Supported molybdenum oxide on zirconia catalysts were prepared by simultaneous reaction of Zr oxychloride and ammonium heptamolybdate in molten K-Na nitrate eutectic at 773 K. It was shown that Zr(IV) and Mo(VI) salts react in the molten nitrate medium leading to solids of high specific surface areas (up to 200 m(2)/g). The solids consist of small crystallites of tetragonal ZrO2 containing polymolybdate species on their surface. Textural properties of the catalysts and their stability to calcination in air were studied as a function of the initial Mo/Zr ratio in the reaction mixture. Surface polymolybdate species stabilize tetragonal zirconia and improve the textural properties of the system. Surface areas twice those obtained by conventional methods were observed. Catalytic activity of samples was studied by the thiophene hydrodesulfurization reaction. Due to the enhanced surface area, Mo loading could be increased up to 12.5 wt% of Mo without loss of intrinsic activity per Mo atom.