ZrO2 as Model Catalysts for Automotive Three Way Catalysts

Promotion Effects in the Oxidation of CO over Zeolite-Supported Rh Nanoparticles

Ceria‐Based Solid Catalysts for Organic Chemistry

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