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 (N 2 ) and NO x storage reduction (NSR) to N 2 by injecting reducing agents like ammonia (NH 3 ), 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 NH 3 , a challenging but rational catalytic technology can be proposed by an alternate switching the inlet gas between NO x containing oxidative gas and H 2 containing reductive one without an operation to change the reaction temperature. Considering the reactivity of NO x higher than that of N 2 , this kind of NO x to NH 3 (NTA) process is promising for synthesizing NH 3 , being valuable not only as fertilizer but also as fuel in near future.