Modulation of gas feed composition (air/N2 cycling) and gas feed flow (on–off air cycling) was investigated in the catalytic wet air oxidation of phenol over activated carbon (AC). Fifty hours lasting experiments were conducted in a laboratory trickle bed reactor at 140–160 °C, 2 bar of oxygen partial pressure and different splits and periods to determine the set of cycling parameters that optimise the periodic reactor operation. To follow the dynamic behaviour of the phenol oxidation, temperature and conversion were continuously monitored by means of computerised data acquisition and automatic liquid sampling. Several long term tests over 144 h were also run using both periodic operating strategies to compare the activity and stability of AC with those obtained in a steady state operation at otherwise same conditions. The results show that, depending on the selection of split and period, modulation of the gas phase significantly improves the stability of AC compared to steady state operation, thereby performing a superior long term phenol conversion.