Effect of Ce/Zr molar ratio on the catalytic performance of Ru/Ce_xZr_1-xO₂ in the wet air oxidation of phenol

A series of Ce_xZr_1-xO₂ catalysts with different Ce/Zr molar ratios were prepared by sol-gel method and characterized by X-ray diffraction (XRD), nitrogen sorption, Raman spectra, oxygen storage capacity (OSC), thermogravimetry (TG) and pyridine adsorption infrared (Py-FTIR) spectra; the performance of Ce_xZr_1-xO₂ in catalytic wet air oxidation (CWAO) of phenol was investigated. The results demonstrate that Ce_xZr_1-xO₂ solid solution is formed by doping ZrO₂ in CeO₂ and the OSC value of Ce_xZr_1-xO₂ increases with an increase in the content of ZrO₂. In comparison with pure CeO₂, Ce_xZr_1-xO₂ solid solution has more Lewis acid sites. The catalytic activity of Ce_xZr_1-xO₂ is related to both OSC and surface acidity; the Lewis acid sites are favorable for the complete oxidation of phenol, whereas high OSC may promote the carbonaceous deposition that leads to catalyst deactivation. The Ru/Ce_0.75Zr_0.25O₂ catalyst exhibits high activity in phenol oxidation; after reaction for 5 h at 160℃ and 2 MPa O₂, phenol conversion and total organic carbon (TOC) rate reach 100% and 99%, respectively.