负载Ni/α-MoC催化剂活性位点的单原子精度STEM-EELS探究

高 猛,许名权,李傲雯* ,周 武*

负载Ni/α-MoC催化剂活性位点的单原子精度STEM-EELS探究

高  猛,许名权,李傲雯* ,周  武*

(中国科学院大学 物理科学学院,北京100049)

       单原子精度的电子能量损失谱是对材料进行原子级精细表征、揭示材料原子尺度结构-物性关系的关键技术,在单原子催化剂等纳米能源材料的表征中具有广阔的应用前景。但长期以来,极差的信噪比限制了单原子电子能量损失谱的广泛应用。本文以负载Ni/α-MoC单原子催化剂为例,展示如何通过优化扫描透射电子显微镜的电子光路以及利用主成分分析法降噪来大幅提高单原子电子能量损失谱的信噪比,进而实现Ni单原子及纳米团簇的原子级化学成像和价态分析。这些单原子电子能量损失谱结果结合其他实验表征的方法以及密度泛函理论计算揭示了Ni/α-MoC催化剂的催化活性中心结构,帮助理解了催化剂的构效关系,也为低原子序数金属原子负载催化剂的表征提供了广泛的借鉴意义。

关键词  扫描透射电子显微学;电子能量损失谱;单原子催化剂;主成分分析法

中图分类号:O469;TH838;O536;TG115.21+5.3  文献标识码:Adoi:10.3969/j.issn.1000-6281.2022.06.001

 

Single-atomic STEM-EELS characterization of the catalytically active sites in supported Ni/α-MoC catalyst

GAO Meng,XU Ming-quan,LI Ao-wen*,ZHOU Wu*

(School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China)

Abstract   Electron energy loss spectroscopy (EELS) with single-atom sensitivity is a key technique for atomic-scale structural characterization of functional materials, and shows promising applications in the studies of energy-related nanomaterials, in particular, single-atom catalysts. However, the extremely low signal-to-noise ratio (SNR) in single-atom EELS has limited its wide applications. Herein, using a supported Ni/α-MoC single-atom catalyst as an example, we demonstrate that by combining the optimization of the electron optics in the scanning transmission electron microscope (STEM) and utilization of the principal component analysis (PCA) denoising method, the SNR of single-atom STEM-EELS can be largely improved, enabling direct chemical imaging and valence state analysis of Ni single atoms and nanoclusters on α-MoC surface with single-atomic sensitivity. Combining with density functional theory calculations and other characterization techniques, the single-atom STEM-EELS results reveal the nature of catalytically active sites in the supported Ni/α-MoC catalysts and help to elucidate its structure-property relationship. Our work paves the way for effective atomic-scale characterization of supported metal catalysts with low-Z (atomic number) metal atoms.

Keywords   scanning transmission electron microscopy; electron energy loss spectroscopy; single atom catalyst; principal components analysis

 

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