Selective activation of C-C bonds in lignin model compounds and lignin for production of value-added chemicals

Lignin is a rich renewable aromatic resource that can produce high-value-added chemicals. Lignin is regarded as one of the three major components of lignocellulosic biomass, which is composed of phenylpropane units connected by C–O bond and C–C bond. The cleavage of two chemical bonds is the main catalytic pathway in the production of chemicals and fuels from lignin. Although the cleavage of C–O converts lignin into valuable aromatic compounds and renewable carbon sources, selective depolymerization for C–C bonds is an important method to increase the yield of aromatic monomers. Therefore, in this review, we summarized the latest research trends on C–C bond selective cleavage in lignin and lignin model compounds, focusing on various catalytic systems, including hydrogenolysis, oxidate, photocatalysis, and electrocatalysis. By analyzing the current status of C–C bond breakage, the core issues and challenges related to this process and the expectations for future research were emphasized.