Oxidative Depolymerization of Lignin to Monophenolic Compounds Catalyzed by Spinel CuCo2O4

Lignin is the only natural polymer compound containing a benzene ring on earth, and its conversion to monophenolic compounds is attracting more attention. Cu-dopped CuCo2O4 is synthesized and further used to catalyze the oxidative conversion of lignin to monophenolic compounds. It is found that the conversion of lignin is affected by the molar ratio of Cu to Co, the amounts of catalyst and H2O2, reaction temperature and time, and CuCo2O4 exhibits excellent catalytic performance. Under the optimized reaction conditions, the total yield of monophenolic compounds reaches 21.7%. CuCo2O4 also possesses good recyclable performance, and the total yield of monophenolic compounds slightly drops to 17.6% after four cycles. A plausible mechanism for the conversion of lignin to monophenolic compounds is proposed. During the depolymerization of lignin, C-O and C-C bonds are broken to form monophenols. This work provides an effective catalyst for the conversion of lignin to monophenol and expands the way of high-value utilization of biomass.