Pt/C catalysts

Implementation of Pt/C catalysts in PEFC technology using recast Nafion as a proton conducting and bonding agent [Raistrick, 1986 Wilson and Gottesfeld, 1992]. 

Proper answers to the above questions can be provided once it is realized that the surface of the catalyst in a fuel cell cathode using a Pt or Pt/C catalyst cannot be... 

Figure 11.13 Linear cyclic voltammograms of different carbon-supported catalysts recorded in an 02-saturated electrolyte (0.5 M H2SO4) (1) Pt/C catalyst (2) Pt/C catalyst in the presence of 1.0 M methanol (3) FePc/C catalyst (4) FePc/C catalyst in the presence of 1.0 M methanol (temperature 20 °C, scan rate 5 mV s rotation speed 2500 rev min ).

The data presented in the preceding sections provide clear proof that the oxidation of both methanol and formaldehyde over carbon-supported Pt/C catalysts can lead to... 

Figure 13.9 Reaction scheme for Ci molecule oxidation on a Pt/C catalyst electrode, including reversible diffusion from the bulk electrolyte into the catalyst layer, (reversible) adsorption/ desorption of the reactants/products, and the actual surface reactions. The different original reactants (educts) and products are circled. For removal/addition of H, we do not distinguish between species adsorbed on the Pt surface and species transferred directly to neighboring water molecule (H d, H ) therefore, no charges are included (H, e ). For a description of the individual reaction steps, see the text.

Figure 15.3 Simulated effectiveness factor for porous carbon electrode as a function of the exchange current density jo and DCo for Ip] = 0.4 V for a 10wt% Pt/C catalyst layer with 7= 10, A = 140m g p = 2gcm, Nafion volume fraction 0.6, thickness p,m, and ionic conductivity 0.05 Scm See the text for details. (Reproduced from Gloaguen et al. [1994], with kind permission from Springer Science and Business Media.)...

The reaction mixture was filtered to remove the Pt/C catalyst and was concentrated to tan solids (26.9 g) nsing a rotary evaporator. 

This technology has broad applicability. For instance, using the same carbon support, test results show that a new Pt/C catalyst with edge-metal location and low dispersion resulted in 36% more activity than ESCAT 20 in a standard nitrobenzene (SNB) test (Figure 6). Using the same technology with a different carbon support yielded a catalyst with 57% more activity than ESCAT 20 in SNB test (16,17). 

The effect of Bi promotion for the selective oxidation of 1-octanol using H202 as oxidant is reported in Table 2. Since decomposition of H202 by Platinum Group Metals is rapid, H202 is fed continuously into the reactor over 2 hours. The results obtained demonstrate that the presence of Bi203 as an additive within the reaction mixture displays no significant influence on catalyst activity. However, Bi promoted Pt/C catalysts, prepared by co-precipitation of... 

The appearance of large amounts of aldehydes in the reaction mixtures is indicative of the presence of stronger acidic sites on the catalyst surfaces. For this reason, a large amount of aldehyde can usually be detected on Pt/Al203 and Pd/Al203 catalysts. The acidic character of Pt/C catalyst could also be detected by this method.290,291... 

A platinum-rhenium composite catalyst supported on the granular activated carbon (Pt-Re/C, 5 wt-Pt%, mixed molar ratio of Pt/Re = 2) [10] was prepared by a "dry-migration method" [33,34] as follows (1) The Pt/C catalyst prepared earlier (5 wt-metal%) was evacuated at 180°C for 1 h (2) The mixture (molar ratio of Pt/Re = 2) of the Pt/C catalyst and a cyclopentadienylrhenium tricarbonyl complex (Re(Cp)(CO)3) were stirred under nitrogen atmosphere at room temperature for 1 h and then heated at 100° for 1 h, with the temperature kept at a constant (3) This mixture was further stirred under hydrogen atmosphere at 240°C for 3 h and finally (4) the Pt-Re/C composite catalyst was evacuated at 180°C for 1 h. A platinum-tungsten composite catalyst supported on the granular activated carbon (Pt-W/C, 5 wt-Pt%, mixed molar ratio of Pt/W = 1) [5,6] was also prepared similarly by the dry-migration method. All the catalysts were evacuated inside the reactor at 150°C for 1 h before use. 

Kinetic analysis with a Langmuir-type rate equation (Equation 13.4) [37] gave us the magnitudes of reaction rate constant (k) and retardation constant due to product naphthalene (K) for the superheated liquid film (0.30 g/1.0 mL) and the suspended states (0.30 g/3.0 mL) with the same Pt/C catalyst as summarized in Table 13.2. It is apparent that excellent performance with carbon-supported platinum nanoparticles in the superheated liquid-film state is realized in dehydrogenation catalysis on the basis of reaction rate and retardation constants. 

Dehydrogenation activities, compared for tetralin and decalin [5,12] under the same superheated liquid-film conditions over the same Pt/C catalyst, exhibited around 3.9-63 times preference of tetralin (Table 13.3), which can certainly be ascribed to advantageous adsorption due to the a-bonding capability of its aromatic part [17-19]. It was, thus, confirmed experimentally that tetralin is superior to decalin as the organic hydrogen carrier for stationary applications in terms of rapid hydrogen supply or power density, provided that the density of fuel storage is unimportant. 

The feasibility of carbon-supported nickel-based catalysts as the alternative to the platinum catalyst is studied in this chapter. Carbon-supported nickel (Ni/C, 10 wt-metal% [12]), ruthenium (Ru/C, 10 wt-metal% [12]), and nickel-ruthenium composite (Ni-Ru/C, 10 wt-metal%, mixed molar ratio of Ni/Ru 0.25,1,4, 8, and 16 [12]) catalysts were prepared similarly by the impregnation method. Granular powders of the activated carbon without the base pretreatment were stirred with the NiCl2, RuC13, and NiCl2-RuCl3 aqueous solutions at room temperature for 24 h, respectively. Reduction and washing were carried out in the same way as done for the Pt/C catalyst. Finally, these nickel-based catalysts were evacuated at 70°C for 10 h. 

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