Abstract
Understanding heterogeneous catalysts is a challenging pursuit due to surface site nonuniformity and aperiodicity in traditionally used materials. One example is sulfated metal oxides, which function as highly active catalysts and as supports for organometallic complexes. These applications are due to traits such as acidity, ability to act as a weakly coordinating ligand, and aptitude for promoting transformations via radical cation intermediates. Research is ongoing about the structural features of sulfated metal oxides that imbue the aforementioned properties, such as sulfate geometry and coordination. To better understand these materials, metal-organic frameworks (MOFs) have been targeted as structurally defined analogues. Composed of inorganic nodes and organic linkers, MOFs possess features such as high porosity and crystallinity, which make them attractive for mechanistic studies of heterogeneous catalysts. In this work, Zr6-based MOF NU-1000 is sulfated and characterized using techniques such as single crystal X-ray diffraction in addition to diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The dynamic nature of the sulfate binding motif is found to transition from monodentate, to bidentate, to tridentate depending on the degree of hydration, as supported by density functional theory (DFT) calculations. Heightened Brønsted acidity compared to the parent MOF was observed upon sulfation and probed through trimethylphosphine oxide physisorption, ammonia sorption, in situ ammonia DRIFTS, and DFT studies. With the support structure benchmarked, an organoiridium complex was chemisorbed onto the sulfated MOF node, and the efficacy of this supported catalyst was demonstrated for stoichiometric and catalytic activation of benzene-d6and toluene with structure-activity relationships derived.
Original language | English (US) |
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Pages (from-to) | 16883-16897 |
Number of pages | 15 |
Journal | Journal of the American Chemical Society |
Volume | 144 |
Issue number | 37 |
DOIs | |
State | Published - Sep 21 2022 |
Bibliographical note
Funding Information:The authors acknowledge support from the Inorganometallic Catalyst Design Center, an EFRC funded by the DOE, Office of Science, Basic Energy Sciences (DE-SC0012702). This work made use of the IMSERC NMR facility at Northwestern University, which has received support from the Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (NSF ECCS-2025633), Int. Institute of Nanotechnology, and Northwestern University for the a600, the Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (NSF ECCS-2025633), NSF CHE-1048773, and Northwestern University for the au400, in addition to the Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (NSF ECCS-2025633), Int. Institute of Nanotechnology, and Northwestern University for the hg400. This work made use of the EPIC facility of Northwestern University’s NU Center, which has received support from the SHyNE Resource (NSF ECCS-2025633), the IIN, and Northwestern’s MRSEC program (NSF DMR-1720139). DRIFTS measurements were conducted at the REACT Facility of Northwestern University Center for Catalysis and Surface Science, which is supported by a grant from the DOE (DE-SC0001329). This work also made use of the Keck-II facility of Northwestern University’s NUANCE Center, which has received support from the SHyNE Resource (NSF ECCS-2025633), the IIN, and Northwestern’s MRSEC program (NSF DMR-1720139). This work made use of the IMSERC Crystallography facility at Northwestern University, which has received support from the Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (NSF ECCS-2025633), and Northwestern University. Metal analysis was performed at the Northwestern University Quantitative Bio-element Imaging Center. This research also used resources of the Advanced Photon Source, a U.S. DOE Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under contract no. DE-AC02-06CH11357. Computational resources, in part, were provided by the Minnesota Supercomputing Institute at the University of Minnesota, and the Research Computing Center at the University of Chicago. Z.H.S. and K.M.F. are supported by the National Science Foundation Graduate Research Fellowship under Grant No. DGE-1842165. R.P. acknowledges the support of the Nanoporous Materials Genome Center, funded by the U.S. Department of Energy, Office of Basic Energy Sciences, under Award DE-FG02-17ER16362, as part of the Computational Chemical Sciences Program. F.A.S. is supported by the Department of Defense (DoD) through the National Defense Science & Engineering Graduate (NDSEG) Fellowship Program. F.A.S. and K.M.F. also acknowledge support from the Ryan Fellowship and the International Institute for Nanotechnology at Northwestern University. T.A.G. acknowledges the support of the U.S. DOE, Office of Science, Office of Workforce Development for Teachers and Scientists, Office of Science Graduate Student Research (SCGSR) program. The SCGSR program is administered by the Oak Ridge Institute for Science and Education (ORISE) for the DOE, and ORISE is managed by ORAU under Contract DE-SC0014664.
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