Hydrodeoxygenation of Lignin‐Derived Monomers and Dimers over a Ru Supported Solid Super Acid Catalyst for Cycloalkane Production

Abstract The monomers and dimers produced via lignin depolymerization are a promising alternative to transportation fuels after hydrodeoxygenation (HDO). However, these compounds contain numerous oxygen‐containing functional groups that are strongly bonded to aromatic rings. Therefore, the conventional HDO of lignin‐derived compounds faces serious problems of catalyst deactivation due to coke deposition and low hydrocarbon yields. A metal–solid super acid catalyst, i.e., Ru(SO₄²⁻)/ZrO₂–CeO₂, is synthesized, characterized, and evaluated for the HDO of various lignin‐derived monomers and dimers in a biphasic n‐dodecane/H₂O system. A high cyclohexane yield of 98.5% is obtained by the HDO of phenol performed at 200 °C and 5 MPa. The “hydrated” configuration can be formed between the hydrogenation intermediates and H₂O on the Ru sites. In addition, the anionic vacancies of ZrO₂–CeO₂ can be occupied by H⁻ derived from the heterolytic cleavage of H₂, leading to the formation of metal hydrides. The strong acidity of SO₄²⁻/ZrO₂–CeO₂ is beneficial for the subsequent deoxygenation of the hydrotreated products. In addition, the biphasic system can minimize the side reactions induced by the strong acidity of the catalyst. The catalytic system also exhibits a good catalytic performance for the HDO of other lignin‐derived monomers and dimers to produce cycloalkanes.