Plasma-Based NH₃ Cracking: A Better Insight in the Performance by Chemical Kinetics Modeling

This study examines performance characteristics of (warm-)plasma-based NH₃ cracking using a detailed plasma chemical kinetics model across a wide range of gas temperatures (T_g = 1000-6000 K) and electron temperatures (T_e = 0-3.5 eV, i.e., 0-40,000 K). NH₃ conversion increases with both temperatures, but the T_g-dependence flattens near full conversion. Pure thermal cracking reaches full conversion at 2300 K and 10 ms, while plasma achieves full conversion at T_e > 2.75 eV for all T_g, even the lowest T_g values investigated. At T_g < 2700 K, high T_e dramatically reduces the time for full conversion, for example, from thousands of years (thermal) to milliseconds (plasma) at T_g = 1100 K, while differences vanish at T_g > 2700 K. Product composition follows thermal equilibrium, showing negligible T_e influence. Importantly, we also suggest strategies for performance improvement. The best energy cost for typical warm plasmas with continuous power is predicted to be 197 kJ/mol-NH₃ at 2500 K, where thermal pathways dominate. Reducing vibrational energy losses suggests potential improvement at T_g ≈1500 K, predicting an energy cost of 157 kJ/mol-NH₃, for so-called "plasma-initialized" thermal cracking. Further reduction in energy cost should be feasible via heat recovery. Overall, our model shows that plasma cracking offers rapid NH₃ conversion with reasonable energy cost.