Ceria-modified zirconia and their effects on the molybdenum oxide dispersion

摘要

The CeO_2 -modified ZrO_2 support was impregnated in an aqueous solution of ammonium heptamolybdate to achieve a loading of 8 wt.% Mo. This material (Mo/Zr(Ce)) was characterized, in comparison with Mo/Zr, by X-ray diffraction, FT-IR and UV―VIS diffuse reflectance spectroscopy as well as low temperature N_2 adsorption and electrical conductivity measurements. The X-ray results showed that the particles size of MoO_3 on Zr(Ce) (24.7 nm) was lower than those on ceria free Zr (36.7 nm). The IR results indicated that a strong interaction between Mo species and zirconia was recognized in the Mo/Zr(Ce) sample by the appearance of a new band at 858 cm~(-1) attributed to a Mo―O―Zr linkage, which was not detected in the Mo/Zr sample. The UV―VIS spectra showed that both octahedral (291 nm) and tetrahedral (249 nm) Mo~(6+) were detected in the Mo/Zr sample where tetrahedral arrangement (246 nm) was only adopted for Mo~(6+) in the Mo/Zr(Ce) sample. The addition of either Ce or Mo to zirconia causes a marked increase in the specific surface area of the samples. The conductivity measurements showed that all samples exhibit a semiconducting behavior.