The CeO2-modified ZrO2 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, adsorption and electrical conductivity measurements. The X-ray results showed that the particles size of MoO3 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) Mo6+ were detected in the Mo/Zr sample where tetrahedral arrangement (246 nm) was only adopted for Mo6+ in the Mo/Zr(Ce) sample. The addition of either Cc 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. (C) 2002 Elsevier Science B.V. All rights reserved.