Abstract
Previous work has shown that introduction of hexafluoroacetylacetone (Facac) units as nonstructural ligands for the zirconia-like nodes of the eight-connected metal-organic framework (MOF), NU-1000, greatly alters the selectivity of node-supported oxy-nickel clusters for ethylene dimerization vs oligomerization. Here we explore a related concept: tuning of support/catalyst interactions, and therefore, catalyst activity, via parallel installation of organic modifiers on the support itself. As modifiers we focused on para-substituted benzoates (R-BA- R = -NH2, -OCH3, -CH3, -H, -F, and -NO2) where the substituents were chosen to present similar steric demand, but varying electron-donating or electron-withdrawing properties. R-benzoate-engendered shifts in the node-based aqua O-H stretching frequency for NU-1000, as measured by DRIFTS (diffuse-reflectance infrared Fourier-transform spectroscopy), together with systematic shifts in Ni 2p peak energies, as measured by X-ray photoelectron spectroscopy, show that the electronic properties of the support can be modulated. The vibrational and electronic peak shifts correlate with the putative electron-withdrawing vs electron-donating strength of the para-substituted benzoate modifiers. Subsequent installation of node-supported, oxy-Ni(II) clusters for ethylene hydrogenation yield a compelling correlation between log (catalyst turnover frequency) and the electron donating or withdrawing character of the substituent of the benzoate units. Single crystal X-ray diffraction measurements reveal that each organic modifier makes use of only one of two available carboxylate oxygens to accomplish grafting. The remaining oxygen atom is, in principle, well positioned to coordinate directly to an installed Ni(II) ion. We postulate that the unanticipated direct coordination of the catalyst by the node-modifier (rather than indirect modifier-based tuning of support(node)/catalyst electronic interactions) is the primary source of the observed systematic tuning of hydrogenation activity. We suggest, however, that regardless of mechanism for communication with active-sites of MOF-supported catalysts, intentional elaboration of nodes via grafted, nonstructural organic species could prove to be a valuable general strategy for fine-tuning supported-catalyst activity and/or selectivity.
Original language | English (US) |
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Pages (from-to) | 3198-3207 |
Number of pages | 10 |
Journal | ACS Catalysis |
Volume | 9 |
Issue number | 4 |
DOIs | |
State | Published - Apr 5 2019 |
Funding
This work was supported as part of the Inorganometallic Catalyst Design Center, an EFRC funded by the DOE, Office of Science, Basic Energy Sciences (DE-SC0012702). HE-XRD and PDF analysis in this work was supported by the Center for Electrochemical Energy Science, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences. We acknowledge Richard Spence, Olaf Borkiewicz and Yang Ren at Sector 11-ID-B at Argonne National Laboratory for assistance with HE-XRD and PDF measurements. This work made use of the J.B. Cohen X-ray Diffraction Facility supported by the MRSEC program of the National Science Foundation (DMR-1121262) at the Materials Research Center of Northwestern University. This work made use of the EPIC and Keck-II facilities of the NUANCE Center at Northwestern University, which has received support from the Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (NSF ECCS-1542205); the MRSEC program (NSF DMR-1720139) at the Materials Research Center; the International Institute for Nanotechnology (IIN); the Keck Foundation; and the State of Illinois, through the IIN.
Keywords
- Hammett constant
- ethylene hydrogenation
- heterogeneous catalysis
- ligand modification
- metal-organic framework
- zirconia-like node
ASJC Scopus subject areas
- Catalysis
- General Chemistry
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CCDC 1855807: Experimental Crystal Structure Determination
Liu, J. (Creator), Li, Z. (Creator), Zhang, X. (Creator), Otake, K.-I. (Creator), Zhang, L. (Creator), Peters, A. W. (Creator), Young, M. J. (Creator), Bedford, N. M. (Creator), Letourneau, S. P. (Creator), Mandia, D. J. (Creator), Elam, J. W. (Creator), Farha, O. K. (Creator) & Hupp, J. T. (Creator), Cambridge Crystallographic Data Centre, 2019
DOI: 10.5517/ccdc.csd.cc2093r6, http://www.ccdc.cam.ac.uk/services/structure_request?id=doi:10.5517/ccdc.csd.cc2093r6&sid=DataCite
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