Ligand-Free Osmium Clusters Supported on MgO. A Density Functional Study

Goellner, Jesse F.; Neyman, Konstantin M.; Mayer, Markus; Nörtemann, Folke; Gates, Bruce C.; Rösch, Notker

doi:10.1021/la9912388

Cited by 46 publications

(63 citation statements)

References 45 publications

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“…DFT calculations [14] show that metal clusters are bonded to MgO by metal-oxygen bonds, [15] consistent with the results observed generally by EXAFS spectroscopy for Group 8 metal clusters on metal oxides [16] and in agreement with our EXAFS results as well. (EXAFS data indicate distortion of CO ligands on adsorbed metal clusters to accommodate to the support surface.)…”

supporting

confidence: 91%

“…The images of the clusters shown in Figure 2 provide a basis for determining a model of the structures of the clusters that include the Osoxygen bonds indicated by the EXAFS data [16] and DFT calculations. [15] We investigated all the models of the structures of the clusters on the MgO(110) face that match the data-that is, those having 3 Os atoms atop Mg atoms arranged in a triangle that is isosceles when viewed from the top and anchored through OsÀO bonds. The models are based on the observed OsÀOs distances and the structures of sites known to exist on MgO(110).…”

mentioning

confidence: 99%

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Atomic Resolution of the Structure of a Metal–Support Interface: Triosmium Clusters on MgO(110)

Kulkarni¹,

Chi

Ortalan³

et al. 2010

Angew Chem Int Ed

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Catalysts are the keys to control of chemical change, being essential for efficient production of chemicals, fuels, and polymeric materials and for pollution abatement. They are likely to be central to new technologies for biomass conversion. Many practical catalysts include metals, usually as nanoclusters or particles dispersed on a porous high-area metal oxide support. When the clusters consist of about 10 or fewer atoms, their properties differ from those of the bulk metal-and depend strongly on the cluster size and interactions with the support.[1] Metal-support interactions may be so significant that clusters of a particular metal on various supports can have widely different catalytic activities and selectivities, as illustrated, for example, by the performance of supported gold [2] and silver clusters.[3]Determinations of nanocluster size and its importance on catalyst performance are now compelling, and high-resolution transmission electron microcopy (TEM) has played an important role in advancing the science.[4] Aberration-corrected scanning TEM (STEM) has recently been used to image individual metal atoms on [5] and in [6] supports, single layers of metal atoms on supports, [7] and clusters of only a few atoms each on [8] and in [6] supports. However, TEM imaging of supported metal nanoclusters has been restricted to the determination of cluster structures and sizes without characterization of the metal-support interface, [9] and understanding of support effects in catalysis remains limited.[10] There is a need for direct determination of atomic-scale structures of metal-support interfaces. Now we show how aberrationcorrected STEM images of extremely small supported metal clusters, complemented by spectroscopy, provide structural information about the metal-support interface.Our goal was to synthesize extremely small and uniform metal clusters on a support and characterize them with atomic-resolution STEM and extended X-ray absorption fine structure (EXAFS) spectroscopy to gain information about both the clusters and the support and the bonding between them. We used a compound of a Group 8 metal with metalmetal bonds as the precursor-[Os 3 (CO) 12 ], which has a stable triangular frame of Os atoms stabilized by the ligands. Our support was high-area powder MgO because it is commonly used in industrial catalysts and consists of highly crystalline particles that expose various faces. The quality of the sample was determined by the MgO calcination temperature (673 K), chosen because it is approximately the highest temperature suitable for decarbonation with partial dehydroxylation of this support without substantial reconstruction or thermal faceting.[11] The success of the synthesis of triosmium carbonyl clusters on MgO is borne out by the EXAFS spectra, indicating an average Os À Os coordination number of 2, within error, as in [Os 3 (CO) 12 ], with its triangular frame, and consistent within error with the adsorption of all the clusters with the metal frames intact. The EXAFS OsÀOs distance (an average ...

