Synthesis of Hydroxylamine via Ketone-Mediated Nitrate Electroreduction

Abstract

Hydroxylamine (HA, NH2OH) is a critical feedstock in the production of various chemicals and materials, and its efficient and sustainable synthesis is of great importance. Electroreduction of nitrate on Cu-based catalysts has emerged as a promising approach for green ammonia (NH3) production, but the electrosynthesis of HA remains challenging due to overreduction of HA to NH3. Herein, we report the first work on ketone-mediated HA synthesis using nitrate in water. A metal–organic-framework-derived Cu catalyst was developed to catalyze the reaction. Cyclopentanone (CP) was used to capture HA in situ to form CP oxime (CP-O) with CN bonds, which is prone to hydrolysis. HA could be released easily after electrolysis, and CP was regenerated. It was demonstrated that CP-O could be formed with an excellent Faradaic efficiency of 47.8%, a corresponding formation rate of 34.9 mg h–1 cm–2, and a remarkable carbon selectivity of >99.9%. The hydrolysis of CP-O to release HA and CP regeneration was also optimized, resulting in 96.1 mmol L–1 of HA stabilized in the solution, which was significantly higher than direct nitrate reduction. Detailed in situ characterizations, control experiments, and theoretical calculations revealed the catalyst surface reconstruction and reaction mechanism, which showed that the coexistence of Cu0 and Cu+ facilitated the protonation and reduction of *NO2 and *NH2OH desorption, leading to the enhancement for HA production.

Efficient electrochemical coupling of nitrate and biomass-derived acetone to acetoxime at a high current density over a Zn/Cu hexagonal nanosheet catalyst

“…64 Upon the introduction of CH 3 COCH 3 into the system, the *NH 2 OH signal significantly weakened (Fig. S37 and S38†), accompanied by the appearance of signals located at 1683 cm −1 of the CN bond, 40,53,65 1027 cm −1 for the N–O stretching of CN–OH, 41 and 1227 cm −1 attributed to the C–C–C asymmetric stretch peak of adsorbed *CH 3 COCH 3 66,67 (Fig. 7b).…”

“…43 Since Jiao successfully constructed acetamide from CO and NH 3 using an electrocatalytic method over Cu-based catalysts, 44 the green synthesis of organonitrogen compounds using readily available carbon/nitrogen-containing small molecules under mild conditions has become an emerging field. 8,45–48 In the field of electrosynthesis of oximes, researchers have successfully synthesized cyclohexanone oxime, 49,50 benzaldoxime, 51 formaldoxime, 52 cyclopentanoxime, 53 and pralidoxime 42 from C-containing (cyclohexanone, benzaldehyde, formaldehyde, acetone, pyridine aldehyde) and N-containing (NO 3 − , NO 2 − , NO) small molecules as reactants. Although there has been some progress in the electrocatalytic C–N/CN field, this reaction typically entails multi-step elementary reactions, rendering it a complex catalytic system.…”