Abstract
The surface properties and states of SnO2-Sb2O4 catalysts were investigated to reveal the promoting effects of the catalyst system. Temperature programmed desorption of oxygen from a series of the catalysts with varying Sb contents (x atomic %) showed that oxygen desorption increased with an increase in x reaching a maximum at x=30% (Fig.1 and 2). The same trend was also observed in the specific activity for the acrylaldehyde formation in the pulse reaction of propene (Fig.4). These results indicate that the catalyst surface is modified properly by the addition of Sb2O4 to SnO2. While X-ray diffraction analysis detected Sb2O4 only for x>30% (Fig.5), XPS revealed the surface enrichment of Sb which b ecomes most remarkable at x=20∼30% (Fig.6). The thickness of the Sb-enriched surface layer was estimated to be 20Å or thinner of from SIMS experiments (Fig.7). It is concluded that the active sites of the SnO2-Sb2O4 catalysts are provided by the Sb-enriched surface layer (Fig.8).
