Mesostructured SiO 2-doped TiO 2 with enhanced thermal stability prepared by a soft-templating sol–gel route

Abstract

Mesostructured SiO 2–TiO 2 mixed oxides have been prepared by a soft-templating sol–gel route, using a non-ionic triblock copolymer as structure-directing agent. Tetraethylorthosilicate (TEOS) and titanium tetraisopropoxide (TTIP) have been employed as Si and Ti sources, respectively. Using a prehydrolysis TEOS step allows mixed oxides to be produced with a homogeneous porosity and with no phase segregation, in a wide range of Si/Ti compositions. Both the hydrolysis molar ratio and the silicon content have been found to be important factors determining the final properties of these materials. For instance, mixed oxides containing low silicon concentrations exhibit N 2 physisorption isotherms typical of mesoporous materials, although with an important contribution of microporosity. On the other hand, increasing the hydrolysis molar ratio makes more difficult to reach a total dispersion of SiO 2 through the TiO 2 matrix. Even with low SiO 2 loadings, the thermal stability is effectively enhanced, when compared to the equivalent pure TiO 2 materials, as a consequence of a delay in the titania crystallization to anatase. Thus, after calcination at 300 °C for 3 h, mixed oxides containing low Si/Ti ratios (⩽20/80) show BET surface area in the range 290–346 m 2/g, while pure TiO 2 materials largely collapse under the same treatment and their BET surface area drop strongly to values around 125 m 2/g. This synthesis route, therefore, provides mesoporous TiO 2-rich materials with enhanced stability and textural properties, which is of high interest for applications as catalysts and supports.