Nitrogen Fixation with Water Vapor by Nonequilibrium Plasma: toward Sustainable Ammonia Production

Ammonia is a crucial nutrient used for plant growth and as a building block in the pharmaceutical and chemical industry, produced via nitrogen fixation of the ubiquitous atmospheric N 2 . Current industrial ammonia production relies heavily on fossil resources, but a lot of work is put into developing nonfossil-based pathways. Among these is the use of nonequilibrium plasma. In this work, we investigated water vapor as a H source for nitrogen fixation into NH 3 by nonequilibrium plasma. The highest selectivity toward NH 3 was observed with low amounts of added H 2 O vapor, but the highest production rate was reached at high H 2 O vapor contents. We also studied the role of H 2 O vapor and of the plasma-exposed liquid H 2 O in nitrogen fixation by using isotopically labeled water to distinguish between these two sources of H 2 O. We show that added H 2 O vapor, and not liquid H 2 O, is the main source of H for NH 3 generation. The studied catalyst- and H 2 -free method offers excellent selectivity toward NH 3 (up to 96%), with energy consumption (ca. 95–118 MJ/mol) in the range of many plasma-catalytic H 2 -utilizing processes.