A kinetic modelling study of ammonia oxidation in a flow reactor

Kinetic modelling of ammonia oxidation in plug flow was performed using Ansys Chemkin-Pro over a range of initial ammonia concentration (2–10%), temperature (1000–1400K) and equivalence ratio (0.8–1.0), to seek mechanistic interpretation of peculiar but interesting phenomena observed experimentally in a flow reactor configuration. where an increase in ammonia initial concentration led to increased ammonia conversion for temperatures up to 1165K, above which the trend was reversed as observed in the experimentation. The simulated results satisfactorily replicated the trends in the experimental measurements and identified key radicals and reaction pathways responsible for the peculiar behaviour. Furthermore, the nitric oxide concentration in the reactor exit stream for oxidation of 10% initial ammonia concentration sharply increased from 0 ppm at 1325K to 497 ppm at 1350K, then decreased with further increasing temperature, which can be attributed to the greater exothermicity of oxidation at higher ammonia initial concentrations. • H abstraction rate increases with temperature promoting NH 3 oxidation >1165K. • OH formation is more sensitive to temperature in 2% NH 3 oxidation at 1125–1175K. • NO formation is promoted by heat released from 10% NH 3 oxidation at ɸ = 1.0. • A higher temperature (1425–2040K) raises the NO destruction rate via N + NO O + N 2 . • N 2 O formation is more sensitive to NH 3 concentrations than to ɸ at low temperatures.