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

Abstract

An experimental strategy was developed to obtain mesoporous SiO 2–ZrO 2 and SiO 2–TiO 2 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 ZrO 2 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 SiO 2–ZrO 2 and SiO 2–TiO 2 mixed oxides dried at atmospheric pressure developed type I isotherms. On the other hand, for the SiO 2–ZrO 2 and SiO 2–TiO 2 mixed oxides that were treated under pressure in the autoclave (at high SiO 2 content) the porosity was improved and mesoporous materials exhibiting type IV adsorption isotherms. Specific surface area and pore size distribution were a function of ZrO 2 and TiO 2 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 m 2/g for the 10 wt% ZrO 2 Si–Zr material. Differences in acidity as determined by pyridine thermodesorption were observed to depend on the synthesis parameters and ZrO 2 and TiO 2 concentration.