Co@CoO: An efficient catalyst for the depolymerization and upgrading of lignocellulose to alkylcyclohexanols with cellulose intact

Abstract

The depolymerization and upgrading of lignin from raw biomass, while keeping cellulose intact is important in biorefinery and various metal-based catalysts have been used in reductive catalytic fractionation, a key method in “lignin-first” strategy. Recently, we found that a core–shell structured Co@CoO catalyst with CoO shell as the real active site had excellent performance in the hydrogenolysis of 5-hydromethylfurfural to 2,5-dimethylfuran due to its unique ability to dissociate H2 and yield active Hδ− species (Xiang et al., 2022). In this work, we report a one-pot depolymerization and upgrading of lignocellulose to alkylcyclohexanols, a flavour precursor, with intact cellulose over this unique core–shell structured catalyst, Co@CoO. Lignin model compounds (β-O-4, 4-O-5, α-O-4) were first used to clarify the activity of Co@CoO catalyst. Then, the one-pot conversion of various organosolv lignin (birch, pine and poplar) to alkylcyclohexanols was realized with the mass yield of alkylcyclohexanols up to 25.8 wt% from birch lignin under the reaction condition of 210 °C, 1 MPa H2, 16 h. Finally, the corresponding woody sawdusts were used as feedstocks and found that the Co@CoO catalyst indeed preferentially depolymerized and upgraded the lignin part and obtained the same alkylcyclohexanols products with the retention of cellulose-rich pulp. The collected alkylcyclohexanols were further esterified to obtain value-added esters, which can be used as flavors. This work will inspire the design of new efficient metal oxide catalysts in lignin fractionation and depolymerization to high-value-added chemicals with intact cellulose.