Galushko Alexey S, Boiko Daniil A, Pentsak Evgeniy O, Eremin Dmitry B, Ananikov Valentine P
Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, Moscow 119991, Russia.
Bridge Institute and Department of Chemistry, University of Southern California, Los Angeles, California 90089-3502, United States.
J Am Chem Soc. 2023 Apr 26;145(16):9092-9103. doi: 10.1021/jacs.3c00645. Epub 2023 Apr 13.
An approach to the spatially localized characterization of supported catalysts over a reaction course is proposed. It consists of a combination of scanning, transmission, and high-resolution scanning transmission electron microscopy to determine metal particles from arrays of surface nanoparticles to individual nanoparticles and individual atoms. The study of the evolution of specific metal catalyst particles at different scale levels over time, particularly before and after the cross-coupling catalytic reaction, made it possible to approach the concept of 4D catalysis-tracking the positions of catalytic centers in space (3D) over time (+1D). The dynamic behavior of individual palladium atoms and nanoparticles in cross-coupling reactions was recorded with nanometer accuracy via the precise localization of catalytic centers. Single atoms of palladium leach out into solution from the support under the action of the catalytic system, where they exhibit extremely high catalytic activity compared to surface metal nanoparticles. Monoatomic centers, which make up only approximately 1% of palladium in the Pd/C system, provide more than 99% of the catalytic activity. The remaining palladium nanoparticles changed their shape and could move over the surface of the support, which was recorded by processing images of the array of nanoparticles with a neural network and aligning them using automatically detected keypoints. The study reveals a novel opportunity for single-atom catalysis─easier detachment (capture) from (on) the carbon support surface is the origin of superior catalytic activity, rather than the operation of single atomic catalytic centers on the surface of the support, as is typically assumed.
提出了一种在反应过程中对负载型催化剂进行空间局部表征的方法。它由扫描电子显微镜、透射电子显微镜和高分辨率扫描透射电子显微镜组合而成，用于确定从表面纳米颗粒阵列到单个纳米颗粒和单个原子的金属颗粒。对特定金属催化剂颗粒在不同尺度水平上随时间的演变进行研究，特别是在交叉偶联催化反应之前和之后，使得接近4D催化的概念成为可能——即跟踪催化中心在空间（3D）中的位置随时间（+1D）的变化。通过催化中心的精确定位，以纳米精度记录了交叉偶联反应中单个钯原子和纳米颗粒的动态行为。在催化体系的作用下，钯单原子从载体中浸出到溶液中，与表面金属纳米颗粒相比，它们表现出极高的催化活性。在Pd/C体系中，单原子中心仅占钯的约1%，却提供了超过99%的催化活性。其余的钯纳米颗粒改变了形状，并能在载体表面移动，这是通过用神经网络处理纳米颗粒阵列的图像并利用自动检测的关键点进行对齐来记录的。该研究揭示了单原子催化的一个新机会——从碳载体表面更容易脱离（捕获）是卓越催化活性的起源，而不是像通常所认为的那样是载体表面单原子催化中心的作用。
