Bulky Calixarene Ligands Stabilize Supported Iridium Pair-Site Catalysts.
Bulky Calixarene Ligands Stabilize Supported Iridium Pair-Site Catalysts.
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DOI：
10.1021/jacs.8b13013
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发表时间：
2019-02
影响因子：
15
通讯作者：
Christian Schöttle;Erjia Guan;A. Okrut;Nicolás A. Grosso‐Giordano;Andrew P Palermo;A. Solovyov;B. Gates;Alexander Katz
中科院分区：
文献类型：
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作者：
Christian Schöttle;Erjia Guan;A. Okrut;Nicolás A. Grosso‐Giordano;Andrew P Palermo;A. Solovyov;B. Gates;Alexander Katz
尽管分子贵金属物种为负载型催化剂的设计提供了活性中心和高度可调的平台，但金属对还原和聚集的敏感性以及随之而来的催化活性和选择性的丧失限制了它们的应用机会。在这里，我们展示了一种新的结构来稳定负载型分子贵金属催化剂，利用金属上空间大小的配体作为替代载体，并在还原环境中涉及稳态催化周转的条件下分离活性中心。这一结果被证明是以含有分散在硅质载体上的P-桥联杯[4]芳烃配体的Ir对中心催化剂为原型的，因为它们提供了容易发生金属聚集的弱相互作用表面。该催化剂在流动反应器中用于乙烯加氢反应。对催化剂使用前后的红外中心和光谱的原子分辨率成像表明，金属抗聚集和失活，保持原子分散，可用于催化。因此，即使催化剂弱地固定在载体上，这种策略也可以使催化剂稳定。
Although essentially molecular noble metal species provide active sites and highly tunable platforms for the design of supported catalysts, the susceptibility of the metals to reduction and aggregation and the consequent loss of catalytic activity and selectivity limit opportunities for their application. Here, we demonstrate a new construct to stabilize supported molecular noble-metal catalysts, taking advantage of sterically bulky ligands on the metal that serve as surrogate supports and isolate the active sites under conditions involving steady-state catalytic turnover in a reducing environment. The result is demonstrated with an iridium pair-site catalyst incorporating P-bridging calix[4]arene ligands dispersed on siliceous supports, chosen as prototypes because they offer weakly interacting surfaces on which metal aggregation is prone to occur. This catalyst was used for the hydrogenation of ethylene in a flow reactor. Atomic-resolution imaging of the Ir centers and spectra of the catalyst before and after use show that the metals resisted aggregation and deactivation, remaining atomically dispersed and accessible for catalysis. This strategy thus allows the stabilization of the catalysts even when they are weakly anchored to supports.