Supported Molecular Iridium Catalysts: Resolving Effects of Metal Nuclearity and Supports as Ligands

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• 作者：Jing Lu ; Pedro Serna ; Ceren Aydin ; Nigel D. Browning ; Bruce C. Gates
• 刊名：Journal of the American Chemical Society
• 出版年：2011
• 出版时间：October 12, 2011
• 年：2011
• 卷：133
• 期：40
• 页码：16186-16195
• 全文大小：995K
• 年卷期：v.133,no.40(October 12, 2011)
• ISSN：1520-5126

文摘

The performance of a supported catalyst is influenced by the size and structure of the metal species, the ligands bonded to the metal, and the support. Resolution of these effects has been lacking because of the lack of investigations of catalysts with uniform and systematically varied catalytic sites. We now demonstrate that the performance for ethene hydrogenation of isostructural iridium species on supports with contrasting properties as ligands (electron-donating MgO and electron-withdrawing HY zeolite) can be elucidated on the basis of molecular concepts. Spectra of the working catalysts show that the catalytic reaction rate is determined by the dissociation of H₂ when the iridium, either as mono- or tetra-nuclear species, is supported on MgO and is not when the support is the zeolite. The neighboring iridium sites in clusters are crucial for activation of both H₂ and C₂H₄ when the support is MgO but not when it is the zeolite, because the electron-withdrawing properties of the zeolite support enable even single site-isolated Ir atoms to bond to both C₂H₄ and H₂ and facilitate the catalysis.