Platinum Metals Rev., 1986, 30, (3), 131
Polymer-Protected Platinum Metals Catalysts
Tailored Metal Catalysts, Catalysis by Metal Complexes
Reidel, Dordrecht,, Edited By Y. Iwasawa 1986, 333 pages, Dfl.155,000,/£42.95
Catalysis has been described as a technological field involving an enormous number of empirical facts intermixed with some general theories. The tailored design of metal catalysts is therefore a topic having an enormous scientific and technological potential, which has become an area of intense research activity since the early work on polymer-attached homogeneous metal complexes began in 1969.
This useful book reviews several topics involving the tailored design of metal catalysts, and the section dealing with polymer-protected colloidal catalysts reviews how polymer-protected colloidal dispersions of platinum group metals can be prepared, characterised and used to make tailored metal catalysts.
Polymer-protected colloidal catalysts not only have the advantages that dispersed metal particles on an inorganic support have over metal powders—these being good dispersion through the use of the support, large surface area and a homogeneous system—but they also have important additional advantages. Colloidal dispersions readily transmit light, allowing them to be used as catalysts in photochemical investigations. The polymer also protects the metal colloid catalyst from deactivation by catalytic poisoning.
Since 1856 when Faraday first worked with gold to prepare monodispersed colloidal metal hydrosols, numerous reducing agents have been employed for the chemical reduction of metal ions. The chemical preparation of polymer-protected colloidal metals leads to three classes of product: a polymer wrapped around each individual colloid, a colloid distributed on or near the surface of the polymer, and the metal colloid distributed inside a polymer resin. In this volume typical examples are presented for the preparation of colloidal dispersions of platinum, palladium and rhodium protected by soluble polymers. Both water-based and alcohol-based reductions are discussed. By altering the reducing conditions the colloidal particle size can be controlled, allowing the activity of the catalyst as well as its selectivity in chemical reactions to be engineered.
In addition to protecting the colloid against aggregation and poisoning, the presence of the polymer provides a means of introducing multifunctionality into the catalyst, by the use of functionalised polymers. One example is the use of colloidal platinum protected by polystyrene resin containing sulphonic acid groups to act as a catalyst for both hydration and dehydrogenation processes. The sulphonated polystyrene acts both as the support for the platinum and as an acid catalyst for hydrogenation.
Continuing research in the field of polymerprotected colloidal catalysts will increase our understanding of these catalysts, and can be expected to lead to new and novel applications for them.