Carbonylation and Decarbonylation of γ-Al2O3-Supported Hexarhodium Clusters:  Characterization by Infrared, 13C NMR, and Extended X-ray Absorption Fine Structure Spectroscopies

Alexeev, Oleg S.; Panjabi, Ghansham; Phillips, and Brian L.; Gates, Bruce C.

doi:10.1021/la0348970

Cited by 12 publications

(14 citation statements)

References 25 publications

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“…He recently co-chaired a DOE workshop on Basic Research Needs: Catalysis for Energy. Rh 6 (CO) 16 also adsorbs without fragmentation of the metal frame on g-Al 2 O 3 , 31,32 MgO, 13 TiO 2 , 14 and zeolite NaY. 17 The adsorption on MgO calcined at 673 K gave a sample with n CO peaks similar to those of [Rh 6 (CO) 15 (COOMg)] À33 and [Rh 6 (CO) 15 ] 2À Mg 2+ .…”

Section: Bruce C Gatesmentioning

confidence: 96%

“…Moreover, the O atom of a CO ligand can be differentiated from the other light scatterers because of the multiple scattering that occurs when there is a linear arrangement of three atoms. 99 The multiple scattering has been demonstrated for supported carbonyl clusters of osmium, 24,44,50,87 ruthenium, 8,100 rhenium, 77,101 rhodium, 16,32 iridium, 38,102 and others. For example, the Os-C and Os-O* distances (O* is carbonyl oxygen) in supported clusters approximated as pentaosmium carbonyls were found to be 1.91 and 3.11 A ˚, respectively; 50 for comparison, the respective distances in crystalline [Os 5 (CO) 14 ] 2À are 1.88 and 3.05 A ˚.103 EXAFS spectroscopy is usually not sufficient to identify hydrocarbon ligands on supported metal clusters.…”

Section: Iiib Characterization Of Ligands On Metal Framesmentioning

confidence: 99%

“…For example, IR, 13 C NMR, and EXAFS data indicated the adsorption of Rh 6 (CO) 16 largely intact on g-Al 2 O 3 . 32 The clusters were decarbonylated at 573 K in helium with the Rh 6 cluster frame remaining intact. EXAFS data showed that the decarbonylation involved shrinkage of the cluster core, with the Rh-Rh bond distance decreasing from 2.75 to 2.67 A ˚.…”

Section: Theoretical Calculationsmentioning

confidence: 99%

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Metal clusters on supports: synthesis, structure, reactivity, and catalytic properties

2010

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This review of structurally simple and essentially molecular metal clusters on solid supports addresses synthesis, characterization, reactivity, and catalysis. Examples of supported clusters made in high yields are Os(3), Ir(4), Ir(6), and Rh(6), and typical supports are MgO, gamma-Al(2)O(3), and zeolites. Supported clusters are synthesized by adsorption of ligated molecular metal clusters, deposition of bare size-selected metal clusters from the gas phase, and adsorption of metal complexes followed by treatment to form clusters. Some metal clusters on supports have been imaged with atomic resolution. Reactions of supported metal clusters include ligand modifications, oxidative fragmentation, and migration leading to aggregation. Reactivities and catalytic properties of the clusters (e.g., for alkene hydrogenation and epoxidation) depend on the cluster size and the support (which acts as a ligand) and are distinct from those of supported particles that resemble bulk metals. Opportunities for deeper understanding of the chemistry of supported metal clusters hinge on improvements in characterization techniques such as X-ray absorption spectroscopy and high-resolution transmission electron microscopy.

