The long-term stability of active carbon in the CWAO of phenol was investigated in a fixed-bed reactor at steady state operation and different oxygen partial pressures, temperatures, phenol inlet concentrations and gas–liquid flow modes. To further improve the catalyst stability, gas feed composition modulation (air/N2) was tested in the slow mode (large period lengths) to establish in situ oxidation–adsorption cycles. The unsteady operation significantly reduced the active carbon burn-off and performed a higher long-term conversion of phenol.