Preparation of Titania−Silica Mixed Oxides by a Sol−Gel Route in the Presence of Citric Acid

Abstract

Titania−silica mixed oxides (denoted as TiO2−SiO2) with different Ti contents are prepared by a sol−gel route in the presence of citric acid (CA). Various characterization techniques, including XRD, FT-IR, N2-adsorption, TEM, solid-state CP-MAS NMR spectroscopy, UV−vis, and NH3-TPD, have been carried out to investigate the physical−chemical properties, states of Ti species, and the formation process of TiO2−SiO2 materials. The characterization results show that the TiO2−SiO2 materials possess a mesoporous silicate framework with high specific surface area and thermal stability. Titanium species in the TiO2−SiO2 materials are mainly present in the form of two-dimensional low polymeric TiOx species, which are uniformly dispersed on the surface of mesoporous silica. Additionally, the titanium species have a strong resistence to high-temperature sintering, even for the sample with high Ti contents (25 wt %). Weak acid sites are observed over TiO2−SiO2 materials, and the amount of acidic sites increases with t...