Platinum nanoclusters

According to anomalous small angle X-ray scattering (ASAXS), this compound slowly decomposes to release redispersible platinum nanoclusters with a mean diameter of 1.2 nm. The protective shell is formed on site by excess aluminium organics. 

Platinum Nanoclusters Size and Surface Structure Sensitivity of Catalytic Reactions... 

Well-defined nanoclusters (w 10-100 A diameter) of several metals have been prepared via the polymerization of metal-containing monomers. The synthetic approach involves the block copolymerization of a metallated norbornene with a hydrocarbon co-monomer which is used to form an inert matrix. Subsequent decomposition of the confined metal complex affords small clusters of metal atoms. For example, palladium and platinum nanoclusters may be generated from the block copolymerization of methyl tetracyclododecane (223) with monomers (224) and (225) respectively. 10,611 Clusters of PbS have also been prepared by treating the block copolymer of (223) and (226) with H2S.612 A similar approach was adopted to synthesize embedded clusters of Zn and ZnS 613,614... 

Figure 2.15 Schematic representation of the silica supported metallic particle with a cubo-octahedral shape (a) and a real particle size distribution of platinum nanoclusters supported on silica (b).

Figure 6.26 On line isotope dilution in LA-ICP-MS for determination of Cu in platinum nanoclusters, (j. S. Becker et al., Int. j. Mass spectrom. 237, 13(2004). Reproduced by permission from Elsevier.)...

Gan S., Liang Y., Baer D.R. et al. (2001) Effect of Platinum Nanocluster Size and Titania Surface Structure upon CO Surface Chemistry on Platinum-Supported Ti02 (110), J. Phys. Chem. B. 105(12), 2412-2416. 

A suitable calibration strategy has been demonstrated for the determination of selected elements, i.e., Pb, Ag and T1 in a small amount of platinum nanoclusters. In on line isotope dilution analysis with LA-ICP-MS, an isotope emiched tracer solution was nebulized by the Aridus microconcentric nebulizer with desolvator. After about 180 seconds, laser ablation of the investigated platinum nanocluster sample was started and after an additional time of 180 seconds 2 % nitric acid nebulized instead of the tracer solution. The isotope ratios of lead ( Pb/ ° Pb), silver ( ° Ag/ ° Ag) and thallium ( ° T1/ ° T1) - with Cu/ Cu for internal standardization - were monitored during the whole experiment. The measuring time for one experiment was <10 min. 

Figure 9.28 Application of online isotope dilution technique for determination of Pb in platinum nanoclusters.

Similar to Ag°, zero-valent platinum nanoclusters were synthesized with cysteine capping ligands under reducing conditions. The platinum clusters showed a larger size... 

Figure Computer modeling of organometallic moities anchored onto the platinum nanocluster, monolayer coverage. A - anchoring of SnR (top view) B -anchoring of SnR2 (side view), R = -C2H5 (Reproduced from ref. 106 with permission)...

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. 

Data in Table 13 show that in the parent platinum catalyst the addition of oxygen to CO had no detectable changes in the spectrum. However, in both Sn-Pt/Si02 catalysts the addition of oxygen resulted in noticeable shift in the CO band frequencies. This shift indicates that in the presence of oxygen the surface composition of the supported tin-platinum nanocluster has been altered and the extent of these changes depends on the Sn/Pt ratio (compare samples (A) and (B)). 

Fig. 18.20 Synthesis of platinum nanoclusters covered with octylsilyl ligands (X) from Pt(dba)2.

Zuo, X.B., Liu, H., Guo, D., Yang, X. (1999) Enantioselective hydrogena tion of p Tuvates over polymer-stabilized and supported platinum nanoclusters, Tetrahedron, 55, 7787-7804. 

Zhang, J., Yan, X.P., Liu, H.F. (2001) Enantioselective hydrogenation of trifluoroacetophenone over polymer-stabilized platinum nanoclusters, J. 

In present work processes of dissolutions are considered for stable platinum nanoclusters and binary nanocluster PtMe (Me is the transition metals, namely Cr, Fe, Co, Ni, Ru) with core-shell stmctuie and n = 42,m = 13 atoms, as well as their surface interaction with particles of environment, i.e., H/), O, OH, H/F, Cf. So, we need examine reaction ability of binary nanoclusters in such environment, including prediction of the nanosystem properties. Evidently, to solve such task one must possess data about potentials of all particle interaction in a chosen system. 

Theoretical consideration of platinum nanoclusters originates from the consumption that atoms in an nanocluster should be located at positions with minimal energy in the force field of surroundings. For this purpose we set definite positions of atoms with an approximate geometry and run optimization by molecular d5mamics method to obtain minimal energy in dependence on internal coordinates. 

According to the Ref. [42, acid anions, such as Cl, CIO, HSO participate directly in the process platinum nanocluster dissolution in electrolytes and change their rates. The ability to dissolution depends not only on the strength of chemical bond of surface atom and adsorption complex but also on the degree of adsorption weakening of bonds between surface atom and its nearest surroundings. In other words, a metal cation departure from the surface follows after specific ion adsorptions at electrodes. Metal surface atom, which interacts with an ion, chemisorbed from solution, do not belongs to the crystal lattice, but still has no stable bond with complex, more or less soluble. 

PLATINUM NANOCLUSTER DISSOLUTION AND ENERGIES OF METAL IONS DELAY FROM THE SURFACE... 

TABLE 5 Calculated activation energies EA(in kJ/mole) of Pt ion departure fiom the surface (100) platinum nanocluster in different complexes. 

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