State of Pt in Dried and Reduced PtIn and PtSn Catalysts Supported on Carbon

The state of platinum in carbon-supported bimetallic PtSn and PtIn catalysts, prepared by two different methods, coimpregnation and successive impregnation, has been investigated by X-ray photoelectron spectroscopy, X-ray absorption fine structure (XAFS), transmission electron microscopy (TEM), and a catalytic test. An important effect of the nature of the second metal in the state of platinum, related to the preparation conditions, has been found. Different states of platinum are found, mainly platinum metal and binary intermetallic compounds with the second metal. The preparation method has a clear effect on the state of platinum in reduced PtSn samples, while it is much lower in the reduced PtIn catalysts. As deduced from TEM, in general in the bimetallic catalysts the mean particle size is smaller and the particle size distribution is narrower than in the monometallic Pt/C catalyst, and there is an effect of the preparation method. In general, PtIn catalysts are more homogeneous than PtSn. Because of the mentioned differences, catalytic activity for cyclohexane dehydrogenation, a structure insensitive test reaction, depends on the second metal and preparation method.