Highly dispersed platinum, oxidation

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

For fuel-cell technology development, it has been important to understand the characteristics and operation of highly dispersed platinum and platinum alloy electrocatalysts. A series of papers on platinum crystallite size determinations in acid environments for oxygen reduction and hydrogen oxidation was published together by Bert, Stonehart, Kinoshita and co-workers.5 The conclusion from these studies was that the specific activity for oxygen reduction on the platinum surface was independent of the size of the platinum crystallite and that there were no crystallite size effects. 

Stonehart examined highly dispersed platinum and alloys of Pt-Pd7a73 and found that with sophisticated catalyst preparation techniques, it was possible to maintain very small crystallites of these binary alloys on carbon supports, and that the alloys were more active than Pt alone for hydrogen oxidation in the presence of both carbon monoxide and... 

The classical oxidative, intramolecular formation of aryl-aryl bonds by thermal cyclodehydrogenation and photocyclization reactions have already been discussed in Sects. 1 and 2 respectively. Compared to the thermal approach, higher yields have often been obtained using classical hydrogen transfer catalysts such as highly dispersed platinum or palladium on suitable supports or Friedel-Crafts type catalysts like the classical AlCl3/NaCl melt (Scholl reaction, see Scheme 26 and 27 [7,38 d,e,108]). 

The deposition-precipitation (DP) method has been scarcely used to prepare platinum supported catalysts [1-5], while it is the preferred method to obtain active gold ones [6-7]. Initially, the deposition-precipitation technique has been developed by Geus and Hermans for the production of highly loaded and highly dispersed metal/oxide catalysts [8]. This technique involves the precipitation of the active phase precursor at fte surface of Ae support and its subsequent deposition whereas nucleation in the solution itself should be avoided. 

Zirconia has been proposed by Hubbard et al. [47] to be a possible superior support material to alumina. For highly dispersed platinum, the oxidation of propane occurs at a rate as high as two orders of magnitude higher over Pt/zirconia than over Pt/alumina. 

The electrocatalytic oxidation of alcohols is possible by using modified conductive polymer electrodes. One of the most interesting examples of such a reaction is the electro-oxidation of methanol with highly dispersed platinum-based particles inserted in a polymeric matrix. 

P.J. Kulesza, B. Grzybowska, M. A. Malik, and M.T. Galkowski, Tungsten oxides as active supports for highly dispersed platinum microcenters Electrocatalytic reactivity toward reduction of hydrogen peroxide and oxygen, J. Electrochem. Soc., 144, 1911—1917 (1997). 

Noble metals (e.g., platinum, gold, and silver), metal oxides, mixed oxides such as spinels, perovskites, and pyrochlores have been investigated, but by far the best catalytic material is highly dispersed platinum. The high cost of this metal stimulated research to look for less expensive alternative materials... 

Becerik I, Kadirgan F. Electr-oxidation of formic acid on highly dispersed platinum and perchlorate doped polypyrrole electrodes. J Electrochem Soc 2001 148 D49-54. 

It was soon found, however, that catalysts in the form of platinum deposited onto carbon black (Pt-C) have a rather important defect, inasmuch as during long-term use in a fuel ceU, the surface of the carbon-black particles becomes oxidized, particularly so at the positive electrode, which upsets the contact between the platinum catalyst and the carbon black (in some cases the crystallites slip away from the carbon black). For this reason it became urgent to search for other supports for the highly disperse platinum catalysts. 

Lei, Z., An, L., Dang, L., Zhao, M., Shi, X, Bai, S. Cao, Y Highly dispersed platinum supported on nitrogen-containing ordered mesoporous carbon for methanol electrochemical oxidation. Micropor. Mesopor. Mater. 119 (2009), pp. 30-38. 

Slavcheva, E. Radev, I. Bliznakov, S. Topalov, G. Andreev, P. Budevski, E. (2007). Sputtered Iridium Oxide Films as Electrocatalysts for Water Splitting via PEM Electrolysis. Electrochim. Acta, Vol. 52, pp. 3889-3894 Soin, N. Roy, S.S. Karlsson, L. McLaughlin, J.A. (2010). Sputter Deposition of Highly Dispersed Platinum Nanoparticles on Carbon Nanotube Arrays for Fuel Cell Electrode Material. Diam. Relat. Mater., Vol. 19, pp. 595-598 Sundmacher, K. (2010). Fuel Cell Engineering Toward the Design of Efficient Electrochemical Power Plants. Ind, Eng. Chem, Res, Vol. 49, pp. 10159-10182... 

I. Becerik, and F. Kadirgan, Electro-Oxidation of Formic Acid on Highly Dispersed Platinum and Perchlorate Doped Polyp5UTole Electrodes, /. Electrochem. Soc., Vol. 148, No. 5, pp. D49-D54, 2001. 

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