Selective hydrodeoxygenation of lignins into cyclohexanols over Ni/CeO2 via hydrogen transfer

Abstract

The production of high-value cyclohexanols from renewable lignins under hydrogen-free conditions is highly attractive but notoriously challenging. Here, we report an efficient strategy for converting various lignin-derived phenolic monomers and lignin oils into cyclohexanols using a Ni/CeO₂ catalyst with isopropanol as the hydrogen donor. This approach achieves an impressive yield of 90.1 % from 2-methoxy-4-propylphenol, demonstrating selective hydrogenation of aromatic rings and cleavage of Ar-OCH₃ bonds while retaining the desired hydroxyl functionalities. Mechanistic investigations reveal that the interplay between Ni and CeO₂ enhances the reduction of Ni species and the creation of oxygen vacancies. Additionally, the charge transfer between Ni and CeO₂ facilitates the formation of Ni^δ+, which promotes the adsorption and activation of aromatic rings. Notably, the Ni/CeO₂ catalyst exhibits excellent stability and broad applicability, delivering a cyclohexanol yield of 66.6% from real lignin oil. This work presents a robust strategy for the high-selectivity conversion of renewable lignin into cyclohexanols via catalytic hydrogen transfer reactions, paving the way for sustainable lignin utilization.