Ammonia synthesis from hydrogen and nitrogen gases by low-temperature radio frequency plasma catalysis.

In the ITER tokamak, injection of nitrogen is foreseen to decrease the heat loads on the divertor surfaces. However, once dissociated, nitrogen atoms react with hydrogen isotopes to form ammonia isotopologues. The formation of tritiated ammonia may pose some issues with regards to tritium inventory and operation duty cycle. In this paper, we report a study of the eect of three parameters of relevance for the fusion environment on the ammonia production, including the presence of a catalytic surface, sample temperature and noble gas addition. Results of ammonia formation from N 2 /H 2 RF plasma (both with and without tungsten or stainless steel surface)show the importance of the presence of a catalyst in the ammonia formation process.By increasing the temperature of the W samples up to 1270 K, ammonia formation demonstrated a continuous decrease due to two major factors. For high temperatures above 650 K and 830 K, for stainless steel and W, respectively, the reduction results from the thermal decomposition of ammonia. For the lower temperature range, the temperature rise leads to the formation of more stable nitrides that do not tend to react further with hydrogen to form NH 2 and NH 3 . Interestingly, the addition of helium or argon to the N 2 /H 2 plasma show opposite eects on the ammonia production.He eectively decreases the percentage of NH 3 by acting as a barrier for the surface processes. On the other hand, argon impacts more the plasma processes probably by increasing the active nitrogen species in the plasma and as a consequence the percentage of formed ammonia.