Roles of free radicals in NO oxidation by Fenton system and the enhancement on NO oxidation and H2O2 utilization efficiency

Low H2O2 utilization efficiency is the main problem when Fenton system was used to oxidize NO in flue gas. To understand the behaviour of the free radicals during NO oxidation process in Fenton system is crucial to solving this problem. The oxidation capacity of ⋅OH and HO2⋅ on NO in Fenton system was compared and the useless consumption path of ⋅OH and HO2⋅ that caused the low utilization efficiency of H2O2 were studied. A method to enhance the oxidation ability and H2O2 utilization efficiency by adding reducing additives in Fenton system was proposed. The results showed that both of ⋅OH and HO2⋅ were active substances that oxidize NO. However, the oxidation ability of ⋅OH radicals was stronger. The vast majority of ⋅OH and HO2⋅ was consumed by rapid reaction ⋅OH + HO2⋅→H2O + O2 , which was the primary reason for the low utilization efficiency of H2O2 in Fenton system. Hydroxylamine hydrochloride and ascorbic acid could accelerate the conversion of Fe3+ to Fe2+, thereby increase the generation rate of ·OH and decrease the generation rate of HO2⋅. As a result, the oxidation ability and H2O2 utilization efficiency were enhanced.