Effect of ceria-doped titania on the structure and acidic properties of MoO3/TiO2 catalysts Original Research Article

To explore the influence of CeO2 doped TiO2 support on the dispersion, structure and acidic properties of molybdenum oxide species, an investigation was undertaken by using XRD, N2 adsorption, FTIR and UV-Vis diffuse reflectance techniques in addition to in situ FTIR-pyridine study. In this work, the MoO3/TiO2 and MoO3/TiO2(CeO2) samples were prepared, at the 8 wt.% Mo loading, by incipient wetness impregnation method. The characterization results suggest that the Mo state in the calcined (773 K) MoO3/TiO2 sample is in X-ray amorphous character and exhibit reasonably higher specific surface area (319 m2 g−1) than that of MoO3/TiO2(CeO2) (273 m2 g−1). The former support also accommodates a sub-monolayer equivalent of MoO3 (8 wt.%) in a highly dispersed state. The UV-Vis spectra indicated that the dispersed Mo in the MoO3/TiO2 sample is in tetrahedral coordination where it is in octahedral coordination on the MoO3/TiO2(CeO2) sample that showed discrete amounts of bulk MoO3 species. It was revealed also that the presence of Ce retarded the strong association rendered between molybdena and titania and thus, an over-layer of MoO3 was detected; as indicated by IR spectroscopy (1067 cm−1), paralleled with an appearance of high intense and sharp XRD lines of TiO2 proposing sintering of the support. The latter result brings up activation of the TiO2 anatase as discrete phase in MoO3/TiO2 (CeO2) as detected from UV-Vis; 380–400 nm. In situ FTIR spectra of pyridine adsorbed on the samples have revealed the following results (i) all the samples exhibit Lewis and Bronsted acid sites (ii) the TiMo and TiCeMo samples exhibit higher Bronsted acidity (1645–1636 and 1543 cm−1) than that of TiCe and rather presented basic sites similar to those offered by TiCe but of lower concentration.