Chlorobenzene total oxidation over palladium supported on ZrO2, TiO2 nanostructured supports

Two series of supported Pd catalysts were synthesized on new mesoporous–macroporous supports (ZrO2, TiO2) labelled M (Zr and Ti). The deposition of palladium was carried out by wet impregnation on the calcined TiO2 and ZrO2 supports at 400 °C (Pd/Zr4, Pd/Ti4) and 600 °C (Pd/Zr6, Pd/Ti6) and followed by a calcination at 400 °C for 4 h. The pre-reduced Pd/MX catalysts were investigated for the chlorobenzene total oxidation and their catalytic properties where compared to those of a reference catalyst Pd/Ti-Ref (TiO2 from Huntsman Tioxide recalcined at 500 °C) and of a palladium supported on the fresh mesoporous–macroporous TiO2 (Pd/Ti). Based on the activity determined by T50, the Pd/Ti and Pd/Ti4 catalysts have been found to be more active than the reference one. Moreover activity decreased owing to the sequence: Pd/TiX ≫ Pd/ZrX and in each series when the temperature of calcination of the support was raised. The overall results clearly showed that the activity was dependant on the nature of the support. The better activity of Pd/TiX compared to Pd/ZrX was likely due to a better reducibility of the TiO2 support (Ti4+ into Ti3+) leading to an enhancement of the oxygen mobility. Production of polychlorinated benzenes PhClx (x = 2–6) and of Cl2 was also observed. Nevertheless at 500 °C the selectivity in HCl was higher than 90% for the best catalysts.