Supported Iridium Cluster Catalysts for Propene Hydrogenation: Identification by X-Ray Absorption Spectra Measured During Catalysis

Panjabi, Ghansham; Argo, Andrew M.; Gates, Bruce C.

doi:10.1002/(sici)1521-3765(19990802)5:8<2417::aid-chem2417>3.0.co;2-g

Cited by 18 publications

(16 citation statements)

References 19 publications

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“…5,8 ) For example, the structures of supported metal clusters as they were working as catalysts for ethylene hydrogenation or propylene hydrogenation have been characterized by EXAFS measurements. The results indicate the presence of Ir 4 supported on MgO 74,76 and on γ-Al 2 O 3 66,74-76 and of Ir 6 and of Rh 6 on MgO. 77 These data show metal-metal coordination numbers that are consistent with the presence of tetrahedral and octahedral clusters, respectively.…”

Section: Nuclearity Of Metal Species (Exafs Ir and Raman Spectroscopi...mentioning

confidence: 87%

Oxide- and Zeolite-Supported Molecular Metal Complexes and Clusters: Physical Characterization and Determination of Structure, Bonding, and Metal Oxidation State

et al. 2006

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This article is a review of the physical characterization of well-defined site-isolated molecular metal complexes and metal clusters supported on metal oxides and zeolites. These surface species are of interest primarily as catalysts; as a consequence of their relatively uniform structures, they can be characterized much more precisely than traditional supported catalysts. The properties discussed in this review include metal nuclearity, oxidation state, and ligand environment, as well as metal-support interactions. These properties are determined by complementary techniques, including transmission electron microscopy; X-ray absorption, infrared, Raman, and NMR spectroscopies; and density functional theory. The strengths and limitations of these techniques are assessed in the context of results characterizing samples that have been investigated thoroughly and with multiple techniques. The depth of understanding of well-defined metal complexes and metal clusters on supports is approaching that attainable for molecular analogues in solution. The results provide a foundation for understanding the more complex materials that are typical of industrial catalysts.

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Section: Nuclearity Of Metal Species (Exafs Ir and Raman Spectroscopi...mentioning

confidence: 87%

Oxide- and Zeolite-Supported Molecular Metal Complexes and Clusters: Physical Characterization and Determination of Structure, Bonding, and Metal Oxidation State

et al. 2006

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“…Although hydrogen interaction with dispersed Ir is important in the catalytic hydrogenation and dehydrogenation of hydrocarbons, 1,4,[16][17][18] a systematic study of this topic is missing. To contribute to this issue, we present here a detailed study on the Ir 4 cluster as well as on the bonding of a hydrogen atom to that species.…”

Section: Introductionmentioning

confidence: 99%

The cluster Ir4 and its interaction with a hydrogen impurity. A density functional study

Bussai

Krüger

Vayssilov

et al. 2005

Phys. Chem. Chem. Phys.

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To contribute to the understanding of how iridium particles act as catalysts for hydrogenation and dehydrogenation of hydrocarbons, we have determined structures and binding energies of various isomers of Ir(4) as well as HIr(4) on the basis of relativistic density functional theory. The most stable isomer of Ir(4) showed a square planar structure with eight unpaired electrons. The tetrahedral structure, experimentally suggested for supported species, was calculated 49 kJ mol(-1) less stable. Hydrogen coordinates preferentially to a single Ir center of the planar cluster with a binding energy of up to 88 kJ mol(-1) with respect to the atom in the H(2) molecule. Terminal interaction of hydrogen with an Ir(4) tetrahedron causes the cluster to open to a butterfly structure. We calculated terminal binding of hydrogen at different Ir(4) isomers to be more stable than bridge coordination, at variance with earlier studies.

