Single‐atom catalysts (SACs) are an emerging class of materials, leveraging maximum atom utilization and distinctive structural and electronic properties to bridge heterogeneous and homogeneous catalysis. Direct imaging methods, such as aberration‐corrected high‐angle annular dark‐field scanning transmission electron microscopy, are commonly applied to confirm the atomic dispersion of active sites. However, interpretations of data from these techniques can be challenging due to simultaneous contributions to intensity from impurities introduced during synthesis processes, as well as any variation in position relative to the focal plane of the electron beam. To address this matter, this paper presents a comprehensive study on two representative SACs containing isolated nickel or copper atoms. Spectroscopic techniques, including X‐ray absorption spectroscopy, were employed to prove the high metal dispersion of the catalytic atoms. Employing scanning transmission electron microscopy imaging combined with single‐atom‐sensitive electron energy loss spectroscopy, we scrutinized thin specimens of the catalysts to provide an unambiguous chemical identification of the observed single‐atom species and thereby distinguish impurities from active sites at the single‐atom level. Overall, the study underscores the complexity of SACs characterization and establishes the importance of the use of spectroscopy in tandem with imaging at atomic resolution to fully and reliably characterize single‐atom catalysts.

中文翻译：

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隐藏的杂质在单原子催化剂成像中产生误报


单原子催化剂（SAC）是一类新兴材料，利用最大的原子利用率和独特的结构和电子特性来桥接多相和均相催化。直接成像方法，例如像差校正高角度环形暗场扫描透射电子显微镜，通常用于确认活性位点的原子分散。然而，由于合成过程中引入的杂质同时对强度产生影响，以及相对于电子束焦平面的位置的任何变化，对这些技术的数据的解释可能具有挑战性。为了解决这个问题，本文对两种含有孤立镍或铜原子的代表性 SAC 进行了全面研究。采用包括 X 射线吸收光谱在内的光谱技术来证明催化原子的高金属分散性。采用扫描透射电子显微镜成像与单原子敏感电子能量损失光谱相结合，我们仔细检查了催化剂的薄样品，以对观察到的单原子物种提供明确的化学鉴定，从而区分杂质与单原子活性位点等级。总体而言，该研究强调了 SAC 表征的复杂性，并确立了将光谱学与原子分辨率成像结合使用以全面可靠地表征单原子催化剂的重要性。