A Study on the Surface Properties of Ceria-Supported Tungsten and Copper Oxides

Abstract

Laser Raman spectroscopy (LRS), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), ultraviolet and visible diffuse reflectance spectroscopy (UV-DRS), and temperature-programmed reduction (TPR) are used to characterize a series of WO 3 /CeO 2 samples. The results indicate that the dispersion capacity of tungsten oxide is about 4.8W 6+ ions nm -2 (CeO 2 ) and the structure of the supported tungsten oxide species is closely related to its loading amount on ceria. For the calcined samples, two distinctly different tungsten species have been identified by various methods. At low WO 3 loading, only the highly dispersed tungsten oxide species are found on the surface possibly formed by the incorporation of the dispersed W 6+ ions into the surface vacant sites of CeO 2 . Increasing the loading amount of tungsten oxide to a value above 4.8W 6+ ions nm -2 (CeO 2 ) leads to the formation of crystalline WO 3 . LRS and IR results of WO 3 /CeO 2 samples prepared by using different precursors have shown that calcination has a dramatic effect on the structure of the final product, which might mostly eliminate the differences of the precursors and result in final products with almost a same structure. TPR results of WO 3 / CeO 2 , CuO/CeO 2 , and CuO/WO 3 -CeO 2 samples reveal that the reduction behaviors of CuO dispersed on CeO 2 and on WO 3 premodified CeO 2 , i.e., WO 3 -CeO 2 , are apparently different. The result emphasizes the importance of the surface structure of the support on the properties of the dispersed metal oxide species; the conclusion is also supported by UV-DRS results. The coordination environments of the dispersed tungsten oxide and copper oxide species are discussed on the basis of the incorporation model (Chen, Y.; Zhang, L.

Effect of titania structure on the properties of its supported copper oxide catalysts

“…It is extremely challenging to measure the individual XRD intensity of crystalline CuO in this case. Therefore, X-ray photoelectron spectroscopy was carried out to determine the dispersion behavior of copper oxide on rutile, as reported elsewhere [32]. Fig.…”

“…5 shows the relationship between the ratio of XPS intensity of Cu2p and Ti2p and copper oxide loadings. The x-value of the intercept of two straight lines represented the dispersion capacity of copper oxide on rutile [32], which was $0.96 mmol/100 m 2 . Clearly, the dispersion capacity of copper oxide on rutile is higher than that on anatase.…”

“…This seems to suggest that Cu d+ might be stable on a rutile surface. On the other hand, considering the similar reduction behavior of dispersed copper oxide species in the rutile-supported sample with that in the ceria-supported sample under XPS measurement, it is reasonable to assume they could have similar reduction behaviors during TPR measurements and dispersed copper oxide species in the CuO/ CeO 2 sample were stepwise reduced in TPR measurements [32]. Accordingly, two low temperature reduction peaks centered at $163 and $230°C could be attributed to the reduction of Cu 2+ ?…”

Influence of ferric oxide modification on the properties of copper oxide supported on γ-alumina

“…Therefore, knowledge of the local structure of the catalyst surface and insight into the factors that determine the surface structure play an important role in further development and optimization of supported metal oxide heterogeneous catalytic systems. Accordingly, a large number of studies have been devoted to exploring the interaction between the support and the dispersed oxide species, and various explanations of models concerning the nature of the interaction have been proposed [11][12][13][14][15][16][17].…”

Structural characterization of Th-doped TiO2 photocatalyst and its extension of response to solar light for photocatalytic oxidation of oryzalin pesticide: a comparative study

“…It is reported that in the case of metal oxides, there is a critical value of dispersion capacity. At values lower than which the oxide might become highly dispersed on the support without the formation of a separate crystalline phase [37,38]. Since no characteristic peaks corresponding to Th species is…”