Selective C–O bond cleavage enhances aromatics production from lignin-derived platform molecules with ethanol as a hydrogen donor

Abstract

Selective catalytic cleavage of C–O bonds during the hydrodeoxygenation (HDO) of lignin-derived phenolics is essential for producing renewable aromatics from biomass. The HDO process typically involves the use of high-pressure molecular hydrogen, which poses safety concerns and lacks sustainability. Herein, we report an effective catalytic approach that integrates the aqueous-phase reforming (APR) of ethanol with the selective HDO of lignin-derived phenol to benzene over a well-defined Pt/Al₂O₃ catalyst. The effects of catalyst support, ethanol-to-water ratios, and reaction temperatures on in situ HDO processes were systematically explored and thoroughly discussed. The competitive routes of C–O bond hydrogenolysis and benzene ring hydrogenation during HDO of phenol were found to be significantly dependent on the H₂ produced by the APR of ethanol and variations in reaction parameters. A lower H₂ pressure, generated from an optimized V_ethanol/V_water of 3 : 5 and a high reaction temperature of 280 °C, favored the selective cleavage of C–O bonds rather than the hydrogenation of benzene rings, resulting in a relatively high phenol conversion of ca. 57% with a benzene selectivity of ca. 97% after 2 h of reaction. The proposed reaction pathways involved in the currently developed in situ HDO process provided a deep understanding of the pronounced selectivity towards benzene formation from phenol under optimized reaction conditions. The conversion of other representative lignin-derived phenolics and ethers further validated the superiority and versatility of the developed catalytic system in producing aromatic compounds from lignin biomass.