Automotive exhaust gas catalysts: Surface structure and activity

Engler, Bernd; Koberstein, E.; Schubert, Paul F.

doi:10.1016/s0166-9834(00)80267-5

Cited by 113 publications

(33 citation statements)

References 6 publications

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“…Since Ce 3+ is bigger than Ce 4+ , a simple reduction leads to a ceria lattice cell expansion. Changes in the ceria lattice parameter can be directly related to the concentration of oxygen vacancies and Ce 3+ cations in this oxide [35][36][37]. Figure 4a shows the lattice parameters for ceria determined from (111) diffraction peaks of TR-XRD patterns for Cu 0.2 Ce 0.8 O 2 under different gases at 400°C.…”

Section: Chemical State Of Cu In Ce 1-x Cu X O 2 Catalystsmentioning

confidence: 99%

Ceria-based Catalysts for the Production of H2 Through the Water-gas-shift Reaction: Time-resolved XRD and XAFS Studies

et al. 2008

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Hydrogen is a potential alternate energy source for satisfying many of our energy needs. In this work, we studied H 2 production from the water-gas-shift (WGS) reaction over Ce 1-x Cu x O 2 catalysts, prepared with a novel microemulsion method, using two synchrotron-based techniques: time-resolved X-ray diffraction (XRD) and X-ray absorption fine structure (XAFS). The results are compared with those reported for conventional CuO x /CeO 2 and AuO x /CeO 2 catalysts obtained through impregnation of ceria. For the fresh Ce 1-x Cu x O 2 catalysts, the results of XAFS measurements at the Cu K-edge indicate that Cu is in an oxidation state higher than in CuO. Nevertheless, under WGS reaction conditions the Ce 1-x Cu x O 2 catalysts undergo reduction and the active phase contains very small particles of metallic Cu and CeO 2-x . Time-resolved XRD and XAFS results also indicate that Cu d+ and Au d+ species present in fresh CuO x /CeO 2 and AuO x /CeO 2 catalysts do not survive above 200°C under the WGS conditions. In all these systems, the ceria lattice displayed a significant increase after exposure to CO and a decrease in H 2 O, indicating that CO reduced ceria while H 2 O oxidized it. Our data suggest that H 2 O dissociation occurred on the O vacancy sites or the Cu-O vacancy and Au-O vacancy interfaces. The rate of H 2 generation by a Ce 0.95 Cu 0.05 O 2 catalyst was comparable to that of a 5 wt% CuO x /CeO 2 catalyst and much bigger than those of pure ceria or CuO.

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Section: Chemical State Of Cu In Ce 1-x Cu X O 2 Catalystsmentioning

confidence: 99%

Ceria-based Catalysts for the Production of H2 Through the Water-gas-shift Reaction: Time-resolved XRD and XAFS Studies

et al. 2008

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“…The use of OSC components was first proposed by Ghandi et al in 1976. [4] Since the pioneering works of Yao and Yu Yao [2] and of Su et al, [5,6] many studies have been devoted to improving knowledge of the kinetics of OSC [7][8][9] and of the mechanisms implicated in surface and bulk oxygen mobility in ceria and related compounds, [10][11][12][13][14] with a special insight into CeZrO x oxides. [15][16][17][18][19] Oxygen diffusivity in these materials can be measured by 18 O/ 16 O isotopic exchange, [20][21][22] while oxygen species (e.g., superoxides, peroxides) that might be involved in the diffusion process can be investigated by electron spin resonance (ESR) [23][24][25][26][27] or FTIR.…”

Section: Introductionmentioning

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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“…Although the promoting effect of ceria was initially attributed to the enhancement of the metal dispersion and the stabilization towards thermal sintering, 2, 3 subsequent work has shown that ceria can act as a chemically active component as well, working as an oxygen reservoir able to deliver it in the presence of reductive gases and to incorporate it upon interaction with oxidizing gases. [4][5][6] The broad use in heterogeneous catalysis of ceria relies on its facile Ce 3+ ↔ Ce 4+ redox conversion; 7 however, the adequate description of the electronic configuration of Ce 3+ ions constitutes a challenge in density functional based theoretical chemistry due to the strongly correlated nature of the 4f electrons. Indeed, the 4f electrons in Ce 2 O 3 are localized and the material behaves like a typical antiferromagnetic Mott-Hubbard insulator.…”

mentioning

confidence: 99%