Nanoparticles, of platinum

Multipods and Dendritic Nanoparticles of Platinum Colloidal Synthesis and Electrocatalytic Property... 

This tin-modified nanoparticle of platinum is totally selective for isobutene. For example, when the Sn/Pts ratio is equal to 0.85, the selectivity to isobutene reaches... 

Nevertheless, classical heterogeneous catalysts like particulate noble metals may be immobilized on the nanotube surface as well. Nanoparticles of platinum or rhodium, for instance, can be deposited on cup-stacked carbon nanotubes by reductive precipitation (Figure 3.114b). The catalysts obtained this way suit an application in fuel cells run on methanol. Electrodes made from the nanotube material exhibit twice the efficiency as compared to the classical material XC-72-carbon. The particles of noble metal on the nanotube surface catalyze the direct conversion of methanol into CO2 (MeOH -1- H2O CO2 -1- 6 H -1- 6e ). A material to be employed in such fuel cells has to meet some essential requirements, including a maximal specific surface, a defined porosity and a high degree of crystalhnity. Carbon nanotubes are endowed with exactly these characteristics, which is why they are the most suitable material for electrodes. Their high price, however, is still prohibitive to an industrial scale application. 

Nonconducting polymers are polymeric binders (epoxy, methacrylate, silicone, araldite) which confer to the conducting composite a certain physical, chemical, or biological stability, while the electrical conductivity is provided by the conducting filler (micro or nanoparticles of platinum, gold, graphite, carbon nanotubes, etc.). 

PVP (poly(7V-vinyl-2-pyrrolidone))-stabilized metal nanoparticles can be readily produced by alcohol reduction of the corresponding metal ions [5,32-34]. Alcohol can be a good reducing reagent of precious metal ions and it changes to aldehyde or ketone by oxidation (Fig. 6.6). This alcohol reduction is mild and easy. PVP-stabilized nanoparticles of platinum group metals can work as effective catalysts. Especially, various alloy nanoparticles can be obtained by this process, especially. 

A simplified scheme of the electrochemical heart of a PEFC is displayed in Fig. 3, where the central solid electrolyte is contacted by two porous gas diffusion electrodes (GDLs), which are in intimate contact to the membrane surface (see below, three phase boundary). At the interface to the membranes, the GDLs contain nanoparticles of platinum (black dots) as electrocatalyst. 

So far, CMK-5 carbons have been much less explored than CMK-3. One possible reason is the difficulty of finding suitable precursors that permit a strict control of the pore wall thickness to obtain stable carbon replicas. There are reports indicating the possibility of preparing CMK-5 with controlled pore wall thickness by using different methods of furfuryl alcohol polymerization and ferrocene as carbon precursors. Also, there are reports on the incorporation of highly dispersed nanoparticles of platinum " and cobalt into CMK-5 to enhance its electrochemical and... 

Multipods and dendritic nanoparticles of platinum colloidal synthesis and electrocatalytic property, in Metal Nanoclusters in Catalysis and Materials Science The Issue of Size Control. Part II Methodologies (eds B. Corain, G. 

This technique is the most widely used and the most useful for the characterization of molecular species in solution. Nowadays, it is also one of the most powerful techniques for solids characterizations. Solid state NMR techniques have been used for the characterization of platinum particles and CO coordination to palladium. Bradley extended it to solution C NMR studies on nanoparticles covered with C-enriched carbon monoxide [47]. In the case of ruthenium (a metal giving rise to a very small Knight shift) and for very small particles, the presence of terminal and bridging CO could be ascertained [47]. In the case of platinum and palladium colloids, indirect evidence for CO coordination was obtained by spin saturation transfer experiments [47]. 

Other one-pot preparations of bimetallic nanoparticles include NOct4(BHEt3) reduction of platinum and ruthenium chlorides to provide Pto.sRuo.s nanoparticles by Bonnemann et al. [65-67] sonochemical reduction of gold and palladium ions to provide AuPd nanoparticles by Mizukoshi et al. [68,69] and NaBH4 reduction of dend-rimer—PtCl4 and -PtCl " complexes to provide dend-rimer-stabilized PdPt nanoparticles by Crooks et al. [70]. 

Thus, silver nanoparticles grow gradually during UV light irradiation (processes al-a3 in Figure 2). Nanoparticles of other noble metals such as gold, copper, platinum, and palladium can also be deposited by this method. 

Electrodeposition of metals can be performed under different electrochemical modes. In the work mentioned in Ref. [18], it was performed in potentiostatic mode. The potential value for formation of platinum nanoparticles is —25 mV vs. SCE the deposition is performed from 2.5 mM solution of H2[PtCl6] in 50 mM KCl. The size of nanoparticles formed depends on the reduction charge. Continuous monitoring of the charge in potentiostatic mode is provided by different potentiostats, for example, by Autolab-PG-stat (EcoChemie, The Netherlands). Conditions for deposition of other metals should be selected according to their electrochemical properties. 

In 2000, Sun and co-workers succeeded in synthesis of monodispersed Fe/Pt nanoparticles by the reduction of platinum acetylacetonate and decomposition of Fe(CO)5 in the presence of oleic acid and oleylamine stabilizers [18]. The Fe/Pt nanoparticle composition is readily controlled, and the size is tunable from 3 to 10 nm in diameter with a standard deviation of less than 5%. For practical use, we developed the novel symthetic method of FePt nanoparticles by the polyol reduction of platinum acetylacetonate (Pt(acac)2) and iron acetylacetonate (Fe(acac)3) in the presence of oleic acid and oleylamine stabilizers in di- -octylether [19,20]. The Fe contents in FePt nanoparticles can be tuned from 23 to 67atomic%, and the particle sizes are not significantly affected by the compositions, retaining to be 3.1 nm with a very narrow size distribution, as shown in Figure 6. 

Arene and olefin compounds, pure or in admixture, are efficient ligands in promoting the aggregation of platinum atoms from mononuclear species to ligand-stabilized soluble clusters and solid-supported nanoparticles (Scheme 14). 

Inaba M, Ando M, Hatanaka A, Nomoto A, Matsuzawa K, Tasaka A, Kinumoto T, Iriyama Y, Ogumi Z. 2006. Controlled growth and shape formation of platinum nanoparticles and their electrochemical properties. Electrochim Acta 52 1632-1638. 

Mizukoshi Y, Takagi E, Okuno H, Oshima R, Maeda Y, Nagata Y (2001) Preparation of platinum nanoparticles by sonochemical reduction of the Pt(IV) ions role of surfactants. Ultrason Sonochem 8 1-6... 

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. 

The concept of using colloids stabilized with chiral ligands was first applied by Bonnemann to hydrogenate ethyl pyruvate to ethyl lactate with Pt colloids. The nanoparticles were stabilized by the addition of dihydrocinchonidine salt (DHCin, HX) and were used in the liquid phase or adsorbed onto activated charcoal and silica [129, 130]. The molar ratio of platinum to dihydrocinchonidine, which ranged from 0.5 to 3.5 during the synthesis, determines the particle size from 1.5 to 4 nm and contributes to a slight decrease in activity (TOF = l s ). In an acetic acid/MeOH mixture and under a hydrogen pressure up to 100 bar, the (R)-ethyl lactate was obtained with optical yields of 75-80% (Scheme 9.11). 

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