Dynamic restructuring drives catalytic activity on nanoporous gold–silver alloy catalysts

Abstract

Bimetallic, nanostructured materials hold promise for improving catalyst activity and selectivity, yet little is known about the dynamic compositional and structural changes that these systems undergo during pretreatment that leads to efficient catalyst function. Here we use ozone-activated silver–gold alloys in the form of nanoporous gold as a case study to demonstrate the dynamic behaviour of bimetallic systems during activation to produce a functioning catalyst. We show that it is these dynamic changes that give rise to the observed catalytic activity. Advanced in situ electron microscopy and X-ray photoelectron spectroscopy are used to demonstrate that major restructuring and compositional changes occur along the path to catalytic function for selective alcohol oxidation. Transient kinetic measurements correlate the restructuring to three types of oxygen on the surface. The direct influence of changes in surface silver concentration and restructuring at the nanoscale on oxidation activity is demonstrated. Our results demonstrate that characterization of these dynamic changes is necessary to unlock the full potential of bimetallic catalytic materials.

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Figure 1: Activation of npAu for selective methanol oxidation.
Figure 2: Pulsed experiments over ozone-treated npAu.
Figure 3: E-TEM analysis of npAu after ozone treatment.
Figure 4: E-TEM analysis of npAu during CO and CH3OH exposure.
Figure 5: AP-XPS analysis of npAu.
Figure 6: Changes in the relative surface concentrations of Ag, O and Au.

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Acknowledgements

This work was supported as part of the Integrated Mesoscale Architectures for Sustainable Catalysis, an Energy Frontier Research Center funded by the US Department of Energy, Office of Science, Basic Energy Sciences under award no. DE-SC0012573. Work at LLNL was performed under the auspices of the US Department of Energy by LLNL under Contract DE-AC52-07NA27344. This research used resources of the Center for Functional Nanomaterials, which is a US DOE Office of Science Facility, at Brookhaven National Laboratory under Contract No. DE-SC0012704. It also used resources of the Advance Light Source, which is supported by the Office of Science of the US DOE under Contract No. DE-AC02-05CH11231. We thank H. Bluhm for advice on the preparation of the AP-XPS experiments and H. Xin for valuable discussion regarding the EELS data.

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C.M.F., R.J.M., J.B. and B.Z. conceived and designed the experimental plan. B.Z. conducted the flow reactor experiments. B.Z. and J.B. prepared the npAu samples. L.W. conceived and conducted the TAP reactor experiments. C.H., M.S., B.A.J.L. and B.Z. conceived and conducted the AP-XPS experiments and analysed the XPS data. E.A.S., D.N.Z. and B.Z. planned and conducted E-TEM experiments. B.Z. wrote the initial draft of the manuscript. All authors discussed the results and contributed to the final preparation of the manuscript.

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Correspondence to Cynthia M. Friend.

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The authors declare no competing financial interests.

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Zugic, B., Wang, L., Heine, C. et al. Dynamic restructuring drives catalytic activity on nanoporous gold–silver alloy catalysts. Nature Mater 16, 558–564 (2017). https://doi.org/10.1038/nmat4824

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