Wet oxidation of phenol on Ce1-xCuxO2-delta catalyst

Ce1-xCuxO2-delta catalysts with 0.05 < x < 0.20 for catalytic wet oxidation of phenol in aqueous solutions have been synthesised using the coprecipita tion method. The three most important synthesis parameters, the concentrati on of the mixed metal salt solution, the rate of coprecipitant addition and the stirrer speed during coprecipitation, were optimised with central comp osite design using the catalytic activity as a response function. The catal ytic activity strongly depends on stirrer speed during coprecipitation. A h igh mutual dispersion of copper oxide and ceria, having the average crystal lite size of about 9 nm, enhances solid solution formation. The unit cell p arameter of ceria decreases when the overall concentration of copper in the catalyst increases, most probably obeying Vegard's law. The catalysts prov ed to be very stable in hydrothermal reaction conditions at low pH values. After 5 h of reaction in the semibatch CST reactor less than 100 ppm of Cu was leached out of catalyst samples that were calcined in a flow of air for 2 h above 1033 K, and only a very low quantity of carbonaceous deposits we re formed on the surface of the catalysts (0.6 wt%). The kinetics of phenol degradation could be interpreted by an equation valid for homogeneous auto catalytic reactions, in which the rate constant depends linearly on the het erogeneous catalyst (Cu) concentration. This demonstrates that the reaction proceeds through a heterogeneous-homogeneous radical-branched chain mechan ism, (C) 1999 Academic Press.