The thermal de-NOx process is one of the most effective methods of reducing the NOx in flue gas. A shortcoming in this process is the narrow temperature range of 870 degrees C to 1100 degrees C in which effective reduction of NO occurs. We approach this problem by adding an agent to the system in order to shift the temperature range to a lower one. The agent that was added was an aqueous solution containing trace amounts of phenolic compounds which is one of the industrial waste products of fluidized catalytic cracking (FCC) in petroleum refinement. The effect of the addition of an aqueous phenol solution on the thermal de-NOx process was investigated in a quartz flow reactor at a temperature, pressure, and residence time of 650-820 degrees C, 1.0 atm, and 1.0-1.2 s, respectively. In the case of 0-400 ppm phenol addition at NO/NH3 = 1.0, O-2 = 4%, NO = 400 ppm, and H2O = 7.4%, profiles of NO, N2O, NO2, NH3, CO, CO2, C2H2 and phenol concentrations were experimentally obtained. The NO concentration significantly decreased over the wide temperature range of 675-820 degrees C.