Ambient-temperature hydrogenolysis of 4-O-5 lignin model compounds to generate cyclohexanes and cyclohexanols enabled by synergy of electronic and solvent effects

Abstract

Hydrogenolytic cleavage of aromatic C-O ether bond in lignin derivatives provides a promising protocol for sustainable lignin upgrading. However, it remains a great challenge to make this attractive strategy occur under ambient temperature. Herein, we reported a solvent and electric cooperative catalytic system for hydrogenolytic cleavage of 4-O-5 lignin models. This proposed catalytic system was constructed by calcium titanate (CaTiO₃)-supported Ru nanoparticles (Ru/CaTiO₃) as the catalyst and isopropanol as the reaction solvent. Very interestingly, the 4-O-5 lignin models could be cleaved by hydrogenolysis at ambient temperature in this constructed catalytic system. Detailed investigations revealed that the hydrogenolysis occurred by the transfer of hydrogens in isopropanol, while the involved H₂ played the role on hydrogenation of the in situ generated acetone, making the Ru⁰ sites available for successive hydrogenolysis. The high activity of this catalytic system (Ru/CaTiO₃ with isopropanol) at ambient conditions originated from the synergistic effect of the more negatively charged metallic Ru⁰ sites (electronic effect) and the isopropanol acting as both the solvent and hydrogen donor (solvent effect).