Active iron species in the catalytic wet peroxide oxidation of phenol over pillared clays containing iron

Phenol oxidation by hydrogen peroxide was performed on iron containing clays, pillared by Al or mixed Al–Fe complexes. The Al–Fe pillared clay has shown good performances towards the total phenol oxidation (80% of TOC abatement at 70 °C). From ESR characterization, it was deduced that on Al pillared clay, iron is present as isolated species, probably located on the clay layer and as oxide clusters, whereas on Al–Fe pillared clay, in addition of these preceding species, an other isolated species was detected, probably located on the pillars. From the catalytic results, it can be concluded that this latter species catalyzes more efficiently the total phenol oxidation than the others do. A long time (350 h) catalytic experiment in a continuous flow reactor has shown the high stability of the Al–Fe pillared clay, the total amount of dissolved iron by the reaction being less than 5 wt.% of the iron initially contained in the catalyst.