Polymer supported metal catalysts

The second general method, IMPR, for the preparation of polymer supported metal catalysts is much less popular. In spite of this, microencapsulation of palladium in a polyurea matrix, generated by interfacial polymerization of isocyanate oligomers in the presence of palladium acetate [128], proved to be very effective in the production of the EnCat catalysts (Scheme 3). In this case, the formation of the polymer matrix implies only hydrolysis-condensation processes, and is therefore much more compatible with the presence of a transition metal compound. That is why palladium(II) survives the microencapsulation reaction... 

The use of polymer-supported metal catalysts for the hydrogenation of thiophe-nie substrates has recently been extended to Ru and Rh complexes anchored to silica via hydrogen bonding [23, 24]. 

Sabadie and Germain [20] have investigated the stereoselectivity of polymer-supported metal catalysts in the hydrogenation of 1,2-dimethylcyclohexene. Depending on the pressure of hydrogen, different ratios of cis- and trans-isomers (0.44 and 0.57 at 1.25 and 10 MPa, respectively) of 1,2-dimethylcyclohexanes were obtained over Pd/APSDVB catalysts. 

TABLE XII Some Selected Applications of Polymer Supported Metal Catalysts from the... 

The use of conducting polymer supported metal catalysts for the main fuel cell reactions (oxygen reduction, hydrogen oxidation, and methanol oxidation) is reviewed and new results are presented for oxygen reduction at polyaniline supported Pt and methanol oxidation at poly(3,4-ethylenedioxythiophene) supported Pt-Ru. It is shown that polymer supported electrodes can provide performances that proach those of comma cial carbon supported catalysts, but tlmt stability problems curr tly make applications in fuel cells impractical... 

In this article, we will discuss the use of physical adsorption to determine the total surface areas of finely divided powders or solids, e.g., clay, carbon black, silica, inorganic pigments, polymers, alumina, and so forth. The use of chemisorption is confined to the measurements of metal surface areas of finely divided metals, such as powders, evaporated metal films, and those found in supported metal catalysts. 

Corain and associates on M /CFP catalysts has been so far focused on this kind of materials. In particular, great attention was paid to the correlation between the morphology of the support and features of CFPs supported metal catalysts, such as their molecular accessibility [14,21,22,25,108] or the size of metal nanoclusters generated inside swollen polymer frameworks (for a specific study see Ref [68]). 

The most spectacular results, in terms of comparison between CFPs- and carbon-supported metal catalysts, were likely provided by Toshima and co-workers [33,34]. As illustrated in Section 3.3.3, they were able to produce platinum and rhodium catalysts by the covalent immobilization of pre-formed, stabilized metal nanoclusters into an amine functionalized acrylamide gel (Scheme 5). To this purpose, the metal nanopartides were stabilized by a linear co-polymer of MMA and VPYR. The reaction between its ester functions and the amine groups of the gel produced the covalent link between the support and the... 

Recently, Chaudhari compared the activity of dispersed nanosized metal particles prepared by chemical or radiolytic reduction and stabilized by various polymers (PVP, PVA or poly(methylvinyl ether)) with the one of conventional supported metal catalysts in the partial hydrogenation of 2-butyne-l,4-diol. Several transition metals (e.g., Pd, Pt, Rh, Ru, Ni) were prepared according to conventional methods and subsequently investigated [89]. In general, the catalysts prepared by chemical reduction methods were more active than those prepared by radiolysis, and in all cases aqueous colloids showed a higher catalytic activity (up to 40-fold) in comparison with corresponding conventional catalysts. The best results were obtained with cubic Pd nanosized particles obtained by chemical reduction (Table 9.13). 

While such a film format is not intended for routine use in e.g. soHd phase synthesis, it has proved useful for spectroscopic mechanistic investigation of polymer-supported metal complex catalysts [49] and we, with our collaborators, are employing such films as a component in nanosecond fluorescence sensing devices [50]. 

Polymers play important roles in water photolysis. For multi-electron processes, polymer supported metal colloids or colloidal polynuclear metal complexes are very useful as catalysts. Unstable semiconductors with a small bandgap which photolyse... 

Polymers are attracting much attention as functional materials to construct photochemical solar energy conversion systems. Polymers and molecular assemblies are of great value for a conversion system to realize the necessary one-directional electron flow. Colloids of polymer supported metal and polynuclear metal complex are especially effective as catalysts for water photolysis. Fixation and reduction of N2 or C02 are also attractive in solar energy utilization, although they were not described in this article. If the reduction products such as alcohols, hydrocarbons, and ammonia are to be used as fuels, water should be the electron source for the economical reduction. This is why water photolysis has to be studied first. 

Studies on the immobilization of Pt-based hydrosilylation catalysts have resulted in the development of polymer-supported Pt catalysts that exhibit high hydrosilylation and low isomerization activity, high selectivity, and stability in solventless alkene hydrosilylation at room temperature.627 Results with Rh(I) and Pt(II) complexes supported on polyamides628 and Mn-based carbonyl complexes immobilized on aminated poly(siloxane) have also been published.629 A supported Pt-Pd bimetallic colloid containing Pd as the core metal with Pt on the surface showed a remarkable shift in activity in the hydrosilylation of 1-octene.630... 

Metal complexes bound to soluble polymers act as homogeneous catalysts they can be selectively precipitated and separated from products, and thus behave as immobilized homogeneous catalysts because of the ease with which they can be separated from reaction products. Alternatively, complexes can be physically trapped within the pores of swellable polymers. In this maimer, they can be effectively immobilized without a direct bond to the support. Polymers may be imprinted to give additional selectivity in the reactions of the supported metal catalysts and reagents. ... 

---