Bimetallic PtSn/C catalysts, prepared on two activated carbon supports of different surface chemistry by two different preparation procedures, have been analyzed by XAFS spectroscopy. The main goal is to identify the effect of the support surface oxidation and the preparation procedure (coimpregnation or successive impregnations) in the interaction of platinum with the support and/or with tin atoms. XAFS results reveal the effect of the mentioned variables in the structure of the supported phase. It has been found in dried samples that the interaction of the platinum species with the support is stronger if the carbon surface is oxidized. The two-step impregnation, compared with the coimpregnation method, renders samples with a stronger platinum-support interaction. Such an interaction determines the distribution of the active phase on the support particles. The structure of the metallic phase after reduction is quite different for samples prepared with the oxidized and nonoxidized carbon support and is also dependent on the preparation procedure. From the XAFS data, the presence of the following platinum containing structures is suggested: PtSn alloy, Pt-O-Sn 2+ species and pure Pt clusters. The relative proportion of these structures in the catalysts and their distribution on the support determine the catalytic activity for cyclohexane dehydrogenation.

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The Rh diamine complex, [Rh(COD)NH2(CH2)2NH(CH2)3Si(OCH3)3] BF4 has been heterogenized by covalent bonding on two carbon xerogels and on carbon nanofibers, with the objective of preparing hydrogenation hybrid catalysts. Gas adsorption, SEM, TEM, DTP, ICP-OES and XPS were used for characterization. The results indicate that the active molecule is mainly located in supermicropores and produces microporosity blockage. The hybrid catalysts are more active than the homogeneous complex, but the Rh complex is partially reduced upon reaction. This modification has been related with the nature of the support, which has also shown to have an effect in the stabilization against sintering of the Rh particles formed. The support porosity is behind differences in selectivity between the catalysts.

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