Laser Raman spectroscopy - A powerful tool for in situ studies of catalytic materials

Advantages and limitations of laser Raman spectroscopy (LRS) as an in situ vibrational spectroscopy for the study of catalytic materials and surfaces under working conditions are discussed. Measurements can be carried out at temperatures as high as 1200 K in controlled atmospheres. Modern instrumentation permits time resolutions in the sub-second regime for materials with high Raman cross sections. Transient studies are thus possible. Several examples are presented of in situ LRS studies including the phase analysis of bismuth molybdate and VPO oxidation catalysts, synergy effects and oxygen exchange in Sb2O3/MoO3 oxide mixtures, intermediates in oxidative coupling of methane, NO decomposition on Ba/MgO catalysts, and transient SERS studies of partial oxidation of methanol on Ag single crystal surfaces and of the reduction of oxide overlayers on electrodeposited Rh layers

Mechanical and Thermal Spreading of Antimony Oxides on the TiO2\mathrm{TiO_2} Surface: Dispersion and Properties of Surface Antimony Oxide Species

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