SO42-/TiO2-SiO2 mixed oxide catalyst, I: Synthesis, characterization, and acidic properties

A series of sulfate-doped titania-silica mixed oxides have been prepared by immersing titania-silica gel in the required volume of sulfuric acid, foll owed by drying. The mixed oxide gel is obtained by hydrolyzing an equimolar mixture of tetraethylorthosilicate (TEOS) and tetrabutylorthotitanate (TBO T) at pH 3. The materials, after calcining at 723 K for 4 h, are characteri zed by XRD, FT-IR, the BET method, and surface acid strength by the Hammett indicator method. The catalytic activity tests are carried in a fixed bed catalytic reactor (i.d. = 10 mm) for alcohol conversion, whereas cumene cra cking/dehydrogenation reactions are carried out in a micropulse reactor. XR D results shows that the titania-silica mixture is amorphous and the crysta llization starts with sulfation. The surface of the mixed oxide contains bo th bridged and normal hydroxyl groups, as observed from FT-IR data. The sur face area of the material is not much altered by sulfation and lies within 50 m(2)/g, The acid strength of 4 wt% SO42-/TiO2-SiO2 is found to be strong er than that of 100% concentrated H2SO4. In the case of 2-propanol conversi on, low acetone selectivity indicates the presence of weak basic sites, whe reas methanol conversion over all solids shows that dehydration follows a p arallel and consecutive pathway. A good correlation is found between the cu mene cracking and the acidity of the catalysts. (C) 1999 Academic Press.