Supported and mixed oxide catalysts based on iron and titanium for the oxidative decomposition of chlorobenzene
Iron oxide supported on titanium dioxide (Fe2O3/TiO2) and iron–titanium mixed oxide (Fe–Ti-oxide) catalysts were prepared via wetness impregnation and sol–gel methods, respectively. The catalytic activity of the two materials for the oxidation of chlorobenzene was studied and compared with the activity of pure titanium and iron oxides as well as MgO-supported iron oxide. Fe2O3/TiO2 and Fe–Ti-oxide have shown higher catalytic activities for the oxidation of chlorobenzene than the corresponding pure iron and titanium oxides at a reaction temperature of 325 °C, and this enhanced activity was more pronounce at higher temperatures. The Fe–Ti-oxide, in particular, exhibited a unique activity for the complete oxidation at relatively low temperature, 325 °C, without the formation of other chlorinated organics. Chlorine, measured by iodometric titration was the only Cl-containing product. The absence of HCl as a product and the negative effect of water suggest that the surface active sites are more likely to be Lewis acid–base sites on which chlorobenzene molecules dissociatively adsorb forming metal–Cl bonds and surface phenolate intermediates. Desorption of Cl2 from the surface and possible interaction of the aromatic ring with metal sites result in the activation of the ring forming partially oxidized intermediates involving lattice oxygen ions. Finally, reactions with molecular oxygen result in the complete oxidation to CO2 and regenerate the surface.
Journal: Applied Catalysis B: Environmental - Volume 80, Issues 1–2, 15 April 2008, Pages 176–184