Plasma-catalytic ammonia synthesis beyond thermal equilibrium on Ru-based catalysts in non-thermal plasma

Recently it was proposed that plasma-catalytic NH3 synthesis with excited N-2 allows for conversions beyond thermal equilibrium. We show that this is indeed possible with experimental data for Ru catalysts at temperatures above 300 degrees C, resulting in significant thermal activity for NH3 synthesis. The resulting NH3 concentration is determined by competition between, on the one hand, dissociative adsorption of ground-state N-2 and adsorption of plasma-generated N radical species with subsequent hydrogenation to NH3, and on the other hand, thermal-catalytic decomposition of NH3. At temperatures below 300 degrees C, plasma-catalytic ammonia synthesis is attributed to adsorption of N radicals, generated in the plasma, with subsequent hydrogenation to NH3. These findings imply that catalysts with thermal activity are not suitable for plasma catalysis, aiming at conversion beyond equilibrium, as these also catalyze the reverse decomposition reaction.

Automated summary

Recent research has shown that at temperatures above 300 degrees C, Ru catalysts exhibit significant thermal activity for NH3 synthesis, while at temperatures below 300 degrees C, plasma-catalytic ammonia synthesis is mainly attributed to adsorption of N radicals.