A study of N2O decomposition rate constant at high temperature: Application to the reduction of nitrous oxide by hydrogen

Atomic resonance absorption spectroscopy has been used to investigate the thermal decomposition of N₂O by monitoring the formation of O atoms behind reflected shock waves in the temperature range 1490–2490 K and at total pressures from 58 to 347 kPa, by using the mixtures of N₂O highly diluted in Ar. For the chosen experimental conditions, the rate coefficient k_1,0 for the reaction N₂O + Ar → N₂ + O + Ar had the greatest effect on the O atom concentration increase, so this reaction rate constant could be deduced by comparison between experiment and computed simulation. In the actual temperature range, we found k_1,0 (cm³ mol^?1s^?1) = 7.2 × 10¹⁴ exp(?28878/T(K)), with an overall uncertainty evaluated to be less than 20%, by considering all the parameters, which contributed to uncertainties in the rate constant determination. The possible absorption at the O triplet emission line of N₂O has been investigated. The absorption cross section of N₂O at the O line has been estimated and taken into account for the determination of k_1,0 at high concentrations of N₂O and at temperatures lower than 1850 K. The effect of the presence of impurities like H₂O on rate constant determination has been examined and was found to be negligible. The choice of the rate coefficient for the consumption of O atoms by reaction with N₂O and that of the high‐pressure limiting rate coefficients k_1,∞ were also discussed. The rate constant reported in the present study was compared with the literature values and was found to be overall higher than those determined experimentally by other teams in the last decade. Finally, the effect of the modified constant value on reaction rate of diluted Ar–N₂O mixtures and H₂–N₂O–Ar systems was investigated. In the temperature range 1500–2500 K, the use of the rate constant deduced from this study has led to a better prediction of N₂O decomposition and N₂O reduction by H₂ than with lower rate constants proposed in the literature. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 357–375, 2009