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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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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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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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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DOI: https://doi.org/10.1038/s41557-018-0125-5