Microwave-Enhanced Hydrodeoxygenation of Lignin-Derived Phenolics over Pt/HY Catalysts

Abstract

The upgrading of lignin-derived bio-oil via hydrodeoxygenation (HDO) remains challenging due to the stability of C–O bonds in phenolic compounds and the severe conditions typically required. In this work, microwave (MW)-assisted HDO of m-cresol, guaiacol, and vanillin was investigated for the first time over bifunctional Pt/HY catalysts under mild conditions (150–200 °C, 10 bar H2) and directly compared with conventional heating. Microwave irradiation significantly enhanced reaction rates, enabling complete m-cresol conversion within 30 min, whereas conventional heating required up to 120 min under identical conditions. Among the catalysts evaluated, Pt/HY(80) exhibited superior performance, achieving high hydrocarbon selectivity due to its balanced Brønsted acidity and enhanced mesoporosity, which mitigated diffusion limitations. In contrast, highly oxygenated substrates such as vanillin showed reaction stagnation at the creosol intermediate stage, accompanied by substantial apparent reactant retention. Control experiments under H2-free conditions revealed progressive disappearance from the liquid phase (m-cresol < guaiacol < vanillin), indicating strong adsorption and micropore blockage effects. These findings highlight the critical interplay between acidity, pore architecture, and molecular structure in determining HDO efficiency. Overall, microwave-assisted bifunctional catalysis enables efficient biomass upgrading under substantially milder conditions than typically reported, while revealing transport–acidity trade-offs that govern the conversion of increasingly complex bio-oil components.