Influence of the meso-macroporous ZrO2-TiO2 calcination temperature on the pre-reduced Pd/ZrO2-TiO2 (1/1) performances in chlorobenzene total oxidation

The effect of two calcining temperatures (400 degrees C, 600 degrees C) on the texture, structure and thermal stability of a meso-macroporous ZrO2-TiO2 of equal molar amount (ZrTix; x = 4, 6) synthesized from hydrothermal conditions using a surfactant and metal alkoxide precursors was studied. Pd (0.5 wt.%) was dispersed on these innovative supports (Pd/ZrTix; x = 4, 6) by a classic wet impregnation and calcined at 400 degrees C. The resulting catalysts were characterized by Elemental analysis (EA), X-Ray Diffraction (XRD), N-2 adsorption-desorption, H-2-Temperature Programmed Reduction (H-2-TPR), Pd dispersion and tested as pre-reduced in the total oxidation of chlorobenzene. It was found that the calcination temperature did not provoke a significant effect on the physicochemical properties of the resulting binary oxide except the acidity which significantly decreased. The support was stable against phase transformation upon calcination as no crystalline phase could be detected indicating a homogeneous mixing of the Zr and Ti components. The Specific Surface Areas (SSAs) were superior to 400 m(2)/g even after calcination at 600 degrees C. The Pd dispersion was around 40% and the palladium was totally reduced before catalytic testing. Lowering the temperature of calcination of the support enhanced the performances of the catalyst. Indeed PhCl conversion increased as the calcination temperature decreased and correlates with the Pd dispersion and SSA of the catalyst. A significant amount of polychlorinated benzenes PhClx (x = 2-6) was detected in the course of the reaction which practically disappeared at 100% PhCl conversion. This amount was reduced by a factor 2 as the temperature of calcination decreased. Compared to the performances of Pd/Ti-x and Pd/Zr-x for the same reaction, all things being kept equal, calcined ZrO2-TiO2 supports show higher surface areas and higher thermal stability than their ZrO2 and TiO2 counterparts. In terms of activity for PhCl total oxidation based on T-50 values the ZrO2-TiO2 supports showed an intermediate behaviour while a beneficial effect was observed regarding the by-products production which is the lowest herein for the Pd/TiZr4 catalyst. (C) 2011 Elsevier B.V. All rights reserved.