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Section: Bruce C Gatesmentioning

confidence: 96%

Section: Iiib Characterization Of Ligands On Metal Framesmentioning

confidence: 99%

Section: Theoretical Calculationsmentioning

confidence: 99%

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Metal clusters on supports: synthesis, structure, reactivity, and catalytic properties

2010

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“…Metal carbonyl clusters have been explored as molecular precursors of uniform supported metal clusters, , via cluster decarbonylation with retention of the metal framework. For example, Ir 4 /γ-Al 2 O 3 was synthesized by adsorption of Ir 4 (CO) 12 followed by decarbonylation.…”

Section: Experimental and Computational Approaches In The Investigati...mentioning

confidence: 99%

Beyond Ordered Materials: Understanding Catalytic Sites on Amorphous Solids

et al. 2017

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Amorphous materials are widely used as components of solid catalysts, and have been the subject of much applied research. In some instances, their catalytic performance is demonstrably superior to that of their crystalline counterparts, due in part to their greater flexibility. Amorphous or disordered phases can also be generated from crystalline phases under reaction conditions, thus ex-situ observations of long-range order may provide an incomplete or misleading picture. Until recently, theorists and experimentalists have mostly neglected these important materials in fundamental studies, preferring instead to study “well-defined” (often crystalline) catalysts that are potentially more tractable and amenable to computational modeling of their structure-activity relationships. The amorphous materials were assumed to be simply non-uniform versions of compositionally-similar materials with long-range order, having the same key features at short and medium length scales. In this Perspective, shortcomings of this assumption are discussed, as well as challenges inherent in tackling amorphous catalysts more directly, namely, identifying and describing the active sites (especially under reaction conditions), discerning how subtle structural variations modulate site activity, and building atomically detailed models of amorphous catalysts. Three important classes of amorphous catalytic materials are highlighted to illustrate key issues: amorphous oxides, metal ions atomically dispersed on amorphous supports, and supported metal clusters. Amorphous and disordered silicas, aluminas, and silica-aluminas, are discussed in terms of challenges and progress toward identifying how their local structural disorder and surface heterogeneity may impact the behavior of active sites. Promising models of amorphous materials with atomistic detail and increased fidelity to experiment are becoming available. However, for reactions in which small fractions of sites dominate the total activity, computational estimates of the observed kinetics will require statistical sampling methods, even for the most detailed catalyst models. Further developments in in situ and operando characterization techniques and computational modeling will advance our understanding of amorphous catalytic materials and the impact of structural disorder

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“…In a recent paper the XAFS spectra of a Rh(0) 6 metal cluster and Rh 6 (CO) 16 on alumina showed that the Rh-Rh distances are 2.68 and 2.75 Å, respectively. 9 The XAFS spectrum of the Rh(0) 6 metal cluster resembles that of the bulk metal except the amplitude is lower. However, the absorption spectrum of the Rh carbonyl complex shows a significant phase shift due to the longer Rh-Rh distance.…”

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confidence: 97%

In Situ XAFS and NMR Study of Rhodium-Catalyzed Dehydrogenation of Dimethylamine Borane

et al. 2005

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In situ X-ray absorption fine structure spectroscopy (XAFS) and 11B NMR were used to study the rhodium-catalyzed dimerization reaction of dimethylaminoborane, (CH3)2NHBH3 or DMAB. XAFS spectra show that the active form of the rhodium catalyst is most likely composed of a six-atom Rh core surrounded by tightly bound external ligands. NMR results show the presence of monomeric dimethylamine borane (CH3)2NBH2, providing evidence that hydrogen formation from the homogeneous Rh species occurs by an intramolecular pathway. This is in contrast to thermal pathways that involve intermolecular B-N concurrent with hydrogen formation. This work shows that in situ XAFS spectroscopy offers a unique experimental tool to differentiate between heterogeneous and homogeneous catalysis.

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Carbonylation and Decarbonylation of γ-Al₂O₃-Supported Hexarhodium Clusters: Characterization by Infrared, ¹³C NMR, and Extended X-ray Absorption Fine Structure Spectroscopies

Cited by 12 publications

References 25 publications

Metal clusters on supports: synthesis, structure, reactivity, and catalytic properties

Metal clusters on supports: synthesis, structure, reactivity, and catalytic properties

Beyond Ordered Materials: Understanding Catalytic Sites on Amorphous Solids

In Situ XAFS and NMR Study of Rhodium-Catalyzed Dehydrogenation of Dimethylamine Borane

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