Reversing Size‐Dependent Trends in the Oxidation of Copper Clusters through Support Effects

Mammen, Nisha; Tyo, Eric C.; Yang, Bing; Halder, Avik; Seifert, Sönke; Pellin, Michael J.; Vajda, Štefan; Narasimhan, Shobhana

doi:10.1002/ejic.201701355

Cited by 23 publications

(41 citation statements)

References 40 publications

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“…This suggests that cluster mobility is difficult on the oxide support, in link with the experimental evidence that clusters do not sinter in the considered oxidative conditions. 34,[52][53] The GCBH approach generated a wide range of stoichiometries from Cu 4 O 2 to Though the precise agreement between such a prediction and experimental measurement is still challenging due to the approximate nature of the density functional, the impacts of clusters' structural fluxionality on the description of the phase diagram is however an intrinsic property that must be taken into account for investigating the stabilities of similar system. 57 If we consider type 1 and type 2 clusters separately, and assume that isomer equilibrium is seen only within the same type of isomers, the optimal stoichiometries of clusters of each type change with a similar trend, but the two types of Cu 4 O x clusters show different phase transition temperatures (Figure 1(c) Table S2).…”

Section: Introductionmentioning

confidence: 99%

Structural Rearrangements of Subnanometer Cu Oxide Clusters Govern Catalytic Oxidation

2020

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Sub-nanometer metal oxide clusters are very important materials, widely used for example in catalysis or electronic devices such as sensors. Hence, it is critical to understand the atomic structures and properties of subnanometer metal oxide clusters under a reactive gas environment, such as O 2. We consider here experimentally-accessible precise-size Cu clusters (Cu 4) supported on partial hydroxylated amorphous alumina and show that such clusters can access, in catalytic conditions at high temperature under a pressure of O 2 , a large ensemble of oxidized structures, representing a large variety of oxygen content, of geometries in link with the support, and of catalytic activities for oxidation reactions, as seen from their reducibilities. A 1 grand canonical basin hopping method based on first-principles energy, reveals an ensemble of 24 configurations for the Cu 4 O x cluster of low free energy, less than 0.8 eV above the global minimum. The low free energy ensemble consists of clusters of different stoichiometries, which are mainly Cu 4 O 3 and Cu 4 O 4 in the temperature range of 200−400 ℃ and under a pressure of 0.5 bar of O 2. The presence of several competitive isomers at each composition implies that cluster fluxionality impacts the phase diagram, which should be ensemble-averaged. In terms of catalytic oxidation activity, Cu 4 O 3 isomers present highly variable O abstraction energy: the most stable isomers are inactive for alkane oxidative dehydrogenation, but isomerization to metastable isomers, that proceed with low barrier, enable to create active configurations with low O abstraction energy. O atoms with lowest anionic character, and thus of more electrophilic nature, present the best oxidation capability. In contrast, all Cu 4 O 4 isomers show a low O abstraction energy and a high potential catalytic activity. This manuscript demonstrates the unique structural and electronic properties of sub-nano Cu oxides clusters and illustrates the critical roles of configuration ensembles and rearrangement to highly reactive metastable cluster isomers in nanocatalysis.

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Section: Introductionmentioning

confidence: 99%

Structural Rearrangements of Subnanometer Cu Oxide Clusters Govern Catalytic Oxidation

2020

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“…[4][5][6][7][8] XANES is sensitive to geometry and to the oxidation state of the metal center, which makes it an important tool to distinguish between different structures. [9][10][11][12] The pre-edge region can be used to estimate the ligand field, spin state, and centrosymmetry of the site. [13][14][15][16][17] On the other hand, the rising-edge region can give information about geometric structure, metal-ligand overlap, ligand arrangement, and charge on the metal center.…”

