A site-isolated mononuclear iridium complex catalyst supported on MgO: Characterization by spectroscopy and aberration-corrected scanning transmission electron microscopy
A site-isolated mononuclear iridium complex catalyst supported on MgO: Characterization by spectroscopy and aberration-corrected scanning transmission electron microscopy
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DOI：
10.1016/j.jcat.2009.11.017
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发表时间：
2010-02
影响因子：
7.3
通讯作者：
Alper Uzun;V. Ortalan;N. Browning;B. Gates
中科院分区：
文献类型：
--
作者：
Alper Uzun;V. Ortalan;N. Browning;B. Gates
通过Ir（C_2H_4）_2（acac）（acac为CH_3COCH_COCH_3）与高脱羟基MgO反应，制备了负载型单核铱乙烯配合物。通过扩展X射线吸收精细结构（EXAFS）和红外光谱（IR）对负载物种进行表征表明，所得负载有机金属物种为Ir（C2 H4）2，由Ir（C2 H4）2（acac）解离成acac配体，并将Ir（C2 H4）2物种键合到MgO表面形成。通过像差校正的扫描透射电子显微镜（STEM）获得这些单核复合物的位点隔离的直接证据;图像表明在不存在任何簇的情况下存在铱复合物。当铱配合物用CO探测时，所得的IR光谱证明在MgO表面上形成了Ir（CO）2配合物。ν CO带的宽度表明金属-载体结合的显著变化，与MgO表面的异质性一致; STEM图像不足以表征这种异质性。在流动反应器中，负载铱配合物在室温和常压下催化乙烯加氢，EXAFS光谱表明单核铱物种保持完整。所用催化剂的STEM图像证实，几乎所有的铱络合物保持完整，但该方法足够灵敏，可以检测到铱在载体上的小程度聚集。
Supported mononuclear iridium complexes with ethene ligands were prepared by the reaction of Ir(C2H4)2(acac) (acac is CH3COCHCOCH3) with highly dehydroxylated MgO. Characterization of the supported species by extended X-ray absorption fine structure (EXAFS) and infrared (IR) spectroscopies showed that the resultant supported organometallic species were Ir(C2H4)2, formed by the dissociation of the acac ligand from Ir(C2H4)2(acac) and bonding of the Ir(C2H4)2species to the MgO surface. Direct evidence of the site-isolation of these mononuclear complexes was obtained by aberration-corrected scanning transmission electron microscopy (STEM); the images demonstrate the presence of the iridium complexes in the absence of any clusters. When the iridium complexes were probed with CO, the resulting IR spectra demonstrated the formation of Ir(CO)2complexes on the MgO surface. The breadth of the νCObands demonstrates a substantial variation in the metal–support bonding, consistent with the heterogeneity of the MgO surface; the STEM images are not sufficient to characterize this heterogeneity. The supported iridium complexes catalyzed ethene hydrogenation at room temperature and atmospheric pressure in a flow reactor, and EXAFS spectra indicated that the mononuclear iridium species remained intact. STEM images of the used catalyst confirmed that almost all of the iridium complexes remained intact, but this method was sensitive enough to detect a small degree of aggregation of the iridium on the support.