Effect of the crystallite size in the structural and textural properties of sulfated and phosphated titania

Sulfated and phosphated titania (TiO2) were obtained by the sol–gel method. The sulfation was prepared in situ using sulfuric acid as hydrolysis catalyst, or by impregnation with ammonium sulphate. Phosphated sol–gel titania was synthesized with phosphoric acid. Long thermal treatments were carried out from 100 to 1000 8C to study the crystallization process of titania. All present phases were nanocrystalline, and the anatase–rutile polymorphic transformation was dependent on the crystallite size of the materials and on the preparation method. The smallest crystallite values were obtained for the phosphated samples. Titania sulfated by impregnation was found to be an efficient and selective catalyst towards propene, whereas di-isopropylether was obtained only in the catalyst prepared in situ with H2SO4.