The effect of reaction conditions on the apparent deactivation of Ce–Zr mixed oxides for the catalytic wet oxidation of phenol

A series of Ce–Zr mixed oxides with different composition have been characterized and used as catalysts in the catalytic wet oxidation (CWO) of phenol. The addition of Zr significantly enhanced the redox and catalytic activity of ceria. However, a catalytic activity drop occurred for zirconium contents higher than 80%, which is related with a ZrO2 segregation observed in Zr-rich oxides. The effects of the temperature of reaction, the oxygen partial pressure and the phenol/catalyst ratio on the activity for the oxidation of phenol and the selectivity to CO2 were also investigated. The values for CO2 selectivities were greatly influenced by the formation of a carbonaceous deposit adsorbed on the catalyst surface. The results indicated that these C-deposits can be totally oxidized by selecting appropriate operating conditions, thus obtaining catalytic systems with a very promising performance for phenol abatement. A mechanism is proposed to interpret the role of the carbonaceous deposits in the oxidation of phenol as a function of the reaction conditions.

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► Carbonaceous deposits are formed on Ce–Zr oxides during the CWAO of phenol.
► The mineralization of phenol is favoured by using Ce–Zr compositions close to 50%.
► Temperatures higher than 160 °C are required to oxidize the carbonaceous deposits.
► The carbonaceous deposits can be removed by calcination at 350 °C.