Vanadium oxide supported on zirconia and modified with MoO3 was prepared by adding Zr(OH)(4) powder into a mixed aqueous solution of ammonium metavanadate and ammonium molybdate followed by drying and calcining at high temperatures. In the case of calcination temperature at 773 K, for samples containing low loading V2O5 below 15 wt.%, vanadium oxide was in a highly dispersed state, while for samples containing high-loading V2O5 equal to or above 15 wt.%, vanadium oxide was well crystallized due to the V2O5 loading exceeding the formation of a monolayer on the surface of ZrO2. The experimental results indicate that the presence of MoO3 and V2O5 retards the crystallization of the zirconia and stabilizes the tetragonal ZrO2 phase without phase transition to cubic ZrO2 phase. The ZrV2O7 and Zr(MoO4)(2) compounds were formed through the reaction of V2O5 and ZrO2 or MoO3 and ZrO2 at 873 K and the compound decomposed into V2O5, MoO3, and ZrO2 at high temperatures, which were confirmed by Fourier transform infrared (FrIR) and Raman spectroscopies, solid-state V-51 nuclear magnetic resonance (NMR), and X-ray diffraction (XRD). IR spectroscopic studies of ammonia adsorbed on V2O5-ZrO2/MoO3 showed the presence of both Lewis and Bronsted acids. (c) 2004 Elsevier B.V. All rights reserved.