Pt catalysts particle size

Catalyst layer architecture As a consequence of the diminishing remrns from ever higher dispersion, the effort to increase the active catalyst surface area per unit mass of Pt has centered in recent years primarily on optimization of catalyst layer properties, aiming to maximize catalyst utilization in fuel cell electrodes based on Pt catalyst particle sizes of 2-5 nm. High catalyst utilization is conditioned on access to the largest possible percentage of the total catalyst surface area embedded in a catalyst... 

Figure 21 shows a TEM micrograph of a carbon/supported Pt catalyst with Pt catalyst particle size centered around 2 nm. The micrograph depicts the nanogeometry of such supported Pt catalysts and... 

The reactor system works nicely and two model systems were studied in detail catalytic hydrogenation of citral to citronellal and citronellol on Ni (application in perfumery industty) and ring opening of decalin on supported Ir and Pt catalysts (application in oil refining to get better diesel oil). Both systems represent very complex parallel-consecutive reaction schemes. Various temperatures, catalyst particle sizes and flow rates were thoroughly screened. 

Pt catalysts was the dehydrogenation to toluene, which was independent of catalyst particle size. Meanwhile, the selectivity for RO of MCH on iridium and ruthenium was 50% and RO was found to occur only at unsubstituted C-C bonds. 

Pt-alloy catalysts, 40 132-133 Pt microcrystal particle size on soot, 40 ... 

We are developing a new method for preparing heterogeneous catalysts utilizing polyamidoamine (PAMAM) dendrimers to template metal nanoparticles. (1) In this study, generation 4 PAMAM dendrimers were used to template Pt or Au Dendrimer Encapsulated Nanoparticles (DENs) in solution. For Au nanoparticles prepared by this route, particle sizes and distributions are particularly small and narrow, with average sizes of 1.3 + 0.3 nm.(2) For Pt DENs, particle sizes were around 2 nm.(3) The DENs were deposited onto silica and Degussa P-25 titania, and conditions for dendrimer removal were examined. 

Catalyst Particle size Pt loading Sn loading Dispersion BET surface... 

Phenyl-1,2-propanedione (Aldrich, 99%) was hydrogenated in a pressurized reactor (Parr 4560, V=300 cm ) in the absence of external and internal mass transfer limitation (verified experimentally). The reactor was equipped with an propeller type stirrer (four blades, propeller diameter 35 mm) operating at stirring rate of 1950 rpm. The hydrogen (AGA, 99.999%) pressure was 6.5 bar and teii ierature was 15 - 35°C. Pt/Al203 (Strem Chemicals, 78-1660) was used as a catalyst. The catalyst mass and liquid volume were 0.15 g and 150 cm, respectively The metal content was 5 wt.%, BET specific surface area 95 m / g, the mean metal particle size 8.3 nm (XRD), dispersion 40% (H2 chemisorption), the mean catalyst particle size 18.2 pm (Malvern). Catalysts were activated under hydrogen flow (100 cm / min) for 2 h at 400°C prior to the reaction. 

Selectivity to the desired product depends on the nature of the catalyst (particle size, alloyed phases and support) and the reaction conditions. Compared to the high selectivity to glyceric acid with pure gold, Pd addition promotes further transformation to tartronic acid, and Pt the transformation of glyceric acid to glycolic acid. Catalysts with larger metal particle size showed lower catalytic activity than catalysts with smaller particle size, while selectivity followed the opposite trend. 

The inferiority of the PEDOT/PSS supported catalyst to the carbon supported catalyst can largely be accounted for by the slightly higher Pt-Ru particle size, which decreases the available surface area, and lower catalyst utilization (16). Thus optimization of the support material (to prevent poisoning and conductivity loss) and metal deposition procedure should allow one to achieve comparable, if not superior, performances to commercial carbon supported catalysts. 

The size of the water droplet is influenced by the ratio of water to surfactant and the surfactant concentration (at fixed water/oil ratios). As the ratio of water to surfactant increases, the size of the water droplet increases and consequently, the catalyst size also increases. However, a maximum particle size is reached and further increasing the water-to-surfactant ratio has no effect on catalyst size [27, 28, 31]. For example, in a microemulsion system of water/n-heptane with the surfactant sodium dioctyl sulfosuccinate the Pt-Ru particle size increases from 2.4 0.1 to 3.2 0.1 nm when the ratio of water to sodium dioctyl sulfosuccinate increases from 4 to 8 [28]. However, increasing the water-to-dioctyl-sulfosuccinate ratio to 10 does not result in any fijrther increase in catalyst size [28]. Droplet size can also be controlled by varying the surfactant concentration while keeping the concentrations of water and oil constant. For example, increasing the surfactant concentration, with constant water and oil concentrations, increases the number of droplets. As a result, droplet size decreases, resulting in fewer metal ions per droplet and a consequently decreased particle size. 

This preparation method of catalyst array has an advantage, which is that the high surface-area catalysts can be screened under similar circumstances as are used in the traditional half-cell electrochemical testing. An additional advantage is that through this approach, the effect of other chemical/physical variables besides composition can also be studied, for example, variables such as Pt loading and catalyst particle size, as has been done in Guerin s work. 

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