A Reaction-Pathway-Guided Development of a Kinetic Mechanism for Formation during Thermal Decomposition

Nitrous oxide ( ) is a potent greenhouse gas and an important intermediate in ammonia-based energy systems, and its thermal decomposition can be accompanied by undesirable formation. Despite extensive kinetic modeling efforts, existing reaction mechanisms exhibit large discrepancies in predicting while providing comparable accuracy for major species such as , , and . This study proposes a systematic framework to analyze formation pathways during thermal decomposition and to develop an improved reaction mechanism with enhanced predictive accuracy. Flow-reactor experiments were conducted at 1100–1500 K and residence times of 0.25–1.00 s, and the results were compared with predictions from five detailed mechanisms. Rate-of-production analysis revealed that is primarily formed through the , while subsequent – cycling reactions regulate the net concentration under high-temperature and long-residence-time conditions. To quantitatively assess model performance, normalized and weighted root-mean-squared error metrics (NRMSE and wRMSE) were employed. Although existing mechanisms showed similar accuracy for decomposition, they exhibited more than a sixfold variation in prediction error. Guided by pathway analysis and statistical evaluation, the rate constants of two key reactions were systematically optimized using a two-step RMSE-minimization procedure. The resulting reaction mechanism reduced the overall wRMSE from 0.289, obtained with the best-performing existing mechanism (OKA2018), to 0.128, corresponding to an approximately 55.7% reduction in prediction error, while improving the reproduction of both and concentration profiles. These results support more reliable kinetic predictions for thermal abatement, -control strategies, and ammonia-based combustion systems.