Oxide- and Zeolite-supported Molecular Iridium Complexes and Clusters

Download or read book Oxide- and Zeolite-supported Molecular Iridium Complexes and Clusters written by Jing Lu and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The stability and performance of supported catalysts are 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 systemically varied catalytic sites. Starting with a molecular iridium complex precursor, Ir(C2H4)2(acac) (acac is acetylacetonate), highly uniform isostructural supported Ir(C2H4)2 complexes were prepared on MgO, [gamma]-Al2O3, zeolite HY zeolite H[beta], and zeolite HSSZ-53 supports. The structure and transformation of these supported iridium complexes were characterized with infrared (IR) spectroscopy, X-ray absorption spectroscopy (XAS), and scanning transmission electron microscopy (STEM). By treatments in H2, the supported iridium complexes were converted into: (a) small clusters consisting of only a few atoms (~Ir4) at 353 K, and (b) bigger clusters approximately 1 nm in diameter (~Ir40) at 673 K. Moreover, the isostructural Ir(C2H4)2 complexes were transformed into Ir(CO)2, Ir(CO)(C2H4), Ir(CO)(C2H4)2 and Ir(CO)2(C2H4) complexes on supports by treatments in various mixtures of flowing C2H4, CO, and helium. Thus, this set of samples provides supported iridium species with systematically varied supports, ligands and nuclearities. The catalytic performances of these iridium complexes and clusters were evaluated for ethylene hydrogenation and H-D exchange in the conversion of H2 and D2. Furthermore, the cluster formation (sintering) process from supported iridium complex catalysts in contact with H2 was also investigated. The data identify support and ligand effects in catalytic reaction mechanisms and in sintering behavior of the metal species. The results are expected to contribute to fundamental understanding of structure, bonding, and reactivity of supported catalysts, suggesting further opportunities for design and discovery of hydrocarbon conversion catalysts.