Oxygen Vacancy Clusters Promoting Reducibility and Activity of Ceria Nanorods

Liu, Xiangwen; Zhou, Kebin; Wang, Lei; Wang, Baoyi; Li, Yadong

doi:10.1021/ja808433d

Cited by 1,112 publications

(888 citation statements)

References 29 publications

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“…The exposed surfaces for CeO 2 nanorods have mostly been confirmed as {110} and {100} planes [26,30,41]. Although the d-spacing along the long side of CeO 2 (rod) of 0.31 nm by analysis of our TEM images suggests the presence of {111} planes in line with recent other work [43], we adopt here the assignment of {110} planes. A more detailed EM analysis would be necessary to resolve this issue for our ceria nanorods.…”

Section: Catalytic Activity Measurementssupporting

confidence: 69%

Gold Stabilized by Nanostructured Ceria Supports: Nature of the Active Sites and Catalytic Performance

et al. 2011

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The interaction of gold atoms with CeO 2 nanocrystals having rod and cube shapes has been examined by cyanide leaching, TEM, TPR, CO IR and X-ray absorption spectroscopy. After deposition-precipitation and calcination of gold, these surfaces contain gold nanoparticles in the range 2-6 nm. For the ceria nanorods, a substantial amount of gold is present as cations that replace Ce ions in the surface as follows from their first and second coordination shells of oxygen and cerium by EXAFS analysis. These cations are stable against cyanide leaching in contrast to gold nanoparticles. Upon reduction the isolated Au atoms form finely dispersed metal clusters with a high activity in CO oxidation, the WGS reaction and 1,3-butadiene hydrogenation. By analogy with the very low activity of reduced gold nanoparticles on ceria nanocubes exposing the {100} surface plane, it is inferred that the gold nanoparticles on the ceria nanorod surface also have a low activity in such reactions. Although the finely dispersed Au clusters are thermally stable up to quite high temperature in line with earlier findings (Y. Guan and E. J. M. Hensen, Phys Chem Chem Phys 11:9578, 2009), the presence of gold nanoparticles results in their more facile agglomeration, especially in the presence of water (e.g., WGS conditions). For liquid phase alcohol oxidation, metallic gold nanoparticles are the active sites. In the absence of a base, the O-H bond cleavage appears to be rate limiting, while this shifts to C-H bond activation after addition of NaOH. In the latter case, the gold nanoparticles on the surface of ceria nanocubes are much more active than those on the surface of nanorod ceria.

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Section: Catalytic Activity Measurementssupporting

confidence: 69%

Gold Stabilized by Nanostructured Ceria Supports: Nature of the Active Sites and Catalytic Performance

et al. 2011

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“…However, the separation between OH − and O 2− in O 1s CLSs decreases by 0.3 eV when a single oxygen vacancy is replaced by a linear surface oxygen vacancy cluster (LSVC). 16,20 These findings lead us to believe that vacancy clusters are not formed on the ceria electrode surface under +1.2 V applied bias but rather isolated surface vacancies linked with surface Ce 3+ occur under these conditions, as previously observed in other systems. 16 In contrast, the value of calculated OH − O 1s CLS (∼2.7 eV) does not change significantly when the OH − coverage increases from 1 / 16 to 3 / 16 for a given vacancy coverage.…”

Section: ■ Results and Discussionmentioning

confidence: 55%

“…16,20 These findings lead us to believe that vacancy clusters are not formed on the ceria electrode surface under +1.2 V applied bias but rather isolated surface vacancies linked with surface Ce 3+ occur under these conditions, as previously observed in other systems. 16 In contrast, the value of calculated OH − O 1s CLS (∼2.7 eV) does not change significantly when the OH − coverage increases from 1 / 16 to 3 / 16 for a given vacancy coverage. This finding agrees well with the measured local potentials under −1.2 V applied bias ( Figure 3C), where no significant difference in local potentials between OH − and O 2− is detected.…”

Section: ■ Results and Discussionmentioning

confidence: 55%

“…12,13 The catalytic behavior of ceria is directly linked to its accessible mixed valence Ce 3+ /Ce 4+ redox states, its oxygen storage capacity, 6 and surface vacancy concentrations. 16 Recent in situ studies on ceria and doped ceria have shown that surface oxygen vacancies are either linked to underlying Ce 3+ ions or clustered around Ce 3+ ions when vacancy concentrations are high. 16,17 While the oxygen mobility and catalytic behavior of ceria have been directly linked to the surface oxygen vacancy concentration, 16 the mechanisms of catalysis and electrocatalysis remain largely unknown.…”

