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Ruthenium catalysts (1–5 wt%) were prepared by exchange or impregnation of different supports: CeO₂, TiO₂, or ZrO₂. Their activity for acetic acid oxidation in aqueous solutions was investigated in a batch reactor (20 bar O₂, 0.083M CH₃COOH, 200°C). Ru catalysts supported on a high-surface area ceria have an excellent activity for the title reaction. The following order of activity was obtained: Ru>Ir>Pd≈Fe≈Cu>Ag≈Ni≈Co≈Cr≈unpromoted CeO₂, which can be correlated with the tendency of the metals to remain in the metallic form. The operating Ru/CeO₂ catalyst would be composed of large Ru⁰ particles with surface Ruⁿ⁺ species: the prereduced catalysts are more active than the preoxidized ones and turnover frequencies are higher on the larger Ru particles which are less oxidizable. The catalysts were examined by XRD and TEM before and after the oxidation reaction. Only metallic Ru could be seen …