(278d) Supported Molecular Catalysts: Characterization of the Metal and Metal-Support Interface Structures by Atomic-Resolution Transmission Electron Microscopy and Spectroscopy

Supported iridium catalysts, which are active for numerous hydrocarbon conversions, offer many advantages in characterization, because known organometallic chemistry  guides the precise synthesis of essentially molecular iridium complexes and clusters and because the heavy Ir atoms on supports can be readily imaged  by scanning transmission electron microscopy. Oxide- and zeolite-supported isostructural Ir(C₂H₄)₂ complexes were prepared from Ir(C₂H₄)₂(acac). The transformation of the ligands and of the iridium nuclearity were tracked with time-resolved IR, EXAFS, and XANES spectroscopies with the samples in reactive atmospheres and undergoing catalysis of reactions such as ethylene hydrogenation. The data indicate the movements of Ir atoms and the early stages of cluster formation and show how the ligands (including the supports) influence the catalytic properties and the tendency of the iridium to form clusters—thus, the basis for designing the catalysts.