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Catalysis at the Solid-Liquid Interface

Robert J. Angelici, Iowa State University Dept. of Chemistry
Keith Woo, Iowa State University Dept. of Chemistry
Aaron Sadow, Iowa State University Dept. of Chemistry
Andreja Bakac, Ames Laboratory

A variety of reactions that lead to new and useful chemical products require catalysts that must be added to the reaction solutions in order for the reactions to occur. Despite the importance of such catalysts, their use in commercial applications is limited by the costs involved in separating the products from the catalysts after the reaction is complete. One method of simplifying this separation is to tether the catalyst molecule to a solid particle. In this way the catalyst can be separated from the desired products of the reaction by filtering the catalyst particles out of the solution.

An example of this type of catalyst is shown below (A):

It consists of a rhenium complex B tethered through a hydrocarbon chain to solid particles of silica (SiO₂). The simple complex B had previously been observed (Espenson) to catalyze the oxidation of sulfides, e.g.,

However, complex B is soluble in the reaction solution and is difficult to separate from the products. By creating a linker between B and SiO₂ as in A, the catalytic complex B can be removed from the reaction solution by simply filtering off the catalyst particles. Despite the attachment of B to SiO₂, it remains highly active for the oxidation of sulfides according to equation (1). 

A goal of research in this area is to create other catalysts in which metal complex catalysts are linked to silica particles. Commercial applications of these catalysts will lead to the production of a wide range of products.

Funded Projects

Catalytic Conversion of Carotenoids From Renewable Resources: New Catalysts and Processes for Nutritional Products

Richard C. Larock, Iowa State University Department of Chemistry

Richard C. Larock in his laboratory.

Catalytic conversion of carotenoids represents a tremendous opportunity to develop new processes for the transformation of bio-renewable resources to valuable human nutritional products. The proposed research will focus on the conversion of a commercially available carotenoid, "lutein" [(3R,3'R,6'R)-lutein], which is recognized for the prevention of age-related macular degeneration and other blinding conditions, to other value-added products that also have potential therapeutic applications. Environmentally "clean" conversion pathways involving oxidation/reduction and isomerization will be investigated through the development of appropriate homogeneous and heterogeneous catalysts. Commercial routes to the targeted compounds will produce new human nutritional components and value-added phytochemicals. C. Procedures: Despite the recognized importance of carotenoids for human health, many potentially useful compounds are found in only trace quantities in their natural sources and are very difficult to prepare by total synthesis. The objectives of this research are:

1. to establish direct, catalytic conversion routes for the transformation of readily-available carotenoids, such as lutein, to other value-added, relatively-scarce human nutritional products;

2. to develop highly active, selective, and stable homogeneous and heterogeneous catalysts for these conversion pathways; and

3. to provide a basis for process conceptualization and engineering that is economically attractive and environmentally superior. This is the initial effort in a potentially much broader effort to establish catalytic processes for the conversion of carotenoid natural products to other valuable products which benefit human health and nutrition.