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Exploring the nature of active chromium catalysts during tetramerization of ethylene by (coupled) operando spectroscopy

通过（耦合）原位光谱探索乙烯四聚过程中活性铬催化剂的性质

基本信息

批准号：
281469981
负责人：
Professor Dr. Matthias Bauer
金额：
--
依托单位：
Leibniz-Institut für Katalyse e. V. an der Universität Rostock (LIKAT)
依托单位国家：
德国
项目类别：
Research Grants
财政年份：
2015
资助国家：
德国
起止时间：
2014-12-31 至 2019-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/281469981?language=en
关键词：
Exploring nature active chromium catalysts

项目摘要

Linear olefins such as 1-hexene and 1-octene are important building blocks for polymer production. They are generally produced by homogeneous catalytic ethylene oligomerization using complex Cr catalysts (assembled in situ from a Cr precursor and suitable ligands) in the presence of Al-based activators. While yields of >90 % are achieved for 1-hexene with bidentate diphosphinoamine ligands (PNP), maximum 1-octene yields are still much lower and differ significantly depending on the type of Cr precursor, Al activator and PNP ligands. Detailed knowledge of the role of these components for the formation of the (still widely unknown) active Cr complex and the catalytic performance is highly desired to support rational catalyst design. However, so far conclusions on valence state and structure of the active Cr species formed in situ have been derived almost exclusively from treatment of well-defined separately prepared Cr complexes with ethylene or from ex situ characterization of Cr species isolated from the reaction mixture. Consequently, these results may not reflect the true situation under reaction conditions.It is the aim of this project to explore the nature of the catalytically active species as well as of intermediate reaction steps and deactivation pathways in tetramerization of ethylene under relevant conditions (flowing ethylene at 60°C and a pressure of 15-20 bar) by monitoring the reaction with a tailored combination of spectroscopic operando techniques (EPR, XAS, XES, UV-vis, FTIR-ATR and Raman spectroscopy). Special emphasis is put on coupling several methods in the same experiment since this widens the range of accessible information under exactly comparable conditions. Apart from simultaneous Raman/ATR/UV-vis spectroscopy already available at LIKAT, EPR and synchrotron X-ray spectroscopy will be simultaneously coupled for the first time in the same experiment. This will facilitate identification of different coexisting Cr species, since EPR can detect selectively individual Cr(I) and Cr(III) moieties while XAS is active for all Cr valence states but reflects an average of all present Cr species only. Using this advanced characterization platform and the catalytic system Ph2P-N(iPr)-PPh2/Cr(acac)3/MAO cyclohexane as a reference, the influence of dedicated modifications of the PNP ligand (different substituents at Ph and N), the Cr precursor and/or the aluminium activator on structure and valence state of the in situ formed active Cr complex and, consequently, on the catalytic performance will be studied.

直链烯烃如1-己烯和1-辛烯是用于聚合物生产的重要结构单元。它们通常通过在Al基活化剂存在下使用络合物Cr催化剂（由Cr前体和合适的配体原位组装）的均相催化乙烯低聚来制备。虽然对于具有双齿二膦基胺配体（PNP）的1-己烯实现了> 90%的产率，但是最大1-辛烯产率仍然低得多，并且取决于Cr前体、Al活化剂和PNP配体的类型而显著不同。非常需要详细了解这些组分对于形成活性Cr络合物（仍然广泛未知）和催化性能的作用，以支持合理的催化剂设计。然而，到目前为止，在原位形成的活性铬物种的价态和结构的结论几乎完全来自于处理定义明确的单独制备的铬络合物与乙烯或从异位表征的铬物种分离的反应混合物。因此，委员会认为，本研究的目的是探索在相应条件下乙烯四聚反应中催化活性物种的性质以及中间反应步骤和失活途径（在60°C和15-20巴的压力下流动的乙烯），通过用光谱操作技术的定制组合监测反应，（EPR、XAS、XES、UV-vis、FTIR-ATR和拉曼光谱）。特别强调耦合几种方法在同一个实验，因为这扩大了范围内的可访问的信息完全可比的条件下。除了LIKAT已经提供的同步拉曼/ATR/紫外可见光谱外，EPR和同步加速器X射线光谱将首次在同一实验中同时耦合。这将有助于鉴别不同的共存Cr物质，因为EPR可以选择性地检测单个Cr（I）和Cr（III）部分，而XAS对所有Cr价态都有活性，但仅反映所有存在的Cr物质的平均值。使用这种先进的表征平台和催化体系Ph 2 P-N（iPr）-PPh 2/Cr（acac）3/MAO环己烷作为参考，将研究PNP配体（在Ph和N处的不同取代基）、Cr前体和/或铝活化剂的专用改性对原位形成的活性Cr络合物的结构和价态以及因此对催化性能的影响。