Visible-Light-Driven Reductive Amination of Lignin-Derived Aldehydes and Native Lignin Bio-Oil Using Ru@CeO ₂ /ZrO ₂

Lignin is the most abundant renewable source of aromatic carbon; however, sustainable routes for transforming lignin-derived molecules into nitrogen-containing value-added chemicals are less explored. In particular, photocatalytic nitrogen functionalization of lignin-derived substrates has been rarely demonstrated despite its potential for mild, energy-efficient biomass upgrading. Herein, we report the visible-light-driven photocatalytic reductive amination of lignin-derived aromatic aldehydes to aromatic amines under environmentally benign conditions. A Ru@CeO 2 /ZrO 2 heterojunction photocatalyst enables efficient C–N bond formation in water at room temperature and low hydrogen pressure (1.5 bar) using visible light, thereby avoiding stoichiometric reductants and harsh thermocatalytic conditions. The catalyst exhibits high activity and selectivity across a broad range of lignin-derived aldehydes. The photocatalytic application is extended to produce amines through stepwise oxidative depolymerization-assisted amination of lignin bio-oil derived from wheat straw, demonstrating compatibility with complex biomass streams relevant to biorefinery applications. Sustainability assessment using CHEM21 green metrics reveals excellent material efficiency, including an atom economy of 90.6%, reaction mass efficiency of 82.2%, and a low process mass intensity (PMI = 1.4, reduced to 1.2 upon scale-up), corresponding to an overall process efficiency of ≈91%. Mechanistic studies indicate that visible-light excitation promotes efficient interfacial charge separation within the Ru@CeO 2 /ZrO 2 heterojunction and enables hydrogen activation at Ru sites for selective reductive amination. This work introduces a photocatalytic strategy for nitrogen functionalization of lignin-derived feedstocks and highlights a sustainable route for producing aromatic amines from renewable biomass under mild photocatalytic conditions.