Coupling nitric oxide capture with ammonia production using Fe(II)(DMPS)₂ in the impeller-based wet nitric oxide absorption process

The integration of absorption and electrochemical processes is considered a feasible and sustainable solution for treating air pollutants such as nitric oxide (NO), which can be continuously captured and converted into industrially useful chemicals such as ammonia (NH₃). However, the poor solubility of NO, even in specialized absorbents, most notably iron (Fe)-chelate-based ones, hinders the real-world application of absorptive capture, and rapid oxidative deactivation of the absorbents by molecular oxygen further weakens its application potential. Here, we conducted the co-reduction of the oxidized (deactivated) absorbent for continuous NO capture, as well as NO to NH₃. First, we obtained NO removal efficiencies of 87.4% and 67% under anaerobic and aerobic conditions, respectively, using Fe(II)(DMPS)₂ compared to Fe(II)(cysteine)₂ and Fe(II)EDTA. Then, we demonstrated that the impeller-based scrubber exhibited the highest NO absorption performance and kinetics. Using response surface methodology and confirmation experiments, we obtained optimal values for a pH of 7.38, molar ratio of 2.29, and liquid-to-gas ratio of Fe(II)(DMPS)₂ of 13.89, with over 96% NO removal under anaerobic conditions. Finally, we confirmed an average NO removal efficiency of 76.6% and conversion efficiency of 98% NO-to-NH₃ through the electro-regeneration of Fe(II)(DMPS)₂-NO in the presence of 8% O₂. Our findings strongly support the idea that problematic nitrogenous air pollutants can be captured and upcycled into valuable chemicals continuously and sustainably.