Study of the Structure, Acidic, and Catalytic Properties of Binary Mixed-Oxide MoO 3 −ZrO 2 Systems

Abstract : Binary mixed-oxide materials based on MoO3−ZrO2 (1−68 wt/wt MoO3 nominal content) were prepared by a sol−gel method. The samples were characterized after calcination at 873 K by X-ray diffraction, Raman, UV−vis, and infrared spectroscopy. An increase in the molybdenum content produces an increase in the surface area up to ca. 140 m2 g-1 for a nominal MoO3 content of ca. 20 wt/wt. Simultaneously, the progressive generation of Brönsted acid sites attributed to the presence of surface polymolybdate species takes place. The Zr(MoO4)2 crystalline phase coexists with polymolybdate species for catalysts with a nominal MoO3 content higher than 20 wt/wt. These samples show a lower surface area, but the number of Brönsted acid sites per unit of surface area remains almost constant up to ca. 30 wt/wt MoO3 content. A relationship between the structure of molybdenum surface species, the surface acidity determined by the adsorption of 2,6-dimethylpyridine, and the catalytic behavior of materials in the 2-propanol dehydration are reported.