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 N2. 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 NH3 by nonequilibrium plasma. The highest selectivity toward NH3 was observed with low amounts of added H2O vapor, but the highest production rate was reached at high H2O vapor contents. We also studied the role of H2O vapor and of the plasma-exposed liquid H2O in nitrogen fixation by using isotopically labeled water to distinguish between these two sources of H2O. We show that added H2O vapor, and not liquid H2O, is the main source of H for NH3 generation. The studied catalyst- and H2-free method offers excellent selectivity toward NH3 (up to 96%), with energy consumption (ca. 95–118 MJ/mol) in the range of many plasma-catalytic H2-utilizing processes.

Plasma technology provides a sustainable, fossil-free method for N 2 fixation, i.e., the conversion of inert atmospheric N 2 into valuable substances, such as NO x or ammonia. In this work, we present a novel gliding arc plasmatron at atmospheric pressure for NO x production at different N 2 /O 2 gas feed ratios, offering a promising NO x yield of 1.5% with an energy cost of 3.6 MJ/mol NO x produced. To explain the underlying mechanisms, we present a chemical kinetics model, validated by experiments, which provides insight into the NO x formation pathways and into the ambivalent role of the vibrational kinetics. This allows us to pinpoint the factors limiting the yield and energy cost, which can help to further improve the process.

N-based fertilisers are paramount to support our still-growing world population. Current industrial N2 fixation is heavily fossil fuel-dependent, therefore, a lot of work is put into the development of fossil-free...