Supported metal carbonyl clusters and complexes: Formation, reactivity, and catalytic properties

Well-defined metal species on surfaces were synthesized by adsorbing the metal carbonyl complexes HRe(CO)5, CH3Re(CO) 5, H3Re3(CO)12, and Pt3Ru 6(CO)21(mu3-H)(micro-H)3 on metal oxide and zeolite supports. Characterization of the supported species by X-ray absorption spectroscopy (XAS) and infrared (IR) spectroscopy provided the structural information required to elucidate the chemistry involved in forming of supported species; together with catalytic performance data, the results provide a basis for determining relationships between properties of the supported species such as the oxidation states of the metals and the performance of the materials as catalysts. In prospect, such information can be applied to design of new catalysts.;Samples prepared by adsorbing CH3Re(CO)5 on zeolite HY and zeolite NaY were characterized by IR and XAS to determine the structure and uniformity of the supported metal species. Results show that H + on HY zeolite and CH3- on CH3Re(CO) 5 react to produce methane, and uniform surface sites. When either H + or CH3- are missing, nonuniform species form.;Samples prepared by adsorption of H3Re3(CO) 12 on gamma-Al2O3, were treated under various conditions, and tested as catalysts for n-butane conversion in the presence of H2. Characterization by XAS of the spent samples and catalyst performance data allow resolution of the separate effects of rhenium oxidation state and rhenium cluster size on the catalytic activity and selectivity---these are both favored by larger cluster sizes and higher electron densities on the rhenium.;gamma-Al2O3-supported Re3 clusters synthesized from H3Re3(CO)12 were used as catalysts for the conversion of methylcyclohexane. The catalyst performance data show that the activity and selectivity can be greatly modified if the catalyst is first used at 773 K. These changes in catalyst performance are attributed to changes in the Re3 cluster frame, determined by XAS and not to aggregation.;Samples prepared by adsorbing HRe(CO)5 or CH3Re(CO) 5 on TiO2 (anatase) were characterized by XAS and IR spectroscopies. Adsorption of each led to bonding of the complexes to the TiO2, decarbonylation of the complexes, and formation of surface species including carbonates. Data show that when CH3Re(CO)5 is adsorbed, the CO ligands react with OH groups on TiO2; forming water, and carbonates species on TiO2.