Efficient Oxidative Cleavage of β-O-4 linkage in Lignin Model Compounds Enabled by a Simple Anderson-Type Polyoxometalate

Abstract

In this work, a simple Anderson-type polyoxometalate (POM), (NH4)4[CuMo6O24H6] (hereafter referred to as CuMo6), was utilized. This Anderson-type POM can be synthesized easily through a straightforward procedure. After undergoing a simple pretreatment, the catalyst demonstrated exceptional activity in the oxidative cleavage of the β-O-4 bond in the lignin model compound 2-phenoxy-1-phenylethanol (PP-ol) by using oxygen as a green oxidant. Under the reaction conditions of 140°C for 5 hours, excellent reaction activity and good product selectivity were achieved. XRD, FTIR, XPS and STEM analyses confirmed the successful synthesis of CuMo6 and characterized its structural features. It is demonstrated that the Anderson-type POM has a structure similar to that of single-atom catalysts. Py-IR, NH3-TPD and UV-Vis spectroscopy were employed to examine the changes in the catalyst before and after pretreatment, highlighting the significant role of the pretreatment. Additionally, EPR spectroscopy was employed to investigate the three distinct radical species involved in the reaction. Through experiments, the roles of these different radicals were explored, and the reaction mechanism has been updated with new insights. Furthermore, the catalyst exhibited outstanding activity in the oxidative depolymerization of birch lignin, achieving a total yield of dimers and monomers of 53.4%. This work successfully achieves efficient cleavage of lignin and its model compounds using a simple Anderson-type POM.