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.

Plasma is gaining interest for CH 4 conversion into higher hydrocarbons and H 2 . However, the performance in terms of conversion and selectivity toward different hydrocarbons is different for different plasma types, and the underlying mechanisms are not yet fully understood. Therefore, we study here these mechanisms in different plasma sources, by means of a chemical kinetics model. The model is first validated by comparing the calculated conversions and hydrocarbon/H 2 selectivities with experimental results in these different plasma types and over a wide range of specific energy input (SEI) values. Our model predicts that vibrational− translational nonequilibrium is negligible in all CH 4 plasmas investigated, and instead, thermal conversion is important. Higher gas temperatures also lead to a more selective production of unsaturated hydrocarbons (mainly C 2 H 2 ) due to neutral dissociation of CH 4 and subsequent dehydrogenation processes, while three-body recombination reactions into saturated hydrocarbons (mainly C 2 H 6 , but also higher hydrocarbons) are dominant in low temperature plasmas.

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An inductively coupled plasma, connected to the sampling cone of a mass spectrometer, is computationally investigated. The occurrence of rotational motion of the auxiliary and carrier gas flows is studied. The effects of operating parameters, i.e., applied power and gas flow rates, as well as geometrical parameters, i.e., sampler orifice diameter and injector inlet diameter, are investigated. Our calculations predict that at higher applied power the auxiliary and carrier gas flows inside the torch move more forward to the sampling cone, which is validated experimentally for the auxiliary gas flow, by means of an Elan 6000 ICP-MS. Furthermore, an increase of the gas flow rates can also modify the occurrence of rotational motion. This is especially true for the carrier gas flow rate, which has a more pronounced effect to reduce the backward motion than the flow rates of the auxiliary and cooling gas. Moreover, a larger sampler orifice (e.g., 2 mm instead of 1 mm) reduces the backward flow of the auxiliary gas path lines. Finally, according to our model, an injector inlet of 2 mm diameter causes more rotations in the carrier gas flow than an injector inlet diameter of 1.5 mm, which can be avoided again by changing the operating parameters.