Platinum-graphite catalysts

Fig. 5-47 Agglomeration of platinum crystallites in a platinum/graphite catalyst quantification of the process byXPS (top middle) and visualization byTEM (bottom) (BASF, Ludwigshafen, Germany)...

X-Ray studies confirm that platinum crystallites exist on carbon supports at least down to a metal content of about 0.03% (2). On the other hand, it has been claimed that nickel crystallites do not exist in nickel/carbon catalysts (50). This requires verification, but it does draw attention to the fact that carbon is not inert toward many metals which can form carbides or intercalation compounds with graphite. In general, it is only with the noble group VIII metals that one can feel reasonably confident that a substantial amount of the metal will be retained on the carbon surface in its elemental form. Judging from Moss s (35) electron micrographs of a reduced 5% platinum charcoal catalyst, the platinum crystallites appear to be at least as finely dispersed on charcoal as on silica or alumina, or possibly more so, but both platinum and palladium (51) supported on carbon appear to be very sensitive to sintering. 

Oxidation of Highly Dispersed Platinum on Graphite Catalysts in Gaseous and Aqueous Media... 

Catalyst. A highly dispersed platinum on graphite catalyst was prepared following a method described by Richard and Gallezot 20). 

The experimental data presented in this paper demonstrates the potential of CuCl/HCl electrolysis for nuclear hydrogen production. The CuCl/HCl electrolysis reaction requires a cation exchange membrane in order to produce hydrogen at a current density that exceeds 0.1 A-cm-2. In order to carry out the hydrogen production reaction a platinum electro-catalyst is required. The copper(I) oxidation reaction, on the other hand, does not require a Pt catalyst. This reaction proceeds quite readily on Pt-free graphite electrodes. Methods to mitigate the passage of the copper ion species across the membrane need to be developed to maintain the performance of the cell at the desired level. 

Table 1. Fraction platinum atoms exposed as determined with CO chemisorption (FE00) and cyclic voltammetry (FE ) for a 3.35 wt% Pt/graphite catalyst used in the ethanol oxidation at 298 K and MGP oxidation at 323 K. Conditions C°eth(ino,=100 mol/m3 C°MQP= 100 mol/m3, Q - 2.5 kg/m3, pH-8.0.

The catalyst is platinum-based for both the anode and cathode. To promote hydrogen oxidation, the anode uses either pure platinum metal catalyst or, as is common in most modem PEFC catalysts, a supported platinum catalyst, typically on carbon or graphite for pure hydrogen feed streams. For other fuels, such as reformate (containing H2, CO2, CO, and N2), the desired catalyst is an alloy of platinum containing mthenium. Oxygen reduction at the cathode may use either the platinum metal or the supported catalyst. 

CARBON - CARBON AND ARTIFICIALGRAPHITE - APPLICATIONS OF BAKED AND GRAPHITIZED CARBON] (Vol 4) -With osmium tetroxide catalyst [PLATINUM-GROUP METALS, COMPOUNDS] (Vol 19)... 

The critical and predominant rationale in the utilization of the above components is a significant distinction between the photoelectrode and the electrolyte Fermi levels this induces, upon irradiation, a certain potential difference and consequently a measurable current will be supplied by the apparatus. Regarding counter-electrodes, graphite and platinum catalysts can be mentioned. 

An interesting catalyst is the platinum supported on graphite. Fig. 12 shows a bright field image. The... 

The reduction is usually made in a multi-compartment electrochemical cell, where the reference electrode is isolated from the reaction solution. The solvent can be water, alcohol or their mixture. As organic solvent A,A-dimethyl form amide or acetonitrile is used. Mercury is often used as a cathode, but graphite or low hydrogen overpotential electrically conducting catalysts (e.g. Raney nickel, platinum and palladium black on carbon rod, and Devarda copper) are also applicable. 

Platinum was introduced on the activated support by a competitive cation exchange technique. An amount of 100 g of a 8 wt% Pt solution of platinumtetrammine hydroxide (Johnson Matthey) was added dropwise to a suspension of 40 g graphite in 800 ml 1 M ammonia (Merck p.a.) and stirred at ambient temperature for 24 hours. The catalyst was subsequently separated by filtration on a Millipore filter (HV 0.45m), washed with distilled water and dried in a vacuum oven at 373 K. The dried catalyst was reduced in flowing hydrogen at 573 K for 2 hours and stored under air before use. 

Another material has some importance for oxygen reduction, not as an electrocatalyst but because other properties make it a good supporting material for catalysts that is, carbon, graphite, used with dispersed platinum particles or adsorbed coordination compounds. The main reduction product on carbon itself... 

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