Bimetallic and multi-component catalysts typically exhibit composition-dependent activity and selectivity, and when optimized often outperform single-component catalysts. Here we used ambient-pressure X-ray photoelectron spectroscopy (AP-XPS) and in situ and ex situ transmission electron microscopy (TEM) to elucidate the origin of composition dependence observed in the catalytic activities of monodisperse CoPd bimetallic nanocatalysts for CO oxidation. We found that the catalysis process induced a reconstruction of the catalysts, leaving CoOx on the nanoparticle surface. The synergy between Pd and CoOx coexisting on the surface promotes the catalytic activity of the bimetallic catalysts. This synergistic effect can be optimized by tuning the Co/Pd ratios in the nanoparticle synthesis, and it reaches a maximum at compositions near Co0.24Pd0.76, which achieves complete CO conversion at the lowest temperature. Our combined AP-XPS and TEM studies provide direct observation of the surface evolution of the bimetallic nanoparticles under catalytic conditions and show how this evolution correlates with catalytic properties.

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The data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request.

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This work was supported by the Office of Basic Energy Sciences of the US Department of Energy under contract no. DE-AC02-05CH11231 through the Chemical Sciences, Geosciences, and Biosciences Division. Funding from the same contract for the ALS and beamline 9.3.2 is also acknowledged. Partial work on CoPd nanoparticles synthesis and characterization were supported by US National Science Foundation (DMR-1809700) and Jeffress Trust Awards Program in Interdisciplinary Research from Thomas F. and Kate Miller Jeffress Memorial Trust. Partial work on electron microscopy carried out at the Center for Functional Nanomaterials, Brookhaven National Laboratory, was supported by the US Department of Energy, Office of Basic Energy Sciences, under contract no. DE-AC02-98CH10886.

Author information


  1. Department of Chemistry, University of California, Berkeley, Berkeley, CA, USA

    • Cheng Hao Wu
  2. Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA

    • Cheng Hao Wu
    • , Hai-Tao Fang
    •  & Miquel B. Salmeron
  3. Department of Chemistry, University of Virginia, Charlottesville, Virginia, USA

    • Chang Liu
    •  & Sen Zhang
  4. Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York, USA

    • Dong Su
    •  & Huolin L. Xin
  5. School of Materials Science and Engineering, Harbin Institute of Technology, Harbin, China

    • Hai-Tao Fang
    •  & Baran Eren
  6. Department of Chemistry, University of Pennsylvania, Philadelphia, PA, USA

    • Christopher B. Murray
  7. Department of Materials Science and Engineering, University of California, Berkeley, Berkeley, CA, USA

    • Miquel B. Salmeron


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The project was conceived by C.H.W. and C.L. under the supervision of S.Z, M.B.S. and C.B.M. Catalyst synthesis, basic characterization and catalytic activity measurements were performed by C.L. and S.Z. AP-XPS experiments were conducted by C.H.W., H.-T.F. and B.E. Ex situ TEM and elemental mapping were done by D.S. In situ TEM and EELS measurements were performed by H.X., C.H.W. and S.Z. Ex situ XAS measurements were done by C.H.W. The analysis and interpretation of all spectra (XPS, XAS and EELS) were done by C.H.W. All authors contributed to the writing of the manuscript.

Competing interests

The authors declare no competing interests.

Corresponding authors

Correspondence to Sen Zhang or Christopher B. Murray or Miquel B. Salmeron.

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