(575a) Zeolite-Supported Molecular Iridium Complexes: Effects of Ligands on Catalytic Properties for Conversion of Ethylene and Hydrogen

Zeolite HY-supported metal complexes constituting a family of isostructural species were synthesized from the precursors M(ethylene)2(acac) and M(CO)2(acac) [acac is acetylacetonate; M is Ir or Rh]. The resulting complexes initially were M(ethylene)2 and M(CO)2, each bonded to two O atoms of the zeolite, as shown by IR and EXAFS spectra. The supported species were modified by treatment in reactive gases, so that the latter complex was changed to one incorporating one CO ligand and one ethylene ligand. Thus, three precatalysts of each metal were formed, differing in the ligands bonded to the metal. The activities of these species were detemined as initial rates of ethylene hydrogenation, ethylene dimerization, and H-D exchange in the reaction of H2 with D2. Spectra of the working catalysts confirmed that the initial performance corresponded to the initial composition. The results determine how the ligands affect the catalytic activity and selectivity, the first such systematic data for supported metal catalysts.