Synthesis, pore texture and surface acid-base character of TiO2/carbon composite xerogels and aerogels and their carbonized derivatives

Synthesis of TiO2/C composite xerogels and aerogels were obtained by polyme rization of a mixture of resorcinol, formaldehyde and tetrabutyl orthotitan ate. Samples so obtained were dried with supercritical CO2 (aerogel) or at 110 degrees C in an oven (xerogel). The aerogel was prepared with two diffe rent initial TiO2 contents of 30 and 49%. Both aerogels and thr xerogel wer e subsequently carbonized in an inert atmosphere at 500 and 900 degrees C. Surface area and porosity of the samples were measured by CO2 adsorption at 273 K and mercury porosimetry; X-ray diffraction (MD) technique was used t o 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 decomposi tion reaction of isopropanol. Finally, some of these samples were used as s upports for tungsten oxide catalysts and also tested in the above reaction. The composite aerogel with the lower TiO2 content and its carbonized deriv atives had the more developed meso- and macroporosity, indicative of the im portance of both the supercritical drying process of these materials and of the TiO2 content. In this case, the composite aerogel carbonized at 500 de grees C had the highest activity of propene production and therefore, the h ighest surface acidity, because of the good accessibility of the surface ac id sites. The tungsten oxide catalyst supported on it also presented the hi ghest conversion in the above reaction, although in this case acetone and d iisopropyl ether were also obtained. (C) 2000 Elsevier Science B.V. All rig hts reserved.