Plasma-enhanced low-temperature SCO of NH3 over Cu-Mn/SAPO-34 catalyst under oxygen-rich conditions

Abstract

The global emission of ammonia in the atmosphere can lead to the production of secondary inorganic aerosols. The selective catalytic oxidation of NH₃ (NH₃-SCO), producing harmless N₂ and H₂O, is considered as a promising technique for solving NH₃ pollution issues. This work investigates the NH₃-SCO over a Cu-Mn/SAPO-34 catalyst coupled with dielectric barrier discharge (DBD) plasma at low temperatures under oxygen-rich (20 vol%) conditions. The results indicate that 90 % NH₃ conversion and 97 % N₂ selectivity can be achieved at an energy density (ED) of 36 J/L and a low temperature of 160 °C with a good stability. Unlike the conventional thermal-catalytic process, plasma-assisted NH3 SCO process was not affected by gas hourly space velocity (1.2 × 10⁴ to 3.6 × 10⁴h⁻¹) and slightly affected by the relative humidity (0–80 %). According to an infrared spectroscopy and an in-situ optical emission spectroscopic diagnostic, plasma discharge causes NH₃ conversion to form NH and NH₂ radicals, as well as O₂ conversion to form active oxygen species (e.g., O radical and O₃). The reactions of NH_x and active oxygen species produce NH₄NO₃, which subsequently converts to N₂ over Cu-Mn/SAPO-34 catalyst. The electron impact dissociation, short-lived active oxygen species (e.g., O radical) and O₃ contribute to 22.2 %, 20 % and 57.8 % of the total NH₃ conversion, respectively. This work successfully demonstrates an innovative cost-effective NH₃-SCO process using a plasma-coupled catalyst under low-temperature and oxygen-rich conditions.