Development of an Effective Au: Pd Bimetallic Heterogeneous Catalyst for Oxidative Lignin Depolymerization to Low Molecular Weight Aromatics

Lignin, a phenolic-rich biomass component, holds promise for producing value-added products. However, its complex structure and recalcitrance present challenges for its effective utilization. To overcome this, a AuPd/Li−Al layered double hydroxide (LDH) catalyst was developed to facilitate lignin depolymerization. Various AuPd bimetallic nanoparticle compositions were supported on a basic Li−Al LDH support via a sol-immobilization method and characterized using N₂-physisorption, X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). The catalysts were then evaluated in the oxidation of several benzylic alcohols using O₂ as the oxidant, from which Au₇Pd₃/Li−Al LDH and Au₁Pd₁/Li−Al LDH were identified as possessing promising catalytic activity. Further investigations focused on the aerobic oxidation of β-O-4 linked lignin model dimers under atmospheric pressure. The tested catalysts demonstrated sequential oxidation of the model compounds, leading to cleavage of the β-O-4 linkage. Finally, the catalysts were applied to the oxidative deconstruction of γ-valerolactone (GVL) extracted maple lignin at 120 °C. Au₁Pd₁/Li−Al LDH emerged as the most effective catalyst, yielding a range of aromatic monomers with a total monomer yield of 27 %. These results highlight the potential of the Au₁Pd₁/Li−Al LDH catalyst system as an eco-friendly approach for lignin depolymerization under mild conditions.