Effect of niobium on the surface properties of Nb2O5-SiO2-supported Mo catalysts

Nb2O5–SiO2 oxides with different Nb content (0.8–4.4 wt.%) were prepared by impregnation of silica with ethanol solution of niobium ethoxide, Nb(OC2H5)5. Mo catalysts supported on the Nb2O5-SiO2 carriers were prepared by wetness impregnation method of the supports with an aqueous solution of ammonium heptamolybdate, (NH4)6Mo7O24. The samples were characterized by X-ray photoelectron spectroscopy (XPS) and diffuse reflectance spectroscopy (DRS). The chemical state and dispersion of metal components (Nb and Mo) were studied in the oxides and Mo-containing catalysts. It was shown a good correlation between the amount of Nb and XPS intensity Nb/Si ratios in oxide supports. Generation of new acid sites (Lewis and Brönsted) in Nb2O5-SiO2 samples was easily understood when considering the change in the binding energies of Nb 3d and O 1s photoelectrons, due to a strong interaction between Nb atoms and silica. It was found that addition of niobium improves the dispersion of molybdenum on silica.