Theoretical and kinetic modeling study of hydrazine oxidation

The present work constitutes the first theoretical and kinetic modeling study of hydrazine oxidation, which may be important for burnout in ammonia-fueled combustion. The kinetics of the oxidation of N 2 H 4 , N 2 H 3 and tHNNH by molecular oxygen were investigated via a quantum chemistry/canonical transition state theory approach. Geometries and anharmonic frequencies were obtained with derived density functional theory, and energies from coupled cluster calculations (CCSD(T)) extrapolated to the infinite basis set limit, with corrections for core-valence electron correlation, scalar relativistic effects, and higher level correlation up to lambda coupled cluster, CCSDT(Q) Λ . The key reactions occurred on the N 2 H 4 O 2 potential energy surface, where the results indicated a fast reaction of N 2 H 3 with HO 2 via singlet adducts to yield tHNNH + H 2 O 2 and HNN(H)O + H 2 O, while reaction on the triplet surface proceeds via a bound complex followed by a tight, submerged barrier to yield N 2 H 4 + O 2 . The results were incorporated in a detailed reaction mechanism, which was used to interpret the shock tube results from Michel and Wagner (1965) on the effect of O 2 on hydrazine conversion at 1100-1400 K. The kinetic model captured qualitatively the observed behavior, but underestimated the reaction rate under oxidizing conditions. The hydrazine pyrolysis chemistry dominated conversion at reducing conditions and/or high temperature. At oxidizing conditions and intermediate temperatures ( ≲ 1400 K), reactions of N 2 -amines with HO 2 and O 2 were important for the oxidation rate. • The present work constitutes the first theoretical and kinetic modeling study of hydrazine oxidation. • The kinetics of the oxidation of N 2 H 4 , N 2 H 3 and tHNNH by O 2 were investigated by ab initio theory. • Reactions on the N 2 H 4 O 2 potential energy surface were particularly important. • The kinetic model captures the effect of O 2 addition on N 2 H 4 , consumption in shock tube. • The hydrazine pyrolysis chemistry dominates at reducing conditions and/or high temperature, while at oxidizing conditions and intermediate temperatures, reactions of N 2 -amines with HO 2 and O 2 were important for the oxidation rate.