Catalysts, polymer-protected platinum

Polymer-Protected Platinum Catalysts in the Nanometer Size Range... 

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. 

MAYER MARK Polymer Protected Platinum Catalysts... 

The Pti samples (182) were prepared as colloids, protected by a PVP polymer film. Layer statistics according to the NMR layer model (Eqs. 28-30) for samples with x = 0,0.2, and 0.8 are shown in Fig. 63. The metal/ polymer films were loaded into glass tubes and closed with simple stoppers. The NMR spectrum and spin lattice relaxation times of the pure platinum polymer-protected particles are practically the same as those in clean-surface oxide-supported catalysts of similar dispersion. This comparison implies that the interaction of the polymer with the surface platinums is weak and/or restricted to a small number of sites. The spectrum predicted by using the layer distribution from Fig. 63 and the Gaussians from Fig. 48 show s qualitative agreement w ith the observed spectrum for x = 0 (Fig. 64a). 

For ftirther refinement of the Pt catalyst we made use of Tiirkevich s method to prepare ultrafine and monodisperse Pt sols ho,). Employing polymer surfactants as protective agents a first successful attenpt was made to render the intervention of these particles specific. Th is polyvinylpyridine absorbs well to the 30 X platinum particles rendering their surface anphiphilic. Hydrophobic relays such as long chain siibstituted viologen radicals are readily trapped by these particles and subsequently affect water reduction. In contrast the oxidized sensitizer is rejected from the Pt surface by l drophobic and electrostatic interactions. Thus, short-circuitiy of the back reaction is avoided. 

Supported platinum, rhodium, and ruthenium complex catalysts have been used extensively in the reaction of trisubstituted silanes with acetylene in the gas phase, predominantly in a continuous-flow apparatus. Formation of a polymer layer on the surface after immobilization of the platinum complex has protected the catalyst against leaching in long-term hydrosilylation tests [91]. 

These data are corroborated by results obtained from continuous photolysis experiments. Cabowax-20M protected Pt catalyst when coupled to Ru02 fails to split water under illumination of a cyclic system containing Ru(bipy)3+ as a sensitizer and methylvio-logen as an electron relay. By contrast, if the Pt microspheres are protected by PVP-Ci6 simultaneous H2 and 02 productions are observed. The lack of specificity of the Carbo-wax 20 M protected particles is attributed to the strongly hydrophylic nature of this protective polymer providing facile access of the Ru(bipy)3+ cation to the platinum surface. Uncharged hydrophylic polymers appear thus unsuitable for Pt protection in this cyclic water decomposition system. 

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