Biorefining is the general term given to the conversion of lignocellulosic biomass into valuable products and energy. To date, the majority of lignocellulosic biorefinery approaches have focused on optimizing the conversion of cellulose to ethanol, leaving lignin as an underutilized biomass component. Lignin consists of phenolic subunits, from which it follows that value-added products can be obtained from lignin depolymerization. However, lignin utilization is particularly challenging due to its high structural irregularity and recalcitrance. The goal of this study was to develop a AuPd/Li-Al layered double hydroxide (LDH) bimetallic catalyst for lignin depolymerization to high-value aromatics. AuPd bimetallic nanoparticles in different molar ratios were supported on a basic Li-Al LDH support using a sol-immobilization method. Synthesized catalysts were characterized using N₂-physisoprtion, X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM), after which the catalysts were evaluated in test reactions, namely, the oxidation of 1-phenyl ethanol with O₂, in addition to other simple benzylic alcohols. Based on the results, Au₇Pd₃/Li-Al LDH and Au₁Pd₁/Li-Al LDH were identified as possessing promising catalytic activity. The properties of these two catalysts were further studied in the aerobic oxidation of benzylic alcohol groups in β–O–4 linked lignin model dimers under atmospheric pressure. Sequential oxidation of the model compounds was observed, resulting in cleavage of the
β-O-4 linkage. Finally, these two catalysts were tested in the oxidative deconstruction of γ-valerolactone (GVL) extracted maple lignin at
120 °C, again using O₂ as the oxidant. Au₁Pd₁/Li-Al LDH was found to be the most effective catalyst, giving a range of aromatic monomers in 27% total monomer yield. Based on these results, the Au₁Pd₁/Li–Al LDH catalyst system shows the potential to be an eco-friendly catalyst for lignin depolymerization under mild conditions.

Mark Crocker

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