Carbon monoxide adsorption platinum-supported catalysts

Abstract To date, microcalorimetry of CO adsorption onto supported metal catalysts was mainly used to study the effects induced by the nature and the particle size of supported metallic clusters, the conditions of pretreatment and the support materials on the surface properties of the supported metallic particles. The present chapter focuses on the employ of adsorption microcalorimetry for studying the interaction of carbon monoxide with platinum-based catalyst aimed to be used in proton exchange membrane fuel cells (PEMFCs) applications. 

Fig. 4 Energy distribution function, (p(e t) (cmol/kJ/mol/), against the dimensionless product of the lateral interaction energy (P) and the local isotherm (0)P0, for carbon monoxide adsorption over a bimetalhc Pto.25-Rho.75 silica supported catalyst, at 698 K. Source From Gas chromatographic kinetic study of carbon monoxide oxidation over platinum-rhodium catalysts, in J. Chromatogr.

The adsorption of CO on a series of platinum based catalysts was also carried out by microcalorimetry technique, supplying information about the number, the strength distribution and the heat associated to the carbon monoxide adsorption on available Pt surface sites. Table 12.2 lists some literature reports on the average heats of CO adsorption over different platinum supported catalysts. In this table, the experimental data on powdered catalysts were collected from the vicinity of room temperature up to 130 C. Prior to CO adsorption, the samples were reduced at 200 or 500 C under hydrogen flow. 

However, although the determination of the heat of adsorption of carbon monoxide on platinum have been reported in the literature (Table 12.2), the possible use of adsorption microcalorimetry as an available technique for giving valuable information in PEM fuel cells smdies has not been reported. In what follows, recent results from our work in the field of microcalorimetry of CO adsorption on Pt/C catalysts are presented [65-67]. The catalysts used in these studies were different commercial carbon-supported platinum, with high Pt loading, aimed to be used in PEMFCs applications. Particular emphasis on the sample history (preparation method, the support material, the metal loading) and the pre-treatment of the catalysts on the CO poisoning effect on supported platinum is paid. 

The application of selective chemisorption to supported Pt catalysts is well established but there have been valuable additional studies of the use of hydrogen in the pulse-flow technique and of CO adsorption using TPD and carbon monoxide. Recently the usual assumption about the stoicheiometry for hydrogen adsorption, Ptg/H = 1 has been questioned. For the Council of Europe Pt-Si02 catalyst, where a weak metal-support interaction was postulated, 1.75 hydrogen atoms per surface metal atom were found at 300 K in two adsorbed forms (the formation of jSa was activated). Recent work on selective chemisorption applied to metals of catalytic interest other than platinum will now be examined. 

Jackson, S. D. et al. Supported metal catalysts Preparation, characterization, and function 11. Carbon monoxide and dioxygen adsorption on platinum catalysts. Journal of Catalysis 139, 207-220 (1993). 

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