2 research outputs found
Isostructural Zeolite-Supported Rhodium and Iridium Complexes: Tuning Catalytic Activity and Selectivity by Ligand Modification
A family
of isostructural, essentially molecular complexes of rhodium
and of iridium anchored to HY zeolite was synthesized from MÂ(C<sub>2</sub>H<sub>4</sub>)<sub>2</sub>(acac) and MÂ(CO)<sub>2</sub>(acac)
(M = Rh, Ir; acac is acetylacetonate), with the initial supported
species being MÂ(C<sub>2</sub>H<sub>4</sub>)<sub>2</sub> and MÂ(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
Dealuminated zeolite HY was used
to support IrÂ(CO)<sub>2</sub> complexes
formed from IrÂ(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