Mechanism of catalytic decomposition of pentachlorophenol by a highly recyclable heterogeneous SiO2–[Fe-porphyrin] catalyst

A novel heterogenized FeR4P–SiO2 shows enhanced catalytic efficiency for PCP conversion vs. the homogeneous FeR4P catalyst. The heterogenized FeR4P–SiO2 catalyst is highly recyclable in the presence of imidazole in solution. EPR and DR-UV–Vis data provide direct evidence that high-valent iron species [R4P+FeIVO] are formed in the heterogenized FeR4P–SiO2 system. The electron spin density of the a1u cation radical (Por+) is mainly localised on the tetrapyrole frame, and this results in the observed weak magnetic coupling between the S = 1 oxo-ferryl moiety (FeIVO) and the S′ = 1/2 porphyrin cation radical (Por+). A catalytic cycle mechanism is suggested. Accordingly, the reduction in [R4P+FeIVO] can proceed via a substrate molecule, in a one electron-transfer, thus producing [R4PFeIV] plus a radical entity derived from the substrate. Then, a second electron-transfer to [R4PFeIV] leads to the regeneration of the initial R4PFeIII state. This second electron can originate from either a substrate molecule or a radical substrate species.

Efficient catalytic decomposition of PCP is achieved by a highly recyclable heterogenized FeR4P–SiO2 catalyst. The catalytic reactive intermediate R4P+FeIVO has been detected by EPR and DR-UV–Vis specrsocpy in the heterogeneous phase.Figure optionsDownload high-quality image (90 K)Download as PowerPoint slide