Upgrading of nitrate to hydrazine through cascading electrocatalytic ammonia production with controllable N-N coupling

Abstract

Nitrogen oxides (NO_x) play important roles in the nitrogen cycle system and serve as renewable nitrogen sources for the synthesis of value-added chemicals driven by clean electricity. However, it is challenging to achieve selective conversion of NO_x to multi-nitrogen products (e.g., N₂H₄) via precise construction of a single N-N bond. Herein, we propose a strategy for NO_x-to-N₂H₄ under ambient conditions, involving electrochemical NO_x upgrading to NH₃, followed by ketone-mediated NH₃ to N₂H₄. It can achieve an impressive overall NO_x-to-N₂H₄ selectivity of 88.7%. We elucidate mechanistic insights into the ketone-mediated N-N coupling process. Diphenyl ketone (DPK) emerges as an optimal mediator, facilitating controlled N-N coupling, owing to its steric and conjugation effects. The acetonitrile solvent stabilizes and activates key imine intermediates through hydrogen bonding. Experimental results reveal that Ph₂CN* intermediates formed on WO₃ catalysts acted as pivotal monomers to drive controlled N-N coupling with high selectivity, facilitated by lattice-oxygen-mediated dehydrogenation. Additionally, both WO₃ catalysts and DPK mediators exhibit favorable reusability, offering promise for green N₂H₄ synthesis.