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/m³ (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[sbnd]CeO₂> Pd/CuOCeO₂> Pd/ZnOCeO₂> Pd/CeO₂. Pd/ZrO₂[sbnd]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.