Enzyme Mimetic Active Intermediates for Nitrate Reduction in Neutral Aqueous Media

Abstract

Nitrate is a pervasive aquatic contaminant of global environmental concern. In nature, the most effective nitrate reduction reaction (NRR) is catalyzed by nitrate reductase enzymes at neutral pH, using a highly‐conserved Mo center ligated mainly by oxo and thiolate groups. Mo‐based NRR catalysts mostly function in organic solvents with a low water stability. Recently, an oxo‐containing molybdenum sulfide nanoparticle that serves as an NRR catalyst at neutral pH was first reported. Herein, in a nanoparticle‐catalyzed NRR system a pentavalent MoV(=O)S4 species, an enzyme mimetic, served as an active intermediate for the NRR. Potentiometric titration analysis revealed that a redox synergy among MoV−S, S radicals, and MoV(=O)S4 likely play a key role in stabilizing MoV(=O)S4, showing the importance of secondary interactions in facilitating NRR. The first identification and characterization of an oxo‐ and thiolate‐ligated Mo intermediates pave the way to the molecular design of efficient enzyme mimetic NRR catalysts in aqueous solution.

Computational Insight into Metallated Graphynes as Single Atom Electrocatalysts for Nitrogen Fixation

“…Similarly, the PDS of the mixed pathway is also the first hydrogenation step along the intermediates N 2 **, N 2 H**, NHNH**, NHNH 2 **, NH*, NH 2 *, and NH 3 *, and the largest increase in Gibbs free energy is also 0.206 eV. Therefore, the consecutive and mixed pathways dominate the NRR processes on Mo-TEB with a considerably small energy barrier of 0.206 eV, consistent with that of some experimental and theoretical works, ,,, which thus validates the reliability of our results. In addition, Figure b–e shows Gibbs free energies for the other four catalysts, that is, V-, Os-, Tc-, and W-TEB, whose PDSs are N 2 ** → N 2 H**­(0.236 eV), NH 2 * → NH 3 *­(0.329 eV), N* → NH*­(0.427 eV), and NH* → NH 2 * (0.466 eV), respectively.…”

“…63 Hence, the five possible NRR catalytic mechanisms, namely, the distal, alternating, enzymatic, consecutive, and mixed, are discussed below, with the Gibbs free energy diagrams listed in Figure 6a. Therefore, the consecutive and mixed pathways dominate the NRR processes on Mo-TEB with a considerably small energy barrier of 0.206 eV, consistent with that of some experimental and theoretical works, 47,60,62,64 which thus validates the reliability of our results. In addition, Figure 6b− In order to deeply understand the catalytic mechanism, Figures 6f and S11 show the changes of U L s with respect to the N 2 adsorption energies as well as TM charge changes.…”

Atomically Precise Integration of Multiple Functional Motifs in Catalytic Metal–Organic Frameworks for Highly Efficient Nitrate Electroreduction

“…At the end of electrolysis, all peaks of In III /In II and adsorbed NO 3 – were restored both in the electrolyte ( Figure 2 g middle panel, end OCP curve) and in ambient conditions ( Figure 2 g bottom panel, red curve), confirming the recovery and stability of the In8 MOF catalyst. 40 All of these data are in agreement with the dynamic ligand dissociation model proposed from electrochemical characterizations. Furthermore, similar in situ Raman characteristics were observed at pH = 2 and 3, which is not surprising as In8 shows analogous redox behaviors in the optimal pH range of 1–3 ( Figure S15 ), following the same dynamic ligand dissociation mechanism.…”

“…, in situ -formed In II ) could serve as the binding and catalytic sites for nitrate reductions. At the end of electrolysis, all peaks of In III /In II and adsorbed NO 3 – were restored both in the electrolyte (Figure g middle panel, end OCP curve) and in ambient conditions (Figure g bottom panel, red curve), confirming the recovery and stability of the In8 MOF catalyst . All of these data are in agreement with the dynamic ligand dissociation model proposed from electrochemical characterizations.…”

Constructing Ru@C3N4/Cu Tandem Electrocatalyst with Dual‐Active Sites for Enhanced Nitrate Electroreduction to Ammonia

“…[15][16][17][18] Therefore, using nitrate as nitrogen source not only provide a sustainable alternative for renewable NH 3 production, but also decrease negative impact on the environment and human health. [19][20][21][22][23] At present, the main challenge of the electrochemical nitrate-to-ammonia was the poor selectivity and Faraday efficiency (FE) for ammonia due to the multiple eightelectron transfer process and competitive hydrogen evolution reaction (HER). [24][25][26][27][28] Previous studies indicated that Cu-based catalysts exhibit high catalytic activity for nitrate electroreduction owing to the similar energy levels features between d-orbital of Cu and the lowest unoccupied molecular 𝜋* orbital of nitrate.…”