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

Abstract

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.