Catalytic performance of an Fe-based supported polyoxometalate catalyst in the oxidative cleavage of β-O-4 lignin model compounds

Abstract

In this work, we developed an Fe supported POM catalyst (Fe/Cs-PMA), exhibiting high activity in the oxidative cleavage of β-O-4 bonds in a lignin model compound, 2-phenoxy-1-phenylethanol (PP-ol). The yield of phenol and benzoic acid (BA) reached 90% and 76%, respectively, at 140 °C for 12 h. STEM and EXAFS suggest that single atom Fe species were formed and anchored on the POM, which promotes the transformation of Mo⁶⁺ to Mo⁵⁺and increases the Lewis acid sites, both enhancing the reaction performance. Reaction pathway studies shows that PP-ol is first transformed to 2-phenoxy-1-phenylethanone (PP-one), and then converted to phenol and BA by activating C_β–O bonds, where BA comes from the oxidation of acetophenone. The reaction mechanism studies by EPR shows the strong signal of the ¹O₂ radical in Fe/Cs-MPA, indicating that ¹O₂ was an important species for O₂ activation. Moreover, this Fe/Cs-PMA catalyst also had good performance in the oxidative depolymerization of primary birch lignin, and the yield reached 17.7%. This work provided a simple and low cost polyoxometalate supported single Fe atom catalyst to depolymerize lignin and lignin model compounds to monomers.