Structure of Nano‐sized CeO<sub>2</sub> Materials: Combined Scattering and Spectroscopic Investigations

Marchbank, Huw R; Clark, Adam H.; Hyde, Timothy I.; Playford, Helen Y.; Tucker, Matthew G.; Thompsett, David; Fisher, Janet M.; Chapman, Karena W.; Beyer, Kevin A.; Monte, Manuel J.S.; Longo, Alessandro; Sankar, Gopinathan

doi:10.1002/cphc.201600697

Cited by 21 publications

(23 citation statements)

References 31 publications

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“…XAS methods can readily be used to probe the in situ redox properties of ceria and to determine the oxidation state of cerium with a high degree of certainty using HERFD-XANES. Here we undertook quantitative assessment of the proportion of Ce(IV) and Ce(III) using Ce L3-edge XANES through a peak fitting methodology [34][35][36] , possible due to the high energy resolution achievable using HERFD-XANES techniques 34,37,38 . Figure 2.…”

Section: Resultsmentioning

confidence: 99%

Unusual Redox Behavior of Ceria and Its Interaction with Hydrogen

et al. 2019

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The reaction between ceria and hydrogen has been subject to numerous theoretical and experimental studies due to its importance as a catalytic material. Here we present dynamic and reversible evolution of the cerium oxidation states observed through X-ray Absorption Spectroscopy experiments in addition to the investigation of associated lattice expansion and contraction through X-ray diffraction and PDF methods. Employing a novel calculation of the temperature dependence of the Gibbs free energy through consideration of the relationship between the instantaneous thermal lattice expansion and the rate of change of the cerium oxidation state, the unusual redox chemistry is reported here. This unusual behaviour is interpreted as due to the formation of a metastable cerium oxyhydride as suggested.

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Section: Resultsmentioning

confidence: 99%

Unusual Redox Behavior of Ceria and Its Interaction with Hydrogen

et al. 2019

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“…This value of energy gap between eg and t2g is in good agreement with previously published values. [53][54][55] Now, looking at the experimental HERFD-XANES spectra of CeO2 NPs, one can observe that all the A, B1, B2, C1 and C2 feature are presented at the same energy position as in bulk CeO2. A value of ca.…”

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confidence: 98%

Size Dependence of Lattice Parameter and Electronic Structure in CeO₂ Nanoparticles

et al. 2020

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Intrinsic properties of a compound (e.g. electronic structure, crystallographic structure, optical and magnetic properties) define notably its chemical and physical behavior. In the case of nanomaterials, these fundamental properties depend on the occurrence of quantum mechanical size effects and on the considerable increase of the surface to bulk ratio. However, the literature on this size-dependence and on the involved mechanisms is quite elusive and scarce. Here, we explore the size-dependence of both crystal and electronic properties of CeO2 nanoparticles (NPs) with different sizes by state-of-the art spectroscopic techniques. XRD, XPS and HERFD-XANES demonstrate that the as-synthesized NPs crystallize in the fluorite structure and they are predominantly composed of Ce IV ions. The strong dependence of the lattice parameter with the NPs size was attributed to the presence of adsorbed species at the NPs surface thanks to FTIR and TGA measurements. In addition, the size-dependence of the t2g level in the Ce LIII XANES spectra was experimentally observed by HERFD-XANES and confirmed by theoretical calculations.

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“…The Ce 4+ ···O 2– nearest neighbor distance is 2.368 Å in the DFT optimized cubic unit cell compared with the experimental value of 2.343 Å (ICSD structure code 182988). 70 , 71 The (110) surface contains exposed sixfold co-ordinated Ce 4+ cations with a planar arrangement of four oxygen anions around each cation in the surface. Each O 2– anion in the (110) surface is three co-ordinate with two surface and one sub-surface Ce 4+ neighbor.…”

Section: Resultsmentioning

confidence: 99%

Gas Phase Glycerol Valorization over Ceria Nanostructures with Well-Defined Morphologies

et al. 2021

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Glycerol solutions were vaporized and reacted over ceria catalysts with different morphologies to investigate the relationship of product distribution to the surface facets exposed, particularly, the yield of bio-renewable methanol. Ceria was prepared with cubic, rodlike, and polyhedral morphologies via hydrothermal synthesis by altering the concentration of the precipitating agent or synthesis temperature. Glycerol conversion was found to be low over the ceria with a cubic morphology, and this was ascribed to both a low surface area and relatively high acidity. Density functional theory calculations also showed that the (100) surface is likely to be hydroxylated under reaction conditions which could limit the availability of basic sites. Methanol space-time-yields over the polyhedral ceria samples were more than four times that for the cubic material at 400 °C, where 201 g of methanol was produced per hour per kilogram of the catalyst. Under comparable glycerol conversions, we show that the rodlike and polyhedral catalysts produce a major intermediate to methanol, hydroxyacetone (HA), with a selectivity of ca. 45%, but that over the cubic sample, this was found to be 15%. This equates to a 13-fold increase in the space-time-yield of HA over the polyhedral samples compared to the cubes at 320 °C. The implications of this difference are discussed with respect to the reaction mechanism, suggesting that a different mechanism dominates over the cubic catalysts to that for rodlike and polyhedral catalysts. The strong association between exposed surface facets of ceria to high methanol yields is an important consideration for future catalyst design in this area.

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Structure of Nano‐sized CeO₂ Materials: Combined Scattering and Spectroscopic Investigations

Cited by 21 publications

References 31 publications

Unusual Redox Behavior of Ceria and Its Interaction with Hydrogen

Unusual Redox Behavior of Ceria and Its Interaction with Hydrogen

Size Dependence of Lattice Parameter and Electronic Structure in CeO₂ Nanoparticles

Gas Phase Glycerol Valorization over Ceria Nanostructures with Well-Defined Morphologies

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Structure of Nano‐sized CeO2 Materials: Combined Scattering and Spectroscopic Investigations

Cited by 21 publications

References 31 publications

Unusual Redox Behavior of Ceria and Its Interaction with Hydrogen

Unusual Redox Behavior of Ceria and Its Interaction with Hydrogen

Size Dependence of Lattice Parameter and Electronic Structure in CeO2 Nanoparticles

Gas Phase Glycerol Valorization over Ceria Nanostructures with Well-Defined Morphologies

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Structure of Nano‐sized CeO₂ Materials: Combined Scattering and Spectroscopic Investigations

Size Dependence of Lattice Parameter and Electronic Structure in CeO₂ Nanoparticles