Synergistic Effect of Mediated Electrochemical Reduction and Mediated Electrochemical Oxidation on NO Removal by Electro-Scrubbing

Abstract

A combined MER (mediated electrochemical reduction) and MEO (mediated electrochemical oxidation) approach was examined for the first time for the efficient removal of NO by electro-scrubbing. The generation of a mediator (Ni(I) from Ni(II)(CN) 4 2− in 9 M KOH) by electrochemical reduction was identified by the changes in the ORP value and potentiometric titration. The Ni(I) formation found to be 9% (4.3 mM) in 2 h electrolysis, which is decreased to 1.83 mM (4%) during addition of NO demonstrates NO removal occurred. The MER of NO at the cathodic half-cell by electro-scrubbing revealed the formation of NH 3 and N 2 . The reductive removal efficiency of NO was almost 100% up to a gas flow rate of 0.25 g min −1 . At the anodic half-cell, the Co(III) mediator from Co(II)SO 4 in 5 M H 2 SO 4 was generated electrochemically with concomitant conversion of NO to NO 3 − in the solution phase with a removal efficiency of 28%. The combination of MEO and MER with electro-scrubbing demonstrates 97% removal efficiency of NO up to 0.5 g min −1 . The combined removal approach is more suitable for high concentrated NO with energy efficiency of 0. Abundantly generated nitric oxide (NO) gas that includes power plant and steel plant etc., is decomposed by many technologies, such as wet scrubbing, catalytic oxidation, and selective catalytic reduction (SCR).1-3 The reduction of NO leads a combination of cationic intermediates and products, N 2 O, NH 2 OH, N 2 , and NH 3 , in the solution phase. [4][5][6] The reduction products varied depending on the catalyst and experimental conditions: on TiO 2 in the colloid solutions to produce NH 3 ; 4 in heterogeneous catalytic reduction process with NH 3 as the reactant produced N 2 ; 7,8 and N 2 O formed on boron-doped graphene method.9 At the same time, the oxidation of NO leads to the anionic products of NO 2 and NO 3 − . 10,11 Heterogeneous catalytic oxidation at the gas phase produced NO 2 , 12 but solution phase oxidation by ozone and H 2 O 2 produced the NO 3 − product. 1,13 Because of the catalytic reaction, NO is solubilized in an aqueous solution, otherwise it less soluble or insoluble in an aqueous solution.14 Using this approach, many oxidant-15,16 and reductant-17 containing wet-scrubbing processes have been adopted in NO removal. Note that the above methods require a continuous catalyst or reactant feed to make the process sustainable.An electron considered to be a green catalyst and can be feed continuously to regenerate the spent catalyst sustainably. Using this approach, electrogenerated Ce(IV) and Mn(III) mediators have been used to oxidize NOx to NO 3 − in HNO 3 medium. 18,19 In a similar method, electrogenerated Ag(II) with a wet scrubber in the name of 'electro-scrubbing' have used NOx oxidation to NO 2 in a single stage scrubber and NO 3 − in a two stage scrubber column. 20 In the presence of SO 2 in NO oxidation using the electrogenerated Ag(II) mediator in highly concentrated nitric acid have shown NO 2 with 60 to 80% of NO 3 − formation. [21][22][23] Note that unless...

Sustainable removal of N2O by mediated electrocatalytic reduction at ambient temperature electro-scrubbing using electrogenerated Ni(I) electron mediator

“…The supporting information section outlines the following: complete experimental details for the preparation of nickel cyanide complex reported elsewhere [46]; electrolytic cell setup with a wet scrubber for the active electron mediator generation and removal of N2O gas (based on our experience [47,48] along with a schematic presentation (Fig.SI 1)); and the analysis type and conditions used in the present investigation.…”

Homogeneous Ni(I)tetra Sulfonated Phthalocyanine Electrocatalyst Generated at Low Overpotential Clubbed with a Wet‐Scrubbing Column for High Efficiency NO Reduction to NH3

“…Furthermore, the formation of NH 3 was constant throughout the study, suggesting that no additional reaction occurred (Figure 7). In the previous work, NH 3 formation decreased with reaction time where Ni(I)CN 4 3À homogeneous electrocatalysts were used [19]. The reduction potential of Ni(I)CN 4 3À is approximately À 0.8 V, which could have induced the further reduction of NH 3 with NO to N 2 .…”

“…A wet-scrubbing column can be an excellent choice to scale up without increasing the electrode area and electrocatalyst contact area with NO gas.. [19] Although the cobalt tetrakis(Nmethyl-2-pyridyl)phorphine complex has been applied to reduce NO to NH 3 at a potential of À 0.7 V at pH 4, [20] it was a fundamental study and was never combined with a wetscrubber to increase the contact of the reactants. A solution of a homogeneous electron mediator, instead of electrode modification, was introduced with an electrogenerated homogenous mediator ion.…”

“…A solution of a homogeneous electron mediator, instead of electrode modification, was introduced with an electrogenerated homogenous mediator ion. [19] On the other hand, the electrogenerated Ni(I)(CN) 4…”

“…3À homogenous mediator has been used in NO reduction to NH 3 ; [19] the applied reduction potential was À 0.8 V (vs. Ag/AgCl) with an electrolyte of 9 M KOH. The Pt cathode increased NO reduction to NH 3 by electro-scrubbing under similar conditions.…”