Visualizing Under-Coordinated Surface Atoms on 3D Nanoporous Gold Catalysts
Update: 2016-02-02 13:56:09      Author: yangjuan@csrc.ac.cn

The underlying mechanisms of gold catalysis towards oxidation reactions have been debated for many years. Recently, free-standing nanoporous gold (NPG) was found to exhibit similar catalytic activities toward oxidation reactions as oxide-supported gold nanoparticles. [1] Moreover, NPG can retain the high catalytic activities at much larger characteristic lengths (>30 nm) in comparison with the critical size of ~5 nm for gold nanoparticles. [2] This unsupported, stable gold catalyst provides a model system to explore the underlying mechanisms of gold catalysis. In line with extensive discussion on catalysis of gold nanoparticles, high-resolution scanning transmission electron microscopy (HR-STEM) observations suggest that the intrinsic catalysis of NPG appears to be associated with the under-coordinated surface atoms. [3] However, the detailed description on the intrinsic correlation between the density of under-coordinated surface atoms and the catalytic activity of NPG remains to be unknown. 

Recently, by combining spherical aberration corrected (Cs-corrected) high angle annular dark field (HAADF) STEM with discrete tomography, Pengfei Guan from the CSRC in collaboration with researchers in Tohoku University [4] resolve this debate by reconstructing 3D atomic configurations of NPG ligaments. In this study, the reconstructed 3D atomic configurations of NPG ligaments give the quantitative descriptions of the number fraction and area density of under-coordinated atoms on the surface of gold ligaments of NPG with different sizes (Figure 1). Combining with truncated octahedral gold particles and the density of catalytically active sites for oxidation reactions (Figure 2), the qualitative agreement between the 3D atomic characterization and chemical experiments in the active atomic sites and under-coordinated surface atoms provides an important insight that the surface defects play an important role in the catalysis of NPG. 

1.png                             

 

Figure 1. Discrete tomography of nanoporous gold.

 

2.png

 

Figure 2. Quantitative measurements of under-coordinated surface atoms on NPG ligaments and truncated octahedral gold particles.

For more information, please see the paper: “Visualizing Under-Coordinated Surface Atoms on 3D

Nanoporous Gold Catalysts”, Advanced Materials 2015, DOI: 10.1002/adma.201504032

References:

[1] A. Wittstock , V. Zielasek , J. Biener , C. M. Friend , M. Bäumer , Science 2010 , 327 , 319 .

[2] Y. Ding , M. W. Chen , MRS Bull. 2009 , 34 , 569

[3] T. Fujita , P. F. Guan , K. McKenna , X. Y. Lang , A. Hirata , L. Zhang , T. Tokunaga , S. Arai , Y. Yamamoto , N. Tanaka , Y. Ishikawa , N. Asao , J. Erlebacher , M. W. Chen , Nat. Mater. 2012 , 11 , 775 .

[4] Pan Liu , Pengfei Guan , Akihiko Hirata , Ling Zhang , Luyang Chen , Yuren Wen , Yi Ding , Takeshi Fujita , Jonah Erlebacher, Mingwei Chen, Advanced Materials 2015, DOI: 10.1002/adma.201504032

 


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