Catalytic Depolymerization and Deoxygenation of Lignin

Depolymerization and subsequent deoxygenation of lignin using heterogeneous catalysts is critically reviewed. As biomass contains a substantial fraction of water, emphasis is laid on exploring the catalytic chemistry in the presence of subcritical and supercritical water as solvent. Four main routes, i.e., hydrolysis, cracking, reduction, and oxidation, are outlined for lignin depolymerization. The detailed catalytic chemistry toward C. C and C. O bond cleavage on lignin linkages is then discussed. The reduction of oxo functional groups on the depolymerized phenols is presented as well.