Platinum monodispersed

The specihc surface area of an ideal, monodisperse catalyst per unit of its mass is related to its diameter das S = 6/pd, where p is the density. In the case of platinum. 

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. 

Heiz, U., Sanchez, A., Abbet, S., and Schneider, W.-D., Catalytic oxidation of carbon monoxide on monodispersed platinum clusters Each atom counts. J. Am. Chem. Soc. 121, 3214 (1999). 

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. 

Peng [4] prepared monodispersed nanoparticles between 1 and 20 nm consisting of gold, silver, copper, and platinum, which were used as high efficiency industrial catalysts. 

Figure 4.7 shows TOF as a function of the particle size of a monodisperse supported platinum catalyst Pt/Al203 in the reaction of deep methane oxida tion. One can see that equation (4.91) is sufficient to describe the experimental data when the Pt particles are more than 2 nm in size. When they are smaller, TOF deviates from the monotonous dependence (4.91). The reason may be a considerable change in the chemical composition of the anchored active com ponent due to the strong interaction of this component with the carrier surface. 

The next section will describe the experimental techniques we use to synthesize and study clusters and present typical data. The following section will discuss the cluster size sensitive behavior observed in kinetic studies of H-H and C-H bond activation reactions as well as the size sensitive behavior of hydrogen uptake, and discusses the potential implications of these experiments in catalysis and chemisorption. The last section gives the highlights of recent studies of the electronic properties of mass selected, monodispersed, platinum clusters containing up to 6 Pt atoms supported on Si02. 

As discussed earlier, it is now possible to make and study deposits of monosized, highly dispersed, transition metal clusters.(S) In this section we summarize results from the first measurements of the valence and core level photoemission spectra of mass selected, monodispersed platinum clusters. The samples are prepared by depositing single size clusters either on amorphous carbon or upon the natural silica layer of a silicon wafer. We allow the deposition to proceed until about 10 per cent of the surface in a 0.25 cm2 area is covered. For samples consisting of the platinum atom through the six atom duster, we have measured the evolution of the individual valence band electronic structure and the Pt 4f... 

Highly monodispersed platinum-based nanoparticles Pt, Pt-Ru, Pt-Ru-Sn ° were synthesized by y- or electron beam-radiolysis and then deposited onto Vulcan carbon powder with high loadings (up to... 

Inhomogeneous gold polycrystallites with compact structure and a broad range of orientations were formed after 45 min of ultrasonic treatment in a home-developed sonoreactor at the constant temperature. Sonication for additional 40 min recrystallized highly monodisperse platinum nanoparticles with smaller size. The fastest catalysis was enabled by platinum nanoparticles after sonication in the poly vinyl pyrrolidone solution for one hour, while the lowest activity was found for particles after the ultrasonic treatment for 20 min in the ethylene glycol solution. Amorphous and polycrystalline platinum nanoparticles before and after sonication in water have similar catalytic efficiencies. 

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