TiO_2 on magnesium silicate monolith: effects of different preparation techniques on the photocatalytic oxidation of chlorinated hydrocarbons

摘要

In this article, the comparative results of the photocatalytic oxidation of trichloroethylene (TCE) alone and a mixture of chlorinated hydrocarbons (trichloroethylene, perchloroethylene and chloroform) in gas phase, obtained with three different monolithic catalysts in a flat reactor frontally illuminated with a Xenon lamp are presented. The three catalysts incorporate titanium dioxide (TiO_2) as active phase on a magnesium silicate support, by means of different procedures: (ⅰ) incorporation of commercial TiO_2 powder into the silicate matrix ("massic monolith"); (ⅱ) sol-gel coating of the silicate support; (ⅲ) impregnation with a commercial TiO_2 aqueous suspension of the same silicate support. In the first case, the massic monolith was made from a 50:50 w/w mixture of magnesium silicate and "Titafrance G5" TiO_2 powder. In the second case, a magnesium silicate monolith was coated with several layers of an aqueous TiO_2 sol prepared from hydrolysis and condensation of titanium tetra-isopropoxide (Ti(OC_3H_7)_4) in excess of acidified water (acid catalysis). The third catalyst was prepared by impregnating the same silicate support with several layers of "Titafrance G5" TiO_2 powder water suspension. All the catalysts were thermal treated under comparable conditions in order to fix the TiO_2 active phase to the silicate support. Although the performance of the massic monolith was better than the sol-gel monolith, the latter is of great interest because this technique allows the chemical composition of the active films to be easily modified.