The difficulty of reducing nitrogen oxides in the presence of oxygen

Abstract

A hypothesis is made, based on the literature, which makes it very unlikely that NO can be selectively reduced by any reducing agent other than ammonia. The hypothesis is based upon the very fast reduction of NO2, even in the presence of oxygen, and an easy reoxidation of NO to NO2 which are both preferential to NO reduction in the presence of oxygen. The particular feature of ammonia originates from the fact that in parallel with this reaction, both reactants, under limiting conditions (defined by temperature), participate in a second scheme which leads to the formation of surface complexes dissociating into N2 and/or N2O. These surface complexes are most probably NH4NO2 and NH4NO3. In the presence of oxygen only this second scheme leads to the formation of N2 and or N2O and is even accelerated by the re‐oxidation of NO to NO2.