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 TiO2 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 TiO2 located within the mesopores. We show that the mixed oxide monoliths are excellent support materials for gold catalysts.