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 2 wt%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 2 wt% Fe/SiO2 was examined toward catalytic wet peroxide oxidation (CWPO) of phenol in up flow fixed bed reactor at pH 4, 80 °C, LHSV 6 h−1 with 200 ppmw phenol and 1300 ppmw 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.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Selective extraction deposition (SED) method proposed to prepare solid catalyst containing isolated iron sites. ► CWPO of phenol with in situ deposition of iron ions demonstrated high TOC removal (90%) and stability. ► Dynamic behavior of iron that includes its SED–leaching–condensation along the catalysts layer was observed.