Improved catalytic wet peroxide oxidation of phenol over Pt-Fe₂O₃/SBA-15: Influence of platinum species and DFT calculations

In this study, Pt-Fe₂O₃, Pt, and Fe₂O₃ catalysts supported on SBA-15 were prepared for catalytic wet peroxide oxidation (CWPO) of phenol at low temperatures. Pt-Fe₂O₃/SBA-15 and Pt/SBA-15 had higher H₂O₂ decomposition rates at 20 °C compared with that of Fe₂O₃/SBA-15, which is representative of a conventional CWPO catalyst. Although H₂O₂ was decomposed at a higher rate by Pt/SBA-15 than Pt-Fe₂O₃/SBA-15, Pt/SBA-15 barely exhibited any phenol removal activity. Meanwhile, Pt-Fe₂O₃/SBA-15 showed a superior phenol removal activity, indicating that Pt-Fe₂O₃/SBA-15 efficiently utilizes H₂O₂ for the CWPO reaction. To establish a correlation between the H₂O₂ decomposition activity and the phenol removal activity, characterization of the catalysts and density functional theory (DFT) calculations were conducted. TEM, XPS, and H₂-TPR verified that Fe₂O₃ affected the state of the impregnated Pt via metal-support interactions, which enabled the formation of Pt⁴⁺ species in the Pt-Fe₂O₃/SBA-15 catalyst. DFT calculations revealed that PtO₂ can selectively generate OH radicals, while Pt converts OH radicals into H₂O via further reactions. As predicted by DFT calculations, EPR spectra demonstrated that OH radicals were formed by Pt-Fe₂O₃/SBA-15 but not by Pt/SBA-15. In conclusion, Pt⁴⁺ species in the Pt-Fe₂O₃/SBA-15 catalyst via interactions between Pt and Fe₂O₃ led to highly efficient phenol removal with H₂O₂.