Robust Carbon-Carbon Cleavage in Lignin to Produce Phenol and Cyclohexanone

The challenge of breaking 5-5′ bonds in lignin, attributed to their high bonding energy, has prompted the development of a new transformation pathway. Biphenyl, an important model compound for lignin, contains these 5-5′ bonds, making it crucial to devise a strategy for their cleavage in lignin transformation. This study introduces a novel method for transforming biphenyl, involving selective hydrogenation to cyclohexylbenzene by Ni/SiO₂ catalyst, followed by its oxidation to phenol and cyclohexanone through a radical mechanism. Results demonstrate that the catalysts with small particles have strong catalytic activity, while there is little difference in selectivity. The reason for the high selectivity of cyclohexylbenzene is due to the limited adsorption of cyclohexylbenzene on Ni/SiO₂. This work presents a fresh approach to breaking resilient C—C bonds in lignin.