MPSC6 binuclear complexes immobilized on graphene oxide for oxidation of lignin model compounds and lignin

Abstract

An efficient process for the oxidative degradation of lignin using M-GO (MPSC6 binuclear complexes immobilized on graphene oxide) biomimetic catalysts in acetonitrile was developed in this work. Different M-GO catalysts (M=Co, Cu, Zn and Ni) were used to catalyze the depolymerization of lignin model compounds and organosolv lignin. The results showed that the immobilization of MPSC6 complexes on GO was favorable for regulating the valuable depolymerization of the model compounds and lignin. The optimal solid catalyst Co-GO exhibited high catalytic activity, which showed a 83.04% conversion of phenolic β-O-4 lignin model compound, a 91.26% conversion of veratryl alcohol and a 96.24% conversion of vanillyl alcohol with a catalyst/model compound ratio of 50 mg:10 mmol and a dosage of 15 mmol H2O2 at 80 °C for 3 h. The stuctural changes of organosolv lignin occurred in catalytic oxidation were analyzed in terms of O/C ratio, molecular weight and OH content of lignin samples, and a plausible mechanism involving the formation of aromatic products and muconolactone from lignin depolymerization over M-GO was also proposed.