CORRELATIONS BETWEEN X-RAY PHOTOELECTRON-SPECTROSCOPY DATA AND CATALYTIC PROPERTIES IN SELECTIVE OXIDATION ON SB-SN-O CATALYSTS

A series of SbSnO catalysts has been studied by X-ray photoelectron spectroscopy (XPS) as a function of Sb content (from 1.7 to 39.7 atom%) and activation temperature. At low activation temperature (500 °C) surface and bulk compositions are comparable, while at higher activation temperatures strong surface enrichment in Sb occurs. Detailed analysis of the XPS line shapes shows that two phases may exist at the surface of the catalyst. The first one, which is observed at low Sb content and low activation temperature (500 °C), is assigned to Sb(V) in solid solution in the SnO2 lattice. The second one, which is observed for Sb contents larger than 5% or for high-temperature activations, is assigned to an Sb2O4 phase. Catalytic properties for selective oxidation of propylene were studied in the 350 to 400 °C range. The selectivity for acrolein increases when surface Sb content is increased either by enhancement of the Sb concentration or by higher activation temperature. It is then postulated that the catalytic phase, which gives selective oxidation, consists of an Sb2O4 phase lying at the surface of a solid solution of Sb (V) in SnO2. © 1979.