Molybdenum(VI) species have been deposited on zirconia materials by adsorption equilibrium procedures using two precursors: (i) an isopolyanion salt: ammonium heptamolybdate and (ii) low-nuclearity oxoperoxo molybdenum complexes. Two zirconia supports have been considered: calcined zirconia (ZrO2) and the parent zirconium oxyhydroxide (ZrOx(OH)(4-2x)). After drying, the catalysts have been calcined and characterized by chemical analysis, powder X-ray diffraction, thermogravimetry, Raman and UV-vis diffuse reflectance spectroscopies, X-ray photoelectron spectroscopy, nitrogen physisorption experiments, and TEM and EDX analysis. In contrast to ZrO2, quantitative grafting of molybdenum species can be obtained when zirconium oxyhydroxide is used. With this material, the anchoring of low-nuclearity oxoperoxo species leads to higher specific surface areas than with ammonium heptamolybdate, and hence to lower molybdenum surface densities. (C) 2007 Elsevier B.V. All rights reserved.