BDE-Driven Sustainable Synthesis of Lignin-Derived Hydroxybenzonitriles via Tandem Green Cyanation and Gas-Phase Hydrodeoxygenation

Abstract

Lignin valorization through catalytic upgrading to nitrogen-containing aromatics represents a critical pathway for sustainable chemical production. Using vanillin, a key lignin depolymerization product, as a platform molecule, we demonstrate the first integrated strategy combining cyanide-free cyanation and gas-phase hydrodeoxygenation (HDO) to synthesize hydroxybenzonitriles (HBNs). Bond dissociation energy (BDE) analysis revealed the cyano group’s selective retention (C≡N: 136.21 kcal/mol vs C–O: 62.44–116.17 kcal/mol), guiding targeted HDO pathway design. A green H2O/HCOOH system achieved 99.2 mol% vanillonitrile yield under mild conditions (85 °C, 12 h), surpassing conventional DMF-based methods. Engineered Mo/TiO2 catalysts with triple functional sites (oxygen vacancies, suitable content of Mo5+, strong metal–support interaction) achieved 57.6% HBN yield in continuous gas-phase HDO, outperforming Mo/ZrO2. The catalyst retained 90% of its initial activity over eight cycles due to enhanced metal–support interactions. This work establishes a sustainable route for lignin-to-chemical conversion, advancing catalyst design principles for biomass upgrading.