Supported-Metal Catalysts in Upgrading Lignin to Aromatics by Oxidative Depolymerization

Supported gold and platinum particles on titanium oxide catalysts were evaluated in the oxidative depolymerization of lignins toward high added value aromatics under mild conditions (T: 150 degrees C, P-air: 20 bar, C-NaOH: 10 g/L, 1 h). Kraft and ethanol Organosolv lignins were engaged in the study. Gold catalyst showed a strong tendency to further oxidize aromatics produced from lignin depolymerization to volatile compounds leading to very low yield in target molecules. On the contrary, platinum-based catalysts were allowed to observe enhanced yields that were attributed to its ability to preserve lignin's substructure during the reaction. A kinetic model was constructed based on the results observed, which allowed us to identify the occurrence of condensation reactions during lignin oxidation and degradation of the produced aromatic compounds as the main limitations to reach high product yields. Insights on lignin oxidation and the catalyst's role lead through this study would help to reach higher control over lignin valorization.