Trace Methane Destruction within the Effluent of Microwave Plasma

Atmospheric methane concentrations have more than doubled since preindustrial times, intensifying the global climate crisis. We experimentally examined the performance of microwave plasma for the destruction of trace methane (<1 mol %), emulating a cow barn. We evaluated a range of gases in the plasma and injected methane-containing air downstream, aiming to use excited species formed in the plasma to convert methane into valuable products, as well as species with a lower global warming potential, such as CO<inf>2</inf>. Fourier transform infrared spectroscopy (FTIR) was used to measure the concentration of methane and other IR-active products within the reactor effluent. Our analysis indicates that none of the tested experiments demonstrate lower energy costs than the already existing methods for the removal of trace methane, with only oxygen showing the potential of becoming as energy-efficient. However, we also demonstrated the simultaneous destruction of trace methane and the production of NO<inf>x</inf>, achieving an energy cost of 3 MJ/mol(NO<inf>x</inf>). This is of particular interest to agriculture as this process offers opportunities to efficiently produce nitrate fertilizers while simultaneously eliminating enteric methane emissions. This work thus shows how plasma can be used for both atmospheric methane reduction and sustainable NO<inf>x</inf> fixation in agriculture.