Abstract
Geometric or electronic confinement of guests within nanoporous hosts holds promise for imparting catalytic functionality, including single-metal-atom catalytic functionality, to existing materials. When the nanoporous host is a metal-organic framework (MOF), single-metal-ion catalysts have typically been installed by grafting to an open site on an inorganic node, with the node effectively becoming the support for the catalyst. This approach, however, imposes compositional constraints, as the node not only needs to be receptive to grafting, but also must be capable of stabilizing the framework against solvent evacuation, chemical exposure, and heating. Here, we show that disk-like, Anderson polyoxometalate clusters (RhMo6O24n− and Mo7O24m−; POMs) can be confined in pore-specific and orientation-specific fashion within the hierarchically porous, Zr(iv)-based MOF, NU1K. Self-limiting loading of one cluster per pore, and associated nano-confinement, serve to isolate each POM and prevent consolidation caused by sintering. Additionally, the oriented confinement serves to expose individual rhodium atoms to candidate gas-phase reactants, while enabling the rhodium atom to employ a well-defined oxy-molybdenum cluster, rather than a MOF node, as a support. Synchrotron-based difference-electron-density maps and differential pair-distribution-function analyses of scattered X-rays establish cluster siting and orientation and confirm isolation. Nanoconfined (i.e., MOF- and POM-confined) single-rhodium(iii)-atoms are catalytically competent for an illustrative gas-phase reaction, CO oxidation by O2, with the MOF-isolated POM enormously outperforming nonporous, MOF-free, solid (NH4)3[H6RhMo6O24]·6H2O. This work highlights the value of MOF-based nano-confinement and oriented isolation of planar POMs as a means of uniformly presenting and stabilizing potent single-metal-atom catalysts, in reactant-accessible form, on well-defined supports.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 18226-18234 |
| Number of pages | 9 |
| Journal | Journal of Materials Chemistry A |
| Volume | 10 |
| Issue number | 35 |
| DOIs | |
| State | Published - Aug 17 2022 |
Funding
J. T. H. thanks Prof. Bruce Gates for useful discussions. 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). Q. L. thanks Weiren Chen for EXAFS fitting. Q. L. acknowledge the financial support from the National Natural Science Foundation of China (No. 11705205). W. B. acknowledge the financial support from the Natural Science Foundation of China (No. U1832168, 22175051), the Anhui Provincial Natural Science Foundation (No. 1808085MB26). Z. L. gratefully acknowledges support from the National Natural Science Foundation of China (21601047), the Fundamental Research Funds for the Central Universities (2018B17614), and the China Scholarship Council (CSC) (201806715039) during his visit to Northwestern University. This work made use of the J. B. Cohen X-ray Diffraction Facility supported by the IMRSEC program of the National Science Foundation (DMR-1121262) at the Materials Research Center of Northwestern University. This work made use of the Reactor Engineering and Catalyst Testing (REACT) core facility of the Center for Catalysis and Surface Science at 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. Use of the Advanced Photon Source is supported by the U.S. Department of Energy, Office of Science, and Office of Basic Energy Sciences, under Contract DE-AC02-06CH11357. Materials Research Collaborative Access Team (MRCAT, Sector 5-BM) operations are supported by the Department of Energy and the MRCAT member institutions. The REACT Core facility acknowledges funding from the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Catalysis Science program (DE-SC0001329) used for the purchase of the Altamira BenchCAT4000 reactor system and Agilent 7890 GC and the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Catalysis Science program (DE-FG02-03ER15457) used for the purchase of the Nicolet 6700 FT.
ASJC Scopus subject areas
- General Chemistry
- Renewable Energy, Sustainability and the Environment
- General Materials Science