A Synthetic Approach to Active Site Deconvolution in Supported Cr Catalysts for Olefin Polymerization

烯烃聚合负载型 Cr 催化剂活性位反褶积的合成方法

• 批准号: 0854425
• 负责人: Susannah Scott
• 金额: $ 49.43万
• 依托单位: University of California-Santa Barbara
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-03-01 至 2013-02-28
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0854425&HistoricalAwards=false
• 关键词: Synthetic; Approach; Active; Site; Deconvolution

0854425 Scott, Susannah L. The goal of the project is to develop a unified framework for understanding and controlling the ability of supported metal oxide catalysts used in olefin transformations, specifically olefin metathesis and polymerization, to self-activate in the presence of the substrate. The activity profiles and product distributions for well-defined model catalysts will be correlated with sites of well-defined geometrical and electronic structure. Ultimately, knowledge of active site structures will facilitate the re-engineering of these catalysts by allowing the selection of combinations of sites to generate a desired product distribution, for example, polymer molecular weight and branch content. Furthermore, elucidation of catalyst activation mechanisms will indicate strategies to make the activation more efficient.Intellectual MeritThe goal of this project is to solve a longstanding and complex problem in a very successful class of industrial catalysts. Phillips catalysts for olefin polymerization (CrOx/SiO2) were discovered half a century ago, and their remarkable ability to self-activate in the presence of olefin has been the subject of much speculation ever since. Until the nature of the active sites is known, it is unlikely that we will be able to determine how they are formed or why this catalyst is so effective at reviving deactivated sites. Related catalysts containing supported group 6 metal oxides of Mo and W are also self-activating, but they promote olefin metathesis rather than polymerization. The proposed approach to determining how self-activation occurs combines synthesis of individual, well-defined active site candidates with analysis of the multiple active sites present on the heterogeneous catalysts. Experimental approaches will be integrated with computational modeling of reaction mechanisms to identify key transition states. The PIs propose to probe initiation mechanisms and match activity profiles and product distributions of the component active sites in the heterogeneous systems with those of structurally well-defined sites.The synthetic approach to active site investigation is complementary to the combinatorial approach to catalyst discovery. Once interesting catalyst formulations are identified and optimized by screening (parallel or otherwise), further improvements depend on the ability to manipulate active site structure. Identifying the structural features that control reactivity by synthesizing model compounds has long been a successful strategy in homogeneous catalysis. The extension of this strategy in heterogeneous catalysis can be accomplished by combining expertise in organometallic synthesis, surface science, kinetics/mechanistic analysis of complex systems and catalyst modeling and evaluation.Broader ImpactsHeterogeneous polyolefin catalysts are multifunctional materials with the ability to oligomerize, polymerize, copolymerize, terminate and reactivate, creating polymer resins with desirable combinations of physical properties. In parallel, recent advances in the synthesis of single-site catalysts have led to polymers with very low polydispersities, as well as elegant mechanistic studies of polymerization mechanisms. The complexity of the heterogeneous catalysts is enabling in both its flexibility and its diversity, and therefore deserving of the same systematic investigation in order to fully realize its benefits.Execution of this project requires strong skills in both chemical engineering and chemistry. Graduate students will develop a deep understanding of both fields as members of an interdisciplinary research team. They will learn to appreciate and implement the strengths of each discipline's approach to problem-solving. Students will also experience the close connection between computational and experimental modeling of active sites. Technical success in this work provides a powerful justification for interdisciplinary training of catalysis researchers.

0854425 Scott，Susannah L.该项目的目的是开发一个统一的框架，以理解和控制烯烃转化中使用的支持的金属氧化物催化剂的能力，特别是烯烃的分解和聚合，以在底物存在下自动激活。定义明确的模型催化剂的活性曲线和产品分布将与定义明确的几何和电子结构的位点相关。最终，主动位点结构的知识将通过允许位点组合的选择来生成所需的产品分布，例如聚合物分子量和分支含量，从而有助于对这些催化剂的重新设计。此外，阐明催化剂激活机制将表明使激活更有效的策略。Intlectual值得该项目的目标是在非常成功的一类工业催化剂中解决一个长期且复杂的问题。菲利普斯（Phillips）催化剂用于烯烃聚合（CROX/SIO2），在半个世纪前发现了它们的出色自我激活能力，从那以后，它们就一直是人们猜测的主题。在已知活动位点的性质之前，我们不太可能能够确定它们的形成方式，或者为什么该催化剂在恢复失活的位点上如此有效。含有含有的MO和W组的6个金属氧化物的相关催化剂也是自动激活的，但它们促进了烯烃的分解而不是聚合。确定自我激活如何发生的建议方法结合了单个，定义明确的活性位点候选物的合成与对异质催化剂上存在的多个活性位点的分析。实验方法将与反应机制的计算建模集成，以识别关键过渡态。 PI提议探测启动机制，并匹配异质系统中组件活性位点的活性位点的活性曲线和产品分布，并具有结构良好的定义位点。主动位点研究的合成方法是与催化剂发现的组合方法互补的。一旦通过筛选（并行或其他方式）鉴定并优化了有趣的催化剂制剂，进一步的改进就取决于操纵活动位点结构的能力。长期以来，通过合成模型化合物来识别通过合成模型化合物来控制反应性的结构特征一直是均质催化的成功策略。 The extension of this strategy in heterogeneous catalysis can be accomplished by combining expertise in organometallic synthesis, surface science, kinetics/mechanistic analysis of complex systems and catalyst modeling and evaluation.Broader ImpactsHeterogeneous polyolefin catalysts are multifunctional materials with the ability to oligomerize, polymerize, copolymerize, terminate and reactivate, creating polymer resins with desirable物理特性的组合。同时，单位催化剂合成的最新进展导致聚合物具有非常低的多分散性，以及聚合机制的优雅机械研究。异质催化剂的复杂性具有其灵活性和多样性，因此应进行相同的系统调查，以充分实现其益处。对该项目的执行需要化学工程和化学方面的强大技能。研究生将作为跨学科研究团队的成员深入了解这两个领域。他们将学会欣赏并实施每个学科解决问题的方法的优势。学生还将体验活动站点的计算和实验建模之间的密切联系。这项工作的技术成功为催化研究人员的跨学科培训提供了强大的理由。