Effect of oxygen on N2O and NO formation from NH3 oxidation over MnOx/TiO2 catalysts

The relationship between the formation of N2O and NO and the absence and presence of O-2 in NH3 oxidation process over MnO,/TiO2 catalysts was studied in this work. Experimental results demonstrated that evident N2O and NO formed when only NH3 with no gaseous O-2 was introduced into the reactor, validating N2O originated from NH3 oxidation by lattice oxygen or surface absorbed oxygen in MnO,./TiO2 catalysts. In addition, remarkable NO was found during experiments, which provided a new N2O formation pathway NH3 >N >N2O or NH3 >N >N0 >N2O in NH3 catalytic oxidation process. Afterwards, different concentrations of O-2 were introduced into the reactor to explore the effect on N2O and NO generation. At the same temperature, O-2 moderately promoted the oxidation of NH3, but it did not strongly enhance it, implying the weaker oxidation performance of O-2 than the catalyst oxygen in Mn(0.1)/Ti. The NO formation increased monotonically with the temperature, whatever the O-2 concentration. However, the N2O concentration did not always coincide with the monotonous variation tendency as NO. With 4% or 8% O-2, the N2O formation suddenly turned down above 350 degrees C, and the more O-2 led to the greater reduction. (C) The Authors. Published by Elsevier Ltd.