Noble metal particles, influence

From catalysis it is well-known that the metal-substrate interaction influences the reactivity of supported nanoparticles. For instance, for noble metal particles on oxidic supports, the hydrogenation and hydrogenolysis activity is much greater if the support has a higher acidity (high concentration of acidic —OH groups at the surface) than for neutral or alkaline oxidic supports. The influence of the presence of a support on the catalytic activity of metal nanoparticles has been ascribed to [70, 75-79] ... 

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

Electrons are transferred through the catalyst support to the catalyst nanoparticle while protons are transferred from the catalyst surface to the electrolyte phase. It is obvious that the ion conducting phase needs to be extended into the volume of the catalyst layer in order to minimize noble metal particles which are either not contacted or buried too deep in the electrolyte. It has to be noted that reactant presence at the reaction site can also be achieved by reactant diffusion from the gas phase through a thin electrolyte film covering the platinum particle. Reactant transport properties therefore have a significant influence on the design and... 

Jacobs G., Ji Y., Davis B.H., Cronauer D., Kropf J., and Marshall C.L. 2007. Fischer-Tropsch synthesis Temperature programmed EXAFS/XANES investigation of the influence of support type, cobalt loading and noble metal promoter addition to the reduction behaviour of cobalt oxide particles. Appl. Catal. A Gen. 333 179-91. 

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). 

The influence of the nature of the metal particles was also analyzed. Many noble metal/ceiia-containing supports combinations were tested [12,38,39]. 

However, while the commonly used refractory oxide supports, silica and alumina, increase the metal dispersion, they are not inert, especially toward the non-noble metals and less conspicuously also toward the noble metals. The physical and chemical interactions between the active metal, the oxide support and the environment affect the surface properties of the catalyst and consequently influence the shape of crystallites and the particle size distribution. Two sets of experimental observations involving surface phenomena are of interest in the present context Cl) The average size of the... 

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