Atomic origins of the high catalytic activity of nanoporous gold

Abstract

Distinct from inert bulk gold, nanoparticulate gold has been found to possess remarkable catalytic activity towards oxidation reactions. The catalytic performance of nanoparticulate gold strongly depends on size and support, and catalytic activity usually cannot be observed at characteristic sizes larger than 5 nm. Interestingly, significant catalytic activity can be retained in dealloyed nanoporous gold (NPG) even when its feature lengths are larger than 30 nm. Here we report atomic insights of the NPG catalysis, characterized by spherical-aberration-corrected transmission electron microscopy (TEM) and environmental TEM. A high density of atomic steps and kinks is observed on the curved surfaces of NPG, comparable to 3–5 nm nanoparticles, which are stabilized by hyperboloid-like gold ligaments. In situ TEM observations provide compelling evidence that the surface defects are active sites for the catalytic oxidation of CO and residual Ag stabilizes the atomic steps by suppressing {111} faceting kinetics.

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Figure 1: TEM micrographs and chemical analysis of NPG.
Figure 2: Surface atomic structure of NPG.
Figure 3: STEM image viewed along [001].
Figure 4: HRTEM characterization and theoretical modelling of NPG surface strain.
Figure 5: HRTEM observation viewed along under catalytic reactions for CO oxidation.
Figure 6: HRTEM observation of low-Ag NPG viewed along in pure gas environments using environmental TEM.

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Acknowledgements

We thank R. E. Dunin-Borkowski and E. A. Stach for fruitful discussions and comments. This work was sponsored by JST-PRESTO, JST-CREST and the Sekisui research fund. J.E. is supported by grant NSF DMR-1003901. We thank the Center for Computational Materials Science, Institute for Materials Research, Tohoku University, for providing us with the Hitachi SR11000 (model K2) supercomputing system and T. Tanji for the gas mixture used in the environmental TEM.

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M.C., T.F. and J.E. conceived and designed the experiments. T.F. and A.H. contributed to the microstructural characterization. P.G. simulated the structures computationally. X.L. and L.Z. fabricated the materials. K.M. modelled the nanoporous structure. Y.I., N.A. and Y.Y. contributed to the evaluation of catalytic performance. T.F. T.T., S.A., Y.Y. and N.T. contributed to environmental TEM observations. M.C., T.F., J.E. and K.M. wrote the paper. All of the authors discussed the results and commented on the manuscript.

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Correspondence to Takeshi Fujita or Mingwei Chen.

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Fujita, T., Guan, P., McKenna, K. et al. Atomic origins of the high catalytic activity of nanoporous gold. Nature Mater 11, 775–780 (2012). https://doi.org/10.1038/nmat3391

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