Preparing and characterizing an optimal supported ceria catalyst for the catalytic wet air oxidation of phenol

The activity of several supported ceria catalysts for the catalytic wet air oxidation of phenol was investigated using an autoclave reactor. Results indicated that the support and the Ce content are both important factors affecting phenol conversion, whereas BET surface area had no appreciable effect. CeO2/γ-Al2O3 was found to be the most active catalyst among the five tested. This superior activity was verified by O2-temperature programming desorption (O2-TPD), showing that CeO2/γ-Al2O3 had the most exchangeable structure O2 (capping O2), and by H2-temperature programming reduction (H2-TPR), showing that it had the highest H2 consumption (the most H2-reducible Ce species in the catalyst). For the CeO2/γ-Al2O3 catalyst, the optimal Ce content was about 20 wt.%. X-ray diffraction (XRD) analysis and evaluation of full width at half maximum (FWHM, 2θ=28.5°) of the XRD pattern showed that formation of larger crystals of CeO2 at Ce content above 20 wt.% caused a decrease in the catalytic activity of CeO2/γ-Al2O3. The superior activity of CeO2/γ-Al2O3 at 20 wt.% Ce content was confirmed by O2-TPD. The results of O2-TPD and H2-TPR of CeO2/γ-Al2O3 with various Ce contents showed that not all the H2-reducible Ce species were associated with capping O2. Using the optimal CeO2/γ-Al2O3 catalyst (loading 3.0 g/l), about 100% phenol conversion and 80% chemical oxygen demand (COD) removal was achieved after 2 h reaction at 180 °C and 1.5 MPa O2 partial pressure. Although the efficacy of CeO2/γ-Al2O3 is somewhat less than that of pure CeO2, the much lower cost of the former renders it a feasible catalyst for the catalytic wet air oxidation (CWAO) of phenol.