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.

Automated summary

Using advanced quantum chemistry methods, this study explores the pathways of NOX formation and reduction and determines new kinetic parameters. Energy barrier analysis reveals that NO is mainly produced through a sequence of reactions rather than the traditional reaction. The formation of NO2 depends largely on O and HO2 radicals, while the active O atom promotes both the formation and destruction of NO2.