A kinetics mechanism of NOX formation and reduction based on density functional theory

NOX are serious pollutants emitted during combustion, which are greatly harmful to human health and the environ-ment. However, previous studies have not accurately elucidated the NOX conversion mechanism in complicated com-bustion reactions. To reveal the micro-chemical mechanism of NOX conversion and obtain accurate kinetics data, advanced quantum chemistry methods are employed in this study to systematically explore the pathways of NOX for-mation and reduction, and determine the new rate coefficients. An energy barrier analysis revealed that during NOX formation (N2 -N2O -NO-NO2), NO is primarily produced by a sequence of reactions (N2 + O -N2O -NO) rather than the traditional reaction (O + N2 -NO+N). Meanwhile, NO2 formation (NO-NO2) largely depends on the O and HO2 radicals, while the active O atom can promote both the formation and destruction of NO2. During NOX reduction (NO2 -NO-N2O -N2), NO2 reduction (NO2 -NO) is closely related to H, CO, and O, whereas CO plays a critical role in NO2 destruction. However, NO reduction (NO-N2O) is unfavourable because of a high en-ergy barrier, while N2O reduction (N2O -N2) is strongly affected by the O atom instead of CO. HONO is mainly formed when NO2 reacts with the HO2 and H radicals, and when NO reacts with OH radicals; thus, HONO consumption largely depends on OH and H radicals. Based on the transition state theory, we obtained new kinetic parameters for NOX conversion, which supplement and correct critical kinetics data obtained from the current NOX model. Perfor-mance assessment of the proposed NOX kinetic mechanism reveals that it can improve the existing NOX kinetic mode, which is in good agreement with experimental data.