Section: ■ Introductionmentioning

confidence: 99%

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Mechanistic Studies of Water Electrolysis and Hydrogen Electro-Oxidation on High Temperature Ceria-Based Solid Oxide Electrochemical Cells

et al. 2013

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Through the use of ambient pressure X-ray photoelectron spectroscopy (APXPS) and a single-sided solid oxide electrochemical cell (SOC), we have studied the mechanism of electrocatalytic splitting of water (H 2 O + 2e − → H 2 + O 2− ) and electro-oxidation of hydrogen (H 2 + O 2− → H 2 O + 2e − ) at ∼700°C in 0.5 Torr of H 2 /H 2 O on ceria (CeO 2−x ) electrodes. The experiments reveal a transient buildup of surface intermediates (OH − and Ce 3+ ) and show the separation of charge at the gas−solid interface exclusively in the electrochemically active region of the SOC. During water electrolysis on ceria, the increase in surface potentials of the adsorbed OH − and incorporated O 2− differ by 0.25 eV in the active regions. For hydrogen electro-oxidation on ceria, the surface concentrations of OH − and O 2− shift significantly from their equilibrium values. These data suggest that the same charge transfer step (H 2 O + Ce 3+ ⇔ Ce 4+ + OH − + H • ) is rate limiting in both the forward (water electrolysis) and reverse (H 2 electrooxidation) reactions. This separation of potentials reflects an induced surface dipole layer on the ceria surface and represents the effective electrochemical double layer at a gas−solid interface. The in situ XPS data and DFT calculations show that the chemical origin of the OH − /O 2− potential separation resides in the reduced polarization of the Ce−OH bond due to the increase of Ce 3+ on the electrode surface. These results provide a graphical illustration of the electrochemically driven surface charge transfer processes under relevant and nonultrahigh vacuum conditions. ■ INTRODUCTIONUnderstanding the mechanisms of charge separation and charge transfer at electrochemical interfaces is essential for the rational development of electrochemical devices, such as batteries, fuel cells, electrolyzers, and supercapacitors. 1,2 However, the materials and operating conditions employed in real world applications of these technologies are usually quite different from those used in surface science studies on model systems (i.e., the "pressure and materials gap"). 3−5 This disconnect is particularly problematic with high temperature electrochemical energy conversion devices with multicomponent materials (e.g., solid oxide fuel cells, electrolyzers, and electrocatalytic fuel processors) 6 for which in situ surface experiments at cell operating temperatures (typically >500°C) are challenging. 7 Because of the experimental constraints of most surface science experiments, the knowledge and understanding of the surface processes at relevant conditions are limited and rely on extrapolations from ultrahigh vacuum (UHV) conditions and modeling studies. 8 As a result, the electrochemical surface processes are not well understood. For example, the nonFaradaic electrochemical modification of catalytic activity (NEMCA or EPOC) 9 can significantly enhance the rates of catalytic transformation of over 100 reactions, 3,10 yet the origins of this enhancement are not fully understood. 3 Even the mechanism ...

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“…Although there is as yet no consensus on the effect of the ceria nanoshape on the catalyst selectivity, the catalysts containing nanorods and nanocubes exhibited higher coke resistance compared with polyhedral ceria catalysts. It has been claimed that oxygen storage and release can occur both at the surface and in the bulk of ceria nanorods and nanocubes but it is restricted only to the surface of nanopolyhedra [27]. This would benefit the gasification of coke deposits [28].…”

Section: Introductionmentioning

confidence: 99%

The influence of nano-architectured CeO supports in RhPd/CeO2 for the catalytic ethanol steam reforming reaction

Divins

Casanovas

et al. 2015

Catalysis Today

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a b s t r a c tThe ethanol steam reforming (ESR) reaction has been tested over RhPd supported on polycrystalline ceria in comparison to structured supports composed of nanoshaped CeO2 cubes and CeO2 rods tailored toward the production of hydrogen. At 650-700 K the hydrogen yield follows the trend RhPd/CeO2 -cubes > RhPd/CeO2 -rods > RhPd/CeO2 -polycrystalline, whereas at temperatures higher than 800 K the catalytic performance of all samples is similar and close to the thermodynamic equilibrium. The improved performance of RhPd/CeO2 -cubes and RhPd/CeO2 -rods for ESR at low temperature is mainly ascribed to higher water-gas shift activity and a strong interaction between the bimetallic-oxide support interaction. STEM analysis shows the existence of RhPd alloyed nanoparticles in all samples, with no apparent relationship between ESR performance and RhPd particle size. X-ray diffraction under operating conditions shows metal reorganization on {1 0 0} and {1 1 0} ceria crystallographic planes during catalyst activation and ESR, but not on {1 1 1} ceria crystallographic planes. The RhPd reconstructing and tuned activation over ceria nanocubes and nanorods is considered the main reason for better catalytic activity with respect to conventional catalysts based on polycrystalline ceria.

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Oxygen Vacancy Clusters Promoting Reducibility and Activity of Ceria Nanorods

Cited by 1,112 publications

References 29 publications

Gold Stabilized by Nanostructured Ceria Supports: Nature of the Active Sites and Catalytic Performance

Gold Stabilized by Nanostructured Ceria Supports: Nature of the Active Sites and Catalytic Performance

Mechanistic Studies of Water Electrolysis and Hydrogen Electro-Oxidation on High Temperature Ceria-Based Solid Oxide Electrochemical Cells

The influence of nano-architectured CeO supports in RhPd/CeO2 for the catalytic ethanol steam reforming reaction

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