Kinetic Study on the Reactions of NH₃ Oxidation and NO Formation in NH₃/CH₄ Combustion

Ammonia (NH₃) is increasingly recognized as an important sustainable energy carrier, and methane (CH₄) is typically added to combustion systems to enhance their combustion performance. Reaction pathways of NH₃/CH₄ combustion require further clarification. In the present study, the key reactions of NH₃ oxidation and NO formation in NH₃/CH₄ combustion were revealed at the subatomic level. The CCSD-(T)/cc-pvqz//B3LYP/6-311 + G-(d,p) and CBS-QB3 methods were used to calculate the molecular structures, transition states, and energy barriers of all reactions. The rate constants were calculated by the transition state theory with the Wigner tunneling correction, and the results in the present study agree well with previous experimental data and theoretical calculation. Moreover, rate constants were fitted to the Arrhenius equation over the temperature range of 300-2500 K to obtain activation energies. Notably, rate constants and activation energies were determined for the reactions (NH₃ + CH₃ → NH₂ + CH₄ and HNO + HO₂ → NO + H₂O₂) that were revealed by the present study. This study will contribute to the understandings of fuel performance in the new era for sustainable energy.