Application of Ce0.33Zr0.63Pr0.04O2-supported noble metal catalysts in the catalytic wet air oxidation of 2-chlorophenol: Influence of the reaction conditions
Résumé
A series of noble metal (Pt, Pd, Ru) loaded Ce0.33Zr0.63Pr0.04O2 catalysts were used in the Catalytic Wet Air Oxidation (CWAO) of 2- chlorophenol (2-CP) at relatively low temperature (393 K). Among the investigated noble metals, Ru exhibited the best activity. To optimize the reaction conditions, the effects of different parameters, such as the nature of the ruthenium precursor, the reaction temperature, the total pressure, the initial 2-CP concentration and the initial pH of the 2-CP solution on the catalytic performances of 3 wt.% Ru/Ce0.33Zr0.63Pr0.04O2 were evaluated. It was confirmed that the nature of the ruthenium precursor had nearly no effect on the activity of Ru/Ce0.33Zr0.63Pr0.04O2. The activation energy for the 2-CPCWAO over Ru/Ce0.33Zr0.63Pr0.04O2 was calculated to be 34 kJ mol-1. Unexpectedly, the 2-CP removal rate was 0.5 order with respect to the initial 2-CP concentration. Furthermore, the CWAO of 2-CP changed from first order (‘‘oxygen diffusion control'') to zero order (‘‘kinetic control'') with respect to the oxygen partial pressure, when the total pressure was higher than 4 MPa. The 2-CP conversion increased with the pH of the initial 2-CP solution. The dechlorination reaction is promoted at higher pH. However, too high pH hindered the total mineralization of 2-CP due to the possible poisoning effect of adsorbed carbonate and hydroxycarbonate species. The optimum initial pH was about 6.