Entropic contributions enhance polarity compensation for CeO2(100) surfaces

Capdevila‐Cortada, Marçal; López, Núria

doi:10.1038/nmat4804

Cited by 93 publications

(101 citation statements)

References 60 publications

(57 reference statements)

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“…Capdevila-Cortada et al showed that surface disorder created by partial removal of O could kinetically stabilise the bare (100) surface through fast surface diffusion process among nearly degenerate VO configurations. [46]. Judging from the positive value of the VO formation energy on fully water covered (100) surface, we infer that full water coverage can also provide a stabilisation mechanism for CeO2 (100) surface.…”

Section: Discussionmentioning

confidence: 74%

Theoretical insights into the hydrophobicity of low index CeO2 surfaces

Fronzi

Assadi

Hanaor

2019

Applied Surface Science

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The hydrophobicity of CeO2 surfaces is examined here. Since wettability measurements are extremely sensitive to experimental conditions, we propose a general approach to obtain contact angles between water and ceria surfaces of specified orientations based on density functional calculations. In particular, we analysed the low index surfaces of this oxide to establish their interactions with water. According to our calculations, the CeO2 (111) surface was the most hydrophobic with a contact angle of Θ = 112.53° followed by (100) with Θ = 93.91°. The CeO2 (110) surface was, on the other hand, mildly hydrophilic with Θ = 64.09°. By combining our calculations with an atomistic thermodynamic approach, we found that the O terminated (100) surface was unstable unless fully covered by molecularly adsorbed water. We also identified a strong attractive interaction between the hydrogen atoms in water molecules and surface oxygen, which gives rise to the hydrophilic behaviour of (110) surfaces. Interestingly, the adsorption of water molecules on the lower-energy (111) surface stabilises oxygen vacancies, which are expected to enhance the catalytic activity of this plane. The findings here shed light on the origin of the intrinsic wettability of rare earth oxides in general and CeO2 surfaces in particular and also explain why CeO2 (100) surface properties are so critically dependant on applied synthesis methods. of the contact angle of water at the surface (Θ). Typically, materials are defined as super-hydrophilic if Θ is close to 0°, and super-hydrophobic if Θ is larger than 150°.Recent experiments have identified robust intrinsic hydrophobicity of surfaces in rare-earth oxides (REOs), giving a prospect to multiple novel applications [3][4][5][6]. Moreover, the wetting characteristics of this class of material are of importance towards interpreting and improving their catalytic activity. In particular, hydrophobicity confers resistance to water deactivation at catalyst surfaces and enhances the adsorption of organic compounds. Consequently, hydrophobicity, or organophilicity, is frequently associated with higher performance and is often a desired trait in applications involving the oxidation of organic compounds and selective synthesis [7][8][9][10][11]. The lower levels of hydroxyl ion driven surface defects associated with hydrophobicity are further known to enhance luminescence [12]. In recent years, interest in hydrophobic surfaces has been further driven by heat transfer applications, as dropwise water condensation has been found to be a highly effective heat transfer mechanism. As intrinsically hydrophobic ceramic materials, REOs are particularly attractive for such applications, relative to surface functionalised materials, owing to their thermal and chemical robustness.Because of its diverse functionality and the facile tunability of its bulk-and surface properties, cerium oxide, crystallising in a cubic fluorite structure, is the most widely studied REO [13,14]. CeO2 is often studied in nanoparticle, pristine and do...

