Catalytic wet oxidation of phenol with Fe–ZSM-5 catalysts

Abstract

Fe–ZSM-5 and Fe₂O₃/ZSM-5 zeolite catalysts were prepared and tested for catalytic wet oxidation of phenol. First, Fe–ZSM-5 and Fe₂O₃/ZSM-5 zeolite catalysts were prepared by the hydrothermal synthetic and incipient wetness impregnation method and characterized to determine the framework and extra-framework Fe³⁺ species. Second, the catalytic properties of Fe–ZSM-5 in the oxidation of phenol were systematically studied to determine the optimum technological parameters by investigating the effects of reaction temperature, pH, catalyst concentration and stirring rate on the conversion of phenol. In addition to the phenol conversion, selectivity to CO₂ and concentration of aromatic intermediates in the oxidation of phenol with the two catalysts were analyzed under the same optimum conditions. Leaching of iron from the catalysts, as well as the catalytic stability of Fe–ZSM-5, was also tested. Finally, the kinetics of catalytic wet oxidation of phenol with Fe–ZSM-5 was studied. The experimental results showed that both the framework and extra-framework Fe³⁺ species were present in Fe–ZSM-5. The oxidation reaction with Fe–ZSM-5 was performed well at a temperature of 70 °C, pH of 4, catalyst concentration of 2.5 g L⁻¹, stirring rate of 400 rpm and reaction time of 180 min. The conversion of phenol reached 94.1%. From the catalytic results of the two catalysts, it can be concluded that the framework Fe³⁺ species may be more efficient in phenol oxidation than the extra-framework Fe³⁺ species, the stability of Fe–ZSM-5 was better and a relatively low decrease in activity could be found after three consecutive runs. The activation energy of 27.42 kJ mol⁻¹ was obtained for phenol oxidation with Fe–ZSM-5.