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

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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.