A site-isolated mononuclear iridium complex catalyst supported on MgO: Characterization by spectroscopy and aberration-corrected scanning transmission electron microscopy |
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| Authors: | Alper Uzun Volkan Ortalan Nigel D. Browning Bruce C. Gates |
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| Affiliation: | 1. Department of Chemical Engineering and Materials Science, University of California, Davis, One Shields Avenue, Davis, CA 95616, USA;2. Lawrence Livermore National Laboratory, Livermore, CA 94550, USA;1. Department of Chemical and Biological Engineering, Koç University, Rumelifeneri Yolu, Sariyer 34450, Istanbul, Turkey;2. Koç University TÜPRA? Energy Center (KUTEM), Koç University, Rumelifeneri Yolu, Sariyer 34450, Istanbul, Turkey;3. Department of Chemical Engineering, Bogazici University, Bebek 34342, Istanbul, Turkey;1. Department of Chemical and Biological Engineering, Koç University, Rumelifeneri Yolu, Sariyer, 34450, Istanbul, Turkey;2. KÜTEM (Koç University TUPRAS Energy Center), Koç University, Rumelifeneri Yolu, Sariyer, 34450, Istanbul, Turkey;3. Koç University, Surface Science and Technology Center (KUYTAM), Koç University, Rumelifeneri Yolu, Sariyer, 34450, Istanbul, Turkey;1. Department of Chemical and Biological Engineering, Koç University, Rumelifeneri Yolu, Sariyer 34450, Istanbul, Turkey;2. Koç University TÜPRA? Energy Center (KUTEM), Koç University, Rumelifeneri Yolu, Sariyer 34450, Istanbul, Turkey;1. Department of Chemical and Biological Engineering, Koç University, Rumelifeneri Yolu, 34450, Sariyer, Istanbul, Turkey;2. Koç University TüPRA? Energy Center (KUTEM), Koç University, Rumelifeneri Yolu, 34450, Sariyer, Istanbul, Turkey;3. Department of Chemistry, Koç University, Rumelifeneri Yolu, 34450, Sariyer, Istanbul, Turkey;4. Koç University Surface Science and Technology Center (KUYTAM), Koç University, Rumelifeneri Yolu, 34450, Sariyer, Istanbul, Turkey;1. Dalian National Laboratory for Clean Energy, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China;2. University of Chinese Academy of Sciences, Beijing 100049, China;3. School of Materials and Textile Engineering, Jiaxing University, Jiaxing 314001, Zhejiang, China;4. Shanghai Synchrotron Radiation Facility, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201204, China;5. State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China;1. Department of Chemical and Biological Engineering, Koç University, Rumelifeneri Yolu, Sariyer, 34450, Istanbul, Turkey;2. Koç University TÜPRA? Energy Center (KUTEM), Koç University, Rumelifeneri Yolu, Sariyer, 34450, Istanbul, Turkey;3. Turkish Petroleum Refineries Co. (TÜPRA?) R&D Center, Guney Mah. Petrol Cad., Korfez, 41790, Kocaeli, Turkey;4. Koç University Surface Science and Technology Center (KUYTAM), Koç University, Rumelifeneri Yolu, Sariyer, 34450, Istanbul, Turkey |
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| Abstract: | Supported mononuclear iridium complexes with ethene ligands were prepared by the reaction of Ir(C2H4)2(acac) (acac is CH3COCHCOCH3) with highly dehydroxylated MgO. Characterization of the supported species by extended X-ray absorption fine structure (EXAFS) and infrared (IR) spectroscopies showed that the resultant supported organometallic species were Ir(C2H4)2, formed by the dissociation of the acac ligand from Ir(C2H4)2(acac) and bonding of the Ir(C2H4)2 species to the MgO surface. Direct evidence of the site-isolation of these mononuclear complexes was obtained by aberration-corrected scanning transmission electron microscopy (STEM); the images demonstrate the presence of the iridium complexes in the absence of any clusters. When the iridium complexes were probed with CO, the resulting IR spectra demonstrated the formation of Ir(CO)2 complexes on the MgO surface. The breadth of the νCO bands demonstrates a substantial variation in the metal–support bonding, consistent with the heterogeneity of the MgO surface; the STEM images are not sufficient to characterize this heterogeneity. The supported iridium complexes catalyzed ethene hydrogenation at room temperature and atmospheric pressure in a flow reactor, and EXAFS spectra indicated that the mononuclear iridium species remained intact. STEM images of the used catalyst confirmed that almost all of the iridium complexes remained intact, but this method was sensitive enough to detect a small degree of aggregation of the iridium on the support. |
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