Complete oxidation of toluene on Pd/modified-CeO2 catalysts

In this study, a series of 0.5 wt% Pd/modified-CeO2 catalysts with different metal additives were prepared by incipient-wetness impregnation method. The samples were characterized by powder X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. The catalysts were tested for total oxidation of toluene, the feed concentration was 8.564 g/m(3) (2085 ppm) with GHSV of 10,000 h(-1). The XRD patterns only showed intense CeO2 peaks, no characteristic peak for palladium and additive oxides were observed, inferring that the particle size of palladium was less than 4 nm and additive oxide was also well-dispersed. The TEM images confirmed that the average particle size of palladium was 2-4 nm and they were well dispersed on the support. After loading different modifiers, the concentration of metallic palladium species increased. The activities of the catalysts decreased in the order: Pd/ZrO2CeO2>Pd/MnO2-CeO2> Pd/CuOCeO2>Pd/ZnOCeO2>Pd/CeO2. Pd/ZrO2-CeO2 showed the highest activity among all catalysts. The presence of additives increased the oxygen storage of CeO2. Adding additives on the Pd/CeO2 created the synergetic effect, resulting in high activity for complete oxidation of toluene. (C) 2016 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.