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“…MgO powder (97%, EM Science) was used as received. The BET surface area of MgO 673 was approximately 60 m 2 g -1 , 11 and that of MgO 973 was approximately 18 m 2 g -1 . 2 The treatment gases used in the sample preparations were He (Matheson, 99.999%, purified by passage through traps to remove traces of O 2 and moisture) and H 2 (Matheson, 99.999%, or generated by electrolysis of water in a Balston generator (99.99%)) and purified by flow through traps.…”

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confidence: 99%

Nanoclusters of Iridium Oxide and of Rhodium Oxide Supported on MgO

Lai

Gates

2001

Nano Lett.

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MgO-supported Ir 4 and Rh 6 , prepared from [Ir 4 (CO) 12 ] and [Rh 6 (CO) 16 ], respectively, on MgO, were partially oxidized at 323 K, with partial destruction of the metal frames, and reformed by treatment in H 2 . Oxidation at higher temperatures resulted in total oxidation of the clusters with breakup of the metal frames, and treatment in H 2 led to near reconstruction of the metal clusters, but with some migration and aggregation. The results imply that the oxidized nanoclusters were site isolated on the support surface; this is the first report of oxide clusters of noble metals. The metal oxide clusters are catalytically active for CO oxidation.Nanoclusters or nanoparticles dispersed on porous supports are the common form of solid catalyst, offering the advantages of high surface area per unit volume of the catalyst and a large fraction of the catalytically active material at surfaces, where it is accessible to reactants. Typical catalysts for oxidation reactions are metal oxides and noble metals, and the latter, in operation, typically consist of nanoparticles of metal covered in part with surface oxide layers. Gas-phase oxide nanoclusters 1 have been investigated as structurally well-defined models of oxidation catalysts, but these have been restricted to oxides of nonnoble metals. Supported nanoclusters of noble metals have been thoroughly investigated, 2-4 but there are only few reports of supported nanoclusters of metal oxides, and these are oxides of non-noble metals (Fe, 5 Mo, 6 and W 7 ) supported in zeolites. We now report oxide nanoclusters of noble metals dispersed on oxide supports and their catalytic performance for oxidation of CO.The supported samples were prepared with standard airexclusion techniques by formation of nanoclusters of metal on a high-area MgO support followed by oxidation to convert the metal nanoclusters into metal oxide nanoclusters. The supported nanoclusters Ir 4 /MgO and Rh 6 /MgO were prepared from the precursors [Ir 4 (CO) 12 ] (Strem, 98%) and [Rh 6 -(CO) 16 ] (Strem, 98%), respectively. Rh 6 /MgO was synthesized by adsorption of [Rh 6 (CO) 16 ] on MgO calcined at 673 K (MgO 673 ), followed by decarbonylation in He at 573 K; Ir 4 /MgO was synthesized by adsorption of [Ir 4 (CO) 12 ] on MgO 973 followed by decarbonylation in He at 593 K. The methods are described elsewhere. 2,8-10 The decarbonylated samples were pretreated in H 2 at 573 K prior to oxidation and reduction treatments. Reagent-grade n-hexane (Aldrich), used as a solvent to bring the metal carbonyl precursors in contact with the support, was dried over sodium benzophenone ketyl. MgO powder (97%, EM Science) was used as received. The BET surface area of MgO 673 was approximately 60 m 2 g -1 , 11 and that of MgO 973 was approximately 18 m 2 g -1 . 2 The treatment gases used in the sample preparations were He (Matheson, 99.999%, purified by passage through traps to remove traces of O 2 and moisture) and H 2 (Matheson, 99.999%, or generated by electrolysis of

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Supported Iridium Cluster Catalysts for Propene Hydrogenation: Identification by X-Ray Absorption Spectra Measured During Catalysis

Cited by 18 publications

References 19 publications

Oxide- and Zeolite-Supported Molecular Metal Complexes and Clusters: Physical Characterization and Determination of Structure, Bonding, and Metal Oxidation State

Oxide- and Zeolite-Supported Molecular Metal Complexes and Clusters: Physical Characterization and Determination of Structure, Bonding, and Metal Oxidation State

The cluster Ir4 and its interaction with a hydrogen impurity. A density functional study

Nanoclusters of Iridium Oxide and of Rhodium Oxide Supported on MgO

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