Polymer-protected platinum nanoparticle

Stable platinum colloids were prepared by reducing dihydrogen hexachloroplatinate H2PtCl in the presence of protective polymers. In this chapter, we report the results for several nonionic polymers and cationic polyelectrolytes and their ability to stabilize such platinum colloids. The sizes of the platinum particles were investigated by transmission electron microscopy (TEM) and found to be in the nanometer size range. The catalytic activity of these systems was tested by the hydrogenation of cyclohexene, dsp-cyclooctene, and 1-hexene. A variety of polymer-protected platinum nanoparticles showed catalytic activity, and conversions of 100 % were obtained in most cases. 

Catalytic Hydrogenations. Table IV shows some results for the catalytic hydrogenation of cyclohexene, and a selection of results obtained for the hydrogenation of cis-cyclooctene and 1-hexene is given in Table V. The results show that a variety of polymer-protected platinum nanoparticles are catalytically active, and conversions of 100 % were obtained in most cases. The catalysts could be employed either directly as a colloidal dispersion or as a solid after the evaporation of the solvent and the subsequent redissolving in the mixture for liquid-phase hydrogoiation. Unlike most catalysts systems, they could be stored in air for several weeks/months and still showed very good catalytic activity. 

Dendrimer-protected colloids are capable of adsorbing carbon monoxide while suspended in solution, but upon removal from solution and support on a high surface area metal oxide, CO adsorption was nil presumably due to the collapse of the dendrimer [25]. It is proposed that a similar phenomena occurs on PVP-protected Pt colloids because removal of solvent molecules from the void space in between polymer chains most likely causes them to collapse on each other. Titration of the exposed surface area of colloid solution PVP-protected platinum nanoparticles demonstrated 50% of the total metal surface area was available for reaction, and this exposed area was present as... 

In the early work on the thermolysis of metal complexes for the synthesis of metal nanoparticles, the precursor carbonyl complex of transition metals, e.g., Co2(CO)8, in organic solvent functions as a metal source of nanoparticles and thermally decomposes in the presence of various polymers to afford polymer-protected metal nanoparticles under relatively mild conditions [1-3]. Particle sizes depend on the kind of polymers, ranging from 5 to >100 nm. The particle size distribution sometimes became wide. Other cobalt, iron [4], nickel [5], rhodium, iridium, rutheniuim, osmium, palladium, and platinum nanoparticles stabilized by polymers have been prepared by similar thermolysis procedures. Besides carbonyl complexes, palladium acetate, palladium acetylacetonate, and platinum acetylac-etonate were also used as a precursor complex in organic solvents like methyl-wo-butylketone [6-9]. These results proposed facile preparative method of metal nanoparticles. However, it may be considered that the size-regulated preparation of metal nanoparticles by thermolysis procedure should be conducted under the limited condition. 

Fig.l Schematic representing the stabilisation of palladium nanoparticles using different protecting groups (a) surfactants (b) polymers and (c) ligands. Reproduced with the permission of Johnson-Matthey (J. Cookson, Platinum Metals Rev., 2012, 56, 83). 

---