Electrocatalytic cleavage of a lignin β-O-4 model compound and coupling with nitrogen-containing aromatics using Prussian blue analogue-derived nickel–cobalt spinel

Electrochemical conversion of lignin for the production of high-value heterocyclic aromatic compounds has great potential. We demonstrate the targeted synthesis and cation modulation of NiCo₂O₄ spinel nanoboxes, synthesized via cation exchange and calcination oxidation. These catalysts exhibit excellent efficacy in the electrocatalytic conversion of lignin model compounds, specifically 2-phenoxy-1-phenylethanol, into nitrogen-containing aromatics, achieving high conversion rates and selectivities. These catalysts were synthesized via a cation exchange and calcination oxidation process, using Prussian blue nanocubes as precursors. The porous architecture and polymetallic composition of the NiCo₂O₄ spinel demonstrated superior performance in electrocatalytic oxidative coupling, achieving a 99.2 wt% conversion rate of the 2-phenoxy-1-phenylethanol with selectivities of 37.5 wt% for quinoline derivatives and 31.5 wt% for phenol. Key innovations include the development of a sustainable one-pot synthesis method for quinoline derivatives, the elucidation of a multistage reaction pathway involving CO bond cleavage, hydroxyaldol condensation, and CN bond formation, and a deeper mechanistic understanding derived from DFT simulations. This work establishes a new strategy for lignin valorization, offering a sustainable route to produce high-value nitrogen-containing aromatics from renewable biomass under mild conditions, without the need for additional reagents.