Fe/SiO₂ heterogeneous Fenton catalyst for continuous catalytic wet peroxide oxidation prepared in situ by grafting of iron released from LaFeO₃

Functionalization of silica-gel by immobilization of iron ions at its surface was carried out through a novel method - selective extraction-deposition (SED) in acidic solution using LaFeO₃ orthoferrite with perovskite structure as a solid precursor. Isolated Fe-ions produced as a result of precursors decomposition in acidic aqueous solution were trapped by silica surface silanols. The presence of iron in the only one state of isolated surface ions over 2wt%Fe/SiO₂ material at the Fe content corresponded to surface silanols concentration was confirmed using ESR, Mossbauer spectroscopy, UV Raman, FTIR and XPS techniques. Catalytic performance of 2wt% Fe/SiO₂ was examined toward catalytic wet peroxide oxidation (CWPO) of phenol in up flow fixed bed reactor at pH 4, 80°C, LHSV 6h^-1 with 200ppmw phenol and 1300ppmw hydrogen peroxide in water. It was demonstrated that mixing of LaFeO₃ with silica-gel gives an advanced catalytic material with high activity (TOC removal of 90%) and stability without iron leaching. This effect is due to dynamic behavior of iron that includes its SED-leaching-condensation along the catalysts layer. In this case, the LaFeO₃ has a multiple function-active catalytic component, precursor of iron ions and buffer controlling the pH along the catalysts layer.