In-situ transfer hydrogenolysis of lignin into phenolic monomers over Ni0.5Co1.5Al catalyst

Hydrogenolysis of lignin to produce valuable aromatic chemicals under mild conditions can effectively realize the value-added utilization of lignin. In this work, catalytic transfer hydrogenolysis (CTH) of dealkaline lignin (DL) over Ni0.5Co1.5Al catalyst was studied for the production of phenolic compounds, and the reaction mechanism was elucidated through the reaction of 2-phenoxy-1-phenylethanol (PPE) in deuterated isopropanol (CD3CD(OD)CD3) and D2. Moreover, we investigated the CTH behaviors of various lignin including organic solvents lignin in birch (OL), acidic solvents lignin in birch (AL) and birch powder (BW) to explore the suitability of the Ni0.5Co1.5Al catalyst. The results showed that Ni0.5Co1.5Al was able to catalyze the hydrogenolysis of various lignin into phenolic monomers using isopropanol as an in-situ hydrogen source. Under optimized conditions, the hydrogenolysis of DL over Ni0.5Co1.5Al achieved 43.30 wt% lignin oil yield. The experimental results of isotope labeling experiments exhibited that the active hydrogen generated by isopropanol is used for the cleavage of C-O bonds, and the electronic interactions between Ni and Co promotes the C-O bonds breaking. Isopropanol can not only be a hydrogen donor, but also act as a reaction solvent to stabilize intermediates and enhance the yield of phenolic compounds in the lignin CTH process.