Platinum duster

Kowalska, E., Remita, H., Colbeau-Justm, C., Hupka, J., and BelloniJ. (2008) Modification of titanium dioxide with platinum ions and dusters application in photocatalysis. Journal of Physical Chemistry C, 112 (4), 1124-1131. 

The role of tbe additives, which may be used in bi- or muitnnetaltic combinations (Re, Ir, Ru, Ag, Au, Ge etc.) is poorly umterstood. They help to enhance the properties of platinum hy keeping it in a suitable state of dispersion, and to modulate the acidic character of the support. They appear to oppose the sintering of metallic crystallites by the formation of alloys or polymetallic dusters. 

What are transition metal clusters and why are they interesting For example what are the properties of a 5-atom platinum cluster Is it similar to bulk platinum or does it behave more like the atom What we are discovering is that below a certain size each small n-atom duster has unique chemical and electronic properties, it behaves neither iike the atom, the bulk, nor even 1i ke other clusters of the same metal. Thus there are opportunities to exploit their novel properties by making it possible to create new materials with potential applications in such diverse areas as solid state physics, electronics, chemistry and catalysis. 

Figure 6. Hydrogen uptake for rhodium, platinum and nickel cations as a function of duster size. H/M is the measured hydrogen to metal stoichiometry of the duster.

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... 

Homs and co-workers described the linkage of ethene and C02 on a supported platinum/tin complex yielding 3-hydroxypropionic acid [73], Another approach to utilizing C02 was pursued by Tominaga and Sasaki, namely hydroformylation with C02 [74]. 1-Hexene, for instance, reads with a mixture of C02 and H2 in the presence of ruthenium dusters giving heptanals, heptanols, and, in small amounts, the undesired hexane as a result of simple hydrogenation. Mechanistically it is assumed that a retro water gas shift reaction occurs, in which CO and H20 are formed from C02 and H2. This carbon monoxide undergoes ordinary hydroformylation with the alkene and H2. 

These results agree well with electrochemical experiments. If dichloromethane solutions of different Msj dusters are contacted to Pt electrodes to which 20 V dc is applied, the duster molecules are degraded as a result of the contact with the electrodes. [109] Polarization effects may be the reason for the decomposition. Electrophoresis is observed without any indication of duster decomposition if the platinum electrodes dip into water layers covering the organic phase in a U-tube. The black, thermodynamically unstable microcrystalline products formed on the Pt surfaces have been identified by X-ray powder diffraction to be novel [(Mi3)J metal modifications. The results from the diffraction experiments indicate a structure consisting of cubic dose packed M13 dusters which are linked via their triangular faces to form a kind of pseudo dose packed structure with M13 dusters as building blocks. 

Wang et al. [121] reported that the NaY zeolite containing Pt carbonyl dusters of the family [Pt3(CO)6] (n = 3, 4) is catalytically active for the shift reaction at 27-150°C and that the photocatalytic reaction was about 38 times faster than the catalytic reaction at 25 °C. Since the platinum carbonyls present in the used catalyst were identified only by infrared spectroscopy, there remains doubt about what they were as well as what the catalytically and photocatalytically active spedes might have been. 

The infrared spectrum of CO adsorbed on a vapor derived < 1.0 nm platinum colloid stabilized by iro-butylaluminoxane in methylqrclohexane showed only a linear CO stretch at 2035 cm. This particle size is witliin the range for the larger molecular platinum carbonyl duster anions, and the colloidal platinum can in fact be hydrolysed to mixtures of [Pt9(CO)ig] and [Pti2(CO)24] after CO adsorption. [229]... 

Fukuoka, A., Higashimoto, N., Sakamoto, Y., Sasaki, M., Sugimoto, N., Inagaki, S., Fukushima, Y. and Ichikawa, M. (2001) Ship-in-botde synthesis and catalytic performances of platinum carbonyl dusters, nanowires, and nanopartides in micro- and mesoporous materials. Catalysis Today, 66, 23. 

---