Understanding non-equilibrium [formula omitted]/[formula omitted] chemistry in plasma-assisted low-temperature [formula omitted] oxidation

Abstract

Ammonia represents one of most promising zero-carbon energy solutions to address the increasingly urgent climate change problem. However, the existing utilization of ammonia faces significant challenges from low chemical reactivity and high N2O/NOx emissions, which cause severe inefficiency issues such as cold start and cycle variability of power generation, and detrimental effects on air quality, respectively. A sustainable and energy-efficient approach to tackle the above challenges is low temperature plasma which enables non-equilibrium energy and chemical utilization of ammonia such as oxidation using renewable electricity. As such, this work, for the first time, explores plasma assisted ammonia oxidation at room temperature with a focus on unveiling non-equilibrium NOx/N2O reaction pathways by combining in-situ laser diagnostics with plasma modeling. We found that the non-equilibrium plasma controls the NOx formation by supplying O/H/N atoms via electron-impact dissociation and collisional quenching of excited species. The N2O formation follows a two-step mechanism, where electron-impact reactions first provide amine radicals which further react with NOx to generate N2O. These pathways facilitate a high-efficiency and environment-friendly operation of plasma assisted ammonia oxidation with enhanced reactivity and reduced NOx/N2O emissions through manipulating mixture compositions and plasma discharge parameters.