WO3/CeO2 nanocomposite powders:: Synthesis, characterization, and reactivity

WO3/CeO2 nanocomposite powders, characterized by increasing W/Ce atomic ratio, were prepared by depositing, by wet impregnation, different amounts of WO3 on the CeO2 surface. The powders were characterized by means of X-ray photoelectron and diffuse reflectance infrared Fourier transform spectroscopic techniques as well as thermal analysis. The WO3/CeO2 samples are slightly reduced with respect to the pure oxides: the presence of W( V) and Ce( III), in addition to W( VI) and Ce( IV), is evident at the interface supported/ supporting oxides. Interesting information concerning particle dimensions and growth mode derive by X-ray diffraction and transmission electron microscopy. New acidic/basic and redox sites are evident on the surface of the WO3/CeO2 nanocomposites. The interaction with methanol was also investigated. Methanol interacts both molecularly and dissociatively with the WO3/CeO2 surface; the dissociation is prevalent on the sample characterized by a lower content of WO3, whereas a mainly molecular interaction is observed with increasing amount of tungsten oxide. Oxidation of methanol is evident from T g 423 K on the sample with [ W/Ce](nominal) = 0.025 and from T >= 473 K on the one richer in WO3. The reactivity toward methanol oxidation is higher in the sample with a lower content of WO3, but the sample richer in WO3 shows a higher selectivity with respect to formation of carbon dioxide.