Platinum colloidal, hydrogenation catalyst

Ru(bipy)3 formed in this reaction is reduced by the sacrificial electron donor sodium ethylenediaminetetra-acetic acid, EDTA. Cat is the colloidal catalyst. With platinum, the quantum yield of hydrogenation was 9.9 x 10 . The yield for C H hydrogenation was much lower. However, it could substantially be improv l by using a Pt colloid which was covered by palladium This example demonstrates that complex colloidal metal catalysts may have specific actions. Bimetalic alloys of high specific area often can prepared by radiolytic reduction of metal ions 3.44) Reactions of oxidizing radicals with colloidal metals have been investigated less thoroughly. OH radicals react with colloidal platinum to form a thin oxide layer which increases the optical absorbance in the UV and protects the colloid from further radical attack. Complexed halide atoms, such as Cl , Br, and I, also react... 

Toshima et al. obtained colloidal dispersions of platinum by hydrogen- and photo-reduction of chloroplatinic acid in an aqueous solution in the presence of various types of surfactants such as dodecyltrimethylammonium (DTAC) and sodium dodecylsulfate (SDS) [60]. The nanoparticles produced by hydrogen reduction are bigger and more widely distributed in size than those resulting from the photo-irradiation method. Hydrogenation of vinylacetate was chosen as a catalytic reaction to test the activity of these surfactant-stabilized colloids. The reaction was performed in water under atmospheric pressure of hydrogen at 30 °C. The photo-reduced colloidal platinum catalysts proved to be best in terms of activity, a fact explained by their higher surface area as a consequence of their smaller size. 

Supported palladium and platinum modified by chiral compounds are largely used as pure heterogeneous hydrogenation catalysts. However, recent studies have been performed starting with catalysts of colloidal nature and particles with dimensions of only a few nanometers. Their development continues to attract substantial interest for three main reasons ... 

Kohler, J.U. and Bradley, J.S., A kinetic probe of the effect of a stabilizing polymer on a colloidal catalyst accelerated enantio selective hydrogenation of ethyl pyruvate catalyzed by poly(vinylpyrroli-done)-stabilized platinum colloids, Langmuir, 14, 2730,1998. 

Acetylbenzofuran or 2-(l-hydroxyethyl)benzofuran was hydrogenated to 2-(l-hy-droxyethyl)-2,3-dihydrobenzofuran in high yields over Raney Ni in ethanol at room temperature and 0.2-0.3 MPa H2 (eq. 12.1 ll).215 The selective transformation of 2-acetylbenzofuran to 2-(l-hydroxyethyl)benzofuran was successful over platinum oxide in ethanol (eq. 12.111), while the hydrogenation over a colloidal platinum on Norit catalyst from chloroplatinic acid and platinum oxide gave a mixture of 2-(l-hy-droxyethyl)benzofuran, 2-ethylbenzofuran, and their 2,3-dihydro derivatives. 

The doping of noble metal catalyst precursors is not restricted to the early transition metal series. Toshima has reported significant promotion of catalytic activity in the hydrogenation of acrylic acid by the addition of neodymium ions to palladium particles. Recently, Liu and coworkers have studied the influence of metal ions on the hydrogenation of o-chloronitrobenzene over platinum colloidal clusters, and the metal complex effect on the catalytic performance of metal... 

In batch and continuous tests the performance of the colloidal catalyst systems has been compared to conventional Pt/C-systems. The potential of the colloidal heterogeneous catalyst lies in the possibility of fine tuning the properties for specific applications by the addition of special dopants or poisons to the precursor. The infiuence of metal ions on the hydrogenation of o-chloronitrobenzene over platinum colloids, and the effect of metal complexes on the catalytic performance of metal clusters have also been demonstrated [133-135]. 

Carl Ludwig Paal and others used colloidal platinum and palladium catalysts in liquid phase hydrogenation reactions at low temperatures. Aromatic and unsaturated aliphatic compounds such as aldehydes or ketones were easily hydrogenated by either platinum or palladium. Aladir Skita collaborated with Paal in publishing a patent that described some of this work. The colloidal metals could be stabilized by the use of albumen from egg whites, but they were not really practicable and it was difficult to separate them from products. An outline of an early colloidal catalyst preparation is given in Table 3.4. 

Although Ru(bipy)2+ alone will not split water into hydrogen and oxygen, it has been accomplished with Ru(bipy)2+ using various catalysts or radical carriers. Perhaps the most studied system for the photoreduction of water involves using methyl viologen as the quencher, EDTA as an electron donor (decomposed in the reaction) and colloidal platinum as a redox catalyst (Figure 1.19). 

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