One metal is enough: a nickel complex reduces nitrate anions to nitrogen gas

Abstract

A nickel complex was found to be capable of stepwise reducing nitrate to dinitrogen gas using carbon monoxide as the reaction partner.

Oxygen atom transfer promoted nitrate to nitric oxide transformation: a step-wise reduction of nitrate → nitrite → nitric oxide

“…Kinetic measurements (vide supra) confirmed clearly that the first step of the reaction (Scheme 1, pathway II) is the slowest step of the reaction; hence, a rate-determining step. Therefore, the overall second-order rate constant (k2= 2.4 × 10 −2 M -1 s −1 ) is equal to the rate constant of the conversion of 2 to 3 (Figure 4a 28 and the binding constants calculations further support our proposal of two OAT reactions with different reaction rates (r2 >>> r1). The Kb(Co II -NO2 -) is higher than that of Kb(Co II -NO3 -); hence the reaction moves in the forward direction once the NO2generates from NO3in OAT-1.…”

“…Discussion on the OAT chemistry 28 and metal-induced activation of O-atom 24 (vide supra) undoubtedly support our supposition of a faster OAT-2 than the OAT-1, as non-coordinated O-atom of NO3is difficult to abstract by VCl3 than Co 2+ -coordinated O-atoms of nitrite moiety. 24,28 Recent reports on Lewis acid induced OAT reactions showed an increase in the oxidizing power of M-oxygen adducts and their OAT reaction rate 40 , which coincides with the activation of N2 by Lewis acid. 28,41 Further, the difference in the rates of the NO3 − & NO2 − reduction were supported by the inert and labile behavior of Co-complexes.…”

“…28 Kim and co-workers reported that the alteration of O-atom's electrophilic behavior in NO3species, induced by the Sc 3+ metal (Lewis acid) binding, showed the NO3to NO2reduction, which was not observed in the absence of Sc 3+ ion, suggesting the Oatom activation upon Sc 3+ binding. Discussion on the OAT chemistry 28 and metal-induced activation of O-atom 24 (vide supra) undoubtedly support our supposition of a faster OAT-2 than the OAT-1, as non-coordinated O-atom of NO3is difficult to abstract by VCl3 than Co 2+ -coordinated O-atoms of nitrite moiety. 24,28 Recent reports on Lewis acid induced OAT reactions showed an increase in the oxidizing power of M-oxygen adducts and their OAT reaction rate 40 , which coincides with the activation of N2 by Lewis acid.…”

“…27 However, the conversion of NO3to NO using a single catalyst is barely explored; Yunho Lee and co-workers testified Ni catalyzed the transformation of inorganic NO3to N2 via NO2intermediate using the carbon monoxide (CO) as oxophilic species. 28 In biological systems 3, 5a and biomimetic 22-23, 27, 29 /or catalytic reactions 24 , the approach towards converting NO3to NO is usually a two-enzymes/-catalysts-induced two-step process in two different reactions (i.e., NO3reduction followed by NO2reduction) 5a . However, only a few reports simultaneously carry out both the NO3and NO2reduction using a single metal center in a biomimetic system.…”

Nitrate reduction by electrochemical processes using copper electrode: evaluating operational parameters aiming low nitrite formation

“…For electroreduction and electrocatalytic processes, the electrode material is also an important parameter. Several electrodes can be used to propitiate the nitrate reduction, such as nickel (Simpson & Johnson 2004;Gwak et al 2019) and iron (Jonoush et al 2020). However, copper (Pérez-Gallent et al 2017;Beltrame et al 2019) is the one the most used, due to the similarity of the energy levels of the copper 'd'-orbital with the nitrate Lumo π* molecular orbital (Garcia-Segura et al 2018).…”