Hydrodeoxygenation of Lignin Phenol Derivatives to Aromatic Hydrocarbons: A Mini-Review of Metal/Acid Bifunctional Catalysts

Lignin-derived phenolic compounds present two major drawbacks: high oxygen content and limited stability. Catalytic hydrodeoxygenation is an exceptionally promising approach to convert these derivatives into valuable chemicals or fuels, a process that is crucial for achieving two-carbon emission targets. This review describes recent progress and key challenges in metal/acid bifunctional catalysts for hydrodeoxygenation of lignin-derived phenolics, both domestically and internationally. The current research status is examined, focusing on metal–oxygen affinity, geometric effects, and types of acid sites, including Brønsted and Lewis acids along with their synergistic interactions. This review also investigates metal–acid effects from the perspective of metal sites, analyzing metal/acid bifunctional catalysts for hydrodeoxygenation reactions through surface species modifications, Brønsted acid enhancements, oxygen defect engineering, and interfacial engineering strategies. Various modification approaches for bifunctional catalysts are discussed, along with the reaction mechanism for transforming lignin phenolic derivatives into aromatic compounds. Lastly, the challenges and critical directions for future research in lignin phenolic derivative applications are summarized, emphasizing the need for purposeful catalyst design and a deeper comprehension of reaction mechanisms to optimize biomass resource efficiency.