Electrocatalytic Nitrate Reduction to Hydroxylamine followed by Oxime formation

Nitrate ions reached the position of an omnipresent pollutant during the past century, as anthropic activities led to an increase in their concentration in many water bodies such as lakes, rivers and groundwater. The accumulation of this chemical is being mitigated by implementing new wastewater treatment technologies. Electrocatalysis has the potential to act on the system by selectively reducing the nitrate ions in the solution, opening at the conversion of this persistent chemical into added-value, N-based products. Even if this usually aims at ammonia production, in contrast to the energy-consuming Haber-Bosch process, this work focuses on the electrocatalytic nitrate reduction (NORR) to hydroxylamine (HA), testing promising materials chosen among electrocatalysts with good activity toward NORR. The reactivity of HA makes its overreduction to ammonia a consistent side-process, but the nucleophilicity of the same allows the pursuit of cascade electrochemical-chemical reaction design, leading to C-N coupled precursors. Adding a carbonylic species to the catholyte, the newly formed HA fast reacts with it, forming the corresponding oxime. The latter, being more stable and less compatible with the catalyst, hinders the ammonia formation and allows for better storage and quantification of the target product. The electrocatalyst showing selectivity for HA has been tested in various pH conditions, investigating the performance toward NORR and the influence of the cascade chemical reaction via chronoamperometric experiments and quantification of the products in the catholyte.