Decomposition of nitrous oxide at medium temperatures

Flow reactor experiments were done to study the decomposition of N2O at atmospheric pressure and in a temperature range of 600-1000 degrees C. Dilute mixtures of N2O with H-2 CH4, CO with and without oxygen with N-2 as carrier gas were studied. To see directly the relative importance of the thermal decomposition versus the destruction by free radicals (i.e.: H, O, OH) iodine was added to the reactant mixture suppressing the radicals' concentrations towards their equilibrium concentrations. The experimental results were discussed using a detailed chemistry model. This work shows that there are still some uncertainties regarding the kinetics of the thermal decomposition and the reaction between N2O and the O radical. Using the recommendations applied in this work for the reaction N2O + M <-> N-2 + O + M and for N2O + O <-> products, a good agreement with the experimental data can be obtained over a wide range of experimental conditions. The reaction between N2O and OH is of minor importance under present conditions as stated in latest literature. The results show that N2O + H <-> N-2 + OH is the most important reaction in the destruction of N2O. In the presence of oxygen it competes with H + O-2(-) + M <-> HO2 + M and H + O-2 <-> O + OH, respectively. The importance of the thermal decomposition (N2O + M <-> N-2 + O + M) increases with residence time. Reducing conditions and a long residence time lead to a high potential in N2O reduction. Especially mixtures of H-2/N2O and CO/H2O/N2O in nitrogen lead to a chain reaction mechanism causing a strong N2O reduction. (C) 2000 by The Combustion Institute.