Enhanced ammonia production through non-thermal plasma-assisted synthesis: Tailoring titanium oxynitride photocatalysts for optimal performance

A plasma assisted ammonia synthesis over a titanium oxynitride catalyst has been studied in a micro dielectric barrier discharge reactor. The titanium oxynitride were prepared by nitridation of TiO₂ at the temperatures ranging from 650 to 850 °C, allowing control over the nitrogen content and plasmonic properties of the catalyst. Without the catalyst, the highest NH₃ yield of 0.233 vol% and energy efficiency of 0.68 g kWh⁻¹ were observed at the stoichiometric H₂/N₂ feed ratio of 3.0. However, the optimal H₂/N₂ feed ratio shifted to 2.0 was observed over the TON-650 catalyst with a further improvement in the NH₃ yield to 0.272 vol% and energy efficiency of 0.79 g kWh⁻¹. For TON-750, the optical H₂/N₂ feed ratio further decreased to 1.0, achieving a NH₃ yield of 0.253 vol% and a higher energy efficiency of 0.83 g kWh⁻¹. These enhancements are attributed to a synergetic effect between plasma and titanium oxynitride surface. A general trend was observed demonstrating that the optimal H₂/N₂ feed ratio is inversely proportional to the amount of total nitrogen content in the catalysts. This work demonstrates an effective and economically viable method for on-site, on-demand, small-scale ammonia synthesis.