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p-Hydroxybenzoic acid (p-HBZ) degradation was achieved using catalytic wet hydrogen peroxide oxidation over Fe/TiO 2 and Ru-Fe/TiO 2 under mild conditions. The results showed that 71 % of p-HBZ conversion was obtained after 10 min of reaction over the 0.5Ru-3Fe/ TiO 2 catalyst calcined under oxygen. The influence of the H 2 O 2 /p-HBZ molar ratio (5:1, 10:1 and 15:1), reaction temperature (25, 40 and 60°C), Fe loading (1, 2 and 3 wt%) and thermal treatment was studied. Characterization studies were performed by X-ray diffraction, N 2 physisorption at 77 K, H 2 -TPR and elemental analysis, showing that close interaction between Ru and iron oxide species is necessary to obtain active and stable catalysts. Graphical Abstract 0.5Ru-3Fe/TiO 2 C catalyst shows a high activity for the degradation of p-HBZ at 60°C by CWHPO in the presence of H 2 O 2 . The system could be considered as a Fenton-like reaction due to the generation of radicals from H 2 O 2 as well as the presence of iron sites on the catalyst.

Catalytic wet air oxidation using heterogeneous catalysts is a promising technology for treatment of wastewaters. Wastewaters from olive oil mills are difficult to clean because effluents contain high levels of phenolic compounds that cannot be removed by biological treatment or incineration. Therefore, we tested the catalytic wet air oxidation of p-hydroxybenzoic acid, as model molecule of olive oil mills wastewaters, over Ru-supported CeO2–TiO2 mixed oxides. We focussed on the Ce/Ti molar ratio because this ratio modifies the properties of the Ru catalysts. Supports were prepared by using the sol–gel method. The Ru catalysts were prepared by impregnation. Those products were characterized by N2 adsorption–desorption, X-ray diffraction, H2 chemisorption, transmission electron microscopy and inductively coupled plasma. Catalytic wet air oxidation of p-hydroxybenzoic acid was performed in a batch reactor at 140 °C and 50 bar of air. Our results show that the most efficient catalyst was Ru with a Ce/Ti ratio of 1/5, which converted totally p-hydroxybenzoic after 7 h of reaction without Ru leaching. We explain this finding by an enhanced dispersion of Ru due to better structural properties of the CeO2–TiO2 support.© 2015, Springer International Publishing Switzerland.Postprint (author's final draft