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 η¹(C)-aldehyde adsorption configuration, dominant on Ag(111), enhances carbonyl electrophilicity and facilitates C = O polarization, promoting nucleophilic attack by methylamine. In contrast, the η²(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.