A molybdenum catalyst mimics the function of biological enzyme

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 low water stability. In our paper, 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 plays a key role in stabilizing MoV(=O)S4, showing the importance of secondary interactions in facilitating NRR. The first identification and characterization of oxo- and thiolate-ligated Mo intermediates pave the way to the molecular design of efficient enzyme mimetic NRR catalysts in an aqueous solution.