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Section: Discussionmentioning

confidence: 74%

Theoretical insights into the hydrophobicity of low index CeO2 surfaces

Fronzi

Assadi

Hanaor

2019

Applied Surface Science

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“…For the (100) surface, half of the topmost oxygens were moved from the surface top layer to the bottom layer in order to reduce the polarity and render the system stoichiometric. Starting from this trench-like structure, two other low-energy reconstructions were investigated 33 . Each of these reconstructions allows for a different coordination shell around single-atom Pt.…”

Section: Methodsmentioning

confidence: 99%

“…Therefore, we focus on these slabs as models for local, nanostructured regions (for example, step or edge sites) 24 . The low coordination of the surface oxygen atoms on the oxygen-terminated version increases their mobility 33 . As such, (100) restructures into various coexisting patterns at elevated temperatures encountered during pretreatment.…”

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confidence: 99%

Dynamic charge and oxidation state of Pt/CeO2 single-atom catalysts

2019

Self Cite

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The catalytic activity of metals supported on oxides depends on their charge and oxidation state. Yet, the determination of the degree of charge transfer at the interface remains elusive. Here, by combining density functional theory and first-principles molecular dynamics on Pt single atoms deposited on the CeO 2 (100) surface, we show that the common representation of a static metal charge is oversimplified. Instead, we identify several well-defined charge states that are dynamically interconnected and thus coexist. The origin of this new class of strong metal-support interactions is the relative position of the Ce(4f) levels with respect to those of the noble metal, allowing electron injection to (or recovery from) the support. This process is phonon-assisted, as the Ce(4f) levels adjust by surface atom displacement, and appears for other metals (Ni) and supports (TiO 2 ). Our dynamic model explains the unique reactivity found for activated single Pt atoms on ceria able to perform CO oxidation, meeting the Department of Energy 150 °C challenge for emissions.

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“…This method has been used extensively in the case of ceria to describe its 4f states. [94][95][96] Although one can choose the on-site Hubbard interaction self-consistently, 97,98 it is usually chosen to fit to a given property, and that makes the method less robust and generalizable. Despite the fact that there are methods that have been developed to improve the robustness of calculation for periodic systems, including Green's function for periodic systems, 99 wave function in DFT embedding scheme for periodic systems, 100,101 hybrid functionals based on screened Coulomb potential, [102][103][104] and periodic coupled cluster, [105][106][107] there is still a need of reliable and affordable method for surface-deposited nanoclusters.…”

Section: Notes On the Computational Methodsmentioning

confidence: 99%

Surface‐supported cluster catalysis: Ensembles of metastable states run the show

Zandkarimi

Alexandrova

2019

WIREs Comput Mol Sci

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It has recently been shown that the dynamic behavior of surface‐supported nanocluster catalysts in realistic reaction conditions defies conventional models used in catalysis. This opens new doors in catalysis by giving more leverage in catalyst design, but also requires a major revision of the understanding of how dynamic heterogeneous catalytic interfaces operate, as well as of the computational approaches of catalyst modeling, and experimental methods of catalyst characterization. Major aspects of the new paradigm include the collective action of many catalyst states that form a statistical ensemble in reaction conditions, the catalytic activity and selectivity being driven by rare and metastable catalyst states, reaction thermodynamics and kinetics being controlled by different states of the catalyst, broken scaling relationships, non‐Arrhenius behaviors, and catalyst dynamic restructuring being an essential part of the reaction mechanism. For computation, this complexity means the departure from the standard density functional theory calculations of reaction mechanisms on a single catalyst structure. For experiment, it calls for the development of operando characterization tools with the per‐site resolution and the ability to find the minority sites that govern the catalytic activity. For catalyst design, the goal becomes the creation of the catalyst state (geometric and electronic) that might not be present in the as‐prepared catalyst, but would develop in the reaction conditions and would have the desired activity then. While cluster catalysts are the most dramatic in their dynamic fluxionality, other amorphous interfaces also exhibit some of it, and thus are also subject to similar paradigm revision. This article is categorized under: Structure and Mechanism > Reaction Mechanisms and Catalysis

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Entropic contributions enhance polarity compensation for CeO2(100) surfaces

Cited by 93 publications

References 60 publications

Theoretical insights into the hydrophobicity of low index CeO2 surfaces

Theoretical insights into the hydrophobicity of low index CeO2 surfaces

Dynamic charge and oxidation state of Pt/CeO2 single-atom catalysts

Surface‐supported cluster catalysis: Ensembles of metastable states run the show

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