Zhao Yanyan, Yan Xingxu, Yang Ke R, Cao Sufeng, Dong Qi, Thorne James E, Materna Kelly L, Zhu Shasha, Pan Xiaoqing, Flytzani-Stephanopoulos Maria, Brudvig Gary W, Batista Victor S, Wang Dunwei
Department of Chemistry, Merkert Chemistry Center, Boston College, Chestnut Hill, Massachusetts 02467, United States.
Department of Chemical Engineering and Materials Science and Department of Physics and Astronomy, University of California - Irvine, Irvine, California 92697, United States.
ACS Cent Sci. 2018 Sep 26;4(9):1166-1172. doi: 10.1021/acscentsci.8b00335. Epub 2018 Jul 25.
Heterogeneous catalysts with atomically defined active centers hold great promise for high-performance applications. Among them, catalysts featuring active moieties with more than one metal atom are important for chemical reactions that require synergistic effects but are rarer than single atom catalysts (SACs). The difficulty in synthesizing such catalysts has been a key challenge. Recent progress in preparing dinuclear heterogeneous catalysts (DHCs) from homogeneous molecular precursors has provided an effective route to address this challenge. Nevertheless, only side-on bound DHCs, where both metal atoms are affixed to the supporting substrate, have been reported. The competing end-on binding mode, where only one metal atom is attached to the substrate and the other metal atom is dangling, has been missing. Here, we report the first observation that end-on binding is indeed possible for Ir DHCs supported on WO. Unambiguous evidence supporting the binding mode was obtained by diffuse reflectance infrared Fourier transform spectroscopy and high-angle annular dark-field scanning transmission electron microscopy. Density functional theory calculations provide additional support for the binding mode, as well as insights into how end-on bound DHCs may be beneficial for solar water oxidation reactions. The results have important implications for future studies of highly effective heterogeneous catalysts for complex chemical reactions.
具有原子级明确活性中心的多相催化剂在高性能应用方面极具潜力。其中，具有多个金属原子活性部分的催化剂对于需要协同效应的化学反应很重要，但比单原子催化剂（SAC）更为罕见。合成此类催化剂的困难一直是一个关键挑战。最近从均相分子前体制备双核多相催化剂（DHC）的进展为解决这一挑战提供了一条有效途径。然而，目前仅报道了侧基结合的DHC，即两个金属原子都固定在支撑底物上。而竞争的端基结合模式，即只有一个金属原子附着在底物上而另一个金属原子悬空的情况一直未被发现。在此，我们首次报道观察到负载在WO上的Ir DHC确实可能存在端基结合。通过漫反射红外傅里叶变换光谱和高角度环形暗场扫描透射电子显微镜获得了支持这种结合模式的明确证据。密度泛函理论计算为这种结合模式提供了额外支持，并深入了解了端基结合的DHC如何有利于太阳能水氧化反应。这些结果对未来复杂化学反应高效多相催化剂的研究具有重要意义。
