Metal nanoparticles synthesis carbon-supported

Xin and co-workers modified the alkaline EG synthesis method by heating the metal hydroxides or oxides colloidal particles in EG or EG/water mixture in the presence of carbon supports, for preparing various metal and alloy nanoclusters supported on carbon [20-24]. It was found that the ratio of water to EG in the reaction media was a key factor influencing the average size and size distribution of metal nanoparticles supported on the carbon supports. As shown in Table 2, in the preparation of multiwalled carbon nanotube-supported Pt catalysts... 

Transition metal nanoparticles supported on different substrates are used as catalysts for different reactions, such as hydrogenations and enantioselective-synthesis of organic compounds, oxidations and epoxidations, reduction, and decomposition [24,25], Among the supports that have been applied in the preparation of supported transition metal nanoparticles are active carbon, silica, titanium dioxide, and alumina. 

Adams et al. [78,79] have reported a series of synthesis of mixed-metal cluster compounds. One example, Pt2Ru4(CO)is, is depicted in Figure 1(b). This mixed cluster compound was investigated to study the effect of Pt-Ru nanoparticles developed after the precursor annealing on carbon [80]. In line with the spectroscopic and microscopic measurements, the authors demonstrated that mixed Pt-Ru nanoparticles, with an extremely narrow size distribution (particle size 1.4nm), reflect an interaction that depends on the nature of the carbon support. Furthermore, as revealed by EXAFS, the Pt-Pt, Pt-Ru, and Ru-Ru coordination distances in the precursor (2.66, 2.64, and 2.84 A) [79] changed to 2.73, 2.70, and 2.66 A, respectively, on the mixed-metal nanoparticles supported on carbon black, with an enhanced disorder [80]. Furthermore, some metal segregation could be... 

Such a reaction of Fe(CO)5 (at 293-363 K, PVP) without ultrasonic radiation proceeds very slowly and only after few days there, a material is formed with very low Fe content (2%, the isolated particles 2-5 nm in size). It is of interest that the sonochemical decomposition of Fe(CO)5 does not proceed in the presence of PVP if THF is used as the solvent, but the reaction is very effective when anisole is used as the solvent and PFO is used as the polymer matrix [93]. A black product formed contains up to 10% (in mass) of the spheric particles of nonoxidized Fe (mainly y-Fe, with little content of a-Fe) with 1-12 nm in size (the mean diameter is 3nm, as shown in Figure 3.7). It is likely that the big particles present the flocks of little ones ( 2-2.5nm). The sonochemical synthesis allows us to produce the functionalized amorphous nanoparticles of ferric oxide with 5-16 nm in diameter [94]. The ultrasonic irradiation in the PFO presence allows us to also produce the stabilized nanoparticles of copper, gold, and so on. In the literature the findings are not about the bimetallic particle formation in the ultrasonic fields by carbonyl metal reduction in the polymer matrices presence (as, for example, in the case of the carbon-supported Pt-Ru from PtRu5C(CO)i6 reduced clusters [95]). 

SYNTHESIS OF METALLIC NANOPARTICLES SUPPORTED ON CARBON NANOTUBES... 

PtRu is the base binary catalyst for the synthesis of ternary catalysts serving as anode materials in low-temperature fuel cells. Various preparation methods of carbon supported ternary catalysts have been proposed (1) synthesis of the ternary nanoparticles, followed by deposition onto the carbon surface (one step method) (2) deposition of all the precursors on the carbon support, followed by reduction (one step method) (3) deposition of the precursor of the third metal on preformed PtRu/C, followed by reduction (two step method). Many investigations have been made to improve the performance of the PtRu binary catalysts with the incorporation of a third metal, such as W, Mo, Sn, Os, etc. 

The synthesis methods used for the preparation of carbon supported PtRuMo nanoparticles could be classified as adsorption of metal colloids onto the carbon surface, or impregnation of carbon support with metals precursor solution. Additionally, the incorporation of the metals has been carried out in a (1) one step method or with simultaneous incorporation of the three metals, and in (2) two step methods or sequential incorporation of Mo and PtRu nanoparticles ... 

CVD is a general method for the commercial production of carbon nanotubes. For this idea, the metal nanoparticles are mixed with a catalyst support such as MgO or AI2O3 to enhance the surface area for higher revenue of the catalytic reaction of the carbon feedstock with the metal particles. One matter in this synthesis method is the removal of the catalyst support via an acid treatment, which sometimes could destroy the primary structure of the carbon nanotubes. However, other catalyst supports that are soluble in water have verified effective for nanotube development. 

Many ORR experiments have been made on electrocatalysts composed by Pt and Pd with the addition of non-noble metals, such as Co, Fe, and Ni. However, under electrochemical conditions these non-noble metals might leach out from the electrocatalyst, as demonstrated in previous investigations [25]. In order to avoid this problem, Yang and co-authors [26] have investigated PdPt-based electrocatalysts for the ORR in absence and in the presence of methanol, because the long-term stability of Pd in acidic solution is comparable to that of Pt (but this depends on the potential - additionally, Pt may stabilize Pd atoms in the alloy). It was report a novel strategy for surface and structure-controlled synthesis of carbon-supported Pd3Pti nanoparticles for the ORR as well as for methanol-tolerant ORR electrocatalyst. The influence of the surface composition and structure of the PdsPti/C on the ORR activity in the absence and presence of methanol was also reported. 

Shao et al. produced high-surface-area-modified tungsten carbide (WC) by TPR without significant loss of carbon support [46], This method can also be used for scale up synthesis of kilogram metal carbide nanoparticles with particle size in the range of 10-50 nm. The Pt catalyst supported on tungsten carbide on Ketjenblack (KB) showed a better oxygen reduction reaction activity compared to conventional catalyst, Pt/KB. 

Another obstacle for DMFC applications is the low catalytic activity of electrodes for both the oxygen reduction reaction and the methanol oxidation reaction. It is well known that the catalytic activity of an electrocatalyst is strongly dependent on the particle dispersion of the active components. Many doping techniques have been explored to widely distribute the active components on the catalyst supports [145-148]. In addition to the synthesis method, catalyst support also plays an important role in the dispersion of active components. Carbon materials with high surface areas (e.g., Vulcan XC72 carbon black) have been widely employed as electrocatalyst supports to enhance the dispersion of metal nanoparticles and thus to increase the utilization of the precious metal eatalyst... 

All these new synthetic carbons display specific advantages for the synthesis of supported metal nanoparticles for PEMFCs. Composites could combine several interesting characteristics like, for instance, the high conductivity of nanotubes and the 3D structure of the gels. 

There is an exhaustive literature dealing with the synthesis of carbon-supported Pt-based nanoparticles (see, e.g.. Refs. [51-53] and references therein), but only a brief review of the most relevant elaboration techniques will be given here. The preparation of metal nanopartides is... 

Researchers have looked not only for novel catalysts with different chemical compositions but also for new preparation routes. The use of different methodologies for the synthesis of metal nanoparticles supported on high surface area carbon or other conducting supports plays a crucial role in the development of fuel cell technology [26,55,100]. Many research groups have described that the activity of these materials is highly dependent on their composition, morphology, and size [101,102]. Thus, several methods for the synthesis of nanostructured... 

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