Abstract
The removal of nitric oxide (NO), which is an aggregation agent for fine dust that causes air pollution, from exhaust gas has been considered an important treatment in the context of environmental conservation. Herein, we propose a sustainable electrochemical NO removal system based on the reversible Fe2+/Fe3+-ethylenediamine tetraacetic acid (EDTA) redox reaction, which enables continuous NO capture and storage at ambient temperature without the addition of any sacrificial agents. We have designed a flow-type reaction system in which the NO absorption and emission can be separately conducted in the individual reservoirs of the catholyte and anolyte with the continuous regeneration of Fe2+-EDTA by the electrochemical reduction in Fe3+-EDTA. A continuous flow reaction using a silver cathode and glassy carbon anode showed that the concentrations of Fe2+ and Fe3+-EDTA in the electrolyte were successfully maintained at a 1:1 ratio, which demonstrates that the proposed system can be applied for continuous NO capture and storage.
Highlights
The removal of nitric oxide (NO) in exhaust gas generated by the combustion of fossil fuels has been considered an important treatment to ensure a clean atmospheric environment [1,2,3]
We designed a flow-type reaction system in which the NO absorption and emission can be separately conducted in the individual reservoirs of the catholyte and anolyte with the continuous regeneration of the Fe2+-ethylenediamine tetraacetic acid (EDTA) by the electrochemical reduction of Fe3+-EDTA
We discovered that the reduction reactivity of Ag was lower than that of GC, the Ag cathode-GC anode electrode configuration stabilized the Fe2+- and Fe3+-EDTA ratio to 1:1 for a long period
Summary
The removal of nitric oxide (NO) in exhaust gas generated by the combustion of fossil fuels has been considered an important treatment to ensure a clean atmospheric environment [1,2,3]. We designed a flow-type reaction system in which strong NO absorption and fast NO emission was separately conducted in the individual reservoirs of the catholyte and anolyte with the continuous regeneration of Fe2+-EDTA by the electrochemical reduction in Fe3+-EDTA (Scheme 1a). The novelty of our system is that (i) NO capture can be performed semi-permanently without the addition of consumable compounds and degradation of catalysts; (ii) side reactions involving harmful fumes and pipe blockage do not occur; (iii) it is an energy-efficient process compared to SNCR and SCR because electrical energy can be directly consumed by the NO capture reaction; and (iv) valuable NO-derived chemicals such as ammonia or nitric acid can be synthesized by post-treatment. The NO removal efficiency of the full-cell reaction was not sufficient for practical use, we ensured that the concept of using the reversible electrochemical Fe-complex redox cycle at ambient temperature and pressure could be a promising and environmentally friendly NO removal method that is an alternative to SCR and SNCR. MO, USA, ≥99.0%), triphenylphosphine-3,3 ,3 -trisulfonic acid trisodium salt (TCI, >97.0%), 1,10-phenanthroline (SAMCHUN, Seoul, Korea, 99.0%), N2 (Sinyang Oxygen (medical), Seoul, Korea, 99.9%), NO (Sinyang Oxygen (medical), 99.9%), deionized water (18 MΩ, Smart2Pure 6 UV/UF, ThermoFisher, Waltham, MA, USA), ethyl alcohol (SAMCHUN, 99.9%), sulfuric acid (DUKSAN, Seoul, Korea, Extra Pure GRADE), sodium hydroxide (Sigma-Aldrich, ≥98%), ammonium chloride (Sigma-Aldrich, ACS reagent, ≥99.5%), phenol (Sigma-Aldrich, ACS reagent, ≥99.0%), sodium citrate tribasic dehydrate (Sigma-Aldrich, ACS reagent, ≥99.0%), sodium hypodhlorite solution (SigmaAldrich, available chlorine 4.00–4.99%), sodium nitroprusside dihydrate (Sigma-Aldrich, ACS reagent, ≥99%), sarcosine ethyl ester hydrochloride (TCI, >98.0%), methanol (Alfa Aesar, 99%), pyridine-2-carboxaldehyde (Alfa Aesar, 99%), sodium cyanoborohydride (Alfa Aesar, 95%), hydrochloric acid (Alfa Aesar, ACS, HCl 36.5~38.0%), sodium bicarbonate (Alfa Aesar, 99+%), methylene chloride (Fisherbrand, NH, USA, ACS Grade), magnesium sulfate heptahydrate (Alfa Aesar, 99+%), trimethylamine (Alfa Aesar, 99%), ethyl acetate (Alfa Aesar, 99%), benzene (Alfa Aesar, 99.8%), 1,2-bis(diphenylphosphino)ethane (Alfa Aesar, 97+%), and oleum (Sigma-Aldrich, 20% free SO3 basis) were purchased and used without pretreatment
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