(490f) Elucidating Mechanisms of Electrochemical Nitrate Reduction on Oxide-Derived Silver Catalysts

Nitrate contamination of groundwater supplies due to fertilizer runoff represents a significant engineering challenge.¹ One promising remediation strategy is via electrochemical reduction of nitrate, which can occur in an environmentally-friendly manner if benign N₂ can be selectively formed. However, promoting that selectivity while maintaining sufficient activity and current efficiency has proven elusive.

In this presentation, we describe our recent computational and experimental work to develop transition metal nitrate reduction catalysts. Our experimental results show that an oxide-derived silver (OD-Ag) catalyst demonstrates particularly high catalytic activity for nitrate reduction to nitrite, which was suggested previously as a rate-determining step of the overall process.² This OD-Ag catalyst can then be combined with a Pd catalyst for the efficient selective hydrogenation of nitrite to N₂. Particularly interesting is the ability to tightly control formation of nitrite or ammonia as the primary product on OD-Ag by manipulating reaction potential; this contrasts with copper catalysts, for which the product distribution changes more gradually.

Density functional theory (DFT) calculations on model planar and stepped surfaces show that the undercoordinated nature of the OD-Ag catalysts provides a particular advantage for nitrate reduction due to relatively strong adsorption of nitrate and weak adsorption of hydrogen and hydroxyl species. Our detailed mechanistic calculations show that the silver-based catalysts are restricted to pathways utilizing an H-mediated dissociation of the N-O bond; this allows tighter control of the reduction product than on copper, which is able to utilize pathways involving direct and/or H-mediated N-O dissociation depending on the applied potential. Our results suggest the possibility of further engineering structural features toward the design of an optimal nitrate reduction catalyst.

1. Martínez, J., Ortiz, A. & Ortiz, I. Appl. Catal. B Environ. 207, 42 (2017).
2. Reyter, D., Bélanger, D., and Roué, L., J. Phys. Chem. C 113, 290 (2009).