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纳米银颗粒作为多相催化剂催化丙烯环氧化生成环氧丙烷和不对称环氧化较大的烯烃(如苯乙烯)生成手性环氧化物的可能性。这些研究建立在密歇根大学利尼克早期生产环氧乙烷的工作基础上。在工业上，多相银催化剂几乎完全用于该反应。环氧乙烷是一种关键化学品，用于合成乙二醇(防冻剂)、乙醇胺和洗涤剂。Linic的计算表明，银的特定表面将对所需产品提供更高的选择性。然后开发了新的合成策略来合成特定形状的银纳米结构。有证据表明，良好的银纳米结构可以作为乙烯部分氧化的高选择性催化剂，丙烯部分氧化为环氧丙烷的挑战是合乎逻辑的延伸。对于这一重要的大规模化学过程，没有选择性的多相催化剂。等电点分析表明，催化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特定形状的表面终止。PI假设，在丙烯的直接环氧化反应中，由Ag(100)面特定端接的银纳米立方体和纳米线催化剂将比由(111)面端接的传统球形银颗粒具有更高的选择性。PI假设，特定的金属银纳米结构，通过手性修饰剂的增强，将是较大的烯烃(例如苯乙烯)不对称环氧化形成手性环氧化物的有前景的多相催化剂。目前，复杂而昂贵的均相催化剂被用于手性氧化反应，因为它们比传统的多相固体催化剂具有更高的区域和立体选择性。该研究项目试图通过利用不同形状和不同表面端基的金属纳米颗粒控制合成的最新进展，建设性地整合纳米科学和多相催化领域，设计高选择性的无机催化剂。这项研究的成功结果的变革性是相当明显的。一条多相催化合成环氧丙烷的新路线具有大规模的商业意义。此外，与均相催化剂相比，开发可行的多相催化剂用于手性烯烃环氧化反应将提供显著的优势，包括容易分离产品，更长的催化剂寿命，更容易的催化剂再生，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.