Bimetallic nanoclusters

N. Toshima, Polymer-capped bimetallic nanoclusters as active and selective catalysts, in N. Ueyama, A. Harada (eds.) Macromolecular Nanostructured Materials, Kodansha/ Springer, Tokyo/Berlin, 2004, 182. 

The irradiation conditions were chosen to avoid overlap of the implanted Ne atoms with the already formed clusters the Rp of the Ne ions is indeed about 410 nm with a straggling of about 100 nm. Therefore irradiating ions release part of their energy crossing the region in which the bimetallic nanoclusters are present (centered around a depth of 70 nm). 

The alkaline EG synthesis method has been successfully applied to the preparation of unprotected bimetallic nanocluster colloids with controllable composition. Figure 3 shows the TEM image of bimetallic Pt/Ru nanoclusters (Pt/Ru molar ratio = 1 1.9, total metal concentration 1.85 g/1) with an average particle size of 1.9 nm and a size distribution from 1.4 to 2.4 nm. XRD pattern of the bimetallic nanoclusters is shown in Figure... 

Pt/Rh bimetallic nanoclusters were similarly prepared by this alkaline EG method [12]. The particle sizes of bimetallic Pt/Rh nanoclusters (0.37 g/1 in total metal concentration) ranged from 0.9 to 2.1 nm with an average diameter of 1.3 nm. A combined EDX analysis, using an electron beam of 1.0 nm in diameter, revealed that both signals of Pt and Rh existed in each individual particle and the average ratio of Pt to Rh (1.4 1) was close to the charged ratio (1.33 1) in the preparation, proving the formation of bimetallic nanoclusters. 

Figure 3. TEM image and size distribution of Pt/Ru bimetallic nanoclusters (1.85g/l) stabilized by EG and simple ions [13].

Toshima, N. and Hirakawa, K., Polymer protected bimetallic nanocluster catalysts having core/shell structure for accelerated electron transfer in visible-light-induced hydrogen generation, Polymer J., 31, 1127, 1999. 

In addition to simple metallic nanostructures, more complex intermetallic species have also been synthesized through the introduction of more than one metal. For instance, bimetallic nanoclusters may be generated via three routes within a dendritic host (Figure 6.33). In addition to already being proven for core-shell nanoclusters, this route should also be amenable for the growth of trimetallic nanostructures for interesting catalytic applications. 

Figure 6.33. Schematic of the three methods used to generate bimetallic nanoclusters within a dendritic host. Reproduced with permission from Scott, R. W. J. Wilson, O. M. Crooks, R. M. J. Phys. Chem. B 2004,109, 692. Copyright 2004 American Chemical Society.

LEIS has been used to investigate adsorbate induced segregation at the surfaces of bimetallic nanoclusters [84]. van den Oetelaar et al. showed that for Pt/Pd catalysts with low metal dispersions of about 0.3 and 0.8, Pd surface... 

Bromley ST, Sankar G, Catlow CRA, Maschmeyer T, Jenkins BEG, Thomas JM (2001) New insights into the structure of supported bimetallic nanocluster catalysts prepared from carbonylated precursors a combined density functional theory and EXAFS study. Chem Phys Lett 340 524... 

Methods of Controlled Surface Reactions (CSRs) and Surface Organometallic Chemistry (SOMC) were developed with the aim to obtain surface species with Sn-Pt interaction. In CSRs two approaches have been used (i) electrochemical, and (ii) organometallic. Characteristic feature of the organometallic approach is that both CSR and SOMC results in almost exclusively supported alloy type bimetallic nanoclusters. Studies on the reactivity of tin organic compounds towards hydrogen adsorbed on different transition and noble metals have revealed new aspects for the preparation of supported bimetallic catalysts. 

The hydrogen chemisorption on the supported bimetallic nanoclusters can completely be suppressed ... 

In additional experiments it has been shown that iron is interacting with platinum, i.e., it is located in atomic closeness to Pt. In the bimetallic nanocluster, due to the high electropositivity of iron, there is an electron transfer from iron to platinum. The net result is the formation of electron deficient iron species at the Pt surface. The authors suggested that these electron-deficient or low-valent iron species on the Pt surface might act as Lewis acid adsorption sites. These sites, due... 

It should be emphasized that after TPRe run up to 350 °C, all alloy-type Sn-Pt/Si02 catalysts without re-reduction had very low activity. Thus, on platinum nanoclusters covered by bulk type tin-oxide layer the number of required metal ion - metal nanocluster ensemble sites is very low. The experimental data given in Table 11 strongly indicated that the activity of the alloy type Sn-Pt/Si02 catalysts was controlled by the surface composition of the bimetallic nanoclusters and the reduced form of the Sn-Pt nanoclusters is more active than a fully oxidized form. Additional experiments have proven that the activity of catalysts used in TPRe experiments can be completely restored after reduction in hydrogen at 340 °C. 

Figure 43 shows that the higher the temperature of oxidation the higher the amount of the hydrogen consumed in high temperature part of TPR for the reduction of separate rhenium oxide species. The low temperature peak between 200 and 300 C indicates the presence of the oxide precursor of bimetallic nanoclusters that can be formed during the reduction of bimetallic catalysts. All... 

The same group reported a second multiphase flow system for the aerobic oxidation of alcohols, catalyzed by bimetallic nanoclusters (Au-Pt and Au-Pd) in a packed-bed configuration [29]. In addition, the direct oxidative methyl ester formation of various aliphatic and benzylic alcohols was achieved, showing much higher yields and selectivities as compared with its batch counterpart. 

Reactivity of Bimetallic Nanoclusters Toward the Oxygen Reduction in Acid Medium... 

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