Immobilization of Homogeneous Catalysts: Supported Aqueous Phases, Ion Exchange Resins, and Membranes

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Effective immobilization of homogeneous catalysts is technologically important for the petrochemical and fine- chemical industries. This work addresses techniques for catalyst immobilization that are applicable both to large- scale and to small-scale production. The use of supported aqueous-phase (SAP) catalysts has already been shown to be effective for hydroformylation of a variety of olefins. The present work examines the unique properties of SAP catalysts using physicochemical approaches, in particular the role of water in the determination of catalytic activity. The SAP concept is also extended to catalytic oxidations. Additionally, other immobilization techniques are explored, including ion-exchange resins as a means to immobilize catalysts with functionalized ligands, and the use of very large, but soluble, ligands combined with membrane separation technology. Many homogeneous (soluble) catalysts are known to facilitate chemical transformations with high selectivity under mild conditions, but their commercial use is inhibited by the high cost of separating the products from the solution containing the catalyst and the fact that reusing the catalyst is often difficult if not impossible. Immobilization techniques offer the prospect of circumventing these problems by making the homogeneous catalysts behave more like heterogeneous catalysts. Accomplishing this while preserving the desirable catalytic properties has proven to be difficult, but the benefit in potential new processes would be enormous.