Single-site catalysts with active species anchored over metal-organic framework (MOF) supports have garnered significant interest in recent years. Catalysts with vanadium oxide (VOx) species immobilized over Zr-NU-1000 and Hf-MOF-808 (which have nodes containing six Zr(IV) or Hf(IV) ions, respectively) were recently characterized experimentally (Otake et al. J. Am. Chem. Soc. 2018, 140, 8652) and were reported to be active for the selective oxidation of benzyl alcohol to benzaldehyde. Here, we report a detailed computational investigation of these VOx-incorporated MOF catalysts (V-MOF) by employing density functional theory. Based on the mode of VOx attachment, various structures are explored, and their relative stabilities and computed IR spectral features are reported. Mechanisms for the selective oxidation reaction are investigated. The analysis of electron flow in the turnover-limiting C-H activation step shows that the hydrogen-atom abstraction process involves a concerted proton-coupled electron-transfer mechanism. The results of this study suggest that in addition to the identity of the metal in the node, the MOF node architecture plays a crucial role in driving the catalytic activities of V-MOFs.
Bibliographical noteFunding Information:
The authors thank O. K. Farha, X. Zhang, and Y. Chen for insightful discussion. This work was supported as part of the Inorganometallic Catalyst Design Center, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award DE-SC0012702. M.M. acknowledges a doctoral dissertation fellowship from the University of Minnesota. The authors acknowledge Minnesota Supercomputing Institute (MSI) at the University of Minnesota for providing computational resources. J.S. has been funded by Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) within project 430942176. L.G. acknowledges the Alexander von Humboldt Foundation for a Humboldt Research Award.
- DFT modeling
- metal-organic framework
- proton-coupled electron transfer
- single-site catalyst