Synthesis, pore texture and surface acid–base character of TiO 2/carbon composite xerogels and aerogels and their carbonized derivatives

Abstract

Synthesis of TiO 2/C composite xerogels and aerogels were obtained by polymerization of a mixture of resorcinol, formaldehyde and tetrabutyl orthotitanate. Samples so obtained were dried with supercritical CO 2 (aerogel) or at 110°C in an oven (xerogel). The aerogel was prepared with two different initial TiO 2 contents of 30 and 49%. Both aerogels and the xerogel were subsequently carbonized in an inert atmosphere at 500 and 900°C. Surface area and porosity of the samples were measured by CO 2 adsorption at 273 K and mercury porosimetry; X-ray diffraction (XRD) technique was used to determine the crystallographic structure of the inorganic constituent of the composite (anatase or rutile); and acid–base surface characteristics of these materials were studied by testing them as catalysts in the decomposition reaction of isopropanol. Finally, some of these samples were used as supports for tungsten oxide catalysts and also tested in the above reaction. The composite aerogel with the lower TiO 2 content and its carbonized derivatives had the more developed meso- and macroporosity, indicative of the importance of both the supercritical drying process of these materials and of the TiO 2 content. In this case, the composite aerogel carbonized at 500°C had the highest activity of propene production and therefore, the highest surface acidity, because of the good accessibility of the surface acid sites. The tungsten oxide catalyst supported on it also presented the highest conversion in the above reaction, although in this case acetone and diisopropyl ether were also obtained.