Platinum particles separation

Attempts to support colloidal platinum particles with surfactant zinc porphyrin micelles allow hydrogen production at lower platinum concentrations than when the porphyrin and the particle are separate but an irreversible electron donor is still necessary for hydrogen production.116... 

It is important to understand the dynamics of photogenerated electrons and holes and their role in semiconductor systems to facilitate the design and development of efficient photocatalysts (Anpo, 2002 Anpo and Che, 1999 Matsuoka and Anpo, 2005). As reported earlier (Anpo and Che, 1999), the presence of a small number of platinum particles on TiC>2 is known to strongly increase the yield of photoreactions. This effect is attributed to a migration of the photoformed electrons from the conduction band of TiC>2 to the platinum particles, whereas the holes remain in the valence band, leading to effective charge separation of the... 

EBL was used to fabricate uniform platinum nanoparticle arrays on Si02 (mean platinum particle diameter 30-1000 nm 52,53,106,107,398)), and evaporation techniques were used to prepare smaller particles and a continuous platinum film. The EBL microfabrication technique allows the production of model catalysts consisting of supported metal nanoparticles of uniform size, shape, and interparticle distance. Apart from allowing investigations of the effects of particle size, morphology, and surface structure (roughness) on catalytic activity and selectivity, these model catalysts are particularly well suited to examination of diffusion effects by systematic variations of the particle separation (interparticle distance) or particle size. The preparation process (see Fig. 1 in Reference 106)) is described only briefly here, and detailed descriptions can be found in References 53,106,399). 

Especially at elevated temperature small particles tend to agglomerate, therefore a spatial separation is important. It was found [31] that the platinum surface area correlates with the BET surface of the carbon carrier material. This is easily understandable as a better dispersion of the noble metal particles leading to higher electrochemical activity. But as soon as the platinum particles reside in very small pores, smaller than 40 nm, they do not contribute to the electrochemical reaction anymore... 

A challenging problem is to address the effect of adsorbed hydrogen on NMR response of small platinum particles (see Section 3.1.3.2 in Ref 27). EQCM probably presents a separate possibility to get microscopic information if applied less straightforwardly (not reduced to a weighting instrument). This technique is sensitive to hydrogen adsorption and able to tell the difference of sulfate and perchlorate coadsorption with hydrogen (see Ref 238 for a brief review of earUer works). Recently developed EQCM... 

This paper focuses on the effects of the carbon and ethylidyne-derived adlayers in electrooxidation. We present brief accounts of how the adlayers were characterized, both electrochemically and in vacuum, and will describe adlayer characterization in more detail in a separate publication [19]. To our knowledge, the effects of carbon adlayers on single crystal electrodes have not been studied, although the situation is somewhat analogous to platinum particles deposited on graphite electrodes, about which quite a bit is known [20,21]. The e ylidyne adlayer is derived from adsorption of ethylene in vacuum [22,23]. Electrochemical adsorption of ethylene and electroreduction to ethane have also been previously studied [24-28]. 

A method to prepare nanosized particles which is based on a very different concept to those mentioned above is the process based on reversed-microemulsions. A recent overview of this method has been given by Pileni (24). In such a technique, the water-soluble reactants are included in the water droplets in reversed micelles. Because the droplets exchange their contents rather frequently the two reactants will therefore mix and form an insoluble substance which then aggregates into particles. The particle size is mainly determined by the droplet size. A typical microemulsion droplet is of the order of 20-40 nm, which means that the particle size will be inside this size range. As an example of this, platinum particles can be produced by using platinum chloride and hydrazine in separate microemulsion droplets. Hydrazine reduces the platinum ions to metallic platinum and nanosized particles are... 

For multicomponent porous materials with mixed wettability, which are widely used in applied electrochemistry (e.g., fuel cell electrodes containing platinum particles on carbonaceous supports along with different additives), it is possible to investigate separately the structure (pore volume distribution versus pore size) for hydrophilic and hydrophobic (liophilic and liophobic) pores and to evaluate some important parameters, such as the dependence of the fraction p of the pore surface occupied by the hydrophobic (liophobic) components on the pore size. 

Sobczynski A, Bard AJ, Campion A, Fox MA, MaUouk T, Webber SE, White JM (1987) Photoassisted hydrogen generation platinum and cadmium sulfide supported on separate particles. J Phys Chem 91 3316-3320... 

This paper identifies alumina, rare earths, platinum, and magnesia as important SOx capture materials. Alumina is either incorporated directly into the matrix of a cracking catalyst or added as a separate particle. Cerium is shown to promote the capture of SO2 on high alumina cracking catalyst, alumina, and magnesia. Other rare earths are ranked by their effectiveness. The promotional effect of platinum is shown between 1200 and 1400 F for SO2 capture on alumina. Silica, from free silica or silica-alumina in the matrix of cracking catalyst, acts as a poison by migrating to the additive. 

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