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

The reaction of N${}_2$O with H is the key step in consumption of nitrous oxide in thermal processes. The major product channel is N${}_2$ + OH, while NH + NO constitute minor products. In addition, a pathway involving HNNO, initiated by N${}_2$O + H (+M) $\rightleftarrows$ 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 k${}_3$ and k${}_4$ 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 N${}_2$O–H${}_2$ 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 N${}_2$O consumption and formation of NH${}_3$. In addition, selected literature results on the N${}_2$O–H${}_2$ system are re-examined and the implications for the other product channels of N${}_2$O + H, in particular NH + NO, are discussed.

Novelty and significance statement

This study provides the first detailed kinetic analysis of the N${}_2$O/H${}_2$ 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.