Utilization of Reactive Nitrogen Compounds for Nitrogen Circular Economy

Nitrogen oxides (NO_x) should be purified according to environmental regulations, being restricted increasingly year by year. A wide variety of denitration technologies, such as selective catalytic reduction (SCR) of NO_x to nitrogen (N₂) and NO_x storage reduction (NSR) to N₂ by injecting reducing agents like ammonia (NH₃), has so far been developed practically. Sophisticated catalytic approaches are perhaps mandatory for the sustainability in energy including complete purification of NO_x. As one of the solutions to overcome problems for environment and resource simultaneously, this concept article focuses on the utilization of reactive nitrogen (N_r) compounds, mainly NO_x, for encouraging an opening to consider nitrogen circular economy. For the recycling of NO_x via NH₃, a challenging but rational catalytic technology can be proposed by an alternate switching the inlet gas between NO_x containing oxidative gas and H₂ containing reductive one without an operation to change the reaction temperature. Considering the reactivity of NO_x higher than that of N₂, this kind of NO_x to NH₃ (NTA) process is promising for synthesizing NH₃, being valuable not only as fertilizer but also as fuel in near future.