Electrochemical C–N coupling via adsorption modulation: selective synthesis of amines from biomass-derived 5-hydroxymethylfurfural

The electrochemical C–N coupling of biomass-derived 5-hydroxymethylfurfural (HMF) with methylamine offers a promising sustainable route to value-added amines. However, achieving high selectivity remains challenging due to competing side reactions, including C = O hydrogenation and C–C dimerization. This paper describes tailoring the surface structure of Ag catalysts to modulate HMF adsorption and intermediate hydrogenation behavior and thus enhancing C–N coupling selectivity. Ag nanoparticles, predominantly exposing the (111) facet, exhibit higher selectivity compared with Ag nanocubes mainly enclosed by (100) planes. The Ag(111) facet favors the C–N coupling pathway by regulating both adsorption geometry and hydrogenation ability. In-situ Raman spectroscopy and density functional theory (DFT) calculations reveal that an η 1 (C)-aldehyde adsorption configuration, dominant on Ag(111), enhances carbonyl electrophilicity and facilitates C = O polarization, promoting nucleophilic attack by methylamine. In contrast, the η 2 (C,O)–aldehyde configuration, more common on Ag (100), stabilizes the C = O bond, limiting its reactivity. Moreover, Ag(111) shows enhanced imine hydrogenation activity, further improving amine selectivity. This study highlights the significance of facet-dependent adsorption modulation in steering reaction pathways and advancing sustainable electrochemical synthesis.