Suppressing the formation of NOx and N2O in CO2/N2 dielectric barrier discharge plasma by adding CH4: scavenger chemistry at work

Abstract

The need for carbon negative technologies led to the development of a wide array of novel CO₂ conversion techniques. Most of them either rely on high temperatures or generate highly reactive O species, which can lead to the undesirable formation of NO_x and N₂O when the CO₂ feeds contain N₂. Here, we show that, for plasma-based CO₂ conversion, adding a hydrogen source, as a chemical oxygen scavenger, can suppress their formation, in situ. This allows the use of low-cost N₂ containing (industrial and direct air capture) feeds, rather than expensive purified CO₂. To demonstrate this, we add CH₄ to a dielectric barrier discharge plasma used for converting impure CO₂. We find that when adding a stoichiometric amount of CH₄, 82% less NO₂ and 51% less NO are formed. An even higher reduction (96 and 63%) can be obtained when doubling this amount. However, in that case the excess radicals promote the formation of by-products, such as HCN, NH₃ and CH₃OH. Thus, we believe that by using an appropriate amount of chemical scavengers, we can use impure CO₂ feeds, which would bring us closer to ‘real world’ conditions and implementation.