2 research outputs found

    Isostructural Zeolite-Supported Rhodium and Iridium Complexes: Tuning Catalytic Activity and Selectivity by Ligand Modification

    No full text
    A family of isostructural, essentially molecular complexes of rhodium and of iridium anchored to HY zeolite was synthesized from M­(C<sub>2</sub>H<sub>4</sub>)<sub>2</sub>(acac) and M­(CO)<sub>2</sub>(acac) (M = Rh, Ir; acac is acetylacetonate), with the initial supported species being M­(C<sub>2</sub>H<sub>4</sub>)<sub>2</sub> and M­(CO)<sub>2</sub>, each bonded to the zeolite through two M–O bonds. Each was used as a catalyst at 300 and 373 K and atmospheric pressure for the conversion of ethylene in the presence of H<sub>2</sub> (and sometimes D<sub>2</sub>), giving ethane and, when the metal was rhodium, butenes, and, when D<sub>2</sub> was present, HD. The high degree of uniformity of the metal complexes allowed a precise spectroscopic elucidation of the predominant species present during catalysis. The CO ligands were inhibitors of the catalytic reactions, with the metal dicarbonyl complexes lacking measurable activity under our conditions. The CO ligands also served as probes helping to characterize the structures and electronic properties of the catalytic metal complexes. The data show that subtle changes in the bonding of the ligands markedly affect the catalytic performance

    Iridium Complexes and Clusters in Dealuminated Zeolite HY: Distribution between Crystalline and Impurity Amorphous Regions

    No full text
    Dealuminated zeolite HY was used to support Ir­(CO)<sub>2</sub> complexes formed from Ir­(CO)<sub>2</sub>(C<sub>5</sub>H<sub>7</sub>O<sub>2</sub>). Infrared and X-ray absorption spectra and atomic resolution electron microscopy images identify these complexes, and the images and <sup>27</sup>Al NMR spectra identify impurity amorphous regions in the zeolite where the iridium is more susceptible to aggregation than in the crystalline regions. The results indicate the value of electron microscopy in characterizing the amorphous impurity regions of zeolites and a significant stability limitation of metals in these regions of zeolite catalyst supports
    corecore