XAFS study of dried and reduced PtSn/C catalysts: Nature and structure of the catalytically active phase

Bimetallic PtSn/C catalysts, prepared on two activated carbon supports of d ifferent surface chemistry by two different preparation procedures, have be en analyzed by XAFS spectroscopy. The main goal is to identify the effect o f the support surface oxidation and the preparation procedure (coimpregnati on or successive impregnations) in the interaction of platinum with the sup port 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 dr ied samples that the interaction of the platinum species with the support i s stronger if the carbon surface is oxidized. The two-step impregnation, co mpared with the coimpregnation method, renders samples with a stronger plat inum--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 oxi dized and nonoxidized carbon support and is also dependent on the preparati on procedure. From the XAFS data, the presence of the following platinum co ntaining structures is suggested: PtSn alloy, Pt--O-Sn2+ species and pure P t clusters. The relative proportion of these structures in the catalysts an d their distribution on the support determine the catalytic activity for cy clohexane dehydrogenation.