Synthesis and characterization of mesoporous materials: Silica–zirconia and silica–titania

An experimental strategy was developed to obtain mesoporous SiO2–ZrO2 and SiO2–TiO2 mixed oxides by a sol–gel method, treating the gels hydrothermally. The solids were characterized by nitrogen physisorption, pyridine thermodesorption, 29Si nuclear magnetic resonance, SEM and X-ray diffraction. The effects of ZrO2 content, the generated pressure in the synthesis vessel and further modification of this type of procedure on the solids properties were studied. It was found that SiO2–ZrO2 and SiO2–TiO2 mixed oxides dried at atmospheric pressure developed type I isotherms. On the other hand, for the SiO2–ZrO2 and SiO2–TiO2 mixed oxides that were treated under pressure in the autoclave (at high SiO2 content) the porosity was improved and mesoporous materials exhibiting type IV adsorption isotherms. Specific surface area and pore size distribution were a function of ZrO2 and TiO2 content. The materials exhibited narrow pore size distributions with pore diameters in the region of mesopores at about 4 nm and high surface areas, the highest being 481 m2/g for the 10 wt% ZrO2 Si–Zr material. Differences in acidity as determined by pyridine thermodesorption were observed to depend on the synthesis parameters and ZrO2 and TiO2 concentration.