Surface characterization of Li-modified platinum/tin catalysts for isobutane dehydrogenation

The superficial properties of different Pt/y-Al2O3 catalysts, modified by the addition of tin and/or lithium, were studied by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy, BET, and 2-propanol transformation. The results obtained were correlated with the behavior of the catalysts in applied reactions such as the dehydrogenation of isobutane. To obtain very well defined bimetallic superficial phases; tin was introduced by means of surface organometallic chemistry on metals techniques and the nature of the bimetallic-active sites so obtained was compared with the ones prepared by conventional procedures. XPS measurements indicate that tin is present in both zeroth valent and oxidized states. The addition procedure of both tin and lithium has a marked influence on the characteristics of the surface of the catalysts. The order in which lithium is added generates solids having different properties in relation to texture, dispersion, and catalytic behavior, for both Pt and PtSn systems.