Structure and catalytic activity of Sb oxide highly dispersed on SnO 2 for propene oxidation

Abstract

Two series of SbSn oxide catalysts having different Sb content and different particle sizes of SnO 2 were prepared and their propene oxidation activities were examined. Sb oxide in these SbSn oxide catalysts was noncrystalline in the Sb content range of 5 to 50 at%. The concentration of Sb ions dissolved into SnO 2 lattice was estimated to be lower than 10% from the change of IR transmissions. Laser Raman and Auger electron spectroscopic analyses suggested that part of the Sb oxide is present as noncrystalline Sb(III) and Sb(V) oxides dispersed on SnO 2, whose proportion depends on the particle size of SnO 2. In the propene oxidation, the initial rates of acrylaldehyde formation increased with the increase in surface Sb content and passed through maxima at certain compositions. For both series of catalysts, the high rates and high acrylaldehyde selectivities were obtained at around the surface ratio of Sb Sn = 1 2 − 1 3 . A bifunctional mechanism in propene oxidation over these catalysts is discussed. The differences between SnO 2 and TiO 2 in their role as a support are also discussed.