Intramolecular Hydrogen Bonding Facilitates Electrocatalytic Reduction of Nitrite in Aqueous Solutions

Abstract

This work reports a combined experimental and computational mechanistic investigation into the electrocatalytic reduction of nitrite to ammonia by a cobalt macrocycle in an aqueous solution. In the presence of a nitrite substrate, the Co­(III) precatalyst, [Co­(DIM)­(NO2)2]+ (DIM = 2,3-dimethyl-1,4,8,11-tetraazacyclotetradeca-1,3-diene), is formed in situ. Cyclic voltammetry and density functional theory (DFT) calculations show that this complex is reduced by two electrons, the first of which is coupled with nitrite ligand loss, to provide the active catalyst. Experimental observations suggest that the key N–O bond cleavage step is facilitated by intramolecular proton transfer from an amine group of the macrocycle to a nitro ligand, as supported by modeling several potential reaction pathways with DFT. These results provide insights into how the combination of a redox active ligand and first-row transition metal can facilitate the multiproton/electron process of nitrite reduction.

Metal‐free Transformations of Nitrogen‐Oxyanions to Ammonia via Oxoammonium Salt

“…À has further been confirmed by employing 15 S13), which can be attributed to the N-sites of oxoammonium cation and nitrate anion, respectively. Monitoring the reaction of 1 a with t BuONO or NO 2 gas in CDCl 3 by 1 H NMR exhibits a singlet at d % 4.2 ppm (Figure S14), [24] which can tentatively be assigned to the coformation of H 2 gas during the generation of diaryl oxoammonium species 2 a.…”

“…À by [Co(DIM)Br 2 ] + supported by a redox-noninnocent ligand (DIM = 2,3-dimethyl- 1,4,8,11-tetraazacyclotetradeca-1,3-diene) yields NH 3 as the sole reduction product. [15] Nevertheless, the approach of transition-metal-mediated activation of NO 3…”

Recent advances in electrocatalytic nitrite reduction

“…In another study, nitrite electroreduction was performed by [Co(DIM)Br 2 ] + , where DIM = 2,3-dimethyl-1,4,8,11-tetraazacyclotetradeca-1,3-diene. 77 [Co(DIM)(NO 2 ) 2 ] + was formed during the nitrite reduction. Then, one-electron reduction of this complex was coupled to the loss of the nitrite ligand to provide the active catalyst [Co(DIM)(NO 2 )] + .…”

Biomass Juncus derived carbon decorated with cobalt nanoparticles enables high-efficiency ammonia electrosynthesis by nitrite reduction

“…9 Therefore, the articial denitrication of NO 2 À into harmless or, better yet, value-added products is of signicant importance to public health and mitigation of the nitrogen cycle unbalance. The ambient electrocatalytic NO 2 À reduction reaction (NO 2 RR) is regarded as a simple and on-site route to convert NO 2 À pollutants into other reductive products, [10][11][12][13][14][15][16][17][18][19] of which NH 3 as an indispensable chemical commodity and an alternative carbon-free fuel is of key importance to many industrial processes and human life. 20,21 Recently, N 2 -to-NH 3 xation in aqueous solution has attracted wide research attention, but such a conversion process achieves rather low NH 3 yield and faradaic efficiency (FE) due to the chemical inertness and low solubility of N 2 .…”

“…11 Recent studies show that cobalt macrocyclic complexes can selectively drive the six-electron NO 2 RR process with high activity. 11,12 However, homogeneous catalysts typically exhibit limited reduction current densities (<100 mA cm À2 ) [36][37][38] and suffer from separation difficulties. 39 In this regard, the design of efficient and robust Co-based heterogeneous catalysts is highly needed for kinetically fast NO 2 RR electrocatalysis.…”