Catalytic wet air oxidation (CWAO) of phenol was carried out under atmospheric pressure of oxygen at 160 degrees C in a stirred batch reactor over copper catalysts supported by CeO2-ZrO2. The copper with different loadings were impregnated over the composite support by a sonication process. The catalysts were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray analysis (EDX), Brunauer-Emmett-Teller (BET) specific surface area and Fourier-transformed infrared analyses. Characteristic peaks attributed to copper were not found in XRD patterns even at high loadings, but based on EDX results, the existence of copper particles was confirmed. It means that sonochemical synthesis method even at high loadings produced small copper particles with low crystallinity and excellent dispersion over the CeO2-ZrO2 composite. FESEM micrographs indicated just slight enhancement in particle size at high loadings of Cu. Blank CWAO experiments illustrated low conversion of phenol using bare CeO2-ZrO2 support. Although some agglomeration of particles was found at high loadings of copper but owning to the fact that almost all ZrO2 particles incorporated into the CeO2 lattice at high contents of Cu, catalyst activity not only did not decrease but also the phenol conversion reached to the higher values. The optimal catalyst loading for phenol degradation was found to be 9 g/l. Complete conversion of phenol was achieved using CuO/CeO2-ZrO2 in 9 g/l catalyst loading with initial phenol concentration of 1000 ppm after 3 h of reaction.

Non-noble metal Ni with different loadings was coated on precipitated CeO 2 -ZrO 2 support by the sonochemistry method and examined for catalytic wet air oxidation of phenol. The structure of the nanocatalysts was determined by BET, FESEM, XRD, and FTIR analyses. The results showed non-uniform morphology of the nanocatalyst at lower Ni contents changed to homogenous morphology with spherical nano particles at higher Ni contents. While the size of NiO crystals remained constant with rising Ni content, the crystallinity of NiO significantly increased. If the crystallinity of NiO was 100% in 20% wt Ni/CeO 2 -ZrO 2 , the crystallinity of NiO in 5% wt Ni was found to be 41.13%. The average particle size in Ni(15%)/CeO 2 -ZrO 2 was 77 nm in which 85.71% of particle diameters were less than 100 nm. Catalytic wet air oxidation of phenol with different Ni loadings indicated improvement of phenol destruction at higher amounts of active phase. Removal of phenol increased with increasing catalyst loading from 4 to 9.0 g/l but further increase to 10 g/l declined the catalyst reactivity. ª 2014 The Authors. Production and hosting by Elsevier B.V. on behalf of King Saud University. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).