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Direct photo-oxidation of methane to methanol over a mono-iron hydroxyl site

An Author Correction to this article was published on 11 July 2022

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Abstract

Natural gas, consisting mainly of methane (CH4), has a relatively low energy density at ambient conditions (~36 kJ l−1). Partial oxidation of CH4 to methanol (CH3OH) lifts the energy density to ~17 MJ l−1 and drives the production of numerous chemicals. In nature, this is achieved by methane monooxygenase with di-iron sites, which is extremely challenging to mimic in artificial systems due to the high dissociation energy of the C–H bond in CH4 (439 kJ mol−1) and facile over-oxidation of CH3OH to CO and CO2. Here we report the direct photo-oxidation of CH4 over mono-iron hydroxyl sites immobilized within a metal–organic framework, PMOF-RuFe(OH). Under ambient and flow conditions in the presence of H2O and O2, CH4 is converted to CH3OH with 100% selectivity and a time yield of 8.81 ± 0.34 mmol gcat−1 h−1 (versus 5.05 mmol gcat−1 h−1 for methane monooxygenase). By using operando spectroscopic and modelling techniques, we find that confined mono-iron hydroxyl sites bind CH4 by forming an [Fe–OH···CH4] intermediate, thus lowering the barrier for C–H bond activation. The confinement of mono-iron hydroxyl sites in a porous matrix demonstrates a strategy for C–H bond activation in CH4 to drive the direct photosynthesis of CH3OH.

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Fig. 1: Design and synthesis of the PMOF-RuFe(OH) catalyst and the flow reactor for photo-oxidation of CH4 to CH3OH.
Fig. 2: Characterization of PMOF-RuFe(OH).
Fig. 3: Photocatalytic performance.
Fig. 4: Investigation of the mono-iron hydroxyl site for C–H activation.

Data availability

Additional experimental details of characterization and catalysis, DFT calculations and DFT-calculated structures are available in the Supplementary Information and Supplementary Data.

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Acknowledgements

We thank EPSRC (EP/I011870, EPSRC EP/V056409), the Royal Society and University of Manchester for funding. We thank EPSRC for funding and the EPSRC National Service for EPR Spectroscopy at Manchester. This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement no. 742401, NANOCHEM). We thank I. da Silva, B. Wang, W. Lu, Y. Ma, J. Zhang, L. Zeng, R. Wei and H. Wilson for help. We thank Diamond Light Source for access to the beamline B22. We acknowledge Advanced Photon Source (APS) at Argonne National Laboratory and Aichi Synchrotron Radiation Centre (AichiSR) for the provision of beamtime at 10-BM and BL11S. A portion of this research used resources at the Spallation Neutron Source, a DOE Office of Science User Facility operated by Oak Ridge National Laboratory (ORNL). The computing resources at ORNL were made available through the VirtuES and the ICE-MAN projects, funded by Laboratory Directed Research and Development program and Computer and Data Environment for Science (CADES).

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B.A., C.W., S.Y. and M.S. conceived the idea and designed the project. S.Y. and M.S. directed and supervised the research. B.A., Z.L., X.Z., Y.C. and Z.Z. performed the synthesis, catalysis and mechanism study. Z.W., A.M.S., Z.L., F.T. and E.J.L.M. contributed to the EPR experiments. Z.L. and Y.C. performed the computational work. X.H., M.D.F., L.S.N., A.J.R.-C., C.W. and W.L. contributed to the data analysis. B.A., Z.L., S.Y. and M.S. wrote the paper, with input from all authors.

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Correspondence to Sihai Yang or Martin Schröder.

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Supplementary Methods, Text, Figs. 1–56, Tables 1–18, refs. 1–109 and Notes.

Supplementary Data

Cartesian atomic coordinates.

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An, B., Li, Z., Wang, Z. et al. Direct photo-oxidation of methane to methanol over a mono-iron hydroxyl site. Nat. Mater. 21, 932–938 (2022). https://doi.org/10.1038/s41563-022-01279-1

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