Self-hydrogen transfer hydrogenolysis of β-O-4 bonds in lignin model compounds over NiCu/Al2O3 catalyst
Hydrogenolysis of β-O-4 linkages in lignin to produce aromatic compounds is attractive but challenging. Currently, external hydrogen source like hydrogen gas or hydrogen-donor solvent is necessary during hydrogenolysis, leading to high cost and low selectivity of products. Herein, a NiCu/Al 2 O 3 catalyst was prepared for self-hydrogen transfer hydrogenolysis (SHTH) of C β -O bond using inherent C α H-OH structure as H-source. A β-O-4 model compound, 2-phenoxy-1-phenethanol, was completely transformed into acetophenone and phenol at 220 ℃ under 1 MPa N 2 for 2h. The SHTH reaction proceeded through a dehydrogenation reaction followed by a hydrogenolysis reaction. Hydrogen radicals released from C α H-OH group generated a “hydrogen pool” on the catalyst surface, which inserted into the formed β-O-4 ketone intermediate to cleave the C β -O bond. The catalyst presented outstanding reusability and universality during the SHTH reaction. Moreover, the methoxy groups at aryl positions impeded the SHTH process, and the steric effect was related to the amount and position of methoxy groups. This study realizes the utilization of structural hydrogen from lignin model compounds for its C β -O bond cleavage , providing an economical and sustainable method toward lignin valorization.
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