Assessment of Fe2O3/SiO2 catalysts for the continuous treatment of phenol aqueous solutions in a fixed bed reactor

Different iron-containing catalysts have been tested for the oxidation of phenol aqueous solutions in a catalytic fixed bed reactor in the presence of hydrogen peroxide. All the catalysts consist of iron oxide, mainly crystalline hematite particles, over different silica supports (mesostructured SBA-15 silica and non-ordered mesoporous silica). The immobilization of iron species over different silica supports was addressed by direct incorporation of metal during the synthesis or post-synthesis impregnation. The synthesis conditions were tuned up to yield agglomerated catalysts with iron loadings between 10 and 15 wt.%. The influence of the preparation method and the type of silica support was evaluated in a catalytic fixed bed reactor for the continuous oxidation of phenol in terms of catalysts activity (phenol and total organic carbon degradation) as well as their stability (catalyst deactivation by iron leaching). Those catalysts prepared by direct synthesis, either in presence of a structure-directing agent (Fe₂O₃/SBA-15(DS)) or in absence (Fe₂O₃/SiO₂(DS)), achieved high catalytic performances (TOC reduction of 65% and 52%, respectively) with remarkable low iron leaching in comparison with their silica-based iron counterparts prepared by impregnation. Catalytic results have demonstrated that the synthesis method plays a crucial role in the dispersion and stability of active species and hence resulting in superior catalytic performances.