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supporting

confidence: 91%

mentioning

confidence: 99%

Atomic Resolution of the Structure of a Metal–Support Interface: Triosmium Clusters on MgO(110)

Kulkarni¹,

Chi

Ortalan³

et al. 2010

Angew Chem Int Ed

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“…These distances are markedly greater (by about 0.2-0.3 Å) than the metal-metal distances in the free (gas-phase) clusters (e.g., Ir 4 , 2.44 Å) [51]. Similar results have been determined for supported Os 5 C [52] and Rh 6 [53]. These comparisons led the Rösch group [51,52] to conclude that some ligands remain on the clusters after decarbonylation; this conclusion may be quite general.…”

Section: Structural Characterizationsupporting

confidence: 77%

“…Similar results have been determined for supported Os 5 C [52] and Rh 6 [53]. These comparisons led the Rösch group [51,52] to conclude that some ligands remain on the clusters after decarbonylation; this conclusion may be quite general. The candidate ligands include C (from CO ligands of the precursor) and H (from the support).…”

Section: Structural Characterizationsupporting

confidence: 72%

Well-Defined Metallic and Bimetallic Clusters Supported on Oxides and Zeolites

Guzmán

2009

Model Systems in Catalysis

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Immobilized metallic and bimetallic complexes and clusters on oxide or zeolite supports made from well-defined molecular organometallic precursors have drawn wide attention because of their novel size-dependent properties and their potential applications for catalysis. It is speculated that nearly molecular supported catalysts may combine the high activity and selectivity of homogenous catalysts with the ease of separation and robustness of operation of heterogeneous catalysts. This chapter is a review of the synthesis and physical characterization of metallic and bimetallic complexes and clusters supported on metal oxides and zeolites prepared from organometallic precursors of well-defined molecularity and stoichiometry. IntroductionRational design of catalysts guided by fundamental principles correlating composition, structure, and ligand environment with catalyst activity and selectivity has been a longstanding goal in the field of catalysis [1, 2]. Several approaches have been pursued to identify the nature of the active centers, reaction mechanisms, and the kinetics of catalytic processes, including experimental and theoretical investigations of model systems and industrial catalysts. Nevertheless, our understanding of the relationship between active center properties and catalytic performance is far from complete. Even the most thoroughly characterized supported metal catalysts prepared conventionally from salt precursors are less than well understood, because of the limitations of both the samples (nonuniformity of the metal entities) and standard characterization methods, such as N 2 -adsorption, temperature programmed reduction (TPR), etc. In the last few decades, researchers have worked toward the development and use of simple models of supported

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“…The MgO(100) surface in general is highly studied as a supporting material for metal clusters. 28,29 Hence, motivation exists to investigate a model system of sub-nanometer Pt and Pt-Zn clusters deposited on MgO(100) surfaces. It is noted that, previously, others have shown that nanometer sized clusters of group 10 elements (in particular, clusters of Pt, Pd, and Pt-based bi-metallics) undergo morphological changes when deposited on oxide supports, including MgO.…”

Section: Introductionmentioning

confidence: 99%

Pure and Zn-doped Pt clusters go flat and upright on MgO(100)

Shen

Dadras

Alexandrova

2014

Phys. Chem. Chem. Phys.

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Pure and doped sub-nanoclusters can exhibit superb catalytic activity, which, however, strongly depends on their size, shape, composition, and the nature of the support. This work is about surface-deposited sub-nano Pt-based clusters, which are promising catalysts for the reactions of dehydrogenation. Using density functional theory and ab initio calculations, and an ab initio genetic algorithm for finding the global minima of clusters, we found a peculiar effect that Pt 5 and Pt 4 Zn clusters exhibit upon deposition on MgO(100). Both of them change shapes from the gas phase 3-D form to a planar form, and they stand upright on the support. Several reasons are responsible for this behaviour. In part, clusters go flat due to the electron transfer from the support. Indeed, the anionic Pt 5 À and Pt 4 Zn À species are flat also in the gas phase. Charging induces the second-order Jahn-Teller effect (or partial covalency) facilitated by the recruitment of the higher-energy 6p atomic orbitals on Pt into the valence manifold, and that is the reason for the planarization of the anions. Secondly, clusters maximize interactions with the surface O atoms (resulting in further favouring of 2-D structures over 3-D), and avoid contacts with surface Mg atoms (resulting in upright morphologies).

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Ligand-Free Osmium Clusters Supported on MgO. A Density Functional Study

Cited by 46 publications

References 45 publications

Atomic Resolution of the Structure of a Metal–Support Interface: Triosmium Clusters on MgO(110)

Atomic Resolution of the Structure of a Metal–Support Interface: Triosmium Clusters on MgO(110)

Well-Defined Metallic and Bimetallic Clusters Supported on Oxides and Zeolites

Pure and Zn-doped Pt clusters go flat and upright on MgO(100)

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