Ruthenium nanoparticles supported on CeO₂ for catalytic permanganate oxidation of butylparaben

This study developed a heterogeneous catalytic permanganate oxidation system with ceria supported ruthenium, Ru/CeO₂ (0.8‰ as Ru), as catalyst for the first time. The catalytic performance of Ru/CeO₂ toward butylparaben (BP) oxidation by permanganate was strongly dependent on its dosage, pH, permanganate concentration and temperature. The presence of 1.0 g L^-1 Ru/CeO₂ increased the oxidation rate of BP by permanganate at pH 4.0-8.0 by 3-96 times. The increase in Ru/CeO₂ dosage led to a progressive enhancement in the oxidation rate of BP by permanganate at neutral pH. The XANES analysis revealed that (1) Ru was deposited on the surface of CeO₂ as Ru^III; (2) Ru ^III was oxidized by permanganate to its higher oxidation state Ru^VI and Ru^VII, which acted as the co-oxidants in BP oxidation; (3) Ru^VI and Ru^VII were reduced by BP to its initial state of Ru^III. Therefore, Ru/CeO₂ acted as an electron shuttle in catalytic permanganate oxidation process. LC-MS/MS analysis implied that BP was initially attacked by permanganate or Ru^VI and Ru^VII at the aromatic ring, leading to the formation of various hydroxyl-substituted and ring-opening products. Ru/CeO₂ could maintain its catalytic activity during the six successive runs. In conclusion, catalyzing permanganate oxidation with Ru/CeO₂ is a promising technology for degrading phenolic pollutants in water treatment.