Abstract
Single-site Ir(CO)2 complexes bonded to high-surface-area metal oxide supports, SiO2, TiO2, Fe2O3, CeO2, MgO, and La2O3, were synthesized by chemisorption of Ir(CO)2(acac) (acac = acetylacetonate) followed by coating with each of the following ionic liquids (ILs): 1-n-butyl-3-methylimidazolium tetrafluoroborate, [BMIM][BF4], 1-n-butyl-3-methylimidazolium acetate, [BMIM][Ac], and 1-(3-cyanopropyl)-3-methylimidazolium dicyanamide, [CPMIM][DCA]. Extended X-ray absorption fine structure spectroscopy showed that site-isolated iridium was bonded to oxygen atoms of the support. Electron densities on the iridium enveloped by each IL sheath/support combination were characterized by carbonyl infrared spectroscopy of the iridium gem-dicarbonyls and by X-ray absorption near-edge structure data. The electron-donor/acceptor tendencies of both the support and IL determine the activity and selectivity of the catalysts for the hydrogenation of 1,3-butadiene, with electron-rich iridium being selective for partial hydrogenation. The results resolve the effects of the IL and support as ligands; for example, the effect of the IL becomes dominant when the support has a weak electron-donor character. The combined effects of supports and ILs as ligands offer broad opportunities for tuning catalytic properties of supported metal catalysts.
Highlights
Dispersed metal catalysts on supports are drawing wide attention, because they offer new catalytic properties[1,2,3,4,5] and an efficient use of expensive transition metals.Notwithstanding numerous recent investigations of structure and performance of such catalysts on supports such as metal oxides,[6,7,8,9,10,11,12,13,14] there is only limited insight into how to control their catalytic properties
Electron densities on the iridium enveloped by each ionic liquids (ILs) sheath/support combination were characterized by carbonyl infrared spectroscopy of the iridium gem-dicarbonyls and by X-ray absorption near-edge structure data
No vibrational bands associated with iridium carbonyls were detected in the ltrates, and the spectra of the washed samples still indicated the presence of the iridium carbonyls ( the peak positions and shapes were changed by the treatments, as illustrated in Fig. S54 in the Electronic supplementary information (ESI)† for [BMIM][BF4]-coated Ir(CO)2/MgO). These results show that the iridium complexes remained bonded to the support even a er the samples were coated with the ILs and did not dissolve in the IL
Summary
Dispersed metal catalysts on supports are drawing wide attention, because they offer new catalytic properties[1,2,3,4,5] and an efficient use of expensive transition metals.Notwithstanding numerous recent investigations of structure and performance of such catalysts on supports such as metal oxides,[6,7,8,9,10,11,12,13,14] there is only limited insight into how to control their catalytic properties. Molecules nearby metal centers on surfaces may act as ligands, as illustrated by electron-donor ethylenediamine coatings of platinum nanowires,[23] which in uence the selectivity of the platinum for catalytic hydrogenation of nitroaromatics. The class of coatings in uencing catalytically active metals in supported catalysts has recently been extended to include ionic liquids (ILs), which have been shown to enhance catalytic selectivity in cyclooctadiene hydrogenation.[26] Many ILs are available, offering a wide range of electron-donor/acceptor properties. They can be quite stable on surfaces, and in
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
