Fenton-like oxidation of phenol with in-situ generated hydrogen peroxide and Pd/Fe-zeolite catalysts

Abstract

Two types of iron-containing zeolites with different surface hydrophobicity, Fe-ZSM5 (SiO₂/Al₂O₃ = 26) and Fe-ZSM5 (SiO₂/Al₂O₃ = 236) were studied as adsorbents and catalysts for oxidation of phenol by means of a Fenton-like process at ambient conditions and nearly neutral pH, with and without in-situ generation of H₂O₂. Adsorption of phenol is more favorable on high silica Fe-ZSM5 (236) zeolite due to its higher surface hydrophobicity. Palladium (Pd) immobilization on Fe-ZSM5 zeolites has a positive impact on phenol degradation with a synergistic role of Pd and Fe (II)/(III) for activation of H₂O₂. The best result for phenol conversion and mineralization was observed over both hydrophilic and hydrophobic 0.1 wt.% Pd/Fe-ZSM5 with commercial H₂O₂ achieving ≥ 90% conversion of phenol (100 mg/L) in 4 h and 60–63% mineralization in 6 h with 5 g/L catalyst and 5 g/L H₂O₂. In addition, Pd/Fe-ZSM5 can be used for in-situ formation of H₂O₂ using formic acid as H-source and externally supplied oxygen. The combination of these processes provided by this adsorbent/catalyst material is exploitable for on-site oxidative regeneration of zeolite adsorbents. This study shows that Fe-containing zeolites are promising catalysts for a combined approach of adsorption/oxidative degradation of phenol by commercial or in-situ produced H₂O₂.