Mechanical and Thermal Spreading of Antimony Oxides on the TiO2 Surface: Dispersion and Properties of Surface Antimony Oxide Species

Abstract

Mixed metal oxides are important industrial catalysts for the selective oxidation and ammoxidation of aromatics and alkenes and often contain Sb oxides as a component. For the preparation of a catalytically relevant system on the basis of monolayer-type catalysts, an alternative route as compared to the conventional impregnation was chosen by milling the dry compounds in a planetary mill. To get a closer insight into the spreading and oxidation properties of antimony oxide on titania, only the binary oxidic compounds Sb oxide and TiO2 as support were investigated in the present study. Photoelectron spectroscopy (XPS) investigations for surface analysis and X-ray absorption spectroscopy (XANES) for bulk phase analysis were applied. The various Sb oxides (Sb2O3, Sb2O4, and Sb2O5) show totally different spreading behavior. Only with the Sb(III) oxide on titania a significant increase of dispersion was detectable by means of XPS and temperature programmed reduction (TPR). The temperature of oxidation of the supported Sb(III) oxide in air was 100 °C lower as compared to the bulk phase oxidation. The final formula after oxidation of Sb(III) oxide can be calculated from XANES results as Sb6O13 and does not end up at a stoichiometry of Sb2O4.