Synthesis of ordered mixed titania and silica mesostructured monoliths for gold catalysts

Mesostructured silica-titania mixed oxide monoliths, in which the nanocrystalline titania is well dispersed inside the silicate framework, have been synthesized by a liquid crystalline templating approach in combination with sol-gel processing. Control over the different hydrolysis and condensation rates of silicon and titanium alkoxides was achieved by complexation of the titanium species to the poly(ethylene oxide) (PEO) part of a block copolymer, such as Pluronic F108. The block copolymer serves two distinct functions: (a) as a structure-directing agent and (b) as a moderator of the hydrolysis rate of titanium alkoxide. The amorphous titania inside the silica framework is converted by calcination treatment into anatase phase TiO ₂ incorporated on the silica. The structure and composition of the resulting material was characterized by X-ray diffraction, UV-visible absorption spectroscopy, Raman spectroscopy, and transmission electron microscopy. The monoliths have an ordered mesostructure with very small crystallites of anatase TiO ₂ located within the mesopores. We show that the mixed oxide monoliths are excellent support materials for gold catalysts.