Unraveling the Reaction Mechanism of HCN Intervention on the NPAHs Formation in NH₃/Acenaphthylene Combustion using Theoretical Calculations

The objective of this study is to elucidate the nitrogen chemistry mechanisms underlying the reaction between NH₃ and polycyclic aromatic hydrocarbons (PAHs), resulting in the formation of nitrogen-containing polycyclic aromatic hydrocarbons (NPAHs). This study employs the acenaphthylene radical as a model system and combines G3(MP2,CC)//B3LYP/6-311+G(d,p) theory with transition state analysis to systematically map potential energy surfaces for HCN-C₂H₂ addition reactions at various sites. The MESS program was carried out to determine rate constants across temperatures of 300-2500 K and pressures ranging from 0.01 to 100 atm. Findings reveal a kinetic preference for C-terminal HCN addition over N-terminal pathways, with rate constants increasing by 2-3 orders of magnitude under low-temperature and high-pressure conditions. Moreover, competitive interactions between HCN and C₂H₂ were observed during the formation of PAHs. At elevated temperatures, comparable rate constants suggest that HCN disrupts traditional hydrogen-abstraction-acetylene-addition (HACA) mechanisms, thereby promoting the formation of NPAHs. Furthermore, theoretical calculations and kinetic simulations confirm the interaction between HCN and PAHs, which can effectively slowdown the formation of larger PAHs species. These findings provide a viable strategy for optimizing ammonia combustion systems and advancing low-emission energy technologies.