Section: Introductionmentioning

confidence: 99%

Interpreting the Operando XANES of Surface-Supported Subnanometer Clusters: When Fluxionality, Oxidation State, and Size Effect Fight

et al. 2020

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X-ray absorption near edge structure (XANES) spectroscopy is widely used for operando catalyst characterization. We show that, for highly fluxional supported nanoclusters, the customary extraction of the oxidation state of the metal from the XANES data by fitting to the bulk standards is highly questionable. The XANES signatures, as well as the apparent oxidation state for such clusters arise from a complex combination of many factors, and not only from the chemical composition in reaction conditions (e.g. oxygen content in oxidizing astrosphere). The thermallyaccessible isomerization and population of several structurally distinct cluster forms, clustersupport interaction, and intrinsic size effects all impact the metal oxidation state and XANES signal. We demonstrate this on copper oxide clusters with different compositions, Cu4Ox(x = 2-5) and Cu5Oy (y = 3, 5), deposited on amorphous alumina and ultrananocrystalline diamond (UNCD), for which we computed the XANES spectra and compare the results to the experiment. We show in addition that fitting the experimental spectrum to calculated spectra of supported clusters can in contrast provide good agreement and insight on the spectrum-composition-structure relation. Experimental XANES interpreted using the proposed fitting scheme shows the partial reduction of Cu oxide clusters at rising temperatures, and pinpoints the specific stoichiometries that dominate in the ensemble of cluster states as the temperature changes.

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“…Tiny Cu n clusters is another example. In contrast to the gas-phase Cu n clusters, which are more difficult to oxidize the smaller they are, the supported on amorphous alumina Cu 4 were found to be oxidized easier compared to Cu 12 and Cu 20 [188]. This can be seen in the theoretically-obtained phase diagrams presented in Figure 13.…”

Section: Catalytic Applications Of Size-selected Clustersmentioning

confidence: 88%

“…This can be seen in the theoretically-obtained phase diagrams presented in Figure 13. The predictions were proven by experimentally-measured temperature at which the transition from Cu n O n/2 to Cu n occurs in a H 2 -rich environment [188]. The studies of small metal clusters and also of metal alloys have shown that expensive metals can be substituted by cheaper ones while keeping the catalytic efficiency at the same level [161,189].…”

Section: Catalytic Applications Of Size-selected Clustersmentioning

confidence: 88%

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Gas-Phase Synthesis of Functional Nanomaterials

Popok

Kylián

2020

Applied Nano

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Nanoparticles (NPs) of different types, especially those of metals and metal oxides, are widely used in research and industry for a variety of applications utilising their unique physical and chemical properties. In this article, the focus is put on the fabrication of nanomaterials by means of gas-phase aggregation, also known as the cluster beam technique. A short overview of the history of cluster sources development emphasising the main milestones is presented followed by the description of different regimes of cluster-surface interaction, namely, soft-landing, pinning, sputtering and implantation. The key phenomena and effects for every regime are discussed. The review is continued by the sections describing applications of nanomaterials produced by gas aggregation. These parts critically analyse the pros and cons of the cluster beam approach for catalysis, formation of ferromagnetic and superparamagnetic NPs, applications in sensor and detection technologies as well as the synthesis of coatings and composite films containing NPs in research and industrial applications covering a number of different areas, such as electronics, tribology, biology and medicine. At the end, the current state of the knowledge on the synthesis of nanomaterials using gas aggregation is summarised and the strategies towards industrial applications are outlined.

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Reversing Size‐Dependent Trends in the Oxidation of Copper Clusters through Support Effects

Cited by 23 publications

References 40 publications

Structural Rearrangements of Subnanometer Cu Oxide Clusters Govern Catalytic Oxidation

Structural Rearrangements of Subnanometer Cu Oxide Clusters Govern Catalytic Oxidation

Interpreting the Operando XANES of Surface-Supported Subnanometer Clusters: When Fluxionality, Oxidation State, and Size Effect Fight

Gas-Phase Synthesis of Functional Nanomaterials

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