Wet air oxidation of phenol at mild conditions with a Fe/activated carbon catalyst

A home-made Fe/activated carbon (Fe/AC) catalyst has been tested for the wet oxidation of phenol in a cocurrent down-flow fixed bed reactor at relatively mild conditions (100–127 °C and PO2PO2 = 8 atm), initial pH of 3.5 and a wide range of spatial time values (20–320 gCAT h/gPh). Complete phenol conversion and 80% TOC removal were reached at 127 °C and 320 gCAT h/gPh. The Fe/AC catalyst has also shown a convenient chemical stability in long-term experiments, Fe leaching being almost negligible. It has been proved that oxidation of phenol takes place on the catalyst surface via a heterogeneous mechanism, the contribution of homogeneous reaction being no significant. The oxidation intermediates have been identified, consisting of ring intermediates (p-benzoquinone, p-hydroxybenzoic and traces of hydroquinone) that are further oxidized to short chain acids (mainly maleic, malonic, acetic and formic acids). The three last showed to be highly resistant to further oxidation, these being the responsible of the TOC remaining after complete removal of phenol.