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Free-atom-like d states in single-atom alloy catalysts

Nature Chemistry volume 10, pages 1008–1015 (2018)Cite this article

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Abstract

Alloying provides a means by which to tune a metal catalyst’s electronic structure and thus tailor its performance; however, mean-field behaviour in metals imposes limits. To access unprecedented catalytic behaviour, materials must exhibit emergent properties that are not simply interpolations of the constituent components’ properties. Here we show an emergent electronic structure in single-atom alloys, whereby weak wavefunction mixing between minority and majority elements results in a free-atom-like electronic structure on the minority element. This unusual electronic structure alters the minority element’s adsorption properties such that the bonding with adsorbates resembles the bonding in molecular metal complexes. We demonstrate this phenomenon with AgCu alloys, dilute in Cu, where the Cu d states are nearly unperturbed from their free-atom state. In situ electron spectroscopy demonstrates that this unusual electronic structure persists in reaction conditions and exhibits a 0.1 eV smaller activation barrier than bulk Cu in methanol reforming. Theory predicts that several other dilute alloys exhibit this phenomenon, which offers a design approach that may lead to alloys with unprecedented catalytic properties.

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Fig. 1: DOS plots show the free-atom-like nature of the Cu 3d states in AgCu.
Fig. 2: Evidence of charge transfer.
Fig. 3: Newns–Anderson–Grimley adsorption model.
Fig. 4: The formation of new bonds.
Fig. 5: Adsorption energy trends.
Fig. 6: Free-atom-like state in reaction conditions.
Fig. 7: Alternative narrow d-band alloys.

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Acknowledgements

Funding for this project was provided by the Alexander von Humboldt Foundation and the Max-Planck Society. We also thank the Helmholtz-Zentrum Berlin for their infrastructure support and Höchstleistungsrechenzentrum Stuttgart for access to the supercomputer HazelHen.

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Authors and Affiliations

  1. Max-Planck Institute for Chemical Energy Conversion, Department of Heterogeneous Reactions, Mülheim an der Ruhr, Germany

    M. T. Greiner, S. Beeg & R. Schlögl

  2. Fritz-Haber Institute of the Max-Planck Society, Department of Inorganic Chemistry, Berlin, Germany

    M. T. Greiner, T. E. Jones, S. Beeg, L. Zwiener, M. Scherzer, F. Girgsdies, A. Knop-Gericke & R. Schlögl

  3. National Research Council, Institute of Materials, Trieste, Italy

    S. Piccinin

  4. Technical University of Chemnitz, Institute of Chemistry, Chemnitz, Germany

    M. Armbrüster

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  1. M. T. Greiner
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Contributions

M.T.G. and T.E.J. conceived, designed and planned the project. M.T.G. measured and analysed the photoemission spectra as well as activation energies. T.E.J. performed the theoretical calculations. R.S., S.P. and A.K.-G. provided direction, guidance and assistance in the data interpretation. S.B. assisted in photoemission measurements. L.Z. synthesized the samples used for the activity measurements. M.A. synthesized the bulk metal samples. M.S. and F.G. measured and analysed the X-ray diffraction data. M.T.G. and T.E.J. wrote the manuscript. All the authors provided input and advice while writing manuscript drafts. M.T.G. and T.E.J. contributed to this work equally.

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Correspondence to M. T. Greiner or T. E. Jones.

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Supplementary Figures 1–12, Supplementary Tables 1 and 2, Supplementary Data and Discussion

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Greiner, M.T., Jones, T.E., Beeg, S. et al. Free-atom-like d states in single-atom alloy catalysts. Nature Chem 10, 1008–1015 (2018). https://doi.org/10.1038/s41557-018-0125-5

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