Noble metal particles, influence materials

Influence of Noble Metal Particles on Semiconducting and Insulating Oxide Materials... 

For the detailed study of reaction-transport interactions in the porous catalytic layer, the spatially 3D model computer-reconstructed washcoat section can be employed (Koci et al., 2006, 2007a). The structure of porous catalyst support is controlled in the course of washcoat preparation on two levels (i) the level of macropores, influenced by mixing of wet supporting material particles with different sizes followed by specific thermal treatment and (ii) the level of meso-/ micropores, determined by the internal nanostructure of the used materials (e.g. alumina, zeolites) and sizes of noble metal crystallites. Information about the porous structure (pore size distribution, typical sizes of particles, etc.) on the micro- and nanoscale levels can be obtained from scanning electron microscopy (SEM), transmission electron microscopy ( ), or other high-resolution imaging techniques in combination with mercury porosimetry and BET adsorption isotherm data. This information can be used in computer reconstruction of porous catalytic medium. In the reconstructed catalyst, transport (diffusion, permeation, heat conduction) and combined reaction-transport processes can be simulated on detailed level (Kosek et al., 2005). 

Taking into account all these factors, it has been found that the most appropriate supports for PFMFCs catalysts are carbon blacks of ca. 250 m g BFT surface area, and the most widely used is Vulcan XC-72R commercialized by Cabot. ° ° Due to the importance of the surface chemistry of these supports, and its influence in the supported active metal phase, ° ° different chemical modifications of the support have been also investigated. The chemical nature of the carbon surface produces different electronic interactions between the noble metals and the carbon support, and affects the metal particle morphology, and influences the catalytic activity. Additionally, during the last few years, new alternative materials to carbon blacks have also been used, especially on the basis of their porous structure (nanotubes, mosoporous carbons) or their microstructure (nano- and microfibers, and microspheres). 

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