TiO2 on magnesium silicate monolith: effects of different preparation techniques on the photocatalytic oxidation of chlorinated hydrocarbons

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 (TiO2) as active phase on a magnesium silicate support, by means of different procedures: (i) incorporation of commercial TiO2 powder into the silicate matrix (“massic monolith”); (ii) sol–gel coating of the silicate support; (iii) impregnation with a commercial TiO2 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” TiO2 powder. In the second case, a magnesium silicate monolith was coated with several layers of an aqueous TiO2 sol prepared from hydrolysis and condensation of titanium tetra-isopropoxide (Ti(OC3H7)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” TiO2 powder water suspension. All the catalysts were thermal treated under comparable conditions in order to fix the TiO2 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.