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Evidence of radical chemistry in catalytic methane oxybromination

Nature Catalysis volume 1, pages 363–370 (2018)Cite this article

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Abstract

Unravelling the pathways of catalytic methane functionalization sets the foundations for the efficient production of valuable chemicals and fuels from this abundant feedstock. The catalytic oxybromination of methane into platform compounds bromomethane and dibromomethane constitutes a prominent example, although it displays a puzzling reaction network that has been speculated to involve free-radical intermediates. Here, photoelectron photoion coincidence spectroscopy with synchrotron radiation was used to provide evidence of the evolution of gaseous methyl and bromine radicals over (VO)2P2O7 and EuOBr catalysts and the strong correlation between the formation of methyl radicals and the production of bromomethanes. Complemented by kinetic data on methane oxybromination and non-catalytic methane bromination, these results imply the surface-catalysed generation of bromine radicals and molecular bromine followed by the gas-phase methane bromination, which is rationalized by density functional theory calculations. The findings emphasize the role of both surface and gas-phase steps in halogen-mediated C–H bond activation over heterogeneous catalysts.

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Fig. 1: Kinetics of methane oxybromination, bromination and oxidation.
Fig. 2: PEPICO reactor set-up for radical detection.
Fig. 3: Radical detection in catalytic methane oxybromination.
Fig. 4: Reaction profile of catalytic methane oxybromination.

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Acknowledgements

This work was supported by the Swiss National Science Foundation (project no. 200021-156107) and the Swiss Federal Office of Energy (contract no. SI/501269-01). D. Teschner from the Fritz Haber Institute of the Max Planck Society, Berlin; L. Szentmiklósi from the Centre for Energy Research, Hungarian Academy of Sciences, Budapest; and M. Moser are acknowledged for their help in performing prompt gamma activation analysis.

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Authors and Affiliations

  1. Institute for Chemical and Bioengineering, Department of Chemistry and Applied Biosciences, ETH Zurich, Zurich, Switzerland

    Vladimir Paunović & Javier Pérez-Ramírez

  2. Laboratory for Synchrotron Radiation and Femtochemistry, Paul Scherrer Institute, Villigen, Switzerland

    Patrick Hemberger & Andras Bodi

  3. Institute of Chemical Research of Catalonia (ICIQ), Barcelona Institute of Science and Technology, Tarragona, Spain

    Núria López

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Contributions

J.P.-R. conceived and coordinated all stages of this research. V.P. prepared and characterized the catalysts, and performed and analysed the steady-state tests. V.P., P.H. and A.B. conducted operando PEPICO spectroscopy experiments. P.H. and A.B. analysed the results of PEPICO spectroscopy. N.L. conducted the DFT calculations. The data were discussed among all the authors. V.P., P.H. and J.P.-R. wrote the paper with feedback from the other authors.

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Correspondence to Javier Pérez-Ramírez.

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Paunović, V., Hemberger, P., Bodi, A. et al. Evidence of radical chemistry in catalytic methane oxybromination. Nat Catal 1, 363–370 (2018). https://doi.org/10.1038/s41929-018-0071-z

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