Catalytic wet peroxide oxidation of phenol over Fe/AC catalysts: Influence of iron precursor and activated carbon surface

Different activated carbon-supported Fe catalysts have been prepared and tested in CWPO of phenol. Three well characterized activated carbons and two iron precursors (iron nitrate and iron pentacarbonyl) have been used. The behavior of these catalysts in CWPO has been related with their porous structure, surface composition, in terms of oxygen groups and Fe distribution onto the catalyst particles. The catalysts with a more uniform distribution of Fe showed a higher oxidation activity than the ones with an internal (egg-yolk type) or external (egg-shell type) distribution. These last provoke a faster decomposition of H2O2 mainly to O2, non-reactive at the mild reaction temperature used (50 °C). No significant differences were observed from the iron precursors. Complete conversion of phenol and almost 80% mineralization were obtained in less than 2 h with the best catalyst. The residual by-products consisted in short-chain organic acids without significance in terms of toxicity. Fe leaching was observed in all the cases which can be mainly attributed to the presence of oxalic acid as oxidation by-product, refractory to the CWPO process investigated. The intensity of Fe leaching was related with the concentration of oxalic acid.