The characteristics of wet air oxidation of phenol over CuOx/Al2O3 catalysts: Effect of copper loading

The nature of active copper species is well-known to vary with copper loading, i.e., isolated Cu2+ to bulk CuO. In this work, however, the effect of copper loading on the activity and the selectivity was investigated for the wet oxidation of phenol over CuOx/Al2O3 catalysts. The activity and the mineralization selectivity of the catalysts increased with copper loading up to 7 wt% and remained almost the same at a higher loading. The optimum copper loading was about 7 wt% for the wet oxidation of phenol over CuOx/Al2O3 catalysts in this work. The nature of copper species with different loading was characterized with TPR, XRD, and XANES. The chemical states of copper in the CuOx/Al2O3 catalysts were confirmed as varying with copper loading: isolated Cu2+ ions for 1 wt%; highly dispersed Cu2+ cluster for 5 wt% and 7 wt%, and bulk CuO for 10–25 wt%. The stability of the CuOx/Al2O3 catalysts with different copper loading was also studied with respect to carbonaceous deposits and copper leaching.