Exploiting links between nano-technology and heterogeneous catalysis: Shaped silver nano-particles as selective catalysts for partial oxidation of olefins to form chiral and..

本研究的目的是探索异形银纳米颗粒作为丙烯环氧化反应生成环氧丙烷和较大烯烃（即苯乙烯）不对称环氧化反应生成手性环氧化物的多相催化剂的潜力。这项研究建立在密歇根大学Linic早期生产环氧乙烷的工作基础上。多相银催化剂在商业上几乎只用于该反应。环氧乙烷是用于合成乙二醇（防冻剂）、乙醇胺和洗涤剂的关键化学品。Linic的计算表明，Ag的特定表面会对所需的产物提供更高的选择性。为合成形状特异的银纳米结构，开发了新的合成策略。随着明确定义的银纳米结构可以成为乙烯部分氧化的高选择性催化剂的证明，丙烯部分氧化成环氧丙烷的挑战是一个逻辑延伸。对于这个重要的、大规模的化学过程，没有选择性的多相催化剂。PI表明，金属银颗粒的形状与其性能之间存在着关键的联系，而影响其性能的主要因素是颗粒的形状特异性表面终止。PI假设，以Ag（100）面为端部的银纳米立方体和纳米线催化剂在丙烯的直接环氧化反应中，比以（111）面为端部的传统球形银颗粒具有更强的选择性。PI假设，特定的金属银纳米结构，用手性改性剂增强，将是大烯烃（例如苯乙烯）不对称环氧化形成手性环氧化物的有希望的非均相催化剂。目前，复杂而昂贵的均相催化剂被用于手性氧化反应，因为它们比传统的非均相固体催化剂具有更高的区域选择性和立体选择性。本研究项目旨在整合纳米科学和多相催化领域，利用不同形状和不同表面末端的金属纳米颗粒的受控合成的最新进展来设计高选择性无机催化剂。这项研究的成功结果的变革性是非常明显的。一种新的多相催化合成环氧丙烷的方法具有大规模的商业意义。此外，开发可行的非均相手性烯烃环氧化反应催化剂将具有明显的优势，包括易于产物分离，更长的催化剂寿命，更容易再生，以及可能使用更便宜和更环保的氧化剂，如氧气。

0966700LinicThe objective of the proposed work is to explore the potential of shaped Ag nano-particles as heterogeneous catalysts for the epoxidation of propylene to form propylene oxide and for the asymmetric epoxidation of larger olefins (i.e., styrene) to form chiral epoxides. The studies build on earlier work by Linic at the University of Michigan to produce ethylene oxide. Heterogeneous Ag catalysts are almost exclusively used for this reaction commercially. EO is a critical chemical used in the synthesis of ethylene glycol (antifreeze), ethanolamines, and detergents. Computations by Linic suggested that particular faces of Ag would offer higher selectivity to desired products. Novel synthetic strategies were then developed for the synthesis of the shape-specific Ag nano-structures. With the demonstration that well-defined Ag nano-structures can be highly selective catalysts for partial oxidation of ethylene, the challenge of propylene partial oxidation to propylene oxide is a logical extension. There are no selective heterogeneous catalysts for this important, large scale chemical process. The PI has shown that there exists a critical link between the shape of catalytic metallic Ag particles and their performance, and that the main factor affecting the performance is the shape-specific surface termination of the particles. The PI hypothesizes that Ag nano-cube and nano-wire catalysts, terminated specifically by the Ag(100) facet, will be significantly more selective in direct epoxidation of propylene than conventional spherical Ag particles, which are terminated by the (111) facet. The PI hypothesizes that specific metallic Ag nanostructures, enhanced with chiral modifiers, will be promising heterogeneous catalysts for asymmetric epoxidation of larger olefins (for example styrene) to form chiral epoxides. Currently, complex and expensive homogeneous catalysts are used for chiral oxidation reactions as they offer greater regio- and stereo-selectivity than conventional heterogeneous solid state catalysts. The proposed research project attempts to constructively integrate the fields of nanoscience and heterogeneous catalysis by taking advantage of recent advances in the controlled synthesis of metallic nano-particles of different shapes and different surface terminations to design highly selective inorganic catalysts. The transformative nature to the successful outcome of this study is quite apparent. A new heterogeneously-catalyzed route to propylene oxide has large scale commercial implications. Furthermore, developing viable heterogeneous catalysts for chiral olefin epoxidation reactions would offer significant advantages with respect to their homogeneous counterparts including easy product separation, longer catalyst lifetime, easier catalyst regeneration, and possible utilization of cheaper and environmentally friendlier oxidizing agents such as oxygen.