Synchronizing Lewis-Acid C─O Bond Activation and Ethanol-Derived Hydrogen Transfer Over RuO₂/ZnO Carbon Aerogels for Technical Lignin Depolymerization.

Abstract

Technical lignin depolymerization is constrained by a kinetic mismatch between the cleavage of residual aryl ether bonds and the stabilization of the resulting highly reactive fragments that are generated. This imbalance promotes rapid C─C condensation, and thereby limits aromatic monomers formation. Herein, a lignosulfonate-derived RuO₂/ZnO carbon aerogel is constructed to synchronize C─O bond activation by Lewis acid sites with ethanol-mediated hydrogen transfer depolymerization of enzymatic hydrolysis lignin under N₂. A metal-directed gelation calcination route that organized Ru and Zn species within a polyacrylamide-lignosulfonate network. This process yields a hierarchically porous, N-doped carbon framework with closely connected and electronically coupled RuO₂/ZnO domains, this architecture creates a coupled catalytic microenvironment. Zn-containing Lewis acidic sites polarize oxygenated linkages, whereas Ru sites activate ethanol to deliver transferable hydrogen species. ZnCl₂ serves as a mobile Lewis acid cocatalyst to further promote aryl ether and β-O-4 activation. Under optimized conditions, phenol, guaiacol, and syringol type monomers are produced without external H₂, increasing the aromatic monomer yield from 16.5% to 21.2%. Mechanistic studies and calculations reveal that ZnCl₂ accelerates C─O bond activation, while the RuZn interface stabilizes quinone methide-like intermediates through ethanol-derived hydrogen transfer.