An experimental, theoretical and kinetic modeling study of the N₂O-H₂ system: Implications for N₂O + H

The reaction of N₂O with H is the key step in consumption of nitrous oxide in thermal processes. The major product channel is N₂ + OH, while NH + NO constitute minor products. In addition, a pathway involving HNNO, initiated by N₂O + H (+M) ⇄ HNNO (+M) (R3, R4), has been inferred from experiment and theory by Burke and coworkers. At longer reaction times, the reaction may reach partial equilibration, and in addition to k₃ and k₄ the importance of this channel depends on the thermodynamic properties of HNNO and its consumption reactions, mainly HNNO + H. In the present work, we re-examined the thermochemistry of HNNO and calculated rate constants and branching fractions for the HNNO + H reaction. Experiments on the N₂O–H₂ system were conducted in a high-pressure flow reactor at 100 atm as a function of temperature (600-925 K) and stoichiometry and explained in terms of an updated chemical kinetic model. The results
support the importance of the HNNO pathway, which results in inhibition of N₂O consumption and formation of NH₃. In addition, selected literature results on the N₂O–H₂ system are re-examined and the implications for the other product channels of N₂O + H, in particular NH + NO, are discussed. Novelty and significance statement This study provides the first detailed kinetic analysis of the N₂O/H₂ system at high pressure and intermediate temperatures, based on flow reactor results and high-level theoretical calculations. The experimental conditions augment the importance of a reaction pathway involving HNNO as intermediate. Inclusion in the model of a subset for HNNO, including present calculations for HNNO + H, is crucial for capturing the observed behavior.