Mechanism of the reaction of NO and NH₃ on vanadium oxide catalyst in the presence of oxygen under the dilute gas condition

The NONH₃ reaction on vanadium oxide catalyst under the dilute gas condition was markedly accelerated by the addition of O₂. The oxygen species responsible for the acceleration of the reaction has been found to be the V³⁺O species on the catalyst; the rate of the NONH₃ reaction at a given O₂ concentration was in proportion to the amount of the V³⁺O species in the catalyst. On the basis of the results of the kinetics of the reaction in the presence of O₂, the adsorptions of NH₃ and NO, and the reaction of adsorbed NH₃ and gaseous NO, the mechanism of the NONH₃ reaction on vanadium oxide catalyst under the dilute gas condition has been established as follows: NH₃ is strongly adsorbed adjacent to V³⁺O as NH₄ ⁺ (ad), whereas, NO is hardly adsorbed on the catalyst. Then, agaseous NO reacts with the adsorbed NH₃, i.e., NH₄ ⁺ (ad), to form N₂, H₂O, and VOH. The VOH species is reoxidized to V³⁺O by either gaseous O₂ or bulk V³⁺O species. The rate of the NONH₃ reaction in the presence of O₂ has been proven to agree with that calculated by using the transition state theory together with the above-mentioned mechanism.