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Metal-organic frameworks (MOFs) with nodes consisting of zirconium oxide clusters (Zr6) offer new opportunities as supports for catalysts with well-defined, essentially molecular, structures. We used the precursor Rh(C2H4)2(acac) (acac is acetylacetonate) to anchor Rh(I) complexes to the nodes of the MOF UiO-67 and, for comparison, to the zeolite dealuminated HY (DAY). These were characterized experimentally by measurement of catalytic activities and selectivities for ethylene hydrogenation and dimerization in a once-through flow reactor at 298 K and 1 bar. The catalyst performance data are complemented with structural information determined by infrared and extended X-ray absorption fine structure spectroscopies and by calculations at the level of density functional theory, the latter carried out also to extend the investigation to a related MOF, NU-1000. The agreement between the experimental and calculated structural metrics is good, and the calculations have led to predictions of reaction mechanisms and associated energetics. The data demonstrate a correlation between the catalytic activity and selectivity and the electron-donor tendency of the supported rhodium (as measured by the frequencies of CO ligands bonded as probes to the Rh(I) centers), which is itself a measure of the electron-donor tendency of the support.
Bibliographical noteFunding Information:
We thank Professors Omar K. Farha and Joseph T. Hupp and Dr. Manuel A. Ortuño and Dr. Andreas Mavrandonakis for helpful discussions. This work was supported as part of the Inorganometallic Catalyst Design Center, an Energy Frontier Research Center funded by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences (DESC0012702). We gratefully acknowledge beam time at Beamline 2-2 at the Stanford Synchrotron Radiation Light-source supported by the DOE Division of Materials Sciences under Contract DE-AC02-76SF00515. We thank the beamline scientists, Nebojsa Marinkovic and Syed Khalid, for valuable support.
- Density functional theory
- Ethylene dimerization
- Ethylene hydrogenation
- Metal-organic framework nodes
- Rhodium complexes
- Supported catalyst