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 Cc content are both important factors affecting phenol conversion, whereas BET surface area had no appreciable effect. CeO2/gamma-Al2O3 was found to be the most active catalyst among the five tested. This superior activity was verified by O-2-temperature programming desorption (O-2-TPD), showing that CeO2/gamma-Al2O3 had the most exchangeable structure O-2 (capping O-2), and by H-2-temperature programming reduction (H-2-TPR), showing that it had the highest H-2 consumption (the most H-2-reducible Cc species in the catalyst). For the CeO2/gamma-Al2O3 catalyst, the optimal Ce content was about 20 wt.%. X-ray diffraction (XRD) analysis and evaluation of full width at half maximum (FWHM, 2theta = 28.5degrees) of the XRD pattern showed that formation of larger crystals Of CeO2 at Cc content above 20 wt.% caused a decrease in the catalytic activity of CeO2/gamma-Al2O3. The superior activity of CeO2/gamma-Al2O3 at 20 wt.% Ce content was confirmed by O-2-TPD. The results of O-2-TPD and H-2-TPR of CeO2/gamma-Al2O3 with various Cc contents showed that not all the H-2-reducible Ce species were associated with capping O-2. Using the optimal CeO2/gamma-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 180degreesC and 1.5 MPa O-2 partial pressure. Although the efficacy of CeO2/gamma-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. (C) 2004 Elsevier B.V. All rights reserved.