It is difficult to obtain an initial high NOx removal efficiency of 80% or more, due to the oxidation and reduction cycle of NO and NO2 [4]. Lee et al. [45] carried out electron beam treatment (0.7 MeV, 35 mA) by adding microwave (MW) process to enhance the removal efficiency of NO. This test was conducted using simulated gases (1 vol% of NO in nitrogen, air, 1 vol% of NH3 in nitrogen, and pure water) at 5 L/min of inlet gas flow rate. Compared to single EB process, the required irradiation dose could be reduced by 30% range of the (70–80)% of removal efficiency. However, MW was not affected by the removal efficiency over 90%, and MW was effective only in the dose range of (8–24) kGy