Industrial Ziegler-type hydrogenation catalysts made from Co(neodecanoate)2 or Ni(2-ethylhexanoate)2 and AlEt3: evidence for nanoclusters and sub-nanocluster or larger Ziegler-nanocluster based catalysis.
Industrial Ziegler-type hydrogenation catalysts made from Co(neodecanoate)2 or Ni(2-ethylhexanoate)2 and AlEt3: evidence for nanoclusters and sub-nanocluster or larger Ziegler-nanocluster based catalysis.
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由 Co(新癸酸酯)2 或 Ni(2-乙基己酸酯)2 和 AlEt3 制成的工业齐格勒型加氢催化剂：纳米团簇和亚纳米团簇或更大的齐格勒纳米团簇催化的证据。
DOI：
10.1021/la200053f
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发表时间：
2011
期刊：
影响因子：
--
通讯作者：
R. Finke
中科院分区：
文献类型：
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作者：
W. Alley;Isil K. Hamdemir;Qi Wang;A. Frenkel;Long Li;Judith C. Yang;L. Menard;R. Nuzzo;S. Özkar;K. Yih;Kimberly A. Johnson;R. Finke
齐格勒型氢化催化剂对于工业过程，即苯乙烯嵌段共聚物的大规模选择性氢化是重要的。齐格勒型氢化催化剂由第8-10族过渡金属预催化剂加上烷基铝助催化剂组成（并且它们与齐格勒-纳塔聚合催化剂不同）。然而，近50年来，齐格勒型氢化催化的两个未解决的核心问题是催化剂合成后存在的金属物质的性质，以及主要负责催化氢化活性的物质是否是均相的（例如，单金属络合物）或异质（例如，齐格勒纳米簇，定义为由齐格勒型氢化催化剂前体的组合制成的金属纳米簇）。现有文献的批判性综述（Alley等人，J. Mol. Catal. A：2010，315，1-27）和最近发表的使用Ir模型体系的研究（Alley等Inorg.Chem.2010，49，8131-8147）有助于指导目前对齐格勒型氢化催化剂的研究，所述齐格勒型氢化催化剂由工业上有利的前体Co（新癸酸酯）（2）或Ni（2-乙基己酸酯）（2）加上AlEt（3）制成。本文所用的方法和途径平行于研究Ir模型系统所用的方法和途径。具体地，Z-对比扫描透射电子显微镜（STEM）、基质辅助激光解吸电离质谱（MALDI MS）和X射线吸收精细结构（XAFS）光谱的组合用于表征氢化之前和之后的过渡金属物质。动力学研究，包括汞（0）中毒实验，用来测试哪些物种是最活跃的催化剂。主要的研究结果是，在催化环己烯氢化之前和之后，存在的物种包括从亚纳米到纳米尺度颗粒的金属簇尺寸的广泛分布，估计平均簇直径为约1 nm的Co和Ni。XAFS结果还意味着催化剂溶液是上述金属簇加上未还原的金属离子的混合物。基于动力学的Hg（0）中毒证据表明，Co和Ni齐格勒纳米团簇（即，M（≥4））是这些工业体系中活性最高的齐格勒型加氢催化剂。总的来说，本研究的新奇和主要结论如下：（i）本研究检查了由实际工业前体材料制成的基于Co和Ni的催化剂，这些催化剂在其表征方面是众所周知的问题;（ii）本文报道的Z对比STEM结果代表了据我们所知工业Co和Ni齐格勒型氢化催化剂的最佳显微镜分析;（iii）这项研究是第一次明确应用一种已建立的方法，使用多种分析方法和基于动力学的研究，以区分这些齐格勒型系统中的均相催化和多相催化;和（iv）该研究与Ir模型齐格勒催化剂体系的成功研究平行，从而受益于与那些先前不可得的发现的比较，尽管Ir相对于Ni或Co的更大的M-M键能和附聚倾向是值得注意的重要差异。总体而言，这项工作的主要结果是，它提供了领先的假设，在未来的工作中试图反驳，即，亚M（≥4）到更大的M（n）齐格勒纳米簇是齐格勒型氢化系统中占主导地位的工业Co和Ni加AlR（3）催化剂。
Ziegler-type hydrogenation catalysts are important for industrial processes, namely, the large-scale selective hydrogenation of styrenic block copolymers. Ziegler-type hydrogenation catalysts are composed of a group 8-10 transition metal precatalyst plus an alkylaluminum cocatalyst (and they are not the same as Ziegler-Natta polymerization catalysts). However, for ∼50 years two unsettled issues central to Ziegler-type hydrogenation catalysis are the nature of the metal species present after catalyst synthesis, and whether the species primarily responsible for catalytic hydrogenation activity are homogeneous (e.g., monometallic complexes) or heterogeneous (e.g., Ziegler nanoclusters defined as metal nanoclusters made from combination of Ziegler-type hydrogenation catalyst precursors). A critical review of the existing literature (Alley et al. J. Mol. Catal. A: Chem. 2010, 315, 1-27) and a recently published study using an Ir model system (Alley et al. Inorg. Chem. 2010, 49, 8131-8147) help to guide the present investigation of Ziegler-type hydrogenation catalysts made from the industrially favored precursors Co(neodecanoate)(2) or Ni(2-ethylhexanoate)(2), plus AlEt(3). The approach and methods used herein parallel those used in the study of the Ir model system. Specifically, a combination of Z-contrast scanning transmission electron microscopy (STEM), matrix assisted laser desorption ionization mass spectrometry (MALDI MS), and X-ray absorption fine structure (XAFS) spectroscopy are used to characterize the transition metal species both before and after hydrogenation. Kinetic studies including Hg(0) poisoning experiments are utilized to test which species are the most active catalysts. The main findings are that, both before and after catalytic cyclohexene hydrogenation, the species present comprise a broad distribution of metal cluster sizes from subnanometer to nanometer scale particles, with estimated mean cluster diameters of about 1 nm for both Co and Ni. The XAFS results also imply that the catalyst solutions are a mixture of the metal clusters described above, plus unreduced metal ions. The kinetics-based Hg(0) poisoning evidence suggests that Co and Ni Ziegler nanoclusters (i.e., M(≥4)) are the most active Ziegler-type hydrogenation catalysts in these industrial systems. Overall, the novelty and primary conclusions of this study are as follows: (i) this study examines Co- and Ni-based catalysts made from the actual industrial precursor materials, catalysts that are notoriously problematic regarding their characterization; (ii) the Z-contrast STEM results reported herein represent, to our knowledge, the best microscopic analysis of the industrial Co and Ni Ziegler-type hydrogenation catalysts; (iii) this study is the first explicit application of an established method, using multiple analytical methods and kinetics-based studies, for distinguishing homogeneous from heterogeneous catalysis in these Ziegler-type systems; and (iv) this study parallels the successful study of an Ir model Ziegler catalyst system, thereby benefiting from a comparison to those previously unavailable findings, although the greater M-M bond energy, and tendency to agglomerate, of Ir versus Ni or Co are important differences to be noted. Overall, the main result of this work is that it provides the leading hypothesis going forward to try to refute in future work, namely, that sub, M(≥4) to larger, M(n) Ziegler nanoclusters are the dominant, industrial, Co- and Ni- plus AlR(3) catalysts in Ziegler-type hydrogenation systems.