This work utilizes an Anderson-type polyoxometalate (POM) with a simple structure, (NH4)4ZnMo6O24H6 (denoted as ZnMo6), which is synthesized through an uncomplicated procedure. When water is employed as both an environmentally benign solvent and a hydrogen source under a nitrogen atmosphere, the catalyst shows remarkable efficacy in cleaving the β-O-4 linkage within the lignin model substrate 2-phenoxy-1-phenylethanol (PP-ol). Operating at 160 °C for 4 h, the system achieved high conversion with favorable product selectivity and was also effective in breaking α-O-4 and 4-O-5 bonds in corresponding model compounds. The formation and structural details of ZnMo6 were verified using XRD, FTIR, XPS, and STEM. The results indicate structural parallels between Anderson-type POMs and single-atom catalysts. To elucidate the catalyst’s properties and function, Py-IR spectroscopy, along with TPD and TPR measurements, was conducted. In situ adsorption experiments further characterized the interaction of three different molecular species with the catalyst surface. Integrated with control tests, these observations support proposed reaction mechanisms, thereby contributing to the understanding of catalytic transfer hydrogenation applied to lignin. Moreover, ZnMo6 exhibited high activity in the depolymerization of two distinct lignin sources, affording both dimeric and monomeric products with collective yields surpassing 25%. In summary, this study demonstrates efficient cleavage of lignin and model compounds via a structurally minimal Anderson-type POM, offering new perspectives and empirical support for the use of such POMs in lignin valorization.
Yang et al. (Mon,) studied this question.